2

STUDY OF

BASIC COMPONENTS OF HYDRAULICS IN WIRE ROD MILL

M.V.KRISHNA REDDY N.ABHISHEK

1210808132 1210808141

S.BHARGAV V.S.K.GUPTA

1210808152 1210808164

V.PREM KUMAR

1210808165

Under the guidance of

T.JAGADEESHWARA RAO

AGM(Mech)

Wire Rod Mill ,Visakhapatnam Steel Plant

3

CERTIFICATE

This is to certify that the Study report entitled Study of basic components of hydraulics in wire

rod mill of Visakhapatnam steel plant is being submitted by

M.V.KRISHNA REDDY 1210808132

N.ABHISHEK 1210808141

S.BHARGAV 1210808152

V.S.K.GUPTA 1210808164

V.PREM KUMAR 1210808165

In partial fulfillment of the degree of Bachelor of Technology in mechanical branch in

GITAM INSTITUTE OF TECHNOLOGY,GITAM UNIVERSITY is a record of

bonafied work carried out by them under my guidance and supervision.

T.JAGADEESWARA RAO

(Asst. General. Manager)

WRM DEPARTMENT, VSP

4

ACKNOWLEDGEMENT

It is my pleasure and duty to express my indebtedness to Sir T. Jagadeeswara Rao

(AGM) WRM DEPARTMENT, VSP for providing us the guidance and required assistance to

enable us to undergo our training a success and helped us a lot in acquiring knowledge about the

working of industrial equipments related to the subject.

I would also like to thank Dr.S.Kamaluddin, Head of the department of mechanical

engineering GITAM INSTITUTE OF TECHNOLOGY for extending his help towards making

the training a success

I also thank training and development centre (T&DC), VSP for introducing us to the

industry and for holding such useful project training.

Lastly, I would like to thank all the employees of vsp with kind cooperation without

whom it would not have been possible to travel through various departments in the plant and

complete the project successfully.

5

OVERVIEW OF VIZAG STEEL PLANT

VISAKHAPATNAM STEEL PLANT, the first coast-based Integrated Steel Plant of

India is located 26km southwest of Visakhapatnam city. It was on 17th APRIL 1970, when the then

Prime Minister Smt. INDIRA GANDHI had officially announced the decision of Govt. of India to

set up an integrated Steel Plant at Visakhapatnam who also did the formal inauguration on 20th

January.

The project was estimated to cost Rs. 3897.28 crores, based on prices as on 4th quarter

of 1981.But during the implementation of VSP, it has been observed that the project cost has

increased substantially over the sanctioned cost, mainly due to price escalations and under

provisions in DPR estimates. In view of this and the critical fund situation, alternatives for

implementation.

6

Steel comprises one of the most important inputs in all sectors of economy.

Steel industry is both a basic and a core industry. The economy of any nation depends on a strong

base of iron and steel industry in that nation. Iron & steel making, as India has known a craft for a

long time. The growth of steel industry in India can be conveniently studied by dividing the period

into pre & post independence era. By 1950, the total installed capacity for ingot steel production

was 1.5 million tonnes per year. The capacity increased by 11 folds to about 16 million tones by

nineties. Presently in India, steel products are being produced from 4 different sources, namely

integrated Steel plants, Re-rolling Mills, Alloy & special steel plants. In integrated steel plants,

naturally occurring raw materials are processed into finished (steel) products in various stages.

Visakhapatnam Steel Plant is the first shore-based integrated steel plant,

constructed with former USSR collaboration. It is the first integrated steel plant constructed in

South India, with many modern technological features, some of them for the first time in the

country. Among these are:

7 meter tall coke ovens with Dry quenching of coke

On ground blending of sinter base mix

Conveyer charging and bell less top for Blast furnace

Cast house slag granulation for Blast furnace

100% continuous casting of liquid steel

Gas expansion turbine for power generation utilizing Blast furnace top gas pressure

Hot metal desulphurization

Extensive treatment facilities of effluents for ensuring proper environmental protection

Computerization for process control

7

Sophisticated high speed and high production rolling mills

Major Sources of Raw Materials:

Water Supply: Operational water requirement of 36 mgd is being met from the Yeluru Water

Supply Scheme

Power Supply: Operational power requirement of 180 to 200 MW is being met through Captive

Power Plant. The capacity of power plant is 286.5 MW.VSP is exporting 60 MW power to APSEB.

