The correct treatment of zinc alloy die casting can greatly reduce the production cost, especially because the consumption of zinc alloy is at least 30% of the total cost of a die casting manufacturer. By increasing the understanding of the characteristics and formation process of zinc alloy slag, the corresponding measures can be taken to minimize the generation of slag.
1. loss rate
Zinc alloy is the biggest single consumption material of zinc alloy die-casting manufacturers. The loss of metal in the melting process of zinc alloy inevitably causes the increase of production cost. Effective control of metal loss can increase the profit of die-casting manufacturers to a large extent. On the contrary, because of the bad control measures in the production, too much slag will cause the production cost to rise.
According to the statistics with die-casting manufacturers, there is about 3% to 5% loss in zinc alloy die-casting. This figure is only applicable to die-casting manufacturers with good management. 5% loss rate refers to the die-casting manufacturers that produce small castings. These die-casting manufacturers usually have high burr return charge for zinc alloy die-casting. For die-casting manufacturers with disordered management, the slag loss will be much higher.
2 zinc slag
The slag in zinc alloy die casting includes metal oxide suspended in liquid metal and iron aluminum intermetallic phase. Most of the slag is available zinc alloy, usually accounting for 70% - 80%. In die casting production, because of the hot chamber die casting process, it is inevitable that zinc alloy contacts with iron. The melting degree of Fe Al mesophase in zinc alloy die casting is very low, and its specific gravity is lower than that of zinc alloy. Therefore, feal3 solid particles are separated from the molten metal and suspended on the surface of the molten metal together with metal oxides to form a "paste" slag. The slag accumulates with time and the amount of molten metal, which must be removed in the production of zinc alloy die casting.
3. Generation of slag
Any situation that will lead to oxidation, the formation of iron aluminum intermetallic phase, and the mixing of molten metal into the slag will negatively affect the amount of slag produced.
The rough edges of ingots and zinc alloy die castings shall be stored in a dry place and shall not be mixed with other materials. The metal materials shall be stored outdoors as far as possible to expose them to the external climatic conditions, because doing so will increase the degree of oxidation of the metal materials.
It is inevitable to produce certain oxidation when melting metal ingot and zinc alloy die casting blank. However, when adding metal into the liquid metal pool, attention should be paid to minimize the interference, even if the liquid metal pool is subject to the minimum disturbance. A thin layer of slag should be reserved on the surface of the molten metal pool to reduce the chance of exposing the fresh molten metal to the air. Only when the slag reaches 1-2cm thick can the slag be removed. There is a high ratio of surface area / volume of small rough cutting, burr and waste material from ground cleaning. The wet / oily thin parts returned to work or machining waste may not be worth remelting in die casting factory. The materials listed above should generally be sold to zinc alloy plants or scrap metal recyclers. However, if there is a large amount of small waste in the die-casting factory, a one-to-one feasibility study can be carried out to determine whether it is economical to clean the small waste, dry and extrude it into small pieces, and then remelt it.
4 Calculation of slag loss
In order to manage slag loss properly, it is very important to keep accurate metal balance records. This includes the quantity purchased, the weight of castings produced, and the amount of slag produced. Accurate records can be made by comparing the data in different time (generally by month), and any change of slag quantity can be found in time. In addition to slag loss, metal loss will also be caused by weight errors during processing, receiving and delivery, improper inventory records, and other unpredictable factors. These additional losses shall be deducted when calculating the overall slag loss of the plant.