Lubrication is a major challenge for manufacturers who deal with extreme working conditions. These conditions may include temperature extremes, low and high shaft speeds, low and high pressures, concentrated process and atmospheric contaminants, etc. Though mineral oil based fluid lubricants are the common lubrication choice for such applications, still they are limited by their operational efficiencies. These lubricants function as long as the shaft speeds, and surface areas allow effective formation of the oil film between the operating temperatures -20°C and 100°C (-4°F to 212°F). Now, you may ask how manufacturers are overcoming this challenge. The answer lies in dry film lubricants. What are these lubricants? What are the different types of dry film lubricants? Read this post to know the answer.
An Introduction to Dry Film Lubricants
Dry film lubricants, also known as solid film lubricants, are solid materials which are applied to interacting surfaces to avoid friction. These materials may be applied in any of the following ways:
- As an additive to the fluid lubricant
- In its purest form or
- Is alloyed or added to the surface while the component is being manufactured
Solid film lubricants are proven to minimize galling and seizing, especially in extremely low or high temperature environments, where regular fluid lubricants may vaporize or freeze completely.
The next section highlights different types of specific dry film lubricants used across various industries.
Industrial-grade Dry Film Lubricants: A Practical Guide
There are various types of solid film lubricants used today. However, the most popular types include the following:
WS2 per Process SL-39 – AMS2530 and DOD-L-85645A Type I
Tungsten Disulfide Coating, Thin Lubricating Film, Binder-Less, Impingement Applied
Per the Specification: This product is typically used on metal parts and selected nonmetallic parts where the thickness of friction reducing coating is under 0.00002″. It is also ideal for applications where wear, galling, seizure and fretting needs to be minimized. However, its usage is not limited to such applications.
This lubricating film is shown to be compatible with fluids such as reagent-grade water, petroleum-based hydraulic fluids, petroleum-based oils and greases, SAE phosphate ester test fluid #1, silicone fluids, UDMH compatible greases, IFRNA compatible greases, solid rocket propellants, nitrogen tetroxides, liquid oxygen and hard radiation environments.
MoS2 per Process SL-39 – AMS2526
Molybdenum Disulfide Coating, Thin Lubricating Film, Impingement Applied
Per the Specification: This product is used on metal parts and selected nonmetallic parts that require a coating under 0.0001″ thickness for reducing wear or minimizing galling. However, its usage is not limited to such applications.
This lubricating film may be applied to surfaces of ferrous and nonferrous metals and alloys, thermoplastic and thermosetting polymers and rubber. Aluminum, magnesium and ferrous alloys, other than corrosion-resistant types, either coated or in contact with other parts having this coating, may be susceptible to corrosion.
This lubricating film has been shown to be compatible with such fluids as distilled water, petroleum based hydraulic fluid, SAE phosphate ester test fluid #1, silicone fluid, UDMG compatible grease, IFRNA compatible grease, solid rocket propellants, nitrogen tetroxide and liquid oxygen.
MoS2 per Process DL-99 – AS5272 Type I, II and III
Lubricant, Solid Film, Heat Cured, Corrosion Inhibiting
Per the Manufacturer: These dry film lubricants are paint-like coatings containing molybdenum disulfide and corrosion inhibiting pigments. These heat curing materials prevent corrosion, galling, seizing and fretting. They are low friction coatings that can operate in a wide temperature ranges and in extreme pressure environments.
These lubricants are ideal for parts that are operated in a corrosive environment, or may be stored for long periods of time. Also, it is ideal for parts that are seldom lubricated and where permanent lubrication is desired, or where clean operation is desired.
These lubricants have been shown to be compatible with or resistant to isopropyl and ethyl alcohol, mineral spirits/paint thinners, toluene, acetone, skydrol 500, hydraulic fluids, anti-icing fluids, diethanolamine, and hydrochloric acid (10%), sodium hydroxide (10%), distilled water, jet fuels and trichloroethylene.
Determining the correct lubricant for your application
The determining factors when looking at dry/solid film lubricants are basically the same for each of the lubricants:
- Eliminate or reduce galling and fretting
- Extend wear life
- Operating conditions prevent the usage of ordinary oils and greases
WS2 per Process SL-39: This has been extensively used in stainless steel fastening applications, precision bearings and gears in vacuum applications or as a sole lubricant and many industrial and automotive applications as a co-lubricant. WS2 has also seen extensive use as a semi-permanent mold release used on cores, inserts, ejector pins and more. It has the lowest coefficient of friction and the widest operating temperature range. It is also the thinnest of the dry film lubricants and does not usually affect precision machine tolerances.
MoS2 per Process SL-39: MoS2 is very similar to WS2 and has been used in many of the same applications. It is usually less expensive than the WS2 coating, it does not have the wide operating temperature range. It is a vacuum compatible lubricant and has better sliding wear resistance than WS2.
MoS2 per Process DL-99: These lubricants have been used extensively in military and aerospace applications, as well as many industrial and automotive applications requiring permanent long-term lubrication. This coating is thicker than the impinged coatings and provides excellent corrosion resistance.
The final determination as to what lubricant will best suit your application, is best left to your lubrication engineer. Microsurface Corporation will assist in this determination based on your application’s operating environment and our knowledge of similar uses. Also, we can provide prototype coating so that you can evaluate the coating(s) in your specific application.