Process Specification for Polytetrafluoroethylene (PTFE) – Impregnated or Codeposited Surface Treatment of Aluminum Alloys
This process specification establishes the engineering requirements for producing a hard, PTFE-impregnated or codeposited coating on metal alloys and the properties of the coating. PTFE is commonly known as Teflon.
2.0 PROCESS DESCRIPTION
This type of Teflon coating produces a hard, wear resistant coating with a low coefficient of friction that becomes an integral part of the substrate. The particles are mechanically bonded to the surface and the resulting new surface layer is resistant to chipping, flaking and peeling.
The Teflon coating is applied to a metal substrate in a multi-step process that starts with specialized cleaning treatments. The substrate’s surface is then enhanced by conversion deposition, thermal spray or a blend-matrix of all three processes, depending on the type of coating to be applied. The process continues with the controlled infusion of engineered polymers or other dry-lubricating particles and/or metals. The final treatment insures the particles have thoroughly integrated into the surface.
Teflon-impregnated or codeposited Teflon surface coatings on aluminum alloys are also known by the registered trademark name of Tufram, one of General Magnaplate’s coatings. This process is typically used to increase the surface hardness and resistance to abrasion and corrosion in aluminum alloys containing less than 5% copper or 8% silicon or a total of 8% of both by the formation of a dense, Teflon-impregnated aluminum oxide or codeposited Teflon-aluminum oxide layer. Alloys with higher silicon content alone can be coated satisfactorily with proper precautions in processing. Careful consideration should be given to the use of this process on highly stressed parts because of the lowered fatigue resistance and on parts with sharp corners or edges where chipping may result.
Typical components processed include: guide rails, impeller blades, valves, and molds. The thickness of the coating will range from 0.0004 – 0.003 inches, normally with 50% growth and 50% penetration per surface (minimum practical thickness is 0.0005 inch). The thickness requirements do not apply to blind holes and recesses with depth greater than twice the diameter or in open holes with depth greater than seven times the diameter unless a specific coating thickness is specified in those areas. Typically, holes and slots are masked and then chemical conversion coated per NASA/JSC PRC 5005.
This specification shall be applicable whenever the Teflon-impregnated or Teflon-codeposited process is invoked per section 4.0, “Usage”.
Unless otherwise specified on the engineering drawing, all parts shall be heat treated to the required temper, final machined, brazed, welded and formed prior to the application of the coating.
This process specification shall be called out on the engineering drawing by using a drawing note that identifies the process specification and the type.
The two types of Teflon coatings are:
Type 1 Teflon-impregnated aluminum oxide
Type 2 Codeposited Teflon and aluminum oxide
If a specific type is not specified, type 1 shall be supplied.
An example of a drawing note would be:
Tufram H+ maintains maximum hardness, corrosion resistance and lubricity.
MASK ALL HOLES AND SLOTS AND APPLY TEFLON IMPREGNATED ALUMINUM OXIDE COATING PER NASA/JSC PRC 5011 TYPE 1 (GENERAL MAGNAPLATE TUFRAM H+ OR EQUIVALENT). ALODINE CONVERSION COAT (CLASS 1A) ALL HOLES AND SLOTS PER NASA/JSC PRC 5005.