How to buy economical and practical tensile testing machine
Regarding the purchase of the electronic tensile testing machine in the overall construction plan of the flexible packaging laboratory, the performance and specifications should be comprehensively considered according to the needs of the used film, and comparisons are made from the following aspects:
First, you should first consider the need to test the range of material tension.
The difference in the range of tension determines the difference between the sensors used and the structure of the tension machine, but this has little effect on the price (except for the door type). For general flexible packaging manufacturers, a pull range of 200 Newtons is sufficient. Therefore, it is also decided to use a single arm type.
Corresponding to the single-arm type is a gantry structure, which is adapted to a relatively large pulling force, such as one ton or more. Therefore, soft packaging manufacturers basically do not need.
two, Test the problem of the trip.
According to the performance and requirements of the flexible packaging film, the stroke can be 500 - 600mm . For materials with an elongation of more than 1000%, a stroke of 1000 or 1200 mm can be used .
three, Standard configuration issue.
The three basic configurations of intelligent: host, microcomputer, and printer, if the microcomputer is powerful, you can print directly. It can also be equipped with a regular computer. With a computer, you can perform complex data analysis, such as data editing, partial magnification, adjustable report formats, and statistical analysis of groups.
If equipped with a computer, the manufacturer should be equipped with the appropriate software control system.
Fourth, the output results.
The output results can be set: zui force value, elongation, tensile strength, elongation anyone, elongation force constant value, yield strength, modulus of elasticity, test force large ZUI 8. This can be said to be a comprehensive result of the output of the microcomputer when the microcomputer is operated. Some manufacturers in foreign countries can generally output these 8 items. Some domestic manufacturers can output 5-6 items, and some manufacturers can only output zui value, average value, and zui small value.
5. Can be used as an experimental project.
Flexible packaging requires a multi-purpose tensile machine, that is, on the basis of different fixtures, it can be used for stretching, compression, bending, tearing, shearing, 180 degree peeling, and 90 degree peeling test.
In addition to the above items, some high-end tensile machines on the market have developed a friction coefficient tester that can test the friction coefficient because of its high sensor accuracy (some up to within 100,000 parts). Such as Japan Shimadzu, Beijing Landmeike and other companies.
Sixth, the main configuration of product machinery:
Transmission, screw drive and rack drive, the former is expensive, high precision, high test repeatability; the latter is cheap, low precision, low test repeatability.
The lead screw has a decisive effect on the measurement of the pull force accuracy. Generally there are ball screws, trapezoidal screws, and general screw. Among them, the accuracy of the ball screw is high, but its performance depends on the operation of the computer servo system, and the whole price is relatively expensive. With the general screw and the lead screw, the precision required for flexible packaging, that is, 0.5 - 1% accuracy can be achieved .
Transmission, geared and chain drive, the former is expensive for high precision; the latter is cheap for low precision.
The main cost of the sensor lies in the life. Photoelectric induction is one of the more advanced technologies. It can be used more than 100,000 times. It can be achieved by import and domestic joint ventures.
Seven, test speed.
The national standard stipulates that the test speed is 200mm/min, the market equipment is between 10~500mm/min , and some of them are 0.01~500mm/min . The former generally uses the ordinary speed control system, the cost is low, and the roughness affects the accuracy; the latter The servo system is expensive and has high precision. For flexible packaging enterprises, the servo system is selected, and the speed range of 1~500mm/min is sufficient, so that the accuracy is not affected and the price is within a reasonable range.
Eight, measurement accuracy.
Accuracy issues, including force measurement accuracy, speed accuracy, deformation accuracy, and displacement accuracy. These precision values ​​zui can be up to plus or minus 0.5 . But for the average manufacturer, achieving 1% accuracy is sufficient. In addition, the force value resolution can almost reach one in 100,000.
The above basic configuration is around 30,000 yuan.
At present, there are many tensile testing machines for testing the tensile properties of materials on the market, but not all testing machines are suitable for the tensile testing of flexible packaging materials. This paper combines the material testing standards in China and analyzes the selection of the tensile testing machine for soft packaging materials. Indicators of particular concern.
The tensile properties of plastics and rubbers are one of the important properties of Zui in the mechanical properties, which largely determines the use of plastics and rubber. The tensile properties can be tested by a tensile test.
1. Tensile properties of high molecular polymers
When used as a material, it is required that the polymer has the necessary mechanical properties. It can be said that for most applications of high molecular polymers, mechanical properties are more important than other physical properties.
