Key points
Paul Mitchell, managing director of Bowman International, explores how self-lubricating bearings can remove the burden of correct lubrication to help improve safety, cut costs and extend the lifetime of equipment.
Dealing with OEMs, distributors and logistics companies, we understand more than most what customers need from a bearing. Whether it is a standard catalogue item or a special order, customers are wanting more and more for their suppliers to take responsibility for helping them to select the right bearing.
In many cases this means addressing the three main reasons for bearing failure; bearing fatigue, making the wrong selection of bearing type and material, and incorrect lubrication.
An alternative lubrication solution?
Any engineer will know that the topic of lubrication – or tribology – is an extremely complex one. There are not enough words in this magazine, let alone on this page, to cover the subject in anywhere near the detail required to do it justice.
However, one thing is clear; there are so many varying factors which influence the decision over how best to lubricate a bearing, it is not always an easy choice to make.
Even once that difficult decision has been made, consideration must also be given to the ongoing requirement for lubrication. In many sectors it is either difficult, cost-prohibitive or impossible to service bearings because of the environment in which they operate.
In others it is the nature of the industry that busy operatives simply will not take the time to keep bearings adequately lubricated. Whether manual or automated, regular lubrication of process equipment to ensure performance and extend the lifetime can be expensive too.
For some applications, the answer could lie in the specification of self-lubricating plain bearings. And there are now a host of proven solutions that can help keep maintenance to a minimum in even the most hostile of environments.
Self-lubricating bearings are the solution
Self-lubricating bearings are also referred to as graphite plug bearings, because they are lubricated for life with solid graphite plugs.
Graphite is mechanically forced into holes into the bearing. A film of graphite is then transferred to the shaft as it begins to turn, offering continuous lubrication over long periods without maintenance.
With the capability to withstand high temperatures up to 425°C (800°F) and cryogenic temperatures down to -200°C (-400°F), they are ideally suited for applications where no external lubrication can be provided, for high temperature applications where oil or grease would carbonise, and for bearings which will be immersed in water.
This includes high temperature applications such as ovens, kilns, dryers and injection moulding machines, together with dry applications such as printing, textiles, food, cosmetics and pharmaceutical machinery.
Wet application would include submersed pumps, textile finishing, chemical processing, water turbines and lock gates – all of which are hostile environments and difficult to access for servicing, which clearly makes a maintenance-free solution hugely appealing.
Reducing requirements
Another option that is proving increasingly popular in a wide range of applications is to choose a different material that can prevent the need for lubrication.
Bearings made from the latest, value-added alloys can deliver enhanced benefits, including the capability to take far higher loads and corrosion-free operation – thus giving longer life and greater reliability.
Before such innovations in materials, designers were faced with the choice of utilising oversized bearings in order to take the required loads, which would add weight and take up more space to get the necessary load and lubricity level, or switch to hardened steel, which requires regular lubrication.
Instead, the higher load and lubricity ratings delivered by new materials allow manufacturers to use smaller bearings with higher load ratings to save space and weight, or replace existing bearings and get a much higher load rating and longer life. It means longer lasting bearings and, in some cases, cost-savings too – a win-win situation.
Extended choice
There are other options, of course. Leading suppliers can offer a wide range of lubricants with varying temperature ranges to meet specific requirements, whilst lubricant additives are also available to impart anti-wear properties in marginal lubrication conditions such as stainless steel shaft applications.
Alternatively, wrapped PTFE lined bearings include a lead-free polymer fibres mixture layer, which effectively coats the mating surface of the bearing assembly to form an oxide-type, solid lubricant film.
With lower wear, a low coefficient of friction and good sliding characteristics, it makes these bearings suitable for a wide range of applications where self-lubricating properties are hugely advantageous.
Take advice
Whatever your application, the most important thing is to speak to the experts. At best a bearing failure is a huge inconvenience, at worst it is extremely costly and potentially dangerous, so it is crucial to get it right.
Whether you need to lubricate or can source a maintenance-free solution, the most important thing is to use a supplier that can take a holistic approach to all bearing types, materials and lubricants. Without that whole-market view, you could be missing out on efficiencies that you didn’t even know exist..
