How to choose the hottest rubber tensile testing m

2022-08-23
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How to choose rubber tensile testing machine

testing the tensile properties of rubber samples is one of the important indicators of rubber quality testing. Almost all quality laboratories in rubber related industries will be equipped with one or more rubber tensile testing machines. However, the author found during maintenance that the configuration of rubber tensile testing machines in many laboratories may not fully meet the requirements of relevant standards. Among them, there are not only unprofessional reasons for the user's tester selection personnel, but also insufficient and careless communication among the manufacturer's salesperson. Of course, there are also some reasons why most users of industrial and mining enterprises do not have a strong sense of standards and are reluctant to invest

then, what kind of rubber tensile testing machine should we choose to do the rubber tensile test

first of all, we should understand: according to the relevant standards, what data do we need? Generally speaking, the tensile test of rubber requires the following parameters or seven parameters

1 The maximum force (tensile strength) that occurs when the specimen is stretched to fracture

2. The force value (breaking strength) when the sample breaks

3. The stress value corresponding to the yield point (tensile stress at the yield point)

4. The force value when the specimen is stretched to a given elongation (constant elongation stress)

5. Elongation of the specimen when it is stretched to a given stress (elongation at constant stress)

6. Elongation corresponding to yield point (elongation at yield point)

7. Elongation at break (elongation at break) of the specimen

II. According to the requirements of the above measured parameters. There are two items of data to be tracked in the process of rubber tensile test: tensile force value and gauge distance change

therefore, the rubber tensile testing machine used to test the tensile properties of rubber must meet the following four requirements:

1 Large stroke

due to the large deformation of rubber during stretching, especially latex products, the elongation may be as high as 1000%. Therefore, before the rubber sample breaks, it must be ensured that the gripper has enough travel

2. High precision and high frequency data acquisition

it does not need a lot of force to stretch the rubber, and the tension measurement range does not need to be very large, so the accuracy of the force value is high. Generally, the testing machine is required to be able to calculate the force value with a precision of more than two digits after the decimal point. In addition, because testing the tensile properties of rubber requires several tensile values in the tensile process, and the tensile test cannot be repeated, it is very important to record the tensile force value of each test section immediately and accurately for the success of the test

3. Accurate gauge distance measuring and recording device

the measurement of the gauge distance of the sample is to calculate the weight of the rubber elongation. 3. Take the breaking load test of the safety belt as an example to obtain the data, so the tensile testing machine must accurately measure the strain of the sample in the rubber tensile test and record it immediately

4. A device that can accurately describe the stress-strain curve

there is a close relationship between the tensile value and the gauge distance in the tensile sample. For example, the constant tensile stress of the sample requires measuring the force value of the sample stretching to the given elongation, while the constant stress requires measuring the gauge distance of the sample stretching to the given stress. After the test is completed, the accurate stress-strain curve can reproduce the test process, and clearly reflect the value of each test section, which is convenient for calculating the items required by the test.

III. The National Rubber plan subsidy of 70million yuan for the tester. Reference for the selection of tensile testing machine

in summary, the tester selects a suitable rubber tensile testing machine

1 according to the following methods Range of travel of the testing machine

the gauge distance of ordinary standard thickness samples (the thickness of type 1, 2, and 4 dumbbell shaped samples is 2.0 ± 0.2mm, and the thickness of type 3 samples is 1.0 ± 0.1mm) at fracture is generally within 1 meter; The gauge distance of samples with special thickness, such as those of medical rubber gloves, may exceed 1 meter when they are broken. Therefore, the moving range of the fixture is generally between 1 m and 1.5 m, which is suitable for the tensile test of various rubber samples. It is not difficult to meet this requirement. The mechanical transmission part of general rubber tensile testing machine can meet this requirement

2 tension measuring and recording device of rubber tensile testing machine

there are mainly two types of tension measuring and recording devices of tension testing machine: mechanical instrument type and sensor type. The mechanical instrument type tension measuring device mainly relies on the reaction force in the tension process, drives the pointer on the instrument panel to rotate and mark the tension value through mechanical transmission devices such as springs and weights, and uses the traditional recorder to record the force value time curve. The mechanical instrument tensile testing machine is cheap, but its performance cannot meet the requirements of rubber tensile testing. It can only deal with the tensile value alone, and cannot record the slightly changed tensile value, and effectively link the tensile value with the sample gauge distance. The tensile testing machine equipped with appropriate precision tensile sensor can accurately record the tensile value at each moment, and process and calculate it through relevant programs to meet the requirements of rubber tensile test

