Section 2 - Participant Manual - What is Torque

7/31/2019 Section 2 - Participant Manual - What is Torque

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What is Torque

Participant Manual


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Copyrigh t Not ic e 2008 Ingersoll Rand Company

Propr ie t ary Not ic es and Disc la im er

PROPRIETARY NOTICES

2008 Ingersoll Rand Company

CONFIDENTIAL AND TRADE SECRET INFORMATION. This manual contains confidentialand trade secret information owned by Ingersoll Rand Company (hereinafter referred to asProprietary matter. In consideration of the disclosure of the Proprietary Matter herein to theauthorized recipient hereof, the recipient shall treat the Proprietary Matter as secret andconfidential; shall not disclose or give such Proprietary Matter to third parties withoutexpress written authorization of INGERSOLL RAND; shall not use the Proprietary Matterexcept to the extent necessary to use or service the equipment disclosed herein; shalldisclose such Proprietary Matter only to those of its employees whose use of knowledge ofthe Proprietary Matter is necessary. This manual shall be returned upon request by Ingersoll

Rand Company. The unauthorized use of this manual may be punishable by law.

DISCLAIMERS

PROVIDED AS IS. THIS MANUAL AND THE CONTENTS HEREOF ARE PROVIDEDAS IS AND WITHOUT ANY IMPLIED WARRANTIES.


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What is TorqueParticipant Manual V1 3 of 30Last updated: 10/1/2008 | 2007 Ingersoll Rand Company

Table of Contents

Course Overview .................................................................................................................... 4

Definition of Terms .................................................................................................................. 5

Requirements of a Reliable Joint ............................................................................................ 6

The Fastener ........................................................................................................................... 7

Joint Type ............................................................................................................................. 11

Joint Design .......................................................................................................................... 12

Assembly Tool Consideration ............................................................................................... 14

Fastening Basics ................................................................................................................... 16

Tightening Strategy ............................................................................................................... 17

Torque Control ...................................................................................................................... 19

Torque Control with Angle Monitoring ................................................................................... 20

Angle Control ........................................................................................................................ 21

Yield Control ......................................................................................................................... 22

Prevailing Torque Tightening Strategy .................................................................................. 23

Drag Torque Strategy ........................................................................................................... 24

Notes ..................................................................................................................................... 25

Sales & Product Support ....................................................................................................... 27


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Course Overview

Business RationaleThis training course is designed to give you a better understanding of the precision fastening toolsand knowledge to better sell the tools.

Course Agenda

Day One Day Two Day ThreeIntroduction Programming of Controller On

ScreenProgramming of ControllersThrough ICS

Torque Overview ICS Loading ICS Multisync and PowerheadProgramming

Controller Overview Software Loading to ControllersTool Overview

Peripheral Overview


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Definition of TermsAlgorithm A computable set of steps to achieve a desired result. In tightening, a method of

determining a fixed point on the tightening curve by measurement of various tighteningparameters

Angle The angular rotation turned by the fastener during the tightening processCFM Cubic Feet per Minute. A measure of flow (usually used for air flow)Dynamic Load External load on the joint changes when the joint is in serviceFrictionCoefficient

A ratio of the frictional force and normal reaction between two contacting slidingsurfaces, for threaded fasteners its numerical value, is usually in the 0.08 to 0.30range.

Friction Factor A factor used to calculate the expected fastener clamp load, its value, k, is normally inthe 0.15-0.20 range.

Galling Very high friction under the bolt head or notGradient The rate of change of torque over a fixed value of angle often referred to as the joint

rate.HP Horsepower. A unit of power output.Inspection Fixed upper and lower values of torque, angle or gradient that are used for

accept/rejectMPa MegaPascals. Metric (ISO) unit of mechanical stress. 1 Mega Pascal = 1 Newton of

force per square millimeter of the fasteners cross-sectional area. (N/mm)Preload orClamp Load

The initial tensile clamping load induced in the fastener by tightening

PrevailingTorque

Torque generated by the fastener during run-down before any fastener preload isgenerated.

PSI Unit of mechanical stress. Pounds of force per square inch of the fasteners cross-sectional area.

