Tribology in Cold Pilgering

Abstract

The lubricants that are used today by Sandvik Materials Technology AB in the cold pilger process contain chlorinated paraffins. Due to environmental, economic and health reasons, these lubricants have to be replaced. The method for trying out new pilger lubricants today is full scale trials in cold pilger mills. The main aim of this thesis has been to investigate whether it is possible to evaluate pilger lubricants by using some standard laboratory tribological test methods. In addition to this, a review of published literature and a description of the cold pilger process in tribological terms have also been conducted. The literature review included the published work pertaining to cold pilgering in tribology related scientific journals and books. This review indicated that only very limited information is available in open literature and the survey was therefore broadened to include other similar metal working processes. The test methods that have been used are the sliding four ball test machine and the SRV (Schwingung Reibung Verschleiß) reciprocating friction and wear tester. The test specimens for the four ball machine were standard bearing steel balls. In the SRV tests, cylinder on disc and a ball on disc test specimen configurations were used. The cylinder specimens were manufactured from the tube material and the disc specimens were made of mandrel material. The balls for the SRV were made of standard stainless steel. In the four ball machine, both the wear preventive characteristics and extreme pressure properties have been evaluated. In the SRV Optimol machine, seizure and wear tests have been performed. To analyse the surfaces, Wyko 1100 NT optical surface profiler has been used. A more thorough analysis of test specimen surfaces was also carried out by using SEM/EDS at SMT. The results show that the SRV cylinder on disc and ball on disc seizure tests are very representative of the cold pilger process. The ranking of various lubricant formulations from these tests correlate very well to the ranking from the full scale cold pilger trials. The surface damage modes and material transfer in the tests correspond well with those observed in the actual process. The SRV wear test corresponds only to a limited extent and the reason for this is that the ranking of cold pilger lubricants is not based on wear.The four ball EP tests do not correlate that well with the real ranking. This is attributed to the use of different test specimen material in four ball tests as compared to that actual tube/mandrel materials and the test method may not reproduce the conditions prevalent in the cold pilger process. The four ball wear tests do not correlate at all to the actual ranking of lubricant formulations owing to the same reasons and also in view of the fact that the ranking is not based on wear.Validerat; 20101217 (root