The purification effect of the aluminum alloy melt in the furnace refining process is limited, and the melt is prone to secondary pollution in the flow process, so it is difficult to control impurities (hydrogen, alkaline metals, non-metallic inclusions) in the melt, In particular, during the high-temperature and rainy season from June to September each year, the porosity and inclusions in the ingot seriously affect its internal quality, resulting in a decrease in the yield of aluminum products. Therefore, on-line degassing device is a subject that has been the focus of research and improvement in our company's melting and casting branch. In recent years, several casting lines have undergone technological transformation, and three different on-line degassing devices have been installed: (1) Aplur rotary nozzle degassing device was used on the No. 1 foundry line and the 25 t production line. Since then, on the basis of the introduction of equipment, according to actual production conditions, a cost-effective and convenient degassing device was designed together with the supplier. (2) We added a simple and practical degassing device we developed on the 5# casting line. It was refined with multiple small rotors on the flow cell. The rotors were partitioned by partitions so that there was no metal between the castings. Retention, without heating insulation, operating costs substantially reduced, degassing effect is very good; this degassing device to avoid the general degassing device metal volume is large, cast dry material between the more dry material or need to heat insulation, high operating costs and other issues. (3) Make a compact degassing device. Its width and height are close to the flow channels, and fixed nozzles are provided at the lower side of the sides for air supply. The device occupies a very small area, has little dry material, is easy to operate, and has a high degassing efficiency. The degassing rate is more than 36% when the argon gas is used, and the cost is only 1/4 to 1/3 of the conventional degassing device. Reduce operating costs by more than 30%. We will use this degassing device in large quantities in the future. These sets of devices have proven to be effective not only in the purification but also in the environment. The following only describes the Aplur rotary nozzle degassing device in detail. The principle and flow of other degassing devices are similar.
1 Degassing process and principle Refined gas process: Inert gas storage tank → On-line degassing device Gas control cabinet → Graphite rotor nozzle → Treated aluminum alloy melt → Purify degassing treatment.
Working principle: A degassing device is placed between the holding furnace and the casting machine. In the degassing treatment pool, the nitrogen gas blown into the aluminum alloy melt is chopped by a rotating graphite rotor to form a large number of dispersed air bubbles, so that the aluminum alloy liquid and Nitrogen is fully contacted in the treatment tank. According to the pressure difference and surface adsorption principle, the gas bubbles absorb the hydrogen in the melt in the melt, and adsorb the oxidation slag (large in the manner of collision, small radial interception). Rising to the surface of the melt forms scum. The aluminum alloy melt flows from the outlet of the degassing device (located in the lower part of the scum) to the casting machine, and the aluminum alloy liquid continuously enters the degassing device, nitrogen is continuously blown in, and the purification of the aluminum alloy liquid is achieved along with the purification treatment. .
2 Main components of the degassing device 2.l The treatment tank treatment tank consists of two chambers, the clean room and the heating and heat preservation room, separated by SiC material partitions, and the bottoms of the two chambers are connected, and the aluminum alloy solution is removed in the clean room. After the slag is removed from the gas, it flows into the heat preservation room and is kept warm from the bottom of the partition. The heat preservation room is heated by immersing the aluminum alloy solution into the U-shaped silicon carbon holding jacket silicon carbide protection tube. The casing of the box is made of 10 mm steel plate. The inner lining is made by casting the whole refractory material. The upper side of the side wall is provided with observation and inspection slag, and the bottom is provided with slag cleaning port. Before and after the treatment box is a separate internal cavity. It is convenient for the heater to conduct directly, and the treated aluminum alloy liquid is transported under the subsurface. Under the proposal of our company, there is a slag door in the lower part of the two side walls of the box. The slag in the cavity can be completed without starting the box cover, prolonging the service life of the chamber inside the box, and the heat insulation performance is also improved. The reduction of heat compensation by the heater fully meets the requirements of the production process on the temperature; the enclosure is good, and the air can be prevented from entering the box and the aluminum alloy solution can be prevented from secondary pollution. With a hydraulic tilting device, it can be fully discharged after the casting work is finished or when the alloy is replaced. The inside of the tank can be completely emptied. The heater does not have to be electrically energized for a long time, which can reduce the power consumption relatively.