Raw Material Source

Iron Ore Lumps & Fines Bailadilla, MP

BF Lime Stone Jaggayyapeta,AP

SMS Lime Stone UAE

BF Dolomite Madharam,AP

SMS Dolomite Madharam,AP

Manganese Ore Chipurupalli,AP

Boiler Coal Talcher,Orissa

Coking Coal Australia

Medium Coking Coal (MCC) Gidi/Swang/Rajarappa/kargali

8

MAJOR DEPARTMENTS OF VSP

Raw materials handling plant (RMHP):

VSP annually requires quality raw materials viz. iron ore, fluxes; coking and non coking coals etc.

to the tune of 12 to 13 million tons for producing 3 million tonnes of liquid steel. To handle such a

large volume of incoming raw materials received from different sources and to ensure timely supply

of consistent quality of feed materials to different VSP consumers, Raw Material Handling Plant

serves a vital function.

Coke Ovens and Coal Chemical Plant (CO and CCP):

Coke is manufactured by heating of crushed coking coal in the absence of air at a

temperature of 1000c and above for about 16 to 18 hours. At VSP there are three coke oven

batteries, 7m tall and having 67 ovens each. The carbonization takes place at 1000c to 1050c in

absence of air for 16 to 18 hours. The useful coal chemicals are extracted in coal chemical plant

from C. O. Gas. After recovering the coal chemicals the gas is used as a by-product fuel by mixing

it with gases such as BF Gas, LD Gas etc.

Sinter Plant (SP):

Sinter is a hard and porous ferrous material obtained by agglomeration of iron fines,

coke breeze, lime stone fines, metallurgical wastes viz. flue dust, mill scale, LD slag etc.

9

Sinter is a better feed material to blast furnace in comparison to iron ore lumps and its

usage in blast furnaces help in increasing productivity, decreasing the coke rate and improving the

quality of hot metal produced.

Blast Furnaces (BF):

Hot metal is produced in the Blast Furnaces, which are tall vertical furnaces. The

furnace is named as Blast Furnace as it runs with a blast at high pressure and temperature. Raw

Materials such as sinter, iron ore lumps, fluxes and coke are charged from the top and hot blast at

1100c to 1300c and 5.75 KSCG pressure is blown almost from the bottom. VSP has two 3200

cu.metre. Blast Furnaces namely Godavari and Krishna named after the two rivers of AP.

Steel Melt Shop (SMS):

Steel is an alloy of iron with carbon up to 1.8%. Hot metal produced in Blast Furnace

contains impurities such as Carbon, Silicon, Manganese, and Sulphur and phosphorous is not

suitable as a common Engineering Material. To improve the quality, the impurities are to be

eliminated or decreasing by oxidation process.

VSP produces steel employing three numbers of top blown Oxygen Converters. Each

converter is having 133cu.metre volume capable of producing 3 million tones of liquid steel

annually. The hot metal, steel scrap, fluxes form a part of the charge to the converters.

Continuous Casting Department (CCD):

10

Continuous casting may be defined as teaming of liquid steel in a mould with a false

bottom through which partially solidified ingot is continuously withdrawn at the same rate at which

liquid steel is teamed in the mould.

At VSP there are six-4 strand continuous casting machines capable of producing 2.82

Million tons per year, Blooms of size 250x250 mm and 250x320 mm.

ROLLING MILLS :

Blooms produced in SMS-CCD do not find much applications as such and are required to be shaped

into products such as billets, round, squares, angles (equal and unequal, channels, I-PE beams, HE

beams, wire rod and reinforcements by rolling them in, there sophisticated high capacity, high

speed, fully automated rolling mills, namely Light and Medium Merchant Mills (LMMM), Wire

Rod Mills (WRM) and Medium Merchant and Structural Mill (MMSM).

1. Light and Medium Merchant Mills: - LMMM comprises of two units in the billets/break

down mill 250 320 mm size blooms are rolled into billets of 125 mm size after heating them in two

nos. of walking beam furnaces of 200T/hr capacity each. This unit comprises of 7 stands (2

horizontal 859 1200mm) and 5 alternations vertical and horizontal stands (730 1000 mm and 630

1000 mm) billets are supplied from this mill to bar mill of LMMM, wire rod mills (WRM).

