Now the casting process of aluminum ingot china generally adopts the casting process, that is, the aluminum liquid is poured directly into the mold and taken out after cooling. The quality of the product is mainly at this step, and the entire casting process is also based on this process. The casting process is a physical process in which liquid aluminum is cooled and crystallized into a solid aluminum ingot.
1. Continuous casting
Continuous casting can be divided into two methods: mixing furnace casting and external casting. Both use continuous casting machines. Mixing furnace casting is to put aluminum liquid into the mixing furnace, and then cast by the mixing furnace. It is mainly used to produce aluminum ingots and casting alloys for remelting. Outer casting is directly cast into the casting machine by lifting the ladle. It is mainly used when the casting equipment can not meet the production, or the quality of the incoming material is too poor to directly enter the furnace. Because there is no external heating source, it is required to have a certain temperature for the ladle. Generally, it is 690 to 740 ° C in summer and 700 to 760 ° C in winter to ensure that the aluminum ingot has a good appearance.
For casting in the mixing furnace, the ingredients must be passed first, then poured into the mixing furnace, stirred evenly, and then added with flux for refining. The casting alloy ingot must be clarified for more than 30min, and the slag can be cast after clarification. During casting, the furnace eyes of the mixing furnace are aligned with the second and third casting molds of the casting machine, which can ensure that the liquid flow changes and there is a certain mobility when changing the mold.
The furnace eye and the casting machine are connected by a launder. The launder is shorter, which can reduce the oxidation of aluminum and avoid vortex and splash. When the casting machine is stopped for more than 48h, the mold must be preheated for 4h before restarting. The aluminum liquid flows into the casting mold through the launder, and the oxide film on the surface of the aluminum liquid is removed with a shovel, called dross. After flowing a full mold, move the launder to the next mold, the casting machine is continuously advancing. The casting mold advances in sequence, and the molten aluminum gradually cools. When it reaches the middle of the casting machine, the molten aluminum has solidified into an aluminum ingot, which is marked with a smelt number by the printer.
When the aluminum ingot reaches the top of the casting machine, it has completely solidified into an aluminum ingot. At this time, the casting mold is turned over, the aluminum ingot is released from the mold, and falls on the automatic ingot receiving trolley. ingot. The casting machine is cooled, but water must be supplied after the casting machine is turned full circle. Each ton of molten aluminum consumes about 8-10t of water, and in the summer, a blower is required to cool the surface. The ingot belongs to flat die casting, the solidification direction of the aluminum liquid is from bottom to top, and the upper middle finally solidifies, leaving a groove-shaped depression. The solidification time and conditions of each part of the aluminum ingot are not the same, so its chemical composition will also be different, but its overall conformity to the standard.
Common defects of 99.9% aluminum ingot used in remelting are:
①Stomata. The main reason is that the casting temperature is too high, there is more gas in the aluminum liquid, there are many air holes (pinholes) on the surface of the aluminum ingot, the surface is dark, and thermal cracks occur in severe cases.
② Slag inclusion. The main reason is that first, the slag is not clean, causing slag inclusion on the surface; second, the temperature of the aluminum liquid is too low, causing slag inclusion inside.
③Ripple and flash. The main reason is that the operation is not precise, the aluminum ingot is too large, or the casting machine is not running smoothly.
④ Crack. The cold crack is mainly caused by the casting temperature being too low, which makes the aluminum ingot crystal not dense, causing looseness and even cracks. Hot cracks are caused by high casting temperature. ⑤ Segregation of ingredients. Mainly caused by uneven stirring during casting of the alloy.