Furan self-hardening resin sand technology has been applied in China since the 1980s. Due to its good collapsibility, self-hardening characteristics and high dimensional accuracy of the produced castings, it has greatly reduced the labor intensity of workers and significantly improved the casting workshop Working environment, and significantly improved the production technology level and casting quality of China''''s foundry enterprises, so it has been widely promoted, and the traditional wet mold drying sand has been gradually eliminated, and it has become the only molding process for medium and large iron castings and medium and large iron castings. An important molding process for steel castings and aluminum castings. After nearly 20 years of development, whether it is resin sand production equipment or resin sand raw and auxiliary materials, domestic related products have reached the level of similar foreign products. In recent years, the export business of castings has continued to grow. Many domestic small and medium-sized foundry companies, and even some companies that have been using machine-shaped green sand production lines, have begun to adopt the furan self-setting resin sand production process. However, due to the understanding of the process characteristics of resin sand, The lack of technical personnel and production experience, there are many problems in the application of resin sand technology, and did not achieve the purpose of reducing production costs and improving casting quality and production efficiency. In the process of technical exchanges and services with customers, sanzhuji often found that some small and medium-sized enterprises did not use the self-setting resin sand process correctly, and the operators lacked understanding of the characteristics of resin sand.

In view of the common problems in the resin sand process of small and medium-sized foundry enterprises, we conducted a more in-depth investigation. Based on the analysis of the existing problems, we concluded the misunderstandings in the use of the resin sand process, and analyzed the process characteristics and economics of the furan self-setting resin sand. We analyzed the reasons for casting quality and other aspects, and put forward some improvement suggestions based on our experience and lessons.
1. Investigation on the use of furan resin sand technology
Some small and medium-sized foundry companies, especially those that still retain green sand (green sand) production lines, have common problems in the resin sand process and can be summarized into three aspects.
1.1 There is a certain degree of blindness when using furan self-hardening resin sand process. Seeing that other companies use resin sand technology to produce export castings, and the process looks much simpler than green sand (green sand), they bought a resin sand production line; they did not plan the type and size of the products before purchasing, and did not consider the company. Whether the process equipment, production technology level and worker operation meet the requirements of resin sand process.
1.2 Not enough attention is paid to the process requirements of furan self-hardening resin sand. Most foundry companies think that as long as there is a continuous sand mixer, a set of resin sand recycling equipment, paint, furan resin and curing agent, they can produce export castings. They do not realize that this is only a necessary condition for the production of resin sand castings, and they ignore the more important The quality of the castings is not as good as that of the green sand castings. For example, the sprue is directly opened in the mold instead of the ceramic tube, resulting in serious sand inclusion defects in the castings; The high strength of the resin sand ignores the high gas-generating characteristics of the resin sand, and the core does not use vented core bone and vented nylon tube, resulting in more pore defects in castings. Mistakes such as these are the root cause of the high casting rejection rate and production cost of these casting companies, and the difficulty in improving the quality of castings.
1.3 Use the green sand (green sand) casting process for furan resin sand. When preparing the resin sand process, the technical personnel of the green sand (green sand) foundry company often prepare the resin sand process according to the habit, so the resin sand process is similar to the green sand process. For example, in the preparation of ductile iron resin sand process, the number of risers is too large, and the total amount of risers is too heavy. In fact, because of the high sand mold strength and small wall offset, the feeding amount of the casting is significantly reduced. During the process, the quantity and quality of risers are reduced, and the utilization rate of molten iron is improved.
Observation of castings: There are pores and sand inclusions on the surface of the castings, and the runner part has serious sand washing, which is the main cause of sand inclusions in the castings. The high collapsibility of furan resin sand can easily cause sand washing. Sanzhuji''''s investigation found that the current application of furan resin sand technology stems from the misunderstanding of the furan resin sand technology and the insufficient understanding of the resin sand technology characteristics by foundry companies, which are concentrated in the following aspects.
2.1 Application conditions of resin sand process
For medium and large castings, the use of self-hardening resin sand technology reduces the labor intensity of modeling, mold repair and casting cleaning, and does not require large-scale drying kilns, eliminating the drying process, saving energy and time, and improving production efficiency and site Utilization rate, and no mold deformation during mold drying, high mold strength and improved casting accuracy.
