What are the sand casting defects and its remedies?

July 30, 2020

Common casting defects in sand casting include pores, sand sticking, sand inclusion, sand hole, sand expansion, cold isolation and insufficient pouring.

low pressure casting machine application

1. Porosity: In the process of producing castings by the sand casting machine, the gas does not escape in time before the molten metal is crusted, resulting in holes-like casting defects. The inner wall of the pores is smooth, bright or slightly oxidized.
After the pores are generated in the casting, its effective bearing area will be reduced, and stress concentration will be caused around the pores to reduce the impact resistance and fatigue resistance of the casting.
The pores also reduce the compactness of the castings, causing some castings that require hydrostatic testing to be scrapped. In addition, pores also have an adverse effect on the corrosion resistance and heat resistance of the casting.

Prevent the generation of pores sand casting defects: reduce the gas content in the molten metal, increase the air permeability of the sand mold, and add an air riser at the highest point of the cavity.

2. Sticky sand: There is a layer of sand that is difficult to remove on the surface of the casting, called sticky sand. The sticky sand not only affects the appearance of the casting, but also increases the workload of cleaning and cutting of the casting, and even affects the life of the machine.

Prevent sand sticking: adding coal powder to the molding sand, and applying anti-sticking sand coating on the surface of the mold.

3. Sand inclusion: grooves and scars sand casting defects formed on the surface of castings are easy to produce when using wet casting to cast thick and large flat castings.
Most of the parts that produce sand in the casting are in contact with the upper surface of the sand mold. The upper surface of the cavity is affected by the radiant heat of the molten metal, which is easy to arch and warp.
When the lifted sand layer is continuously scoured by the molten metal flow, it may break and break, stay in place or be carried into other parts. The larger the upper surface of the casting, the greater the volume expansion of the molding sand, and the greater the tendency to form sand inclusions.

4. Sand hole: the hole type defects filled with molding sand in the inside or surface of the casting.
Such problems can be repaired with Delin machinery technology to repair casting defects, which is simple and easy, saves time and labor, and has a good repair and treatment effect.
And it can repair different materials such as copper, iron, steel, aluminum, etc., instead of the welding repair process, avoid stress damage, and save huge economic losses for the enterprise.

5. Swelling sand: Under the pressure of molten metal during pouring, the mold wall moves and the casting part expands.
In order to prevent sand expansion, the strength of the sand mold, the stiffness of the flask, and the pressure or fastening force of the box should be increased. And appropriately lower the pouring temperature to make the surface of the molten metal crust earlier to reduce the pressure of the molten metal on the mold.

6. Insufficient cooling and pouring: The liquid metal filling ability is insufficient, or the filling conditions are poor. Before the cavity is filled, the molten metal will stop flowing, which will cause insufficient pouring or cold separation defects in the casting.
When the pouring is insufficient, the casting will not be able to obtain a complete shape; during cold isolation, although the casting can obtain a complete shape, the mechanical properties of the casting are seriously damaged due to the existence of incompletely fused joints.
Prevent insufficient pouring and cold isolation: increase pouring temperature and pouring speed.

Solutions to casting defects: casting defects such as porosity, shrinkage, sand hole, sand sticking and cracks, etc., casting defects have always been an unavoidable and difficult problem in the casting industry.
To repair unqualified castings, the conventional method is mainly welding repair, which requires skilled workers, is time-consuming, and consumes a lot of materials.
Sometimes affected by the material of the components, welding can also lead to increased damage, resulting in scrapped components, and increasing the production cost of the company’s equipment

Delin Machinery specializes in the production of the automatic horizontal sand casting machine. It is a machinery manufacturing enterprise integrating scientific research, design, manufacturing, installation, debugging and consulting services. You can click here: automatic horizontal sand molding machine to view more machine introduction, and maybe you are interested in machine video: DL-3040 automatic horizontal sand molding machine working video

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