A

TRAINING REPORT

FOR

THE PARTIAL FULLFILLMENT OF B.TECH DEGREE

IN

MECHANICAL ENGINEERING

AT

NORTHERN RAILWAY, CARRIA GE AND WAGON WORKSHOP

JAGADHRI WORHSHOP

Submitted to:- Submitted By:-

Er. Neeraj Gogia Jasmeet Singh

Roll Number: - 1808524

Mechanical Engineering B.Tech 3rd Year

Haryana engineering college, JAGADHRI

PREFACE

Industrial training is a major part of our course. It is a period in which we are

introduced to the industrial environment or in other words we can say that

industrial training is provided for the familiarization with the industrial

environment. It is the period in which we learn to use the knowledge gained

during the course in the field.

The objective of the training is to raise the level of performance in one or

more of its aspects this may be achieved by providing new knowledge and

information relevant to a job training must be focused on individuals and

situation where the need is greatest. Furthermore, departmental co-

ordination and co-operation provides overviews of the total training and

development processes. I avail this stance in a very satisfactory manner and

think

It will be beneficial for me in building my future.

ACKNOWLEDGMENT

Industrial training is an indispensable part of engineering curriculum. It

provides the students with an opportunity to gain experience on the

practical application of their technical knowledge.

I express my gratitude to all the people at Carriage And Wagon Workshop,

Northern Railway who inspite of their busy schedules took personal interest

to ensure that this training period is a thorough learning process for us. I

have no doubt now that our choice of training was right and the exposure

and experience gained at Workshop has been unique.

I would like to give thanks to Mr. Shivraj Singh (S.E.), Mr. Dyan singh ,Air

Break section, MR.Rajinder Vohra S.E. Mill Wright Shop, Mr.Bagga S.E.

Wheel Shop, Mr. Dolat Singh Machine Shop for giving us this opportunity to

work in the respective department.

Jasmeet singh

CONTENTS

INTRODUCTION

SALIENT FEATURES

SPECIFICATION OF THE POH CYCLE

MILL WRIGHT SHOP

BEARING SHOP

MACHINE SHOP

CNC PLASMA CUTTING MACHINE

MAINTENANCE OF A COIL SPRING

AIR BRAKE SYSTEM

INTRODUCTION

In 1947, after independence, the truncated North-Western Railway, renamed, as East-Punjab railway had no workshop to undertake repairs of Broad Gauge rolling stock. For some time, the repairs to BG stock were carried out at Kalka. Later it was decided to set up the first major post-independence C &W workshop of Indian railways at Jagadhari as part of Northern Railway and foundation stone of the workshop was laid on 08/02/1952.The workshop was set up for undertaking the POH of 75 units of coaching stock and 225 units of goods stock per month.

The workshop capacity has since been expanded and developed and over a period of time the target outturn of the workshop has been increased to current level of 1150 units of wagon and 135coaches per month. This includes 17 A.C. coaches. Besides IOH of18 A.C. coaches are carried out per month.

A store depot is attached to the workshop and is headed by Dr . Chief Material Manager.

A 55-bedded hospital is also attached to the workshop. Medical Superintendent heads the hospital and functions under the administrative control of Chief Works Manager.

Kalka workshop is also under the administrative and technical control of Chief Work Manager, Jagadhari Workshop, and caters to POH and manufacture of Narrow Gauge stock and foundry activities.

Jagadhari Workshop has achieved a landmark by establishing its quality system in accordance with ISO 9001-2000 requirements. Six shops viz, carriage bogie shop, roller bearing shop, wheel shop, A.C. electrical shop, DV section and SAB section had earlier been awarded ISO 9002-1994 certification in July 2000.

Jagadhari workshop has also been established its own Basic Training Center (BTC) for providing training to the artisan staff and its apprentice. Training is being revamped by improving course content, providing modern training aids and suitable training to trainers and by providing training notes to each trainee.

SALIENT FEATURES

Work force employed (Including Stores, Accounts &

medicals) 7066No.

Units of energy consumed per month.

7.00Lac.units

Connected load 13933Kw.

Maximum demands 4500Kva.

Covered area 70265.2sq.mts.

Total area

286Acres.

Number of staff quarters.

1926Nos.

CNC& high capacity machines

31Nos.

Total Machinery and plant.

794 Nos.

Track length.

Total budget per year.

Rs.255.71Crores.

Scrap disposal (till feb.2004) Rs.46.45Crores.

SPECIFICATION OF POH CYCLE

Sr.No.

Symbols Stand For

1. A Verification of deficiencies.

2. B Pre-inspection and lifting.

3. C Stripping.

4. D Body repair, modification and alteration.

5. E Painting.

6. F Fitting of water tank, plumbing and leakage testing.

7. G Repair to interior panels.

8. H Fitments of shutters.

9. I Fitments of doors.

10. J Fitments of births and seats.

11. K Vacuum /air break testing and final works

12. L Final inspection and dispatch.

13. M Fitment of axle pulley, tension rod and testing of coach wiring.

14. N Testing of branch wiring.

MILLWRIGHT SHOP

Millwright

A millwright is a craftsman or tradesman engaged with the construction and maintenance of machinery.

Early millwrights were specialist carpenters who erected machines used in agriculture, food processing and processing lumber and paper. In the early part of the Industrial Revolution, their skills were pressed into service building the earliest powered textile mills.

Modern millwrights work with steel and other materials in addition to wood and must often combine the skills of several skilled trades in order to successfully fabricate industrial machinery or to assemble machines from pre-fabricated parts. The modern millwright must also be able to read blueprints and other schematics to aid him in the construction of complex systems. Millwrights are frequently unionized, although experienced millwrights often set themselves up as independent contractors.

Forming a helical gear for traverser at millwright shop

The modern millwright

A millwright today is someone who maintains or constructs industrial machinery for assembly lines, pumping stations and other utilities, print shops, and other industries employing fixed heavy machinery.

General duties

Millwrights are usually responsible for the unassembled equipment when it arrives at the job site. Using hoisting and moving equipment, they position the pieces that need to be assembled. Their job requires a thorough knowledge of the load bearing capabilities of the equipment they use as well as an understanding of blueprints and technical instructions.

Millwrights must be able to read blueprints and schematic drawings to determine work procedures, to construct foundations for and to assemble, dismantle and overhaul machinery and equipment, using hand and power tools and to direct workers engaged in such endeavors. The use of lathes, milling machines and grinders may be required to make customized parts or repairs. In the course of work, millwrights are required to move, assemble and install machinery and equipment such as shafting, precision bearings, gear boxes, motors, mechanical clutches, conveyors, and tram rails, using hoists, pulleys, dollies, rollers, and trucks. In addition, a millwright may also perform all duties of general laborer, pipefitter, carpenter, and electrician. A millwright may also perform some of the duties of a welder, such as arc welding, mig welding and oxyacetylene cutting.

Millwrights are also involved in routine tasks, such as lubrication of machinery, bearing replacement, seal replacement, cleaning of parts during an overhaul and preventitive maintenance.

Millwrights also must have a good understanding of fluid mechanics (hydraulics and pneumatics), and all of the components involved in these processes, such as valves, cylinders, pumps and compressors.

Modern standards of practice for millwrights also require working within precise limits or standards of accuracy, at heights without fear; the use of logical step-by-step procedures in work; planning, solving problems and decision-making based on quantifiable information.

Millwrights are trained to work with a wide array of precision tools, such as vernier calipers, micrometers, dial indicators, levels, gauge blocks, and optical and laser alignment tooling.

Areas of specialty

A typical job description for an industrial maintenance mechanic (millwright) often includes the primary purposes of installing, maintaining, upgrading and fabricating machinery and equipment according to layout plans, blueprints, and other drawings in industrial establishment.

Millwrights in the power generation industry assemble, set, align and balance turbines/rotors. Millwrights also perform critical lifts involving major components to be flown level at up to and within .005” (5 thousandths of an inch). Millwrights are generally chosen to work on tasks associated with flying and setting heavy machinery.

Millwrights are also in demand as teachers for vocational programs, both at the high school level and in post-secondary institutions. Many high schools feature fabrication courses that include metal work, where the experience of a qualified millwright is valuable. Often, these millwrights are paid a premium based on their years of field experience.

A high percentage of millwrights join unions to help protect their interests. Those with a high level of skill often start their own businesses as independent contractors.

Training

Most millwrights are educated through apprenticeship programs where they receive a combination of classroom education along with a good deal of on-the-job training. Most programs last about four years. Apprentices are usually paid a percentage of the average millwright's wage, and this percentage increases with experience.

