Practice of the non box molding process of the hot

Practice of box less molding process of chilled resin sand

Abstract: through the analysis of various process characteristics of chilled resin sand, we boldly make use of the high-strength characteristics of its molding sand, omit the metal sand box, and use the solidified sand mold to directly close the box for pouring, so it is called box less molding (also known as box free molding for automobile front-end module, engine periphery, body, seat frame, battery bracket, power battery pack shell, etc.)

I Preface

chilled resin sand has been used in China's foundry industry for more than 20 years since the 1970s. The process coverage is getting higher and higher. Most manufacturers have application experience. Its process characteristics have been widely known and recognized by everyone. Its related raw and auxiliary material supporting industries are also beginning to take shape. Various related sand treatment equipment, both imported and domestic, have also emerged, The cold setting resin sand casting process has formed a large-scale industry climate, and its production process has become a synonym for high cost and high quality. With the continuous development of modernization in China, the demand for high-quality castings will be greater and greater, and the process prospect will be broader and wider. However, looking at the application history of chilled resin sand, it seems that China has only changed the bonding material of molding sand in the application of this process. The original clay sand process and tooling have not been greatly changed. There is a feeling of wearing new shoes and following the old path. However, resin sand has its own process characteristics and characteristics. If you can't adapt to this characteristic, you can't get the most economical and convenient operation benefits, Since 1983, our factory has used resin sand as the main molding material. At the beginning, we have established the prototype of box free molding process. After the joint venture in 1995, we inherited the process tradition before the joint venture. Up to now, almost 100% of the box free molding process has a history of more than ten years. We have accumulated some experience in the box free molding process. Here is a brief introduction

II The main process characteristics of chilled resin sand

uncured molding sand has good fluidity, which brings convenience for manufacturing sand molds and sand cores with complex shapes, and greatly reduces the labor intensity of workers

the sand mold has large rigidity, poor yielding when pulling out the mold, and high requirements for the mold. However, castings with high model reduction can be obtained, which improves the accuracy grade of castings and appropriately reduces the machining allowance

since the molding sand is heated and dehydrated during the curing process of acid self hardening resin sand, if the metal pattern is used, the temperature of the molding sand near the metal pattern cannot be increased due to the cooling effect of the metal pattern. At the same time, due to the temperature difference, condensate water is generated on the surface of the metal pattern, which makes this part of the molding sand unable to be effectively dehydrated and reduces the surface strength of the sand pattern; When the wood pattern is used, the low thermal conductivity of the wood pattern will not hinder the temperature rise of the molding sand, that is, there is no condition to significantly reduce the strength of the sand mold surface. However, the factors of temperature rise and moisture will cause the expansion of the model, which further increases the difficulty of the model

the cured molding sand has high final strength. Generally, under the daily working conditions of ordinary high-speed stirring cage type sand mixer, 1% of the resin can reach the tensile strength of about 1MPa and the bending strength of about 1.5MPa. The normal handling of daily production will not cause the fracture of sand mold and sand core, and the core bone can be used sparingly for the clay core with ordinary shape and section

although it has good collapsibility, when the standard sand box is used to make a large amount of sand, the molding sand around the sand box can not effectively collapse and still maintain the normal temperature strength, which brings great difficulties to sand removal. Manual sand removal is not easy, and mechanical sand removal is like dismantling equipment

the cold hardening resin sand modeling method belongs to the fluid sand modeling, and there is no compaction process with great strength in the whole modeling process, so the overall sand density is lower than that of clay sand and other sand types that must go through the compaction process, so the air permeability is good

molding sand has low moisture content and little moisture absorption tendency. It is allowed to be stored for a certain time without affecting the use

molding sand costs more. Based on 1% of the resin and 40% of the curing agent, according to the market price at the end of 1997, the resin was 11900 yuan/ton and the curing agent was 3080 yuan/ton. The cost of resin and curing agent per ton of molding sand reached 131.32 yuan. According to the sand iron ratio of 4.5 for pump castings, the cost of resin and curing agent per ton of castings reached 590.94 yuan

from the above description, it can be seen that chilled resin sand is an excellent molding and core making process. It optimizes a number of molding sand parameters and is the preferred material for manufacturing high-precision castings. However, due to its high cost and delayed hardening characteristics, its application scope is limited. It may never replace the mechanical molding of clay sand single piece and large-scale simple castings, because although they also have high casting precision, However, due to the delay hardening, the mold can not be lifted immediately, which can not improve the output of products, nor has the advantage of casting cost. However, it is a superior process for the production units of multi variety, small batch and complex castings to improve the grade of casting products, because we can obtain high-grade castings without increasing or even reducing the investment of tooling to replace sand such as clay sand

