Nowadays aluminum ingot forging technology usually adopts casting technology, that is, pouring aluminum liquid directly into the mold and taking it out after cooling.
The quality of the product is mainly in this process, and all forging technology is also based on this process. The forging process is a physical process in which liquid aluminum is cooled and crystallized into solid aluminum ingots.
1. Continuous casting
Continuous casting can be divided into two methods: mixing furnace casting and external casting. Both use successive forging machines. Mixing furnace casting is the process of casting molten aluminum into the mixing furnace and then casting from the mixing furnace. It is mainly used to produce aluminum ingots and forged alloys for remelting. Outer casting is carried out by lifting the ladle directly to the forging machine. It is mainly used when the forging equipment cannot be produced satisfactorily, or the quality of the incoming material is too poor to directly enter the furnace. Because there is no external heating source, it is necessary to carry a certain temperature, usually 690 ~ 740 ℃ in summer and 700 ~ 760 ℃ in winter to ensure that the aluminum ingot has a good appearance.
Mixing furnace casting, first through the ingredients, and then poured into the mixing furnace, mix evenly, and then participate in the flux for the essence. It is necessary to clarify the alloy ingot for more than 30min. After clarifying, the slag can be cast. During casting, the furnace eye of the mixing furnace is aligned with the second and third casting molds of the forging machine, so as to ensure a certain mobility when changing the liquid flow and changing the mold. The furnace hole and the forging machine are connected with a flow slot. The flow slot is shorter, which can reduce the oxidation of aluminum and avoid the formation of vortexes and splashes. When the forging 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 the die is full, the launder is moved to the next casting die, and the forging machine runs one after another. The casting mold moves in sequence, and the molten aluminum gradually cools. When it reaches the middle of the forging machine, the molten aluminum is now condensed into an aluminum ingot, which is marked with a smelt number by the printer. When the aluminum ingot reaches the top of the forging machine, it has been completely condensed into aluminum ingots. At this time, the casting mold is turned over, the aluminum ingot is released from the mold, and falls on the active ingot receiving trolley.The stacking machine actively stacks and bales it. Products aluminum ingots. The forging machine is cooled by water spray, but it is necessary to feed the water after the forging machine is turned full circle. Each ton of aluminum liquid consumes about 8-10t of water. In the summer, a blower is required to cool the surface. The ingot is attributed to flat die casting. The direction of the aluminum liquid condensation is from bottom to top. The center of the upper part finally condenses, leaving a groove-shaped depression. The coagulation 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 specifications.
The common disadvantages of aluminum ingots for remelting are: ① Porosity. 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 first reason is that the first is that the slag is not clean, which constitutes the surface of the slag; the second is that the temperature of the aluminum liquid is too low, which constitutes the internal slag. ③Ripple and flash. The first is that the operation is not precise, the aluminum ingot is made too large, or the casting machine is not running smoothly. ④ Crack. The cold crack is mainly caused by the casting temperature is too low, so that the aluminum ingot is not crystallized densely, which constitutes a loose or even crack. Hot cracking is caused by the high casting temperature. ⑤ Segregation of ingredients. The first is caused by uneven mixing when forging the alloy.
2. Vertical semi-continuous forging
Vertical semi-continuous forging is mainly used for the production of aluminum wire ingots, plate ingots and various deformed alloys for processing profiles. The aluminum liquid is poured into the mixing furnace after the ingredients, because of the special needs of the wire, it is necessary to participate in the central tray Al-B to remove the titanium and vanadium (wire ingot) in the aluminum liquid before forging; the plate ingot needs to participate in the Al-Ti–B alloy (Ti5%B1%) for detailed treatment. Make the appearance arrangement finer. The high magnesium alloy is added with 2# refined agent, the dosage is 5%, and the mixture is evenly mixed. After standing for 30 minutes, the scum is stripped and can be cast. Before casting, the chassis of the forging machine is raised, and the moisture on the chassis is blown off with compressed air. Then raise the chassis into the crystallizer, apply a layer of smooth oil to the inner wall of the crystallizer, put some cooling water into the water jacket, put the dry and preheated distribution plate, active conditioning plug and flow groove, so that the distribution plate A mouth is located in the center of the crystallizer. At the beginning of casting, press the active conditioning plug by hand, block the flow nozzle, cut the furnace eye of the mixing furnace, and let the aluminum liquid flow into the distribution plate through the flow groove. When the aluminum liquid reaches 2/5 in the distribution plate, the active Adjust the plug so that the molten aluminum flows into the crystallizer, and the molten aluminum is cooled on the chassis. When the liquid aluminum reaches 30mm high in the crystallizer, the chassis can be lowered, and cooling water is started. The active conditioning plug controls the liquid aluminum to flow into the crystallizer in a balanced manner, and insists that the aluminum liquid in the crystallizer has the same height. The scum and oxide film on the surface of the aluminum liquid should be removed in time. When the length of the aluminum ingot is about 6m, block the furnace eye, remove the distribution tray, stop the water supply after the aluminum liquid has completely condensed, remove the water jacket, take out the cast aluminum ingot with a monorail crane, and follow the required scale on the sawing machine Saw off, then prepare for the next casting.
