Casting Process of Lost Foam for Anode Steel Claw

1.Part Analysis

Anode steel claws for electrolytic aluminum are also called electrolytic claws. There are parallel three claws, four claws, three-dimensional four claws, six claws, eight claws, double anode steel claws and other models. Holingol field anode steel claws are four claws. The anode steel claw is an important conductive part of the electrolytic aluminum industry. It forms an anode guide rod group together with the aluminum guide rod and the anode carbon block, which is used as the anode of the electrolytic cell and electrolytic aluminum.

2.analysis of casting process

According to the size of the sand box and the size of the parts of the polar steel claw, a casting scheme of one box and two pieces is selected. The foundry in Huolinguole area adopts the bottom casting process, I .e. the four claws of the anode steel claw are upward, and risers are placed on each claw for feeding. Combined with production, the advantages of this kind of casting scheme are obvious feeding effect, and the steel claws are not easy to have casting defects such as shrinkage cavity and shrinkage porosity. However, this kind of casting method has obvious disadvantages. 1. Burying the box is time-consuming and laborious. After burying the steel claws, it is necessary to scrape off the paint at the bottom of the claws and apply hot glue, and then place the risers; 2, the post-treatment is more complicated, to cut off each riser and then on the milling machine, time-consuming and laborious; 3. The most important thing is that the production rate of this casting scheme is low, resulting in high casting cost and lower enterprise profits. 4. Considering the size of the sand box, the height of the sand box is not suitable for bottom pouring, and the thickness of the bottom sand and the top sand is not enough. One is easy to damage the sand box, and the other is easy to cause the waste. Therefore, the top pouring scheme is adopted.

3.Process Engineering

Lost foam casting is divided into three parts: white area, yellow area and black area, and each part is closely linked and has strong correlation. No problems can occur in each part, otherwise qualified products cannot be cast.

1、 White area part

The white area part is the foam model making part, only the model size is qualified without defects can cast qualified products. There are two methods for making white molds, namely, manual cutting molds and molding molds.

The shrinkage of the anode steel claw is 0.02.

Manual cutting die needs to be equipped with cutting platform, voltage stabilizer, resistance wire, ps board, wallpaper knife, sandpaper, nails, paper tape and other items.

The first point of manual cutting is to make a template, which is engraved according to the size of the part plus the amount of shrinkage. Divide the anode steel claws into various parts and make templates respectively. Can be divided into: shoulder, riser, claw, welding guide rod platform four parts. Then according to the size of each part of the material, fixed template production white mold.

Attention should be paid to manual mold cutting. The size must be correct, the surface must be smooth, no grooves can appear, and the amount of adhesive is less, otherwise a large amount of gas will be generated. It is easy to reverse spray during casting to ensure that the four claws are on the same straight line.

The molding machine is divided into two parts: advance and molding.

The pre-hair process uses an electric pre-hair machine. Compared with the steam pre-hair machine, the pre-hair beads have low water content and full pre-hair.

The pre-release density is set to 23g/L, and it is easy to form when the pre-release density is large, but the gas volume is large during casting, and the carbon increase phenomenon occurs, and the pre-release density is small and it is not easy to form. The more important parameters in the advance process are advance temperature and advance time. Too high advance temperature will cause bead agglomeration, and too long time will also cause agglomeration. Adjust the time appropriately according to the temperature. Preheat the advance machine before advance, and start feeding advance after reaching the advance temperature.

At the scene of Huolingol, the advance temperature is set between 111 and 112 degrees, and the advance time is about 320s, which should be adjusted appropriately according to the situation. For the first three times of advance, the beads completed in advance should be weighed to check whether they meet the density requirements, and then adjust the parameters appropriately according to the results. When the advance density meets the requirements and is stable, continuous automatic advance can be performed. After the advance is completed, the discharging time should be adjusted appropriately. If the discharging is incomplete, the remaining material will agglomerate. Therefore, after discharging, check whether the barrel has no remaining material through the observation window.

After the pre-firing is completed, the beads arrive at the aging bin, and the beads can only be used after two hours of aging. The bead should not be placed for more than 48 hours, otherwise the pentane gas in the bead will be emitted, causing some difficulties in the molding process.

