How to judge the quality of castings

Update:07 Jan 2021

Appearance quality refers to the surface roughness, surface defects, dimensional deviation, shape deviation, and weight deviation of the casting; internal quality mainly refers to the chemical composition, physical properties, mechanical properties, metallographic structure of the casting and the holes, cracks, inclusions, and Segregation, etc.; the quality of use refers to the durability of the casting under different conditions, including wear resistance, corrosion resistance, chilling and heat resistance, fatigue, shock absorption and other performance, as well as machinability, weldability and other process properties.

The quality of castings 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 maintenance life of the machine tool; the size of the impeller, casing and the inner cavity of the hydraulic parts, the accuracy of the molding line and the surface roughness of various pumps directly affect the pump And the working efficiency of the hydraulic system, energy consumption and the development of cavitation, etc.; the strength and resistance to chilling and heat of the internal combustion engine cylinder block, cylinder head, cylinder liner, piston ring, exhaust pipe, etc., directly affect the working life of the 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 properties of the metal material, the rationality of the design must also be considered from the perspective of the casting alloy and casting process characteristics, that is, the obvious size effect and solidification and shrinkage , Stress and other issues to avoid or reduce the occurrence of defects such as segregation, deformation, and cracking of castings.

Secondly, there must be a reasonable casting process. That is, according to the structure, weight and size of the casting, the characteristics of the casting alloy and the production conditions, the appropriate parting surface, shape, and core making method should be selected, and the casting rib, cold iron, riser and gating system should be reasonably set. To ensure high-quality castings.

The third is the quality of raw materials for casting. The quality of metal furnace charge, refractory materials, fuel, flux, modifier, foundry sand, sand binder, paint and other materials is substandard, which will cause pores, pinholes, slag inclusions, sand sticking and other defects in the castings, which will affect the appearance quality of the castings And internal quality, if serious, the casting will be scrapped. The fourth is process operation. It is necessary to formulate reasonable process operation procedures to improve the technical level of workers so that the process regulations can be implemented correctly.

In casting production, the quality of castings must be controlled and inspected. First, we must formulate the process rules and technical conditions from raw materials and auxiliary materials to the control and inspection of each specific product. Each process is strictly controlled and inspected in accordance with the process rules and technical conditions. Finally, the quality of the finished castings is inspected. To be equipped with reasonable testing methods and appropriate testing personnel. Generally, for the appearance quality of castings, comparison samples can be used to judge the surface roughness of castings; fine cracks on the surface can be inspected by coloring method or magnetic powder method. The internal quality of castings can be inspected and judged by audio frequency, ultrasound, eddy current, X-ray and γ-ray methods.More about:Auto parts aluminum die casting