Basic technical requirements for EPC production in

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The basic technical requirements of lost foam production in small and medium-sized enterprises

Abstract: This paper introduces some problems that often occur in the production process of some small and medium-sized enterprises in lost foam casting production due to their insufficient understanding and attention to the technical problems of lost foam production, and points out the corresponding solutions adopted in production practice

key words: Lost Foam Casting; Model; Pouring; Paint

this paper introduces some problems that often appear in the production process of some small and medium-sized enterprises in the production of lost foam casting due to their insufficient understanding and attention to the technical problems of lost foam casting, and points out the corresponding solutions taken in practice

As a near static forming method of castings, EPC technology has developed rapidly in recent years. In foreign countries, due to the continuous completion and operation of mechanized and automated lost foam casting production lines and the remarkable economic and social benefits, the lost foam casting technology shows strong vitality. Although the application of lost foam casting technology in China made slow progress some time ago, it has developed rapidly in recent years. In particular, due to less investment in EPC equipment and short process route, many original small and medium-sized foundry enterprises are also increasingly adopting this technology. However, some enterprises fail to pay attention to some operation problems, which leads to some problems in the production process and has a great impact on the quality of castings

1. model making

in the lost foam casting process, model making is a very important link. The selection of EPS raw materials, the processing technology of the model, dimensional accuracy, model density, the amount of pyrolysis products during pouring and other factors are the premise of obtaining high-quality castings. The existing models of small and medium-sized enterprises can be made in the following ways: (1) cut and bonded with packaged EPS plates. (2) Self made molds and entrusted to foreign factories for processing. (3) Self made simple pre delivery molding equipment. Using the above method to make the model, there is a common phenomenon that we do not pay attention to the change of pattern density, especially when the model is commissioned to be processed by an external factory, the moisture is not easy to control, and there are often phenomena such as molten iron reverse spraying from the gate during pouring, or cold shut and insufficient pouring of castings. Therefore, in the production process, we should strengthen the inspection of the model density and increase the drying time of the model; After EPS beads are selected through process experiments, the raw material manufacturer cannot be changed at will; In advance, use weighing tools to control bead density, and change the method of controlling bead density based on manual experience; After adopting the above methods, the problem has been solved

2. Problems in vibration

vibration compaction is one of the four key technologies of EPC. The function of vibration is to make dry sand produce dynamic flow in the sand box, improve the filling property and density of dry sand, and prevent casting defects. When the dry sand is vibrated and filled, the ideal situation is that the dry sand flows orderly in the vibration process, and on the premise of ensuring that the model does not deform, it is evenly filled to all parts of the model, so that the molding sand in the sand box can obtain a higher and more uniform filling density. The vibration table of EPC in small and medium-sized enterprises is mostly self-made equipment. During vibration, the most common phenomenon is due to improper vibration operation, resulting in pattern deformation, coating layer cracking, etc., resulting in corresponding casting defects. Some vibration tables are easy to deform due to excessive exciting force and unbalanced polarization blocks of the same group of motors. Therefore, the exciting force, amplitude and vibration time should be adjusted; For castings with large size and simple structure, the three-dimensional vibration of six motors can be changed into the vertical or horizontal vibration of two motors in the heat management system with harsh requirements; In particular, the parameters of the shaking table are tested and adjusted by the testing instrument to make it meet the design requirements

3. problems in the use of coating

in the lost foam casting process, the use of coating can improve the rigidity and strength of the pattern, isolate the EPS pattern from the mold, and prevent sand sticking and mold collapse; During the casting process, the high-temperature decomposition products of the pattern are allowed to be discharged smoothly through the coating in time. Coatings are generally made of Jinan resin composites, silicon carbide semiconductor materials, Qingdao graphene materials, rubber materials, Zibo high-performance fluorosilicone materials, advanced ceramic materials, Yantai non-ferrous precious metal new materials, polyurethane, rare earth functional materials, Jining bio based polyamide, graphene materials, Tai'an high-performance glass fibers, Weihai carbon fibers, biomedical materials, etc, Laiwu special alloy and powder metallurgy materials, Liaocheng polycarbonate materials, etc. have high-profile composition within the temperature rise of 30 ℃ in China. The proportion of each component has a great impact on the performance of the coating. However, some enterprises are not very clear about the role of paint composition. They change the paint formula and preparation process at will, or continue to prepare and use when there is a lack of a component, resulting in a significant decline in paint performance; Some enterprises have problems in the pattern dip coating and drying process. Sometimes, in order to shorten the time, the next dip coating is carried out before the first coating is dry, resulting in insufficient drying inside the model, in which there is water; However, in summer, only air drying method is used, so there is instability in the process, resulting in backflow or porosity during pouring; The coating thickness did not notice that it changed according to different castings, pouring temperature and hot metal indenter

only by paying attention to and solving the above problems and working hard on the operation details, the casting defects caused by the coating will not occur

4. There are problems in the pouring process

during the pouring of EPC, in order to exhaust the gas and the gasification residue of the pattern, the sprue should have enough height to make the liquid metal have enough pressure head to promote the stable and rapid mold filling of the liquid metal flow, so as to ensure the integrity and clarity of the casting surface. In practice, some enterprises use the original sprue cup for sand casting, which is easy to cause the workpiece to be scrapped due to the unstable liquid flow due to its small size. In order to ensure that there is enough flow to make the pouring process flow continuously and quickly establish the starting head, a larger sprue cup can be used; The sprue is made hollow to reduce the gas generation and reverse injection and increase the pressure head at the beginning of pouring

EPC adopts negative pressure dry sand vibration molding, and the mold strength is much greater than that of green sand when using this method. The stability of the mold can be improved by using negative pressure pumping method, and the pyrolysis and gasification products produced during pattern gasification can be pumped away in time. However, in the production process, some factories only pay attention to the surface negative pressure before pouring, but the change of negative pressure is often ignored during pouring, resulting in casting defects. This problem can be solved by adjusting the negative pressure in the pouring process according to the size of the casting and the amount of pyrolysis products

5. Conclusion

due to its characteristics of less equipment investment and low cost, EPC technology has also been used in recent years, such as PPS, ASA, pctg and engineering alloy materials, and has also developed rapidly. Many original small and medium-sized foundry enterprises are also increasingly using this technology. However, some enterprises fail to pay attention to some operation details in the process of mold, coating, vibration method and pouring, which makes the casting quality unstable in the production process. This paper introduces these problems and improvement methods here, hoping to provide you with some reference. (end)

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