Rc Measured hardness on the Rockwell C scaleScatter The spread of resulting torque values. Usually three Standard Deviations above and

below the set-pointService Loads Loads imposed on the bolted joint from external sources

Snug orThresholdTorque

A torque value below the final tightening torque from which point computation of theangle turned or the torque gradient is commenced

Static Load External load on the joint is constant when the joint is in serviceStick-slip Very high friction conditions in the threads causing them to bind (stick) and then

release (slip) as torque is applied. Often occurs as an oscillation.Tensile Strength The maximum stress that a fastener can be subjected to before it fractures.TensionStresses

Stresses in the fastener acting along the axis of the fastener

Threshold orSnug Torque

A torque value below the final tightening torque from which point computation of theangle turned or the torque gradient is commenced

Torque The effort required to overcome friction between the threaded fastener and theclamped parts in order to generate clamp load or tension in the fastener

Torsion Stresses Shear stress on the fastener originating from the applied torque

Windows Inspection parameters at the end of the tightening process. (They are also used for thebasis of calculation of capability indices Cp and Cpk.)

Yield controlledtightening

Tightening the fastener to its yield point under combined tension and torsion stressesusing a special algorithm.

Yield Strength The stress that a fastener is subjected to before it is forced to deform a certain amount(usually 0.2% of fastener grip length)


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Summary

Millions of nuts and bolts (threaded fasteners) are assembled every year to join partstogether. Fasteners are a critical element of most mechanical assemblies. The behavior of a bolted

joint is influenced by many factors including the initial level of fastener preload, or clamp load, that isdeveloped during tightening.

When a bolt is tightened, it develops tensile stresses (clamp load) and torsion stresses. It isthe tensile load that compresses the clamped parts and keeps the joint together. To properlyunderstand the fastening process requires a working knowledge of the requirements of a bolted joint.

Requirements of a Reliable Joint

There are five major areas to consider in achieving a reliable bolted joint:

The fastener quality

Calculation of the required clamping load Knowledge of the application and joint dynamics Controlled tightening process Maintenance of bolt clamp load under the action of the service conditions.

Fastener Quality

The quality is often considered a given in these days of supplier ISO certification and SPC techniquesapplied to most manufacturing processes.

However, the integrity of the fastened joint can be compromised by fasteners with material or threaddefects, particularly if the external loads are dynamic.

Calculation of the Required Clamping Load

It is necessary to calculate what the fastener clamp load should be to withstand the external loadsthat the assembly must sustain. Calculations based on mathematical models are available.

Application and Joint Dynamics

The application dynamics must be established. For example, will the joint be subjected to elevated orcryogenic temperatures, corrosion; thermal expansion effects of dissimilar materials and are theexternal loads static or dynamic?

Controlled Tightening Process

A controlled tightening strategy should be specified.

Maintenance of Fastener Clamp Load

If dynamic transverse forces are present, the fastener may require some form of self-locking.


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Functional Design

What forces will the fastener be subject to: tension, shear or bending? If the forces are significant, wemay need to use a fastener that can better withstand them or a tightening strategy that will ensuremaximum clamping load from the fastener after tightening.

Thread Types

What type of threads does the fastener have? Thread forming screws, if being tightening with a DCelectric fastening system, will need to be carefully selected as there will be a significant prevailingtorque throughout the tightening process.

Washers

Different types of washers can affect the torque-tension relationship.

Driving Recess

Will there be a problem locating or engaging the fastener drive?

Head Style

Once the fastener drive is engaged, will alignment be a problem? The driver must be perpendicular tothe fastener, with no side loading, in order for the torque reading to be precise.

Strength Grade

What is the strength grade of the fastener, does the companion thread have sufficient strength andengagement?

Materials

Are the materials of the fastener and companion threads compatible, will there be any problems inengaging the fasteners together?

Finish and Coating

Are the fasteners plain or plated? What is the plating? Zinc is frictional, particularly if both the bolt andnut are zinc plated. Cadmium plate has higher lubricity.

Prevailing Torque

Does the fastener have a locking element or locking compound? The compounds physicalcharacteristics can be affected by speed and may change during fastener rundown.

Friction

Frictional variations caused by the surface finish and lubrication conditions of the joint componentscan cause many inconsistencies in the tightening processes and the resulting clamp load scatter.This is illustrated using the following graph.


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Torque-Preload Relationship

The Torque-Preload relationship for a bolted joint is shown below. When the bolt is tightened to aconstant torque, T, the resulting preload or clamp load, Fp, obtained, depends on the frictioncoefficient, , of the bolt and clamped parts.

The example shown shows two different friction coefficients, = 0.10 (oily bolt) and = 0.18 (drybolt). The preload obtained with the oily bolt, Fp 2, is much greater than that obtained with the drybolt, Fp1, although the applied torque was identical. The amount of clamp load scatter that you canget within a batch of bolts tightened to the same torque can be 25-30%.

Thread types

Threads are most commonly manufactured by thread rolling between two dies. It is a very repeatableprocess and the finished product, when done correctly, produces high quality parts. If it is not donecorrectly, thread defects can be produced that can cause premature failure under alternating loads.

