(1) Introduction to various tests
It is difficult to distinguish the white spot defects of gears by naked eyes. It is necessary to carry out relevant tests to accurately determine whether there are white spot defects and the degree of defects. The following mainly introduces three kinds of tests for white spot defects: white spot inspection with carburizing agent. White spot can react with many kinds of carburizing agents. In the experiment, people often use kerosene, methanol, propane and nitrogen to test the carburizing defects of gears. The two groups of test results are almost the same. In the actual production of the factory, it is necessary to select the appropriate combination for inspection according to the actual situation; use the quenching treatment to carry out white spot inspection. Air delay and salt bath furnace can identify the white spot defect. If the gear has white spot defect, white spot will appear on its surface after quenching treatment. Similar to carburizing agent, the best quenching method should be selected according to the actual situation of factory production ; white spot inspection should be carried out with cleaning agent. The cleaning agent can alleviate the defect of white spot to a certain extent. It can be seen from the test that a small amount of white spot will appear when cleaning the gear with gasoline, and the white spot will be completely removed when cleaning the gear with ultrasonic technology, but the economic cost of the latter is high, and the general factory will not use this cleaning method.
(2) Analysis and introduction of defect diagnosis
White spot is a general term for gear defects. White spot defects have a more refined classification. According to the distribution of white spots on gears and their related characteristics, they can be divided into single white spot and continuous white spot. The former is mainly distributed on the teeth, the top and root of the teeth are randomly distributed, the shape is close to the circle, and there is no clear distinction between them. The latter is mainly distributed on the tooth surface, which is banded, gray white in color, with clear boundaries.
Different kinds of speckles need corresponding metallurgical technology to analyze the causes of their formation, but the detection principle of different technologies is roughly the same, that is, to detect the white spot defect by detecting the hardness of the gear. There are two main analysis methods: metallographic analysis and microhardness analysis. Both of them need to dissect the gear. The former is to observe the composition of the gold photo layer under the microscope. The composition of the white spot defect is different from that of the normal part. The latter is to test the hardness of gear sheet layer by special instrument. The hardness of the part with white spot defect is higher than that of the center part and lower than that of the carburized layer, which is roughly the same as that of the excessive layer.
(3) The cause of white spot
The causes of single white spot and continuous white spot are the same in all parts. The defects of the two are described separately below. The main causes of the former are as follows: before the carburizing process, the cleaning of the gear is not in place, which causes the pollution of the carburizing medium; too many gears are put into the carburizing medium at one time, which results in the fact that the activated carbon can not be evenly attached to each part of the gear. The latter has the following reasons: when grinding after carburizing, the gear position is not placed properly, resulting in the grinding of its contour is not symmetrical enough, resulting in the defects of carburized layer; the staff did not stop the grinding wheel regularly for cooling, resulting in high temperature oxidation of carburized layer.