Plastic belongs to the field of polymer, and polymer by long chain molecular composition, molecular motion has the obvious characteristics of the relaxation, so plastic is all known materials in the widest range of variability of the mechanical properties, the tensile properties of it is the most important and the most basic properties of its mechanical properties, it in a large extent determines the use of this kind of plastic and rubber. The tensile property is good or bad, can be detected by the plastic pull machine. Tensile test is one of the most widely used methods to study the mechanical strength of plastic materials in recent years. According to the different load test method, the plastic tensile testing machine can be divided into two categories, pendulum type tensile testing machine and electronic tensile testing machine. On the plastic pull test requirements and the purchase of the standard introduction
In tensile test, the size of the specimen, though small, but the elongation of the material generally higher, so for the detection of flexible packaging material tensile properties need to be equipped with travel greater tensile machine, or fixture operation may will exceed the stroke limit, resulting in equipment damage. Note that in the elongation calculation, we only collect two marking the elongation value between samples. Marking is completed through the printed or hand draw in the preparation of sample, different criteria are given to the distance are different, and the same standard is often for different materials are given different sample sizes, so the distance between the markings are different. However, such conducive to detect elongation very large or very small materials and get accurate test results. For plastic film, marking the distance between is usually between 25 ~ 50mm. Because the specimen in the tensile test elongation is not only within the markings, usually between two fixtures in the sample will get different degree of tensile deformation. Standard and marking distance corresponding to the fixture between the initial distance in 80 ~ 115 mm or less, if the sample between the two fixtures can maintain the same elongation and hypothesis was 50.0%, the effective stroke of the tensile machine required at 480 to 690 mm, if elongation for 1000 specimen, the effective stroke of the tensile machine at least 880mm to ensure the normal test for.
The following is a brief introduction of the plastic tensile testing machine at the time of the purchase of the four conventional considerations:
1) range selection: according to the test materials of the maximum load to select test machine for maximum load (Ji Liangcheng) recommended load material testing in the range of the testing machine of 70% - 90% is better, so as to ensure the test resolution can also prolong the service life of the testing machine.
2) precision level selection: the current domestic testing machine precision commonly used 1 grade and 0.5 grade two, for material testing and general choice test 1 machine completely enough, no need to spend money to improve the accuracy of testing machine for scientific research and analysis materials requires 0.5 level accuracy for testing machine 0.5; and the 1 grade precision in technical difference is not obvious, methods and means of verification is basically the same, this is not the same point, along with the development of sensor technology, the sensor element linearity has reached a very high level, as long as the measuring circuit has no defects, good anti-jamming performance, all the testing machine will reach 0.5 level of accuracy is no problem, for electrical measurement has far exceeded the limit level 0.5, relative error of national standard definition of questionable.
3) resolution and dynamic performance (bandwidth) selection: the resolution is an important parameter in the testing machine, the appropriate resolution will be conducive to measure the resolution, measurement, a smaller indexing, the effective resolution and dynamic performance is a pair of contradictions, blindly increase the effective resolution is at the expense of the dynamic properties (bandwidth) cost, reduced bandwidth directly leads to the result is material yield fluctuation is not obvious or even yield is the phenomenon of a platform, so there is no selection is also on the parameters of the effective.
4) synchronization performance choice: material acquisition test data is in the materials at the same time the load and deformation, if the two synchronization will appear before toward the load to deformation or towards the front in the manifestation of the load, for in return to measure elastic materials appear with a load corresponding two deformation problem, into the return curve does not coincide with the phenomenon of deformation.