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2021.7.28
Zinc alloy has good casting properties, mechanical properties and toughness. It is widely used in traditional mechanical parts, hardware, locks, toys and other industries. Zinc alloy also has excellent heat conduction performance, good vibration damping characteristics and good electromagnetic shielding performance. Therefore, the application in electronics, telecommunications and household appliances is growing, especially the electronic products that need to solve the problem of electromagnetic shielding. Read this article and you will have a comprehensive understanding of zinc alloy materials.
A good zinc alloy must have the following three characteristics:
1. High purity: low impurity content of zinc ingot: Based on high-purity zinc raw materials, such as high-quality 0# zinc ingot.
2. Low melting point: the melting point of good zinc alloy is controlled at 380-390 ℃. The crucible temperature can be controlled below 420 ℃.
3. Less zinc slag: less zinc slag is produced during melting.
1. Knock off to see the section. If the section is fine, it is generally better.
1. The high melting point of zinc alloy die casting will destroy the composition of zinc alloy die casting
When the crucible temperature exceeds 420 ℃, the magnesium and aluminum in the zinc alloy will be lost, the composition of the alloy will be changed, the product quality will be affected, and the scrap rate will increase.
2. Zinc alloy die casting has high melting point, low energy consumption and low cost
Generally, in the production process, the set temperature of zinc alloy die casting is 410 ℃, and the poor zinc alloy may need to be set above 430 ℃. Take a 88T zinc alloy die casting machine from a zinc alloy die casting manufacturer as an example: when the temperature increases by 10 ℃, the annual electricity cost increases by $768, and if diesel is used, the cost increases by about $1229.
3. The melting point of zinc alloy die casting is high and the service life of hot working parts is reduced
The crucible temperature should be about 410 ℃ normally. If the temperature is too high, it will accelerate the wear and corrosion of the hammer handle head, hammer handle, steel trexate, gooseneck and crucible, and the hammer head will be stuck in serious cases. Take gooseneck as an example: generally, a better gooseneck costs about 5000 yuan. Generally, the service life of the normal gooseneck is more than 1.5 million molds. If the alloy solution corrodes the gooseneck seriously, the production of 1 million molds may cause problems in its production. If it is serious, it may be directly scrapped and the cost will increase significantly.
4. Zinc alloy material has high melting point and reduced mold life
The melting point of zinc alloy material increases, which will cause great damage to the mold, reduce the service life of the mold, aggravate the corrosion of the mold, shorten the service life of the mold and increase the cost of each mold product.
5. High melting point, more zinc slag and increased cost of effective alloy
According to 18500 yuan per ton of zinc alloy, the cost of 3% zinc slag is about 555 yuan. In production, every 1% reduction of zinc slag is equivalent to an increase of 1% in the yield of the product. In terms of die-casting cost, the cost of die-casting is reduced by 1%.
Zinc alloy ingots stored in a humid and dirty environment will increase zinc slag, reduce the amount of effective alloy and reduce the product quality of zinc alloy die castings. Therefore, the environment for storing zinc alloy ingots should be managed.
1. Ensure that the stacking area is clean and dry.
2. Sampling inspection (or regular inspection) shall be conducted for zinc alloy before use.
1. Temperature
The recommended furnace temperature is 415-430 ℃ for zinc alloy. The upper limit of the die-casting temperature of thin-wall parts and complex parts can be taken, but it shall not exceed 430 ℃. The higher the furnace temperature is, the higher the slag quantity will be increased at the same time. Experienced die casting workers observe the melt with naked eyes from the following three aspects:
– If the molten liquid is not too viscous and clear after slag scraping, and the slag is not rising quickly, it indicates that the temperature is appropriate.
– If the melt is too viscous, the temperature is low.
-. After slag scraping, a layer of white frost will appear on the liquid level, and the liquid zinc will turn red and slag is too fast, indicating that the temperature is high and should be adjusted in time.
2. Control (can be carried out from the following four aspects):
– If there is any error between the actual temperature of the melting furnace of the die casting machine and the display of the melting furnace, the portable thermometer shall be used to check the melting furnace temperature regularly.
– Conditional central melting furnace and die casting machine furnace are used as holding furnace, so as to avoid large temperature change caused by direct addition of zinc ingot in zinc pot. Centralized melting can ensure the stability of alloy composition. Or adopt advanced automatic metal liquid feeding system, which can maintain stable feeding speed, temperature of alloy liquid and liquid level height of zinc pot.
– If the zinc pot is directly fed, it is suggested to add the whole alloy ingot at one time instead of small alloy ingots for many times, which can reduce the temperature change caused by feeding.
– Zinc alloy ingots need to be pre heated.
3. Peripheral tools
It is not allowed to use iron crucible and iron operating tools to contact alloy liquid. Stainless steel spoon should be used.
1. Avoid stirring the alloy liquid in the zinc pot as much as possible. Any way of stirring will lead to more contact between the alloy liquid and oxygen atoms in the air, so as to form more scum.
2. The heating and temperature rise shall be uniform to prevent explosion and local overheating. The melting temperature shall be strictly controlled. The higher the temperature, the more zinc slag.
3. Don’t pick up slag too often. When the molten alloy is exposed to the air, it will oxidize and form scum. Retaining a thin layer of scum on the furnace surface is conducive to no further oxidation of the liquid in the pot.
4. When scraping slag, use a porous filter（Ф 6 mm) disc shaped slag raking rake, gently scrape under the scum, avoid the stirring of alloy liquid as far as possible, lift the scraped slag, gently knock the slag raking rake at the edge of the zinc pot to make the metal liquid flow back to the zinc pot.
5. Control the proportion of return material, and the return material shall not exceed 30%.
– Aluminum: Increase the fluidity of liquid metal. Reduce erosion of ferrous materials such as Goosenecks, molds and crucibles.
– Copper: Increase the hardness and strength of the alloy; Improve the wear resistance of the alloy. Reduce intergranular corrosion.
– Magnesium: Reduce intergranular corrosion. Refine the alloy structure to increase the strength of the alloy; Improve the wear resistance of the alloy.
Harmful impurity hazard:
– Iron: Iron is the main element causing zinc slag. Excessive iron will combine with aluminum and zinc to form intermediate products (fe2al5 and feal3) and reduce the content of aluminum. The formation of hard particles makes the surface polishing difficult; Shall not exceed 0.10%.
– Lead (PB), tin (SN) and chromium (CD): The main elements leading to intergranular corrosion, which will lead to blistering and cracking of electroplating products.
Threshold value of each element content:
– Lead: not more than 0.004%.
– Tin: not more than 0.002%.
– Chromium: not more than 0.003%.
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