During the casting process of copper castings, porosity is a common defect that can seriously affect the mechanical properties, surface quality, and subsequent processing performance of the castings. To avoid the formation of pores, comprehensive control is required from multiple aspects such as raw materials, melting process, mold design, pouring process, and subsequent processing. Here are some key measures and methods:

1. Quality control of raw materials

The purity of raw materials is an important factor affecting the formation of pores. Copper and its alloys are prone to absorbing gases, especially hydrogen, during the smelting process. Therefore, when selecting raw materials, pure copper materials should be used as much as possible, and waste materials containing oil, moisture, or oxides should be avoided. At the same time, raw materials should be pre treated, such as cleaning, drying, etc., to reduce the introduction of gases and impurities into the melt.

2. Optimization of melting process

During the smelting process, copper liquid is prone to absorbing gases, especially at high temperatures. To reduce gas absorption, the following measures can be taken:

Control melting temperature: Excessive melting temperature will increase the absorption of gas by copper liquid, so it is necessary to control the melting temperature within a reasonable range as much as possible to avoid overheating.

Use of covering agent: During the smelting process, covering agents (such as borax, charcoal, etc.) can be used to cover the surface of the copper liquid, forming a protective layer to reduce the contact between the copper liquid and air, thereby reducing gas absorption.

Degassing treatment: During the smelting process, degassing agents (such as phosphor copper, borax, etc.) can be added or inert gases (such as nitrogen, argon) can be used for blowing to help remove gases from the copper liquid.

3. Mold design and exhaust

The design of molds has a significant impact on the generation of pores. Reasonable mold design can effectively reduce the formation of pores:

Exhaust system design: A reasonable exhaust system should be designed in the mold to ensure smooth gas discharge during the pouring process. Gas accumulation in the mold can be avoided by setting up exhaust slots, exhaust holes, and other methods.

Mold surface treatment: The smoothness and coating of the mold surface can also affect the discharge of gases. It should be ensured that the surface of the mold is smooth to avoid gas retention caused by rough surface.

Mold preheating: The mold should be preheated before pouring to reduce gas release caused by low mold temperature. At the same time, preheating can also reduce the cooling rate of castings and lower the probability of pore formation.

4. Control of pouring process

The pouring process is an important link that affects the formation of pores. A reasonable pouring process can reduce the entrapment of gases:

Pouring speed control: If the pouring speed is too fast, it will cause turbulence in the copper liquid, which is prone to gas entrapment; If the pouring speed is too slow, it may cause the copper liquid to cool too quickly, increasing the chance of gas evolution. Therefore, the appropriate pouring speed should be controlled to ensure smooth filling of the mold with copper liquid.

Pouring temperature control: If the pouring temperature is too high, it will increase the absorption of gas by the copper liquid, while if the temperature is too low, it may cause poor fluidity of the copper liquid and easily form pores. Therefore, the pouring temperature should be controlled within a reasonable range to ensure that the copper liquid has good fluidity.

Optimization of pouring method: Bottom injection or side injection pouring methods can be used to reduce the turbulence of copper liquid during the pouring process, thereby reducing the entrapment of gas.

5. Cooling and solidification process control

The precipitation of gas during cooling and solidification is one of the main reasons for the formation of pores. To reduce the generation of pores, the following measures can be taken:

Control cooling rate: Excessive cooling rate will increase the chance of gas precipitation, so the cooling rate should be appropriately controlled to ensure that the gas can be smoothly discharged during the solidification process of the copper liquid.

Directional solidification: By controlling the cooling direction of the mold, directional solidification of the casting can be achieved, which can reduce the formation of pores. Directional solidification can allow gas to be discharged in a specific direction during the solidification process, avoiding the formation of pores inside the casting.

6. Subsequent processing and testing

After solidification, castings can further reduce the influence of porosity through subsequent processing:

Heat treatment: Heat treatment (such as annealing, aging treatment, etc.) can improve the internal structure of castings and reduce the influence of porosity. During the heat treatment process, gas can further diffuse and be discharged, reducing the presence of pores.

Non destructive testing: Non destructive testing (such as X-ray testing, ultrasonic testing, etc.) can timely detect porosity defects in castings and carry out corresponding repairs or treatments to ensure the quality of castings.

7. Environmental control

The environment of the casting workshop can also affect the formation of pores. The workshop should be kept clean and dry to avoid the formation of pores due to impurities such as moisture and oil in the air entering the copper liquid. At the same time, the ventilation and exhaust system in the workshop should also be maintained in good condition to ensure that the gases generated during the casting process can be discharged in a timely manner.

8. Optimization of alloy composition

Different copper alloy compositions have varying sensitivities to gases. By optimizing the alloy composition, the absorption of gas by copper liquid can be reduced. For example, adding certain alloying elements (such as phosphorus, silicon, etc.) can improve the degassing performance of copper liquid and reduce the formation of pores.

Pores are a common defect in the casting process of copper castings, but by comprehensively controlling multiple aspects such as raw materials, melting process, mold design, pouring process, cooling process, and subsequent treatment, the generation of pores can be effectively reduced. In actual production, the above measures should be flexibly applied according to specific casting conditions and casting requirements to ensure the quality and performance of castings.