Elsevier

Wear

Volume 208, Issues 1–2, 1 July 1997, Pages 155-160
Wear

Laboratory wear testing of polyurethane elastomers

https://doi.org/10.1016/S0043-1648(96)07514-XGet rights and content

Abstract

A dry sand–rubber wheel abrasion test was used to investigate the wear behaviour of polyurethanes. The dry sand–rubber wheel abrasion test (DSRW test) is an approved ASTM test designed primarily for testing metals, therefore, in this study the set of test conditions was optimized for use with polyurethane elastomers. The wear performance of polyurethanes was assessed for the range of Shore hardness 85A to 65D, and a correlation was identified between the wear rate and the sample hardness. Polyurethane elastomers can be separated into three classes according to their hardness and wear performance, and each class shows a different dependence on the specimen temperature. This work has implications for use of the DSRW test for the prediction of field performance of polyurethanes.

Introduction

Polyurethanes are widely used in the mining industry because of their moderate cost, excellent mechanical properties and high wear resistance compared with alternative polymeric systems. Much of the published work with respect to the applications of polyurethanes in the mining industry has been reviewed in our previous paper [1]. In that paper we discussed the wear properties of a series of polyurethane blends with poly(dimethylsiloxane)s.

Laboratory test protocols for predicting the wear performance of polymeric materials are complex owing to the many parameters that can affect wear behaviour. Hoge and Eadara list seven parameters that need to be considered in evaluating the wear performance [2]. Three of these are considered in this paper, namely the hardness, temperature and test duration. Hoge and Eadara also describe a few of the many tests available for assessing the wear resistance of a material in the laboratory, for which the test results need to match those for the field application of interest. This is often difficult to achieve, and in many cases accelerated laboratory tests have been found not to simulate adequately the performance of a particular material in the field. The dry sand–rubber wheel (DSRW) wear tests reported in this paper are considered to simulate best the conditions found in many mining applications.

The DSRW test is an ASTM test [3]designed primarily for testing metal specimens, so the test conditions had to be modified for use with polyurethanes. Wear performances obtained using the modified DSRW test conditions have been previously reported [1]for laboratory produced blends of thermoplastic polyurethanes with poly(dimethylsiloxane) (PDMS). The aim of the present work was to gain an insight into the relationship between the wear resistance and hardness of polyurethane and to evaluate the effect of evolved heat on the wear performance of these materials. To confirm the observed dependence of the wear performance on the temperature of the polymer sample, studies were also carried out using the erosion test method.

Section snippets

Materials

The thermoplastic polyurethanes studied were Dow Pellethane 2103-55D (Pel55D), supplied by Era Polymers, Elastollan 11-85A-10-000 (Ela85A), supplied by BASF, and a commercial product obtained in pellet form from Urethane Compounds, Australia with a Shore hardness of 93A (UC93A). The thermoset blends (APP93A and APP65D), with Shore hardnesses of 93A and 65D respectively, were supplied as cast sheets of 1 mm thickness by Advanced Polymer Products, Australia.

The thermoplastic polyurethanes were

Durometer hardness

The Shore hardness was measured following the ASTM standard for rubber properties and durometer hardness [4]. This standard requires the test specimens to be greater than 6 mm in thickness, therefore a number of specimens cut from the extruded tapes were stacked to achieve this thickness, according the accepted ASTM practice. The Shore A and D hardness ranges overlap, with D being the higher of the two. According to the ASTM, there is no simple conversion between the two ranges, since this will

Wear (DSRW) and polyurethane hardness

Polyurethanes over a range of hardness were assessed using the DSRW test apparatus. In all cases the wear rate was found to be constant with time when the rested protocol was used. However, when the unrested protocol was used, the wear rate was sometimes found to vary with time. This is demonstrated in Fig. 4, where the plot of the unrested Pel55D data shows a non-linear relationship, displaying a decrease in the wear rate compared with that of the rested samples. However, for the softer Ela85A

Conclusions

The DSRW wear test has been optimized for use with polyurethanes. Using this technique a correlation between wear rate and Shore hardness for polyurethanes has been found, which is consistent with previous reports in the literature. This correlation has been used to explain how the heat evolved during the abrasion process impacts on the wear resistance of polyurethanes of different hardness. An increase in temperature caused by the friction between the sample and the abrasive can soften the

Acknowledgements

We would like to acknowledge CRA, Advanced Technical Development, for funding this project, Advanced Polymer Products (APP), Urethane Compounds (UC), E-Plas, Flexichem, Era Polymer (agents for Dow) and BASF for supplying materials, the CRC for Polymer Blends and the Centre for Advanced Materials Technology (CAMT) at Monash University for access to their equipment.

Biographies
David Hill is an associate professor in the Polymer Materials and Radiation Group in the Department of Chemistry at the University of Queensland. He joined the staff of the University in 1967. His research interests are in the relationships between copolymer structure and properties, polymer radiation chemistry, copolymerization kinetics and mechanisms and biomedical applications of polymers.
Mitchell Killeen has completed a PhD in the Polymer Materials and Radiation Group at the

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Biographies
David Hill is an associate professor in the Polymer Materials and Radiation Group in the Department of Chemistry at the University of Queensland. He joined the staff of the University in 1967. His research interests are in the relationships between copolymer structure and properties, polymer radiation chemistry, copolymerization kinetics and mechanisms and biomedical applications of polymers.
Mitchell Killeen has completed a PhD in the Polymer Materials and Radiation Group at the University of Queensland, in the area of wear performance of polyurethane blends. He is now employed by Montell Australia Pty Ltd in their Melbourne Office.
James O'Donnell was the professor of Physical Chemistry at the University of Queensland until his death in 1995.
Peter Pomery is a senior lecturer in the Polymer Materials and Radiation Group in the Department of Chemistry at the University of Queensland. He joined the staff of the University in 1971. His research interests are in the areas of polymerization kinetics and mechanisms, high energy radiation effects on polymers, and ESR spectroscopy.
David St. John is a professor in the Department of Mining, Minerals and Materials Engineering at the University of Queensland. Prior to joining the staff of the University of Queensland in 1995 he was manager of materials technology at the CRA Research and Technology Centre in Perth, Western Australia. His research interests are in the areas of solidification and casting technologies and the mechanical performance of materials.
Andrew Whittaker is a senior research fellow in the Centre for Magnetic Resonance at the University of Queensland. His principal research interests are in solid-state NMR, polymer chemistry and physics, molecular motions in polymers and polymer blend systems.

1

Current address: Deptartment of Mining and Metallurgical Engineering, University of Queensland, Brisbane, Qld 4072, Australia.

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