Main Points of Zinc Alloy Die Casting Process
First, the development of zinc alloy die casting process need to consider the following questions:
1. Metal liquid in the pouring system can clean, smooth flow, will not produce separation and eddy current.
2. There is no sharp corner area or death zone exists?
3. Gating system is there any change in cross-sectional area?
4. Exhaust groove, overflow groove position is correct? Is it big enough? Will it be blocked? Gas can be effective, smooth discharge? Application of computer simulation filling process is to analyze the above phenomena, to judge to choose reasonable process parameters.
Second, the paint produced gas analysis
Coating properties: If the gas is large on the zinc alloy die casting porosity has a direct impact.
Spraying process: excessive use, resulting in a large amount of gas volatility, too much punch lubricant, or charred, are the source of gas.
1. To solve the zinc alloy die-casting hole approach
First analyze what is the cause of the pores, and then take the appropriate measures.
a. dry, clean alloy material.
b. control the melting temperature, to avoid overheating, degassing treatment
c. A reasonable choice of die-casting process parameters, especially the injection speed. Adjust the high speed switching start point.
d. Sequential filling facilitates the discharge of cavity gas. Spur sprue and runner have enough length (> 50mm) to facilitate smooth flow of alloy liquid and gas to be discharged. It can be changed of the thickness of the gate, the direction of the gate, in the formation of stomata position set up overflow slot, exhaust slot. The sum of the cross-sectional area of overflow product cannot be less than 60% of the sum of the cross-sectional area of the gate, otherwise, the slag discharging effect is poor.
e. Choose good performance coatings and spray control.
Third, how to measure the temperature
Zinc Alloy Die casting Melting Temperature Control and Its Influence
Zinc alloy melting is an important part of the die-casting process. The melting process is not only to obtain the molten metal solution, but more importantly, the chemical composition is in compliance with regulations, which can make the zinc alloy die-casting have good crystalline structure and small gas and inclusion Liquid metal. During the smelting process, the interaction between the metal and the gas and the interaction of the molten metal with the crucible cause the composition to change, resulting in inclusions and inspirations. Therefore, the correct melting process is an important guarantee for obtaining high quality castings.
1. Zinc alloy die-casting the best melting temperature: die-casting zinc alloy melting point of 382 ~ 386 ℃, the appropriate temperature dwarf control of zinc alloy composition is an important factor in the control. In order to ensure a good flow of liquid alloy filling cavity, die-casting machine zinc liquid metal temperature is 415 ~ 430 ℃, thin-walled parts, complex parts die-casting temperature is capped; thick-walled pieces, simple pieces desirable lower limit. Central metal melting furnace temperature of 430 ~ 450 ℃. The temperature of the molten metal entering the gooseneck is basically the same as that of the zinc pot. By controlling the temperature of the metal pot of the zinc pot, the pouring temperature can be accurately controlled.
2. When the melting temperature is too high
Iron crucible reaction with zinc faster, iron oxidation reaction occurs on the surface of the crucible Raw Fe2O3 oxide and other elements will react with the zinc solution to generate FeZn13 compound (dross), dissolved in the zinc solution. Aluminum, magnesium loss, metal oxidation speed, burning loss increased, dross increased. Thermal expansion will occur stuck hammer phenomenon. Iron cast iron crucible iron alloy melting more, high temperature zinc and iron react faster. Hard particles of iron-aluminum intermetallic compounds are formed, causing excessive wear of the hammerhead and gooseneck. Iron cast iron crucible iron alloy melting more, high temperature zinc and iron react faster. Hard particles of iron-aluminum intermetallic compounds are formed, causing excessive wear of the hammerhead and gooseneck. An increase in fuel consumption. The higher the temperature, the castings are coarse and the mechanical properties are reduced.
3. When the melting temperature is too low
Alloy flow is poor, is not conducive to forming, affecting the quality of die-casting surface.
4. How to keep the temperature stable
Now the die-casting machine melting pot or melting furnace is equipped with temperature measurement and control system, regularly check to ensure the accuracy of temperature measuring instruments, regularly with a portable thermometer (thermometer) actual furnace temperature measured to be corrected. Experienced die-casting union with the naked eye to observe the melt, if the slag after the melt is not too viscous,
Zinc alloy die-casting knowledge is also more clear, starting from the slag is not fast, indicating that the temperature is appropriate; melt too thick, then the temperature is low; soon after the dross flooded a layer of hoarfrost, slag too fast, that High temperature, it should be promptly adjusted. The best way is to use the central melting furnace, die-casting furnace for holding furnace, in order to avoid the zinc pot directly add molten zinc ingot cause significant temperature changes. Centralized melting ensures stable alloy composition. Or the use of advanced metal automatic feeding system, to maintain a stable feed rate, the temperature of the alloy liquid and zinc pot liquid height. If it is directly added in the zinc pot, it is recommended to join the entire alloy ingot changed to multiple times into small pieces of alloy ingots, can reduce the temperature changes caused by the feed rate.
5. Control of Zinc Slag, The transition from a solid state to a liquid state through a molten alloy is a complex physical and chemical process. Gas and molten metal chemical reaction, in which the most intense reaction of oxygen, the alloy surface is oxidized to produce a certain amount of scum. Scum contains oxides and iron, zinc, aluminum intermetallic compounds; scum scraped from the melt surface usually contains about 90% of the zinc alloy. The reaction rate of zinc dross formation increases exponentially with the melting temperature. Under normal circumstances, the original zinc alloy ingot slag production less than 1%, within the range of 0.3 to 0.5%; and remelting nozzle, scrap and other slag production is usually between 2 ~ 5%. To reduce the generation of dross:
a. As far as possible to avoid agitation of the alloy liquid in the zinc pot, any agitation will lead to more contact of the alloy liquid with the oxygen atoms in the air to form more scum.
b. strictly control the melting temperature, the higher the temperature, the more dross.
c. Do not be too frequent slag. When the molten alloy is exposed to the air oxidation occurs, the formation of scum, leaving a thin layer of the surface of the scum furnace conducive to the liquid without further oxidation.
d. When using a porous (Ф6 mm) plate-shaped slag-rake for skimming, gently scrape it under the scum so as to avoid agitation of the alloy liquid as much as possible. Gently knock, so that the liquid metal back to the zinc pot.
e. electroplating scrap containing copper, nickel, chromium and other metals are insoluble in zinc, zinc alloy will remain in the presence of hard particles, polishing and machining problems, and to avoid the nozzle directly into the zinc die-casting machine Remelting furnace re-die casting.
f. The surface of the nozzle material is oxidized in the process of die-casting and the content of zinc oxide far exceeds that of the original alloy ingot. When these nozzle materials are remelted in the zinc pot, since the zinc oxide is in a viscous state under high temperature conditions, Remove it from the zinc pot, it will take away a lot of alloy composition.