STANDARD PROCESSES - DESCRIPTION AND OPERATION
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1. General
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This section gives the information related to the standard processes of:
-STANDARD TORQUES (Ref. ATA 20-21),
-STALOK FASTENERS (Ref. ATA 20-22),
-LINES (Ref. ATA 20-23),
-CONTROL CABLES AND PULLEYS (Ref. ATA 20-24),
-INSTALLATION OF EXPENSION JOINTS (Ref. ATA 20-26),
-ELECTRICAL BONDING (Ref. ATA 20-28),
-O-RING INSTALLATION (Ref. ATA 20-29).
STANDARD TORQUES - DESCRIPTION AND OPERATION
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1. General
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This section gives the tightening torques for:
-standard threaded fasteners,
-pipes unions (not for oxygen),
-flight control threaded fasteners,
- oxygen unions,
-electrical component fasteners.
TIGHTENING TORQUES FOR STANDARD THREADED FASTENERS - MAINTENANCE PRACTICES
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TASK 20-21-11-911-001
Tightening Torques for Standard Threaded Fasteners
1. Reason for the Job
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This subject gives the different tightening torques applicable to the
standard screw heads and nuts. It also gives the correction coefficient that
you must use when you apply a lubricant to install the fasteners.
The applicable torques are given in the maintenance procedure.
The torque values are applicable for the first and the second oversize of
the same screw/nut assembly.
2. Job Set-up Information
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A. Fixtures, Tools, Test and Support Equipment
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REFERENCE QTY DESIGNATION
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R No specific Torque Wrench : range 0.00 to 1.20 m.daN
R (0.00 to 9.00 lbf.ft)
B. Referenced Information
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REFERENCE DESIGNATION
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SRM 514900
20-21-11-991-020 Fig. 201
20-21-11-991-001 Fig. 202
20-21-11-991-003 Fig. 203
20-21-11-991-022 Fig. 204
20-21-11-991-034 Fig. 205
20-21-11-991-005 Fig. 206
3. Job Set-up__________
Subtask 20-21-11-911-054
A. General
(1) The threaded fasteners are identified with a standard number written on the head (example: ABS, AN, ASNA, NAS, ASN, NSA, MS). They are installed in standard conditions and lubricated.
(2) Be careful when you remove threaded fasteners. Before you apply a tightening torque to a fastener, make sure that you know its correct part number. To find the correct part number of a fastener (screw, washer, nut), refer to the installation figure of the IPC.
(3) The torque values of the nuts and the screws are given with their initial lubricants. These torque values are available for the different screw/nut diameters: - The minimum value - The nominal value - The maximal value.
(4) Installation of used screws and nuts:
(a) If you use screws and nuts again: - The preload is weaker because the effect of the lubricant decreases. - It causes local damage to the protection of the screws and nuts which can cause corrosion (nuts and screws in plated steel) or seizure (nuts and screws in titanium or stainless steel). - It can cause damage to the mating surfaces. - It can decrease the torque for self-locking nuts.
R R R R R (b) To use nuts and screws again, obey the conditions that follow: - Do not use aluminum nuts again. - For other materials, make shure that the screws and nuts are serviceable (get approval from your quality departement or qualified mechanic) - The protection (or the fasteners) must not be damaged. (Examine the threads of the screw and the nut, the mating surfaces of the nut and the wrench, the shank and the head of the screw).
R (5) Tightening Procedures.
R (a) Apply the tightening torques with:
R - Torque wrenches
R - Calibrated screwdrivers.
R (b) If you use torque wrenches or calibrated screwdrivers, make sure
R that:
R 1_ The calibration of the tools is correct.
R 2_ The torque is applied correctly.
R You can apply unwanted torsion or flexion to the component if:
R - The position of the wrench (or the screwdriver) is
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