MAY 2015 Chapter 20 Standard Practices Page 20.27
20-92 Thermal Fitting Parts
General Procedures for using heat to fit parts during assembly or evaluating parts that
may have been overheated in service:
Aluminum parts must not be heated above 200ºF for more than 5 minutes. Higher
temperatures or longer times adversely affect strength and corrosion properties. Scrap
any aluminum parts suspected of going above 325ºF regardless of time at temperature.
Steel parts (bare) – Maximum temperature 300ºF. Higher temperature can reduce the
strength or cause temper brittleness in some alloys.
Steel parts (cadmium plated) – Maximum temperature 300ºF. Higher temperatures
will melt the plating and adversely affect steel strength by a process called liquid metal
embrittlement.
Bearings and carburized parts such as gears, clutch shafts, and clutch housings should
not be heated above 300ºF. Higher temperatures will reduce the surface hardness and
increase wear rates.
Always heat parts in an oven with temperature control set no greater than the maximum
temperature allowed for the part.
Always attach a pyrometer and thermocouple to the smallest aluminum part in the oven.
Never depend on the oven control to determine part temperature.
Cooling a part for thermal fitting at assembly is not recommended. Water vapor from the
air will condense on the part and frequently introduce water into the assembly causing
severe internal corrosion over time.
20-93 Replacement Component Identification (Data) Plates
In order to issue a replacement component identification plate for field installation, RHC
must first receive the old identification plate in legible condition. If old identification
plate is lost or destroyed, then RHC must have an original letter (photocopies or faxes
are NOT acceptable) from customer’s Civil Aviation Authority authorizing identification
plate replacement AND stating component name, part number, and serial number for each
requested identification plate. There is a charge for each plate issued.
Identification plates may be carefully removed using a sharp plastic scraper. If necessary,
use a heat gun to soften plate adhesive. Retain in a dry, contaminate-free area until ready
for reinstallation.
Damp wipe local area with acetone or equivalent solvent prior to reinstallation. Residual
adhesive on identification plate is usually sufficient for good adhesion. If necessary, use
B270-9 adhesive or equivalent to secure.
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