Zinc alloy melting is an important part of the die casting process. The melting process is not only to obtain molten metal, but more importantly, to obtain a chemical composition that meets the requirements. The zinc alloy die casting can obtain a good crystal structure and gas. The correct zinc alloy die-casting process regulations are an important guarantee for obtaining high-quality castings.
1. The best melting temperature for zinc alloy die-casting: The melting point of zinc alloy for die-casting is 382~386℃, and proper temperature control is an important factor for zinc alloy composition control. In order to ensure the good fluidity of the alloy liquid to fill the cavity, the temperature of the molten metal in the zinc pot of the die-casting machine is 415~430℃. The upper limit of the die-casting temperature for thin-walled and complex parts can be taken; the lower limit for thick-walled and simple parts can be taken. The temperature of the molten metal in the central smelting furnace is 430~450℃. The temperature of the molten metal entering the gooseneck is basically the same as the temperature in the zinc pot. The pouring temperature can be accurately controlled by controlling the temperature of the molten zinc in the zinc pot.
2. (When the melting temperature is too high) the iron crucible reacts quickly with the zinc liquid, and the iron oxidation reaction occurs on the surface of the crucible to produce Fe2O3 and other oxides; the iron element will also react with the zinc liquid to form FeZn13 compound (zinc slag), which is dissolved in the zinc In the liquid. Burning of aluminum and magnesium elements,
Metal oxidation speeds up, burning loss increases, and zinc dross increases. The effect of thermal expansion will cause the hammer head to jam. More iron is melted into the alloy in the cast iron crucible, and the reaction between zinc and iron is accelerated at high temperatures. Hard particles of iron-aluminum intermetallic compounds are formed, causing excessive wear on the hammer head and gooseneck. More iron is melted into the alloy in the cast iron crucible, and the reaction between zinc and iron is accelerated at high temperatures. Hard particles of iron-aluminum intermetallic compounds are formed, causing excessive wear on the hammer head and gooseneck. Fuel consumption increases accordingly. The higher the temperature, the coarser the crystals of the castings and the lower the mechanical properties.
3. (When the melting temperature is too low) the alloy has poor fluidity, which is not conducive to forming and affects the surface quality of die castings.
4. (How to keep the temperature stable) Current die-casting machine melting pots or furnaces are equipped with temperature measurement and control systems. Regular inspections are used to ensure the accuracy of temperature measuring instruments. The actual temperature of the furnace is measured regularly with a portable thermometer (thermometer). Correction. Experienced die-casting unions observe the melt with the naked eye. If the melt is not too viscous and clear after scraping, the slag does not rise quickly, indicating that the temperature is appropriate; if the melt is too viscous, it indicates that the temperature is low; A layer of hoar frost appears on the liquid surface after the slag, and the slag rises too fast, indicating that the temperature is too high and should be adjusted in time. The best method is to use a central melting furnace and a die-casting machine furnace as a holding furnace, so as to avoid large temperature changes when the zinc ingot is directly added to the zinc pot to melt. Concentrated smelting can ensure the stability of the alloy composition. Or adopt an advanced molten metal automatic feeding system, which can maintain a stable feeding speed, alloy liquid temperature and zinc pot liquid level. If the material is added directly in the zinc pot, it is recommended to add the whole alloy ingot at one time to multiple small alloy ingots, which can reduce the temperature change caused by the addition.
5. (Control of zinc slag) It is a complicated physical and chemical process to change from solid to liquid by melting alloy. The gas reacts with the molten metal chemically, and the oxygen reaction is the strongest, and the surface of the alloy is oxidized to produce a certain amount of scum. The dross contains oxides and intermetallic compounds of iron, zinc and aluminum. The dross scraped from the surface of the melt usually contains about 90% of zinc alloy. The reaction rate of zinc dross formation increases exponentially as the melting temperature rises. Under normal circumstances, the slag output of the original zinc alloy ingot is less than 1%, which is in the range of 0.3 ~ 0.5%; while the slag output of remelting nozzles and waste workpieces is usually between 2% and 5%.