How to repair crack defects in gravity casting?

Cracks in castings can be divided into hot cracks and cold cracks. So how to repair the crack defects in gravity casting?
1. Gravity casting rupture
Thermal cracking occurs.
Usually, at the end of the gathering, the metal forms at high temperatures close to the solidus line. The characteristics of its shape are short and wide defects, curved shape, and oxidation in the joints. Unreasonable pouring scheme, severe alloy shrinkage, core sand shrinkage, and unreasonable casting process may all lead to hot cracking. The sulfur and phosphorus in steel can damage its heat resistance, leading to an increased tendency towards hot cracking.
Hot crack prevention
Reasonable adjustment of alloy elements (strict control of sulfur and phosphorus content in steel), rational planning of casting schemes, adoption of synthesis methods, and innovative sand making methods are all effective measures to prevent hot cracking.
2. Gravity casting cold treatment
Cold cracks appear.
Cold cracking refers to the elastic state of an alloy after cooling to a low temperature. If the strength of the alloy exceeds this temperature, cold cracking will occur. The cold crack defects formed at low temperatures are relatively small, continuous and straight, with clean seams and occasional mild oxidation. Irregular parts, especially castings with large wall thickness differences, especially large thin castings, are prone to cold cracking.
Cold crack prevention
Usually, the step to reduce internal stress in castings or decrease alloy brittleness is to protect the formation of cold cracks. For example, iron and phosphorus in iron can significantly reduce the impact resistance of alloys, increase brittleness, and easily lead to cold cracking, so strict restrictions should be imposed when smelting metals.
Provide additional information and equipment analysis.
Casting glue: Simple and rough casting. Generally, the repaired area does not require further treatment and there are no special hardness requirements. This type of casting has low added value. Welding repair materials: More than 90% of casting companies choose welding repair materials to solve casting defects encountered in production. Due to the use of metal filling materials (welding materials are generally matched with casting materials), the welding performance can basically meet the standards of the base material, with simple operation and high welding efficiency, which has been recognized and trusted by many manufacturers. There are various types of welding equipment on the market currently, and the equipment used for repairing defects is roughly as follows:
Welding machine: Cast iron and steel castings are commonly used for welding. Liquid aluminum extrusion, aluminum alloy gravity casting, aluminum alloy casting.
Benefits: Maintenance, high efficiency.
Defect: After welding, the hardness of the solder joint is too high, there is internal stress, and it is easy to produce cracks. Usually, annealing heat treatment is also required to meet processing requirements. Moreover, due to the limitations of welding conditions, secondary defects such as porosity and slag inclusion are prone to occur inside. Argon arc welding is commonly used for precision casting (alloy steel, stainless steel precision casting) and aluminum alloy die-casting parts. Some mold manufacturers and repair shops also use this welding machine to repair mold defects. Advantages: High welding efficiency and higher precision than electric welding machines. There are various types of welding wires, among which stainless steel and aluminum alloy products are widely used. Suitable for high-strength welding.
Disadvantage: Used for repairing defects and small defects (pores and sand holes). Due to excessive impact, there are traces on the edge of the melt pool. Welded steel parts have hard spots. Color castings or thin-walled parts are prone to thermal deformation during welding due to the influence of heat. The technical requirements for operation are very high.
Cold welding machine: It is a repair technology that was just born at the beginning of the 21st century. Due to the minimal heat generated during the welding process of the workpiece, it has become a cold welding machine. After several years of development, the application direction and technology of welding machines have made great progress, and they have already occupied a considerable share in the repair market. Classified by repair products, there are: electric spark welding machine patches and repair machines.
Welding machine repair: Using the principle of instantaneous high-frequency discharge, the welded piece (0.05-0.20mm) is attached to the surface of the workpiece, with a thickness consistent with the thickness of the welded piece. The welding quality depends on whether the discharge is uniform. Suitable for workpiece wear and repair in ultra poor machining, it has a certain impact on the mold market. This machine can also fill defects (such as sand holes) with welding powder (or processing waste) and repair them through discharge. The repaired workpiece has a small color difference. The disadvantage is that the patching speed is slow.
The common disadvantage of cold welding machines is that their welding efficiency is higher than that of electric welding machines and argon arc welding machines, but their outstanding advantages in repairing millimeter level defects and machining defects make people choose cold welding.