Influence of Carbon-Containing Additives in the Composition of Copper-Based Friction Material on Boundary Friction in Mi
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uence of Carbon-Containing Additives in the Composition of Copper-Based Friction Material on Boundary Friction in Mineral and Synthetic Oils V. P. Biryukova, *, A. F. Il’yushchenkob, A. V. Leshokb, and T. I. Pinchukb aMechanical
Engineering Research Institute, Russian Academy of Sciences, Moscow, 101000 Russia Powder Metallurgy Institute, National Academy of Sciences of Belarus, Minsk, 220005 Belarus *e-mail: [email protected]
b
Received February 5, 2020; revised June 10, 2020; accepted June 15, 2020
Abstract—This study provides the results of analyzing the influence of carbon-containing powder additives in the form of powders of fine GK-1 pencil graphite, GE-1 coarse graphite, and foundry coke fractions smaller than 63 and 100–200 μm on the setting and transfer of materials using mineral and synthetic oils. It is established that foundry coke powder allows for improving the resistance of material during seizure. Thus, an increase in the seizure load from 1.4 to 1.7 MPa for mineral oil and from 1.0 to 1.4 MPa for synthetic oil is registered at a sliding speed of 2 m/s. The use of finely dispersed pencil graphite as part of the friction material during friction in synthetic oil increases the speed during seizure; thus, an increase in speed up to 4 m/s is registered at a load of 1 MPa, while an increase in speed for pure 12% bronze is not higher than 2 m/s. Keywords: score, setting, friction material, wear, friction coefficient, counterbody, tin bronze, boundary friction, pencil graphite, elemental graphite, foundry coke DOI: 10.3103/S1068366620050074
INTRODUCTION Despite the higher cost of their source powders, copper-based powder friction materials are still in demand thanks to good processability in production and high tribological characteristics, high heat conductance and conformability, and a high ratio of the material friction coefficient to the material wear at braking, which is very important for improving the performance efficiency of friction units [1, 2]. Pure copper powder is used rarely as the base of friction materials because it has a high coefficient of friction with steel and is carried over to the counterpart in a small number of cycles, and thus creates conditions for surface setting. In most cases tin powder is added to copper for producing bronze with enhanced tribological properties. The content of tin in these materials ranges from 6 to 12%; tin is contained there as both a homogeneous solution and a solution with solid intermetallic shots [3, 4]. The scoring resistance and friction coefficient of friction powder composites are improved by doping with respective additives. The main friction material additives are carbon-containing additives in the form of various graphite grades the content of which ranges from 10 to 50 vol % [3, 4]. As noted in [5–8], scoring is a three-phase process: phase one is the destruction of the lubricant layer; phase two is the formation and destruction of adhesive bonds
among contacting surfaces; and phase three is an increase of formed adhesive bonds to a critical
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