The concave areas on the surface of copper castings are called depressions, which can be caused by:
1. In situations where the performance of the machine’s injection mechanism is poor (such as in old vertical machines), when the working fluid pressure is unstable, the injection pressure is also unstable. The pressure pushing the metal is discontinuous, causing the skin layer of the copper casting to form more than once, but the edge position of the skin layer is different each time. Some edges of the previous skin layer are not covered by the latter, resulting in strip shaped depressions.
2. During filling, the gas is squeezed between the metal flow and the cavity wall without being expelled, resulting in a depression. The surface of this depression is smooth and clean, often appearing in the difficult to exhaust cavity, while copper castings are on the edge of the end.
3. There is residue in the mold cavity, which has been mentioned earlier in the cause of undercasting. But when it occurs, the residue in the mold cavity is not in the form of a sheet, but with various irregular shapes. The height of the residue above the mold surface is not high, so the copper casting is also relatively shallow.
4. The hot spot area of copper castings is filled with voids inside. When shrinkage occurs, although the skin layer has strength, it is still affected by internal shrinkage and the surface appears concave, which is called shrinkage.
Copper castings are closely related to daily life. For example, commonly used doorknobs, door locks, radiators, plumbing pipes, iron pots, gas stoves, irons, etc. are all castings.
Copper castings should have the correct casting process. According to the structure, weight, and size of the casting, the characteristics of the casting alloy, and production conditions, appropriate parting surfaces, shapes, and core making methods are selected, and casting ribs, cold iron, risers, and gating systems are correctly set. The improvement of the quality of bed castings, the development of machine tool equipment manufacturing, and the overall level of improvement are beyond discussion, ultimately affecting the competitiveness of China’s machine tool equipment manufacturing industry in the market. Continuously improving the quality of machine tool castings, thereby improving the overall level of machine tool manufacturing.
Copper castings account for a large proportion of the weight, and many structural components and major components are made of castings as raw materials, which are closely related to the quality and accuracy of machine tools. The quality of machine tool castings has a significant impact on the overall quality, lifespan, and accuracy retention of the machine tool.
The cleaning of each process of copper casting electroplating should be carried out to prevent the residual solution in the pores from affecting the next process; The actual surface area of copper castings is many times larger than the calculated surface area, and the impact current density during electroplating is about three times higher than that of ordinary parts. The pre plating time is also longer than that of ordinary parts; When pre plating copper, the parts and hanging tools should be frequently shaken together to ensure uniform and consistent coating color, and to prevent the occurrence of spots during silver plating that may affect the appearance quality of the coating.
Copper castings are mainly used as blanks for machine parts, and some castings can also be directly used as machine parts. Castings account for a large proportion in mechanical products, such as tractors, where the weight of castings accounts for about 50-70% of the total weight of the machine, agricultural machinery accounts for 40-70%, and machine tools, internal combustion engines, etc. account for 70-90%. Among various types of castings, there are many types of castings used for machinery, with complex shapes and large amounts, accounting for about 60% of the total production of castings. Next are steel ingot molds for metallurgy and pipelines for engineering.
The metal structure of copper castings is looser than that of rolled and rolled copper materials, with rough and porous surface. In addition, the surface of copper castings often contains a portion of molding sand, paraffin, and silicate substances. If not cleaned thoroughly, it often leads to local plating failure. Therefore, the key to solving the silver plating quality of copper castings is to clean the surface of copper castings and add appropriate process steps. The following process can be used for general copper castings: alkaline chemical degreasing → hot water washing → water washing → immersion in 25% hydrofluoric acid → water washing → mixed acid corrosion → water washing → 5% alkaline solution immersion → water washing → pre copper plating → water washing → silver plating → water washing → passivation → water washing → film removal → water washing → bright dipping → water washing → hot water washing → drying → inspection.
Due to the porous metal structure of copper castings, strict process requirements are required during the electroplating process:
1. The cleaning of each process should be carried out to prevent the residual solution in the pores from affecting the next process;
2. The actual surface area of copper castings is many times larger than the calculated surface area, and the impact current density during electroplating is about three times higher than that of ordinary parts. The pre plating time is also longer than that of ordinary parts;
3. When pre plating copper, the parts and hanging tools should be frequently shaken together to ensure uniform and consistent coating color, and to prevent the occurrence of spots during silver plating that may affect the appearance quality of the coating;
4. When silver plating, the current is charged down the slot, and the impact current density is used to electroplate the workpiece while shaking it for 5 minutes, and then it is converted to normal current density;
5. The passivation treatment after silver plating requires additional cleaning. Rinse in flowing clean water for 10-20 minutes, then rinse with hot water and dry immediately. The oven temperature can be controlled at 100-150 ℃ for a slightly longer time to prevent mold spots.
Post time: Aug-30-2023