How To Control The Material Loss Of Zinc Alloy Die Casting

How To Control The Material Loss Of Zinc Alloy Die Casting

1. Loss rate

Zinc alloy is the largest single consumption material of zinc alloy die casting manufacturers. The loss of metal in the melting process of zinc alloy will inevitably increase the production cost. Effectively controlling the loss of metal can increase the profits of die-casting manufacturers to a great extent. On the contrary, excessive slag caused by poor control measures in production will increase the production cost.

According to the statistics of die-casting manufacturers, there is a loss of about 3% to 5% in zinc alloy die-casting. This figure is only applicable to well managed die-casting manufacturers. The loss rate of 5% refers to the die-casting manufacturers producing small castings. These die-casting manufacturers usually have high rough edge recycling of zinc alloy die-casting parts. For die-casting manufacturers with chaotic 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 metal mesophase. 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, the contact between zinc alloy and iron is inevitable. The melting degree of iron aluminum 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 molten metal and suspended on the surface of molten metal together with metal oxides to form “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 metal mesophase, and the mixing of molten metal into slag will negatively affect the amount of slag produced.

The rough edges of metal ingots and zinc alloy die castings should be stored in a dry place and avoid mixing with other materials. Try to avoid storing metal materials outdoors and exposing them to external climatic conditions, because doing so will increase the degree of oxidation of metal materials.

When melting metal ingots and rough edges of zinc alloy die castings, a certain amount of oxidation is inevitable. However, when adding metal materials into the metal liquid pool, attention should be paid to minimize the degree of interference; Even if the molten metal pool is subject to the smallest disturbance as possible. A thin slag layer shall be reserved on the surface of the molten metal pool to reduce the exposure of fresh molten metal to air. The slag shall be removed only when the slag is 1 ~ 2cm thick. There is a high surface area / volume ratio for small rough cuts, burrs and waste materials cleaned from the ground. The returned materials or machining waste of wet / oily thin parts may not be worth remelting in die casting manufacturers. The materials listed above should generally be sold to zinc alloy plants or scrap metal recyclers. However, if the die-casting manufacturer has a large amount of small waste, a one-step feasibility study can be conducted to determine whether it is economical to clean, dry and extrude the small waste into small pieces, and then remelt.

4. Calculation of slag loss

In order to properly manage the slag loss, it is very important to keep accurate metal balance records. This includes the purchase quantity, the weight of castings produced, and the amount of slag produced. Accurate record can find any change of slag quantity in time by comparing the data in different time. In addition to the loss of slag, the loss of metal will also be caused by processing, weight error during 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.

The slag loss can be calculated by several different methods, one of which is to calculate the percentage of purchased metal materials or additives, or to consider the slag loss as a function of the finished product yield of zinc alloy die castings. When estimating the slag loss as a function of the finished product yield of zinc alloy die castings, it must be recognized that most of the loss comes from remelting rough scrap and scrapped castings. The main reason is that the burr material has a larger surface area / volume ratio than the new metal ingot. In addition, these remelted materials will be mixed with more impurities, especially iron dissolved from the holding tank and gooseneck on the die casting machine, both of which will produce more slag.

5. Examples

If the slag loss rate of new material and return material is 0.6% and 4.5% respectively, and the yield of castings is 50%, therefore, the total slag loss is 5.13kg or 5.13% of the net weight of castings.

Assuming that the slag loss of melting new material and return material is the same as the above example, but the casting yield is 60%, the total slag loss is 3.62kg, and the casting yield increases from 50% to 60%. The slag loss caused by each 100kg casting (net weight) is reduced from 5.13kg to 3.62kg, which is about 29%.

6. Treatment of slag

Even if all necessary measures are taken to reduce the generation of slag, scum containing 70% – 80% useful alloy still needs to be removed from the furnace surface regularly. For the solidified slag, the die-casting manufacturer can pay a small fee and let the alloy manufacturer recycle it into usable alloy. The die-casting manufacturer can also recycle the usable alloy mixed in the slag by itself. Furthermore, it can be sold to scrap dealers, smelters or alloy factories.

Die casting manufacturers recover the available zinc alloy die-casting waste by themselves. Usually, a special smelting furnace, a stirrer or other devices that can be used to mix molten metal and flux (slag remover) are required. Melting furnaces and storage furnaces used in the production of castings are generally not suitable for the treatment of slag. There are several different patented flux on the market, which can be used to separate the slag into usable metals, oxides and metal mesophase. If used properly, some of these fluxes will produce little or no smoke. Using these smokeless or low smoke fluxes will reduce exhaust emissions.