Common casting method of aluminum ingot-continuous casting
Continuous casting can be divided into two ways: mixing furnace casting and external casting. Continuous casting machines are used. Mixing furnace casting is to pour liquid aluminum into the mixing furnace and then cast by the mixing furnace. It is mainly used to produce aluminum ingots and casting alloys for remelting. External casting is directly cast into the casting machine by lifting the bag, mainly in the casting equipment can‘t meet the production, or the quality of the incoming material is too poor to be directly used in the furnace. Because there is no external heat source, it is required to carry the bag with a certain temperature, generally 690 ~ 740℃ in summer and 700 ~ 760℃ in winter, in order to ensure that the aluminum ingots have a better appearance.
Mixing furnace casting, first through the ingredients, and then poured into the mixing furnace, mixing evenly, and then add flux for refining. Casting alloy ingots must be clarified for more than 30min, after clarification, slag can be cast. When casting, the furnace hole of the mixing furnace is aligned with the second and third molds of the casting machine, so as to ensure a certain flexibility when the liquid flow changes and the mold changes. The furnace hole and the casting machine are connected by a flow groove. It is better to have a shorter flow groove, which can reduce the oxidation of aluminum and avoid eddy and splash. When the casting machine is stopped for more than 48h, the mold should be preheated for 4h before restarting. The liquid aluminum flows into the mold through the flow groove, and the oxide film on the surface of the liquid aluminum is removed with a shovel, which is called slag raking. When a mold is filled, the flow slot is moved to the next mold. The casting machine moves continuously. The mold progresses in turn, and the molten aluminum gradually cools. When it reaches the middle of the casting machine, the molten aluminum has solidified into aluminum ingots, and the smelting number is marked by the printer. When the aluminum ingot reaches the top of the casting machine, it has been completely solidified into aluminum ingot. At this time, the casting mold turns over, and the aluminum ingot is released from the mold and falls on the automatic ingot pickup car. The stacker automatically stacks and bales the finished aluminum ingot. The casting machine is cooled by water spray, but the water can only be fed after the casting machine is started for a full circle. Each ton of liquid aluminum consumes about 8-10t of water. In summer, it needs to be cooled by a blow blower. The ingot is a flat mold casting, the solidification direction of liquid aluminum is from the bottom to the top, the middle of the last solidification, leaving a trench shrinkage. The solidification time and conditions of different parts of aluminum ingot are not the same, so its chemical composition will be different, but on the whole it is in line with the standard.
The common defects of remelting aluminum ingots are:
(1) Pores. The main reason is that the casting temperature is too high, the liquid aluminum contains more gas, and the surface of the aluminum ingot is full of pores (pinholes), and the surface is dark, and hot cracks are generated when it is serious.
(2) The slag. The main reason is that one is not clean, resulting in surface slag inclusion; Second, the temperature of liquid aluminum is too low, resulting in internal slag inclusion.
(3) Ripples and frills. The main reason is that the operation is not fine, the aluminum ingot is too big, or the casting machine is not running smoothly.
(4) Crack. Cold crack is mainly casting temperature is too low, resulting in aluminum ingot crystallization is not compact, resulting in loose and even crack. Thermal cracks are caused by high casting temperature.
(5) Composition segregation. It is mainly caused by uneven stirring when casting alloy.