Millwright shopMillwright shop is meant for the maintenance of the machines and the damaged parts of Crain, traversers, overhead Crain’s, and lifting machines etc.

This shop contains workers and engineers who look after all the work of maintenance in the whole workshop. The gears such as spur gear, helical or sprockets are regenerated on milling machine and clutches and other such parts are made on shaping machine and centre lathes are used for other general operations.

A damaged sprocket of a CrainSPUR GEARSA gear is made by cutting a series of equally spaced, specially shaped grooves on the periphery of a wheel. To calculate the dimensions of a spur gear, you must know the parts of the gear. You also must know the formulas for finding the dimensions of the parts. To cut the gear you must know what cutter to use and how to index the blank, so the teeth are equally spaced and have the correct profile.

MACHINING THE GEARUse the following procedures to make a gear with the dimensions given in the preceding example: 1. Select and cut a piece of stock to make the blank. Allow at least 1/8 inch excess materialon the diameter and thickness of the blank for clean-up cuts.2. Mount the stock in a chuck on a lathe. At the centre of the blank, face an area slightly larger than the diameter of the required bore.

3. Drill and bore to the required size (within tolerance).

4. Remove the blank from the lathe and press it on a mandrel.

5. Set up the mandrel on the milling machine between the centers of the index head and the footstock. Dial in within tolerance.

6. Select a No. 5 involute gear cutter (8 pitch) and mount and center it.

7. Set the index head to index 24 divisions.

8. Start the milling machine spindle and move the table up until the cutter just touches the gear blank. Set the micrometer collar on the vertical feed handwheel to zero, then hand feed the table up toward the cutter slightly less than the whole depth of the tooth.

9. Cut one tooth groove. Then index the workpiece for one division and take another cut. Check the tooth dimensions with a vernier gear tooth caliper as described previously. Make the required adjustments to provide an accurately “sized” tooth.

10. Continue indexing and cutting until the teeth are cut around the circumference of theworkpiece.

When you machine a rack, space the teeth by moving the work table an amount equal to the circular pitch of the gear for each tooth cut. Calculate the circular pitch by dividing 3.1416 by the diametral pitch:

You do not need to make calculations for corrected addendum and chordal pitch to check rack teeth dimensions. On racks the addendum is a straight line dimension and the tooth thickness is one-half the linear pitch.

Helical gearA helix is a line that spirals around a cylindrical object, like a stripe that spirals around a barber pole. A helical gear is a gear whose teeth spiral around the gear body. Helical gears transmit motion from one than the diameter of the required bore. shaft to another. The shafts can be either parallel or set at an angle to each other, as long as their axes do not Intersect Helical gears operate more quietly and smoothly than spur gears because of the sliding action of the spiral teeth as they mesh. Also, several teeth make contact at the same time. This multitooth contact makes a helical gear stronger than a comparable spur gear. However, the sliding action of one tooth on another creates friction that could generate excessive heat and wear. Thus, helical gears are usually run in an oil bath. A helical gear can be either right-handed or left-handed. To determine the hand of a helical gear, simply put the gear on a table with its rotational axis perpendicular to the table top. If the helix moves upward toward the right, the gear is right-handed. If the helix moves upward to the left, the gear is left-handed. To mill a helical gear, you need a dividing head, a tailstock, and a lead driving mechanism for the dividing head. These cause the gear blank to rotate at a constant rate as the cut advances. This equipment is an integral part of a universal knee and column type of milling machine. When a helical gear is manufactured correctly, it will mesh with a spur gear of the same diametral pitch (DP), with one gear sitting at an angle to the other. The

dimensions of a helical gear would be the same as those of a comparable spur gear if the helical gear’s teeth were not cut at an angle. One of these differences is shown in the following example:You will need a 10-inch circular blank to cut 20 one-quarter-inch wide slots spaced one-quarter of an inch apart parallel to the gear’s axis of rotation. But you will need a 10.6-inch circular blank to cut the same slots at an angle of 19°22´ to the axis of rotation. Helical gears are measured at a right angle to the tooth face in the same manner as spur gears with the same diametral pitch.

Forming a new sprocket for CrainGEAR TRAIN RATIOWhen a helix is milled on a workpiece, the workpiece must be made to rotate at the same time it is fed into the revolving cutter. This is done by gearing the dividing head to the milling machine table screw. To achieve a given lead, you must select gears with a ratio that will cause the work to rotate at a given speed while it advances a given distance toward the cutter. This distance will be the lead of the helical gear. The lead of the helix is determined by the size and the placement of the change gears. Before you can determine which gears are required to obtain a given lead, you must know the lead of the milling machine. The lead is the distance the milling machine table must move to rotate the spindle of the dividing head one revolution. Most milling machines have a table screw of 4 threads per inch with a lead of 0.250 inch (1/4 inch) and a dividing head (index head) with a 40:1 worm-to-spindle ratio. When the index head is connected to the table through a 1:1 ratio, it will cut a lead of 10 inches. Thus, 40 turns of the lead screw are required to make the spindle revolve one complete revolution (40 0.250 inch = 10 inches). Therefore, 10 will be the constant in our gear train ratio formula, All ratios other than 1:1 require modification of the geartrain.From this formula, we can also say that the

Lead of the machine / Lead of the helix to cut = Product of the driving gears tooth numbers / Product of the driven gear tooth numbers

MANUFACTURING A HELICAL GEAR

At this point of manufacture a helical manufacture a helical do the following:1. Find the DP. the chapter, you are ready to gear. In a case where you must gear from a sample, you should

2. Measure the OD. This is also the ROD.

3. Find the ADD.

4. Find the RPD.

5. Find the NT.

6. Find the NPD.

7. Find the

8. Find the RPC.

9. Find the lead.

10. Find the change gear.

11. Find the NTCS.

12. Make sure the cutter has the correct DP and cutter number.

13. Find your corrected chordal addendum and chordal thickness.

14. Find your corrected whole depth (WD).

15. Determine what kind of material the sample gear is to be made of.

Now you are ready to machine your gear.Use the following hints to manufacture a helicalgear:

1. Make all necessary calculations that are needed to compute the dimensions of the gear.

2. Set up the milling machine attachments for machining.

3. Select and mount a gear cutter.

4. Swivel the milling machine table to the helix angle for a right-hand helix; face the machine and push the milling machine table with your right hand. For a left-hand helix, push the table with your left hand.

5. Set the milling machine for the proper feeds and speeds.

6. Mount the change gears. Use the gear train ratio formula to determine your change gears.

7. Mount the gear blank for machining. 8. Set up the indexing head for the correct number of divisions.

9. Before cutting the teeth to the proper depth, double check the setup, the alignment, and all calculations.

10. Now you are ready to cut your gear.

11. Remove and deburr the gear.

Millwright shop

BEARING SHOP

Bearing

A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.

Overview

Plain bearings use surfaces in rubbing contact, often with a lubricant such as oil or graphite. A plain bearing may or may not be a discrete device. It may be nothing more than the bearing surface of a hole with a shaft passing through it, or of a planar surface that bears another (in these cases, not a discrete device); or it may be a layer of bearing metal either fused to the substrate (semi-discrete) or in the form of a separable sleeve (discrete). With suitable lubrication, plain bearings often give entirely acceptable accuracy, life, and friction at minimal cost. Therefore, they are very widely used.

However, there are many applications where a more suitable bearing can improve efficiency, accuracy, service intervals, reliability, speed of operation, size, weight, and costs of purchasing and operating machinery.

Thus, there are many types of bearings, with varying shape, material, lubrication, principal of operation, and so on. For example, rolling-element bearings use spheres or drums rolling between the parts to reduce friction; reduced friction allows tighter tolerances and thus higher precision than a plain bearing, and reduced wear extends the time over which the machine stays accurate. Plain bearings are commonly made of varying types of metal or plastic depending on the load, how corrosive or dirty the environment is, and so on. In addition, bearing friction and life may be altered dramatically by the type and application of lubricants. For example, a lubricant may improve bearing friction and life, but for food processing a bearing may be lubricated by an inferior food-safe lubricant to avoid food

contamination; in other situations a bearing may be run without lubricant because continuous lubrication is not feasible, and lubricants attract dirt that damages the bearings.

Principles of operation

There are at least six common principles of operation:

plain bearing, also known by the specific styles: bushings, journal bearings, sleeve bearings, rifle bearings

rolling-element bearings such as ball bearings and roller bearings jewel bearings, in which the load is carried by rolling the axle slightly off-center fluid bearings, in which the load is carried by a gas or liquid magnetic bearings, in which the load is carried by a magnetic field flexure bearings, in which the motion is supported by a load element which bends. angular contact bearing

Motions

Common motions permitted by bearings are:

Axial rotation e.g. shaft rotation Linear motion e.g. drawer spherical rotation e.g. ball and socket joint hinge motion e.g. door, elbow, knee

Friction

Reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extended use at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing a fluid between surfaces or by separating the surfaces with an electromagnetic field.

