The production of wet molding clay sand steel castings abroad has a long history of application and development. According to the statistics of Japan Foundry Association in 1985, the production of Wet Mold clay sand steel castings in Japan accounts for more than 57% of the total steel castings, with a considerable proportion. Supported by its high-quality raw material supply and advanced process equipment, the United States has formed a complete production technology of wet molding clay sand railway steel castings. For example, Dreiser industries uses the wet molding clay sand process to produce steel castings including railway truck side frame, bolster, coupler, tail frame, impact seat and buffer.
On the one hand, the influence of the proportion of clay and molding sand on the properties of cast steel castings is also reflected in the theoretical analysis of the casting process.
O. A. olasupo, omotoyinbo, J.A., haeri, S.M., DAS, B.M. studied the physical and mechanical properties of molding sand with various additives such as sawdust, flour, cereal plants and refractory clay. F. F. o. orumwense studied the effects of moisture and sawdust on the collapsibility and brittleness of molding sand. D. Benny karunakar has established a network calculation system for molding sand properties, raw materials and process parameters. This system takes the original sand particle size, actual clay and moisture content as the input, and takes the molding sand properties such as green compression (tensile) strength and permeability as the output value. After comparing the output value with the actual molding sand properties, it is found that it is in good agreement. Based on this, the relationship equation between raw materials and molding sand properties is established. Crandell, G. pointed out that cellulose plays a good role in improving the expansion defects of wet molding clay sand steel castings.
Jidosha imono KK of Japan has proposed a patent that adding a mixture of methylcellulose and sodium polyacrylate into green molding clay sand can reduce the amount of water, make molding sand have better compactability and surface stability, and keep the wet compressive strength unchanged. Kas’yanov, i.m. proposed adding a corn derivative as an additive to the wet clay sand. The wet clay sand has good process performance. Clarke and Brian believe that in terms of ensuring the molding performance of molding sand, moisture should not be regarded as a measure. Even if the moisture content is the same under other conditions, the molding performance of molding sand is also different, and the moisture content should change with the change of other additives.
Barlow, Jo and others can accurately predict the occurrence of chemical sand sticking by using the thermodynamic model between liquid steel and wet mold and considering carbon diffusion. Draper, A.L. mainly studied the influence of the atmosphere in the mold on the penetration of liquid steel into the wet mold. The penetration is obvious in the oxidizing atmosphere, and the neutral and vacuum can avoid the penetration. At the same time, it is pointed out that the increase of molding sand moisture, the weakening of compaction and the increase of sand particle size will promote the penetration. The British foundry workers’ Association has proposed a new type of Wet Mold clay sand coating without drying before pouring. This coating will not affect the mold performance, is non-toxic, harmless and low cost. Hess, K studied the relationship between the allowable maximum mold filling time of Wet Mold clay sand steel castings and pouring temperature, formability and dimensional accuracy of steel castings.
It can be seen from the above that there are few units engaged in the research of wet molding clay sand steel castings in China. Although there are some successful examples, there is a big gap in theory compared with foreign countries. Abroad, both technically and theoretically, has entered a more mature stage. In recent years, the number of units engaged in the research and development of green clay sand components is decreasing day by day. The technological progress and innovative practice of green clay sand are more concentrated in the fields of green clay sand quality control and rapid detection of molding sand performance. There are many factors affecting the process of green molding clay sand, which are greatly affected by environmental factors. Therefore, in order to obtain satisfactory molding sand performance, molding sand quality control is particularly key, which involves the development of new equipment and new control system. The performance test of green clay sand molding sand is basically completed by manual test in the laboratory and production line, with poor accuracy, great influence of human factors, real-time and weak representativeness. Therefore, it is necessary to develop a computer online test system for the performance of green clay sand molding sand. It can quickly reflect and use the calculation program to directly control the addition of components, adjust the molding sand performance to the target performance value and control it accurately, It can effectively ensure the quality of molding sand and reduce the scrap rate of steel castings. Therefore, in the future, more and more automatic testing instruments and equipment for molding sand performance will be used in the production of green molding clay sand process, which will develop in the direction of digitization, miniaturization, continuity and systematization.