Understand common problems and solutions for stainless steel casting processing

Stainless steel casting processing is a complex process. Even under strictly controlled production conditions, some problems may occur due to materials, molds, process parameters or environmental factors. Understanding these common defects and their solutions is of great significance to ensuring the quality of castings and controlling production costs. This article will discuss several typical problems and their response strategies.

1. Problems of pores and shrinkage cavities

Porosity and shrinkage cavities are one of the defects that easily occur in the casting process. Porosity usually appears as a smooth hole on the surface or inside of the casting, which is mostly caused by gas in the cavity, poor exhaust of the mold, or air entrapped during melting. Shrinkage cavities are mostly irregular in shape and often appear in thick parts of the casting. This is caused by the volume shrinkage of the molten metal when it solidifies and the volume shrinkage is not fully compensated.

• Countermeasures: In order to reduce pores, it is necessary to fully bake the mold and sand core to ensure their dryness; improve the design of the pouring system to ensure smooth filling of the molten metal; and appropriately increase the pouring temperature to facilitate gas escape. For shrinkage cavities, the key is to optimize the design of the riser and cold iron to achieve sequential solidification, so that the casting gradually solidifies from the far end toward the riser, so that the riser can fully replenish the molten metal.

2. Crack problem

Cracks can be divided into hot cracks and cold cracks. Hot cracks occur at the end of high-temperature solidification, and the cracks are tortuous and the surface is oxidized; cold cracks occur after the casting is cooled to an elastic state, and the cracks are straight and not oxidized. The causes include improper structural design of the casting (such as a large difference in thickness), cooling too fast, or poor core yieldability, etc.

• Countermeasures: Reasonably design the casting structure to avoid sharp edges and sudden changes in thickness; select appropriate molding sand and core sand to ensure good yield; control the cooling rate and slow-cool the casting if necessary; adjust the chemical composition of the metal to improve its thermal crack resistance.

3. Sand and roughness on the surface

Sand sticking to the surface means that a layer of molding sand is firmly adhered to the surface of the casting and is difficult to clean. This is usually caused by the penetration of the metal liquid into the gaps between the sand grains, chemical reaction with the molding sand or sintering together. The pouring temperature is too high, the refractoriness of the molding sand is insufficient, or the sand mold is not compact enough.

• Countermeasures: Select raw sand with high refractory resistance, such as zircon sand or chromite sand in cast steel; apply high-quality refractory paint on the surface of the mold cavity to form an effective isolation layer; control the appropriate pouring temperature to avoid excessively high temperatures while ensuring mold filling; improve the compactness and uniformity of the sand mold.

4. Dimensional accuracy deviation

The actual size of the casting does not match the requirements of the drawing, which may be related to the accuracy of the mold, inaccurate calculation of expansion and contraction during the casting process, or irregular molding operations.

• Countermeasures: Ensure that the mold itself has qualified dimensional accuracy and wear resistance; accurately design and make the scale of the mold according to the linear shrinkage rate of the alloy; strictly control the standardized operations of modeling, core making and other processes to reduce human errors.

There are various problems in stainless steel casting processing, and their solutions need to be adjusted according to the specific causes. Establishing a standardized process flow and strengthening the control and inspection of each link are the fundamental ways to reduce defects and stably produce qualified castings. Through continuous experience accumulation and process optimization, production levels and product quality can be effectively improved.