Why is the gating system of EPC not coated with paint?

Coating is one of the key technologies in EPC production. Production practice has proved that the success or failure of castings in EPC production depends on the quality of coatings 30%. In order to improve the strength of foam pattern, prevent its deformation and improve the quality of castings, refractory coatings are coated on the inner and outer surfaces of foam pattern to improve its surface strength, heat resistance, chemical stability, metal liquid corrosion resistance and sand adhesion resistance. So what is the coating process of EPC? Brief Introduction of EPC Coatings China is one of the earliest countries in the world to produce by casting, and also the first country to use refractory coatings. The use of paints can be traced back to the Han Dynasty. However, in the casting production of today's era, people have insufficient understanding of the importance of casting coatings; However, with the continuous improvement of the market requirements for the surface quality and internal quality of castings, the role of coatings is becoming more and more important. The application of coating is to prevent casting from producing defects such as sand sticking, sand inclusion, sand holes, air holes, surface carburization and sulfur increase. Effective measures to improve the surface quality and grade of castings, reduce the workload of cleaning castings, improve the working environment and improve economic benefits. EPC is a new casting method developed in 1980s. The performance and function of the coating greatly enhance the effect of EPC, and its quality not only affects the vaporization of foam pattern and the inhalation of gas; But also closely related to the surface quality, surface defects, casting accuracy and internal quality of castings. The EPC coating should have good coating properties, good suspension, suitable density, viscosity and rheological properties, as well as good air permeability, heat preservation, crack resistance, high and low temperature strength and sintering peeling performance. EPC coating technology 1, the first patent about this technology was published in 1958 (Shroyer, 1958), but its rapid development and application was still in the last twenty years, and it was widely used in the mass production of cast aluminum, cast iron and cast steel, especially the cylinder heads of automobiles and marine engines. Lost foam casting is to coat the foam model similar in size and shape to the casting with special refractory coating and dry it, then bury it in dry sand for vibration modeling and then pour it. The high-temperature liquid metal liquefied the model and occupied the position of the original foam model, and solidified and cooled to form the casting. Because of its original characteristics, the surface smoothness of castings obtained by this method is much higher than that of traditional clay sand casting and sand casting, and there is no need for core making, parting and sand sticking, which is easy to clean and has a good casting environment. It can be used to cast complex engine cylinder block and cylinder head, and provide more freedom in product design. 2. Interface reaction of metal/foam model/coating/molding sand. Refractory coating for EPC is the barrier between foam model and molding sand. In the pouring process, refractory coating is a part of the whole system of liquid metal/foam model/coating/molding sand. Therefore, a full understanding of a series of reactions in this whole system is helpful to understand the function and performance requirements of coatings in EPC process. The filling mechanism of metal in EPC process has always been a hot research topic. Amount of EPC coating: 1. Add about 80% water (1kg paint, water is about 0.8kg) according to the weight of the paint, stir for 1 hour, and then brush (medium or low stirring is best, with few bubbles). The amount of water added can be determined according to the brushing situation, but it should not be too much. Otherwise, the coating is too thin and the coating thickness can't meet the requirements. Too little water, high viscosity, difficult to brush, uneven coating, different thickness. 2, according to the process situation, generally brush 2-3 times. Thick parts with low negative pressure can be brushed for three times, and the coating thickness is above1mm. 3. The water content of dip coating process is about 85%, and it should be carried out under low-speed stirring. Suitable viscosity, dip coating twice can reach the appropriate thickness (0.8- 1.2mm). EPC coating 1 precautions for use, mechanical sand adhesion. The coating has high fire resistance, and chemical sand sticking will never occur. However, it has good air permeability. If the negative pressure is too high, molten steel will penetrate the paint, causing mechanical sand sticking. The recommended negative pressure is -0.03-0.04. The coating should be thin and uniform, and the inner gate should be thick. 2. carbon defects. The pouring temperature of thin-walled parts is low, which is easy to produce wrinkled skin and streamlined carbon residue. Generally, the temperature can be controlled around 1550 degrees. The above is the EPC coating process for you. EPC coating belongs to environmental protection coating, which can be used after adding water and stirring. The coating has good coating performance, does not flow, and is especially suitable for large-scale dip coating process. The coating has strong adhesion, no bubbles and no cracking.