for example, in our workshop, there are more than 700 product parts that need to be produced all year round, and there are dozens of parts that need to be produced every month, and the production quantity of each part is generally no more than 10. Generally, there are one to two (two to three boxes) of the parting surface of each part, and at most five (six boxes). A considerable number of parts need stepped parting or horizontal and vertical mixed parting. If you want to use a special sand box, there should be at least hundreds or even thousands of sand boxes of different specifications, If the standard sand box is adopted, the sand consumption is too large. The box free molding brings us the most economical way to solve these problems, and accelerate the expansion and development of China's plastic extruder market

III Process method of cold hardening resin sand box less molding

1. specific process equipment and requirements of mold less molding process

(1) The model must be equipped with moulding board and sand frame. Generally, the model should be fixed on the moulding board. The pouring system and riser system should be made according to the process requirements. The moulding board should be made with locating pins. The sand frame can be made into a fixed bucket shape or flexible straight square according to the conditions of the moulding box

(2). During the modeling of the outer model box, the reinforcement shall be placed in the molding sand as the framework of the box. The box larger than 1200mm shall use the welded steel pipe frame as the framework. At the same time, the steel pipe protruding from the box can be used as the lifting tool for lifting the turnover. For the mold box that can be manually assembled, a transparent space shall be made on the sand frame to form a lap. For the mold box whose size is less than 1200mm but must be mechanically lifted, a lifting ring must be placed at the corner of the box

(3). A perforated flat plate shall be placed at the bottom of the mold box to ensure the flatness of the mold box and provide a clamping point for the clamping rod. The sand box with rungs used in clay sand modeling in the past can also be used as the bottom plate

(4). The square steel pipe is used as the clamping rod of each section specification. Generally, two clamping rods are used for one type box

2. specific process parameters of non box molding

(1) The minimum sand intake on the side is 50mm, and the minimum sand intake on the bottom is 30mm

(2). Maximum size of type box 1600mm × 1600mm；

(3). The minimum thickness of one valve box shall be 50mm, and the ratio of side length to thickness (height) shall not exceed 8

3. process flow of non box molding process and molding department (Figure omitted)

4. process advantages of box less modeling

(1) The size and shape of the mold box can be determined according to the size of the casting at will, which overcomes the unnecessary sand consumption caused by the use of the standard sand box and reduces the sand iron ratio

(2). A large amount of metal materials used to make sand boxes are saved

(3). Save a lot of auxiliary space occupied by stacking sand boxes

(4). As the sand box is eliminated, the time for manufacturing a special sand box is saved, which greatly shortens the production cycle of new products

(5). Because there is no sand box, the original graphene quantum battery is changed from semi closed to fully open, which further enhances the air permeability of the box and basically eliminates the occurrence of invasive pore defects

(6). Due to the high collapsibility of the resin sand, the casting is completely separated from the molding sand after pouring, but the molding sand and the sand box cannot be separated, and the sand dropping process is omitted without the sand box. Therefore, the sand treatment equipment becomes simple, and the noise and dust pollution in the workshop are greatly reduced

(7). The weight of the moulded box and the labor intensity of the combined box are reduced

5. shortcomings of box less modeling

(1) For molding sand with relatively high sand mixing quality and uneven sand mixing, it is easy to form cracks and fractures, resulting in scrapping of the mold box

(2). It is not suitable for large castings, especially those with large wall thickness or height parameters

IV Conclusion the production practice of our factory has proved that the process method or method of non box molding is the best process method for the production of resin sand casting unit with multiple varieties and small batches of products. Up to now, we have used the box free molding process to cast steel, cast copper and other casting alloys (ZG, ZG, zg1cr13, ZG2Cr13, zg1cr18ni9ti, zcuzn16si4, zcusn10zn2, etc.). The maximum box size is 1600mm, the maximum casting solid size is 1200mm, the maximum metal indenter (with riser pouring height) is 1500mm, the maximum pouring weight is 1000kg, and the dry mold box free rate is 100%

production practice has proved that the non box molding can effectively reduce the sand iron ratio. The average sand iron ratio has decreased from 4.5 in the past to about 4.1 at present, saving about 10% of the molding sand cost; It saves a lot of expenses for adding and updating sand boxes every year; The utilization rate of the site has been greatly improved. Under the condition of not expanding the plant, the site originally used for stacking sand boxes has been vacated to expand production. In the 15 years of production, the output has tripled, and great comprehensive benefits have been achieved