2.2 Lifting system In order to ensure its accurate positioning, two hydraulic cylinders are used as lifting devices, which are used to control the vertical up and down movement of the heating system of the graphite rotor and the U-shaped silicon carbide heater, and can be rotated in a 90° horizontal direction. The hydraulic system is relatively More stable and accurate positioning.
2.3 Heating System The heating system uses immersed heaters. U-shaped silicon carbide rods cover cylindrical silicon carbide or silicon nitride protection tubes. A thermocouple is provided in the tube to achieve automatic temperature control and the power can be arbitrarily adjusted within the range of 2 kW to 26 kW. The temperature control system uses a more advanced power integration unit to achieve full automatic control, to avoid the shortcomings of lack of buffer stage for heaters to turn on or off. U-shaped silicon carbide heaters are constantly subjected to main currents in frequent power-on and power-off. Unbuffered stage heaters are susceptible to aging and have a short life.
2.4 Graphite Rotors The rotating nozzles of graphite rotors are made of high-purity graphite. In addition to the structure of the nozzles, the bubbles should be dispelled. In addition, the centrifugal force generated by stirring the aluminum alloy melt is used to evenly mix the melt into the nozzle and the gas that is ejected horizontally. , The formation of gas / liquid jet, increase the contact area of ​​the bubble and the aluminum alloy liquid and contact time, improve the degassing purification effect. The rotational speed of the graphite rotor can be controlled by the inverter, up to 400 r/min. The graphite rotor size is Φ150 mm to 250 mm, and the impeller size is Φ250 mm to 350 mm. The high-purity anti-oxidation graphite rotor is characterized by high strength, high temperature resistance, and resistance to aluminum flow corrosion. During the process of purification and degasification, the surface of the aluminum alloy liquid inside the box is covered with nitrogen gas to protect the part of the graphite rotor exposed to the aluminum alloy liquid from being in an inert gas to prevent the high temperature oxidation of the rotor and extend the service life of the rotor. The impeller shape is streamlined and can be By reducing the resistance during rotation, the frictional flushing force between the impeller and the aluminum alloy fluid is also relatively small.
2.5 Control System The control system consists of two parts, gas and electrical, each with its own control cabinet.
(l) Gas control: Includes nitrogen and compressed air control with manual/automatic control. According to actual needs, according to the processing / maintaining the two states automatically adjust the argon supply, and through the electromagnetic gas flow meter can be seen in the computer operation screen accurate nitrogen flow, nitrogen flow automatically set according to process requirements, automatically lock to ensure the entire During the treatment, the nitrogen flow is even and stable, and the operation is convenient and reliable. The compressed air is mainly sealed between the lid and the box to ensure that the heat is not lost.
(2) Electrical control: The electronic control part mainly includes transmission control and temperature control. The transmission control unit controls the lift and rotation of the graphite rotor, and is equipped with a variable frequency stepless speed control device, so that the rotor can be speed-regulated without obstruction. The temperature control unit mainly controls the heating function of the heater. Electronic control system adopts PLC centralized control. The acquisition parameters of various control units enter the central processor. For each process parameter, the actuators are monitored on-line via human/machine operation screens. If there is a fault, the alarms are automatically triggered and can be remotely controlled.
1 Degassing process and principle Refined gas process: Inert gas storage tank → On-line degassing device Gas control cabinet → Graphite rotor nozzle → Treated aluminum alloy melt → Purify degassing treatment.
Working principle: A degassing device is placed between the holding furnace and the casting machine. In the degassing treatment pool, the nitrogen gas blown into the aluminum alloy melt is chopped by a rotating graphite rotor to form a large number of dispersed air bubbles, so that the aluminum alloy liquid and Nitrogen is fully contacted in the treatment tank. According to the pressure difference and surface adsorption principle, the gas bubbles absorb the hydrogen in the melt in the melt, and adsorb the oxidation slag (large in the manner of collision, small radial interception). Rising to the surface of the melt forms scum. The aluminum alloy melt flows from the outlet of the degassing device (located in the lower part of the scum) to the casting machine, and the aluminum alloy liquid continuously enters the degassing device, nitrogen is continuously blown in, and the purification of the aluminum alloy liquid is achieved along with the purification treatment. .