During casting, the temperature of the molten aluminum in the mixing furnace is maintained at 690-710°C, the temperature of the molten aluminum in the distribution tray is maintained at 685-690°C, the forging speed is 190-21Omm/min, and the cooling water pressure is 0.147-0.196MPa. The forging speed is proportional to the wire ingot with a square cross section:
VD=K
Where V is the forging speed, mm/min or m/h; D is the ingot section side length, mm or m; K is the constant value, m2/h, usually 1.2 to 1.5.
Vertical semi-continuous forging is a sequential crystallization method. After the aluminum liquid enters the casting hole, it starts to crystallize on the chassis and the inner wall of the mold. Because the cooling conditions of the center and the side are different, the crystal constitutes a mode with a low center and a high periphery. The chassis is lowered at a constant speed. The upper part is continuously injected with aluminum liquid, so that there is a semi-condensing area between the solid aluminum and the liquid aluminum. Because the aluminum liquid is shortened when condensing, plus a layer of smooth oil on the inner wall of the crystallizer, with the lowering of the chassis, the condensed aluminum After exiting the crystallizer, there is also a circle of cooling water eyes in the lower part of the crystallizer. The cooling water can be sprayed onto the surface of the aluminum ingot that has been taken off for secondary cooling, until the entire wire ingot casting is stopped.
Sequential crystallization can establish more satisfactory coagulation conditions, and it is more favorable with regard to the crystal size, mechanical properties and electrical conductivity. Compared with the ingots, there is no difference in mechanical properties in the height direction, the segregation is also smaller, the cooling rate is faster, and a very fine crystallization arrangement can be obtained.
The surface of the aluminum wire ingot should be flat and smooth, without slag, cracks, porosity, etc. The length of the surface crack is not more than 1.5mm, the depth of the surface slag and ridge wrinkle cracks should not exceed 2mm, and the cross section should not have cracks, pores and slag, less than There are no more than 5 slag inclusions in lmm.
The shortcomings of aluminum wire ingot mainly include: ① cracks. The reason for this is that the temperature of the aluminum liquid is too high, the speed is too fast, and the residual stress is increased; the silicon content in the aluminum liquid is greater than 0.8%, which generates aluminum silicon and the same melt, and then generates certain free silicon, which increases the thermal cracking of the metal: Or lack of cooling water. When the mold surface is rough or smooth oil is not used, cracks may also occur on the surface and corners of the ingot. ② Slag inclusion. The slag inclusion on the surface of the aluminum wire ingot is caused by the shaking of the aluminum liquid, the cracking of the oxide film on the surface of the aluminum liquid, and the appearance of the scum on the side of the ingot. Sometimes smooth oil can also bring some slag. The internal slag is formed because the temperature of the aluminum liquid is too low, the viscosity is large, the slag cannot float in time, or the aluminum liquid surface changes frequently during casting. ③ Cold partition. The main reason for forming the cold partition is that the liquid level in the crystallizer is too large, the casting temperature is low, the ingot speed is too slow or the forging machine vibrates and reduces unevenness. ④ Porosity. The stomata here refers to small stomata with a diameter less than 1 mm. The reason for this is that the casting temperature is too high and the condensation is too fast, so that the gas contained in the aluminum liquid cannot escape in time. After condensation, it gathers into small bubbles and remains in the ingot to form pores. ⑤ The appearance is rough. Because the inner wall of the crystallizer is not smooth, the smoothing effect is not good, and it forms an aluminum knob on the surface of the crystal when severe. Or because the iron-to-silicon ratio is too large, uneven cooling occurs. ⑥ Aluminum leakage and re-analysis. The first is the operation problem, and the severe ones also constitute tumor crystals.
3. Guarantee of ingot quality
(1) Aluminum ingot for remelting. The most important technical condition in the process of ingot casting is the casting temperature. During the casting process, it is necessary to strictly control the casting temperature, which is usually 30 to 50°C higher than the condensation temperature of the molten aluminum.
(2) Wire ingot. The casting of the wire ingot is slightly more complicated, and the condition to be controlled is the ingot speed. The ingot speed is related to the ingot diameter. The casting temperature is maintained at 680～690℃, the cooling water pressure is 0.147～0.196MPa, and the aluminum liquid on the inner wall of the crystallizer is controlled horizontally at 30mm. You can achieve better quality by manipulating the above conditions and stepping up operations.
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