How to select bearing lubrication for hot environments

The temperature of furnaces can reach 1,800 degrees Celsius. For applications exposed to these extremes, how important is choosing and applying the right kind of lubrication? Here, Chris Johnson, managing director of SMB Bearings, explains the vital importance of high temperature lubricants in industry.

 
Choosing the correct lubricant is crucial in ensuring the optimal performance of bearings and preventing their failure. Lubricants, whether oils or greases, operate as a thin film that protects the components of a bearing from contacting one another and causing friction. Although the causes of bearing failure are myriad, research has estimated that in approximately four out of every five cases of bearing failure, the fault lies with the lubrication.
 
Different lubricants are required for different functions and purposes, depending on the load, speed and temperature, among other factors. Oils and greases are the most common types of lubricant. Temperatures impact the viscosity of both, so high temperature applications require lubricants that can withstand the heat, without becoming a leaky mess. Choosing the correct one is essential to optimise performance, keep maintenance costs low and, ultimately, prevent bearings from failing.
 
Some greases are specifically designed to operate at high temperatures but also offer a range of additional properties such as wider temperature range endurance and the ability to perform well under high loads and at high speeds. For example, drone manufacturers may not know where their products will be used at the time of manufacture. From the Sahara desert, to the Arctic, the bearing lubricant will need range.
 
Semiconductor manufacturing is another area where high temperature lubricants are essential. The manufacturing process involves subjecting silicon wafers to extremely high temperatures, sometimes up to a thousand degrees. However, the process also requires a clean room. The ‘cleanliness’ of a room is determined by how many particulates of a specific size exist per cubic meter.
 
In the manufacture of computer chips, the process could be jeopardised by a single particle of dust. This necessitates using lubricants that can both withstand high temperatures and are also immune to the risks of outgassing — when lubricant begins vaporising and contaminates the environment.
 
Closer to home, the ovens we all rely on in our daily lives also require high temperature lubricants for the bearings they use. However, in addition to temperature requirements, they must also be resistant to regular cleaning and conform with strict hygiene regulations. H1 approved lubricants are necessary where there may be incidental contact with food and H2 approved lubricants where greases are used but there is no contact.
 
In addition to greases, dry lubricants or solid lubricants can offer the answer to high temperature problems. These materials are capable of reducing friction between two surfaces even when they are in a solid state. Graphite is a popular choice here, but other materials used include molybdenum disulphide and tungsten disulphide. These have a wide range of applications but are often specified in vacuum environments because they offer a reduced risk of contamination. Their advocates also celebrate reduced maintenance costs as relubrication is not necessary.
 
There are a range of high temperature lubricants for different purposes. Choosing the correct one and applying and maintaining it correctly is not simply an optional extra. Opting for a standard lubricant, even one with a relatively wide temperature range, is likely to create problems in more extreme applications. Some applications involve exposure to temperatures of up to 1,800 degrees Celsius. When facing high temperatures, appropriate lubrication is among the single most important factors in reducing maintenance costs and preventing the risks of bearing failure.