Dry lubricants are materials that reduce friction between surfaces without needing a liquid or oil base. They use solid substances to create a protective, low-friction layer and enhance performance and longevity in machinery and components.
Explore the world of dry lubricants, from their unique properties to the various types like graphite, PTFE, and molybdenum disulfide. Discover how these non-liquid lubricants reduce friction, withstand extreme conditions, and find applications in industries from aerospace to food processing, ensuring cleaner, more efficient machinery operation.
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| Lubricants |
All About Dry Lubricants - Properties And Types
In machines and engines there are parts that move in relative motion to each other which leads to friction and wear. Lubrication is necessary to ensure the moving parts work efficiently. Lubrication helps the moving part to bear high speeds, loads and pressure depending on the operating conditions.
The main types of lubrication are solid lubrication, fluid lubrication and gaseous lubrication. In solid lubrication, dry/solid lubricants are used to reduce friction and wear.
Dry lubricant can be used in granular form, powder form or as a thin film between the two moving parts to reduce friction and wear. Dry lubricant prevents the direct content between the two moving parts under various loading conditions.
Dry lubricants are the only option available when the operating conditions are extreme. Dry lubricants can be used in high temperature, pressure and vacuum conditions. They have high thermal stability to stay in form at high temperatures. In such conditions liquid lubricants and greases cannot be used for lubrication.
Dry lubricants can be used at cryogenic temperatures because the liquid lubricants may become viscous or solidify.
Most of the dry lubricants have a layered crystal structure. For example, Tungsten disulfide (WS2), Molybdenum disulfide (MoS2), Hexagonal Boron Nitride (hBN) and Graphite (C). These lubricants have strong covalent bonds between the atoms within the layers and the layers are connected together by weak Van der Waals forces.
When a shear force is applied the layers easily slide past each other which leads to a low coefficient of friction. The layers with strong covalent bonds offer good load carrying capacity and protect the moving parts from severe wear.
Another dry lubricant is PTFE (Polytetrafluoroethylene) and it can be used to reduce friction and wear. It is a synthetic fluoropolymer and is non-reactive. It cannot be wetted by water or water containing substances and can be used as a dry lubricant.
Dry lubricants can be applied in different ways on the surface requiring lubrication:
- Dry lubricants can be added in powder form to sintered surfaces and composites. Dry lubricant powders have properties which enable them to create a film and adhere to the surface.
- Paint and spray mixtures can be made using dry lubricants and applied on the surface.
- The surface to be lubricated can be coated with dry lubricants using electroplating, PVD (Physical Vapour Deposition) and CVD (Chemical Vapour Deposition) techniques.
- Dry lubricants can be used as additives in lubricating oils.
Dry Lubricant Types
There are several types of dry lubricants that help reduce friction and wear in machines. Each type has several purposes and benefits. The most common dry lubricants include:
Tungsten Disulfide (WS2)
It has excellent tribological properties including a state of zero friction known as superlubricity. It has high thermal stability and better resistance to oxidation under medium and high temperatures. It can be used as a lubricant in high temperature and high pressure applications. It has excellent wear resistance and is used in lubricating coatings on metal surfaces and as additives in oils.
Molybdenum Disulfide (MoS2)
It exhibits a low coefficient of friction and can work effectively up to a temperature of 800° C. It can be used in the form of fine dry powder, paste or as suspension in oil and grease. It has a better load carrying capacity than other dry lubricants. It can be used for lubrication in air and vacuum. It is widely used in space applications and it can perform well up to a temperature of 1000° C.
Hexagonal Boron Nitride (hBN)
It is used for lubrication in high temperature applications. It has exceptionally high thermal and chemical stability and exhibits resistance to oxidation in air up to a temperature of 1000° C. It is used in applications where the cleanliness of the working environment is critical. It is also known as ‘White Graphite’.
Graphite (C)
It has a low coefficient of friction and high thermal stability. However, it requires the presence of adsorbed moisture or water vapour to achieve low coefficient of friction. It can be used in powder form or as a suspension in oil or grease. It can work effectively as a lubricant at temperatures up to 375° C in an oxidising environment and much higher temperature in absence of air..
PTFE (Polytetrafluoroethylene)
It is an organic lubricant and has properties like low coefficient of friction, chemically inert, biocompatibility and high melting point. It can be used for lubrication in light load applications. It is widely used as a lubricant in bearing and seals applications. PTFE shows a low coefficient of friction in vacuum because it lacks chemical reactivity. It does not have a layered structure but micromolecules of PTFE can easily slide past each other like in lamellar structures.
Common Uses of Dry Lubricants
Dry lubricants are widely used in various industries due to their unique ability to reduce friction without the use of liquid or grease-based lubricants.
Unlike traditional oils, dry lubricants rely on materials like graphite, molybdenum disulfide, or PTFE (polytetrafluoroethylene) that provide a thin, protective layer between surfaces. This property makes them ideal for applications where liquid lubricants could cause contamination, such as in electronics, aerospace, and food processing.
For example, in food-grade machinery, where exposure to oils could compromise sanitation standards, dry lubricants keep components moving smoothly without risking contamination.
One of the primary applications of dry lubricants is in high-temperature environments where oils or greases would break down.
In industries like manufacturing and automotive, dry lubricants are often applied to parts that operate under extreme heat, such as bearings, gears, and brake systems. Traditional lubricants can vaporize or oxidize when exposed to high temperatures, which can lead to equipment failure.
Dry lubricants, on the other hand, can withstand these conditions, providing consistent performance and reducing the need for frequent maintenance. This makes them indispensable in heavy-duty applications where reliable, long-lasting lubrication is essential.
Dry lubricants are also popular in clean-room environments and precision engineering, where any contaminant from an oil-based lubricant could lead to equipment malfunction.
For instance, in semiconductor manufacturing, even tiny particles of grease or oil could interfere with delicate machinery or affect product quality. By using dry lubricants, manufacturers ensure that parts move smoothly without the risk of leaving residue or particulate matter. In these environments, dry lubricants maintain the cleanliness and efficiency of the equipment, helping industries maintain rigorous standards and improve overall output quality.
Finally, the automotive and aerospace industries rely heavily on dry lubricants for components that require low-friction movement without the risk of collecting dirt or dust. For example, graphite-based lubricants are often applied to locks, hinges, and small moving parts in vehicles and airplanes. These areas benefit from a non-greasy solution that prevents sticking and jamming.
In aerospace, where weight and precision are critical, dry lubricants offer reliable performance without adding unnecessary mass or risking oil migration.
Overall, dry lubricants provide efficient, contamination-free solutions across industries, enhancing both equipment durability and operational safety.