What are solid lubricants?

In many of the Molykote® products available, you will see the term ‘solid lubricants’ used in the description of the product. But what are solid lubricants, how do they differ from liquid lubricants and why are they needed?

To explain we first need to look at the different types of lubrication. Normally, the main function of any lubricant is to reduce the friction between two surfaces that are in mutual contact with each other. Failure to provide adequate lubrication can result in many undesirable outcomes such as:-

• Energy loss
• Noise
• Heat generation
• Wear

There are 3 main types of lubrication, hydrodynamic, boundary and mixed lubrication which is somewhere between the first two. Hydrodynamic lubrication occurs where the relative speed of the moving parts combined with the film thickness of a liquid lubricant is enough to separate the two surfaces, think of a car aquaplaning on a thin film of water on a road. However, there are occasions where pure hydrodynamic lubrication is not possible. These can include:-

• When relative speeds are too slow
• Applied loads are too high
• During start up
• High temperatures (typically over 250℃)
• Where the use of a liquid lubricant is either undesirable or not possible

Under these conditions, a solid lubricant could be required. Solid lubricants are materials that, despite being in the solid phase, are able to reduce friction between two surfaces sliding against each other without the need for a liquid oil medium (although in certain cases some liquid lubricants can also contain solid lubricants). Solid lubricants on their own are normally not practical to use for lubrication so they are nearly always used as ingredients in lubricant formulations to make amongst other things:-

• Greases
• Pastes
• Dry film coatings
• Oil dispersions

Solid lubricants can have differing properties for different applications and products. Their use in a formulation either on their own or in conjunction with one or more other solid lubricants is determined by the required attributes of the finished lubricant. Solid lubricants used in relevant Molykote® formulations include:-

• Molybdenum Disulphide
• Graphite
• PTFE
• High Load White Solids

In 1948, American scientist Alfred Sonntag introduced the world’s first molybdenum disulphide (MoS2) lubricants – Molykote® – and began a rich history of customer-driven performance and materials innovation. Molykote® Specialty Lubricants are trusted by engineers, OEMs and product designers worldwide for their ability to meet tough lubrication challenges. From saving energy by reducing friction and wear to improving safety and comfort by reducing NVH.

If you would like to know more about how solid lubricants can help in your application please call our team on 01827 255250 or contact us here.