Lost foam casting is a new casting process with more promising applications. It uses polystyrene foam as a one-time pattern, and uses dry sand without any additives. The mold maintains a certain degree of negative pressure during pouring and solidification. Therefore, using this process, a smooth surface, precise size, and no Castings with flash and dense structure have significant advantages in the production of wear-resistant steel castings.
1. The process of lost foam casting
1.1 Production of foam plastic mold
The dimensional accuracy and surface finish of lost foam castings depend on the quality of the foam pattern. In the experiment, domestic foam plastic sheets were used as the sample material. The requirements for foam plastic sheets are: good internal quality, no pinching and looseness defects; light density, good strength and surface rigidity; density generally within the range of 0.015~0.025g/cm3. The pattern is made by heating wire cutting and hand polishing.
1.2 Coating and coating process In lost foam casting, the foam pattern and the outer surface of the pouring system must be coated with paint. Sanzhuji and the foundry chose water-based paint for experimental casting. The key to coating trial production is to solve the problem of poor wettability of water-based coatings and patterns and difficult coatings. When formulating coatings, the problem of non-wetting of coatings and foam plastics was solved by adding appropriate surfactants and other additives. The trial-produced coatings have good passability, high strength, and certain air permeability. Sanzhuji passed the laboratory The test and the production verification of the foundry enterprise show that the coating process of the coating is: coating large castings by shower brushing method, and dip coating method for small castings. Coating thickness is an important factor affecting the quality of castings. The best coating thickness depends on the size and complexity of the casting. The coating thickness is controlled by adjusting the coating concentration, the number of coatings and the coating operation. Generally, the coating thickness is 3 times. Control within 0.5~3mm. After the paint is applied, it is dried in a drying room at 40-50 degrees Celsius.
1.3 Buried sand lost foam casting adopts dry sand modeling without adhesive, which mainly requires the mold to have good air permeability and uniform and sufficient compactness. Single quartz sand is selected for molding sand, with a particle size of 0.360~0.210mm. The temperature of molding sand should be controlled during use to prevent the shape from being deformed due to excessive temperature. The sand temperature should be lower than 50 degrees Celsius. When buried, the recesses and slots of the casting should be placed on the top and side as much as possible. If it must be placed underneath, the depression must be tamped manually. The number of castings placed in each box is based on the size of the castings. Generally, the spacing is controlled between 100~300mm. The air extraction hoses are evenly arranged around the castings to ensure uniform mold compactness.
1.4 Negative pressure pouring Lost foam casting During pouring and cooling, the mold must maintain a certain degree of negative pressure. Sanzhuji recommends the use of a vacuum negative pressure system, which consists of a water ring vacuum pump, a dust removal purifier, a vacuum tank, a control valve and a sand box. The strength of the mold is closely related to the degree of negative pressure. When the mold negative pressure is greater than 0.025MPa, the mold can maintain sufficient strength and stability. The vacuum degree of the test vacuum tank was 0.08MPa, which was reduced to 0.06MPa during the pouring process. After pouring, determine the delayed vacuuming time according to the size and wall thickness of the casting, so as to solidify the casting under negative pressure and prevent the casting from producing expansion defects. For castings with a medium thickness of 20 to 30 mm, it is generally 3 to 5 minutes.
1.5 Heat treatment of high manganese steel castings In order to obtain a single austenite structure, high manganese steel castings require water toughening treatment. Since high manganese steel has no phase change in the solid state, heat treatment cannot change the grain size of high manganese steel. The improved solid casting can control the boxing time arbitrarily, and the operation is very convenient, so that the castings are boxed at a relatively high temperature. The castings are cooled for a period of time after pouring. The vacuum pump is turned off. The dry sand is in a loose state until the castings are cooled to about 1100 degrees Celsius. Lift out of the sand box and enter the water to cool rapidly. This process is feasible for negative compaction casting of high manganese steel castings. If the process factors are properly controlled, the castings can meet the quality requirements of high manganese steel. The process factors that should be controlled for the direct water quenching process in the cooling process of high manganese steel are: the opening time of the casting and the water entering time. In the test, according to the size and wall thickness of the casting, the solidification time and cooling rate of the casting are estimated, and the time from pouring to cooling to 1100 degrees Celsius is obtained. Finally, the appropriate unpacking time is determined through the test to ensure that the casting is at a high temperature. Water entering at 950°C prevents the precipitation of carbides and reduces the toughness of high manganese steel castings.

2. The superiority of lost foam casting. The production of high manganese steel castings by lost foam casting can show its superiority and solve the problems that are difficult to solve by other casting methods.
2.1 During the design of the casting process, the draft angle and parting surface of the mold are not required, and the dimensional accuracy of the casting is high; the surface finish of the casting obtained by painting the surface can reach the level of investment casting; because the casting can be placed arbitrarily in the mold, The gating system is flexible to set up, the riser and the chilled iron are convenient to place, and it has the effect of negative pressure suction, which is beneficial to the feeding of the casting, and can reduce or eliminate the shrinkage and looseness in the casting.
2.2 High manganese steel anti-wear castings, when a single piece is produced in a small batch, no wooden mold is required, the production cost is low, and the production cycle is short. Mass-produced liner and jaw plate castings are difficult to machine. Generally, they are directly used as blanks. The castings are required to be accurate in size and shape, especially the keyhole spacing requirements are strict. Small holes must be cast, so it is most suitable for negative use. Compaction casting process.
2.3 The most common defects in the production of high manganese steel castings by the lost foam method are wrinkles, slag inclusions and pores. Corresponding measures should be taken mainly from the pattern, sand, coating, pouring temperature and pouring system to overcome the above casting defects and obtain Sound castings.

Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of sand reclamation equipment,foundry machines,Sand casting equipment,GS high efficiency rotary mixer,no-bake resin sand mixer,Jolt squeeze molding machine/Jolt-squeezing moulding machines,Multi- Piston Moulding Machine/Hydraulic multi-piston moulding machine,foundry molding machine,flaskless moulding machine,shot blasting machine,dust collector,according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.