BS ISO 815-1:2014 pdf free.Rubber, vulcanized or thermoplastic — Determination of compression set Part 1: At ambient or elevated temperatures.
This part of Iso 815 specifies methods for the determination of the compression set characteristics of vulcanized and thermoplastic rubbers at ambient (one method) or elevated temperatures (three methods, A, B, and C, depending on the way the test piece is released at the end of the test).
The methods are intended to measure the ability of rubbers of hardness within the range 10 IRHD to 95 IRHD to retain their elastic properties at specified temperatures after prolonged compression at constant strain (normally 25 %) under one of the alternative sets of conditions described. For rubber of nominal hardness 80 IRHD and above, a lower compression strain is used: 15 % for a nominal hardness from 80 IRHD to 89 IRHD and 10 % for a nominal hardness from 90 IRHD to 95 IR[ID.
NOTE I When rubber is held under compression, physical or chemical changes that prevent the rubber returning to its original dimensions after release of the deforming force can occur. The result is a set, the magnitude of which depends on the time and temperature of compression as well as on the time, temperature, and conditions of recovery. At elevated temperatures, chemical changes become increasingly more important and lead to a permanent set.
NOTE 2 Short-time compression set tests, typically for 24 h, at elevated temperatures are commonly used as a measure of the state of cure, a means of material classification, and a specification to ensure the quality of a compound. Longer tests, typically for 1 000 h, at elevated temperatures take account of the effect of ageing and are often used to predict service performance, including that of sealing materials. Short-time tests at ambient temperature show mainly the effect of physical changes (re-orientation of the molecular chains and the fillers).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 188, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests Iso 18899:2004, Rubber — Guide to the calibration of test equipment
ISO 23529:2010, Rubber — General procedures for preparing and conditioning test pieces for physical test methods.
3 Principle
A test piece of known thickness is compressed at standard laboratory temperature to a defined strain, which is then maintained constant for a specified time at standard laboratory temperature or a fixed elevated temperature. The compression is released and, after the test piece has been allowed to recover at a standard laboratory temperature or the elevated temperature for a specified time, the thickness of the test piece is again measured.
4 Apparatus
4.1 Compression assembly, consisting of compression plates, steel spacers, and clamping device. A typical assembly is shown in Figure 1.
4.1.1 Compression plates. comprising a pair of parallel, flat, highly polished chromium-plated steel or highly polished stainless-steel plates, between the faces of which the test piece is compressed.
The plates shall be
— sufficiently rigid to ensure that, with a test piece under load, no compression plate bends by more than 0.01 mm and
— of sufficient size to ensure that the whole of the test piece. when compressed between the plates, remains within the area of the plates.
NOTE A surface finish no worse than Ru 0,4 pm (see ISO 4287) has been found to be suitable. Such an Ru can be obtained by a grinding or polishing operation.
4.1.2 Steel spacer(s), to provide the required compression.
The spacer(s) shall be of such size and shape that contact with the compressed test piece is avoided.
The height of the spacer(s) shall be chosen so that the compression applied to the test piece is
— (25 ± 2) % for hardnesses below 80 IRHD,
— (15 ± 2) % for hardnesses between 80 IRHD and 89 IRHD,
— (10 ± 1) % for hardnesses of 90 IRHD and higher.
4.1.3 Clamping device, a simple screw device (see Figure 1) is adequate.BS ISO 815-1 pdf free download.