Dry film lubricants, alternatively known as solid film lubricants, are lubricating substances that are used to reduce friction between two sliding surfaces. Some of the popular dry film lubricants are graphite, molybdenum disulfide (MoS2), tungsten disulfide (WS2), and PTFE. They form a tough coating over the part and inhibit corrosion. This post discusses properties, applications, methods of application, and conditions in which these film lubricants are applied.
General Properties of Dry Film Lubricants
Each solid film coating substance has different properties.
- MoS2 and WS2 are oilioscopic, which means they cannot tolerate detergents.
- Graphite has high environmental and oxidation temperatures.
- MoS2 and WS2 can tolerate high loads, and perform well in a vacuum.
Conditions in Which Dry Film Coatings Are Applied
Solid film lubricants are perfect alternatives or additives to other conventional lubricants. They are usually applied under the following conditions.
- Reciprocating Motion: A typical application with reciprocating motion depends on a reliable lubricant to minimize wear and tear. Liquid lubricants may lose their ability to maintain a proper lubricating film in extreme conditions such as high pressure or temperature. However, dry or solid lubricants don’t migrate, and they help avoid galling, seizing, fretting and corrosion.
- Extreme Environments: Most dry film coatings can perform at high temperatures, pressures, speeds and other extreme environments. In some cases, liquid lubricants may fail under such conditions. For example – semiconductor manufacturing or high altitude/space applications cause evaporation of typical organic oils and greases. Also, in dry and dirty applications, dry film lubricants will not attract dirt and dust which will create a gummy and abrasive mixture with oil and grease.
- Typical Surfaces: Solid film lubricants are used on all types of surfaces. Bearings, pistons and cylinders, gears, fasteners, pins, injection mold components and many more. Anywhere where long term lubrication and extended service life is beneficial, dry film lubricants can be beneficial.
Methods of Application
Dry film coatings are applied in any of the following ways.
- Brushing/Spraying/and Dipping: Solid film lubricants can be added to specified resins and binders. These lubricants are applied to the specified components, which are often inaccessible to lubrication after assembly. Depending on the base material of the component, various air cure and thermal cure products are available. Specifications for this type of coating include MIL-PRF-46010, AS5272, MIL-L-23398 and more.
- Impingement Coatings: These are anti-friction coatings, typically molybdenum disulfide (MoS2) and tungsten disulfide (WS2) that can be applied at room temperature and do not require a curing process. These are thin coatings, < 0.0001”, that typically do not effect normal machine tolerances. They can work as the sole lubricant and also work well with hydrocarbon based oils and greases. Specifications for this type of coating include AMS2526, AMS2530 and DOD-L-85645
- Composites: Generally, solid film lubricants can be alloyed into polymers and sintered materials for improving certain properties.
Applications of Dry Film Lubricants
There are a variety of applications for dry film lubricants. Many of them are used in automotive, aerospace, and transportation industries. Below are some of the popular applications of dry film lubricants
- Plastic Molding Parts
- Combustion Engines
- Processing Equipment
- Connectors and Couplings
- Cables, Fasteners, and Slide Mechanisms
The choice of the right dry film coating will depend on your application requirements, operating temperatures, pressures and environment. Consult with a lubrication engineer to decide which lubricant will suit your application.