In the machining process of large gears, the pretreatment and inspection of the blanks are crucial initial steps, directly affecting the smooth progress of subsequent machining and the final quality and performance of the gears.
The first step in blank pretreatment is cleaning. During transportation and storage, large gear blanks often accumulate various impurities on their surfaces, such as rust, oil, and dust. These impurities not only affect the accuracy of subsequent machining but may also damage the cutting tools during processing. Therefore, appropriate methods are needed to thoroughly clean the blank surface. For rust, manual polishing with tools such as wire brushes and sandpaper can be used, or mechanical methods such as sandblasting and shot blasting can be employed. Sandblasting and shot blasting can clean the surface more evenly and efficiently, and can also improve the surface roughness of the blank to a certain extent, enhancing the adhesion of subsequent coatings. For oil stains, organic solvents such as gasoline and acetone can be used for cleaning. The blank can be soaked in the solvent or wiped with the solvent to ensure that the oil stains are completely removed.
After cleaning, the blanks must undergo shaping treatment. Large gear blanks may deform during manufacturing and transportation, such as bending or twisting. If the blank is deformed, it's difficult to guarantee the gear's accuracy and tooth profile quality during subsequent processing. There are various straightening methods. For bending deformation, pressure straightening can be used, applying pressure to the blank using a specialized press to restore it to its correct shape. For twisting deformation, torsional straightening can be used, applying torsional force to the blank using specific fixtures and devices to correct its twisted state. During the straightening process, the force and direction of straightening must be strictly controlled to avoid over-straightening or uneven straightening, which could lead to new deformations or internal stresses in the blank.
Next is the pre-treatment of the blank for heat treatment. Large gear blanks typically require heat treatment to improve their mechanical properties, such as increasing hardness, strength, and toughness. However, some pre-treatment work is necessary before formal heat treatment. For example, for some alloy steel blanks, preheating treatment is required to eliminate internal stresses and microstructure inhomogeneities generated during casting or forging, preparing them for subsequent heat treatment. The temperature and time of preheating treatment should be selected appropriately based on the material and specifications of the blank to ensure the preheating effect meets requirements.
After the blank pretreatment is completed, rigorous inspection is necessary. First, a visual inspection is performed to check the blank surface for defects such as cracks, pores, and sand holes. These defects may expand during subsequent processing, affecting the service life and safety of the gears. Minor defects on the blank surface can be detected through visual observation, magnification, or non-destructive testing methods such as magnetic particle testing and ultrasonic testing.
Dimensional inspection is also essential. Appropriate measuring tools, such as calipers, micrometers, and height gauges, should be used to measure all key dimensions of the blank, such as diameter, length, and thickness, to ensure that the blank dimensions meet design requirements. For blanks with complex shapes, a coordinate measuring machine can be used for precise measurement, improving the accuracy and efficiency of dimensional inspection.
Material inspection is equally important. The material of the blank must be checked to ensure it meets design requirements. Chemical analysis, spectral analysis, and other methods should be used to determine whether the content of various elements in the blank is within the specified range. Substandard materials will cause the gears' mechanical properties to fail to meet design standards, affecting their normal use.
Only through rigorous pretreatment and inspection to ensure the quality of large gear blanks meets requirements can they be used in subsequent processing steps, laying a solid foundation for the production of high-quality large gears.