By shape, gains advantage usually by using spheres or rollers, or by forming flexure bearings.

By material, exploits the nature of the bearing material used. (An example would be using plastics that have low surface friction.)

By fluid, exploits the low viscosity of a layer of fluid, such as a lubricant or as a pressurized medium to keep the two solid parts from touching, or by reducing the normal force between them.

By fields, exploits electromagnetic fields, such as magnetic fields, to keep solid parts from touching.

Combinations of these can even be employed within the same bearing. An example of this is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish.

Loads

Bearings vary greatly over the size and directions of forces that they can support.

Forces can be predominately radial, axial (thrust bearings) or Bending moments perpendicular to the main axis.

Speeds

Different bearing types have different operating speed limits. Speed is typically specified as maximum relative surface speeds, often specified ft/s or m/s. Rotational bearings

typically describe performance in terms of the product DN where D is the diameter (often in mm) of the bearing and N is the rotation rate in revolutions per minute.

Generally there is considerable speed range overlap between bearing types. Plain bearings typically handle only lower speeds, rolling element bearings are faster, followed by fluid bearings and finally magnetic bearings which are limited ultimately by centripetal force overcoming material strength.

Play

Some applications apply bearing loads from varying directions and accept only limited play or "slop" as the applied load changes. One source of motion is gaps or "play" in the bearing. For example, a 10 mm shaft in a 12 mm hole has 2 mm play.

Allowable play varies greatly depending on the use. As example, a wheelbarrow wheel supports radial and axial loads. Axial loads may be hundreds of newtons force left or right, and it is typically acceptable for the wheel to wobble by as much as 10 mm under the varying load. In contrast, a lathe may position a cutting tool to ±0.02 mm using a ball lead screw held by rotating bearings. The bearings support axial loads of thousands of newtons in either direction, and must hold the ball lead screw to ±0.002 mm across that range of loads.

Stiffness

A second source of motion is elasticity in the bearing itself. For example, the balls in a ball bearing are like stiff rubber, and under load deform from round to a slightly flattened shape. The race is also elastic and develops a slight dent where the ball presses on it.

The stiffness of a bearing is how the distance between the parts which are separated by the bearing varies with applied load. With rolling element bearings this is due to the strain of the ball and race. With fluid bearings it is due to how the pressure of the fluid varies with the gap (when correctly loaded, fluid bearings are typically stiffer than rolling element bearings).

Service Life

Fluid and magnetic bearings can have practically indefinite service lives. In practice, there are fluid bearings supporting high loads in hydroelectric plants that have been in nearly continuous service since about 1900 and which show no signs of wear.

Rolling element bearing life is determined by load, temperature, maintenance, lubrication, material defects, contamination, handling, installation and other factors. These factors can all have a significant effect on bearing life. For example, the service life of bearings in one application was extended dramatically by changing how the bearings were stored before installation and use, as vibrations during storage caused lubricant failure even when the only load on the bearing was its own weight;[1] the resulting damage is often false brinelling. Bearing life is statistical: several samples of a given bearing will often exhibit a bell curve of service life, with a few samples showing significantly better or worse life. Bearing life varies because microscopic structure and contamination vary greatly even where macroscopically they seem identical.

For plain bearings some materials give much longer life than others. Some of the John Harrison clocks still operate after hundreds of years because of the lignum vitae wood employed in their construction, whereas his metal clocks are seldom run due to potential wear.

Flexure bearings bend a piece of material repeatedly. Some materials fail after repeated bending, even at low loads, but careful material selection and bearing design can make flexure bearing life indefinite.

Although long bearing life is often desirable, it is sometimes not necessary. Harris describes a bearing for a rocket motor oxygen pump that gave several hours life, far in excess of the several tens of minutes life needed.

Maintenance

Many bearings require periodic maintenance to prevent premature failure, although some such as fluid or magnetic bearings may require little maintenance.

Most bearings in high cycle operations need periodic lubrication and cleaning, and may require adjustment to minimise the effects of wear.

Bearing life is often much better when the bearing is kept clean and well-lubricated. However, many applications make good maintenance difficult. For example bearings in the conveyor of a rock crusher are exposed continually to hard abrasive particles. Cleaning is of little use because cleaning is expensive, yet the bearing is contaminated again as soon as the conveyor resumes operation. Thus, a good maintenance program might lubricate the bearings frequently but clean them never.

Tapered roller bearing

Tapered roller bearings are bearings that can take large axial forces (i.e., they are good thrust bearings) as well as being able to sustain large radial forces.

Description

The inner and outer ring raceways are segments of cones and the rollers are also made with a taper so that the conical surfaces of the raceways and the roller axes if projected, would all meet at a common point on the main axis of the bearing.

This conical geometry is used as it gives a larger contact patch, which permits greater loads to be carried than with spherical (ball) bearings, while the geometry means that the tangential speeds of the surfaces of each of the rollers are the same as their raceways along the whole length of the contact patch and no differential scrubbing occurs. When a roller slides rather than rolls, it can generate wear at the roller-to-race interface, i.e. the differences in surface speeds creates a scrubbing action. Wear will degenerate the close tolerances normally held in the bearing and can lead to other problems. Much closer to pure rolling can be achieved in a tapered roller bearing and this avoids rapid wear.

The rollers are guided by a flange on the inner ring. This stops the rollers from sliding out at high speed due to their momentum.

The larger the half angles of these cones the larger the axial force that the bearing can sustain.

Tapered roller bearings are separable and have the following components: outer ring, inner ring, and roller assembly (containing the rollers and a cage). The non-separable inner ring and roller assembly is called the cone, and the outer ring is called the cup. Internal clearance is established during mounting by the axial position of the cone relative to the cup

History

In 1898, Henry Timken was awarded a patent[1] for the tapered roller bearing. At the time, Timken was a carriage-maker in St. Louis and held three patents for carriage springs. However, it was his patent for tapered roller bearings that allowed his company to become successful.

Tapered roller bearings were a breakthrough at the end of the 19th century because bearings used in wheel axles had not changed much since ancient times. They relied on bearings enclosed in a case that held lubricants. These were called journal bearings and depended on lubricants to function. Without proper lubrication, these bearings would fail due to excessive heat caused by friction. Timken was able to significantly reduce the friction on his bearings by using a cup and cone design incorporating tapered bearings which actually rolled, which reduced the load placed on the bearings by distributing the weight and load evenly across the cups, cones, and bearings.

Applications

In many applications tapered roller bearings are used in back-to-back pairs so that axial forces can be supported equally in either direction.

Pairs of tapered roller bearings are used in car and vehicle wheel bearings where they must cope simultaneously with large vertical (radial) and horizontal (axial) forces.

Spherical roller bearings

Spherical roller bearings use rollers that are thicker in the middle and thinner at the ends; the race is shaped to match. Spherical roller bearings can thus adjust to support misaligned loads. However, spherical rollers are difficult to produce and thus expensive, and the bearings have higher friction than a comparable ball bearing since

different parts of the spherical rollers run at different speeds on the rounded race and thus there are opposing forces along the bearing/race contact.

A spherical bearing is a bearing that permits angular rotation about a central point in two orthogonal directions (usually within a specified angular limit based on the bearing geometry). Typically these bearings support a rotating shaft in the [bore] of the inner ring that must move not only rotationally, but also at an angle.

ConstructionConstruction of spherical bearings can be hydrostatic or strictly mechanical. A spherical bearing by itself can consist of an outer ring and an inner ring and a locking feature that makes the inner ring captive within the outer ring in the axial direction only. The outer surface of the inner ring and the inner surface of the outer ring are collectively considered the raceway and they slide against each other, either with a lubricant or a maintenance-free polytetrafluoroethylene (PTFE) based liner. Some spherical bearings incorporate a rolling element such as a race of ball-bearings, allowing lower friction.

HistoryThe Swede Sven Wingquist (1876–1953) invented the spherical bearing in 1907. He founded a global company, AB Svenska Kullagerfabriken, still the world’s leading producer of industrial bearings.

Application

Spherical bearings are used in countless applications, wherever rotational motion must be allowed to change the alignment of its rotation axis. A prime example is a tie rod on a vehicle suspension. The mechanics of the suspension allow the axle to move up and down, but the linkages are designed to control that motion in one direction only and they must allow motion in the other directions. Spherical bearings have been used in car suspensions, driveshafts, heavy machinery, sewing machines, and many other applications.

