Analysis and Control Methods of Common Defects in Precision Casting

Analysis and Control Methods of Common Defects in Precision Casting

There are various types of defects in precision castings, and the causes of defects are also very complex. It is not only related to the casting process, but also to a series of factors such as the properties of the casting alloy, the melting of the alloy, and the properties of the molding material. Today, precision casting manufacturer Tianyao Metal will analyze the causes of casting defects for everyone. Starting from the specific situation, a comprehensive analysis will be conducted based on the characteristics, location, process used, and molding sand used for the defects. Then, corresponding technical measures will be taken to prevent and eliminate defects.

1、 Partial defects cannot be poured to the casting, often appearing in thin-walled areas, the farthest part from the runner, or the upper part of the casting. The incomplete edges and corners are smooth, shiny, and non stick to sand.

Cause of occurrence:

1. Low pouring temperature, slow pouring speed, or intermittent pouring;

2. The cross-sectional area of the transverse and inner runners is small;

Prevention method:

1. Raise the pouring temperature, accelerate the pouring speed, and prevent intermittent pouring;

2. Increase the cross-sectional area of the transverse and inner runners;

2、 Damaged castings are damaged and broken.

Cause of occurrence:

The cross-sectional dimensions of the riser and riser neck are too large; The riser neck has not been made into a tapped section (groove). Or the method of knocking out the sprue is incorrect, causing damage and missing flesh to the casting body.

Prevention method:

Modify the size of the riser and riser neck, create a section for the riser neck tapping, and correctly grasp the direction of pouring the riser.

3、 The fracture surface of gray and pockmarked castings appears gray black or with small black spots, with more central areas and fewer edges. Metallographic observation shows flake graphite. Cause of occurrence:

The bismuth nurtured in front of the furnace is added to the ladle too early or too late, or the bismuth content is insufficient.

Prevention method:

Increase the amount of bismuth added and strictly enforce the pre furnace incubation process.

4、 Cracks (hot cracking, cold cracking): Cracks that penetrate or do not penetrate the outside or inside of castings. During hot cracking, there is a dark or black oxidized surface with a tortuous fracture morphology. Cold cracking is a relatively clean brittle crack with a flat fracture surface and a metallic luster or slight oxidation color. Cause of occurrence:

1. The pouring temperature is too high;

2. The riser neck is too large or too short, causing severe local overheating, or the heavy mouth is too small, resulting in poor filling and contraction;

3. Castings are subjected to excessive impact during cleaning and transportation.

Prevention method:

1. Reduce the pouring temperature;

2. Reasonably design the riser system;

3. Avoid excessive impact on castings during cleaning and transportation.

5、 The pore walls of the pores are smooth and bright, with shapes of circular, pear shaped, and needle shaped. The size of the pores varies, and they occur on the surface or inside of the casting. The pores inside the casting can only be discovered after being smashed or machined. Cause of occurrence:

1. The pouring temperature is low, which prevents the gas from floating and escaping in time;

2. The aluminum content in the furnace charge is high, which is prone to forming hydrogen pores;

Prevention method:

1. Increase the pouring temperature;

2. Do not use scrap steel with excessive aluminum content;

6、 Shrinkage porosity, loose dispersion, and small shrinkage pores with dendritic crystals are called shrinkage porosity, while those smaller than shrinkage porosity are called porosity. Often found in hot weather areas. Cause of occurrence:

1. The pouring speed is too fast and the pouring temperature is too high, resulting in large liquid shrinkage;

2. Improper design of pouring system and riser, unable to achieve sequential solidification;

3. The riser is too small and the filling is not sufficient.

Prevention method:

1. Reduce pouring speed and pouring temperature;

2. Improve the gating and riser system by utilizing sequential solidification;

Precision machining