2. Wire Rod Mills (WRM):- Wire rod mill is a 4 strand, 25 strands fully sophisticated mill. The

mill has 4 zone combination type reheating furnace (walking beam cum walking hearth ) of 200T/hr

capacity for heating the billet received from the billet mill of LMMM to rolling temperature of

1200c.

11

3. Medium Merchant and Structural Mill (MMSM) :- This mill is a high capacity continuous of

20 strands arranged in 3 trains. Roughing train having 8 strands (4 two high horizontal strands, two

vertical strands and two combination)

Intermediate train has six mill strands as per details given below.

2 high horizontal stands

2 combination stands

2 horizontal stands/two universal stands

Finishing train consists of 6 stands namely

2 combination stands

4 horizontal stands/4 universal stands.

WIRE ROD MILL

Introduction

Wire Rod mills (WRM): wire rod mill is a 4 strand, 25 stands fully sophisticated mill. The mill

has 4 zone combination type reheating furnace (walking beam cum walking hearth ) of 200t/hr

capacity for heating the billets received from billet mill of LMMM to rolling temperature of 1200

degrees centigrade. The continuous 4 strand wire mill for the RASHTRIYA ISPAT NIGAM

LIMITED is a high speed roll mill of modern technological design, including equipment for

controlled cooling of rolled product from rolling heat by stelmor method. The mill is designer for

low and high carbon Steel up to 0.9% carbon.

CHARACTERISTIC DESIGN FEATURES OF THE WIRE ROD MILL

High production after a short starting time.

Reliable loading at high speeds.

12

High wire qualities.

Charging material:

BILLET WEIGHT: 1250 kg

CROSS SECTION DIMENSIONS: 125 x 125 mm

BILLET LENGTH: 1044 mm

Rolling Program:

5.5 to 12 mm round

6.0 to 12.7 mm rebar

Maximum coil weight 1200 kg

Outside coil diameter 1250mm

Inside coil diameter 850 mm

Coil height not compacted:

Round approximately 2200mm

Rebar 2200mm

Coil height compacted

Round approximately 1200 mm

Rebar 1350mm

Charging material:

The charging material rolled billets from the billet mill be straight, free from shells, free from

shrinkages cavities and additionally free from cracks as far as quality steel grades are concerned, so

that a continuous and the required quality is guaranteed.

Finished Material :

Based on max temperature difference across the billet cross section of 25 degree centigrade on

entering the mill train, the following tolerance values are obtained:

13

5.5mm 8 mm round (+/-) 0.15 mm

9 mm 12 mm round (+/-) 0.20 mm

Capacity of the Plant

The annual capacity of the rod mill be 850 000 tons of finished wire rods by three shift operation

and specified product mix.

EQUIPMENTS OF WIRE ROD MILL:

1. Roughing train

5 two high horizontal stands 600 mm dia.

2 two high horizontal stands 480 mm dia.

2. Intermediate train

3 two high horizontal stands 480 mm dia.

3 two high horizontal stands 480 mm dia.

3. Intermediate Block

4 single stands two high roughing blocks in HV arrangement.

4. Finishing train

4 one stand wire rod finishing blocks (Morgan type ) with 10 no twist two high rolling

units each in 45 degree arrangement

5. Billet depositing grids, inclined hoist, billet collect device.

6. Furnace approach roller table ejector for rejected billets.

7. Billets ejector.

8. With drawing pinch roll set, billet switch, pendulum shear.

9. 4 cropping and chopping shears.

10. 4 Horizons lopper.

11. Water cooling sections with 3 water cooling boxes each.

12. 4 Rotary cropping and cross cutting shears.

14

13. 2 Chopping shears.

14. Horizontal loppers.

15. 4 Water cooling sections with 3 water cooling boxes each.

16. 4 Pinch roll sets and 4 laying heads.

17. 4 Stelmor conveyors for delayed cooling, 10 cooling zones each.

18. 4 Coil forming chambers with dividing shears.

4 coil receiving stations.

4 Up ender loading stations

19. Power and free hook conveyor.

20. 6 coil compacting presses.

21. 6 coil unloading stations.

22. 4 coil weighing machines.

23. 2 Large coil compactor circuits comprising power and free conveyor, coil Transfer station,

large size coil compactor and unloading station.