Machine shopIt is the place where machining processes and finishing task is given to

various parts like Bridle bar, Piston rod, Control rod , Buffer plunger , etc.

Here, various processes from turning to threading, milling to grinding, etc

are done. Here a total of four columns are arranged and each column

contains different machines. Various important machines and their uses

are given below

Centre lathe : for brake hand, bolt cover, control rod, etc.

Capstan lathe : for turning, drilling threading, etc.

Turret lathe : for heavy work, boring, etc.

Power hacksaw : for cutting operation, etc.

Drill machine : for drilling of upper birth hinge, etc.

Testing lathe : for turning process of small parts like pins, bolts, etc

Grinder machine : for grinding purpose

Milling machine :for milling purpose

Shaper machine : for teething, groove making, etc

Screw cutting machine : for threading if buffer spindle

Machining

Conventional machining, one of the most important material removal methods, is a collection of material-working processes in which power-driven machine tools, such as lathes, milling machines, and drill presses, are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a part of the manufacture of almost all metal products, and it is common for other materials, such as

wood and plastic, to be machined. A person who specializes in machining is called a machinist. A room, building, or company where machining is done is called a machine shop. Much of modern day machining is controlled by computers using computer numerical control (CNC) machining. Machining can be a business, a hobby, or both.

The precise meaning of the term "machining" has evolved over the past 1.5 centuries as technology has advanced. During the Machine Age, it referred to (what we today might call) the "traditional" machining processes, such as turning, boring, drilling, milling, broaching, sawing, shaping, planing, reaming, and tapping, or sometimes to grinding. Since the advent of new technologies such as electrical discharge machining, electrochemical machining, electron beam machining, photochemical machining, and ultrasonic machining, the retronym "conventional machining" can be used to differentiate the classic technologies from the newer ones. The term "machining" without qualification usually implies conventional machining.

Machining Operations

The three principal machining processes are classified as turning, drilling and milling. Other operations falling into miscellaneous categories include shaping, planing, boring, broaching and sawing.

Turning operations are operations that rotate the workpiece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning.

Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the workpiece. Milling machines are the principal machine tool used in milling.

Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the workpiece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills.

Miscellaneous operations are operations that strictly speaking may not be machining operations in that they may not be swarf producing operations but these operations are performed at a typical machine tool. Burnishing is an example of a miscellaneous operation. Burnishing produces no swarf but can be performed at a lathe, mill, or drill press.

An unfinished workpiece requiring machining will need to have some material cut away to create a finished product. A finished product would be a workpiece that meets the specifications set out for that workpiece by engineering drawings or blueprints. For example, a workpiece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal workpiece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish. A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding machines. Many of these same techniques are used in woodworking.

More recent, advanced machining techniques include electrical discharge machining (EDM), electro-chemical erosion, laser cutting, or water jet cutting to shape metal workpieces.

As a commercial venture, machining is generally performed in a machine shop, which consists of one or more workrooms containing major machine tools. Although a machine shop can be a stand-alone operation, many businesses maintain internal machine shops which support specialized needs of the business.

Machining requires attention to many details for a workpiece to meet the specifications set out in the engineering drawings or blueprints. Beside the obvious problems related to correct dimensions, there is the problem of achieving the correct finish or surface smoothness on the workpiece. The inferior finish found on the machined surface of a workpiece may be caused by incorrect clamping, a dull tool, or inappropriate presentation of a tool. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish, and the appearance of waves on the machined surfaces of the workpiece.

Circle interpolating

Circle interpolating, also known as orbital drilling, is a process for creating holes using machine cutters.

Orbital drilling is based on rotating a cutting tool around its own axis and simultaneously about a centre axis which is off-set from the axis of the cutting tool. The cutting tool can then be moved simultaneously in an axial direction to drill or machine a hole – and/or combined with an arbitrary sidewards motion to machine an opening or cavity.

By adjusting the offset, a cutting tool of a specific diameter can be used to drill holes of different diameters as illustrated. This implies that the cutting tool inventory can be substantially reduced.

The term orbital drilling comes from that the cutting tool “orbits” around the hole center. The mechanically forced, dynamic offset in orbital drilling has several advantages compared to conventional drilling that drastically increases the hole precision. The lower thrust force results in a burr-less hole when drilling in metals. When drilling in composite materials the problem with delamination is eliminated

Types of machining operation

There are many kinds of machining operations, each of which is capable of generating a certain part geometry and surface texture.

In turning, a cutting tool with a single cutting edge is used to remove material from a rotating workpiece to generate a cylindrical shape. The speed motion in turning is provided by the rotating workpart, and the feed motion is achieved by the cutting tool moving slowly in a direction parallel to the axis of rotation of the workpiece.

Drilling is used to create a round hole. It is accomplished by a rotating tool that is typically has two or four cutting edges. The tool is fed in a direction parallel to its axis of rotation into the workpart to form the round hole.

In boring, the tool is used to enlarge an already available hole. It is a fine finishing operation used in the final stages of product manufacture.

In milling, a rotating tool with multiple cutting edges is moved slowly relative to the material to generate a plane or straight surface. The direction of the feed motion is perpendicular to the tool's axis of rotation. The speed motion is provided by the rotating milling cutter. The two basic forms of milling are:

Peripheral milling Face milling

Other conventional machining operations include shaping, planing, broaching and sawing. Also, grinding and similar abrasive operations are often included within the category of machining.

The cutting tool

A cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material. The cutting edge serves to separate chip from the parent work material. Connected to the cutting edge are the two surfaces of the tool:

The rake face; and The flank.

The rake face which directs the flow of newly formed chip, is oriented at a certain angle is called the rake angle "α". It is measured relative to the plane perpendicular to the work surface. The rake angle can be positive or negative. The flank of the tool provides a clearance between the tool and the newly formed work surface, thus protecting the surface from abrasion, which would degrade the finish. This angle between the work surface and the flank surface is called the relief angle. There are two basic types of cutting tools:

Single point tool; and Multiple-cutting-edge tool

A single point tool has one cutting edge and is used for turning, boreing and planing. During machining, the point of the tool penetrates below the original work surface of the workpart. The point is sometimes rounded to a certain radius, called the nose radius.

Multiple-cutting-edge tools have more than one cutting edge and usually achieve their motion relative to the workpart by rotating. Drilling and milling uses rotating multiple-cutting-edge tools. Although the shapes of these tools are different from a single-point tool, many elements of tool geometry are similar

Centre lathe

The terms center lathe, engine lathe, and bench lathe all refer to a basic type of lathe that may be considered the archetypical class of metalworking lathe most often used by the general machinist or machining hobbyist. The name bench lathe implies a version of this class small enough to be mounted on a workbench (but still full-featured, and larger than mini-lathes or micro-lathes). The construction of a center lathe is detailed above, but depending on the year of manufacture, size, price range, or desired features, even these lathes can vary widely between models.

Engine lathe is the name applied to a traditional late-19th-century or 20th-century lathe with automatic feed to the cutting tool, as opposed to early lathes which were used with hand-held tools, or lathes with manual feed only. The usage of "engine" here is in the mechanical-device sense, not the prime-mover sense, as in the steam engines which were the standard industrial power source for many years. The works would have one large steam engine which would provide power to all the machines via a line shaft system of belts. Therefore early engine lathes were generally 'cone heads', in that the spindle usually had attached to it a multi-step pulley called a cone pulley designed to accept a flat belt. Different spindle speeds could be obtained by moving the flat belt to different steps on the cone pulley. Cone-head lathes usually had a countershaft (layshaft) on the back side of the cone which could be engaged to provide a lower set of speeds than was obtainable by direct belt drive. These gears were called back gears. Larger lathes sometimes had two-speed back gears which could be shifted to provide a still lower set of speeds.

When electric motors started to become common in the early 20th century, many cone-head lathes were converted to electric power. At the same time the state of the art in gear and bearing practice was advancing to the point that manufacturers began to make fully geared headstocks, using gearboxes analogous to automobile transmissions to obtain various spindle speeds and feed rates while transmitting the higher amounts of power needed to take full advantage of high speed steel tools.

