Elastic, wear-resistant, reliable, space saving and cost effective – that’s what seals are supposed to be. Sealing technology is becoming increasingly important in the design of plant and machinery, as well as in helping to improve the efficiency of complex mechanical components, says Harald Peschke.
Although seals are often the smallest components within a system, they often have the greatest impact on its function. On the positive side, a technical breakthrough in sealing technology can lead to significant improvements in system or machine efficiencies. However, a defective seal can have disastrous consequences – as was the case when the Challenger Space Shuttle exploded due to the failure of a sealing ring in the solid fuel rocket.
A seal is defined as a component or device whose function is to prevent or limit the undesired transfer of substances from one place to another. In technical terms, a distinction is made between ‘contact’ and ‘non-contact’ seals. Furthermore, seals are often classified according to the type of movement of the part to be sealed relative to another: hence the terms ‘static seals’ (no movement), translational seals (linear movement), and rotary seals (rotating movement).
As a supplier of rolling bearings and linear motion systems, sealing technology is a very critical part of product development at Schaeffler. Helping customers to select the right sealing technology and materials are absolutely vital to their applications. Schaeffler’s own standard ‘sealing rings’ catalogue (TPI 128), for example, helps customers to select the most appropriate seal from around 8,000 components and 400 design variants, ranging from non-contact seals for dental drills, which have diameters of a few millimetres and operating speeds of 100,000rpm, through to contact seals for slow rotating wind turbine bearings with diameters of several metres.
As well as this publication, Schaeffler also helps customers by using design calculation and simulation software tools, which are particularly useful when it comes to adapting or refining standard seals, whilst simultaneously generating technical drawings. These software applications are helpful if the mounting situation or operating conditions are unusual and if the behaviour of a standard seal under these conditions needs to be simulated.
Seals also come in a wide variety of materials. Non-contact labyrinth seals, for example, are often made from metallic materials. Static seals – which must provide reliable sealing even if uneven surfaces are involved – and contact seals are normally made from elastomers. Suppliers of bearings will normally be able to advise the customer by conducting the necessary laboratory tests and recommending the most suitable elastomer seal for the application.
Developing seals made from synthetic materials is also critical to the function of rolling bearings. In particular, when it comes to development projects carried out for automotive industry customers, for example, polymer specialists at Schaeffler collaborate closely with the manufacturers of synthetic materials to develop new seal materials. In lightweight engineering and energy saving transmissions in particular, there is likely to be a healthy future for tailor-made synthetic materials that are precisely matched to the specific demands of the application.
As a manufacturer of rolling bearings and linear motion systems, Schaeffler has to keep its knowledge and expertise of synthetic materials and sealing technologies up to date at all times. In addition, having a good feel for which direction the market and competitors are heading is equally important. Providing robust, economical, innovative sealing solutions is critical and so Schaeffler has to offer its customers qualified sealing designs and advise them on which materials to choose and test that material. If Schaeffler becomes involved early in the customer’s design process, this can really make an impact by helping to accelerate the customer’s product development process or minimise product lifecycle costs.
The sealing of the rolling bearing itself is, and will remain, a challenge for many years to come. This is because seals will have to provide more reliable, lower friction sealing implemented within ever-smaller design envelopes. The increasing level of complexity of system components is another key area where sealing technology can make a difference. Take for example, Schaeffler’s ‘UniAir’ valve control system for internal combustion petrol engines. Here, Schaeffler has developed sealing solutions for more than 20 different positions on the valve control system. Much effort here has been put into the reduction of vehicle CO2 emissions by developing seals that minimise frictional losses in the bearings. But achieving higher energy efficiencies often means that system components are being asked to operate in higher compression ratios and temperatures, which means seals and synthetic materials must be designed to withstand such conditions too.
Harald Peschke is Manager of Sealing Technology & Synthetic Materials at Schaeffler. www.schaeffler.co.uk