Lost foam casting is one of the most advanced casting processes in the world at present, which is regarded as a revolution in casting history and "the main way of green intensive casting" in the 21st century. With the development of world industry, it plays a more and more important role in foundry production. Although lost foam casting has a wide range of adaptability, not all castings are suitable for lost foam casting, some castings can barely be done, but the process yield is low or the scrap rate is high. It also has technological limitations, such as foam patterns are easy to be deformed under force; compared with traditional casting methods, it also has the problem of pyrolysis and gasification of foam moulds. Lost foam casting defects also need to be fully understood and eliminated. The common casting defects in lost foam casting are wrinkling, carbon black, deformation, sand sticking, box collapse, stomata, slag inclusion, cold insulation and steel casting surface Carburizing, etc., the first few problems will be explained in the next time, this time the slag inclusion defects sanzhuji combined with their own experience and casting customers''''actual experience are summarized. 
1 slag inclusion defects in lost foam casting. 
Slag inclusion defects refer to the defects formed by dry sand particles, coatings and other inclusions along with the entry of molten iron into the casting during pouring. On the surface of the machined (shot peening) castings, white or black-gray inclusion spots can be seen, single or in pieces, white quartz sand particles, black-gray residue and other inclusions after pyrolysis of slag, paint, foam model. This defect, commonly known as "sand feeding" or "slag inclusion", is a very common defect in lost foam casting. Factories that use lost foam casting are almost universal and are difficult to eradicate completely. Only by taking a variety of measures and careful operation in each process can the "slag inclusion" be reduced to a very low level and satisfactory results can be achieved. Before the lost foam casting is cooled into the box, the sand feeding and slag inclusion defects can be determined according to the surface condition of the casting and gating system. If the sprue cup, sprue, cross sprue, inner gate and gate surface or joint, as well as the casting surface has serious sand sticking or crack sand sticking, it is almost certain that the casting has slag inclusion and sand feeding defects. When you break the sprue bar or sprue reinforcement, you can see that there are white spots on the fracture, and when the fracture is serious, a circle of white spots are formed. Such castings, especially plate-shaped and round cake-shaped castings, will have white and black-gray spot defects on the machined surface. If the process operation rules are not strictly controlled, the production of castings will seriously affect the quality of castings and the progress of order completion.
2 causes of slag inclusion and sand feeding defects. 
Through long-term observation in the foundry using our equipment, sanzhuji has proved that from sprue cup, sprue, cross sprue, inner sprue to castings, it is possible to cause sand feeding in all parts, especially the combination of gating system and castings. In the whole production process, the main causes of slag inclusion and sand defects are coating shedding cracking on the surface of white mold in gating system, coating shedding cracking in the bonding part of white mold, coating shedding cracking on the surface of foam white mold, intight sealing of sprue and so on. Secondly, the selection of process parameters, such as the size of the net pressure head of the gating system, pouring temperature, negative pressure, dry sand particle size, as well as the model transportation process and packing operation have a great influence on the slag inclusion and sand feeding defects of castings. Only by taking systematic measures and careful operation in these links can the slag inclusion defects of castings be reduced and basically eliminated and high quality castings can be obtained. Overcoming the defect of slag inclusion is a systematic project. 
3 methods and measures to reduce and overcome slag inclusion defects. 
The problem of sand feeding and slag inclusion is a difficult problem in lost foam casting. At present, the successful production of lost foam casting is mainly three types of products, namely, anti-wear parts, pipe fittings and box castings, which are rarely machined or unmachined. For castings with many machining surfaces and high requirements, slag inclusion defect is a key problem to be solved. Our experience is that measures can be taken to reduce and eliminate slag inclusion defects from the following aspects: 
3.1 paint, the function of lost foam coating is: 
Improve the surface finish of castings, reduce the roughness of castings by 2Mel, improve the surface quality and performance of castings, reduce and prevent sticking sand and sand hole defects are beneficial to sand removal and sand falling, and smooth discharge of liquid and gas from lost foam melting during pouring through the coating layer into the casting sand, and prevent liquid metal from infiltrating into the sand mold, prevent castings from producing pores, metal penetration and carbon defects to improve the strength and stiffness of the pattern. Preventing deformation and destruction during transportation and sand filling vibration molding is helpful to improve the dimensional accuracy and yield of castings. The coating for lost foam casting is required to have a series of properties, such as strength, air permeability, fire resistance, thermal insulation, explosive heat resistance, heat resistance, hygroscopicity, clearness, coating, suspension, immobility and so on. to prevent slag defects, the coating first requires high strength and fire resistance. It is required that the coating layer coated on the surface of the white mold should not produce cracks and cracks in the process of drying and transportation, that is, the coating should have sufficient room temperature strength; and in the pouring process, under the action of high temperature metal scouring for a long time, the coating layer should not fall off and do not crack, that is, it has high high temperature strength. When the liquid metal enters the mold, the direct gate is tightly closed, and the coating layer on the surface of the casting and gating system does not fall off, crack and crack are the primary conditions to prevent slag inclusion defects. if the gate seal is not tight, the coating layer will fall off, crack and crack, and a large number of sand particles, coatings and inclusions will enter the metal to form slag inclusion defects. Strength and air permeability are two important properties of coatings. sometimes the coating used in gating system is required to have higher fire resistance than casting coating in order to resist the erosion of high temperature metal for a long time without falling off and cracking. The operator must ensure the uniformity of the coating in the process of painting.
3.2 during the packing operation, the coating layer on the surface of the model group (model + gating system) is not allowed to fall off, crack or crack, especially in the joint of straight gate and cross gate, cross gate and inner gate, inner gate and mold, as long as there are loose, crack and unstable connection, it is possible to enter sand. This requires that the strength of the joint should be high, the coating should be relatively thick, the gating system should be rigid enough, and reinforcement or reinforcement sleeve should be set up if necessary. When the model group is placed on the sand at the bottom of the sandbox, it should be smooth, and when it is not allowed to be placed in the air, it will start sand blasting and vibration modeling, so as to avoid cracking the coating layer. Do not add sand violently to the appearance, first add sand with hose, vibrate in real time, and then sand with rain equipment. At the beginning of the vibration modeling, the vibration should be slight, the amplitude of the vibration should be small, and then shake sharply when the dry sand is buried. In the vibration molding, the gating system, especially the sprue, is not allowed to break or bend, so as to avoid the rupture of the coating layer, and the straight gate should be tightly closed to avoid sand. The whole process of packing, sanding, vibration and modeling should be very careful to ensure that there are no shedding, cracking and cracks in the coating layer of the pattern group before pouring. The sprue cup should be cleaned again before pouring to ensure that there is no floating sand, dust and sundries. 
3.3 with regard to the pouring head, temperature and time, the higher the head during pouring, the greater the erosion of the gating system and mold, and the greater the possibility of sand entry caused by the erosion coating, which is different for castings of different sizes. The pouring ladle with suitable capacity should be selected, the pouring height should be reduced as much as possible, the nozzle should be as close to the sprue cup as possible, and small work should be avoided. The higher the pouring temperature, the higher the requirements for the performance of the coating, and the easier it is to produce defects such as sticking sand and slag, so the appropriate pouring temperature should be chosen. For gray iron castings, the discharge temperature is about 1480 ℃, the pouring temperature is 1380Mel 1420 ℃, the pouring temperature of ductile iron castings is above 1500 ℃, the pouring temperature is 1420Mel 1450 ℃, and the pouring temperature of steel castings is 1480Mel 1560 ℃. The pouring time of a box of iron castings which need 300ml / 500kg of molten iron can be controlled at about 10m / m / 20s. 

