After price and delivery time, the most frequently asked question about a product is ‘How long will it last?’ This is usually a very difficult question to answer for rubber products because the expected lifetime is often in tens of years, the service conditions may be complex, and there is a scarcity of definitive data on durability. There is a vast matrix of degradation agents, service conditions, properties of importance and different rubbers. There are also many inherent difficulties in designing tests. In many cases, the timescale involved is such that accelerated test conditions are essential. Whilst large amounts of durability data are generated by accelerated methods, much of it is only useful for quality control purposes and relatively little has been validated as being realistically capable of representing service.
Most assessments of lifetime of rubbers are made by considering some measure of performance, such as tensile strength, and specifying some lower limit for the property, which is taken as the end point. Lifetime is not necessarily measured in time. For example, for some products it will be thought of as number of cycles of use.
The object of this publication is to provide practical guidance on assessing the useful service life of rubbers. It describes test procedures and extrapolation techniques together with the inherent limitations and problems. The Guide aims to make available the wealth of information that can be applied to help maximise the effectiveness of a durability testing programme.
This Guide seeks to be comprehensive but concentrates on the most common environmental effects causing degradation and the most important mechanical properties of rubbers. The test procedures used are outlined and the relevant textbooks and International standards are referenced.
Rapra Technology Limited has just completed a 40 year natural ageing programme and an accelerated testing programme, both on the same set of rubber compounds. The results have been drawn on in this Guide to indicate the limiting factors for particular test methods.
Roger Brown is an internationally acknowledged expert on physical testing and quality assurance of polymers. He has published more than 70 technical papers and three standard textbooks on testing. In addition, he is editor of the journal Polymer Testing. He has over 25 years experience of running the testing laboratories and services at Rapra. Roger is active on many Standards committees and is leader of the British delegation to ISO Technical Committee 45.
This publication is an output from the Weathering of Elastomers and Sealants project which forms part of the UK government’s Department of Trade and Industry’s Degradation of Materials in Aggressive Environments Programme.
This book will be useful for anyone responsible for designing, manufacturing or testing rubber components. It will also be of benefit to suppliers and users of end products, as assessment of useful lifetime is critical to the economics and safety aspects of any component.