For small iron castings weighing less than 200 kg, especially small castings with a certain batch, compared with the green sand (green sand) process, the self-setting resin sand process does not have advantages, which is reflected in the cost of molding sand and production efficiency. On the one hand, this is determined by the process characteristics of self-setting resin sand. First, resin sand belongs to "high-priced" sand. According to the resin addition amount of 1.2%, the sand-to-iron ratio is 3 and the current market price of furan resin, the resin cost of 1 ton casting alone is more than 300 yuan, and the annual output of 10,000 tons casting resin consumption is More than 3 million yuan; Second, compared with the green sand (green sand) molding line, the production efficiency of resin sand is "lower". The hardening time of resin sand is generally about 30 minutes. In addition, the whole cycle is about 1 h at the fastest when the mold is removed, the coating is applied, and the box is closed. The green sand molding line can produce dozens of molds in 1 min. Under guaranteed conditions, the dimensional accuracy and surface quality of the produced castings are equivalent to those of resin sand castings. Sanzhuji''''s downstream casting companies have also used vibration plus multi-contact high-pressure molding machines to produce export flywheel shell castings with a clear surface profile and a weight of 250 kg. The use of resin sand production lines by foundry enterprises is only one direction for enterprises to improve their competitiveness and product quality, but resin sand technology is a production process after all. The core competitiveness of enterprises is product and product quality, regardless of cost or production efficiency. Therefore, the resin sand process is not suitable for the production of small iron castings with a certain batch.
2.2 The collapsibility and gassing characteristics of furan resin sand The easy collapsibility of resin sand can easily cause sand washing.
In the process design of the pouring system, paint should be applied to small and medium castings, sprues and cross runners. When the sprues cannot be painted, flow coating or ceramic pipes should be used to prevent sand inclusion in the castings. The craftsmen did not realize The easily collapsible characteristics of resin sand adversely affect the quality of castings.
The amount of gas generated by resin sand is much greater than that of green sand (green sand), and castings are prone to pores. Therefore, the following points should be paid attention to in sand control: Do not pursue high molding sand strength to reduce the amount of resin added and reduce the resin sand Air volume: Regularly monitor the quality of reclaimed sand equipment and reclaimed sand. If the regeneration is not good, it will increase the thickness of the resin film of the molding sand and the accumulation of the resin volume, which will increase the gas evolution of the resin sand; the quality of the raw sand is also very important, such as sand, The mud content must be strictly controlled. Pay attention to the following factors in the process: place the vent core and nylon vent pipe on the core; reduce the sand-to-iron ratio. When conditions permit, use a special sand box, which can directly reduce the resin cost per ton of cast iron, for example, the sand-to-iron ratio is reduced to 2 , Each ton of castings can reduce more than 100 yuan of resin, and at the same time help to improve the quality and regeneration efficiency of reclaimed sand. During production, molds should be avoided; rapid pouring is another measure to prevent pore defects in resin sand castings.
2.3 The importance of coatings to the surface quality of castings
The surface quality of resin sand castings depends on the quality of the coating and the painting process. The thickness of the sand particles has almost nothing to do with the surface quality of the castings, which is quite different from the characteristics of green sand (green sand). If the paint is not well applied, the castings are prone to physical sand sticking. For small castings, the surface quality of resin sand castings is not as good as that of green sand castings. When choosing raw sand for the furan self-hardening resin sand process, you can choose sand with a coarser grain size, which can increase the air permeability of the molding sand and reduce the amount of resin sand. In order to improve the surface quality of resin sand castings, molding workers should be strictly trained, and flow coating machines should be used when conditions permit.
2.4 The requirements of resin sand modeling on molds
According to our on-site investigation, a considerable number of foundry companies lack sufficient knowledge of resin sand molding molds. Resin sand is self-hardening sand, which requires hard mold removal, which can easily damage the cavity and is difficult to repair. Therefore, the structure of the mold should be reasonable, and the mold material should be good, especially the quality requirements of the casting mold with a certain mass production. The release agent is also very important, it relates to the "life" of the mold and the surface quality of the mold. The quality of castings produced by some companies with resin sand is still inferior to the castings produced by clay sand. An important reason is that the molds are "coarsely manufactured".
3. Based on the above problems, sanzhuji combined with foundry companies to draw the following conclusions
In the current situation where the furan resin sand process is extremely common, many small and medium-sized foundry companies have not achieved the due benefits and high casting quality when using the furan resin sand process. Some foundry companies have encountered problems in the application of the furan resin process There is a certain generality. Therefore, in this article, we analyzed the reasons for the problems in the resin sand process application process, and put forward specific suggestions based on our experience, hoping to help small and medium-sized foundry enterprises to use the resin sand process correctly.

Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of sand reclamation equipment,foundry machines,Sand casting equipment,GS high efficiency rotary mixer,no-bake resin sand mixer,Jolt squeeze molding machine/Jolt-squeezing moulding machines,Multi- Piston Moulding Machine/Hydraulic multi-piston moulding machine,foundry molding machine,flaskless moulding machine,shot blasting machine,dust collector,according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.