How to Identify Casting Quality

Appearance quality refers to surface roughness, surface defect, dimension deviation, shape deviation and weight deviation of castings; intrinsic quality mainly refers to chemical composition, physical property, mechanical property, metallographic structure of castings, as well as voids, cracks, inclusions and segregation existing in castings; using quality refers to castings under different conditions. The working durability under this condition includes wear resistance, corrosion resistance, quench and heat resistance, fatigue, shock absorption and other properties, as well as cutting and weldability.

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 and life-span of machine tools; the dimension, profile accuracy and surface roughness of impellers, shells and hydraulic chambers of various types of pumps directly affect the working efficiency of pumps and hydraulic systems, energy consumption and the development of cavitation erosion; the cylinder block of internal combustion engines; The strength and heat resistance of castings such as cylinder head, cylinder liner, piston ring and exhaust pipe directly affect the working life of the engine.

There are many factors affecting the quality of castings. One is the design technicality of castings. In design, besides determining the geometry and size of castings according to working conditions and properties of metal materials, the rationality of design must also be considered from the angle of casting alloy and casting process characteristics, i.e. obvious size effect, solidification, shrinkage and stress, in order to avoid or reduce the component deviation of castings. Analysis, deformation, cracking and other defects. Secondly, reasonable foundry technology should be adopted. According to the structure, weight and size of castings, casting alloy characteristics and production conditions, proper parting surface, moulding and core-making methods are selected, and casting bars, chills, risers and gating systems are reasonably set up. To ensure the quality of castings. The third is the quality of raw materials for foundry. The quality of metal furnace charge, refractory material, fuel, flux, modifier, casting sand, mould sand binder, coating and other materials is not up to standard, which will cause defects such as blowhole, pinhole, slag inclusion and sand sticking, which will affect the appearance quality and internal quality of the castings, and will cause the castings to be scrapped in serious cases. Fourthly, the process operation should be formulated to improve the technical level of workers so that the process regulations can be implemented correctly.

In foundry production, the quality of castings should be controlled and inspected. First of all, we should formulate the process codes and technical conditions from raw materials and auxiliary materials to the control and inspection of each specific product. The control and inspection of each process are strictly in accordance with the process code and technical conditions. Finally, the quality of the finished castings is inspected. Reasonable testing methods and appropriate testing personnel should be equipped. Generally, the surface roughness of castings can be judged by comparing the sample blocks, and the surface micro-cracks can be checked by coloring method and magnetic powder method. The internal quality of castings can be checked and judged by means of audio, ultrasonic, eddy current, X-ray and gamma-ray.