Improve the yield of Heat-resistant Steel Castings, and effectively control the defects
Analysis and research on the defects of Heat-resistant Steel Castings is one of the key technologies to improve the yield of Heat-resistant Steel Castings. However, its difficulty is not small. Mainly in:
① knowledge, such as alloy, casting process, modeling materials, casting equipment and production process testing and other aspects of knowledge.
② The reasons for the formation of defects in Heat-resistant Steel Castings, a defect can be caused by a variety of reasons, and one cause may cause several defects.
③ constraints of technical measures, such as the use of a measure, can prevent a type of defects, but may lead to another defect.
④ influencing factors difficult to control, such as raw material quality, air temperature and humidity.
In order to reduce the defects of Heat-resistant Steel Castings and improve the yield of Heat-resistant Steel Castings, it is necessary to effectively control the defects of Heat-resistant Steel Castings. The accurate judgment of the defect is a prerequisite for solving the defects of the Heat-resistant Steel Castings. Therefore, it is necessary for the foundry to understand the various means of the defect, including general and special means of analysis, to determine the type of defects, analyze the causes, and then put forward preventive measures, and from the technical and management to be implemented. It is noteworthy that, despite the same type of defects, but for different cast alloy Heat-resistant Steel Castings, the formation of the reasons and prevention measures are different.
Production conditions and problems The improvement in the quality requirements for heat-resistant cast steel has contributed to the development of new casting modeling methods and equipment. New modeling methods and equipment on the performance of sand made a higher demand, sand can be a good solution to heat-resistant steel production in the gas defects.
At present, some of China's foundry production of heat-resistant cast steel surface quality is poor, high scrap rate, the main reason is that the quality of raw materials used in the sand is poor. What are the factors that affect the quality of the Heat-resistant Steel Castings?
1, bentonite. Bentonite plays the role of binder in the sand, the wet bonding force, hot and humid bonding force and reusability is the main indicator of the quality of bentonite. If the quality of the bentonite used, in order to ensure the strength of the sand type need to add more bentonite, sand in the accumulation of non-cohesive dead clay will gradually increase.
2, the compaction rate of sand, that is, the degree of dry and wet sand. Sand is too dry, bentonite cohesive force can not give full play, will result in insufficient strength of sand, is not conducive to gas and other modeling methods on the sand compact, easy to break the sand, Heat-resistant Steel Castings prone to sand and sand Defects; sand is too wet, will cause the poor mobility of sand, sand is not easy to compact evenly, while too much moisture will cause Heat-resistant Steel Castings pores, pinholes, choking fire sand and other defects. Under normal circumstances, high pressure and impact modeling requirements of the molding station at the compaction rate of 35% to 40%.
3, the water content of sand is caused by Heat-resistant Steel Castings pinhole, porosity and other defects of a major factor. When the sand in the most appropriate dry and wet state, the lower the better the water content. The quality of bentonite and pulverized coal and the process of sand blasting directly affect the water content of sand. Foreign use of high-pressure modeling, gas-jet modeling methods to produce automotive Heat-resistant Steel Castings iron and ductile iron casting plant sand water content of most of the 2.3% to 3.8%.
4, sand wet strength reflects the sand to withstand a variety of external forces. Sand in the production process to withstand the mold, handling, under the core, type and other processes, in order to avoid damage and collapse, must have sufficient wet strength. During the pouring process, the sand is also subjected to the erosion and impact of the molten metal and the expansion force when the graphite is precipitated. These causes may cause defects such as sand, loose, and sand. Especially the engine block, cylinder head and other complex Heat-resistant Steel Castings, for the sand wet strength requirements are higher. Under normal circumstances, the sand in the compaction rate of 40%, the wet compressive strength of at least 0.18MPa.