It is emphasized here that the severity of bead agglomeration. If the agglomeration is serious, the side plate of the pre-production machine needs to be disassembled to clean the pre-production machine, which is time-consuming, laborious and delays production. If several beads are agglomerated into a small piece, it will cause complicated feeding of the later forming machine, because the small bead agglomeration will block the muzzle of the material.

After the curing is completed, the curing beads will pass through the automatic feeding system to the forming machine silo. The automatic feeding system consists of a feeding fan, a feeding pipe and a ball valve. The operation that should be paid attention to in the process of automatic feeding is that the first step must be to turn on the fan before slowly opening the ball valve at the lower part of the curing bin. Because if the feed is too much, it will cause the fan to be blocked, causing the motor to overload and cause the motor to burn. On-site three molding machines, through the ball valve after each molding machine to reasonable feed each molding machine.

There is a ventilation valve on the feeding pipeline, and air is added at the same time of feeding to relieve the pressure of the fan and avoid material blocking.

After the mature beads reach the silo of the molding machine, they enter the mold through the feeding pipe. The production of white mold is more manual cutting mold, convenient forming, simple operation, high efficiency, clean and tidy factory.

The molding process mainly lies in the grasp of parameters. Mainly divided into three points, pressure, heating, cooling three parameters.

Generally, the minimum secondary curing pressure of beads is set to 0.6 to 0.7 pressures, and the high limit is about 1.2 pressures. Otherwise the beads will not bulge and mature. And the general pressure during the debugging of the molding machine is a fixed value and cannot be transferred at will. If there is a problem in the white molding process, it can be adjusted by adjusting the heating parameters and cooling parameters.

In the molding process of the molding machine, the heating method can be divided into two methods: time control and pressure control. The pressure penetration method is more intuitive, so Holingol adopts the pressure control method to heat the molding on site. The heating mode mentioned here is that when the solid mold and the moving mold are heated separately, the control mode of the main heating is the time control set by the program. After the heating mode is determined, the control amount of pressure heating can be set, that is, the number of steam penetration, where the number of penetration, that is, the number of times the pressure passes through the lower limit of the electric contact pressure gauge. The number of penetrations is appropriately adjusted according to the model made by the molding machine. If the white mold is not ripe (not ripe, that is, the foam beads do not stick together, and the beads will fall automatically when touched by hand), the surface of the solid mold is not ripe or the surface of the moving mold is not ripe when checking, and then the main heating time or the number of pressure penetrations is adjusted according to the situation. If it is a burning phenomenon (that is, white mold surface wrinkles or hard skin), you can shorten the main heating time or reduce the number of penetration.

After the white mold is cured and formed, it needs to be water-cooled. Because the white mold has not been fixed after molding, the whole is softened. If the water cooling time is insufficient, the most serious will cause the white mold to bend and deform, and the lighter surface will have small bumps like goose bumps, resulting in poor surface quality. Water cooling has a great influence on mold lifting. If the water cooling time is not enough, the white mold will stick to the surface of the mold and it is not easy to mold lifting. The water cooling time setting should be adjusted by the mold temperature and water temperature after mold lifting. When the water and the mold are neither hot nor cool, the mold is most suitable.

The forming mechanism makes half of the anode steel claw, and the two need to be butted and bonded before painting can be applied. During the bonding process, it should be noted that the two white molds should be closely aligned, and the butt joint should be sealed with paper tape, otherwise paint will leak into the white mold.

2. Yellow area

The yellow area is the painted part.

The first step in the yellow area is to stir the paint. Ruiou cast steel paint is selected. The stirring ratio of the paint to water is 1:0.75. The stirring time of the paint is 2.5 hours. After stirring slowly for two hours, the stirring time is half an hour. After stirring, the stirring time is 1.7 to 1.8.