3.4 the pouring process of negative pressure and lost foam casting is generally carried out under vacuum conditions. the function of negative pressure is to compact dry sand, accelerate exhaust and improve mold filling ability. pouring under vacuum sealing condition improves the working environment. The degree of negative pressure has a great influence on the quality of castings. Excessive negative pressure increases the possibility of inhaling dry sand and inclusions when liquid metal flows through cracks and cracks, and also increases the sand sticking defects of castings. The excessive mold filling speed increases the scouring ability of the metal to the sprue and mold, which is easy to make the paint fall off into the metal, and it is also easy to break the coating layer and cause sand. For iron castings, the suitable negative pressure is generally 0.025-0.04MPa.
3.5 setting slag-blocking, slag-skimming and slag-collecting risers, setting slag-collecting risers on the gating system, slag skimming and castings, and taking slag-blocking and slag-skimming measures are helpful to improve the defects of sand intake and slag inclusion. 
3.6 molded sand, too coarse and too fine of molded sand all affect the formation of slag inclusion and sticking sand defects, and excessive coarsening of molded sand results in the increase of slag inclusion defects. Iron castings are generally made of dry quartz sand (water-washed sand) with a particle size of 30pm 50. 
3.7 using hot metal purification technology, the problem of hot metal purification should be considered in the whole forming process of lost foam casting, which is one of the key technologies of lost foam casting. The purification problem should be considered in the whole process from molten iron melting, overheating to pouring into the mold, and filtration technology is one of them.

The above summary is the experience summary of sanzhuji and foundry in the actual casting process, if you are using lost foam casting, I hope it will be helpful to you, if you are going to use lost foam casting, you can contact me in time, I can provide you with a complete set of technical solutions and related equipment.

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.