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Common surface defects of copper castings2025-02-04 14:10:17

There may be a variety of surface defects in the production process of copper casting, which will affect the appearance, performance and service life of the casting. The following are some common copper casting surface defects:

Stomatal defect


Precipitated pores: During the solidification process of copper liquid, due to the decrease of the solubility of gas in copper with the decrease of temperature, the gases originally dissolved in copper liquid (such as hydrogen, oxygen, etc.) will precipitate to form pores. Such pores are usually round or oval, small in size, more evenly distributed, and may appear on the surface or inside the casting. If the porosity is more and dense, it will reduce the density of the casting, resulting in the casting is prone to leakage under pressure, affecting its sealing and pressure resistance.

Invasive pores: the water and organic matter in the modeling material will produce gases under the action of high temperature copper liquid, and if these gases can not be discharged in time, they will invade the copper liquid to form pores. The invasive pores are generally large in size and irregular in shape, and often appear on the surface or near the surface area of the casting. It will destroy the integrity of the surface of the casting, reduce the surface quality of the casting, but also weaken the mechanical properties of the casting.

Trachoma defects


Sand punching: In the copper liquid filling process, due to the large impact force of the copper liquid, the molding sand on the surface of the sand mold may be washed away, and the washed sand particles will be mixed with the copper liquid, and the sand hole will be formed after the casting solidifies. The sand holes formed by punching sand are usually irregular in shape and different in size, and may be mixed with molding sand particles inside, which are mostly distributed near the gate of the casting or the parts where copper liquid is washed seriously during the filling process, which will cause the surface of the casting to be uneven, affect the appearance quality, and may also become the origin point of fatigue cracks during the use of the casting, reducing the strength and reliability of the casting.

Sand removal: In the process of packing, transporting or pouring, due to the lack of compactness of the sand, local damage of the sand, etc., the sand on the surface of the sand may fall into the copper liquid, thus forming sand holes in the casting. The location of sand holes caused by sand removal is relatively random, which may appear in any part of the casting, and its existence will cause uneven defects on the surface of the casting, affecting the assembly accuracy and performance of the casting.

Crack type defect


Hot crack: in the late solidification period of copper casting, due to the different cooling rates of various parts of the casting, large thermal stress is generated, and when the thermal stress exceeds the strength limit of copper, hot cracks will be generated on the surface or inside the casting. The hot crack usually presents an irregular shape, with obvious oxidation color, generally distributed along the grain boundary, and mostly occurs in the thick part of the casting, the corner or the part with complex structure. Hot crack will seriously reduce the mechanical properties of castings, so that castings are easy to break from the crack when bearing the load, which is a more harmful defect.

Cold crack: Cold crack is the crack caused by the effect of factors such as phase change stress and residual stress when the copper casting is cooled to a lower temperature. Cold cracks are generally small, in a straight line, the surface is smooth, no oxidation color, may appear immediately after the cooling of the casting, may also appear after a period of time, often appear in the stress concentration of the casting, such as sharp corners, notches, keyways and so on. Cold cracking will also have a serious impact on the strength and toughness of castings and reduce the service life of castings.

Inclusion defect


Oxidizing inclusion: During the smelting and pouring process, copper is easily oxidized in contact with oxygen in the air to generate oxides such as copper oxide. If these oxides are not removed in time, they will be mixed into the copper liquid and form oxidative inclusion after the casting solidifies. Oxidizing inclusions are generally black or dark gray, irregular in shape and distributed on the inside or surface of the casting, which will reduce the electrical conductivity, thermal conductivity and corrosion resistance of the casting, and also affect the mechanical properties of the casting.

Slag inclusion: In the smelting process, if the slag and other impurities are not fully separated from the copper liquid, they will enter the mold with the copper liquid, forming slag inclusion. The composition of slag inclusion is more complex, usually contains a variety of metal oxides, lining materials, etc., its appearance is mostly block or sheet, the color is similar to slag, will destroy the internal organization uniformity of the casting, when the casting is under load, the inclusion is easy to produce stress concentration, resulting in premature failure of the casting.

Rough surface and other defects


Rough surface: Due to the high surface roughness of the sand mold, improper use of mold release agent, poor flow of copper liquid and other reasons, it will lead to the surface of the copper casting is not smooth, uneven, pitting and other phenomena. Rough surface not only affects the appearance quality of the casting, but also increases the friction resistance of the casting during use, reducing its wear resistance and tightness.

Succulence and lack of meat: In the casting process, due to mold damage, sand deformation, insufficient copper liquid filling and other reasons, it may lead to redundant metal bumps (succulence) or the lack of metal parts (lack of meat). Fleshy will affect the dimensional accuracy and appearance of castings, requiring additional processing to remove; The lack of meat will make the casting unable to meet the design requirements, and may lead to the scrapping of the casting in serious cases.