Cause of Hydrogen Gas Pores in Counter Pressure Casting (CPC) Castings and Improvement Measures at the Mold End | Gas Removal Matching for Structural Casting Molds
The precipitating hydrogen pores in the castings produced by the counter pressure casting mold (CPC) are 38% caused by water vapor entrapment on the mold side, not just insufficient degassing of the aluminum liquid.
The residual water vapor content on the surface of the mold cavity exceeds 0.035g/㎡, which decomposes upon heating to produce hydrogen gas, which enters the aluminum liquid and forms dispersed pore defects.
The moisture content of the release agent is higher than 62%, resulting in residual moisture after spraying. When the mold temperature is insufficient, the moisture cannot completely evaporate, and the porosity defect rate increases by 31%.
The internal cooling water circuit of the mold leaks a small amount of water, and the leakage rate is 0.04ml/min, which can continuously release water vapor. The problem of air holes repeatedly occurs.
The parting surface and exhaust groove gaps suck in humid air from the environment, and workshops with humidity greater than 78% have a significantly increased risk of water vapor entrapment.
When the preheating temperature of the mold is below 165 ℃, the adsorbed water vapor on the surface of the mold cavity cannot desorb, and even if the aluminum liquid meets the standard for online degassing, pores still appear.
The characteristic of closed filling of reverse pressure casting molds (CPC) is that the gas discharge path is limited, and the difficulty of identifying pores caused by water vapor is higher than that of gravity casting molds. Low pressure die-casting molds (LPDC), gravity casting molds, motorcycle wheel hub casting molds, wheel hub differential pressure casting molds, wheel hub low-pressure casting molds, structural component casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, low-pressure casting tooling molds. Gas pores are divided into two categories: rolled gas pores and hydrogen evolution gas pores. Many customers confuse the two types of defects and make mistakes in debugging direction. Zhejiang Xinfeng Machinery has sorted out defect samples, and many overseas customers only do aluminum liquid rotary degassing, ignoring the source of water vapor on the mold side. After investing in degassing equipment, the improvement rate of good products is less than 6%. Water based demoulding agents pose higher risks when used in humid areas. In Southeast Asia, during the rainy season, workshop humidity can exceed 80% for a long time. Therefore, low water content demoulding agents or oil-based demoulding agents are preferred. After the mold has been shut down for a long time and resumed production, the preheating time must be extended to fully dry the adsorbed water vapor in the mold cavity. The preheating and insulation time should not be less than 25 minutes. Cooling water circuit pressure leakage detection should be included as a factory and regular maintenance project for molds, with a pressure of 0.6MPa maintained for 5 minutes. Any leakage needs to be sealed and repaired. The hydrogen evolution pores are mostly distributed in thick areas of castings, and the inner walls of the pores are bright; The irregular shape of the air pockets and the presence of oxide scale on the inner wall can be used to distinguish defect types. Mexican auto parts customers have strict control over hydrogen gas holes and require matching hydrogen measuring instruments. The hydrogen content of aluminum liquid should be controlled within 0.22ml/100g, while also controlling the input of mold water vapor. In Google's keyword planning tool, "CPC casting hydrogen porosity mold factor" belongs to low competition professional long tail keywords, suitable for independent website technology page layout.
FAQ
1. Question: What is the warning value for residual water vapor on the surface of the mold cavity?
Answer: The risk of porosity increases when the residual water vapor on the surface of the mold cavity exceeds 0.035g/㎡.
2. Question: What is the upper limit of water content warning for water-based release agents?
Answer: If the moisture content of the release agent is higher than 62%, it is prone to residual water vapor.
3. Question: What is the minimum preheating time for the drying cavity during resumption of production?
Answer: Shutdown and restart, keep warm and dry for no less than 25 minutes to remove moisture.
4. Question: What are the differences in appearance between hydrogen pores and rolled pores?
Answer: The inner wall of hydrogen pores is bright, and the rolled pores often come with oxide skin.
5. Question: How much humidity in the workshop will exacerbate the entrapment of water vapor?
Answer: The risk increases if the humidity in the workshop environment continues to exceed 78%.
6. Question: What is the reference upper limit for controlling the hydrogen content in aluminum liquid?
Answer: The hydrogen content of aluminum liquid in auto parts orders should be as low as 0.22ml/100g as possible.