Description of Mill Mechanical Equipment:

The inspected billets rolled by the billet unit to the size 125 x 125 x 10400mm are taken

from the billet store and were placed down on the first of the two charging grids in larders of 8 to 10

billets each. The weight capacity of the charging grid is 200tons which conforms to a storage

capacity sufficient to store the production of one hour.

The billets deposited are by means of for operated pawl transfers with

electromechanical drive moved towards the billet cross transport on the grids are passed to over to

that transport one by one.

The billet cross transport which is also arranged at (+/-)0 m takes the individual billets

with drag chains and transports them step by step from the billet charging grid NO.2.

15

In to the area of the inclined elevator. Nine billets in total can be deposited in the area

between billet charging grid and inclined elevator; they rest on roller chain carrier plates during

transport.

The furnace roller table extends from the area of the billet positioning device up on the

charging side of the walking beam the 48 driven rollers of the table are subdivided into two groups

with three disappearing stops between and two fixed stops arranged on both ends of the roller table.

The billets lying on the roller table are carried to the furnace by means of electrically

combined roller table sections with separately divided reversible rollers. The roller table is limited

by a fixed stop at its rear end.

Pneumatically operated disappearing stops prevented succeeding billets from colliding

with proceeding once on individual roller tables. With bottom heaters in the soaking zone has a

nominal through input capacity of 200t/hr.

The charging of the furnace will be done by walking beams, which transfers the 4 billets

together. The walking beams can be lifted and lowered as well as displaced in the longitudinal

direction to transfer the billets through the furnace step at a cycle of 72 sec per stroke.

Uniform heating of the billets is ensured by bottom and top heating to improve the temperature

compensation in the billets, they are pushed together on the soaking hearth in solid masonry at

the end of the furnace. This hearth made of temperature changes resistant and abrasion resistant

material has no load bearing cooled rails, so that no local cold spots can occur on the billets and

existing temperature differences are compared.

THE WALKING BEAM FURNACE OFFERS SEVERAL ADVANTAGES:

Smaller temperature difference across the billet cross section

Safe possibilities to vary billet length and billet cross section

16

Small heat losses due to water cooled rails

Simply emptying of furnace

Smaller wear of lining

The discharging temperature will be 12000 c depending on the steel quality.

On the discharging side of the furnace a billet discharging machine pushes the single billet from

furnace to the stand no.1 by help of rollers then it again aligned the following billet.

After discharging 4 billets, the walking beam moves a further step to refill the empty space

left by the billet ejected.

A hydraulically operated switch guides the billet to the respective stand.

The billet switch, a v-shaped CI design with open top, is lowered and moved underneath

the stand to be charged in the rise working position it is on pass line level and guides the billet

into the free groove in each case. After the initial pass has been carried out the switch is lowered

again and moves underneath the running billet into the receiving position for the next stand.

A four stand pendulum shear with hydraulic drive is arranged. The shear serves for

chopping and dividing the hot billet in case of cold head or rolling mal functions. The rolling

mill train is sub divided into seven roughing mills, an 8 stand intermediate mill and 10 stand rod

finishing mill. Rotary shears, snap shears, cooling sections and controlled material cooling and

placed between or in front of the coil handling facilities.

From stand no.1 to stand no.13 the stands are designed as 4 strands stands.Behind stand

no.13 the intermediate mill is sub divided into 4 single stand lines. A sum of 25 roll stands

results thus for each stand. The roughing comprises of 7 continuous 4 stands horizontal to high

mill stand into sizes.

Five stand 21 with a roll diameter of 600mm and the barrel length of 1000mm and stand

16 with roll diameter of 480mm and a barrel length of 920mm. For all mill stands the pass line

is 900mm above mill floor (=+5350mm). All stands are fitted with variable speed dc drives.

17

Post arranged to the roughing train four rotary shears, one for each stand, is placed for

cropping and chopping if malfunction should occur. Each shear has a variable speed dc drive

mounted on common base plate, which can be hydraulically moved out of the pass line for

maintenance purposes. The shears are operated for start-stop mode.

Every shear is controlled via a photo cell which transmits the cutting command for the front

crop end on the bar head and for the rear crop end at the bar head in connection with the pulse

generator of the last stand of preliminary train and making allowance for the forward slip and shear

staring distance.

