Copper is a non-ferrous metal that is very close to human beings. It is widely used in electrical, light industry, machinery manufacturing, construction industry, national defense industry, etc., and is second only to aluminum in the consumption of non-ferrous metal materials in China. It has high strength, corrosion resistance and casting properties and has been widely used in various industrial sectors for a long time. So how do you avoid the common defects of cast copper parts and what are the reasons?
First, the stomata (bubbles, pupils, air pockets)
Characteristics: The pores are holes existing in the outer or inner part of the casting. They are round, elliptical or irregular. Sometimes, a plurality of pores form an air mass, and the skin is generally pear-shaped. The shape of the pupil is irregular and the appearance is rough. The air pocket is a concave part of the casting, and the appearance is smoother. The visual inspection of the open hole reveals that the subcutaneous pores are mechanically processed and found.
The reason for the composition:
1. The mold preheating temperature is too low, and the liquid metal cools too quickly when it passes through the pouring system.
2. The mold exhaust design is poor, and the gas cannot be discharged smoothly.
3, the paint is not good, its own venting is not good, so that it volatilizes itself or synthesizes gas.
4. There are holes and pits on the outer surface of the mold cavity. After the liquid metal is injected, the gas in the hole and the pit is rapidly contracted to shrink the liquid metal to form the pupil.
5. The mold cavity is rusted and not cleaned.
Ways to avoid:
1. The mold should be fully preheated. The particle size of the coating (graphite) should not be too fine and the gas permeability should be good.
2. Casting by inclined pouring method.
3. The original data should be stored in a ventilated and boring place, and should be preheated during use.
Second, shrinkage holes (shrink)
Characteristics: The shrinkage hole is a rough outer hole existing in the outer surface of the casting or inside. The fine shrinkage hole is a plurality of small shrinkage holes which are scattered, that is, the shrinkage, shrinkage or shrinkage of the crystal grains. Often occurs in the casting inside the runner, the root of the riser, the thick part, the thick and thin transition of the wall and the thick part with a large plane.
The reason for the composition:
1. The mold working temperature control does not reach the directional solidification request.
2. The paint selection is improper, and the thickness of the paint layer in different parts is not well controlled.
3. The position of the casting in the mold is not properly designed.
Ways to avoid:
1. Improve the temperature of the abrasive.
2, adjust the thickness of the paint layer, the paint should be sprayed on average, and the paint should not form part of the paint accumulation phenomenon when it is applied.
3. Heat the mold to stop part or heat it with heat insulation.
4, the hot section is set with copper blocks, and the part stops chilling.