Refining and purification is a significant way to obtain pure and high-quality zinc alloy die casting parts. Zinc alloy can be purified by static clarification, chloride treatment, inert gas blowing and filtration. In this article, we cover some common purification treatment methods of zinc alloy die casting.
1. Chloride treatment
One of the most widely used is chloride treatment. After the alloy is melted, press 0.1% – 0.2% chlorination or 3% – 4% hexachloroethane into the bell jar for slow stirring.
2. Fine ceramic filter metal liquid
Better purification effect can also be obtained by filtering molten metal with fine-grained ceramics. By using a filter with an average particle size of 2-35m and a layer thickness of 105m, nearly 90% of oxides and 85% of metal compounds in za4-1 alloy can be removed. When in use, the filter is placed in the bell jar, heated to 5000C, and put into the holding furnace or ladle. The chemical properties of rare earth elements are relatively active. They can form compounds with low relative density and high melting point with impurities such as O, N and h. These compounds are easily removed from liquid metal together with slag.
3. Refining Agent
In various casting furnaces, refining agent can refine, protect and remove slag from molten metal, thus obtaining high purity products and purifying the melt. For zinc alloy, the commonly used refining agents are hexachloroethane, zinc oxide, rare earth elements, inert gas and other refining agents. In order to prevent impurities, especially Fe from infiltrating into the liquid alloy, the tools should be coated before refining. The coating is mainly composed of zinc oxide, fossil powder, water glass and water.
– Hexachloroethane is non hygroscopic, non remelting, less corrosive and easy to preserve. It can be widely used in various casting alloys instead of chloride refining agent.
– As a kind of casting raw and auxiliary material, zinc oxide flux is mainly used in slag removal and refining of zinc alloy. Zinc oxide is remelted and placed in a drying oven at 100130 ℃ before use. It is used in Zn containing alloys or alloys with no strict requirements on Zn impurities. Its disadvantage is that a large number of harmful gases are produced in the production and the environmental protection is very poor. The slag removal and refining effect of zinc alloy flux is poor, which will cause the impurities and bubbles in the alloy liquid can not be removed completely, and increase the waste products of die casting.
– The chemical properties of rare earth elements are relatively active. They can form compounds with low relative density and high melting point with impurities such as 0, N and h. usually, these compounds are easily removed from liquid metal together with slag to achieve refining effect.
– Inert gases, including nitrogen or nitrogen, are low-cost, pollution-free and are used in various alloys.
The refining agent has good effect on degassing and slag removal of alloy liquid. It is reported that at 450-470 ℃, the chlorination press is pressed into the bell jar to remove nearly 80% of the oxides and 70% of the intermetallic compounds in the zinc alloy liquid, so as to ensure the quality of the alloy. However, it is proved by experiments that the use of chlorination (0.12% of the total amount of refining metal) will increase the melting loss rate of the alloy, and produce a lot of smoke and ammonia gas in the process, which will worsen the operating environment. In many cases, ingots with compact cross-section structure and without slag and inclusions can be obtained only by static clarification. Therefore, the slag making operation and the amount of chlorination needed to be added can be determined according to the amount of recycled materials.