2 Main components of the degassing device 2.l The treatment tank treatment tank consists of two chambers, the clean room and the heating and heat preservation room, separated by SiC material partitions, and the bottoms of the two chambers are connected, and the aluminum alloy solution is removed in the clean room. After the slag is removed from the gas, it flows into the heat preservation room and is kept warm from the bottom of the partition. The heat preservation room is heated by immersing the aluminum alloy solution into the U-shaped silicon carbon holding jacket silicon carbide protection tube. The casing of the box is made of 10 mm steel plate. The inner lining is made by casting the whole refractory material. The upper side of the side wall is provided with observation and inspection slag, and the bottom is provided with slag cleaning port. Before and after the treatment box is a separate internal cavity. It is convenient for the heater to conduct directly, and the treated aluminum alloy liquid is transported under the subsurface. Under the proposal of our company, there is a slag door in the lower part of the two side walls of the box. The slag in the cavity can be completed without starting the box cover, prolonging the service life of the chamber inside the box, and the heat insulation performance is also improved. The reduction of heat compensation by the heater fully meets the requirements of the production process on the temperature; the enclosure is good, and the air can be prevented from entering the box and the aluminum alloy solution can be prevented from secondary pollution. With a hydraulic tilting device, it can be fully discharged after the casting work is finished or when the alloy is replaced. The inside of the tank can be completely emptied. The heater does not have to be electrically energized for a long time, which can reduce the power consumption relatively.
2.2 Lifting system In order to ensure its accurate positioning, two hydraulic cylinders are used as lifting devices, which are used to control the vertical up and down movement of the heating system of the graphite rotor and the U-shaped silicon carbide heater, and can be rotated in a 90° horizontal direction. The hydraulic system is relatively More stable and accurate positioning.
2.3 Heating System The heating system uses immersed heaters. U-shaped silicon carbide rods cover cylindrical silicon carbide or silicon nitride protection tubes. A thermocouple is provided in the tube to achieve automatic temperature control and the power can be arbitrarily adjusted within the range of 2 kW to 26 kW. The temperature control system uses a more advanced power integration unit to achieve full automatic control, to avoid the shortcomings of lack of buffer stage for heaters to turn on or off. U-shaped silicon carbide heaters are constantly subjected to main currents in frequent power-on and power-off. Unbuffered stage heaters are susceptible to aging and have a short life.
2.4 Graphite Rotors The rotating nozzles of graphite rotors are made of high-purity graphite. In addition to the structure of the nozzles, the bubbles should be dispelled. In addition, the centrifugal force generated by stirring the aluminum alloy melt is used to evenly mix the melt into the nozzle and the gas that is ejected horizontally. , The formation of gas / liquid jet, increase the contact area of ​​the bubble and the aluminum alloy liquid and contact time, improve the degassing purification effect. The rotational speed of the graphite rotor can be controlled by the inverter, up to 400 r/min. The graphite rotor size is Φ150 mm to 250 mm, and the impeller size is Φ250 mm to 350 mm. The high-purity anti-oxidation graphite rotor is characterized by high strength, high temperature resistance, and resistance to aluminum flow corrosion. During the process of purification and degasification, the surface of the aluminum alloy liquid inside the box is covered with nitrogen gas to protect the part of the graphite rotor exposed to the aluminum alloy liquid from being in an inert gas to prevent the high temperature oxidation of the rotor and extend the service life of the rotor. The impeller shape is streamlined and can be By reducing the resistance during rotation, the frictional flushing force between the impeller and the aluminum alloy fluid is also relatively small.
2.5 Control System The control system consists of two parts, gas and electrical, each with its own control cabinet.
(l) Gas control: Includes nitrogen and compressed air control with manual/automatic control. According to actual needs, according to the processing / maintaining the two states automatically adjust the argon supply, and through the electromagnetic gas flow meter can be seen in the computer operation screen accurate nitrogen flow, nitrogen flow automatically set according to process requirements, automatically lock to ensure the entire During the treatment, the nitrogen flow is even and stable, and the operation is convenient and reliable. The compressed air is mainly sealed between the lid and the box to ensure that the heat is not lost.
(2) Electrical control: The electronic control part mainly includes transmission control and temperature control. The transmission control unit controls the lift and rotation of the graphite rotor, and is equipped with a variable frequency stepless speed control device, so that the rotor can be speed-regulated without obstruction. The temperature control unit mainly controls the heating function of the heater. Electronic control system adopts PLC centralized control. The acquisition parameters of various control units enter the central processor. For each process parameter, the actuators are monitored on-line via human/machine operation screens. If there is a fault, the alarms are automatically triggered and can be remotely controlled.
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