Influence of various additives on the properties of salt water-soluble carbamide-based pattern compounds

Water-soluble salt carbamide-based patterns are often used to manufacture large case castings by investment casting due to high strength and low linear shrinkage. However, now manufacturing plants gradually transfer to a technological process, when colloidal silica binders are used as a binder for manufacturing ceramic molds, instead of a hydrolysed solution of ethyl silicate, requiring additional studies on potential interactions between a mold and a binder. The paper describes influence of the components of pattern compounds (magnesium sulfate, potassium nitrate, polyvinyl alcohol and dimethylglyoxime) on the properties of salt pattern compositions. A rotational viscometer was used to study influence of the additives on nature of solidification and determine coherence temperature of pattern compounds, which turned out to be within a range of 112–126 oC. The lowest coherence temperature is found for pattern compounds with added potassium nitrate. Linear shrinkage measured with a manual 3D scanner has showed that depending on the composition of the pattern compound it may be low (0.3–0.55%), correlating well with coherence temperature. The higher coherence temperature of the pattern compound, the lower linear shrinkage, and vice versa. The interaction between the colloidal silica and pattern compounds was assessed by wetting angle and a spreading area. Two methods showed contradicting results, but in general it should be noted that added polyvinyl alcohol and dimethylglyo xime contributed to increasing wetting angle, and, consequently, to decreasing the interaction between the binder and the pattern compound. Roughness measured with a profile meter has showed that pattern compounds ensure low roughness within Rz 3.2–6.8 μm, when the pattern compound is solidified in a metal mold. Three-point bending tests showed that added potassium nitrate and polyvinyl alcohol ensured considerable strengthening of pattern compounds, and maximum bending strength was 15.9 MPa.This research received financial support from the Ministry of Science and Higher Education in the Russian Federation (Agreement No. 075-11-2022-023 from 6 April 2022) under the program “Scientific and technological development of the Russian Federation” according to governmental decree N 218 dated 9 April 2010.