GB/T 15256-1994 Determination of low temperature brittleness of vulcanized rubber (multiple specimen method)
Some standard content:
National Standard of the People's Republic of China
Determination of low-temperature brittleness of vulcanized rubber (multiple test piece method) Rubber, vuicanized-Determination of low-temperature brittleness (multiple test piece method) This standard is equivalent to the international standard ISO812-1991 "Determination of low-temperature brittleness of vulcanized rubber". 1 Subject content and scope of application
GB/T15256-94 bzxZ.net
1.1 This standard specifies the procedure for determining the lowest temperature at which vulcanized rubber does not suffer brittle failure when subjected to impact under specified conditions. The brittle temperature (multiple test piece method) measured in this way is not necessarily the lowest temperature at which this material can be used. Because the brittle temperature (multiple test piece method) will change with changes in contact conditions, especially impact velocity. Therefore, the data obtained by this method can only predict the properties of vulcanized rubber at low temperatures in applications where the deformation conditions are similar to those specified in this test. 1.2 This standard specifies two procedures: Procedure A is for determining the brittle temperature (multiple test piece method) and Procedure B is for impacting the specimen at a specified temperature. Procedure B is used for the classification and identification of vulcanized rubber. Note: For similar tests for rubber-coated fabrics, see GB/T12584-90. 2 Reference standards
GB2941 Standard temperature, humidity and time for environmental conditioning and testing of rubber specimens GB9865 Preparation of vulcanized rubber samples and specimens GB/T9868 General rules for rubber to obtain test temperatures above or below normal temperature GB/T12584 Low-temperature impact test for rubber or plastic-coated fabrics 3 Definitions
This standard uses the following definitions:
3.1 Brittle temperature (multiple specimen method): The lowest temperature at which a specimen is impacted under specified low-temperature conditions without causing damage. 3.2 Test speed: The relative linear speed between the impact head of the test instrument and the clamped specimen under impact conditions. 4 Instruments and materials
Various types of impactors should ensure that the instrument parts used meet the following specified requirements. 4.1 Sample holder and impact head (see Figure 1) Approved by the State Administration of Technical Supervision on September 24, 1994 522
Implemented on August 1, 1995
GB/T-15256-94
Holder
Figure 1 Sample holder and impact head
4.1.1 The sample holder shall be rigid and designed to hold the sample in a cantilever beam style. Each sample shall be held stably and securely without deformation of the holder.
4.1.2 The impact head shall move in a direction perpendicular to the upper surface of the sample and impact the sample at a test line speed of 2.0 ± 0.2 m/s. After impact, the moving speed shall remain constant within a range of at least 6 mm. In order to achieve the specified impact speed during and after impact, care shall be taken to ensure sufficient impact energy. Each sample requires at least 3.0 J of impact energy. Therefore, it is necessary to limit the number of impact samples in each test. Note: Any impactor driven by a motor, electromagnetic coil, heavy hammer or spring can be used as long as it meets the requirements of this standard. The speed calibration method for electromagnetic coil driven low temperature impactor is given in Appendix A.
4.1.3 The basic dimensions of the instrument are as follows
. The radius of the impact head is 1.6 ± 0.1 mm,
b. During impact, the gap between the impact head and the sample holder is 6.4 ± 0.3 mm, c. The distance between the center line of the impact head and the sample holder is 8 ± 0.3 mm. 4.2 Temperature display
Use a thermocouple or other temperature sensing device, which can be accurate to ± 0.5 ° C within the test temperature range. Thermocouples composed of constantan wire with a diameter of 0.2~0.5 mm meet the test requirements. The thermocouple end or thermometer mercury ball should be as close to the sample as possible. 4.3 Heat transfer medium
The heat transfer medium can be a liquid or gas medium that can remain fluid at the test temperature and has no effect on the test material. The medium should be controlled within the test temperature ±0.5℃C range (see GB/T 9868). Note: The following fluids can be used.