The inexpensive availability of electronics has again changed the way speed control may be applied by allowing continuously variable motor speed from the maximum down to almost zero RPM. (This had been tried in the late 19th century but was not found satisfactory at the time. Subsequent improvements have made it viable again

Turret lathe and capstan lathe

Turret lathes and capstan lathes are members of a class of lathes that are used for repetitive production of duplicate parts (which by the nature of their cutting process are usually interchangeable). It evolved from earlier lathes with the addition of the turret, which is an indexable toolholder that allows multiple cutting operations to be performed, each with a different cutting tool, in easy, rapid succession, with no need for the operator to perform setup tasks in between (such as installing or uninstalling tools) nor to control the toolpath. (The latter is due to the toolpath's being controlled by the machine, either in jig-like fashion [via the mechanical limits placed on it by the turret's slide and stops] or via IT-directed servomechanisms [on CNC lathes].)

There is a tremendous variety of turret lathe and capstan lathe designs, reflecting the variety of work that they do.

Turret lathe

The turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable. It evolved from earlier lathes with the addition of the turret, which is an indexable toolholder that allows multiple cutting operations to be performed, each with a different cutting tool, in easy, rapid succession, with no need for the operator to perform setup tasks in between, such as installing or uninstalling tools, nor to control the toolpath. The latter is due to the toolpath's being controlled by the machine, either in jig-like fashion, via the mechanical

limits placed on it by the turret's slide and stops, or via electronically-directed servomechanisms for computer numerical control (CNC) lathes.

Capstan versus turret

The term "capstan lathe" overlaps in sense with the term "turret lathe" to a large extent. In many times and places, it has been understood to be synonymous with "turret lathe". In other times and places it has been held in technical contradistinction to "turret lathe", with the difference being in whether the turret's slide is fixed to the bed (ram-type turret) or slides on the bed's ways (saddle-type turret).[3][4] The difference in terminology is mostly a matter of United Kingdom and Commonwealth usage versus United States usage.[2] American usage tends to call them all "turret lathes".

The word "capstan" could logically seem to refer to the turret itself, and to have been inspired by the nautical capstan. A lathe turret with tools mounted in it can very much resemble a nautical capstan full of handspikes. This interpretation would lead Americans to treat "capstan" as a synonym of "turret" and "capstan lathe" as a synonym of "turret lathe". However, the multi-spoked handles that the operator uses to advance the slide are also called capstans, and they themselves also resemble the nautical capstan.

No distinction between "turret lathe" and "capstan lathe" persists upon translation from English into other languages. Most translations involve the term "revolver", and serve to translate either of the English terms.

The words "turret" and "tower", the former being a diminutive of the latter, come ultimately from the Latin "turris", which means "tower", and the use of "turret" both to refer to lathe turrets and to refer to gun turrets seems certainly to have been inspired by its earlier connection to the turrets of fortified buildings and to siege towers. The history of the rook in chess is connected to the same history, with the French word for rook, tour, meaning "tower".

It is an interesting coincidence that the word "tour" in French can mean both "lathe" and "tower", with the first sense coming ultimately from Latin "tornus", "lathe", and the second sense coming ultimately from Latin "turris", "tower". "Tour revolver", "tour tourelle", and "tour tourelle revolver" are various ways to say "turret lathe" in French.

Milling machine

A milling machine (also see synonyms below) is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines.

Unlike a drill press, which holds the workpiece stationary as the drill moves axially to penetrate the material, milling machines also move the workpiece radially against the rotating milling cutter, which cuts on its sides as well as its tip. Workpiece and cutter movement are precisely controlled to less than 0.001 in (0.025 mm), usually by means of precision ground slides and leadscrews or analogous technology. Milling machines may be manually operated, mechanically automated, or digitally automated via computer numerical control (CNC). Milling machines can perform a vast number of operations, from simple (e.g., slot and keyway cutting, planing, drilling) to complex (e.g., contouring, diesinking). Cutting fluid is often pumped to the cutting site to cool and lubricate the cut and to wash away the resulting swarf.

Basic nomenclature

A milling machine is often called a mill by machinists. The term miller also used to be common (19th and early 20th centuries), although it is typically not used today in reference to modern machines. (The term "miller" is one that people today are still familiar with from historical usage, but they generally don't use it anymore unless they are referring to machines built during the term's heyday, which is similar to the way that people today treat terms such as "motor car", "horseless carriage", or "phonograph".)

Since the 1960s there has developed an overlap of usage between the terms milling machine and machining center. NC/CNC machining centers evolved from milling machines, which is why the terminology evolved gradually with considerable overlap that still persists. The distinction, when one is made, is that a machining center is a mill with features that pre-CNC mills never had, especially an automatic tool changer (ATC) that includes a tool magazine (carousel), and sometimes an automatic pallet changer (APC). In typical usage, all machining centers are mills, but not all mills are machining centers; only mills with ATCs are machining centers.

Comparing vertical with horizontalIn the vertical mill the spindle axis is vertically oriented. Milling cutters are held in the spindle and rotate on its axis. The spindle can generally be extended (or the table can be raised/lowered, giving the same effect), allowing plunge cuts and drilling. There are two subcategories of vertical mills: the bedmill and the turret mill. Turret mills, like the ubiquitous Bridgeport, are generally smaller than bedmills, and are considered by some to be more versatile. In a turret mill the spindle remains stationary during cutting operations and the table is moved both perpendicular to and parallel to the spindle axis to accomplish cutting. In the bedmill, however, the table moves only perpendicular to the spindle's axis, while the spindle itself moves parallel to its own axis. Also of note is a lighter machine, called a mill-drill. It is quite popular with hobbyists, due to its small size and lower price. These are frequently of lower quality than other types of machines, however.

A horizontal mill has the same sort of x–y table, but the cutters are mounted on a horizontal arbor (see Arbor milling) across the table. A majority of horizontal mills also feature a +15/-15 degree rotary table that allows milling at shallow angles. While endmills

and the other types of tools available to a vertical mill may be used in a horizontal mill, their real advantage lies in arbor-mounted cutters, called side and face mills, which have a cross section rather like a circular saw, but are generally wider and smaller in diameter. Because the cutters have good support from the arbor, quite heavy cuts can be taken, enabling rapid material removal rates. These are used to mill grooves and slots. Plain mills are used to shape flat surfaces. Several cutters may be ganged together on the arbor to mill a complex shape of slots and planes. Special cutters can also cut grooves, bevels, radii, or indeed any section desired. These specialty cutters tend to be expensive. Simplex mills have one spindle, and duplex mills have two. It is also easier to cut gears on a horizontal mill.

The vertical-vs-horizontal distinction seems trivial from some viewpoints; after all, changing the mounting of a machine part, accessory, or workpiece by 90° is often a straightforward matter. Yet the distinction has recurrently held more importance than one might expect, for similar reasons that the horizontal-lathe-vs-vertical-lathe distinction has mattered. The shape and size of workpieces and the number of sides that they require machining on can make one type of machine more practical than another.

In the pre-NC era, horizontal milling machines appeared first, because they evolved by putting milling tables under lathe-like headstocks. Vertical mills appeared in subsequent decades, and accessories in the form of add-on heads to change horizontal mills to vertical mills (and later vice versa) have been commonly used. Work in which the spindle's axial movement is normal to one plane, with an endmill as the cutter, lends itself to a vertical mill, where the operator can stand before the machine and have easy access to the cutting action by looking down upon it. Thus most diesinking work has always favored a vertical mill. The heavier the workpiece, the more likely one is to want it to sit directly on the table rather than being mounted indirectly on an angle plate (or rotary table or indexing head perpendicular to the table), just as short, heavy workpieces are easier to set up on a vertical lathe or boring mill (and remove later) than on the headstock of a horizontal-axis lathe. Even in the CNC era, a heavy workpiece needing machining on multiple sides lends itself to a horizontal machining center, while diesinking lends itself to a vertical one.

Shaper

A shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is analogous to that of a lathe, except that it is linear instead of helical. A shaper is analogous to a planer, but smaller, and with the cutter riding a ram that moves above a stationary workpiece, rather than the entire workpiece moving beneath the cutter. The ram is moved back and forth typically by a crank inside the column; hydraulically actuated shapers also exist.

Types

Shapers are mainly classified as standard, draw-cut, horizontal, universal, vertical, geared, crank, hydraulic, contour and traveling head.[1] The horizontal arrangement is the most common. Vertical shapers are generally fitted with a rotary table to enable curved surfaces to be machined. The vertical shaper is essentially the same thing as a slotter (slotting machine), although technically a distinction can be made if one defines a true vertical shaper as a machine whose slide can be moved from the vertical. A slotter is fixed in the vertical plane.

Very small machines have been successfully made to operate by hand power. As size increases, the mass of the machine and its the power requirements increase, and it becomes necessary to use a motor or other supply of mechanical power. This motor drives a mechanical arrangement (using a pinion gear, bull gear, and crank, or a chain over sprockets) or a hydraulic motor that supplies the necessary movement via hydraulic cylinders.

