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How to choose the fixture of the electronic universal test machine
Release time：2018-11-23 source：Jinan Hengsi Shanda Instrument Co., Ltd. Browse：
1. We know that by clamping the sample (or product) by clamping the sample, the amount of test force that the clamp can withstand is a very important indicator of the clamp. It determines the size of the fixture structure and the labor intensity of the fixture operation. The sample materials can be divided into metal and non-metallic, and the shapes can be divided into size. The composition of the materials is various. The test force that the sample can withstand is as small as a few dozen centimeters (such as spandex wire for textiles), to dozens of tons (such as ordinary steel, etc.; the domestic electronic universal testing machine test force is 600KN, 0.5-level machine), the sample size is as small as gold wire with a diameter of φ0.006mm, and to PVC pipe with a diameter of 1m. This requires the selection and design of different fixtures according to different test forces and the shape and size of the sample.
2. Requirements for fixture material:
①. For general metal and non-metallic specimens, the jaws of the fixture are in direct contact with the specimens. Generally, high-quality alloy structural steel, alloy high-carbon steel (or low-carbon alloy steel), cold-work mold steel, etc. are used to increase their strength and wear resistance through appropriate heat treatment processes (quenching, carburizing and quenching, etc.). Sometimes special steel is also installed at the jaws, or gold steel sand is sprayed on the surface of the jaws.
②. For some fixtures with small test force, the surface in which they come into contact with the sample is used to use soft rubber. (For example: the clamping surface of plastic film, fiber wire and other samples.)
③ The specific clamping is generally made of high-quality medium-carbon steel and alloy structural steel, and its mechanical properties are increased through appropriate heat treatment processes. Sometimes, non-ferrous metals such as aluminum alloys and special metals are used in order to reduce weight. Sometimes cast structures (cast steel, cast aluminum, etc.)
3. Requirements for fixture structure:
①. The design of the fixture is mainly based on the test standards of the material and the shape and material of the sample (specifically referring to finished and semi-finished products). The above test standards refer to ISO, ASTM, DIN, GB, BS, JIS, etc., as well as enterprise standards, industry standards, etc. These standards generally have strict regulations on sample preparation and test methods. We can design different fixtures according to the different samples and test methods. For fixtures used for special samples (finished and semi-finished products), fixtures are mainly designed based on the shape and material of the sample.
②. The fixture itself does not have a fixed structure (such as the metal wire can be clamped by winding, or two flat plates can be clamped by thin metal plate samples, or the clamping can be clamped by wedges), which is obvious difference from the main machine. The host is similar in both domestic and foreign countries, while the fixture is very different from the fixtures and domestic countries, and there are also big differences between different companies. This mainly depends on the overall level of the company and the accumulation of experience of the designers. However, in some new materials and special materials fixtures, there is still a certain gap in the domestic and foreign levels.
③. The fixture itself is a locking mechanism. We know that the locking structures on the mechanical are: tiles (i.e., threads, screws, nuts), bevels, eccentrics, levers, etc. The fixture is a combination of these structures. There is no fixed structure for the clamps for testing machines. The structure varies greatly according to different samples and test forces. (Specimens with large test forces generally adopt a bevel clamping structure. As the test force increases, the clamping force increases accordingly. Shoulder samples adopt a suspended structure, etc.). If the clamps are divided according to the structure, they can be divided into wedge-shaped clamps (referring to fixtures using the inclined locking principle structure), clamping clamps (referring to fixtures using the single-sided or double-sided threaded top-tightening principle structure. ), winding fixtures (referring to fixtures that are locked by the sample through winding), eccentric fixtures refer to fixtures (referring to fixtures that are structured by the eccentric locking principle), lever fixtures (referring to fixtures that are structured by the lever force amplification principle), shoulder fixtures (referring to fixtures that are suitable for shoulder specimens), bolt fixtures (referring to fixtures that are suitable for test thread strength such as bolts, screws, studs), 90° peeling fixtures (referring to fixtures that are suitable for two samples for hanging and straight peeling), etc. The structures of these fixtures have their own advantages and disadvantages, such as: wedge-shaped fixtures, with small initial clamping force and increasing with the test force. The clamping force increases accordingly. For clamping fixtures, the initial clamping force is large and increases with the test force. The clamping force decreases accordingly.
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