Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
- Vortrag (2)
- Beitrag zu einem Tagungsband (1)
Sprache
- Englisch (3)
Referierte Publikation
- nein (3)
Schlagworte
- Metal sulphides (3) (entfernen)
Eingeladener Vortrag
- nein (2)
A study on metal sulphides in tribofilms of modelled brake wear debris under variable humidity
(2017)
Metal sulphides are needed in brake pad formulations in addition to graphite to compensate the influence of different environments. The sensitivity to humidity differs a lot for each single constituent. Only one component is not sufficient for stabilising the COF and it is also necessary to add more components than only one metal sulphide to graphite. Furthermore, a good mixing process inside the third body during braking is necessary to prevent formation of solid lubricant films which are detrimental for braking. Nevertheless, not every metal sulphide acts as a solid lubricant but most of them have the ability for stabilizing the friction coefficient.
To investigate the influence of metal sulphides in brake pads, powder mixtures with up to three components were tribologically stressed in a pin-on-disc device under different levels of relative humidity. The tests revealed that each metal sulphide causes significant differences in resulting coefficients of friction as well in their sensitivity to humidity, so that only one solid lubricant cannot stabilise the friction behaviour during braking in different environments.
Besides carbon, metal sulphides are used in every standard brake pad formulation as friction stabilisers. In order to investigate their impact, various powder mixtures were tribologically stressed in a pin-on-disc device in order to produce and test artificial third bodies. containing the three main components of a real friction film, namely magnetite, graphite and a metal sulphide of interest. Since the sliding behaviour is influenced by the relative humidity the powder mixtures are tested at low, medium and high moisture levels. The tests revealed that the presence of graphite dominates the friction behaviour as well as the humidity sensitivity.
The powders were prepared by either manual mixing or high energy ball-milling. Interestingly, all ball-milled blends provided coefficients of friction within the desired range for braking, which was attributed to the effect of zirconia particles from wear debris of the milling balls. The zirconia particles prevent the formation of solid lubricant films on the surfaces and support a homogeneous mixture of all constituents of the powder. Optimum brake performance is gained by an optimum combination of solid lubricants and abrasives.