Lost foam casting belongs to the category of “green and environmentally friendly casting” in the entire casting industry. Due to various advantages such as high dimensional precision and low production costs of castings, it is increasingly recognized by more and more domestic casting enterprises. However, at the same time of development, due to the imperfect performance of the pattern material, the use of lost foam (solid) casting in casting steel products can cause defects such as carbonization, porosity, and back spray, which greatly limits the promotion of this technology and severely restricts its application in cast steel. Without a complete set of supporting raw and auxiliary materials, steel casting enterprises have sought another hollow shell casting process of first firing and then pouring, but not Knowing to burn before pouring can only be limited to experimental small-scale production, which can cause a series of problems when producing large quantities of cast steel parts.
The lost foam (full mold) casting method is the most convenient casting operation method where various patterns are coated and directly placed into a sand box for pouring. Lost foam casting is a casting operation in which a white mold is first made, coated with a certain strength, and then placed in a sand box. It is first burned with an open flame and then injected with molten iron.
The comparison between the two operational processes is as follows:
Compared to the two casting methods, the solid casting method saves coating costs by reducing the thickness of the coating layer by 40% compared to the method of first firing and then pouring. In the entire operation, due to the need to make the coating with a certain strength by first firing and then pouring, the process, periodicity, time, energy consumption, etc. of applying the coating are more complex and costly compared to solid casting. Generally, the coating is applied 2-4 times more and takes 2-5 days longer. Lost foam casting involves burning the white mold pattern through various methods, but EPS contains 100% styrene, which has a benzene ring structure. After combustion, carbon tar is formed, which cannot be completely burned out. At the same time, when the carbon tar forms a hard block, even high-temperature molten steel cannot be completely burned, resulting in the presence of carbonization. Burn first and pour later compared to solid casting, with more complex process procedures When any production process changes, it will result in more production variables. First burn and then pour, during the burning process, a certain amount of negative pressure value of the sand box system will be lost. This requires that the vacuum system maintain a stable negative pressure in the sand box during the pouring process. This will cause certain unstable factors in process control. After comparing the above two process schemes, we can clearly understand the superiority of the solid casting method. However, the only fatal point of the solid casting method is the low-carbon and micro reverse spraying of the pattern material. Currently, the global
In the market of pattern materials, it is of utmost importance to find low-carbon, micro spray materials that meet the production requirements of solid casting. Based on this, we have developed a pattern material of expandable acrylic ester EMB (abbreviated as “EMB”) is used to address the quality issues required for solid casting methods.
When casting cast steel parts using lost foam (solid) casting technology, high-quality pattern materials are required: the appearance quality of the pattern, low carbon points, and the absence of backflow and curling phenomena are crucial technical points. Appearance: The original intention of EMB design was to draw inspiration from the appearance of Japanese JSP, allowing the pre packaged sphere to have a melt solubility, which enables us to obtain a more beautiful and smooth appearance surface during molding. Low carbon point: EMB only contains 10% styrene, and the carbon addition calculated from the styrene content is 3.2 carbons. The reason for backflow and gas entrapment: The rapid cracking of the sample material when it encounters molten iron is caused by the high content of pentane in the sample material. When the product is produced by one-step polymerization, its pentane content is wrapped around the core of the sphere. At the same time, due to its high molecular weight, higher pentane is required for pre molding and forming, resulting in a thicker skin and incomplete escape of pentane inside the sample, causing internal gas entrapment and backflow problems. At present, EMB products have improved this type of performance by adding a special locking agent. When the sphere is not pre cast, it can firmly lock the pentane. Once pre cast, it can run faster without affecting the molding process, resulting in a pentane content of less than 3% during casting to reduce internal gas entrapment and backflow. EMB, as a low-carbon product, has a higher content of acrylic esters than ordinary copolymers, with a gas volume of 904.14 mL/g. When we cannot change the total gas volume of the sample material, we can only reduce the backflow by uniformly burning the sample material and transforming it into uniform gas during combustion.
25Mn cast steel castings were successfully cast using EMB third-generation new pattern materials through solid casting. Lost foam casting is a seemingly simple but actually complex process, belonging to a systematic engineering. Every link in the entire production chain requires rigorous attention and cannot be ignored. Although the qualified castings have been obtained in this experiment, we will carry out mass production and gradually industrialize them Track experimental production, hoping to use this successful case to promote the development of lost foam casting in high-end casting products.