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What is Torque?
According to Webster:
- A twisting or wrenching effect, or moment, exerted by a force acting at a distance on a body, equal to the force multiplied by the perpendicular distance between the line of action of the force, and the center of rotation at which it is exerted.
- A force, which tends to produce rotation. The measurement of torque is based on the fundamental law of the lever.
Basic Torque Formula
L (length) x F (force) = T (torque)
Example: A two foot lever at a right angle to the fastener with 200 pounds at the end will produce
400 foot/pounds of torque.
Torque Formula: L x F = T
What are we trying to achieve with a torque wrench?
Answer: Proper Clamping Force
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- Torque is expressed in commonly used units of measurement such as:
- in. lbs. = inch pounds
- in. ozs. = inch ounces
- ft. lbs. = foot pounds
- Nm = Newton meter
- cNm = Centi Newton meter
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Torque and Clamping Force
Controlling the torque applied in tightening threaded fasteners is the most commonly used method for the application of clamping force. There are many factors which may affect the relationship between torque and clamping force of threaded fasteners. Some of these are: the type of lubricant used on the threads, the material from which the bolt and nut are made, the type of washers used, the class and finish of threads and various other factors. It is not possible to establish a definite relationship between torque and clamping force which will be applicable for all conditions.
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Torque Versus Clamping Force
Only a small part of the torque applied to a fastener contributes to clamping force. The remaining, as much as 90% of the total applied torque, is used to overcome friction under the fastener head (or between nut and washer) and friction in thread engagement.
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TORQUE
1. Head Friction: 45% - 55%
2. Thread Friction: 35% - 45%
3. Clamping Force: 10%
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JM Test Systems calibrates and services all CDI Torque Wrenches. For more information regarding rental or purchase of a CDI Torque product, please call 1-800-353-3411 or email us at jmsales@jmtest.com.
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