Comparison of friction coefficient for lubricated and nonlubricated sliding pairs

Labašová Eva, Ďuriš Rastislav, SK

Abstract: In this contribution analysis of experimentally obtained values of friction coefficient is being presented. On the testing machine Tribotestor ’89 ……… selflubricated sliding ……… beds (CuZn25Al6) and for sliding pairs made of bronze material (CuSn12) were compared…

Keywords: friction coefficient, sliding pair, normal load, bronze bushing with inserted graphite beds

1 Introduction

Machine’s parts, industrial equipment and equipment facilitating people’s lives consists of many components. …… These components differ from each other, for example by construction, speed of motion, mechanical parts, surroundings and physical parameters.

1.1 Subheading

Sliding bearings are parts of machines, which help to keep the shafts and axes in structurally required positions. They allow components to rotationally move around their own axis. Sliding bearings also carry load from shafts and axes to other parts of machines…

2 Characteristics of experimental tests

For obtaining the value of friction coefficient the Tribotestor ’89 machine was used. ……… Load force is limited by stepper electromotor and screw gear [4]. ……… The shaft is powered by an electric motor. Scheme of sliding pair is in the Figure 1. Friction coefficient of pertinent sliding couple can be determined by the equation: ,	(1)

where Fn is loading force, μ is friction coefficient, a is arm, Q is force of the friction, r is outer radius of the internal bushing.

Sliding bushings made of material CuSn12 were by cutting operation turned ……… mineral gear oil (CASTROL Manual – EP 80 W) was used.

The material zincaluminium bronze CuZn25Al6 with inserted graphite beds is suitable for higher load forces and lower sliding speed.

Graphite beds serve as lubricating reservoirs and they are diffused on the surface of the bearing.

They cover approximately 20 – 30 % of the whole surface of the bearing.

Figure 1: The scheme of sliding pair

Main advantage of the bearings made of this material, is that they are selflubricating. Proportions of the bushings are shown in Figure 2. In the Figure 3 is a photograph of the tested sliding pairs made of both parameters.

a) internal bushing	b) external bushing
Figure 2: Parameters of bushings made from material CuZn25Al6

3 Analysis of results

In the work, the results of the size of friction coefficient in dependence on the time are being presented. In all cases with constant load force, after run up the course of friction coefficient in dependence on the time was similar.

Figure 6: Variation of the coefficient of friction in the test with the rectangular shape of loading for bushings from material CuSn12Al6

Figure 7: Variation of friction coefficient with the variation of normal load	Figure 8: Variation of friction coefficient of normal load for different material pairs [3]

Two graphs are shown for illustration (Figure 5). During ……… for 60 to 70 % and after the run up its value did not markedly changed. Chawdhury et. al. [2] detected similar dependencies of size of friction coefficient on the size of loading force for different material pairs (Figure 8).

4 Conclusion

The …… Sliding speed of inner bushing was not changed, i.e. its value was all the time 0.8 ms−1. In the observed scope of load (200 N, 400 N, 600 N) the size of friction… In all types of the load, size of friction coefficient for nonlubricated bushings made of CuZn12Al6 with …… made of CuSn12…

Decrease of the value of the friction coefficient with increase of the load probably influences loss of material, smoothing the profile and change of the roughness of the surfaces of both bushings of the sliding pair.

This work has been supported by the Scientific Grant Agency of the Slovak republic VEGA under the Grant No. 1/0390/11 and the Grant No. 1/0389/11.

References

1.	Stachoviak, G. W. et al. Experimental methods in tribology. Oxford : Elsevier, 2004. 354 p. ISBN 0444515895.

2.	Chowdhury, M. A. – Nuruzzaman, D. M. – Roy, B. K. – Islam, A. – Hosain, Z. – Hasan, R. Experimental investigation of friction coefficient and wear rate of stainless steel 202 sliding against smooth and rough stainless steel 304 counterfaces. In Friction and Wear Research. Vol. 1 Iss. 3, October 2013, p. 34–41, [online] www.‌seipub.‌org/‌fwr.

3.	Chowdhury, M. A. – Nuruzzamam, D. M. – Mia, A. H. – Rahaman, M. L.: Friction coefficient of different material pairs under different normal loads and sliding velocities. In Tribology in Industry. Vol. 34, No1, 2012, pp. 18–23, ISSN 03548996.

4.	Ďuriš, R. – Labašová, E. Experimental determination of the coefficient of friction in rotational sliding joint. In Applied Mechanics and Materials. Vol. 309, 2013, p. 50–54, ISSN 16609336 [online] www.‌scientific.‌net/‌AMM.‌309.

Reviewed by: doc. Ing. Milan Naď, CSc.

Contact address

Ing. Eva Labašová, PhD.

Institute of ……… Bratislava

Address…

email: eva.labasova@stuba.sk