Rubber components are used in many demanding applications, from tyres and seals to gloves and medical devices, and failure can be catastrophic. This review of rubber product failure outlines and illustrates the common causes of failure, while addressing ways of avoiding it.
There has been increasing pressure to improve performance so that rubbers can be used at higher temperatures and in harsher environments. For example, the under-the-bonnet temperature has increased in some vehicles and new medical devices require longer lifetimes in potentially degrading biological fluids. The expectations of tyre performance in particular are increasing, and retreads have been in the spotlight for failures.
The definition of failure depends on the application. For example, a racing car engine seal that lasts for one race may be acceptable, but in a normal car a life span of 10 years is more reasonable. If appearance is critical as in surface coatings and paints, then discolouration is failure, whilst in seals leakage is not acceptable. Each rubber product must be fit for the use specified by the consumer.
Failure analysis is critical to product improvement. The problem is obvious to see, for example a hole in a hot water bottle, but the cause of the problem can be much harder to find. It can range from a design fault to poor material selection, to processing problems, to manufacturing errors such as poor dimensional tolerances, to poor installation, product abuse and unexpected service conditions. The rubber technologist must become a detective, gathering evidence, understanding the material type and using deductive reasoning.
Testing and analysis of failed materials and components add to the information available for failure analysis. For example, stored aged tyres appeared superficially to be alright for use, but on drum testing small cracks grew more quickly than in new tyres leading to rapid failure in service.
Quality control procedures such as product inspection, testing and material quality checks can help to reach 100% reliability. In critical applications such as electricians' gloves for high voltage working, gloves are inspected before each use, while engine seals may be routinely replaced before the expected lifetime to avoid problems.
It is customary to hide failures, thus the number of specific cases published in the literature is not high. However, several reviews have been written on specific products and references can be found at the end of this review. Around 400 abstracts from papers in the Polymer Library are included with an index. Subjects covered include tyre wear and failure, seals, engine components, rubber bonding failure, rubber failure due to chloramine in water, tank treads, gloves and condoms, medical devices and EPDM roofing membranes.
2. Failure Analysis
3. The Reasons for Failure
3.1 Design Error
3.2 Inappropriate Material
3.3 Manufacturing Faults
3.4 Incorrect Installation
3.5 Unexpected Service Conditions
3.6 Deliberate or Accidental Misuse
3.7 Strategic Weakness
4. The Causes of Failure
4.3 Effect of Fluids
4.5 Ionising Radiation
4.6 Biological Attack
4.8 Set, Stress Relaxation and Creep
4.10 Electrical Stress
5. Preventing Failure
5.2 Service Trials
5.4 Accelerated Testing
5.5 Quality Control
6. The Literature
6.4 Other Products
Abstracts from the Polymer Library Database
Roger Brown is renowned in the rubber industry for his knowledge of rubber testing, including work on the 40 year ageing of rubber project recently completed at Rapra. He has studied many cases of product failure and has acted as an expert witness. He has published and edited numerous books and reports, and currently works with the Rapra Testing and Quality Group.