Operation

A shaper operates by moving a hardened cutting tool backwards and forwards across the

workpiece. On the return stroke of the ram the tool is lifted clear of the workpiece, reducing the cutting action to one direction only.

The workpiece mounts on a rigid, box-shaped table in fr

ont of the machine. The height of the table can be adjusted to suit this workpiece, and the table can traverse sideways underneath the reciprocating tool, which is mounted on the ram. Table motion may be controlled manually, but is usually advanced by an automatic feed mechanism acting on the feedscrew. The ram slides back and forth above the work. At the front end of the ram is a vertical tool slide that may be adjusted to either side of the vertical plane along the stroke axis. This tool-slide holds the clapper box and toolpost, from which the tool can be positioned to cut a straight, flat surface on the top of the workpiece. The tool-slide permits feeding the tool downwards to deepen a cut. This adjustability, coupled with the use of specialized cutters and toolholders, enable the operator to cut internal and external gear tooth profiles, splines, dovetails, and keyways.

The ram is adjustable for stroke and, due to the geometry of the linkage, it moves faster on the return (non-cutting) stroke than on the forward, cutting stroke. This action is via a slotted link or whitworth link.

Plasma cuttingPlasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch. In this process, an inert gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut,

turning some of that gas to plasma. The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut.

Process

The HF Contact type uses a high-frequency, high-voltage spark to ionise the air through the torch head and initiate an arc. These require the torch to be in contact with the job material when starting, and so are not suitable for applications involving CNC cutting.

The Pilot Arc type uses a two cycle approach to producing plasma, avoiding the need for initial contact. First, a high-voltage, low current circuit is used to initialize a very small high-intensity spark within the torch body, thereby generating a small pocket of plasma gas. This is referred to as the pilot arc. The pilot arc has a return electrical path built into the torch head. The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc. Plasma arcs are extremely hot and are in the range of 25,000 °C (45,000 °F).[1]

Plasma is an effective means of cutting thin and thick materials alike. Hand-held torches can usually cut up to 2 in (48 mm) thick steel plate, and stronger computer-controlled torches can cut steel up to 6  inches (150 mm) thick. Since plasma cutters produce a very hot and very localized "cone" to cut with, they are extremely useful for cutting sheet metal in curved or angled shapes.

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called Arc eye as well as damage from debris.

Starting methods

Plasma cutters use a number of methods to start the arc. In some units, the arc is created by putting the torch in contact with the work piece. Some cutters use a high voltage, high frequency circuit to start the arc. This method has a number of disadvantages, including risk of electrocution, difficulty of repair, spark gap maintenance, and the large amount of radio frequency emissions.[2] Plasma cutters working near sensitive electronics, such as CNC hardware or computers, start the pilot arc by other means. The nozzle and electrode are in contact. The nozzle is the cathode, and the electrode is the anode. When the plasma gas begins to flow, the nozzle is blown forward. A third, less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier.

Inverter plasma cutters

Analog plasma cutters, typically requiring more than 2 kilowatts, use a heavy mains-frequency transformer. Inverter plasma cutters rectify the mains supply to DC, which is fed into a high-frequency transistor inverter between 10 kHz to about 200 kHz. Higher switching frequencies give greater effiencies in the transformer, allowing its size and weight to be reduced.

The transistors used were initially MOSFETs, but are now increasingly using IGBTs. With paralleled MOSFETs, if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter. A later invention, IGBTs, are not as subject to this failure mode. IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors.

The switch mode topology is referred to as a dual transistor off-line forward converter. Although lighter and more powerful, some inverter plasma cutters, especially those without power factor correction, cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so; it is only valid for small, light portable generators). However newer models have internal circuitry that allow units without power factor correction to run on light power generators.

Plasma gouging

Plasma gouging is a related process, typically performed on the same equipment as plasma cutting. Instead of cutting the material, plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different), and a longer torch-to-workpiece distance, to blow away metal. Plasma gouging can be used in a variety of applications, including removing a weld for rework. The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm. Torch leads also can be protected by a leather sheath or heavy insulation.

CNC cutting methods

Plasma cutters have also been used in CNC (computer numerically controlled) machinery. Manufacturers build CNC cutting tables, some with the cutter built in to the table. The idea behind CNC tables is to allow a computer to control the torch head making clean sharp cuts. Modern CNC plasma equipment is capable of multi-axis cutting of thick material, allowing opportunities for complex welding seams on CNC welding equipment that is not possible otherwise. For thinner material cutting, plasma cutting is being progressively replaced by laser cutting, due mainly to the laser cutter's superior hole-cutting abilities.

A specialized use of CNC Plasma Cutters has been in the HVAC industry. Software will process information on ductwork and create flat patterns to be cut on the cutting table by the plasma torch. This technology has enormously increased productivity within the industry since its introduction in the early 1980s.

In recent years there has been even more development in the area of CNC Plasma Cutting Machinery. Traditionally the machines' cutting tables were horizontal but now due to further research and development Vertical CNC Plasma Cutting Machines are available. This advancement provides a machine with a small footprint, increased flexibility, optimum safety, faster operation.

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc. This allows near-laser precision on plasma cut edges. Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing.

MAINTENANCE OF A COIL SPRING

Coil spring is an integral part of the bogie system. They are of two types depending upon their size. One is called Bolster spring (which is of big size coil spring) while the other is called an Axle box (small size coil spring). These springs are maintained through three processes followed in an order, which are short blasting, magnaflux test and load testing. These processes are as follows

Short Blasting Of Coil Spring

This process is done to turn a rusted spring into a rustles spring using the help of a spherical material called short (which is an alloy of steel and iron).

Procedure

The whole procedure is done automatically with the help of a ‘short blasting machine’.

First of all, spherical shorts of dia. 280 micrometer are poured in the inlet tank. Then with the help of a pump these shorts are taken at a height in a tank which has an opening at the bottom connected to a pipe. Below the pipe a blower or a fan is connected to provide the sufficient thrust to these shorts.

At the same time, coils are inserted one by one on a horizontal plane in the machine. In the path, at midway there is the pipe above them, pouring shorts with a high force.

These shorts coming with a high speed hits the rusted coil springs and removes the rust.

These rustles coils then come outside of the machine through another opening. The rust material and the used shorts are collected in a tank. In this way a neat and clean coil spring is obtained.

MAGNAFLUX TESTING OF COIL SPRING

This is the second procedure operated on the coil spring. This is to detect any fault like cracks in the spring. The testing is based on the principle of electric magnetic field.

Procedure

First of all, a coil spring is placed on the testing machine. Below the machine a tank was provided, in that tank we pour our testing agent i.e. a combination of kerosene oil and magnaflux (a chemical powder). It should be poured in a fixed ratio. For every one lt. 0.75gm. Of magnaflux should be added.

On one side of the coil spring a sheet is there, called ‘contact shot’. A piston called as ‘center contact piston’ from the other side emerges and through the spring it touches the ‘contact shot’. With the help of a small pump, oil is taken above to a pipe placed above the coil spring. Oil is poured on the spring, so that it can penetrate into the cracks, if any.

Current supply is made ‘on’. Thus an electromagnetic field is generated around the spring. The surrounding of the spring is then transformed into a dark room with the help of the black curtains. Ultra violet lights are switch ‘on’ which is light blue in color. If any crack was there in the spring, it can be spotted in a white color.

LOAD TESTING

This testing is done to ensure the load bearing strength of the coil spring.

Procedure

In this testing, a coil spring is placed in a load-testing machine where a compressive load acts on it, for some time. If the spring faces that load without any deformation then that spring is considered best for working and safety. These loads applied are fixed for the springs like: -

For the springs like

For axle box of ICF coach - 20 KN

For bolster spring of ICF coach - 32.2 KN

On applying the load, a deflection in millimeter can be seen in the machine. The springs are thus divided into groups according to the deflections they give. This classification is as: -

For axle box facing 20 KN load. Deflection (mm) Group

279-284 A

285-289 B

290-295 C

For bolster spring facing 32.2KN load.

Deflection (mm) Group

301-305 A

306-310 B

311-315 C

Note: - 9.8 KN = 1TonneAfter these three processes, springs are left for painting and are ready for fitting.

AIR BRAKE SYSTEM

On railcars, an air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on March 5, 1872. The Westinghouse Air Brake Company (WABCO) was subsequently organized to manufacture and sell Westinghouse's invention. In various forms, it has been nearly universally adopted.