The important characteristics of threads are shown below. It is important not to have thread defects,particularly below the pitch diameter, as they can become the source of cracks in dynamicapplications and lead to failure.

There are numerous thread types and standards for both inch and metric fasteners. In verygeneralized terms, threads are usually classified as coarse pitch or fine pitch.

Coarse threads have fewer tendencies to cross thread and assemble quicker than equivalent finethreads. They are more tolerant to damage and have greater stripping strength. They tap better intobrittle materials that tend to spall during machining.

Fine threads can support higher clamping loads due to their increased stress area and are moreresistant to self-loosening due to transverse vibration. They tap better into hard materials or thin wallapplications.

Preload

Fp 2

Fp 1

TTorque

= 0.18

= 0.10


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Fastener Strength Grades

Two systems are in common use for gradinginch fasteners, the SAE system and the ASTMstandards.

The SAE system designates grades withnumbers from 1 through 8. These numbers haveno direct relationship to strength except thatincreasing numbers represent increasingstrength.

The ASTM standard grades are designated bytheir specification number and there may existdifferences in grade within these specificationgroups depending on fastener size or material.

For metric fasteners, the ISO standards use anumbering system that reflects the minimumtensile and yield strength. This system uses adecimal number for each strength grade. Thenumber on the left-hand side of the decimalpoint indicates 1/100th of the tensile strength in

MPa and the number on the right hand side theyield strength as a percentage of the tensilestrength.

It is usual to mark the heads of the inchfasteners to indicate their grade as shownaboveusing a number of lines on the bolt headface. In most cases, the manufacturers name orlogo is also present. Metric fasteners aremarked with their grade: 8.8, 10.9 or 12.9.

Inch Fastener Marking

Strength Grade Nom size Yield Strength PSI (min) Tensile Strength PSI (min)SAE grade 5 thru 1 inch 82,000 120,000SAE grade 8 thru 1 inch 130,000 150,000

ASTM A325 type 1 thru 1 inch 92,000 120,000ASTM A490 type 1 thru 1 inch 120,000 150,000

10.9

ACME

Grade

Metric Fastener Marking

Manufacturer

10.9

ACME

Grade

Metric Fastener Marking

Manufacturer

Strength Grade Nom size Yield Strength MPa (nom) Tensile Strength MPa (nom)

ISO 8.8 All 640 800ISO 10.9 All 900 1000ISO 12.9 All 1080 1200


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Joint TypeInfluence of the Joint

The type of joint will need to be considered when choosing a tightening strategy and fastenertightening system. Joints are classified as being soft, medium or hard.

Specification ISO 5393, which is a specification that describes how tools are tested, defines soft andhard joints by their joint rate or the amount of angle to turn the fastener through to reach the targettorque.

An example of a hard joint is a spark plug in a gasoline engine, once it seats you cannot turn itwithout the torque rising rapidly.

An example of a soft joint is a flange coupling with an O-ring or cork gasket where you have to turnthe fastener through a large angle to reach torque.

Most joints that you will encounter will fall between these two extremes. A guideline would be thatmost joints, once snugged or brought together by tightening the fastener, would reach their final

torque in the 60- 180 angle range.

We will see that not all tools are suitable for all joints. The same applies to tightening strategies, somestrategies work better on hard joints than soft joints.

Target torque

Normal angle

for most joints

60- 180

Torque

Angle

TOOL DIVISION103

JOINT TYPES

Hard Joint

30 or less rotation between snug and

final torque(27 between 10% and 100% torque)

Soft Joint

720 rotation between snug and final

torque

(650 between 10% and 100% torque)

JOINT RATES AS DEFINED BY ISO5393

Joint rate highly effects the final clamp load achieved by a

given torque

ClampLoad(t

orque)

Angle (Time)

ClampLoad

Angle


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Joint Design

For successful joint performance, the designer needs to ensure that certain design parameters aremet.

Thread Engagement

The chart on the left shows the required thread engagement, as a factor of the bolt diameter, for fourtypical joint materials.

This shows that for an internal thread manufactured from steel, heat treated to 40 Rc, would requirebetween 0.9 and 1.1 times the fastener diameter of thread engagement. In, addition, there should beat least three unengaged threads so that the most heavily stressed threads, which are the firstengaged threads, do not coincide with the first thread of the fastener.

It is recommended that a number of unengaged threads, at least three, are designed in the joint. Thisinsures that the most heavily stressed first engaged threads do not coincide with the incompletethread contour of the thread run out.