The high molecular polymer has a wide range of mechanical properties in the variability range of all known materials because the high polymer consists of long chain molecules and the molecular motion has significant relaxation characteristics. For example, the high polymer material has a relatively high elongation. Generally, the elongation at break of PE is between 90 % and 950 % (where the elongation of the linear low-density polyethylene LLDPE is high), through special manufacturing processes, some materials. The elongation can be above 1000 %, while the elongation at break of ordinary polymer materials is also between 50 % and 100 %. Generally, a heat shrinkable film, a stretched film, and the like are required to have high tensile properties of the material.
2 , tensile test
Tensile test (stress-strain test) generally involves clamping the two ends of the material sample on two fixtures separated by a certain distance. The two clamps separate and stretch the specimen at a certain speed to measure the stress change on the specimen. Until the sample is destroyed.
The tensile test is one of the widely used methods for studying the mechanical strength of materials, and it is necessary to use a tensile tester with constant speed. According to the different methods of load measurement, the tensile testing machine can be roughly divided into two types: pendulum type tensile testing machine and electronic tensile testing machine. Currently, the electronic tensile testing machine is used more.
3 , electronic tensile testing machine selection index
Since the flexible packaging material is mainly a high molecular polymer or its related materials, as described above, the elongation of the high polymer material is far superior to that of metals, fibers, wood, plates, etc., so the tensile machine for detecting the high molecular polymer There is a certain difference between the tensile testing machine and the tensile testing machine of the usual materials. In particular, it is necessary to pay attention to the effective stroke of the electronic tensile machine and the sample fixture.
3.1 Effective itinerary
When the tensile test is carried out, the size of the sample used is small, but the elongation of the material is generally high. Therefore, it is necessary to equip the tensile force of the flexible packaging material to provide a tensile machine with a large stroke, otherwise the operation of the clamp may exceed The limit of use of the stroke, resulting in damage to the equipment.
GB13022-91 "Test method for tensile properties of plastic film", the calculation formula of elongation at break or yield elongation ( εt , unit is %),
Εt=[(L-L0)*100]/ L0
Where: εt is elongation at break or yield elongation;
L is the distance between the specimens at the time of fracture or at the time of yielding;
L0 is the distance between the marked lines.
It should be noted that in the calculation of the elongation, we only collect the elongation between the two lines on the sample. The marking is drawn on the prepared sample by printing or by hand (the addition of the marking does not have any effect on the sample), and what is the distance between the markings? Most of the distances given by different standards are different. In the same standard, different sample sizes are often given for different materials, so the distance between the lines is different, but this is beneficial for detecting the extension. Very long or very small materials and accurate test results. For plastic films, the distance between the lines is usually between 25 and 50 mm .
Since the deformation elongation of the sample in the tensile test is not only within the marking line, the sample between the two clamps will have different degrees of tensile deformation. In the standard, the initial distance between the clamps corresponding to the distance of the marking is within 80 to 115 mm . If the specimen between the two clamps can maintain the same elongation and is assumed to be 500 %, the effective stroke of the tensile machine needs to be 480. ~ 690mm to ensure the normal operation of the test.
The author of the effective stroke of electronic testing machine currently on the market for a random survey, the survey of 72 domestic and foreign brands of several Taiwan Rally, the travel range of 400mm or less in the distribution of equipment, accounting for 13.9%; stroke 400 ~ 700mm equipment, accounting for 71.9 %; equipment with a stroke of 701 ~ 1000mm , accounting for 10.8 %; equipment with a stroke of more than 1000mm , only 3.4 %. However, in this statistical electronic tensile machine, the large-stroke equipment is not all used for the detection of flexible packaging materials, and partly for the tensile test of artificial wood boards, canvas, curtains, copper and other materials.
3.2 sample fixture
GB13022-91 "Test method for tensile properties of plastic film" describes the fixture as follows: "The test machine should be equipped with a suitable fixture, which should not cause the specimen to break at the fixture. When any load is applied, the fixture on the test machine It should be immediately aligned into a line so that the long axis of the specimen coincides with the direction of stretching through the centerline of the fixture. ... Place the specimen in the two fixtures of the test machine so that the longitudinal axis of the specimen is up and down The center line of the fixture is coincident and elastic, so as to prevent the sample from slipping and breaking in the fixture. The fixture should be lined with elastic material such as rubber. " Because of the special properties of the polymer material and the special use of flexible packaging materials. The method makes the thickness of the sample tested by the soft packaging material very thin, and the general fixture cannot meet the requirements. Improper use may cause the specimen to break at the fixture and cause the test to fail.
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