The Westinghouse system uses air pressure to charge air reservoirs (tanks) on each car. Full air pressure signals each car to release the brakes. A reduction or loss of air pressure signals each car to apply its brakes, using the compressed air in its reservoirs.

Background

Prior to the introduction of air brakes, stopping a train was a difficult business. In the early days when trains consisted of one or two cars and speeds were low, the engine driver could stop the train by reversing the steam flow to the cylinders, causing the locomotive to act as a brake. However, as trains got longer, heavier and faster, and started to operate in mountainous regions, it became necessary to fit each car with brakes, as the locomotive was no longer capable of bringing the train to a halt in a reasonable distance.

The introduction of brakes to railcars necessitated the employment of additional crew members called brakemen, whose job it was to move from car to car and apply or release the brakes when signaled to do so by the engineer with a series of whistle blasts. Occasionally, whistle signals were not heard, incorrectly given or incorrectly interpreted, and derailments or collisions would occur because trains were not stopped in time.

Brakes were manually applied and released by turning a large brake wheel located at one end of each car. The brake wheel pulled on the car's brake rigging and clamped the brake shoes against the wheels. As considerable force was required to overcome the friction in the brake rigging, the brakeman used a stout piece of wood called a "club" to assist him in turning the brake wheel.

The job of a passenger train brakeman wasn't too difficult, as he was not exposed to the weather and could conveniently move from car to car through the vestibules, which is where the brake wheel was (and still is, in many cases) located. Also, passenger trains were not as heavy or lengthy as their freight counterparts, which eased the task of operating the brakes.

A brakeman's job on a freight train was far more difficult, as he was exposed to the elements and was responsible for many more cars. To set the brakes on a boxcar (UIC: covered wagon) the brakeman had to climb to the roof ("coon the buggy" in railroad slang) and walk a narrow catwalk to reach the brake wheel while the car was swaying and pitching beneath his feet. There was nothing to grasp other than the brake wheel itself, and getting to the next car often required jumping. Needless to say, a freight brakeman's job was extremely dangerous, and many were maimed or killed in falls from moving trains.

Complicating matters, the manually operated brakes had limited effectiveness and controlling a train's speed in mountainous terrain was a dicey affair. Occasionally, the brakemen simply could not set enough brakes to a degree where they were able to reduce speed while descending a grade, which usually resulted in a runaway—followed by a disastrous wreck.

When adopted, the Westinghouse system had a major effect on railroad safety. Reliable braking was assured, reducing the frequent accidents that plagued the industry. Brakemen were no longer required to risk life and limb to stop a train, and with the engineer now in control of the brakes, misunderstood whistle signals were eliminated. As a result, longer and heavier trains could be safely run at higher speeds.

During his lifetime, Westinghouse made many improvements to his invention. The United States Congress passed the Safety Appliance Act in 1893 making the use of some automatic brake system mandatory. By 1905, over 2,000,000 freight, passenger, mail, baggage and express railroad cars and 89,000 locomotives in the United States were equipped with the Westinghouse Automatic Brake.

Overview

In the air brake's simplest form, called the straight air system, compressed air pushes on a piston in a cylinder. The piston is connected through mechanical linkage to brake shoes that can rub on the train wheels, using the resulting friction to slow the train. The mechanical linkage can become quite elaborate, as it evenly distributes force from one pressurized air cylinder to 8 or 12 wheels.

The pressurized air comes from an air compressor in the locomotive and is sent from car to car by a train line made up of pipes beneath each car and hoses between cars. The principal problem with the straight air braking system is that any separation between hoses and pipes causes loss of air pressure and hence the loss of the force applying the brakes. This deficiency could easily cause a runaway train. Straight air brakes are still used on locomotives, although as a dual circuit system, usually with each bogie (truck) having its own circuit.

In order to design a system without the shortcomings of the straight air system, Westinghouse invented a system wherein each piece of railroad rolling stock was equipped with an air reservoir and a triple valve, also known as a control valve.

The triple valve is described as being so named as it performs three functions: Charging air into a air tank ready to be used, applying the brakes, and releasing them. In so doing, it supports certain other actions (i.e. it 'holds' or maintains the application and it permits the exhaust of brake cylinder pressure and the recharging of the reservoir during the release). In his patent application, Westinghouse refers to his 'triple-valve device' because of the three component valvular parts comprising it: the diaphragm-operated poppet valve feeding reservoir air to the brake cylinder, the reservoir charging valve, and the brake cylinder release valve. When he soon improved the device by removing the poppet valve action, these three components became the piston valve, the slide valve, and the graduating valve.

If the pressure in the train line is lower than that of the reservoir, the brake cylinder exhaust portal is closed and air from the car's reservoir is fed into the brake cylinder to apply the brakes. This action continues until equilibrium between the brake pipe pressure and reservoir pressure is achieved. At that point, the airflow from the reservoir to the brake cylinder is lapped off and the cylinder is maintained at a constant pressure.

If the pressure in the train line is higher than that of the reservoir, the triple valve connects the train line to the reservoir feed, causing the air pressure in the reservoir to increase. The triple valve also causes the brake cylinder to be exhausted to atmosphere, releasing the brakes.

As the pressure in the train line and that of the reservoir equalize, the triple valve closes, causing the air pressure in the reservoir and brake cylinder to be maintained at the current level.

Unlike the straight air system, the Westinghouse system uses a reduction in air pressure in the train line to apply the brakes. When the engineer (driver) applies the brake by operating the locomotive brake valve, the train line vents to atmosphere at a controlled rate, reducing the train line pressure and in turn triggering the triple valve on each car to feed air into its brake cylinder. When the engineer releases the brake, the locomotive brake valve portal to atmosphere is closed, allowing the train line to be recharged by the compressor of the locomotive. The subsequent increase of train line pressure causes the triple valves on each car to discharge the contents of the brake cylinder to atmosphere, releasing the brakes and recharging the reservoirs.

Under the Westinghouse system, therefore, brakes are applied by reducing train line pressure and released by increasing train line pressure. The Westinghouse system is thus fail safe—any failure in the train line, including a separation ("break-in-two") of the train, will cause a loss of train line pressure, causing the brakes to be applied and bringing the train to a stop.

Modern air brake systems are in effect two braking systems combined:

The service brake system, which applies and releases the brakes during normal operations, and

The emergency brake system, which applies the brakes rapidly in the event of a brake pipe failure or an emergency application by the engineer.

When the train brakes are applied during normal operations, the engineer makes a "service application" or a "service rate reduction”, which means that the train line pressure reduces at a controlled rate. It takes several seconds for the train line pressure to reduce and consequently takes several seconds for the brakes to apply throughout the train. In the event the train needs to make an emergency stop, the engineer can make an "emergency application," which immediately and rapidly vents all of the train line pressure to atmosphere, resulting in a rapid application of the train's brakes. An emergency application also results when the train line comes apart or otherwise fails, as all air will also be immediately vented to atmosphere.

In addition, an emergency application brings in an additional component of each car's air brake system: the emergency portion. The triple valve is divided into two portions: the service portion, which contains the mechanism used during brake applications made during service reductions, and the emergency portion, which senses the immediate, rapid release of train line pressure. In addition, each car's air brake reservoir is divided into two portions—the service portion and the emergency portion—and is known as the "dual-compartment reservoir”. Normal service applications transfer air pressure from the service portion to the brake cylinder, while emergency applications cause the triple valve to direct all air in both the service portion and the emergency portion of the dual-compartment reservoir to the brake cylinder, resulting in a 20–30% stronger application.

The emergency portion of each triple valve is activated by the extremely rapid rate of reduction of train line pressure. Due to the length of trains and the small diameter of the train line, the rate of reduction is high near the front of the train (in the case of an engineer-initiated emergency application) or near the break in the train line (in the case of the train line coming apart). Farther away from the source of the emergency application, the rate of reduction can be reduced to the point where triple valves will not detect the application as an emergency reduction. To prevent this, each triple valve's emergency portion contains an auxiliary vent port, which, when activated by an emergency application, also locally vents the train line's pressure directly to atmosphere. This serves to propagate the emergency application rapidly along the entire length of the train.

Enhancements

Electro-pneumatic or EP brakes are a type of air brake that allows for immediate application of brakes throughout the train instead of the sequential application. EP brakes have been in use in German high-speed trains (most notably the ICE) since the late 1980s, and in British practice since 1949, fully described in Electro-pneumatic brake system on British railway trains. Electro-pneumatic brakes are currently in testing in North America and South Africa in captive service ore and coal trains.

