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.