a. When the temperature drops to -60℃: a silicone fluid with a kinematic viscosity of 5 mm2/s at room temperature can be used. Its chemical properties are close to those of rubber, and it is non-flammable and non-toxic.
b. When the temperature drops to -70℃: methanol or ethanol can be used. c. When the temperature drops to -120℃: methylcyclohexane liquid cooled by nitrogen can be used. 5 Specimens
The specimens should be prepared in accordance with GB9865. Punch out from the film with a suitable cutter. The specimens should be one of the following two types. Type A: Strip specimen with a length of 25 to 40 mm, a width of 6 ± 1 mm, and a thickness of 2.0 ± 0.2 mm; Type B: The thickness of the specimen is 2.0 ± 0.2 mm, and the shape and size are shown in Figure 2. 523
GB/T 15256--94
Figure 2 Type B specimen
Type A specimen can be prepared by another method, using a double-sided parallel sharp blade cutter to punch out in one go, and then cut the strip specimen into the specified length.
If reliable results are to be obtained, a sharp cutter must be used in the specimen preparation. 6 Time interval between vulcanization and testing
Unless otherwise specified, the time interval between vulcanization and testing shall comply with the provisions of GB2941. 7 Procedure
7.1 Procedure A
7.1.1 Test with liquid heat transfer medium7.1.1.1 Before the start of the test, a low-temperature tank should be prepared and the liquid medium should be adjusted to the starting temperature of the specimen. Sufficient liquid should be placed in the low temperature tank to ensure that the specimen is immersed to a depth of about 25 mm. 7.1.1.2 Fix the specimen on the test device and soak it at the test temperature for 5 minutes (see GB/T9868). The free length of the specimen should be greater than 19 mm.
If the effective energy of the impactor reaches the minimum value specified in 4.1.2, 4 type A specimens or 10 type B specimens can be used for each impact.
It is extremely important to tighten the clamp correctly. The clamp should be tightened so that the pressure on each specimen is roughly the same. 7.1.1.3 After soaking for the specified time at the test temperature, record the temperature and impact the specimen once. 7.1.1.4 Check each specimen to determine whether it is damaged. Failure is defined as visible cracks, cracks, or small holes during the test, or complete separation into two pieces or more fragments. When the specimen is not completely broken, bend the specimen at an angle of 90° along the bending direction formed during the impact, and then check the specimen for cracks at the bend.
7.1.1.5 A new specimen shall be used for each impact. 7.1.1.6 When determining the minimum temperature without damage for a vulcanized rubber material, it is recommended to start the test at a temperature lower than the expected minimum temperature without damage, and to conduct a set of tests every 10 minutes until no damage is obtained. Then lower the temperature of the low-temperature tank to the highest temperature at which damage has been observed, and gradually increase the temperature for testing. The temperature increase is recommended to be 2°C. Test at each temperature until no damage is obtained at a certain temperature. Record this temperature as the brittle limit temperature. 7.1.2 Tests with gas heat transfer medium 7.1.2.1 Before the test begins, the refrigeration device shall be adjusted so that the test chamber, test equipment and specimens reach thermal equilibrium at the required temperature (see GB/T 9868).
7.1.2.2 Open the test chamber and conduct the test according to the procedures specified in 7.1.1.2~7.1.1.6, except that the specimen reaches thermal equilibrium at the test temperature for 10 minutes before impact. In order to study crystallization and plasticizer-time related effects, a thermal equilibrium time of more than 1 h may be used.
7.2 Procedure B
7.2.1 Allow the specimen to reach thermal equilibrium at the test temperature specified in the identification or classification of vulcanized rubber (see GB/T9868). Start the test device and impact the specimen once.
GB/T 15256-—94
7.2.2 Remove the specimen from the test chamber and allow the specimen to reach the standard temperature (see GB2941). Check the specimen according to the definition requirements in 7.1.1.4 to determine whether damage has occurred.
