The
purpose of torque loading is to make sure the correct and efficient clamping
together of two surfaces. This prevents over-stressing, distortion,
and shearing of bolts, studs, nuts etc. The majority of bolts, nuts
and unions on aircraft are subject to a standard torque loading. Special
bolts are subjected to torque loading
, which are specified in the aircraft
maintenance manual. There will be a range for the torque value in most cases an Torque
load values are normally determined by friction, type of thread, material,
lubrication and finish of the surfaces of the fasteners.Formula
Torque = Force X Length
Under
tightening of screw fasteners may result in lack of firmness between the
separate parts of the assembly causing fretting corrosion due to relative
movement , and early failure of a component may occur through fatigue or
mechanical breakdown. Conversely, over-tightening is likely to cause
immediate failure of the bolts, distortion of one or more parts of the assembly
leading to eventual failure, or to stress corrosion, or cracking this will
result by the high stressed areas cause by over torque. Due to the varying
effects of friction under different conditions of assembly it is important that
torque be applied in accordance with the manufacturer's instructions. The pre-load applied to a fastener at a
specified lubricated torque would be considerably higher than if the same
torque were applied dry.
Before
even start to use torque wrench make sure All torque wrenches that are used on
aircraft are regularly inspected, tested and calibrated by a facility equipped
to do so.if the serviceable tag indicates as expired. DO NOT USE THE TOOL.
How
to do it :
- Clean, and lubricate the threads(if instructed on AMM) and mating surfaces of nut, bolt and washer.
- Tighten the nut to half the specified torque value.
- Loosen the nut then finally re-tighten to the specified torque value.
- When the torque-loaded fastener is to be secured by means of a split pin or lock wire, tighten first to the low side of the torque range. If necessary, tighten the fastener so that the next slot aligns with the hole, ensuring that the maximum torque is not exceeded. If the maximum torque is reached and the slot in the nut does not line up with the hole in the bolt, the nut and/or washer must be changed.
