How to Clean Steel Castings and the Causes of Cracks?

Ⅰ. What are the common cleaning methods for steel castings?

With the continuous development of social economy and industry, steel castings occupy an increasingly important position in the market, and its development prospects cannot be ignored. What are the common methods of cleaning steel castings?

1. Ordinary cleaning drum: The working principle of the cleaning drum is to install the steel casting and the star iron in the drum. During the rotation of the drum, the steel casting and the star iron are collided and rubbed with each other to remove sticky sand and scale on the surface of steel castings.

The star iron is made of polygonal white cast iron, the size is 20-60mm, and the addition amount is generally 20%-30% of the quality of the steel casting. The dust-laden air formed in the drum during operation is sucked out by the dust collector through the hollow shaft.

2. Shot blasting and shot peening: Shot blasting and shot peening have their own advantages and disadvantages as surface cleaning methods, and they are often used in combination in production. Shot blasting has high cleaning efficiency and low power consumption, so it is used as the main cleaning method;

The shot peening operation is flexible and can clean the inner cavity and deep holes of complex steel casting products, and is generally used as a supplementary means. This can both improve the quality and yield of cleaning and reduce cleaning costs.

Ⅱ. What are the main reasons for cracks in steel castings?

Cracks in steel castings can be divided into hot cracks and cold cracks, both of which are formed due to the resistance of liquid steel to shrinkage and deformation at high temperatures.

Stress is generated after the cooling shrinkage of the casting is blocked. When the stress exceeds the strength or plasticity limit of the molten steel at this temperature, cracks are generated. The reasons for cracks in the casting are as follows.

1. The content of harmful elements such as sulfur and phosphorus is high, and hot cracks are easily formed in steel castings;

2. Inclusions and segregation in the steel are easy to form stress concentration;

3. The greater the linear shrinkage of the molten steel, the greater the tendency of thermal cracking;

4. The poor structure of the steel casting design is prone to local stress concentration, which can also lead to thermal cracks;

5. The pouring temperature of molten steel is too high, which is prone to hot cracks;

6. Improper arrangement of sprue cups and risers of steel castings, resulting in thermal cracks caused by blocked shrinkage;

7. The sand-plastic pestle is too tight, the concession is not good, the shrinkage is hindered, and the hot cracking tendency is increased;

8. Too fast cooling speed of steel castings or too early boxing will cause greater cooling stress and increase the tendency of hot cracking;

9. Improper cutting of sprue cups, risers or improper cleaning of steel castings, and excessive cooling or uneven cooling after heat treatment will also lead to thermal cracking;

10. The steel casting is cooled to a lower temperature range, and cold cracks are formed due to the residual stress of the steel casting or external conditions.