THREAD ENGAGEMENT

MMaatteerriiaall TTyyppee MMiinniimmuumm TThhrreeaadd

EEnnggaaggeemmeennttCCaasstt IIrroonn 11..2255 -- 11..7755 ddSStteeeell,, 220000 HHVV 11..00 -- 11..55 ddSStteeeell,, 440000 HHVV 00..99 -- 11..11 dd

AAlluummiinnuumm AAllllooyyss 22..00 -- 22..55 dd

Minimum of 3Unengaged Threadd = bolt diameter

The actual minimum required threadengagement depends upon material shearstrength, thread fineness and bolt strengthgrade. Values should be determined byactual tests.


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Nuts

Where nuts are used, the nuts should have sufficient resistance to thread stripping. When a nut istightened onto a bolt, the nut compresses and dilates. This can reduce the effective threadengagement. Flanged nuts reduce this effect as well as providing greater bearing areas and resultant

lower bearing stresses.

Nut strength classes should be matched to the companion bolt strength. In general, these nuts willhave a lower strength than the bolt. The higher strength bolt threads resist distortion and contain thenut threads from elastic displacement under load.

Bearing stresses

The bearing stresses under the bolt head and nut face (where applicable) should not exceed thecompressive yield strength of the material on which the fastener is seated. This will minimizeembedding and galling effects due to excessive surface pressures.

The following table provides guidelines for various material types.

MATERIAL TYPE MAXIMUM ALLOWABLEBEARING STRESSES (KSI)

CAST IRON 80

STEEL 20 Rc 70

STEEL 40 Rc 160

ALUMINUM ALLOYS 30


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Assembly Tool Consideration

Air System Considerations

It takes both pressure and flow to make an air tool work. The air compressor must deliver more airthan the tools connected to it will consume. The volume of air is expressed in CFM.

Theoretically, compressors greater than 25HP will deliver 4 CFM/HP. In practice, however, due toefficiency losses from leaks, wear etc. the figure is closer to 3CFM/HP. Therefore, in practical terms,a compressor will deliver a volume 3 times its motor horsepower.

The dynamic air pressure at the tool must be 90psi (6.2 Bar) or the tool may not perform as specified.For every 10psi drop in dynamic air pressure, there will be an 11% drop in output torque from the tool.

Anything that restricts the airflow can also affect the performance. As an example, think of a three-lane highway narrowing down to a single lane for roadwork. Traffic is slower. When a given volume ofair is forced through a narrow passage, it slows down. An air hose that is too small or a narrow air

fitting can be a restriction.

It is important to insure that the length of the air hose does not exceed the maximum values asfollows:

HOSE DIAMETER MAXIMUM LENGTH (FEET)

& 8

10

25

In cases where longer lengths are required, a larger diameter should be used.

DC Electric Systems Considerations

DC electric tools are the current state-of-the-art for the assembly and control of threaded fasteners.They provide numerous benefits that enhance the entire fastening process.

DC electric tools are very accurate, clean and quiet, ergonomic and have a high power-to-weightratio. These systems are more expensive than air tools but have lower operating costs. They can beprogrammed to conduct advanced tightening strategies and can interface with other intelligentdevices.

If the tools are to be used with thread forming fasteners or prevailing torque fasteners, they must be

carefully selected and sized accordingly. With these types of applications, the tools are providingtorque throughout the entire tightening cycle, not just at the end. Under these operating conditions themotor can heat up so a tool with sufficient torque output should be chosen.

As an example, if the prevailing torque of a fastener is 20 Nm and the final tightening torque is 30Nm,do not use a 35Nm tool but rather specify one good for at least 50Nm. This will insure that the tool willnot overheat during service.


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The following Tables provide a brief comparison between the various tool types:

Application Guideline for Ingersoll-Rand Tightening Tools

The information provided in these tables is a guideline only as the performance of the tightening toolsare very often dependent upon the characteristics of the joint being assembled.

