GB/T 7759.2-2014 English PDF (GBT7759.2-2014)

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GB/T 7759.2-2014: Rubber, Vulcanized or thermoplastic -- Determination of compression set at low temperatures
GB/T 7759.2-2014
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 83.060
G 40
GB/T 7759.2-2014 / ISO 815-2:2008
Rubber, vulcanized or thermoplastic - Determination of
compression set - Part 2: At low temperatures
(ISO 815-2:2008, IDT)
ISSUED ON: DECEMBER 22, 2014
IMPLEMENTED ON: JUNE 01, 2015
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of the People's Republic of China;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Principle ... 5
4 Apparatus ... 5
5 Test pieces ... 8
6 Test conditions ... 10
7 Test procedure ... 10
8 Result representation ... 12
9 Precision ... 12
10 Test report ... 12
Rubber, vulcanized or thermoplastic - Determination of
compression set - Part 2: At low temperatures
WARNING: Persons using this Part shall be familiar with normal laboratory
practice. This Part does not purport to address all of the safety problems, if any,
associated with its use. It is the responsibility of the user to establish appropriate
safety and health practices and to ensure compliance with any national regulatory
conditions.
CAUTION: Certain procedures specified in this Part may involve the use or
generation of substances, or the generation of waste, that could constitute a local
environmental hazard. Reference shall be made to appropriate documentation on
safe handling and disposal after use.
1 Scope
This Part of GB/T 7759 specifies the test method for determining the compression set
characteristics of vulcanized rubbers or thermoplastic rubbers at low temperature.
This method is intended to measure the ability of rubbers of hardness within the range
of 10 IRHD ~ 95 IRHD to maintain their elasticity after continuous compression at
specified temperature and compression rate (usually 25 %). When the rubber hardness
is greater than 80 IRHD, a lower compression rate shall be used: compression rate of
15 % for 80 IRHD ~ 89 IRHD, compression rate of 10 % for 90 IRHD ~ 95 IRHD.
NOTE: Rubber undergoes physical and chemical changes when compressed. When the compression
force disappears, these changes prevent the rubber from returning to its original state, thus
generating compression set. The magnitude of compression set depends on the temperature and time
of compression, as well as the temperature and time of recovery. At low temperatures, glass
transition and crystallization effects are the main causes of compression set in rubber. Since these
effects gradually disappear as the temperature rises, all measurements must be made at the test
temperature.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 2941-2006 Rubber - General procedures for preparing and conditioning test
pieces for physical test methods (ISO 23529:2004, IDT)
- Type A: a cylinder of diameter 29 mm ± 0.5 mm and height 12.5 mm ± 0.5 mm;
- Type B: a cylinder of diameter 13 mm ± 0.5 mm and height 6.3 mm ± 0.3 mm.
The results obtained from the two specifications of test pieces may not be the same, and
the test results obtained cannot be compared.
Type A test pieces are suitable for measuring test pieces with relatively low compression
permanent deformation. Using large-sized test pieces can obtain more accurate data.
Type B test pieces are suitable for test pieces cut from finished products. Unless
otherwise specified, when cutting, the test piece shall be taken from the center of the
finished product as much as possible. If possible, when cutting, the axis of the test piece
shall be parallel to the compression direction of the finished product when in use.
5.2 Preparation of test pieces
Whenever possible, each test piece shall be prepared by molding. When preparing test
pieces by cutting and laminating, the lamination shall not exceed three layers. When
using laminated test pieces for finished product performance control, the consent of all
relevant parties shall be obtained.
Cutting of test pieces shall comply with the requirements of GB/T 2941-2006. When
cutting is difficult (forming a concave surface), the shape of the test piece can be
improved by dividing the cutting into two steps: first, cut a large-sized test piece, and
then trim the test piece to the specified size with another cutter.
Laminated test pieces shall be cut from a thin film according to the size specified in 5.1
and then laminated. Each layer shall not be bonded. The laminated test piece is
compressed for 1 min at a compression rate of a few percent to combine the test piece
into a whole. The laminated test piece shall not exceed three layers. Then measure the
total height.
Test pieces prepared by the above different methods may obtain different test results,
and the test results cannot be compared.
NOTE: Special attention shall be paid to the significant effect of vulcanization conditions on the
compression set results. When preparing test pieces using films of different thicknesses and different
molds, the vulcanization conditions shall be adjusted appropriately.
5.3 Number of test pieces
Test 3 test pieces, which can be carried out individually or simultaneously according to
the purpose of the test.
5.4 Interval between vulcanization and test
For all tests, the minimum time between vulcanization and test is 16 h.
Place the compression apparatus (4.1) at a standard laboratory temperature and
carefully clean the operating surfaces. Apply a thin coating of lubricant to the surface
of the compression plates (4.1.1) in contact with the test pieces. The lubricant used shall
not have any effect on the test pieces, and the lubricant used shall be stated in the test
report (see Clause 10).
NOTE: The kinematic viscosity of silicone oil or fluorosilicone liquid at standard laboratory
temperature is 0.01 m2/s, which is a suitable lubricant for most tests.
If a lubricant is not used for some reason, it shall be stated in the test report.
7.2 Height measurement
Measure the height at the center of each test piece at standard laboratory temperature,
to the nearest 0.01 mm.
7.3 Applying compression
Tighten the compression apparatus so that the compression plates are evenly close
together until the selected compression height is reached. Whether a spacer is required
for this operation depends on the design of the compression apparatus.
Except for test pieces of high hardness, the compression rate is (25 ± 2) % of the original
height of the test piece. The compression rate of test pieces of high hardness shall be
(15 ± 2) % or (10 ± 1) % (see 4.1.2).
7.4 Start of test
Immediately place the compression apparatus containing the test piece in the low-
temperature cabinet (4.2) that has reached the specified test temperature (see 6.2).
7.5 End of test
After the test time is reached, release the compression apparatus and start the timing
device (4.3) at the same time. The time taken to release the compression shall not exceed
10 % of the total time between the start of release and the first height measurement (see
7.6). However, when the relationship between the height of the test piece and the time
needs to be determined, the compression shall be released as soon as possible.
7.6 Measurem...