Passenger trains have had for a long time a 3-wire version of the Electro-pneumatic brake, which gives seven levels of braking force. In most cases the system is not fail-safe, with the wires being energized in sequence to apply the brakes, but the conventional automatic air brake is also provided to act as a fail safe, and in most cases can be used independently in the event of a failure of the EP brakes.

In North America, WABCO supplied HSC (High Speed Control) brake equipment for several post-World War II streamlined passenger trains. This was an electrically controlled overlay on conventional D-22 passenger and 24-RL locomotive brake equipment. On the conventional side, the control valve set a reference pressure in a volume, which set brake cylinder pressure via a relay valve. On the electric side, pressure from a second straight-air trainline controlled the relay valve via a two-way check valve. This "straight air" trainline was charged (from reservoirs on each car) and released by magnet valves on each car, controlled electrically by a 3 wire trainline, in turn controlled by an "electro-pneumatic master controller" in the controlling locomotive. This controller compared the pressure in the straight air trainline with that supplied by a self lapping portion of the engineers valve, signaling all of the "apply" or "release" magnets valves in the train to open simultaneously, changing the pressure in the "straight air" trainline much more rapidly and evenly than possible by simply supplying air directly from the locomotive. The relay valve was equipped with four diaphragms, magnet valves, electric control equipment, and an axle-mounted speed sensor, so that at speeds over 60 mph full braking force was applied, and reduced in steps at 60, 40 and 20 mph, bringing the train to a gentle stop. Each axle was also equipped with anti-lock brake equipment. The combination minimized braking distances, allowing more full-speed running between stops. The "straight air" (electro-pneumatic trainline), anti-lock, and speed graduating portions of the system were not dependent on each other in any way, and any or all of these options could be supplied separately. [2]

Later systems replace the automatic air brake with an electrical wire (in the UK, at least, known as a "round the train wire") that has to be kept energized to keep the brakes off.

More recent innovations are electronically controlled pneumatic brakes where the brakes of all the wagons (cars) and locomotives are connected by a kind of local area network, which allows individual control of the brakes on each wagon, and the reporting back of performance of each wagon's brakes.

Limitations

The Westinghouse air brake system is very trustworthy, but not infallible. Recall that the car reservoirs recharge only when the brake pipe pressure is higher than the reservoir pressure, and that the car reservoir pressure will rise only to the point of equilibrium. Fully recharging the reservoirs on a long train can require considerable time (8 to 10 minutes in some cases[3]), during which the brake pipe pressure will be lower than locomotive reservoir pressure.

If the brakes must be applied before recharging has been completed, a larger brake pipe reduction will be required in order to achieve the desired amount of braking effort, as the system is starting out at a lower point of equilibrium (lower overall pressure). If many brake pipe reductions are made in short succession ("fanning the brake" in railroad slang), a point may be reached where car reservoir pressure will be severely depleted, resulting in substantially reduced brake cylinder piston force, causing the brakes to fail. On a descending grade, the unfortunate result will be a runaway.

In the event of a loss of braking due to reservoir depletion, the engineer (driver) may be able to regain control with an emergency brake application, as the emergency portion of each car's dual-compartment reservoir should be fully charged—it is not affected by normal service reductions. The triple valves detect an emergency reduction based on the rate of brake pipe pressure reduction. Therefore, as long as a sufficient volume of air can be rapidly vented from the brake pipe, each car's triple valve will cause an emergency brake application. However, if the brake pipe pressure is too low due to an excessive number of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving the engineer with no means to stop the train.

To prevent a runaway due to loss of brake pressure, dynamic (rheostatic) braking can be utilized so the locomotive(s) will assist in retarding the train. Often, blended braking, the simultaneous application of dynamic and train brakes, will be used to maintain a safe speed and keep the slack stretched as the train crests a grade.

Another solution to loss of brake pressure is the two-pipe system, fitted on most modern passenger stock and many freight wagons. In addition to the traditional brake pipe, this enhancement adds the main reservoir pipe, which is continuously charged with air directly from the locomotive's main reservoir. The main reservoir is where the locomotive's air compressor output is stored, and is ultimately the source of compressed air for all systems that use it.

Since the main reservoir pipe is kept constantly pressurized by the locomotive, the car reservoirs can be charged independently of the brake pipe, this being accomplished via a check valve to prevent backfeeding into the pipe. This arrangement helps to reduce the above described pressure loss problems, and also reduces the time required for the brakes to release, since the brake pipe only has to recharge itself.

Main reservoir pipe pressure can also be used to supply air for auxiliary systems such as pneumatic door operators or air suspension. Nearly all passenger trains (all in the UK and USA), and many freights, now have the two-pipe system.

Accidents

The air brake can fail if one of the cocks where the pipes of each carriage are joined together is accidentally closed. In this case, the brakes on the wagons behind the closed cock will fail to respond to the driver's command. This happened in 1953 to the Federal Express, a Pennsylvania Railroad train pulling in to Washington DC's Union Station, causing the train to crash into the passenger concourse and fall through the floor. Similarly, in the Gare de Lyon train accident a valve was accidentally closed by the crew, reducing braking power.

There are a number of safeguards that are usually taken to prevent this sort of accident happening. Railroads have strict government-approved procedures for testing the air brake systems when making up trains in a yard or picking up cars en route. These generally involve connecting the air brake hoses, charging up the brake system, setting the brakes

and manually inspecting the cars to ensure the brakes are applied, and then releasing the brakes and manually inspecting the cars to ensure the brakes are released. Particular attention is usually paid to the rearmost car of the train, either by manual inspection or via an automated end-of-train device, to ensure that brake pipe continuity exists throughout the entire train. When brake pipe continuity exists throughout the train, failure of the brakes to apply or release on one or more cars is an indication that the cars' triple valves are malfunctioning. Depending on the location of the air test, the repair facilities available, and regulations governing the number of inoperative brakes permitted in a train, the car may be set out for repair or taken to the next terminal where it can be repaired.

StandardizationThe modern air brake is not identical with the original airbrake as there have been slight changes in the design of the triple valve, which are not completely compatible between versions, and which must therefore be introduced in phases. That said, the basic air brakes used on railways worldwide are remarkably compatible.

Vacuum brakes

The main competitor to the air brake is the vacuum brake, which operates on negative pressure. The vacuum brake is a little simpler than the air brake, with an ejector with no moving parts on steam engines or a mechanical or electrical "exhauster" on a diesel or electric locomotive replacing the air compressor. Disconnection taps at the ends of cars are not required as the loose hoses are sucked onto a mounting block.

However, the maximum pressure is limited to atmospheric pressure, so that all the equipment has to be much larger and heavier to compensate. This disadvantage is made worse at high altitude. The vacuum brake is also considerably slower acting in both applying and releasing the brake; this requires a greater level of skill and anticipation from the driver. Conversely, the vacuum brake had the advantage of gradual release long before the Westinghouse automatic air brake, which was originally only available in the direct-release form still common in freight service.

A primary fault of vacuum brakes is the inability to easily find leaks. In a positive air system, a leak is quickly found due to the escaping pressurized air. This problem left the British railways in a terrible condition, where trains would have to be stopped at the top of grades to set the manual brakes on each car. Purchase and maintenance of a mechanical air pump on hundreds of engines is nothing compared to keeping the vacuum line in good order across a fleet of tens of thousands of freight cars.

Electro-vacuum brakes have also been used with considerable success on South African electric multiple unit trains. Despite requiring larger and heavier equipment as stated above, the performance of the electro-vacuum brake approached that of contemporary electro-pneumatic brakes. However, their use has not been repeated

Principal of operation

Followings operations are to be done on the braking system for applying brakes:

Charging the brake system.

Brake pipe throughout the length of the train is charged with compressed air at 5kg/sq.cm.

Feed pipe throughout the length of the train is charged with compressed air at 6 kg/sq.cm.

Control reservoir is charged to 5kg/sq.cm.

Auxiliary reservoir is charged to 6kg/sq.cm.

Brake applicant stage

For brake applicant the brake pipe pressure is dropped by venting air from the drivers brake value subsequently the following a chain takes place.

The control reservoir is disconnected from the brake pipe.

This distributes value connects the auxiliary reservoir to the brake cylinders and the brake cylinders piston is pushed outwards for applicant of brakes.

The auxiliary reservoir is however continuously charged from feed pipe at 6Kg 1cm2.

Brake release Stage

Brake is released by recharging pipe 5Kg2 pressure through the

drivers brake value.

The distributor value isolated the brake cylinders from the auxiliary

reservoir.

The brake cylinder through pressure is vented to atmosphere through

DV and the brake cylinders piston moves in words.