Function of rubber tensile testing machine in test

Function of rubber tensile testing machine in test

More and more rubber tensile testing machines use computers in tensile testing. During the test, the rubber tensile testing machine inputs the collected data (tensile force, gauge distance, etc.) into the computer through the acquisition card or USB interface, and then the special software processes the input data, draws the stress-strain curve of the test sample, calculates the corresponding points on the curve according to the test requirements, directly gives the test data and makes judgment.

Testing the tensile properties of rubber samples is to study the stress-strain curve of rubber samples in the tensile process

1. Breaking strength -- the force value when the sample is broken;

2. Constant stress elongation -- elongation when the sample is stretched to a given stress;

3. Elongation at yield point -- elongation corresponding to yield point;

4. Elongation at break -- elongation at break of sample;

5. Constant tensile stress -- the force value when the sample is stretched to a given elongation;

6. Tensile stress at yield point -- stress value corresponding to yield point;

There are two items of data to be tracked in the process of rubber tensile testing machine: 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 requirements:

1. There is a long enough range of fixture movement.

Due to the large deformation of rubber during stretching, especially latex products, the elongation may be as high as more than 1000%. Therefore, before the rubber sample breaks, it must be ensured that the gripper has enough travel. The gauge distance of rubber standard thickness samples (the thickness of national standard type 1, 2 and 4 dumbbell samples is 2.0 ± 0.2mm, and the thickness of type 3 samples is 1.0 ± 0.1mm) is generally within 1m; For samples with special thickness, such as those of medical rubber gloves, the gauge distance may exceed 1m when breaking. Therefore, the moving range between fixtures is generally between 1m and 1.5m, which can be suitable for the tensile test of various rubber samples.

2. Tension measuring and recording device with sufficient accuracy.

Rubber stretching does not require a large force, and the tensile force measurement range does not need to be large, but there are certain accuracy requirements, and the general accuracy is 0.01N. 

Rubber gauge distance measurement is an important link in tensile test, which directly affects the accuracy of test. At present, there are two main 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 gripper. During the tensile test, observe the change of the gauge on the sample by visual force, 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: (1) observing the sample gauge distance with eyes will cause a certain deviation; (2) Manually moving the gauge rod can not accurately track the gauge change of the sample; (3) While moving the gauge rod, it is difficult for the tester to record the gauge value, and it is more difficult to accurately describe the stress-strain curve after the test.

Automatic gauge distance measurement is more conducive to the detection of rubber tensile properties. At present, many automatic gauge measuring devices of rubber tensile testing machines use contact sensors to measure the change of gauge in real time.

There are two main installation positions of the sensor mobile device: (1) installed on the holder. The sensor with mobile device installed on the holder has certain limitations on the sample. (2) Mounted on gauge. A grating ruler and two horizontal gauge rods with small clips that can move in the vertical direction are vertically arranged at the side of the moving rod of the holder.

3. Gauge distance measurement with sufficient accuracy.

The measurement of sample gauge distance is an important data for calculating rubber elongation, so the rubber tensile testing machine must accurately measure the strain of the sample and record it immediately.

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

The samples are mainly dumbbell shaped. This paper briefly expounds the functional requirements of rubber tensile testing machine in rubber tensile property test, combined with relevant standards and practical experience.