7.2.3 At least 4 type A specimens or 10 type B specimens are required for one test. If the instrument speed during and after the impact meets the requirements in 4.1.2, it is allowed to impact 4 type A specimens or 10 type B specimens at the same time. 7.2.4 Report whether the vulcanized rubber is qualified. If no specimen in a group of specimens is damaged, it is considered qualified. On the contrary, if any specimen in a group of specimens is damaged, it is considered unqualified. 8 Test report
The test report should include the following contents:
The number of this national standard adopted;
All markings of the tested rubber material;
The type of specimen used;
The number of specimens used, the number of specimens impacted during each impact, the heat transfer medium used and the type of test equipment used; the procedure A or procedure B used;
Test temperature;
The brittle temperature (multiple specimen method) in the case of procedure A; whether the rubber material is qualified in the case of procedure B, the tester,
the auditor,
the test date.
A1 Speed calibration before test
A1.1 Principle
GB/T 15256--94
Appendix A
Speed calibration of electromagnetic wire diagram low temperature impact test machine (reference part)
Place a steel ball on the impact mechanism of the test machine. When the impact head stops moving upward due to contact with the mechanical stopper, the height of the steel ball can be measured at this time. The deceleration method of the steel ball conforms to the law of free moving objects under the action of gravity. A1.2 Procedure
A1.2.1 Fixing the ball rack
Unscrew any nut that fixes the guide rod to the armature rack of the electromagnetic coil, put the small hole on the ball rack (see Figure A1) on the guide rod, re-nut and tighten.
A1.2.2 Adjusting the stroke or impact head
Remove the metal shield on the electromagnetic coil, stretch the rubber cushion (see Figure A2) and wrap it around the armature, and replace the electromagnetic coil shield. Insert the standard specimen in the specimen holder of the instrument and lift the impact device by hand until it reaches the bottom of the stroke. The instrument's impact head should contact the specimen but not penetrate into the specimen plane. If the impact head does not contact the specimen, remove the rubber cushion and replace it with a thinner cushion. On the contrary, if the impact head enters the specimen plane, replace the cushion with a thicker one. A1.2.3 Placing the steel ball and measuring tube
Place a steel ball with a diameter of 19 mm on the ball holder (theoretically, the upward stroke of the steel ball does not depend on the mass of the ball, but if the mass is too large, it may hinder the movement of the impact head.) A glass or transparent plastic tube with an inner diameter of at least 25.4 mm is placed vertically just above the steel ball. The tube should have a scale with 5 mm divisions. When the steel ball is at the top of the stroke of the impact mechanism, the zero scale position is aligned with the top of the steel ball. A1.2.4 Measurement and calculation
According to the above test equipment, in the absence of specimens and immersion medium, start the electromagnetic coil and read the height of the steel ball with an accuracy of 5mm. Perform at least five tests and take the average value. Determine the impact head speed \(m/s), the formula is as follows: u = √2gh
Where: g—gravitational acceleration, m/s2 (9.8m/s2); h-average height of the steel ball, m.
·（Al）
Note: The calibration measurement of the impactor should be carried out on an inelastic surface such as a laboratory bench or concrete floor. Because the elastic base may absorb some of the impact energy, thereby reducing the ball height value.