Tool Air Screwdrivers (S) and Nutrunners (N) Air Pulse Air Impact DC DC

Mechanism Direct (stall) Positive jawclutch

Cushion clutch Precisionshut-off clutch

Impulse Impact Clutch Transducer shut-off

Torque 8-120 inlb (S)2-125 Nm (N)

14-165 inlb(S)

3-100inlb(S)3-130inlb(N)

3-100inlb(S)5-25Nm(N)

3-330Nm 20-60,000Nm 0.2-60inlb 2-450Nm

Control none none adjustable adjustable adjustable none adjustable adjustableJoint soft/med soft/med soft/hard soft/hard med/hard soft/hard soft/hard soft/hardSpeed 250-2800 250-2800 250-2800 250-2800 5000-10000 5000-14500 300-2000 100-1300Reaction high high low low none none low high

Vibration none high low none low high none noneOperator skilled skilled unskilled unskilled skilled skilled skilled skilled$ range 200-800 200-800 200-800 200-800 1300-10,000 125-1200 500-1000 12,000

JOINT TYPETOOL TYPE APPLICATION/CONTROL

HARD JOINT SOFT JOINT SELF-TAPPING SHEETMETAL WOODSCREWS

AIRDIRECT/STALL

APPLICATIONCONTROL

GOODFAIR

GOODFAIR

POORPOOR

POORPOOR

GOODPOOR

AIR POSITIVEJAW

APPLICATIONCONTROL

FAIRFAIR

GOODFAIR

GOODGOOD

GOODGOOD

GOODFAIR

AIR CUSHIONCLUTCH

APPLICATIONCONTROL

GOODGOOD

GOODGOOD

GOODGOOD

GOODGOOD

FAIRFAIR

PRECISIONSHUT-OFF

APPLICATIONCONTROL

VERY GOODVERY GOOD

VERY GOODVERY GOOD

VERY GOODVERY GOOD

VERY GOODVERY GOOD

UNSUITABLEUNSUITABLE

AIR PULSE W/OCONTROL

APPLICATIONCONTROL

GOODGOOD

POORPOOR




AIR IMPACTWRENCH

APPLICATIONCONTROL

GOODPOOR

FAIRPOOR




DC CLUTCH APPLICATIONCONTROL

VERY GOODVERY GOOD

VERY GOODVERY GOOD

VERY GOODVERY GOOD

VERY GOODVERY GOOD


DCTRANSDUCER

APPLICATIONCONTROL

EXCELLENTEXCELLENT

EXCELLENTEXCELLENT

EXCELLENTEXCELLENT

EXCELLENTEXCELLENT

NOT JUSTIFIED


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Fastening Basics

Torque and AngleA fastener is tightened by applying a torque and rotating it through a rotational angle as shown above.

The torque is a product of the force applied and the distance from the fastener that it is applied. Thisis measured in Newton-Meters (Nm) in the metric system and foot-pounds or inch-pounds (ft.lbs,in.lbs) in the English system.

The challenge of this module is to understand the fundamentals and the options available. Achievingthis knowledge and understanding will help you to identify applications where controlled or moreadvanced tightening strategies will help you to solve a customer's problem and sell a solution.

.

A tensile force is generated in the fastener and an equal and opposite compression force applied tothe joint.

Joint compression

Bolt tension called preload

or clamp load

We get two equal and

forces opposite forces

Joint compression

Bolt tension called preload

or clamp load

We get two equal and

forces opposite forces

What happens when we tighten a bolt in a joint by applying torque?

Distance(Feet, Meters)

Force(Newtons,

Pounds)

Torque = Force x Distance

AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135


Force(Newtons,

Pounds)


AngleAngle90

135

Factoid:

Angle = rotational travel1 second on your watch = 6


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Tightening StrategyTightening Strategy ConsiderationsWhen deciding on a tightening strategy, the choices are governed by the tightening system availableor the budget dollars approved for the purchase of new equipment. If only very basic fastenertightening systems are available, there will be few, if any, choices. However, if modern DC Electric

systems can be used, then tightening strategies can be developed to produce the best solution for thecustomer.

Most budgets reflect the criticality of the application; a number of criteria are used in making thisassessment.

These criteria may or may not be related:

Safety related where failure may result in catastrophe, death or injury.

Reliability related where failure may result in disability of the equipment

Customer satisfaction related where failure may result in end-customer displeasure.

The quality of the assembly is greatly influenced by the fastener preload and accuracy.

The initial fastener preload level required (preload is the initial tensile clamping load generated by theassembly tightening tool) has to be determined at the joint design stage. This is a complicatedprocess; particularly if the joint is to be exposed to service loads, thermal expansion effects due todissimilar materials or preload loss during service conditions.

Some joints rely on all fasteners to have similar levels of preload. Connecting rods in engines andcylinder heads both require all bolts to have a low scatter in preload between the fasteners to avoidbore distortion in the assemblies.

Conversely, some joints do not warrant in-depth analysis, as preload level and accuracy are not

important. In these cases, simple assembly tools and tightening strategies are chosen.

Tightening Strategy to Achieve Fastener Clamp Load

There are a number of different tightening strategies available, depending upon the assembly toolselected. Not all-manual or power tools are capable of torque or angle measurements, and are notintended for this purpose.