In case of malfunctions, the shear chops the running bar and this operation different from

cropping in so far as the shear blades are not stopped after every cut but keep running with this

operating mode, the dividing lengths are approximately 500mm.

The intermediate mill comprises of six continuous four stand horizontal two high stands and

four single stand 8 HV intermediate blocks, the pre finishers.

At all, the complete intermediate train consists of 8 stands with 3different sizes

Three stands 16 with a roll diameter of 480mm and a barrel length of 800mm,

Three stands 12 with a roll dia of 375mm and a barrel length of 700mm and four pre

finisher block 8 with roll rings 210.5mm dia and the width of 72mm the six horizontal stands

are identical in the design of roughing mill but smaller sized, depending on the reduced rod size.

Behind stand no 13 the roll stand change in to single strand stands.

Guided by rod delivery pipes the 4 stands where spread up to4 uniform finishing lines.

A horizontal looper for each strand ensures stress relieved rolling. A loop is formed on the loop

table with the aid of loop. Supporting roll and being monitored continuously by a photo

cell and controlled by changing pre finisher speed. Immediately before the rolling stock enters

the pre finisher stand, it passes through a snap shear which interrupts the further supply in to the

stand in case of a malfunction of the running strand.

18

The pre finisher roll stands; H-V compact stands are in their design like those of finishing

block. Additional roller in entry guides for all in going ovals and free passage of the roll stock

without guide troughs between the horizontal stands as well as the single strand no twist

intermediate blocks with the horizontal loopers in front ensures optimal surface quality and

tolerances of the material as it leaves the intermediate mill.

To permit adoption of the HOT ROLLING TECHNOLOGY that means: reduction of

material in entry temperature upstream the finishing block plus additional cooling of rolled stock

inside the finishing blocks, one water box 4 finishing blocks. Guide troughs with hinge-mounted

covers are located ahead of behind the water box.

4 cooling pipes in the water box were supplied with 6 bar cooling water. Stripper nozzles

at the entrance and exit side whose jets are directed against the rolling direction got water with

air pressure of 12 bar. On each stand a rotary shear is arranged ahead of the switch and looper

table. The shear operates by the start-stop mode with a variable speed dc drive to crop or to

divide the rod.

Before the material enters the finishing block, it passes another horizontal looper and a

snap shear in front of the block. Their functions and their construction are like those in front of

the pre finishing blocks.

Four single strand 10 stand high speed MORGAN finishing block, which permit the final

speed above 80mts per second at a wire diameter of 5.5mm can be considered one of the high

elements of a high capacity rolling mill. The entire single piece block comprises a base frame

with 10 roll units and roll rings in cantilevered arrangement that are mounted in

horizontal/vertical arrangement in pairs offset by 90 degrees against each other. This allows free

rolling of the wire.

Tungsten carbide is the only material used for rolling rings. This leads to

prolonged tool life, close tolerances and dimensional stability of the groove. However, constant

19

cooling of the roll discs must be guaranteed to avoid inadmissibly high temperatures. The first

two roll units are designed as 8 inches stands because of the high roll pressures and roll

movements produced.

The 6 inches size is sufficient for the remaining 8 stands that follow.

These sizes allow an extremely favorable elongation of the rolling stock.

Two couple 2000 K. W. Dc motors drives the roll units.

The finishing blocks are covered with protective hoods.

Since the roll disc cooling is very important for the wear-resistant material used, the

finishing block is automatically locked against further material supply if cooling water supply

fail. The blocks are integrated with facilities for hot rolling. Provisions will be kept to install in

further a size measuring unit and defect scope after finishing blocks.

At the back of the finishing block, the rolling stock enters the rod cooling line. This cooling

line is a combination of a water cooling section with cooling and equalizing zones, one pinch roll set,

one loop layer and one roller stelmor roller transport system to cool down the rolling stock as desired,

with a delay of insulating hoods, by thermal rolling heat in such a way that wire has subsequently

specific properties that exercise a favorable influence on further working. The intension is to lower the

temperature level to such a extent that a scorbutic structure results which is maintained has uniform as

possible throughout the entire rolling length which corresponds to one coil weight. Different

temperatures can be obtained in front loop layers for different grades, so the desired optimum

properties with regard to metallurgical and mechanical features also obtained.