A2 Velocity Correction During Test
A2.1 The test apparatus is equipped with a ball holder, steel ball and measuring tube (see A1), but without a rubber cushion (test under normal operating conditions). In the absence of specimens and immersion medium, the electromagnetic coil is activated and the height of the steel ball is read to an accuracy of 5 mm. Ten measurements are made, from which the maximum and minimum height values of the steel ball are read. The impactor velocity range is determined using the formula in A1.2.4. This range is called the "stroke top velocity range". A2.2 The test apparatus is equipped as described in A2.1, but with specimens and immersion medium. The brittleness test is carried out according to the method of Chapter 7. The electromagnetic coil is activated each time to read the height of the steel ball. The steel ball height is then converted to velocity as described in A1.2.4. If the velocity is within the predetermined velocity range at the top of the stroke, the test is considered valid. If the velocity is outside the predetermined range, it is considered invalid and no test report should be submitted. In the event of a continuous test failure, the velocity at the top of the stroke is adjusted to be within the permissible predetermined range, which can be achieved by reducing the number of specimens impacted each time. A2.3 A typical example of full speed correction is as follows: The following is a typical example of the full speed correction procedure for electromagnetic coil driven test equipment. a. According to the method specified in A1, in the absence of specimens and immersion media, the impact speed of the impact head at the impact point of the test instrument reaches 526
GB/T15256-94
1.9m/s, which is within the limit range specified in 4.1.2. b. According to the method specified in A2.1, in the absence of specimens and immersion media, the speed range of the impact head at the top of the stroke is 2.5~～2.7m/s, which constitutes the allowable range of this test series. Each time the speed of the impact head at the impact point is measured, the allowable range should be confirmed. According to the procedure specified in A2.2, the test instrument is equipped with specimens and immersion media. During the first electromagnetic coil driven impact, the speed of the impact head at the top of the stroke c.
can reach 2.5m/s. This speed is within the allowable range and this test is valid. d. During the second and third electromagnetic coil driven impacts, the speed of the top of the stroke is 2.4~2.3m/s respectively. These speeds are outside the allowable range, and these two tests are invalid. e: It can be adjusted according to the A2.2 procedure to increase the speed of the top of the stroke. During the fourth and all subsequent continuous electromagnetic coil driven impacts, the speed of the top of the stroke can reach 2.5~～2.7m/s, and these test results are valid.
Thickness 3.2
Figure A1 Ball Rack
Hardness ~70IRHD
Rubber Buffer Pad
Additional Notes:
GB/T15256—94
This standard was proposed by the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of the Beijing Rubber Industry Research and Design Institute of the Ministry of Chemical Industry. This standard was drafted by the Shenyang Fourth Rubber Factory. The main drafters of this standard are Tuo Rui, Lv Heren, and Li Zhaoyun. From the date of implementation of this standard, the former Chemical Industry Department Standard HG 4-841-81 "Determination Method of Brittle Temperature of Vulcanized Rubber" shall be invalidated.1 The test instrument is equipped with a ball rack, a steel ball and a measuring tube (see A1), but without a rubber cushion (test under normal operating conditions). In the absence of a sample and an immersion medium, start the electromagnetic coil and read the height of the steel ball with an accuracy of 5 mm. Make 10 measurements and read the maximum and minimum height values of the steel ball. Use the formula in A1.2.4 to determine the impactor velocity range. This range is called the "top-of-stroke speed range." A2.2 The test equipment is as described in A2.1, but with specimens and immersion medium. The brittleness test is carried out according to the method in Chapter 7, and the height of the steel ball is read each time the electromagnetic coil is activated. Then convert the ball height to velocity as described in A1.2.4. If the speed is within the predetermined speed range at the top of the stroke, the test is considered valid. If the speed is outside the predetermined range, it is considered invalid and no test report should be submitted. When continuous testing is ineffective, the speed of the stroke top can be adjusted within the allowable predetermined range by reducing the number of specimens impacted each time. A2.3 A typical example of the entire speed correction is as follows: The following is a typical example of the entire speed correction procedure of the electromagnetic coil drive test instrument. a. According to the method specified in A1, in the absence of specimens and immersion media, the impact velocity of the impact head at the impact point of the test instrument reaches 526
GB/T15256-94
1.9m/s, which is within the limit range specified in 4.1.2. b. According to the method specified in A2.1, in the absence of specimens and immersion media, the velocity range of the impact head at the top of the stroke is 2.5~～2.7m/s, which constitutes the allowable range of this test series. Each time the impact head velocity at the impact point is measured, the permissible range should be confirmed. According to the procedure specified in A2.2, the test instrument is equipped with a sample and an immersion medium. During the first electromagnetic coil-driven impact process, the impact head speed at the top of the stroke c.
can reach 2.5m/s. This speed is within the allowable range and the test is valid. d. During the second and third electromagnetic wire diagram driven impact processes, the speeds at the top of the stroke were 2.4 to 2.3 m/s, respectively. These speeds were outside the allowable range, and these two tests were invalid. e: Adjust according to procedure A2.2 to increase the speed at the top of the stroke. During the fourth and all subsequent continuous electromagnetic coil-driven impacts, the speed of the top of the stroke can reach 2.5~～2.7m/s, and these test results are valid.
