Surface coating process for copper castings. Copper castings are used to manufacture copper products that require surface spraying, which can effectively isolate air and water. The painting process can generally be divided into: spray painting, powder spraying, and electrophoresis. After surface treatment of the workpiece, appropriate spraying processes and equipment should be selected according to the appearance and requirements of different workpieces. At the same time, attention should be paid to the control of processes such as leveling, drying, and cooling, otherwise it will have a negative impact on product quality.
The combination of cold processing, pre aging, and heat treatment after quenching of copper castings is often used in the manufacturing industry and further processing of semi-finished products. Compared to simple aging, the combination of aging and cold working can alter strength, formability, conductivity, or microstructure. The observed aging material structure is particularly suitable for subsequent processing, with careful control of heat treatment, often combined with additional heat treatment, and can also undergo deformation heat treatment, which is usually used to increase fracture toughness, creep strength, and fatigue strength. People attempt to obtain an appropriate recrystallization grain size with nearly optimal lattice defect distribution and precipitation, which typically consists of a series of solid solution treatments including controlled cooling hot rolling.
The solidification method of copper castings is as follows:
1. Layer by layer solidification: Copper or eutectic copper alloys do not have a solidification zone where liquid and solid coexist during the solidification process, so the outer solid and inner liquid on the cross-section are clearly separated by a boundary (solidification front). As the temperature decreases, the solid layer continuously thickens and the liquid layer continuously decreases. This solidification method for copper castings is layer by layer solidification.
2. Paste solidification: If the crystallization temperature range of copper alloys is wide and the temperature distribution of copper castings is relatively flat, during a certain period of solidification, there is no solid layer on the surface of the casting, and the solidification zone where liquid and solid coexist runs through the entire cross-section, similar to cement solidification. Paste solidification is called paste solidification.
3. Intermediate solidification: Most solidification occurs between layer by layer and paste solidification, known as intermediate solidification. Under normal circumstances, the quality of copper castings is closely related to their solidification method, and the filling of gold facilitates the prevention of shrinkage and porosity; Paste solidification is the solidification method for obtaining compact copper castings.
Copper castings have a loose and porous metal structure, and during the electroplating process, strict process requirements are required:
1. When pre casting, the parts and hanging tools should be shaken frequently 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;
2. The cleaning of each process should be carried out to prevent the residual solution in the pores from affecting the next process;
3. Under electrification, use impact current density to electroplate for 5 minutes while shaking the workpiece, and then switch to normal current density;
4. The passivation treatment of copper castings requires additional cleaning. Rinse with 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.
5. 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 designing machine tool castings for copper casting, in addition to determining the geometric shape and size of the machine tool castings based on working conditions and metal material properties, the correctness of the design should also be considered from the perspective of casting alloys and casting process characteristics, that is, obvious size effects and solidification, shrinkage, stress and other issues, in order to avoid or reduce the occurrence of defects such as component segregation, deformation, and cracking in the copper casting.
It is necessary to 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. To obtain castings.
If there are defects in the copper casting, we need to repair the adhesive. This type of adhesive is room temperature cured and is made from high-performance complexing agents and various powders such as ceramics and alloys. This repair adhesive is good for repairing defects in copper castings. After curing, the adhesive has strong viscosity and can also withstand temperature and oil.
In order to ensure that the color of the cast copper parts is consistent with that of the cast copper parts during filling. We can mix the adhesive into a purple copper color during curing. To reduce internal stress, copper castings should also undergo high-temperature tempering after normalizing. Copper castings with carbon content ≥ 0.35%, disorderly planning, and prone to cracking can only be annealed. Copper castings should not be quenched, otherwise they will easily crack. The steel after normalizing treatment of copper castings has higher mechanical properties and lower cost compared to the steel after annealing, so it is widely used. However, due to the fact that normalizing treatment can cause greater internal stress than annealing, it is only suitable for copper castings with a carbon content less than 0.35%. Because low-carbon copper castings have good plasticity, they are less prone to cracking when cooled.
There are many casting methods for copper castings. We can not only use sand casting, but also extensively use many casting methods such as centrifugal casting and metal mold casting. If we choose metal mold casting when casting. This method can quickly solidify alloys, and it can also improve the quality of castings and significantly reduce defects in castings. This casting method can also reduce porosity. It can also effectively improve the airtightness and mechanical performance of the machinery.
Post time: Sep-08-2023