The following temperature at the loop layer apply for most customary steel grades:

Reinforced steel bars approx 780oc

Normal commercial grades 840oc

Soft grades approx 9000c

20

It is particular important for the consumer that a uniform material guide is supplied against his

order, so that a constant temperature can be maintained at the laying head by manufacture.

The wire leaving the wire rod mill is to show good properties, and has a uniform strength

curve has possible for the entire wire length and across the wire cross section after cooling down. As

the first stage of controlled cooling down in STELMOR cooling line, a water cooling section is used

immediately at the back of finishing block.

To further guide the loops, two guide plates are additionally provided on the exit side of

the protection door in order to make the loops tilt and over transfer them the stelmor conveyor.

As the machine is running, at particular attention should be paid to vibrations due to

unbalances caused by irregularities in mechanical system.

THE ADVANTAGES OF THE STELMOR PROCESS ARE FOLLOWING:

Less scale formation and thus a higher yield.

Higher drawing speeds due to the uniform properties of wire throughout the coli.

Improved uncoiling properties before drawing in the draw shop.

Lower picking costs due to shorter picking times with uniformly thin scale layers that can

easily be picked and mainly consists of FeO, instead of the sticking Fe3O4

The stelmor conveyor has an overall length of 60mts and a width of 1.45mts.

Furnace Details:

Type : Combined type walking beam cum Walking Hearth furnace.

Capacity : 200 T/hr

Dimensions : 42m X 10.92m

Fuel used : Mixed Gases (CO+ coke oven gas)

Calorific Value : 27,000 k cal/Nm3

Gas Flow : 2, 70,000 K cal/t

Thermal efficiency : 70%

Number of billets that can be accommodated 187.

Number of burners : 60 number flat flame

21

: 6 number long flame

Cycle time : 72secs

There were totally four zones in furnace. The temperatures in the four zones are:-

First Zone : 750 to 850c

Second Zone : 850 to 1000c

Third Zone : 1100 to 1200c

Fourth Zone : 1100 to 1200c

(Gas safety precautions: It is unsafe when CO gas exceeding 50 ppm.)

Equipment Features:

- Combined type walking beam cum Hearth furnace.

- Capacity is 200 T/hr.

- Air and gas recuperates for waste heat recovery

- Mixed gases (BF gas +CO+ coke oven gas) of 2200 K cal/ Nm 3

- Microprocessor system for temperature control.

- Four strand mill with 25 stands, Morgan Construction Company from stand 14 to 25

- Morgan No twist finishing blocks facilitating high mill speed of 76 m/sec (5.5 mm wire).

- Controlled cooling of wire rods with Stelmor cooling system for achieving superior

mechanical properties.

- Process control automation by computer and PLC.

- Hook circuit and online coil compactors for packing of wire rod coils.

- Ring grinding shop equipped with CNC.

22

HYDRAULICS

The word hydraulics is derived from the Greek word HYDOR and means water. This comprised

all things in affiliation with water. Today we understand under the term HYDRAULICS the

transmission and control of forces and movement by means of fluid.

The field of Fluid Mechanics is broken down as follows ---

Hydrostatics The mechanics of stills fluid

Hydrodynamics The mechanics of moving fluid.

The transfer of force in Hydraulics is an example of pure Hydrostatics and the conversion of flow

energy in turbine is an example of pure Hydrodynamics.

The special characteristics of HYDRAULIC SYSTEMS-

1. High forces (torques) with compact size, i.e. high power density.

2. Automatic force adoption.

3. Movements from stand still possible under full load.

4. Stepless change (control or regulation) of speed, torque, strokeforce etc, can be achieved simply.

5. Simple over load protection.

6. Suitable for controlling fast movement process and for extremely slow precision movements

7. Relatively simple accumulation of energy by means of gas.

8. Combined with decentralized transforming of the hydraulic energy back in to mechanical energy,

simplified central drive possible, giving a high degree of economy .

23

24

25

.

26

ADVANTAGES OF HYDRAULIC SYSTEMS:

1. Operator at variable speed by varying the pump delivery or using a flow control valve.

2. Hydraulic actuators can be reversed instantly while in full motion with out damage.

3. Over load protection by means of pressure relief valve.

4. High power to weight ratio.

5. Movent from stand still is possible under full load.

DIFFERENCE BETWEEN HYDRAULIC AND PNEUMATICS:

HYDRAULICS PNEUMATICS

1. High stiffness and hard. 1. Low stiffness and soft.

2. It has low and controlling speed. 2. It has high speed and cannot Control.

3. High energy by volume change. 3. Low energy by volume change.

4. Exact speed and positioning. 4. Exact speed and not in the mid way Only at the

positions.

