eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

Development and verification of a test method for determining the compatibility of elastomers with cooling lubricants

125
2022
Stephan Baumgärtel
ict2310325
23rd International Colloquium Tribology - January 2022 325 Development and verification of a test method for determining the compatibility of elastomers with cooling lubricants Dr. Stephan Baumgärtel German Lubricant Manufacturers Association, Hamburg, Germany corresponding author: stephan.baumgaertel@vsi-schmierstoffe.de 1. Introduction Numerous functional elements are used in machine tools and their peropherie, which are conveniently made of elastomers. These are, among other things: • Seals in the machine tool and on piping • Drives of auxiliary units (e.B timing belts, etc.) • Covers and panels (e.B. Bellows etc.) • Connections and connections (e.B hoses, cables (sheaths) etc.) • Other parts in the periphery of machine tools (brackets, fasteners, etc.) The parts come into contact with cooling lubricants both as planned (seals) or accidentally/ unavoidably - both with the fluid and with mists that settle on parts. As long as there is no operational or safety-relevant interference and the components perform the intended functions, operation runs smoothly. The situation only becomes critical when malfunctions occur as a result of malfunctions and solutions have to be found. Therfore, the VSI developed a test method to asses the compatibitlity between coolandt and elastomers. 2. Selection of elastomers by machine/ plant manufacturers It is interesting to see who makes the selection of the respective components and determines their materials. Essentially, 3 parties are eligible: • The designer of the machine tool • The installer of the machine tool in operation • The maintenance technician of the system at the operator MWF producers are rarely asked for comments. According to an internal survey by the VDW (Verein Deutscher Werkzeugmaschinenfabriken e. V.), the followingmaterials for functional parts are mainly used: 1. FKM seals; O-rings 2. PU seals; timing belts; groove rings; 3. NBR wipers and profiles; sealings The selection is made either on the basis of empirical values (evolutionary) or on the basis of the manufacturer‘s specifications. It cannot be ruled out that „what is currently there“ will also be used - otherwise some gross malfunctions cannot be explained. From practice and experience, a prediction on compatibility is not easily possible. The materials and the concepts used are too different for the behaviour to be predictable. In the data sheets, only compatibility with substances is often indicated - but coolants are very complex mixtures! As already described, the range of elastomers used in a processing plant can be very large. When a compatibility assessment takes place, the concept and construction of the plant is usually well advanced - changes are only possible with great effort. Unfortunately, there is usually no suitable material available for this check - with which usually only „laboratory-specific“ tests are undertaken. In order to make an assessment, you need a method that is uniformly applicable and a scale. The methods can be based on standardized tests carried out for similar applications (testing the compatibility of elastomers with motors, transmissions and hydraulic oils). 3. VSI - Method In order to take into account the different types of coolant, model cooling lubricants were selected on the basis of the basic components used - polyalkylene glycols,esters and mineral oil - which act as reference cooling lubricants. In each case, 3 variants were created for the water-miscible MWF,which represent typical concepts: boron-containing, boron-free and boron-free with a high pH value. In addition, two non-water-miscible coolants and two forming lubricants were defined. A laboratory method (DIN ISO 1817: 2008-08) was chosen for the test, in which the test rods - S 2 test specimen (shoulder rod S 2 according to DIN 53504) are immersed in the medium for the test duration. Through preliminary tests and consultation with elastomer manufacturers, the duration and extent of storage per KSS were determined and determined. The duration is uniformly 1000 h, the storage temperature is 60 °C. For water-miscible products, 3 tests are carried out in par- 326 23rd International Colloquium Tribology - January 2022 Development and verification of a test method for determining the compatibility of elastomers with cooling lubricants allel: with water, with the MWF concentrate and with a 10% emulsion. In each case 5 test rods are used per test. The scope of the test includes the following parameters: • Volume change • Shore A Hardness - Change • Tensile strength (change) • Elongation at break (change) • pH value change • Conductivity Change • Sensory testing 4. Verification of the test method with elastomers In the next step, the method was used to carry out tests with a commonly used elastomer group - the PU materials. Both etherand ester-based PU grades have been tested. Especially with products of this group intolerances have been observed in use. Overall, the project has great support from the industry (elastomer, machine tool manufacturers, users). This has been expressed both in the provision of materials and in the execution of tests and communication of the results. The project identified and made available results on more than 30 materials - commercially available and also material under development. 5. Outlook and recommendations The described method allows an assessment of the compatibility of elastomers with cooling lubricants. The generic formulations of the reference cooling lubricants represent the coolant types available on the market. In any case, it is recommended to carry out a test before the use of an elastomer in a MWF-exposed environment in order toavoid unnecessary risks and costs. The VSI test method will be also incorporated into an ISO 1817 standard.