(2) Use appropriate coating: In the production of steel castings by EPC, coating is an important factor affecting carburizing defects of steel castings. Choosing a coating with good air permeability can reduce the amount of carbon increase. Appropriate reduction of coating thickness can also significantly improve the permeability of the coating. In addition, the wettability of Chu material also has a great influence on carburization of castings. Generally speaking, the pouring temperature of EPC is 40-80 "12 higher than that of clay sand process, and the box is generally higher than 1420℃. The pouring methods can be bottom pouring, step pouring and top pouring. For large-area or tall castings, try to use scattered multiple internal sprues or layered pouring to avoid too concentrated sprues. When designing risers, try to use concealed risers. It is also possible to place a small-sized slag collecting riser at the position where carbon defects are easy to appear gradually, so that the liquid containing liquid residues at the front of molten metal can float to the slag collecting riser during mold filling, which can reduce the carburization of castings and improve the quality of castings.
(3) selecte a reasonable pouring proces: selecting a higher pouring temperature, and raise that pouring temperature as much as possible on the premise of not generating sand inclusion and bonding,
(4) Select appropriate negative pressure: Under negative pressure, the decomposition products of EPS will diffuse out of the mold cavity, thus reducing the reaction time of contact with molten metal. Practice has proved that this method can reduce the carburization of castings. However, the negative pressure can't completely discharge the gaseous and liquid products in the gap. If the negative pressure is too large when the molten metal is filled, it will produce the wall-attached effect, which is easy to form turbulence, so that the pattern and its decomposition products will be involved in the molten metal, resulting in defects such as porosity and slag accumulation. Therefore, we should pay attention to the reasonable selection and application of negative pressure. For general steel castings, the negative pressure can be controlled at 0.03'-0.05 MPa.
(5) Properly change and adjust the structural shape or machining allowance of parts: as the casting structure (shape, size, specific surface area, wall thickness, etc.). ) has an influence on carburization, which should be paid attention to in the process of part design, and the casting structure should be simplified as much as possible to remove the redundant part of the casting thickness as much as possible. For the dead corners with slight carbon defects that are not easily eliminated locally, the machining allowance can be appropriately increased to remove the defective parts after machining.
(6) In addition, with the development of EPC technology in China, some new casting processes have emerged, which can also greatly reduce the defects of increasing carbon and hydrogen. Zhao Guang, general manager of Jiangxi Fengyuan Cast Steel Co., Ltd., introduced Mr. Liu Lizhong's "Carbon Emission Law" at the 4th National Technical Exchange Seminar for General Contracting Enterprises. In this method, a large riser is used to replace the gating system, and the top injection method is adopted under high negative pressure. According to reports, due to the large riser, air can smoothly enter the cavity under negative pressure, which accelerates the combustion of the pattern and effectively removes the combustion products from the mold. This method effectively reduces the defects such as carbon enrichment and hydrogen enrichment caused by residual carbon in the pattern. Professor Liu Yuman of China Academy of Management Sciences put forward the EPC method, which can also reduce the influence of hydrocarbon patterns on casting quality, but this technology was only used in the production of simple and thick parts at that time.
In a word, there are many factors that cause carburizing defects in EPC steel castings, and it is impossible to solve the problem by adjusting only one factor or parameter. Instead, we should comprehensively consider the above factors, combine the actual situation of our unit, pay attention to the combination of practice and theory, and work out the best scheme after repeated exploration to achieve the purpose of eliminating and reducing carburizing defects.
Lost foam casting technology is to combine foam plastic models similar in size and shape to castings into model clusters, brush them with refractory paint, dry them and bury them in dry quartz sand for vibration modeling. Under certain conditions, liquid metal is poured to vaporize the models and occupy the model position, and then the required castings are formed after solidification and cooling.