5. Control and regulating the system. 5. No control takes place.

HYDRAULIC CYLINDERS (LINEAR MOTORS):

Hydraulic cylinders serve to carry out translatory (straight) movements and to transfer force by

doing so. In hydraulics a cylinder by name is understood to have a piston free to reciprocate inside.

The two main factors on which a hydraulic systems depends are ---

(1) The maximum force exerted by the piston.

(2) The speed of the piston.

TYPES OF CYLINDERS:

1. Single acting cylinder.

2. Double acting cylinder.

27

SINGLE ACTING CYLINDER: It allows force only one direction. Fluid directed in to

housing of the cylinder displaces the rod and thus forcing it out. Since there is no provision

for retracing the rod, the retracing force can be gravity or some mechanical means such as

spring force.

DOUBLE ACTING CYLINDER:

It permits application of hydraulic pressure on either side of the piston to control

linear motion in either of the motion in either of the two opposite directions. The fig shows a double

acting cylinder with piston rod on one side i.e. a differential cylinder. When oil is supplied via port

A, the piston rod travels out, when supplied via port B, it returns.

Maximum forces are related to the effective areas:

Travel outwards --- piston area,

Travel inwards --- annulus area and the maximum operating pressure.

OIL:

In order to carryout its function properly, the hydraulic fluid used must fulfill some requirements

such as those mentioned below:

QUALITY REQUIREMENTS OF HYDRAULIC FLUID:

1. Prevent rust.

2. Prevent formation of sludge.

3. Depress foaming.

4. Maintain its own stability and there by reduce fluid replacement cost.

28

5. Separate out water.

6. Be compatible with seals and gaskets.

FLUID PROPERTIES:

The following properties are to be considered while selecting a hydraulic oil:

1. Viscosity.

2. Pour point.

3. Lubricating ability.

4. Oxidation resistance.

5. Rust and corrosion protection.

As a power-transmitting medium, the fluid must flow easily through lines. Too much resistance to

flow creates considerable power loss.

The oil used here is HLP46 because the oil is less viscous. The high viscosity oil increases friction

and heat. Number 46 indicates the viscosity index.

DIRECTION CONTROL VALVE:

The basic function of this valve is to direct the flow from the inlet or pressure port to either of two

outlet ports. A 4/3 directional control valve is used for the power pack.

The sectional diagram shows the operation of the control spool by means of hand lever 1. The spool

is fixed rigidly to the operating mechanism 2 and follows its movement.

Return of the spool is by springs 3, which push the spool back into the off-position, after the

operating force stops i.e. the hand lever is released.

29

DIRECTIONAL CONTROL VALVES:-

The purpose of a D.C. Valve is to Direct the flow oil in the Direction we need.

Start, Stop and direction of flow of a pressure tluid is controlled by means of directional

control vctive and thus the direction of movement or holding position of cylinder, or

hydraulic motor is determined.

DC Valves are classified on the basis of

a) Type of internal valving arrangement

The valving element can be of the poppet type in which a piston or ball moves on & off a gear, the

rotary spool type or the sliding spool type in which the spool slides axiaty in a bore.

b) Methods of actuation

- A poppet type valve is usuaty operated by cams or plungers

- Rotary spool type can be manually operated (level or plunger) mechanically operated or

electrically operated with a solenoid Sliding spool type valve can be manual, mechanical, electrical

hydraulic & many others either singly or in combination.

C) No. of flow paths

Here, valves may be of the simple on-off variety or have a wide selection of flow paths through

30

them i.e. 2-way, 3-way & 4-way.

Types of Direction control valves:

The DC valves can be subdivided into

1) Directional Poppet Valves

2) Directional Spool Valves

1) DIRECTIONAl. POPPET VALVES:

Directional poppet valve dttfer mainly tram directional spool valves by their leak-free closing,

which cannot be achieved with spool valves, due to the tolerance required between spool and

housing.

31

32

33

34

35

36

37

38

39

40

Different Switching positions in directional control valves:-

41

42