3. Gauge distance measuring and recording device of testing machine

the gauge distance measurement of rubber is an important link in the tensile test, which directly affects the accuracy of the test. At present, there are mainly two methods of gauge distance measurement: manual measurement and automatic measurement. Manual measurement is to vertically set a ruler and two horizontal gauge rods that can move in the vertical direction beside the moving rod of the fixture. During the tensile test, observe the change of the gauge on the sample by eyes, manually control the two gauge rods to synchronize them with the gauge on the sample, and record the moving distance of the gauge rod on the ruler at the same time. The error of manual measurement is very large: first, visual observation of the sample gauge distance will cause a certain deviation; Secondly, it is always unable to accurately track the gauge change of the sample by manually moving the gauge rod; Third, it is difficult for the tester to record the gauge value while moving the gauge rod, and it is also impossible to accurately describe the stress-strain curve after the test

compared with automatic measurement of gauge distance, it is more conducive to the detection of rubber tensile properties. At present, many automatic gauge measuring devices of tensile testing machines use contact sensors to measure the gauge change in real time. There are two main installation positions of sensor mobile devices: ① installed on the fixture; ② On the sample. There are certain limitations in installing the mobile device on the sensor of the gripper. Because the elastic deformation of the rubber is very large, and there is a big gap between the moving distance of the gripper and the change value of the gauge distance of the sample, the gauge distance sensor installed on the fixture is more suitable for detecting the tensile performance of the sample with very small elastic deformation (such as metal materials), but cannot be used to detect the tensile performance of the rubber

another installation method is to vertically set a tray root grating ruler made of pet and two horizontal distance measuring rods (commonly known as large deformation) with small clips that can be moved in the vertical direction at the edge of the fixture moving rod. The installation method of this sensor is consistent with the use principle of manual measurement mentioned above, except that the ruler is changed into a grating ruler, and the manual operation is changed into that the sample drives the gauge rod to move. The sensor installed on the gauge is suitable for the tensile test of metal or rubber samples with standard thickness, because the force value when stretching these samples is large, and the force value driving the gauge rod to move is very small compared with it. Although it will have a certain impact on the samples, it is not enough to affect the success or failure of the whole test

however, some special samples in rubber tensile property testing cannot be measured by contact sensors, such as medical rubber glove samples. The main component of rubber gloves is natural latex, and the tensile value used in the tensile test is smaller than that of ordinary rubber products. At the same time, GB7543-1996 rubber medical gloves stipulates that the samples for tensile property test are directly cut from the finished rubber medical gloves, and the thickness of the cut samples is very small, only about 0.2mm, so the latex samples with such a thickness can stretch the samples for a long time with only a small force value. Therefore, the contact gauge measurement method will have a great impact on the tensile test of the sample. The reasons are as follows: first, the self weight of the gauge rod contacting the sample will pull the sample downward, affecting the tensile measurement; Second, the clamping of the gauge bar has a certain impact on the tension of the clamped part, so that it cannot be stretched freely

these problems can be avoided by using a non-contact video extensometer. One of the methods is to track the change of the gauge length by using a camera. The sample background adopts black rough non reflective material (such as black rough insulating tape), and the gauge part (that is, the part between the two gauge lines) is painted with paint with high contrast (if the sample color is light, the gauge is painted with black pigment, if the sample color is dark, the gauge is painted with white pigment). Input the image collected by the camera into the computer, adjust the contrast, so that the gauge boundary can be clearly identified on the computer. In the process of stretching, the collected image is processed by computer, the gauge line is tracked, and the gauge value is tested in real time. This measurement method can not only accurately measure the gauge value at each moment, but also will not affect the rubber sweeping method: use a wrench to tighten and stretch the real fixing screw behind the oil pump

* all the above are mechanical testing requirements for rubber materials. The relevant testing of finished rubber parts cannot completely refer to the above methods. For example, the author used to be a material testing machine selected by Japanese guinuchuan rubber and plastic products China Co., Ltd. According to the requirements of finished products, equal load cyclic compression test, plugging force cyclic test, load maintaining endurance test, etc. should be carried out. These tests can no longer be completed by ordinary rubber tensile testing machines. With the progress of material science and the improvement of quality standards, there will be more test requirements. Keeping pace with the times is the only way to deal with it

rubber tensile testing machine is mainly divided into the following three types according to different levels of customer needs:

microcomputer controlled single arm electronic tensile testing machine digital display electronic tensile testing machine microcomputer controlled gantry tensile testing machine

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