The simplest assembly tool is the common screwdriver, in which the applied torque is guessed andthe subsequent clamping load on the fastener is proportional to the strength of the operator.However, this wrist powered manual tool and tightening strategy (guessing) does an adequate job onthousands of applications.

Most industrial applications or mass production assembly techniques require tools and tightening

strategies that provide more control on fastener preload, and often some form of feedback to theoperator that the tightening of the bolted joint was completed satisfactorily.


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For these applications controlled tightening tools are required. The tightening tools require torquetransducers and angle measurement capability. An electronic controller is also required to processthe raw data generated from the transducers. These can be air tools but in the majority of cases areDC Electric tools.Many automotive and Tier 1companies are making a total switch from air to controlled DCtools.

The tightening signature is a plot of torque versus angle and is used to evaluate the tighteningprocess. The terms showed on this example are used throughout this module.

TIGHTENING SIGNATURE

TORQUE

ANGLE

HIGH ANGLE LIMIT

LOW ANGLE LIMIT

HIGH TORQUE LIMIT

LOW TORQUE LIMIT

THRESHOLD

TORQUE

TARGET ANGLE MEASURED

FROM THRESHOLD TORQUE

YIELD TORQUE

TORQUE

GRADIENTT

A

TARGET TORQUE

TORQUE ANGLE

ACCEPTANCE WINDOW

Tightening threaded fasteners is an energy transfer process, and the energy transferred from thetool to the fastener is mainly consumed in overcoming the frictional resistance between the parts.

As much as 90% of the supplied energy may be absorbed in overcoming friction, leaving only 10%to generate clamping load. Because of this, the most common tightening strategy, Torque Control,has severe limitations in providing accurate preload.


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Torque Control

Torque control is the most common tightening strategy in use because it is easy to apply, control andcheck. It can be measured directly with a transducer, or indirectly using a clutch or stall tool. Therelationship between the applied torque and the preload is shown in the empirical formula:

T = Fp x d x k

Where: T = torque, Fp = preload, d = fastener diameter, k = friction factor (normally a value of 0.15-0.20 is used in the equation.)

A target torque is selected to reach a nominal preload equivalent to about 70% of the fastener yieldstrength.

The major drawback with this method is that the resulting clamp load achieved is greatly influencedby friction. Friction is difficult to predict and control, and depends on many variable factors. Theseinclude surface finish on the fasteners and joint components, surface coatings, plated finishes, andlubrication. Even the speed of tightening delivered by the assembly power tool can indirectly

contribute to the frictional variations.

If a higher value is chosen, there is a danger that under low frictional conditions the fastener could betightened to well beyond the yield point and experience excessive plastic deformation (overtightening).

The scatter in preload using this tightening strategy is typically 30%.

TORQUE CONTROL WITH

ANGLE MONITORING

TORQUE

ANGLE

HIGH ANGLE LIMIT

LOW ANGLE LIMIT

HIGH TORQUE LIMIT

LOW TORQUE LIMIT

THRESHOLD

TORQUE

ANGLE FROM THRESHOLD

TORQUE TO FINAL TORQUE

TARGET TORQUE

TARGET TORQUE IS TYPICALLY

60-70% OF YIELD TORQUE

CLAMP LOAD SCATTER 30%

YIELD TORQUE


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Torque Control with Angle Monitoring

An improvement over standard torque control is torque control with angle monitoring. To do this, atool with both torque and angle transducers is required.

This method has no effect on the level or scatter in fastener preload that is achieved, but provides acheck that the assembly tightening process was completed as expected.

By monitoring the angle turned from a pre-selected snug or threshold torque, usually about 30-50% ofthe final tightening target torque, many defects like crossed threads, bottomed-out bolts, or distorted

joint components can be detected with this tightening strategy.

Checks for:Improper assemblyShallow HoleCross ThreadingStripped ThreadsAgain, the scatter in preload using this tightening strategy is typically 30%.

The below examples are of where monitoring the angle can detect faults in the tightening process

You can see that monitoring the angle can detect a lot of tightening defects. However, a lot of customersdont use it or dont know how to set it up. This can be done by running tests on known good joints,calculating the average and standard deviation, then applying 2.5 or 3 times the standard deviation tocalculate the angle high and angle low limits.


