What is iglidur? – And what can it do better than POM?
Lars Butenschön | 1. July 2020
Some time ago I came across this blog post on the net, which finally wants to clear up the “mystery” of iglidur®; what is iglidur and why are customers willing to apparently spend a fortune on plain bearings made of this material?
First of all: I don’t want to bore you, dear reader, with a justification paper or a pamphlet to honour the iglidur® material. Rather, I find that the question of the composition of elaborately labelled and “branded” – i.e. products with fancy brand names – is justified and basically needs to be answered. In the design of machine elements and devices, performance and material characteristics as well as strict standards and guidelines must be observed. Everything must be documented and traceable and must be comparable.
So let’s follow the example from the blog post mentioned at the beginning and draw a frequently asked comparison and look under the engine bonnet of the opponents.
iglidur® against POM or actually against what?
To understand the difficulty of comparing plastics for suitability as plain bearings, it is useful to consider their structure. There is virtually an infinite number of plastics for plain bearing applications. They are often labelled with brand names or consist of several components. In reality, however, these are often “blends” which are ultimately based on a handful of different so-called “base polymers”. Examples in the plain bearing sector are often polyamides (PA, PA6, PA46, PA66) or polyoxymethylene (POM) or – if high temperature resistance or special technical specifications are required – PEEK, PSU, PPSU, PPS and similar. But how do you compare them now?
In the Internet and other literature you can find endless variations of “plastic pyramids“, data sheets and exemplary experiments. But how do you know which plastic is the right one?
Data sheets are important, but provide too few answers
The comparison on the basis of data sheets is apparent, but often provides too little information due to the standardised contents. Many parameters supposedly important for plain bearings are very similar within the same base polymer group. This means that all compounds – whether with a beautiful name or cryptic compound designation – are on a similar level in terms of temperature resistance, density, coefficient of thermal expansion and mechanical strength. The values can be adjusted up and down within certain limits by adding fillers such as fibres or beads. Additives change properties such as UV resistance or fire behaviour.
Nevertheless, despite similarities in the data sheets, the various plastic compounds provide fundamentally different wear results and thus operating times. Even slight changes in the mixing ratio can have a dramatic effect on the wear behaviour. Even the addition of a few % of colour pigments in our development laboratory has already decided on the failure or peak performance of a bearing material.
One of numerous wear tests from the igus® laboratory illustrates this “phenomenon”. This picture shows a standardised test rig on which plain bearings are examined under realistic conditions for the loss of their wall thickness due to various stress scenarios:
All plain bearings were tested under the same conditions: Shafts made of 304 SS, load 1 MPa, 0.3 m/s running speed, room temperature (23°C). We have defined the end of the service life with a wear loss limit of 0.25mm wall thickness. While the two POM variants without additional additives and fillers exit quite early with 7 and 46 hours, the POM with 20% PTFE still achieves 289 hours. The exemplarily matched iglidur® material manages 482 hours.
But how do you know which material will last longer?
igus® has been developing plastics to solve wear problems since 1964. And for about the same amount of time our customers have been asking the same – justified – question – “And how long will it last?”. To answer this question and facilitate the selection of the right material, we have developed the iglidur® service life calculator. Every year our various iglidur® materials undergo thousands of standardised wear tests.
While wear investigations in research are often carried out with the pin-on-disc test set-up, we have decided to align our tests more closely with practical applications. We therefore test the plain bearings ourselves for wear. They run under various conditions with the most varied shaft-bearing pairs. With the test data obtained in this way, the service life of the various materials tested can be calculated for each application – provided sufficient data is available. This is an enormous effort that we have been making for decades with several tens of thousands of tests per year.
The result: a freely accessible product range, where you can find the right material after entering your application parameters. In doing so, the product range includes over 60 different iglidur® materials – from low-cost materials to high-end polymers.
You can then download and store the calculation results together with the corresponding material data sheet. Trust is good, control is better :).
Why the operating time is often more important than the price
If in the end the plain bearing with the best performance is found, the price is added as a selection criterion (whereby it is often not the technical parameters but the price that is the first selection criterion). And yes, even in the test field, the prices of plain bearings vary considerably. Especially for high volumes, where the unit price is dominated not so much by machine costs as by the price per kilogram, cost-effective POM materials without PTFE or other high-quality additives demonstrate their strength.
However, costs for plain bearings consist of more than the pure unit costs. And this is why the questions “What is iglidur?” and “Don’t I pay for the brand name in the end – can’t I use a generic plastic?” are justified but do not go far enough. Plain bearings should preferably cost nothing, but should also not cause any problems. This is because the follow-up costs of poorly selected plain bearings are high.
The replacement of a plain bearing is, depending on the complexity and operating mode of the machine, an enormous task. Machines must be stopped and disassembled. Even if, as a result of bearing damage, no adjacent components – such as the often expensive bearing bolts – are affected, the machine downtime and assembly work cause high costs.
We advise you!
Of course the unit costs of plain bearings still play a central role in many industries. Especially in the automotive sector, but also in household appliances and equipment for sports and leisure or consumer electronics, plain bearings should last a long time, but they should above all cost little. In addition to selecting the bearing material with the best price/performance ratio, other factors are also important, such as a component geometry that is as simple and easy to manufacture as possible. In both cases we would be pleased to support you personally. Online, by telephone or directly on site.