posted on 2017-07-27, 15:09authored byAshok Moodbidri Prabhu
Elastomer compounds have been used in pipe seals for many decades, with their
main problem, the stress relaxation due to various mechanisms. In these
applications, a service life of more than fifty years is expected- and obtained.
The purpose of the programme was to establish mathematical models to enable
longevity of seals to be predicted from laboratory measurements. It seemed that
stress relaxation in compression, together with strain recovery measurements,
would provide a basis for such an investigation. Accordingly, such tests were
carried out with up to 23 rubber compounds, at temperatures of 5°, 23°, 40°, 70°, 100° and and 125° C, with environments of air, mains water and town gas.
The work outlined above is the main thrust of the programme, the data obtained
being the raw material for the development and assessment of mathematical
models associated with the viscoelasticity of the various rubbers. This work has
been supported by supplementary investigations, including:
effect of loading rate
step changes in temperature
inclusion (or not) of mechanical working of the specimen before testing
use of solid phase lubricant
changing the dimensions of the specimen
comparison of air environment with water immersion, and town gas
comparison of air environment with vacuum and nitrogen
An important facet of the work has been the comparison of tensile behaviour with the
bulk of the work carried out in uniaxial compression. A comparatively novel
property has been introduced in this work: strain recovery after compression. This
has proved to be a property related to 'permanent-set', yet more amenable to
interpretation and correlation, recovery data are now available for most of the
conditions in the stress relaxation programme whilst additional results have
been obtained from compression set equipments.
The other objective of this programme is to investigate short comings of BS
2494-1986, the current rubber seal specification, and to suggest new techniques
such as strain recovery.
Finally, the behaviour of seals in simulated service has been investigated to
compare with the data generated in the main programme.
Funding
Department of Trade and Industry, British Standard Institute
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/
Publication date
1991
Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.