1. Scope
This standard includes seven parts, including scope, normative references, terms and definitions, raw and auxiliary materials for rapid shelling, technical requirements for rapid shelling process, inspection methods and appendices.
The standard specifies the raw and auxiliary materials, technical requirements, inspection and testing methods for rapid shell making of silica sol in investment casting, and is applicable to the selection of raw and auxiliary materials, process formulation and process control for rapid shell making of silica sol in investment casting. Combined with the dimensional accuracy requirements of products, this standard is more applicable to investment castings with general dimensional accuracy (inferior to CT5) such as automobiles, mechanical parts and civil hardware. For products with higher accuracy (superior to CT4) requirements in the aerospace field, please refer to this process standard.
2. Reference standards
This standard refers to the refractory material standard, wax standard and silica sol standard related to this investment casting process. At the same time, considering the requirements of highlighting national environmental protection and sustainable development, it refers to the standards on pollution control of investment casting. Importantly, considering the negative impact of unqualified refractory materials on the silica gel drying process, this standard focuses on restricting the alkali ion concentration (converted into conductivity index) in the material testing content, and the testing method refers to relevant national standards.
3. Terms and definitions
This standard specifies the terms and definitions of six investment casting silica sol rapid drying processes, including silica sol, quick-drying silica sol, quick-drying agent, sand/powder, powder-liquid ratio, and rapid shelling.
The silica sol and quick-drying silica sol here refer to the adhesives that can be purchased by investment casting enterprises and meet the requirements of national standards, industrial standards or enterprise application standards. The quick-drying agent is a variety of additives artificially added in order to achieve the quick-drying effect when the silica sol adhesive is used for shell making; Quick-drying silica sol is a silica sol with fast drying function; Commercialized quick-drying silica sol is an adhesive that is provided to investment casting enterprises for rapid shell making after the binder manufacturer adds quick-drying agent to the silica sol.
In the investment casting industry, the concept of “quick drying” for shell making has a long history, but there has been no unified definition. This standard specifies the definition of rapid shell-making, that is, through the use of quick-drying silica sol, quick-drying agent, etc. to modify the shell-making coating, and through the change of environmental parameters of shell-making, the drying time of shell-making is shortened by more than 1/2 compared with the traditional process. Taking ordinary small parts as an example, the surface layer, the transition layer, the double back layer and the slurry sealing layer are made of four half-shaped shells, and the drying time of traditional shell making process is about (6+8+12+12+14) 52 hours; If quick-drying silica sol is used, the drying time of shell making can be reduced to less than 26 h.