BS ISO 815-1-2014 pdf download.Rubber, vulcanized or thermoplastic-Determination of compression set Part 1: At ambient or elevated temperatures.
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 hard nesses below 80 IRHD,
— (15 ± 2) % for hardnesses between 80 IRIID 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.
4.2 Oven, complying with the requirements specified in ISO 188, method A or method B, and capable of maintaining the compression assembly and test pieces at the test temperature within the tolerance specified in 22.
NOTE Test results obtained with ovens for method A can be different from those obtained with ovens for method B.
The time to reach a steady-state temperature depends on the type of oven and the overall heat capacity of the compression assembly. To obtain comparable results in the case of an elevated test temperature and a 24 h test duration, it is necessary to reach the steady-state temperature within the specified tolerances in the interior of the test pieces in not more than 3 h.
4.3 Pair of tongs, for handling the test pieces.BS ISO 815-1 pdf download.