How to work the torke to properly tighten a nut to a bolt?
So what is the purpose of proper torque and the importance of doing it right? When we speak about tightening a nut to a bolt to compress the parts in between them, initially it can be easily screwed in until all the parts between them come together. This is when we work-the-torque! Although we may not be able to see it, a bolt actually stretches similarly to a rubber band, just that at a much slower pace that makes it impossible to see with our naked eyes. As the bolt stretches, it is squeezing every little possible space between the parts. This is when using the correct torque matters! A good stretch prevents loosening of the bolts as well as fatigue. However, without the correct torque, the bolt and nut is either not tightened or tightened to a point where it reaches its weak spot which can easily break.
13 January 2020
CFM56-7B ENGINE STAND
- White oil
- Heavy Duty Grease
- Anti-Seize Compound
- 1/4 “ – 20 Bolts (Quantity 4)
- Flat Washers (Quantity 8)
- Hex Nuts (Quantity 4)
- Torque Wrench
- Size 11 (3/8” Drive) Socket
- Size 11 Wrench
- Metal Plate with 4 Thru Holes and 20mm Thickness
- Metal Plate with 4 Thru Holes and 10mm Thickness
- Normal: 54.51 mm
- Oil: 54.43 mm
- Grease: 54.54 mm
- Anti-Seize: 54.68 mm
- Normal: 54.65 mm
- Oil: 54.53 mm
- Grease: 54.97 mm
- Anti-Seize: 55.27 mm
| Normal | OIL | Grease | Anti-Seize | |
|---|---|---|---|---|
| BEFORE (mm) | 54.51 | 54.43 | 54.54 | 54.68 |
| AFTER (mm) | 54.65 | 54.53 | 54.97 | 55.27 |
| CHANGE (mm) | 0.14 | 0.10 | 0.43 | 0.59 |
| STRETCH (%) | 0.00257 | 0.00184 | 0.00788 | 0.01079 |
When it comes to surfaces with multiple bolts, working-the-torque in proper sequence is very important. This is to ensure that the surfaces are compressed uniformly.
Torque to a maximum of 30% of the final torque value in accordance with the torque sequence and ensure surfaces are compressing uniformly.
Repeat this step with 60% of the final torque value before proceeding with 100%.
When this is done correctly, we get 100%!
When improper torque-ing is done, it results in fatigue in the bolts as it is not properly stretched as per designed. Also when torque sequence is not adhered to, it causes uneven stress and when excessive force is applied, failure occurs.
Below image is an example of improper torque-ing. When the tow bar was used to pull an aircraft, due to the uneven stress, one side of the tow head gave way causing the nuts to rip off.
