GMW14100

Description / Abstract: GMW14100, 4th Edition, December 2011 - Corrosion Protective Coatings Phosphate/Zinc Organic Type

This standard covers the basic requirements for a corrosion protective coating process consisting of zinc phosphate pretreatment, a non-electrolytically applied zinc rich coating, and an organic top coating. Shot blasting as pretreatment in place zinc phosphate is permissible for externally threaded parts or parts with no thread. Shot blasting is not a preferred method for internally threaded parts and shall not be used for nut- washer assemblies. The coating may be applied by dipping or spraying. Part configuration dictates the application process. Internally threaded parts (nut) shall be coated in a canting centrifuge or equivalent equipment.

Note: Any additional approved source of this finish shall have canting centrifuge application or equivalent equipment.

Material Description. The coating system is free of hexavalent chromate, with no hexavalent chromate in final product per GMW3059 requirements. GMW3034 will be used as a referee test. This coating process does not generate hydrogen; however, pretreatment processes i.e. acid pickling could cause hydrogen absorption. Non-electrolytically applied zinc rich coating has high permeability, which allows effusion of hydrogen during curing that might have been absorbed during acid pickling.

Symbols. Not applicable.

Typical Applications. The coating is suitable for bolts, clips, and other ferrous parts where above normal levels of corrosion protection and freedom from hydrogen embrittlement are required.

This finish is not recommended for 360 degree Nylon Patch Nuts.

Internal threaded parts e.g., Nuts M6 may need different treatment.

Remarks. Use of this finish on threaded surface and/or bearing surface of joints could affect the torque-tension relationship. It is recommended that a torque-tension study of the fastener joint should be preformed before releasing this finish on a new application.

Coefficient of friction/torque tension values in this specification are also determined at ambient temperatures. New applications for this finish should be tested to confirm performance under application specific, operating conditions.

Finishes conforming to the requirements of this specification can be used in the application range of -50 to 120°C. For applications outside of this temperature range consult your local Material Engineering (Paint Corrosion engineering for GME) support.