Stainless steel shafts, flange and plain bearings for laboratory presses

Profile

• What was needed: drylin R fixed flange bearings 
• Requirements: High temperatures up to 400°C, pressing forces up to 70 t
• Industry: Mechanical engineering
• Success for the customer: The material iglidur X copes with pressure loads, very high as well as sub-zero temperatures and remains dimensionally stable

All in all, Vogt Maschinenbau GmbH in Berlin, which has been on the market for a good fifteen years, has a very broad wealth of experience. Around 150 projects have been implemented, mainly in Germany, but also internationally. Besides laboratory presses, laboratory rolling mills are also manufactured. The laboratory presses are available in four installation sizes, which differ in the dimensions of the pressing surfaces.  They are used in the entire field of rubber and plastics development and testing and consist of a four-column unit in the so-called under-piston design. This means the piston pushes from bottom to top. An upper counter plate, the yoke plate, absorbs all the pressing pressures. Although you can also press the button the other way round, this procedure is gentler because you are working against gravity.
 

Problem

These laboratory presses have to cope with complex time, pressure and temperature requirements for pressing tests on rubber or plastics, even under vacuum. In some cases, they are used almost daily in four-shift operation. This is not an off-the-peg product, but a customer-specific solution. The laboratory presses are used on the one hand in universities and institutes, but also by industrial companies. While some, for example, are researching the strength of interior panelling made from renewable raw materials or the stiffness of carbon fibres on behalf of the automotive industry, others are carrying out complex receiving tests. Very, very long machine runtimes can occur here. The product range consists of automatic, vacuum, moulding and hand lever presses. They can be equipped with heatable and coolable press plates that reach temperatures of up to 400°C. The pressing forces are up to 70 t.
 
A number of special applications are implemented with the various laboratory presses. The subject of compression moulding may include the so-called 'ophthalmic plaques'. They are used for long-term treatment of patients with cancer of the eyeball. Weakly radiating isotopes are used. The machine is used for moulding individual, trough-shaped geometries for medical technology. The customer's task was to implement a fixed principle cycle for the manufacture of the radioactive implants in a cold forming process using pressure. A cycle with regard to the individual cycle parameter values should be as reproducible as possible and freely programmable with up to seven individual steps. A total of 20 single cycle programmes with individual combinations of values for pressure and time can be run and reproduced at any time. In another application, precious stones are applied in filler end caps with the help of a vacuum press. The way it works is very simple: The gemstone and end cap blanks are inserted into the tool. The workpiece is heated, a vacuum space is created and then evacuated. The mould is closed, upper and lower part are fused together. The end cap with its precious contents can then be removed. One cycle takes about 30 minutes. In total, more than 500,000 end caps have now been produced without any problems.
 
Basically, the main requirement is always that the press plates close. They should also be as parallel to each other as possible. Plane-parallelism is therefore also important. The pressing function and plane-parallelism are implemented via the column guide. In addition, the columns must be able to withstand high temperatures - up to a maximum of 300°C in the short term.

Solution

Tough stainless steel shafts and temperature-resistant and lubrication-free polymer bearings ensure a high level of availability for the heart of the machine, the two pressing plates. They are used exclusively in the guides of the various laboratory presses. The complete four-column unit includes components from igus GmbH, among others. These are corrosion-free and chemical-resistant stainless steel shafts and easy to install, maintenance-free drylin R flange bearings with form-fit inserted liner made of the extremely temperature-resistant and maintenance-free polymer material iglidur X. Only in very large dimensions the liner is replaced by a cylindrical bushing made entirely of iglidur X. The stainless steel shaft is manufactured according to customer drawings and varies in length between 430 and 600 mm depending on the type of press. The diameters of the bearings are between 30, 40 and 50 mm respectively. The polymer bearings replace metal bushings with PTFE coating, which were used from the very start. They have not proved their worth, as the coating has not withstood the high temperatures in the long term, so that the bushing sooner or later seized on the column.
 
The material iglidur X proves itself in the linear motion on the stainless steel shaft, the lifting units. The high-performance polymer copes with pressure loads of up to 150 MPa, short-term high temperatures of up to 315°C and remains dimensionally stable. But the material also shows its strength at minus temperatures. It can also be used in vacuum. Evaporation takes place only to a small extent. In principle, its moisture absorption is low, which also makes underwater use possible. In addition, the material is resistant to radiation, which is proven in special applications in the field of medical technology.
 
The high requirements are met, the guiding behaviour of the lubrication-free polymer bearings is excellent and there is virtually no maintenance. The service life is also good, so that the lubrication-free and maintenance-free polymer bearings should also be used in the future.