It mainly includes appearance quality, internal quality and use quality. Appearance quality refers to surface roughness, surface defect, size deviation, shape deviation and weight deviation of casting; The internal quality mainly refers to the chemical composition, physical properties, mechanical properties, metallographic structure of the casting and the holes, cracks, inclusions, segregation and other conditions existing in the casting; Service quality refers to the working durability of castings under different conditions, including wear resistance, corrosion resistance, cold heat resistance, fatigue, shock absorption and other properties as well as machinability, weldability and other process properties.
Casting quality has a great influence on the performance of mechanical products. For example, the wear resistance and dimensional stability of machine tool castings directly affect the accuracy of the machine tool maintenance life; The size, profile accuracy and surface roughness of impeller, shell and inner cavity of hydraulic parts of all kinds of pumps directly affect the work efficiency, energy consumption and the development of cavitation of pump and hydraulic system. The strength and heat resistance of castings such as cylinder block, cylinder head, cylinder liner, piston ring and exhaust pipe of internal combustion engine directly affect the working life of engine.
There are many factors that affect the quality of castings, the first is the design process of castings. When designing, in addition to determining the geometry and size of the casting according to the working conditions and the performance of the metal material, the rationality of the design must also be considered from the perspective of the casting alloy and the casting process characteristics, that is, the obvious size effect and solidification, shrinkage, stress and other problems, in order to avoid or reduce the generation of defects such as segregation, deformation and cracking of the composition of the casting. The second is to have a reasonable casting process. That is, according to the structure, weight and size of the casting, casting alloy characteristics and production conditions, select the appropriate parting surface and shape, core making method, and reasonably set the casting bar, cold iron, riser and pouring system. To ensure quality castings. The third is the quality of the raw materials used in casting. The quality of metal charge, refractory, fuel, flux, modifier, casting sand, sand binder, paint and other materials is not up to standard, which will cause defects such as pores, pinholes, slag inclusion, sand, etc., affecting the appearance quality and internal quality of castings, and will cause castings to be scrapped in serious cases. The fourth is the process operation, to formulate reasonable process operation procedures, improve the technical level of workers, so that the process procedures are correctly implemented.
In casting production, the quality of castings should be controlled and inspected. First of all, the process code and technical conditions from raw materials and auxiliary materials to the control and inspection of each specific product must be developed. Each process is strictly controlled and inspected in accordance with the process code and technical conditions. Finally, the finished castings are inspected for quality. Reasonable testing methods and appropriate testing personnel should be equipped. In general, the surface roughness of castings can be judged by comparing samples for the appearance quality of castings. The fine cracks on the surface can be inspected by coloring method and magnetic particle method. The internal quality of castings can be checked and judged by audio, ultrasonic, eddy current, X-ray and gamma ray methods.
