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2020.12.24
Zinc alloy die casting is one of the most important die casting in the traditional die casting industry. Because of its low melting point, excellent mechanical properties and easy electroplating, it is widely used in all kinds of die casting parts. However, the traditional zinc alloy die casting manufacturers have been unable to keep up with the pace of the times, so how to explore a new technology to make zinc alloy die casting industry a new industry in the casting industry?
Although the quality standard of zinc alloy die casting has been gradually unified, and its composition requirements are roughly the same, the effect of different kinds of die casting alloy is very different. Some alloys reflect well, others are poor, which is related to the production process. In this article, we explore new production processes by comparing various influencing factors, and prepared die-cast zinc products for comparison.
1. Furnace production process
High purity liquid zinc is used as raw material for alloy production and gas furnace is used to avoid iron increase due to melting of mixer. In order to control the ingot weight within ± 0.3KG, graphite cone flow control technology is used. The process is simple and the production cost is low. However, the defect of gas furnace is that the direct recovery rate is low and the composition uniformity of alloy liquid is poor due to mechanical stirring.
2. Other processes
High power frequency cored furnace is used to melt zinc and remove the slag, and then the liquid zinc flows out from the opening of the furnace, and then flows into the coreless furnace to melt the alloy elements and form alloy liquid. The alloy liquid is poured out by the tilting device, and flows into the holding furnace through the chute, then scooped out by the mechanical spoon, and then injected into the zinc mold.
The biggest defect of this process is that more scum is produced during the tilting process from coreless furnace to resistance furnace. The creeping vibration of linear ingot casting machine is unfavorable to the surface quality of alloy ingot. At the same time, the energy consumption is large.
Through the comparison of the above two processes, it is found that the selection of smelting equipment and the control of smelting process are important factors affecting the production of die-casting zinc products.
The more widely used furnaces include fuel oil reverberatory furnace, gas reverberatory furnace, induction furnace and so on. From the perspective of ensuring product quality, the power frequency coreless furnace is the best smelting equipment for the production of zinc die-casting alloys. The reasons are:
(1) Good sealing, can be less or no charcoal and other covering agent.
(2) Coreless furnace is automatic stirring, which not only reduces the labor intensity, but also reduces the chance of iron tools contacting with zinc alloy melt.
(3) The stirring speed of melt in the furnace is fast and uniform, and can fully react with each other, so the slag forming effect is good and the alloy composition is very uniform.
There are two existing smelting processes: one is to melt copper first and then add Al Zn mg; the other is to melt Al Cu master alloy first and then melt Zn alloy. The former has to be operated at high temperature over 1000 ℃, which is rarely used in production; the latter is widely used, but it still has the disadvantages of high temperature operation and complicated process. In this paper, a series of zinc alloys were prepared directly in the process of zinc melting and casting. Firstly, the required amount of copper is added into zinc melt to melt, and then aluminum magnesium and residual zinc are added in turn. The process has the following control points:
1. Temperature control
The higher the temperature, the metal oxide film dissolved and lost its protective effect. However, high temperature rapid melting can also reduce the oxidation and burning loss. The control melting temperature is generally 100 ℃～ 200 ℃ higher than the liquidus temperature.
2. Control of refining agent
Refining agent is used for degassing and slag removal of alloy liquid. About 80% of oxides and 70% of intermetallic compounds in zinc alloy solution can be removed by pressing ammonium chloride with bell jar at 450 ℃ ~ 750 ℃, thus ensuring the quality of the alloy. However, it is also found that the melting loss rate of the alloy is increased by refining with ammonium chloride, and the alloy ingot 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 ammonium chloride needed to be added can be determined according to the amount of recycled materials.
3. Control of aluminum copper intermediate liquid
The purpose of using aluminum copper intermediate liquid is to add some alloy elements with high melting point and not easy to melt, so as to control the composition more accurately, such as titanium and zirconium. Secondly, using intermediate liquid can avoid Melt Overheating, shorten melting time and reduce burning loss. The intermediate liquid is prepared by fusion method. First, the fusible metal is melted and overheated to a certain temperature, and then the refractory metal is added in batches. The key of this method is to create good dynamic conditions, enlarge and renew the direct contact surface between the base metal and alloy elements.
– The results show that the power frequency coreless furnace is the best choice for alloy production because of its good sealing performance, good slag forming effect, low labor intensity and easy operation.
– The new process makes use of the alloy melting of copper in zinc melt, which can accurately control the composition, so it can directly prepare zinc alloy in the process of zinc melting and casting.