Tightening of Fasteners ..What is Torque ?Torque Measurement Unit ..What Happen to Bolts when Tightened?Torques Values Table..Torquing..Friction..Why Measure Torque ?Torque Wrench Types..Torque Turn..Contents

Tighten with the right torque = long service life from equipment and tools.

Too much torque: deforms the nut and compresses threads.

Too little torque: may allow fastener to work loose.

Failure of fasteners can lead to major repairs andcosts that could have been avoided.

Caterpillar provides charts with general tightening recommendations

Avoid unnecessary costs of Over/Under-Torquing

Tightening of FastenersLoose Bolts Wear of bolt & joining surfacesShear boltVibration, parts come apart

How tight do you fasten a bolt or a nut ?Wrench Tight

Bolt tightened so its stretched- then will hold tightly.Stretch by applying leverage or torque with a wrench.The longer the handle on the wrench, the more torque can be applied.

Force applied to wrench handle when tightening a fastener. or Twisting force acting on a bolt or nut when being tightened with a wrench. What is Torque ?

Force applied is measured in pounds Pounds of force exerted at one foot from the fastener is the applied torque. Measured in pounds - foot ( lb-ft )Metric Newton - meter ( N.m )1 Newton = .224 lbs. of force1 Meter = 3.3 ftTorque = Force X LengthTorque Measurement Unit ..

Problem : To apply 200 lbs of pull to the wrench safely by hand would be very difficult.

Solution : To reduce the amount of pull and yet keep the same torque, we can use a longer wrench.

Not practical to hang weights. We can measure by attaching a Spring Scale.To measure quickly and easily a special tool was designed : Torque Wrench.

Operation PartsWrench TypesBeam Torque Wrench

Operation Clicker Torque WrenchPartsWrench Types

Identified by the movable pointer and dial.Dial TypePre-Set Torque WrenchWrench Types

Adjustable Torque WrenchVaried by twisting the handle. Value desired can be read on the adjusting sleeve.Indicated by an audible click sudden release followed by several degrees of free movement.Wrench Types

(c) After removal of loadElastic DeformationWhat happens to bolts when torqued (tightened) ? (a) Before loading (b) Loaded

e partly elastic and partly plastic, only elastic portion is recoveredPlastic DeformationWhat happens to bolts when torqued (tightened) ?

stretch beyond the elastic state neck out loosening its grip probably break.Plastic DeformationNeckingOver torqued

Specific torque values in Service Manual.General torque values can be used. Torque Values

TorquingWe applythis-----Twisting ForceAnd want this----- Tension(Clamping Force)We measure this tension indirectly by using a Torque Wrench.

Because of the Twisting Force, we have a Friction that affects the Clamping Force. Head of the bolt or nut . . turning against the piece being held.2) Threads of the nut and bolt . . turning against each another.Friction

Surface Texture of bolt & part being holdLubricantType of LubricantMachined or Rolled ThreadsDirt or Rust on Threads Damaged ThreadsBent BoltThe distribution of torque in fastener tighteningFactors That Affect Friction

Consumer demand Industry to increase: Power / Cubic InchPower / DollarProduct Eff. Factor / PoundSafety Standards.Why Measure Torque ?

Older products using oversized parts. To increase : Product Efficiency / Pound Efficient machinery using smaller yet stronger fasteners. Nuts & Bolts Since Fastener is the weakest link of any assembly. Special attention.necessaryIncorrectly tightened will fail before the machine itself fails.

How to Compute Torque when using Adapters?RS = Torque Setting. A = Distance from drive center to handle pull point center. B = Length of adaptor from drive center to nut or bolt center ( Only // to handle ). T = Torque Desired. What should the Setting be when? A = 12 B = 6 and T = 30 lb. ft.

Extensions reduce Torque. Some Force lost in Twisting 20% with a 4extn. 30% with a 6extn.40% with a 8extn. For Impact Tool (150 lb.-ft.) + 4extn.Max. Applied Torque = 120 lb.-ft.

Torque-Turn Actual clamping force or bolt tension can vary when using torque as a means of measuring that tension.Because of this researchers have come with a Torque -Turn method. A combination of torque + a certain number of degrees of rotation of nut or bolt .Torque to 50 10 lb.- ft. plus 180 5Degrees of rotationA degree is 1/360th of the distance around a circle ( symbol )

Torque/Tension Chart(4 bolts same size)

Tension variation increases as torque increases. Dashed line lubricated bolt, reached the tension level with 250lb.- ft. less. Why ???

Turn Portion

Direct RelationshipTension on Elongation bolt or stretch 2,500 lbs .00112,500 lbs .00525,000 lbs .01037,500 lbs .01550,000 lbs .020 Tension / Stretch ratio of 2,500 lbs per .001 stretch.Not constant for all bolts.It depends upon factors: Size, Length & Material

Torque TurnTension variation at 190 lb.- ft. roughly 2,200 lbs. After 120 of rotation roughly 4,300 lbs using torque method roughly 7,400 lbs a difference of 3,100 lbs could be a difference between a quality product and a field failure.

The tool will do what its designed to do, if.. The serviceman uses the tool as it was designed to be used. Always . . . Use a steady even pull, Never . . . Jerk or snap the wrench.Remember !