GMW15854

Description / Abstract: GMW15854, 3rd Edition, January 2019 - High Temperature, Corrosion Resistant Coating for Fasteners and Small Parts

This standard covers the requirements for a high temperature, corrosion resistant coating with friction control. This coating is for ferrous parts only.

Material Description. This coating is a dip-spin or spray type coating which provides corrosion protection in operating range from -50 °C to 450 °C. The coating is a baked on base coat providing corrosion protection. A lubricant-integrated topcoat or additional lubricant maintains consistent friction and is an integral part of an approved coating systems.

Symbols. Not applicable.

Aplicability. This coating is suitable for externally threaded parts (size M6 or greater) and non-threaded ferrous parts where high levels of corrosion protection at high temperature are required. The dip-spin process is not recommended for the following:

•Bolts smaller than M6

•Parts with recessed features (such as internal drive screws)

•Loose washers of all sizes

•Internally threaded parts (nuts)

Remarks.

Dip-spin Coating is a Bulk Process. If parts are prone to nesting, stick together (e.g., flat washers), or easily damaged by mechanical tumbling, do not use dip-spin coating method. Alternatives include spray and dipdrain methods.

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

Polytetrafluoroethylene (PTFE) shall not be used in topcoat or lubricant for this specification due to the expected high operating temperatures.

This coating process does not generate hydrogen; however, pre-treatment processes, i.e., acid pickling, could cause hydrogen adsorption. See precautions in 3.1.1.

The corrosion performance is influenced by part geometry, substrate material, and application process. The coating systems approved to this specification were tested to meet all requirements using common steel parts. For new designs, applications, and parts with complex geometries, or difficult to clean material such as castings and powder metal, extra validation testing is highly recommended.

Special design and process consideration must be made when applying this coating on surfaces that are part of a clamped joint. This includes the bearing surface against which the bolt underhead comes in contact. On a bolt, stud, or screw, this includes the underhead bearing surface. Excessive coating may creep resulting in loss of clamp load.