Detailed explanation of resin sand casting process
1、 Analysis of common problems in resin sand casting process
Since self setting resin sand casting has the advantages of good surface quality, high dimensional accuracy, low reject rate, wide application range, low requirements for workers' technical level, greatly reducing the labor intensity of workers and improving the working environment, more and more domestic companies (or enterprises) choose self setting resin sand casting. Although the self hardening resin sand casting technology has been mature, there are still many problems in the production process.
In the process of self hardening resin sand casting, the following problems should be paid attention to.
1、 Always pay attention to the operation of the equipment
The quality of equipment operation directly affects the cost of casting production and the quality of castings. Therefore, in the process of casting production, attention should be paid to the operation of equipment, and if abnormal operation is found, it should be analyzed and solved in a timely manner. The following two aspects should be paid attention to:&W6 S8 t]! k' J$ i3
1. Pay attention to the operation of dust removal equipment.
The quality of dedusting equipment directly affects the regeneration cost of recycled sand and the quality of castings. In the casting production, it is often difficult to find the abnormal operation of dedusting equipment. However, if the dedusting effect of dedusting equipment is not good, it not only affects the working environment and pollutes the air, but also affects the micro powder content of recycled sand, The direct result is the increase of resin addition during sand mixing and the increase of casting reject rate 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 sand mixing, among which the amount of liquid material (resin, curing agent) is the most critical. In general, the amount of resin added is realized by controlling the voltage of the gear pump motor and the amount of curing agent added is realized by controlling the voltage of the diaphragm pump motor. Due to the change of seasons and weather, the viscosity of liquid materials will change. Under the same voltage, the amount of liquid materials added will fluctuate, and the curing agent is easy to crystallize, causing the blockage of valves and pipes. Therefore, the liquid materials pipes should be cleaned every shift, The amount of liquid material added shall be tested every week to ensure the accuracy of the amount of liquid material added.
2、 Pay attention to the correctness and rationality of the production process
The rationality of the production process directly affects the yield, quality and cost of castings. The following items should be paid attention to when formulating the production process:
1. Determine appropriate LOI value of reclaimed sand)
LOI value, that is, loss on ignition, is an important indicator to measure the film removal rate of recycled sand, and it is also an indicator closely related to the gas generation of molding sand and porosity defects of castings. Iron castings are generally produced with furan resin sand. Practice has proved that LOI value control at about 3% can fully meet the production requirements, while excessive reduction of LOI value is of little significance.
2. Determine the appropriate casting process parameters
(1) Determine appropriate final strength
Generally, after the resin sand is mixed, it can reach the highest strength, that is, the final strength, after about 24 hours of self hardening. Due to different production conditions and scale of each enterprise, the time interval between molding and pouring may not exceed 24 hours, so the final strength shall be determined by the enterprise. For enterprises with small scale and one furnace for several days, the 24-hour final strength standard can be adopted; For enterprises whose mold curing time does not exceed 24 hours, the final strength standard is the strength reached before pouring. At the same time, two tendencies should be overcome in production: on the one hand, blindly improving the strength to ensure quality, which increases the casting cost and causes waste; On the other hand, the strength is reduced to ensure the cost, which results in unstable quality and large fluctuation range, making the casting quality greatly affected by raw materials and operators.
(2) Determine the appropriate sand iron ratio
Since the self hardening resin sand has high strength, after curing, the mold lifting and parting surface are flat, its sand consumption is smaller than that of clay sand, but its sand iron ratio also has certain requirements. If the casting sand 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 of the regenerator, reduce the film removal rate, increase the LOI value, and increase the possibility of casting porosity; If the sand iron ratio is too low, it is easy to run out during pouring and the casting is easy to deform. According to our experience, the sand iron ratio should be 2.2~3:1
(3) Determine the appropriate gating system
The thermal stability of furan resin sand is poor. According to information, when the resin content in the resin sand is 1.4% - 1.6%, its thermal stability is the best. However, in general, the resin content is about 1.2%. Therefore, the design principle of the gating system is to ensure that the molten metal fills the mold cavity quickly and stably within the thermal stability time of the resin. Therefore, when determining the gating system, ceramic pipes should be used as much as possible, And make the inner gates more and more dispersed.
3、 Pay attention to the selection of raw materials
The selection of raw materials has a great impact on the 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. Therefore, the following aspects should be considered.
1. The selection of raw sand The raw sand can be divided into ordinary sand, water washed sand, scrub sand, etc. Since the mud content in scrub sand is very small, it can greatly reduce the waste of resin. It should be preferred, followed by water washed sand, but never use untreated raw sand. When selecting molding sand, first, follow the principle of selecting nearby to reduce transportation costs, and second, try to select raw sand with low angle coefficient.
2. Selection of resin
The selection of resin directly affects the casting quality. If the resin with poor quality is selected, it will not only increase the amount of resin added, but also affect the quality of molding sand, resulting in an increase in casting waste. Therefore, the selection of raw materials cannot be determined only based on the technical data provided by the manufacturer, but should have a better understanding of the manufacturer's production equipment, production process and quality control means, And try to inspect each index of the resin by yourself or ask the relevant inspection department with good reputation for inspection, or use the experience of similar manufacturers for reference, or select the products of well-known large enterprises with good reputation.
3. Selection of other raw materials Other raw materials include curing agent, coating, adhesive, mold release agent, sealing clay bar, etc. The selection of these raw materials should not only consider their quality, but also consider their matching with the main materials, such as easy procurement and transportation. Because the influence of these raw materials on the casting quality is not major, but the influence on the casting cost can not be ignored. For example, the different dosage of curing agent not only affects the production cost due to the influence on the production efficiency of the molding process, but also affects the material cost. In a word, as long as the above aspects are paid attention to, not only can we produce castings that meet customer requirements, but also can reduce casting costs and bring development and benefits to the enterprise.