Solid alloys become liquid alloys through smelting in the die casting
process, which is a complex physical and chemical process. Gas reacts with molten metal, oxygen especially has the strongest reaction with molten metal, which will result in a certain amount of zinc alloy slags because of the oxidized surface. Zinc slags contain oxides and iron, zinc and aluminum intermetallic compounds. The zinc slag which is scraped from molten metal usually contains 90% of zinc alloy
. The reaction rate of zinc slags formation increases exponentially with the smelting temperature.
Under normal circumstances, the amount of slags of original zinc alloy ingots is less than 1% and should be controlled in the range of 0.3% to 0.5%. The amount of slags of die casting parts
with poor quality is usually between 2% and 5%.
Methods of dealing with the zinc slag are as the following
1. Controlling the amount of zinc slags
A. Strictly control the smelting temperature, the higher the temperature is, the more the zinc alloy slag becomes.
B. Try not to stir the alloy liquid in the zinc container as much as possible, because any kind of stir will cause alloy liquids to be in more contact with oxygen atoms in the air, forming more zinc slags.
C. Do not scrape the zinc slag too frequently. Oxidation occurs and zinc slags form when the molten alloy is exposed to the air. Preserving a thin layer of the zinc slag on the surface of the container can prevent molten zinc from further oxidizing in the container.
D. Use a slag rake with many holes and a diameter of 6mm to scrape the zinc slag. Gently scrape under the zinc slag, and try to avoid stirring molten alloy as much as possible. Knock the slag rake at the edge of the container so that molten metal can flow into the container.
2. Dealing with zinc slags
A. Sell zinc slags to the raw material supplier or a specialized treatment plant, because it may be more expensive to deal with the zinc slag by yourself.
B. Deal with the zinc slag by die casting factory. There should be a separate furnace for the zinc slag, and the remelting temperature of the zinc slag should be in the range of 420 to 440℃. Meanwhile, add fluxing agents to the zinc slag. 0.5 to 1.5kg fluxing agents should be added to every 100kg of zinc slags. Uniformly distribute the fluxing agent over the liquid surface, and then use a stirrer to mix the fluxing agent with molten metal for about 2 to 4 minutes. The surface of molten metal will form a layer of stuff looking like mud after heat preservation for 5 minutes, and then scrape the mud.
It is not recommended dealing with the zinc slag by yourself. There are two reasons for that. The first reason is that smelting zinc slags generates smoke dust; the investment of environmental protection equipment is high; the cost is high and you lose more than gain. The second reason is that quality of alloy material is not guaranteed and the finished die casting part has many defects when operation specifications are not followed, which will even have higher costs.