Analysis of common problems in the process of resin sand casting

In the production process of self-hardening resin sand casting, the following issues need to be paid attention to.

A. The operation of the equipment. 

1. Pay attention to the operation of dust removal equipment. In casting production, the operation of dust removal equipment is often not easy to find, but if the dust removal effect of the dust removal equipment is not good, it not only affects the working environment, pollutes the air, but more importantly, affects the fine powder content of recycled sand, and its direct result is to lead to an increase in the amount of resin added when mixing sand and an increase in the scrap rate of castings due to poor air permeability.

2. Pay attention to the operation of sand mixing equipment. Whether the sand mixer can operate normally directly affects the quality of the sand mixing, among which the amount of liquid material (resin, curing agent) added is the most critical. Under normal circumstances, the amount of resin is to control the voltage of the gear pump motor, the amount of curing agent is to control the voltage of the diaphragm pump motor, due to the change of season, weather changes, resulting in the change of liquid viscosity, in the case of the same voltage, the amount of liquid material will fluctuate, and the curing agent is easy to crystallize, causing valves and pipes to be blocked, therefore, the liquid pipeline should be cleaned every shift, and the amount of liquid material added should be tested every week to ensure the accuracy of the liquid material added.

B. Pay attention to the correctness and rationality of the formulated production process 

Whether the production process is reasonable or not directly affects the yield of castings, casting quality and casting costs, when formulating the production process, the following items should be mainly paid attention to:

1. Determine the LOI value of the appropriate recycled sand LOI value, that is, burning reduction, is an important index to measure the defilming rate of recycled sand, and it is also an index closely related to the gas generation of molded sand and the porosity defects produced by castings.

2. Determine the appropriate casting process parameters

(1) Determine the appropriate final strength  Generally, after the resin sand is mixed, after about 24 hours of self-hardening, the highest strength, that is, the final strength, can be achieved. Due to the different production conditions and production scale of each enterprise, the time interval from molding to pouring may not exceed 24 hours, so the determination of the final strength should be determined by the enterprise. Enterprises with smaller scale and one furnace system for several days can adopt the 24-hour final strength standard; For enterprises whose casting curing time does not exceed 24 hours, the strength achieved before pouring is the final strength standard. At the same time, it is necessary to overcome two tendencies in production: on the one hand, blindly increase the strength to ensure quality, so that the casting cost increases and causes waste; On the other hand, it is to reduce the strength in order to ensure the cost, resulting in unstable quality and a large range of fluctuations, so that the quality of the casting is greatly affected by the raw materials and operators.

(2) Determine the appropriate iron sand ratio Due to its high strength, molding after curing, and flat parting surface, self-hardening resin sand has a smaller amount of sand than clay sand, but its sand-iron ratio also has certain requirements. If the casting iron ratio is too high, the production process will not only waste resin and curing agent, but also produce large waste sand blocks, which will increase the burden on the regenerator, reduce the film removal rate, increase the LOI value, and increase the possibility of pores in the casting. If the iron-sand ratio is too low, it is easy to produce running fire during pouring, and the casting is easy to deform. According to our experience, the iron sand ratio should be 2.2~3:1.

(3) Determine the appropriate gating system  The thermal stability of furan resin sand is poor, there is data to introduce, when the amount of resin added in the resin sand is 1.4%-1.6%, its thermal stability is the best, but under normal circumstances, the amount of resin added is about 1.2%, therefore, the design principle of the casting system is to ensure that the metal liquid fills the casting cavity quickly and smoothly in the thermal stability time of the resin, therefore, when determining the gating system, ceramic tubes should be used as much as possible, and the inner gate is more and more dispersed.

C. Pay attention to the selection of raw materials 

The choice of raw materials has a great impact on casting production, because the quality of raw materials affects the quality of castings on the one hand, and the addition and consumption of various materials on the other. To this end, the following aspects should be considered:

1. Selection of raw sand Raw sand is divided into ordinary sand, washed sand, scrubbing sand and other categories. Because the mud content in the scrubbing sand is very small, so it can greatly reduce the waste of resin, should be preferred, and then choose washed sand, but must not use untreated raw sand. When choosing shaped sand, one should follow the principle of nearby selection to reduce transportation costs, and the other should try to choose raw sand with low angular coefficient.

2. Selection of resin The choice of resin directly affects the casting quality. If the poor quality resin is chosen, it not only increases the amount of resin added, but also affects the quality of the molding sand, resulting in an increase in casting waste, so the selection of raw materials can not only be determined according to the technical data provided by the manufacturer, but should have an understanding of the manufacturer's production equipment, production process and quality control methods, and try to inspect the various indicators of the resin by themselves or ask the relevant reputable inspection department to inspect, or learn from the experience of similar manufacturers. Or choose the products of well-known large enterprises with good reputation.

3. Selection of other raw materials Other raw materials include curing agents, coatings, binders, release agents, sealing mud strips, etc., the selection of these raw materials should not only consider their quality, but also consider their matching with the main materials such as procurement, transportation convenience and other issues. Because the impact of these raw materials on the quality of castings is not the main one, but the impact on the cost of casting cannot be ignored, such as the difference in the amount of curing agent, which not only affects the production efficiency of the molding process and affects the production cost, but also affects the material cost. In short, as long as the above aspects are paid attention to, not only can the casting meet the requirements of customers, but also reduce the cost of casting, bringing development and benefits to the foundry.