In the 1960s. Silica sol is used as a binder in various casting fields. Immediately with its incomparable competitive advantage, it gradually replaced the widely used ethyl silicate hydrolysate, which had environmental pollution relatively high cost. Since then, the investment casting industry in Britain, the United States, France, Japan other countries has quickly widely used silica sol. Russia has gradually chosen silica sol since the end of the 1980s achieved remarkable results. However, silica sol is a water-based binder. The gel hardening time of the slurry is very long. it is greatly affected by the temperature humidity of the dry environment. This directly affects the production cycle the quality of castings. The combination of ethyl silicate hydrolyzate silica sol is widely used internationally, which can only reduce production costs, but also shorten the production cycle, thereby ensuring the product quality of castings. With the stricter environmental protection requirements. There are strict restrictions on the VOC content in the air, the ethyl silicate shell workshop has met the requirements. Air filtration is required. Therefore, the use of this alcohol-based ethyl silicate adhesive is on a downward trend. It is being replaced by enhanced quick-drying silica sol. In view of this, this article reviews the research status of enhanced quick-drying silica sol its application in various fields of casting.

1 The current status of foreign research its application in the field of casting

As early as 1980, people used polyvinyl alcohol (PVA), carboxymethyl cellulose other water-soluble polymers as reinforcing agents to modify silica sol. it is applied to investment casting to improve the wet strength of the shell speed up the drying speed, which is favored by precision casting manufacturers. For example, in 1992, Remet company introduced RemasolAdbondB polymer reinforced silica sol. The next year, it launched an improved product RemasolAdbondBV polymer reinforced silica sol. After the 1990s, due to the increasing pressure on environmental protection. Many manufacturers that originally used ethyl silicate to make shells have switched to silica sol. Most of these manufacturers hope to

Under the premise that the plant equipment are basically unchanged. Maintain the original production schedule capacity. For this reason, the most important point is to keep the drying time between the shell layers roughly the same as when using ethyl silicate. In this context, silica sol manufacturers have developed developed the so-called polymer-enhanced quick-drying silica sol with shorter interlayer drying time.

In 1994, DuPont first introduced LudoxSK series silica sol. Such as LudOXSK. B, LudoxSK-R LudoxSK-F, etc. among them. LudoxSK. R is recognized as an ideal substitute for ethyl silicate hydrolysate. LudoxSK used by Glasgow National Engineering Laboratory, Scotland, UK. The wet strength high temperature strength of the shell made by R are about 1 times higher than that of the ethyl silicate shell, the residual strength high temperature air permeability are roughly equivalent. In 2001, Remet launched ADBOND⑧3301 series products (SP.3301 LP.3301), which are mainly used as back layer adhesives. After only 1h of drying between layers, the shell strength can reach the maximum value, which only has high wet strength high temperature strength, but also has low residual strength is easy to peel off. A company used the DCOAT quick-drying silica sol shell process produced by FOSECO to replace the silica sol-ethyl silicate composite shell process to produce 23 final stage guide vanes, all of which met the design requirements. At the 46th Annual Precision Casting Conference in the United States in 1998. The United States Buntrock R&D laboratory published the large particle size high concentration quick-drying silica sol (Megasol silica sol) to the public. The study found that the wet strength of the shell made of the silica sol is more than 1 times higher than that of the standard silica sol, which is completely applicable In investment casting. Many precision casting plants use Megasol to test find that it can completely replace ethyl silicate hydrolysate. The silica sol overcomes the shortcomings of polymer-reinforced silica sol coating slurry, such as easy aging, poor stability, difficulty in effectively monitoring quality. At the end of the 20th century. The United States Buntrock Industries British Wex Chemicals jointly developed the WEXCOAT binder, which is different the general polymer reinforced silica sol. It is by adding polymer, but by adding water-insoluble organic fiber (nylon filament) WEXPERM to strengthen a fiber-reinforced modified silica sol. Because of the presence of fiber. Moisture migrates the inside to the outside, speeding up the drying speed of the shell. In addition, the use of fiber-reinforced coatings increases the thickness of the coating reduces the number of coating layers by one. Production practice has proved that ⅦXCOAT binder is completely suitable for precision casting of non-ferrous, black high-temperature alloys.

2 Domestic research status application in the field of casting

Zhejiang Yuda Chemical Co., Ltd. Tsinghua University jointly developed FS. 30 quick-drying silica sol (now known as FS.I. namely aluminum ion modified quick-drying silica sol), research on its shell making process. Passed the appraisal of the Ministry of Machinery Industry in November 1997. FS. The shell-making cycle shell strength of the quick-drying silica sol are equivalent to those of the traditional ethyl silicate shell. However, the shell-making time is 1/2 to 1/4 of that of ordinary all-silica sol shells, even shorter. But FS. I fast-drying silica sol in the drying speed

There is still a gap between the shell performance the internationally renowned LudoxSK series products. To this end, the above two units have developed FS. II. FS-III Two enhanced quick-drying silica sols. Among them, FS. III Enhanced quick-drying silica sol LudoxSK. R silicon

The drying speed of the sol shell is similar to the performance of the shell. Ma Bo applied FS-II quick-drying silica sol produced by Zhejiang Yuda Chemical Co., Ltd. to investment casting, the effect was good. In addition, Tsinghua University has also developed a latex-enhanced quick-drying silica sol (coded as F). Luo Qiong others used SKP227 quick-drying silica sol produced by Dongguan Huihe Silicon Products Co., Ltd. to manufacture the shell. The study found that SKP. Type 27 quick-drying silica sol type shell is better than ordinary S. 1430 silica sol shell has high strength at room temperature. The high temperature strength is equivalent, the residual strength is low, the collapsibility is good. Under the same process conditions, the drying speed of the former is about 50% faster than that of the latter. Li Yufei others analyzed the current development direction of the domestic precision casting industry, compared the advantages disadvantages of the current precision casting production process, proposed a new energy-saving precision casting adhesive. ZF. 801 type quick-drying silica sol. By analyzing the shell-making time, casting dimensional accuracy, surface quality, normal temperature strength, high temperature strength, residual strength of the ZF-801 quick-drying silica sol shell, the results show that ZF. Type 801 quick-drying silica sol meets the "Eleventh Five-Year" plan to reduce energy consumption. Less pollutant emissions are required, the cost is moderate.

3 Application in ceramic mold casting

As we all know. The binder commonly used in ceramic mold casting is ethyl silicate hydrolysate. Same as investment casting. Ethyl silicate is expensive, the hydrolysis process is complicated, there are serious VOC problems safety hazards. At present, a lot of research has been done on the process improvement of ethyl silicate hydrolysate. However, the production of the main raw material ethyl silicate is still very expensive, the hydrolysis process is complicated, the current development trend. It has become possible for silica sol to completely replace ethyl silicate hydrolysate in ceramic mold casting. In particular, various enhanced quick-drying silica sols have been successfully developed. Early research shows. Silica sol can be used in ceramic mold casting instead of ethyl silicate hydrolysate. It can only meet the basic requirements of traditional ceramic mold casting, but also reduce production costs improve operating conditions. However, because silica sol is a water-based binder. Its gelation hardening time is very long, it cannot reach the production efficiency of ethyl silicate, the drying conditions are difficult to control, the mold elasticity is poor cracks are easy to occur. This severely limits the application of silica sol in ceramic mold casting. In summary, further research on enhancing quick-drying silica sol applying it to ceramic mold casting is to ensure the quality of the mold reduce the production cost the VOC content in the air. Shortening the production cycle is an important direction for its future research.