GB/T 7759.1-2015: Rubber, vulcanized or thermoplastic -- Determination of compression set -- Part 1: At ambient or elevated temperatures

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Scope

This Part specifies methods for the determination of the compression set characteristics
of vulcanized and thermoplastic rubbers at ambient or elevated temperatures.
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 IRHD.
NOTE 1: When rubber is held under compression, physical or chemical changes can occur that
prevent the rubber returning to its original dimensions after release of the deforming force. The
result is a set, the magnitude of which depends on the time and temperature of compression as well
as on the time and temperature 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 22 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 1000 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).
Type B test pieces are preferred when it is required to cut test pieces from products. In
this case, the test pieces shall be taken as near to the center of the product as possible,
unless otherwise specified. When possible, the test piece shall be cut in such a way that
its axis is parallel to the direction of compression of the product in service.
5.2 Preparation
The test pieces shall be prepared by molding each disc, whenever possible. Preparation
by cutting out each disc or by laminating not more than three discs is permitted. The
use of test pieces prepared by laminating several discs for control of finished products
shall be agreed between interested parties.
Cutting shall be performed in accordance with GB/T 2941-2006. When cupping (the
formation of a concave surface) is a problem, the test piece shape can be improved by
cutting it in two stages: first cut an oversize test piece and then trim it to the exact
dimensions with a second cutter.
Laminated test pieces shall conform to the dimensions specified in 5.1 and shall be
prepared by laminating discs or rubber cut from sheets without adhesives. Discs may
be compressed by a few percent for 1 min so that they stick together. The number of
discs laminated to produce a test piece shall not exceed three. The total thickness shall
then be measured.
Test pieces prepared by the various methods described above may give different results
and comparison of values shall be avoided.
NOTE: Attention is drawn to the marked effects of the state of cure on compression set values. It
may be necessary to adjust the cure of molded test pieces to be representative of different thicknesses
of sheets or moldings.
5.3 Number of test pieces
A minimum of three test pieces shall be tested, separately or as a set.
5.4 Time-interval between production and testing
For all test purposes, the minimum time between production and testing shall be 16 h.
For non-product tests, the maximum time between production and testing shall be 4
weeks and, for evaluations intended to be comparable, the tests, as far as possible, shall
be carried out after the same time-interval.
For product tests, whenever possible, the time between production and testing shall not
exceed 3 months. In other cases, tests shall be made within 2 months of the date of
receipt of the product by the purchaser (see GB/T 2941-2006).
5.5 Conditioning

Basic Data

Standard ID	GB/T 7759.1-2015 (GB/T7759.1-2015)
Description (Translated English)	Rubber, vulcanized or thermoplastic -- Determination of compression set -- Part 1: At ambient or elevated temperatures
Sector / Industry	National Standard (Recommended)
Classification of Chinese Standard	G40
Classification of International Standard	83.060
Word Count Estimation	13,186
Date of Issue	2015-05-15
Date of Implementation	2015-10-01
Older Standard (superseded by this standard)	GB/T 7759-1996
Quoted Standard	GB/T 2941-2006; GB/T 3512-2014; ISO 4287; ISO/TR 9272
Adopted Standard	ISO 815-1-2008, IDT
Regulation (derived from)	National Standard Announcement 2015 No. 15
Issuing agency(ies)	General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, Standardization Administration of the People's Republic of China
Summary	This Standard specifies the test method for the determination of vulcanized rubber or thermoplastic rubber at room temperature and high temperature compression set properties. This method is used to measure the hardness in the range 10 IRHD ~ 95 IRHD rubber under specified conditions of temperature and compression ratio (typically 25%), after sustained compression ability to maintain its elasticity. When the rubber hardness greater than 80 IRHD, should be used to lower the compression ratio: 80 IRHD ~ 89 IRHD compression ratio of 15%, 90 LRHD ~ 95 IRHD compression rate of 10%.