Bearings: plastic beats metal

Bearings: plastic beats metal

Today they are used worldwide, high-performance plastics for moving applications. In everyday life in kitchen appliances, bicycles or cars, as well as in industrial environments such as machine tools, filling machines or in pneumatic cylinders. iglidur plastic bearings from igus are increasingly superseding metal solutions. Because lubrication-free and maintenance-free Tribo polymers have numerous advantages.

The “motion plastics” of igus, the plastics specialist, resist rain, salt and extreme temperatures, are impervious to oil and chemicals, are lighter and more energy-efficient than comparable metal solutions, and are also cost-effective. All over the world, design engineers are installing plastic bearings from the Cologne company as long-lasting and cost-effective alternatives to metal bearings. This is due to their special material properties as well as their excellent performance in motion. The ability to withstand stationary stress says little about a bearing’s performance capability. The degree of wear-resistance of a bearing and how low its coefficient of friction does not become apparent until it is used in moving applications, where wear is unavoidable. And this is exactly where the strengths of motion plastics are, the high-performance plastics for motion.

igus offers the largest standard range of lubrication-free polymer bearings. Around 50 materials are available, including 16 full-range materials.

Largest selection for a wide variety of applications

igus GmbH has been developing and producing polymer bearings for over three decades. Under the brand name “iglidur”, igus offers its customers a large selection of standard bearings and customised components especially for moving applications. The bearings are self-lubricating and therefore maintenance-free; they can withstand enormous loads and are nevertheless light in weight. The materials are developed and tested in the industry’s biggest test laboratory. In an area of around 2,750 square metres, more than 135 billion test movements are executed each year. The result of more than 30 years of research and development is the largest standard range of lubrication-free polymer bearings: Around 50 materials are available, including 16 full-range materials. They are in stock in at least 113 dimensions and up to a shaft diameter of at least 50 millimetres in accordance with DIN ISO3547; the largest catalogue bearing has an inner diameter of 195 millimetres. igus has no minimum order quantity and delivery within 24 hours. In addition, there are many materials available in the form of bar stock, liners or, for 3D printing, filament or SLS powder. Polymers enable a great deal of design freedom: with little effort, even extremely complex parts can be made or their characteristics can be significantly influenced by means of specific additives. This is precisely the core competence of igus: the optimisation of technical polymers for use in moving applications.

Wear-resistant, stable and vibration-dampening

To this end, igus has its own material development department, which is continually coming up with new iglidur materials to match specific areas of use. The individual components of the compounds are mixed homogeneously during the injection-moulding process. The excellent performance of iglidur plastic bearings derives from this homogeneous structure, whereby the basis of an iglidur bearing consists of thermoplastic polymers that ensure the bearing’s good basic resistance to wear. Fibres and filling materials increase the bearing’s load-carrying capacity. In addition, solid lubricants have been included in the material. All the components work together and result in very good sliding and abrasion properties. In contrast, rolled metal bearings have a layered structure. The inner layer is very thin and, in the event of high loads, edge pressure or vibrations can easily be stripped off or damaged by dust particles. Moreover, the sliding layer represents a limit to the degree of possible wear. The homogeneous composition of the plastic compounds, in contrast, is considerably more robust as the wall thickness of the bearing acts as a ‘wear zone’. Unlike iglidur bearings made of high-performance plastics, bearings made of metal alloys have to be permanently lubricated, a disadvantage that is cost-intensive and also time-consuming. What’s more, lubrication with grease or oil is becoming increasingly unpopular for hygienic and ecological reasons. Sinter bearings that are commercially available also have oil lubrication incorporated into them and, are therefore not dry-operating bearings. The same applies to rolling bearings, which, especially in the case of needle bearings, are often being replaced with iglidur plastic bearings for technical and economic reasons.

Agricultural engineering as an example: able to cope with stress and resistant to dirt

The agricultural industry alone is a good example of the potential of bearing technology from igus in many very different markets. iglidur bearings that are used in agricultural machinery are extremely resistant to wear and can cope with high surface and edge pressures. They are non-corrosive and resistant to impacts and knocks. Fertilisers, slurry or fuels have no effect on their ability to function. The machines can, therefore, be used reliably even after being out of use for a long time. Especially in agricultural environments where machines can be exposed to extreme amounts of dirt, iglidur bearings guarantee optimum functionality and long operating times. igus has developed special materials in the form of iglidur Q2 and Q290, which are especially suitable for the slow pivoting applications that involve high loads and are typical in the agricultural sector. Bearings made of the low-cost iglidur G are also insensitive to dust and dirt and are therefore especially suitable for agricultural machinery.

