Two processing techniques and flaw detection of large cast steel gear

Steel casting defects are common. Large gears are steel castings in terms of material, and various defects often appear. Before the large cast steel gear has no milling teeth, its defects are easy to deal with, as long as it is cleaned and repaired by welding. As for the deformation caused by heat in repair welding, it is insignificant compared with the remaining machining allowance. However, after gear milling, it is different. The thermal effect of repair welding and deformation on the accuracy of gear have to be considered. Gears are relatively precise parts, and so are large gears. After the big gear is milled, many defects are exposed on the tooth surface.

After rough machining, before heat treatment and milling, large gears usually need ultrasonic inspection according to the different requirements of users for their strength. Ultrasonic flaw detection can detect at least 80% of the internal defects of steel castings. However, ultrasonic flaw detection is based on ultrasonic flaw detection standards. The size of defects is evaluated by equivalent and area. Many defects that do not exceed the standard cannot be reflected in the flaw detection report. These small equivalent and small area defects in the workpiece can not have a great impact on the strength of the workpiece, but they are different after tooth milling. These small equivalent and small area defects are sometimes exposed to the surface of the workpiece, such as large cast steel gears. The strength of the pinion will be greatly affected by the defect of the tooth surface.

There are two methods to deal with tooth surface defects. One is that for small defects with small depth, they will not be treated if grinding does not affect the gear accuracy. Another method is to completely remove the defects and then repair welding. The heat generated by repair welding will have a certain impact on the size of the gear, and it is very troublesome to deal with the deformation of this size. Therefore, it is necessary to reduce the defects exposed after gear milling as much as possible for the processing and production of large steel casting gears.

According to the analysis and practice, within the range of a tooth height from the tooth surface, any defect with an area of more than 80mm2 may be exposed. Therefore, an enterprise standard for the inspection of cast steel large gears can be formulated to limit the allowable area of defects to 80mm2. Using this standard for ultrasonic inspection can undoubtedly effectively control the defects exposed to the tooth surface and will not produce more heat treatment defects, Compared with the method of milling half tooth height before heat treatment, it is much more economical and effective.

Scroll to Top