Casting cracks may occur during precision casting

Casting cracks can occur during investment casting. Are there any ways to prevent them?

1. Casting structure.

During the casting process, factors such as structure, shape, large size, wall thickness, transition, etc. should be fully considered to select appropriate process parameters to prevent casting defects such as pore shrinkage and looseness. The design of the casting and exit system should be reasonable. If a cold iron is used The location of process measures such as these should be reasonable, not only to ensure the internal structure of the casting but also to avoid stress concentration as much as possible.

2. Smelting

During the smelting process, the content of harmful elements such as P and s, as well as the content of gases and impurities such as N, h, O, etc., should be reduced as much as possible. Low steel master alloy has a good effect.

3. Insulation

The main purpose of appropriately extending the holding time of sand castings is to control the unboxing temperature below 70 degrees Celsius to ensure that the sand castings can fully complete liquid-solid shrinkage and avoid stress concentration caused by external forces.

4. Falling sand

During the cleaning process of castings falling sand, it is strictly forbidden to water the sand molds and castings during the boxing process, and it is strictly forbidden to impact the falling sand with strong external forces such as collision boxes to avoid cracks caused by the interaction between external forces and internal stresses.

5. Incision.

According to the casting conditions, select the appropriate hot cutting exit process to ensure that the starting temperature of hot cutting is not lower than 300 degrees Celsius. The gas cutting gun and oxygen blowing pipe are vibrated during operation. After gas cutting the important parts, cover the partition with asbestos cloth or enter the furnace Heat treatment is carried out inside. For castings with complex structures and special process measures, two thermal cuttings are used.

6. Warm up

When dealing with fine casting defects, the preheating principle should be followed. The workpiece is preheated to 108 degrees Celsius during the blow welding process. If large crack defects are found, they should be annealed before treatment.

7. Add annealing.

Precision casting mainly increases the stress annealing process and strictly controls the insulation time and discharge temperature. Its purpose is to reduce new stress concentration during the production process, better clean up the stress in the casting, and prevent cracks.