There are four kinds of testing instruments widely used in abrasion resistance: abrasion testing machine, scratch testing machine, oscillation testing machine and linear abrasion testing machine. The formulation of the coating wear resistance test method standard unifies and standardizes the testing methods and quality requirements of different materials, and also provides the design basis that must be followed for the development of various standard wear resistance test instruments. Below, Shanghai Qianshi will introduce several common wear tests for you.
1. Rotating friction rubber wheel method (Taber test)
Although the methods and instruments specified in the national standard GB/T1768--79(89) have the same working principle, the rotating speed of the rotating disk is not clearly specified, and the test results are only based on the coating quality loss after grinding at the specified grinding speed. (weightless method) single method representation. The rotating friction rubber wheel method can be widely used in the wear resistance test of coatings, coatings and metal and non-metallic materials, but the rubber grinding wheel used for grinding needs to be frequently dressed and updated in time. The international standard ISO7784.2--97 stipulates that the wear resistance of the coating is determined by the rotating friction rubber wheel method, that is, under the specified test conditions that the rotating speed of the rotating disk is 60r/min and the pressure arm bears a certain load, the use of embedded emery abrasives The hard rubber friction wheel wears the surface of the coating, and its wear resistance can be measured by the average value of the coating quality loss (weight loss method) after grinding at the specified number of grinding revolutions or the average grinding revolution required to wear a coating of a certain thickness. Number (revolution method) 2 ways to express and evaluate. Compared with the two methods, the weight loss method has strict requirements on the weighing accuracy of the sample, but it is not affected by the thickness of the coating; while the revolution method is intuitive and convenient, and does not require weighing, but the measurement of the coating thickness is required. Very strict.
2. Test method for wear resistance of coatings
Coating wear resistance refers to the ability of the coating surface to resist a certain mechanical action, which is usually measured by grinding wheel grinding or sand impact test. It is one of the important characteristics of coatings that are often subjected to mechanical wear during use, and It is closely related to the hardness, adhesion, flexibility and other physical properties of the coating. Coating wear resistance test methods commonly used at home and abroad and their main technical characteristics.
3. Falling sand erosion test method
With this test method, the choice of natural sand abrasive will have a direct impact on the test results, so the hardness, particle size and geometry of the sand grains are strictly required. The national standard GB/T5237.5-2000 stipulates that the standard sand that meets the requirements of the GB/T178-77 standard is used as the abrasive. ASTMD968-93 stipulates that the wear resistance of organic coatings is measured by a falling sand wear tester, that is, natural quartz sand from a specified origin is used as abrasive, and it falls freely from a certain height through the tester conduit, and washes the surface of the sample to wear a specified area. The volume (L) of the abrasive consumed by the unit thickness of the coating, and the wear resistance of the coating is evaluated by calculating the wear resistance coefficient. It should be pointed out that in the above two standards using the falling sand scouring test method, although the wear resistance tester with the same main technical parameters is adopted, due to the different particle sizes of the natural sand abrasives used, the same outflow volume is 2L abrasives. The flow rate is not the same, the former is specified as 21 ~ 23.5s, the latter is specified as 16 ~ 18s.
4. Sandblasting impact test method
ASTMD658-81 (86) stipulates that the abrasion resistance of organic coatings is determined by the blast abrasion (sand blasting) test. This method is to adjust the output pressure of the air pump so that the air flow rate at the nozzle of the tester is 0.07m3/min, In order to ensure that an average of (44 ± 1) g of diamond beams impact the coating per minute, and the mass (g) of the abrasive consumed by the coating per unit thickness of the specified area, the wear resistance of the coating is evaluated by calculating its wear resistance coefficient. Abrasion resistance. Therefore, silicon carbide with a particle size range of 75-90 μm must be selected as the abrasive according to the standard, and the output pressure of the gas source and the uniform spray velocity of the abrasive become the decisive factors affecting the test results.
5. Reciprocating transport wear test method
After a specified number of grindings, the wear resistance of the coating was evaluated by the reduction in coating thickness (μm) or coating mass (mg), and by calculating its wear resistance. Both ISO8251-87 and JISH8682 specify the use of a friction wheel abrasion tester to determine the abrasion resistance of anodized films of aluminum and aluminum alloys. This test method is to make the coating layer and the abrasive sandpaper glued on the outer edge of the friction wheel make a plane reciprocating motion under the specified test conditions, and the friction wheel rotates a small angle (0.9o) after each double stroke. The test conditions are easy to control, and there are no problems such as grinding wheel dressing, aging, sand flow rate, sand beam shape, etc. that are difficult to control in other methods, so the repeatability of test results is good, and except for coating, this method It has been widely used in abrasion resistance test of plastic, rubber and metal materials.
In summary, it is not difficult to see that there are various methods for the wear resistance test of coatings at home and abroad, each with its own characteristics. Although people have different understandings on the evaluation of the above-mentioned various test methods and their application performance, in terms of the development and popularization and application of many detection methods, the rotating friction rubber wheel method, the falling sand method and the sandblasting method are still used. law is more common.
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