Thickness 3.2
Figure A1 Ball rack
Hardness ~70IRHD
Rubber buffer pad
Additional instructions:
GB/T15256—94
This standard is proposed by the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of Beijing Rubber Industry Research and Design Institute, Ministry of Chemical Industry. This standard was drafted by Shenyang Fourth Rubber Factory. The main drafters of this standard are Tuo Rui, Lü Heren and Li Zhaoyun. From the date of implementation of this standard, the former Chemical Industry Department Standard HG 4-841-81 "Determination Method of Brittle Temperature of Vulcanized Rubber" shall be invalidated.1 The test instrument is equipped with a ball rack, a steel ball and a measuring tube (see A1), but without a rubber cushion (test under normal operating conditions). In the absence of a sample and an immersion medium, start the electromagnetic coil and read the height of the steel ball with an accuracy of 5 mm. Make 10 measurements and read the maximum and minimum height values of the steel ball. Use the formula in A1.2.4 to determine the impactor velocity range. This range is called the "top-of-stroke speed range." A2.2 The test equipment is as described in A2.1, but with specimens and immersion medium. The brittleness test is carried out according to the method in Chapter 7, and the height of the steel ball is read each time the electromagnetic coil is activated. Then convert the ball height to velocity as described in A1.2.4. If the speed is within the predetermined speed range at the top of the stroke, the test is considered valid. If the speed is outside the predetermined range, it is considered invalid and no test report should be submitted. When continuous testing is ineffective, the speed of the stroke top can be adjusted within the allowable predetermined range by reducing the number of specimens impacted each time. A2.3 A typical example of the entire speed correction is as follows: The following is a typical example of the entire speed correction procedure of the electromagnetic coil drive test instrument. a. According to the method specified in A1, in the absence of specimens and immersion media, the impact velocity of the impact head at the impact point of the test instrument reaches 526
GB/T15256-94
1.9m/s, which is within the limit range specified in 4.1.2. b. According to the method specified in A2.1, in the absence of specimens and immersion media, the velocity range of the impact head at the top of the stroke is 2.5~～2.7m/s, which constitutes the allowable range of this test series. Each time the impact head velocity at the impact point is measured, the permissible range should be confirmed. According to the procedure specified in A2.2, the test instrument is equipped with a sample and an immersion medium. During the first electromagnetic coil-driven impact process, the impact head speed at the top of the stroke c.
can reach 2.5m/s. This speed is within the allowable range and the test is valid. d. During the second and third electromagnetic wire diagram driven impact processes, the speeds at the top of the stroke were 2.4 to 2.3 m/s, respectively. These speeds were outside the allowable range, and these two tests were invalid. e: Adjust according to procedure A2.2 to increase the speed at the top of the stroke. During the fourth and all subsequent continuous electromagnetic coil-driven impacts, the speed at the top of the stroke can reach 2.5~～2.7m/s, and these test results are valid.
Thickness 3.2
Figure A1 Ball rack
Hardness ~70IRHD
Rubber buffer pad
Additional instructions:
GB/T15256—94
This standard is proposed by the Ministry of Chemical Industry of the People's Republic of China. This standard is under the jurisdiction of Beijing Rubber Industry Research and Design Institute, Ministry of Chemical Industry. This standard was drafted by Shenyang Fourth Rubber Factory. The main drafters of this standard are Tuo Rui, Lü Heren and Li Zhaoyun. From the date of implementation of this standard, the former Ministry of Chemical Industry Standard HG 4-841-81 "Determination Method of Brittle Temperature of Vulcanized Rubber" shall be invalidated.
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