Metal or plastic? – four reasons for polymer bearings

Lars Butenschön | 3. April 2020

There are many requirements at bearing points, and they often go beyond what technical data sheets say. There are often “soft” requirements that are difficult to quantify and arise only later in unforeseen operating conditions. During the design phase, it may turn out, for instance, that lubrication should not be used, that role of weight is more important than had previously been thought, that application installation space is limited, that costs must be reduced, or that an extremely low coefficient of friction is necessary. In this blog, I will examine this issue more closely and attempt to explain the advantages of replacing metallic bearings with plastic ones.

1. Polymer bearings are really maintenance-free

In industry, maintenance of machines and systems is frequently accepted as a necessary evil, but this necessity is far less acceptable in products for consumers. You can see this with cars. “Change the oil? I thought the garage always did that … the last time I did it was five years ago … there’s nothing wrong with the car, after all. I always take it to the car wash. ” The same is true of all sorts of other devices. Lawn mowers, washing machines, office chairs. All of them are expected to just work. If anything breaks prematurely, it’s the manufacturer’s fault. (And anyway, the manufacturer put the cleaning intervals in small print on page 34 of the 80-language instruction manual.)

In short, the issue of maintenance is fraught. Plain bearings made of polymer can outlive many other components without any additional care – if they are designed correctly. Why? Because they need no external lubrication. And that has a number of advantages: lubricants enter the environment and reach other points in the device itself, polluting both. They can also cause problems with dust and dirt. Lubrication itself fixes particles, forming an abrasive paste on the bearing point, increasing the coefficient of friction, and increasing the risk of premature bearing failure.

2. Polymer bearings reduce weight

You would be surprised how many different applications require weight reduction, and how many reasons there are to reduce weight. The reasons range from eminently practical ones like making child seat shells easier to carry around to increasing the range or maximum load of transport vehicles. Ecological concerns provide the widest range of reasons. The lighter components, vehicles and devices of all kinds are, the less energy they require to move. This saves fuel and reduces power consumption. Smaller motors also save costs and weight.

3. Polymer bearings save installation space

This cumbersome maxim nevertheless reveals a universal advantage. Bearings can just be manufactured smaller. Complex multi-layer composite systems consisting of lubrication and support layers or complex ball or roller bearing systems are larger and take up more room in the assembly they are part of. To create this room, the structure around the bearing must be larger. This means more mass to be moved. More weight. More drive energy required and higher costs.

4. Polymer bearings reduce costs

For most products, machines and systems, costs are the decisive criterion for component selection. Manufacturing costs for polymer bearings are frequently lower than for metallic plain, roller or ball bearings. That is because of the much more complicated design of the latter. For metallic plain bearings, the cost advantages arise from the manufacturing process (injection moulding as opposed to rolling and punching) and the cost of raw materials. Beyond the unit price, however, there is great savings potential from the elimination of maintenance and lubrication.

Conclusion

But ultimately the deciding factor is the application and the specific requirements mentioned at the beginning of this article. Data sheets and the comparison calculator help – but frequently are no substitute for personal consultation. While the iglidur expert system requires just a few clicks to return information about expected service life of various plain bearing materials, we are happy to advise you personally in order to evaluate the specific requirements at your application’s bearing points and offer you the perfect plain bearing. Try it!