The food industry as an example: non-corrosive and resistant to media

In the food and packaging industry, the absence of lubrication also plays an important role in view of the strict hygienic and safety standards in these sectors. According to the regulations of the Food and Drug Administration (FDA), it must be ensured that products are not contaminated by lubricants or other substances. As a consequence, only plastics that are FDA-compliant and suitable for use with food are used in these sectors. In contrast to metals, plastics are always non-corrosive due to their organic structure and are also resistant to an organic media, including acids, lyes and aqueous salt solutions. “All interior and exterior areas must be able to withstand wet conditions and cleaning chemicals. It must be ensured that, during ongoing operation, malfunctions or unintended shutdowns do not occur under any circumstances”, says Dieter Koller, design engineer at Singer & Sohn GmbH. The company makes special machines for the food industry. In order to avoid dirt and contamination in this industry, iglidur products are being used in a sausage-separating machine instead of the work being done manually. “We used to install needle bearings. But they proved to be unsuccessful in the face of the rough everyday stress associated with operation and cleaning. They are very sensitive in that the bearings had to be replaced as soon as a few drops of water penetrated through the seal during cleaning. This was too costly in the long run. The plastic machine elements, on the contrary, are characterised by a low level of water absorption and are resistant to chemicals”, adds Koller.

Standards and specialists

For most typical bearing applications, five standard iglidur materials are used. But at the same time as companies are concentrating on the production of highly specialised parts and whole branches of industry are increasingly differentiating themselves, the demand is growing for specific materials that have been adapted to particular production environments; in the sterile environment of medical and laboratory equipment, for example, devices must not only be free of oil and grease but must also be anti-bacterial. In turn, other sectors demand materials that are insensitive to air-borne dust particles and fibres; in the textile industry, for example, antistatic plastics that are electrostatically dissipative are used to ensure that statically charged bearings do not attract any lint or dust. From underwater use to high-load applications, from medical technology to the automotive industry: the igus company has developed tailor-made materials for all these cases. Which material is the right one for the respective use can be quickly determined with the help of online tools such as the Product Finder, the Configurator or the Service-life Calculator. The following, among other things, are offered online: service-life calculating programs based on the more than 10,000 bearings tests carried out in the igus test laboratory every year; 3D CAD configurators for complete linear systems with polymer sliding elements; and the important fast “Product Finders”, which help users to find the right material. Users can click on their special requirements (“Longest service life with dry operation”, “Dirt-resistant”, “Vibration-dampening”, “Resistant to chemicals”, “Ability to withstand edge pressure” etc.) and indicate the permissible static surface pressure and the upper long-term and the lower application temperatures.

Polymer bearings are more cost-effective than metal bearings

In all branches of industry, whether in photovoltaic systems, the agricultural and offshore sectors, facade technology or in hydraulic cylinders and actuators, polymer bearings have been replacing metal bearings for a long time now. For engineers, the freedom from lubricants and the non-corrosiveness of the igus motion plastics, as well as their resistance to wear and low coefficients of friction, have become indispensable as they increase the service life of their machines and are also up to 40 per cent less expensive than metal bearings. New materials and properties are continually opening up further possible uses for polymer bearings – even after more than 30 years, igus is still continuing its research activities in the company’s own technical facility. Given that development in the area of shaft materials and surface treatment does not stand still, continuous tests that react to shaft changes and are aimed at a perfect matching of shafts and bearings are absolutely critical . Especially the issue of running partners illustrates the versatility of iglidur bearings, which can be used on very different shafts – and above all on cost-effective, so-called soft shafts. This is a clear advantage over many other types of bearing. In addition to the cost benefits associated with plastic bearings, the user can also utilise a non-hardened shaft and thus reduce his costs even more. Many shaft materials (for example, precision aluminium, steel, stainless steel, carbon fibre) can now be ordered directly from igus together with the bearings. As the company’s slogan says, there is no “one” shaft recommendation. Here as well, it is important to choose the shaft that is best in terms of price and performance, depending on the application in question.

Material of the future

Consistent continuation of the research and development work is necessary in order to be able to offer bearings that are of the best quality and, at the same time, are the most cost-effective. 3D printing is opening up new potential for igus and its customers as, with additive manufacturing and new kinds of high-performance material, two modern technologies that complement each other perfectly have now been brought together. In combination, they guarantee a high degree of freedom in engineering design and, at the same time, a high level of wear resistance of the components that are used. In order to achieve this, igus is researching and developing new 3D materials that are specially designed for moving applications. Since the first iglidur Tribo filament was introduced in 2014, the range of products has been expanded continually. Given the six Tribo filaments that are now included in the product range, bearings or more complex designs can not only be manufactured but can also be used directly in industrial applications. In addition, igus introduced the first Tribo SLS powder for selective laser sintering at the end of last year. But not all companies have their own 3D printer: For these cases, the Cologne company offers a 3D printing service that allows customers to print out their desired parts directly – anywhere in the world.
With 3D printing, igus can also make customer-specific injection moulds made of high-performance plastics in a very short time. With the SLS process, the corresponding tools can be produced in a very short time and used in the standard injection moulding machine. With regard to injection-moulded parts, the customer is offered a large selection of tribologically enhanced iglidur materials whose parameters can be calculated online, including high-performance plastics that can be used in motion applications and are resistant to chemicals, temperature fluctuations or that can withstand especially high loads, can be used universally. With the printed mould tools, the customer gets the possibility of obtaining the special part quickly and cost-effectively even in larger numbers whilst maintaining application suitability. This results in significant advantages, especially in the trial phase: in the test phase, the special part is very close to the production product and, at the same time, the costs are reduced considerably.

Source: Bearings: plastic beats metal

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