GB/T 1683-2018 in English

《GB/T 1683-2018硫化橡胶 恒定形变压缩永久变形的测定方法》由TC35（全国橡胶与橡胶制品标准化技术委员会）归口，TC35SC2（全国橡胶与橡胶制品标准化技术委员会通用试验方法分会）执行，主管部门为中国石油和化学工业联合会。

ChinaStandards.net is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.

This standard is developed in accordance with the rules given in GB/T 1.1-2009.

This standard was proposed by China Petroleum and Chemical Industry Association.

This standard is under the jurisdiction of National Technical Committee on Rubber & Products of Standardization Administration of China (SAC/TC 35).


Rubber, vulcanized - Determination of compression set at constant strain

1 Scope

This standard specifies the test method for determining the compression set of vulcanized rubber at constant strain.

This standard is applicable to evaluate the capability of vulcanized rubber of keeping its elasticity after continuous compression at specified temperature and compression rate.

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
GB/T 3512-2014 Rubber, vulcanized or thermoplastic - Accelerated aging and heat resistance tests - Air-oven method
GB/T 7759.1-2015 Rubber, vulcanized or thermoplastic - Determination of compression set - Part 1: At ambient or elevated temperatures

3 Principle

In this test, the is compression set rate of the vulcanized rubber specimen is determined by compressing the specimen to a specified height and then keeping it at certain temperature for certain time, or infiltrating by medium.

4 Test devices

4.1 Test fixtures

4.1.1 The test fixtures shall include compression plates, limiters and fasteners. See Figure 1 for typical test fixtures.



Keys:

1——fastener;

2——limiter;

3——specimen;

4——compression plate.

Figure 1 Schematic diagram for test fixtures

4.1.2 The compression plates are a pair of parallel, flat and highly polished steel plates, and the specimen is compressed between them. The compression plate shall have a surface roughness Ra of not greater than 1.6μm, and shall also have:

——sufficient rigidity to ensure that it will not deform when compressed; steel plate is recommended.

——sufficient size to ensure that the whole specimen can be located within the compression plate area when it is compressed between two compression plates; 75mm*50mm*10mm (length*width*thickness) is recommended.

4.1.3 For the limiter, corresponding compression rate shall be given, and its shape and size shall protect it from contact with the compressed specimen. The recommended height of the limiter is (8±0.02)mm, (7±0.02)mm or (6±0.02)mm; the selection of limiter height shall meet the requirements of specimen compression rate.

4.1.4 Fasteners are screw devices composed of bolts and nuts.

4.2 Test chamber

4.2.1 It shall meet the requirements of Method A or Method B in GB/T 3512-2014, and can keep the test temperature tolerance within that recommended in 6.4 during the test.

4.2.2 It shall be equipped with a continuously working blower device to keep uniform test temperature in the chamber. The allowable temperature tolerance range of the test area in the test chamber: ±1℃ for 100℃ and below, and ±2℃ for 100~300℃.

4.3 Thickness gauge

It shall meet the requirements of 4.4, GB/T 7759.1-2015, have an accuracy of ±0.01mm (see 7.1, GB/T 2941-2006), and be equipped with a flat circular presser foot having a diameter of (4±0.5)mm and a measuring platform; the pressure applied on the rubber having a hardness of greater than or equal to 35IRHD shall be (22±5)kPa while that applied on the rubber having a hardness of less than 35IRHD shall be (10±2)kPa. The specimen is placed between two parallel planes, and the measurement of the applied pressure shall not cause any obvious deformation of the specimen. Presser foots having the same diameter shall be used for contrast test.

After high temperature aging, the specimen may be deformed unpredictably. Sometimes both surfaces of the specimen are deformed, which makes the height measurement complicated. In this case, a thickness gauge shall be carefully selected to measure the diameter of the presser foot, so as to provide accurate measurement.

4.4 Medium-resistant test vessel

4.4.1 The test vessel shall have a size large enough to completely immerse the test fixture in the test liquid medium, and shall be sealed. The air above the liquid in the test vessel shall be as little as possible.

4.4.2 The material used for the test vessel shall not react with the test liquid and the specimen, for example, copper-containing materials shall not be used.

5 Specimens

5.1 Size

The specimen is a cylinder having a diameter of (10±0.2) mm and a height of (10±0.2) mm, and the height difference of the same group of specimens shall not exceed 0.05mm.

5.2 Preparation of specimens

Specimens shall be vulcanized directly with molds, and their surfaces shall be flat, perpendicular and parallel to each other, and shall be free of bubbles, impurities or damage.

Specimens may also be cut from vulcanized rubber sheets with thickness in accordance with 5.1 by a circular cutter having an inner diameter of (10.2±0.02)mm. During cutting, the cutting edge may be lubricated with neutral soap solution, and the cutting process shall be slow to reduce the diameter taper.

Specimens prepared using different methods listed above may lead to different test results, which are not comparable.

5.3 Number of specimens

The number of specimens in each group shall not be less than three.

5.4 Time interval between vulcanization and test

For all tests, the minimum time interval between vulcanization and test is 16h.

For non-finished product test, the maximum time interval between vulcanization and test is four weeks. For contrast test, the time interval shall be the same as possible.

For finished product test, if possible, the time interval between vulcanization and test shall not exceed three months. In other cases, the test shall be carried out within two months upon being received by the purchaser (see GB/T 2941-2006).

5.5 Conditioning

During the time interval between vulcanization and test, samples and specimens shall be kept away from light and heat as possible.

Prior to the test, the prepared specimens shall be conditioned at a standard laboratory temperature specified in GB/T 2941-2006 for at least 3h. In order to make the results comparable, the same temperature shall be maintained throughout the test.

6 Test conditions

6.1 Selection of constant compression rate

The following selections may be made according to the specimen hardness (Shore A hardness):

——40% compression rate may be selected for specimens having a hardness of less than 50;

——30% compression rate may be selected for specimens having a hardness of 50~75;

——20% compression rate may be selected for specimens having a hardness of greater than 75.

Note: the compression rate may also be selected according to the requirements for actual use.

6.2 Selection of limiters

The limiter with corresponding height may be selected according to the following compression rates:

——a limiter having a height of (8±0.02)mm is selected where the compression rate is 20%;

——a limiter having a height of (7±0.02)mm is selected where the compression rate is 30%;

——a limiter having a height of (6±0.02)mm is selected where the compression rate is 40%.

6.3 Test duration

The test duration may be selected from 24_(-2)^(+0)h, 48_(-2)^(+0)h, 72_(-2)^(+0)h, 96_(-2)^(+0)h, 120_(-2)^(+0)h, 144_(-2)^(+0)h, 168_(-2)^(+0)h, etc., or specified according to the requirements for actual use.

6.4 Test temperature

For the test at normal temperature, the test temperature shall be the standard laboratory temperature (23±2)℃ or (27±2)℃.

For the test at high temperature, the test temperature shall be selected from (70±1)℃, (85±1)℃, (100±1)℃, (125±2)℃, (150±2)℃, (175±2)℃, (200±2)℃, (225±2)℃ or (250±2)℃.

6.5 Test liquid

6.5.1 The test liquid shall be selected according to the test purpose or the actual use environment of rubber material. The same batch of liquid medium shall be used to evaluate the properties of the same batch of rubber materials.

6.5.2 The test liquid may also be selected by referring to Annex A, GB/T 1690-2010.

Foreword i
1 Scope
2 Normative references
3 Principle
4 Test devices
5 Specimens
6 Test conditions
7 Test procedures
8 Test results
9 Test report
Bibliography