General Rules which must be followed:
1. Never over torque a Fastener. To over-torque a Fastener can cause it to stretch beyond normal limits causing Fastener breakage, or loosening of Fastener
2. Never under torque Fasteners because it can cause the Fastener to loosen to break
3. Ensure you know the torque specification
4. Ensure you know the torque specification if you are using a Fastener with lubricant on it or dry
5. As a general rule Fasteners should be lubricated unless manufacturer states otherwise
6. Know how to use a torque wrench. When all else fails read the instructions.
7. When unsure whether a Fastener should be torque to a specification, torque it
8. Do not re-use a Fastener if:
- If it was installed with an impact wrench
- If it could result in a safety risk
Fastener Failure Modes:
• Overloading - Force exceeds Fastener strength, Fastener loosens or shears
• Over-Torque - damaging the threads and deforming the hardware
• Under-Torque - allowing a joint to come loose. It may also allow the joint to flex and thus fail under fatigue.
• Brinelling - caused by poor quality washers, leading to a loss of clamp load and failure of the joint
• Corrosion - caused by the disintegration of an engineered material due to electrochemical oxidation of metals in reaction with an oxidant such as oxygen, this is why Fasteners must be lubricated unless stated by the equipment manufacturer.
• A torque wrench is a tool used to precisely apply a specific torque to a fastener such as a nut or Fastener.
• A torque wrench is used where the tightness of screws and Fasteners is crucial.
• It allows the operator to measure the torque applied to the fastener so it can be matched to the specifications for a particular application. This permits proper tension and loading of all parts.
How to Torque a Fastener?
Using the most common torque wrench which is a "click type" follow these steps;
Step 1: Preset torque value on torque wrench as determined by the equipment manufacturer; or if not available a common torque specification chart. (see below)
Note: When using anti-seize reduce lube torque value by 20%
Step 2: Torque the Fastener to the point where the desired torque is reached, signaling the desired torque by causing a click sound (some torque wrenches will not allow a Fastener to be torque above the setting however some will, be sure and purchase the best torque wrench possible)
If you have questions send an email to Ricky Smith at firstname.lastname@example.org
Tip submitted by Ricky Smith, GPAllied