Gradual effects of scaling and blockage in the water cooling circuit of low-pressure casting molds | Investigation of cooling efficiency attenuation in aluminum casting forming molds
The water cooling pipeline of low-pressure casting molds is gradually clogged due to scaling, resulting in 46% of mold temperature loss control, solidification deviation, and repeated occurrence of shrinkage defects.
The hardness of the cooling water is greater than 220mg/L (calculated as CaCO3), and scale continues to precipitate on the high-temperature pipe wall, reducing the flow cross-sectional area by 11% every 30 days.
The thickness of scale on the inner wall of the waterway is greater than 0.2mm, and the heat transfer coefficient decreases by 42%. At the same flow rate, the temperature of the mold cavity increases by 14-22 ℃.
The bending position of the waterway and the flow velocity of the embedded waterway are below 0.6m/s, causing impurities to settle and accumulate, with priority given to local blockage and uneven cooling.
If the outlet water temperature of the cooling water rises above 11 ℃, it indicates that the heat transfer load of the circuit is overloaded or blocked, and the remote hot section cannot be effectively cooled.
The cooling water has not been added with corrosion and scale inhibitors, and the inner wall of the carbon steel waterway is corroded, with rust residue peeling off, blocking the fine waterway and throttling holes with the water flow.
Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), differential pressure casting molds for wheel hubs, low-pressure casting molds for wheel hubs, motorcycle wheel hub casting molds, gravity casting molds, structural component casting molds, aluminum alloy wheel hub molds, low-pressure casting tooling molds, the cooling system determines the solidification sequence, and many defects are not caused by cavities, but by waterway blockages. Zhejiang Xinfeng Machinery tracks overseas factories. The hardness of groundwater in the Middle East is generally high, and the problem of scale is more prominent than in Southeast Asia. Many customers only focus on flow rate and do not pay attention to the temperature difference between inlet and outlet water. Blockage is a gradual process, and good products slowly decline, which is easily mistaken for aluminum liquid or mold release agent process problems. The diameter of the throttle hole in the waterway is less than 3mm, which is prone to blockage by rust and scale particles. During the design phase, priority should be given to a diameter of ≥ 4mm. It is recommended to perform waterway acid cleaning and descaling every 3 months; Regularly check the hardness and pH value of the closed-loop cooling water system. An independent cooling circuit is superior to a series circuit, and a single blockage will not cause cooling failure in other cavities. Many molds pass the factory pressure test, but after six months of production, the cooling imbalance is a typical manifestation of scale accumulation. Search for "low pressure die casting water circuit scaling" on Google, targeting maintenance engineers from overseas foundries.
FAQ
1. Question: What is the hardness warning threshold for cooling water?
Answer: The risk of scaling is significantly increased when the hardness is higher than 220mg/L (CaCO ∝).
2. Question: Does the thickness of scale affect the critical value of heat transfer?
Answer: If the scale exceeds 0.2mm, the heat transfer efficiency will significantly decrease.
3. Question: What is the recommended minimum flow rate for waterways?
Answer: The flow velocity in areas prone to sedimentation should not be less than 0.6m/s as much as possible.
4. Question: What is the warning line for the temperature difference between the inlet and outlet of a single circuit?
Answer: If the temperature rise of the effluent continues to exceed 11 ℃, blockage needs to be investigated.
5. Question: What is the recommended minimum diameter for throttling holes in fine water channels?
Answer: Priority should be given to ≥ 4mm to reduce the probability of blockage.
6. Question: What is the reference for the regular descaling cycle of waterways?
Answer: It is recommended to maintain acid washing every 3 months for continuous production in hard water areas.