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Angle ControlTo reduce the amount of preload scatter produced by torque controlled tightening, a tighteningstrategy that uses the relationship between the thread pitch and the angle turned during tightening isused. This tightening strategy is called Angle Control or Turn-of-the Nut tightening. The procedurefor this tightening strategy starts with tightening the fastener to an initial threshold torque and then

turning the fastener to a pre-determined angle of rotation. Once the joint is consolidated, the angleturned is proportional to the amount of fastener elongation, which in turn is proportional to the preloadachieved. Friction is not an influence in this portion of the tightening strategy, other than it determinesthe final torque at the end of the process, which is merely monitored for quality purposes.

This strategy was originally developed for yield tightening before transducerized tools and yieldalgorithms were available. Now it is now used in the elastic range of the fastener, using targetpreloads below the yield point of the fastener.The relationship between angle turned and fastener elongation is as follows:

l = 360

l = elongation, = angle turned, P = thread pitch

The final preload is a result of the two steps of the angle strategy. The first step is that controlled bythe snug torque; which is influenced by friction as with torque controlled tightening.

The second step is that controlled by the angle turned which is independent of friction.

This strategy relies on the fact that for every 360 of rotation that the fastener is turned, it will stretchone thread pitch (less the compression of the clamped parts); 90 will stretch the fastener of thethread pitch.The scatter in preload using this tightening strategy is typically15%.

ANGLE CONTROL WITH

TORQUE MONITORING

TORQUE

ANGLE

HIGH ANGLE LIMIT

LOW ANGLE LIMIT

HIGH TORQUE LIMIT

LOW TORQUE LIMIT

THRESHOLD

TORQUE

TARGET ANGLE MEASURED

FROM THRESHOLD TORQUE

TARGET ANGLE IS TYPICALLY

CHOSEN TO PRODUCE A FINAL TORQUE

60-70% OF YIELD TORQUE


YIELD TORQUE


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Yield Control

Tightening to the yield point of the fastener utilizes the maximum preload capacity of the fastener.This strategy calculates the yield point of the fastener under the action of combined tension andtorsion stresses. This is achieved by monitoring the rate of change of torque over fixed angle

increments. The value obtained is the torque gradient, and as the yield point is reached the torquegradient declines rapidly and the tightening process is halted. Typically, the amount of permanentfastener elongation obtained is 0.025 - 0.050 mm. (0.001-0.002 in).

The preload developed depends on the tensile yield strength of the fastener material and the shearstresses developed from frictional forces generated in the threads during tightening. The relationshipis as follows:

Y = + 3 Y = tensile yield strength of fastener = tensile stress = shear stressThis method is much less influenced by friction and joint variations and at the end of the tighteningprocess the final torque and angle can be inspected to check that they fall within pre-determined

limits. In this way, every tightening cycle is 100% checked.

The torque gradient is monitored from the snug point. The gradient will rise until the fastener yieldpoint is approached where it will start to fall. When it falls to 50% of the maximum stored value, thetightening process is halted.

The scatter in preload using this tightening strategy is typically 8%.

YIELD CONTROL WITH TORQUE

AND ANGLE MONITORING

TORQUE

ANGLE

HIGH ANGLE LIMIT

LOW ANGLE LIMIT

HIGH TORQUE LIMIT

LOW TORQUE LIMIT

THRESHOLD

TORQUE

ANGLE FROM THR ESHOLD

TORQUE TO YIELD POINT

TORQUE AT

YIELD POINT

YIELD POINT

T

A

TORQUE

GRADIENT

TORQUE-ANGLE CURVE OF BOLT TIGHTENED

BY COMBINED TORSION AND TENSION

STRESSES

YIELD TIGHTENING


PEAK TORQUE

GRADIENT

50% OF PEAK

GRADIENT


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The following table summarizes the main differences between the three major tightening strategies:

Torque Control Accuracy of clamp load is 30%

Recommended to use angle inspection for fault detectionTarget preload is typically 70% of fastener yield pointLargely influenced by friction

Angle Control Accuracy of clamp load is 15%Application testing is required to establish tightening parametersSnug torque should be selected as low as possible but sufficient to consolidatethe jointUsually used in elastic range of fastenerNot always possible with high prevailing torque applications

Yield Control Accuracy of clamp load is 8%Utilizes maximum clamp load of fastener

Difficult to reproduce in serviceJoint study is required to prove feasibilityNot suitable for applications requiring frequent disassembly and re-tightening

Prevailing Torque Tightening Strategy

This is useful for thread forming applications where the thread forming torque may have a valuesimilar to, or even greater than, the final tightening torque.

This strategy monitors the initial peakprevailing or driving torque to ensure that it

falls between expected limits (cut-in zone). Itthen checks the subsequent mean and peakprevailing torque as the thread is formed(prevailing zone). Finally as the fastenerseats, the final tightening strategy is invokedwhich may be torque control, angle controlor yield controlled tightening (tighteningzone).