In the process of coating brushing, it should be evenly painted. When the brushed model is painted again, it should not be soaked in the coating tank for too long, otherwise the coating will fall off. After each application, the next application will be carried out after the coating is dry. The painted model is placed in a drying room for drying. The temperature and humidity of the drying room affect the quality of the model. The temperature is set between 45 and 50 degrees. During the drying process, the white mold should not be too close to the heating, otherwise the internal deformation of the model will be caused. However, it is not easy to find the coating on the outside, and the residual products will be produced after casting. The humidity is controlled by the exhaust fan, and excessive humidity will cause the paint to dry. During the casting process, the moisture contained in the wet model will vaporize when encountering molten iron, and the upward water vapor will cause the phenomenon of "shooting. The thickness of the model coating completed by brushing should be between 1.5-2.5mm. If it is thick, the air permeability is poor, and if it is thin, the refractoriness is not enough.

Suggestion: Since the white mold made by the molding machine is composed of two pairs of butt joints, there is a gap in the middle of the two halves of the white mold, and the inside of the white mold is a cavity, so water vapor will enter the cavity through the gap during drying. Therefore, it is recommended to cut off the top of the riser after brushing the last coating, so that the inside of the model can also be ventilated and breathable, removing moisture entering the inside of the model.

According to the weather and temperature conditions on the site, heat preservation measures should be taken during the delivery of the model from the white area to the black area. As the temperature difference from the drying room to the outside is too large, the paint will be separated from the bone and the white model will shrink when cold.

2、 Black area part

The black area is the casting part, which is divided into two parts: buried box and casting.

The box-burying process is critical to lost foam casting. When burying the box, the bottom sand is added at the bottom of the sand box first, the thickness of the bottom sand is 100mm, then the bottom sand is leveled and put into the model. If the bottom sand is too thin, it may burn the screen mesh in the pores at the bottom of the sand box, and the uneven bottom sand is easy to cause deformation of the steel claw. After being put into the model, sand shall be added twice for compaction, and shall not be added to the riser once. After adding sand twice, cover the riser with a plastic film, and then add a layer of top sand to protect the plastic film. Otherwise, the plastic film will be scalded if the molten iron splashes out during the casting process, resulting in air leakage and pressure loss and box collapse. After the film is covered, a cross ring is added to the riser to prevent sand from flowing into the casting.

The design size of the riser of the Holingol field anode steel claw is 300mm high and 260mm in diameter. Compared with Heqing site can effectively prevent the emergence of shrinkage.

After the box is buried, push the sand box to the casting position of automatic docking, and make corresponding preparations before casting. The separation tank and negative pressure pipe in the negative pressure system shall be filled with water, and the interface shall be automatically extended to check whether the position is correct. Then open the negative pressure system, for the Holingol site, a box of two pieces should be cast separately, do not do the runner. Due to the large size of the anode steel claw casting, if the two steel claws are cast together, one riser of the two steel claws is a bright riser and the other is a dark riser. The feeding effect of the named riser is obvious, and the feeding effect of the dark riser is poor, resulting in shrinkage and porosity. Casting separately can avoid this phenomenon.

The degree of negative pressure during casting should be kept above 0.5 pressures and between 0.5 and 0.8 pressures. A box of two pieces should be completed within one minute of casting, follow the principle of slow casting, the time should not exceed one minute. And the casting process can not appear cut-off phenomenon, easy to cause the collapse of the box.

After the casting is completed, one of the two negative pressure pipes in the automatic docking system is closed, and the pressure is maintained for 15-20 minutes. After the pressure is maintained, the negative pressure is removed and the casting is kept warm for 2 hours. If the casting is turned over and out too early, the whole casting will be soft, which will cause deformation of the casting.

After two hours of pressure keeping, the used sand can be turned over to produce parts and enter the sand treatment process. After water-cooled sand dropping, the used sand enters the horizontal cooling for main cooling through screening conveying and chain hoist. After the sand temperature drops, the sand returns to the sand storage hopper through pneumatic conveying to achieve the recycling of sand.

4. Summary

According to production practice and theoretical analysis, it is necessary to ensure the dimensional accuracy of the white mold in the white area, the thickness and drying of the coating in the yellow area are thorough, the pouring temperature in the black area should be paid attention to, and the pouring speed should be controlled to meet the conditions. The anode steel claw will have a higher production rate and is not easy to produce waste products. However, the lost foam should pay attention to the production departments, otherwise the finished product rate will be greatly reduced.

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