For gasketed joints, such as a cylinderhead or flanged joint, more even sealingcan often be obtained by tightening allfasteners to a pre-torque. This pre-torqueis usually about 30-50% of the finaltorque. Once all of the fasteners reach thispre-torque then the final tighteningstrategy is applied. In some cases theremay be more than one pre-torque level.

Another strategy sometimes employed is to tighten all the fasteners, then back them all out and thenre-tighten them again. This procedure helps to flatten out any burrs in the threads and improve thefrictional conditions, thus reducing preload scatter.


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In many applications multi-spindle tools are used, usually for cycle rate considerations but also to giveimproved joint performance. An example of this is the connecting rod where dual spindles are used.In this application, it is important to synchronize the spindles so that they complete the tighteningstrategy at the same time. This gives more even clamping and reduced bore distortion of thebearings.

Drag Torque StrategyDrag torque is the torque required to overcome the inherent friction or pressure force

resistance in the movement of an assembly or mechanical component through some predeterminedangle. This technique is often used as a quality inspection procedure. A typical application is themeasurement of engine crankshaft-turning torque in the automotive industry. In this application, thereis usually an initial high inertial torque to get the crankshaft moving, and while this value can bemeasured, it is actually the dynamic torque following this initial torque spike that is the parameterrequired. Similar applications exist for measuring the frictional torque in bearings and hubs.

Application considerations

As we have seen, there are numerous tightening strategies available. The choice will be governed by

the capability of the system available and the complexity and criticality of the application.

The majority of industrial applications specify torque controlled tightening. As we educate ourcustomers more, they will begin to monitor the angle during the tightening process to detect faults.Fault detection is often referred to as 'poke yoke' (Japanese term) or error proofing.

Some customers in automotive applications have migrated to angle controlled tightening to reducethe scatter in fastener preload.

Yield controlled tightening is restricted to applications where the customer truly understands thistechnology and wants to get the maximum clamping load with the minimum of scatter. Examples areconnecting rod, cylinder head and main bearing bolts in high-end automotive engines.

The increased use of light alloys in automotive and other industrial segments and the cost savingsachieved by eliminating the need to machine the companion internal threads has demanded theavailability of custom strategies like the prevailing torque strategy.


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Sales & Product Support

Customer Service

Phone Number: 800-998-0872

Addresses questions regarding:

Orders

Delivery

Stock

Price

Some tool recommendations

When you call be sure to have:

Order Number or Purchase Order Number

Complete model number

Complete application / problem description

Identified potential troubleshooting issues,

repair problems, or quality (incorrect part)

Technical Support

Addresses questions regarding:

Application support

Configurations

Options or accessories

Troubleshooting

Competitive Cross-Over

When you call be sure

to have:

Complete model

number

A complete

description of application or problem

Describe potential troubleshooting issues,repair problems, quality (incorrect part)


28/30


Product Marketing Literature

Product Literature and the irtools.com Web Site

Purpose: To supportyou in your sales efforts

Product Specifications

Features

Benefits

Product Nomenclature

Model Numbers

Accessories

Product support phone numbers

To Order Product Literature

Locate the publication number; typically this in on the lower right corner of the publications back cover.

Then either call or email Ken Cook at:

Phone: 1-800-376-8665, then press2 Email: [email protected]

Inform the representative who you are, e.g., Ingersoll Rand Employee or Distributor

Provide them with the count and where you would like to have the brochures shipped to.

Quick Cross Competitive Crossover

1. Go towww.irtools.com > Contact Us > Quick Cross Competitive Crossover

2. Choose the type of products you want crossed over.

3. Complete and submit the online form.


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Product Warranty

Standard one (1) year product warranty, Cables have a 2 year product warranty

Free of defects in material and workmanship for a period of one (1) year from the original date of

purchase.

This warranty does not cover damage from repairs made or attempted by other than Ingersoll RandCertified Service Centers, abuse, normal wear and tear, lack of maintenance, or accidents

Product Repair & Service Center Locations

Always recommend a Certified Service

Center

Certified Service Technicians

Genuine Ingersoll Rand Parts

Service Locator

Go towww.irtools.com > Service & Support > Service Locator

Customer Training Offered


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Course Test Part ITo assure that we have met the stated objectives, please complete the course testprovided by your instructor. We will review the correct answers once everyone ascompleted their test.

Participant Satisfaction SurveyWe value your feedback and we need to have it to make future improvements tothis course. Please complete the Participant Satisfaction Survey provided by yourinstructor.

Documents

Section 2 - Participant Manual - What is Torque