Influence of coatings for urea-based patterns on the quality of shell molds produced using colloidal silica binders

In the investment casting process, in addition to wax patterns, water-soluble salt patterns made of urea are also used. It is known that urea-based patterns provide high strength and allow the patterns to maintain their shape even if the temperature in the foundry increases. However, due to environmental and production-related reasons, there is currently a growing demand for transitioning to a technological process involving colloidal silica binder. This transition presents challenges related to the manufacturing of ceramic shell molds due to the interaction between the pattern compound and the colloidal silica binder slurry. This study examines the effectiveness of protective coatings based on repair wax, varnish (AK 593), and varnish with rosin, applied to water-soluble urea-based patterns containing additives such as magnesium sulfate, potassium nitrate, polyvinyl alcohol, and dimethylglyoxime. The degree of interaction was assessed by measuring the wetting angle and the spreading area of the colloidal silica binder over the surface of pattern samples with various coatings. It was found that all coatings contributed to an increase in the wetting angle and a reduction in the spreading area. Additionally, ceramic molds and castings made of nickel superalloy were produced using a series of pattern compounds with protective coatings. The surface roughness and dimensional accuracy of the castings were evaluated. It was demonstrated that the protective properties of the repair wax-based coating were insufficient, leading to the formation of cracks and sagging in the mold. This resulted in penetration defects in the castings and a significant decrease in dimensional accuracy. In contrast, when using coatings based on varnish and varnish with rosin, no defects were observed in the mold or castings, making these coatings recommended as protective solutions for urea-based pattern compounds in contact with colloidal silica binder slurries.

1. Kanyo J.E., Schafföner S., Uwanyuze R.S., Leary K.S. An overview of ceramic molds for investment casting of nickel superalloys. Journal of the European Ceramic Society. 2020;40(15):4955—4973. https://doi.org/10.1016/j.jeurceramsoc.2020.07.013

2. Selvaraj S.K., Sundaramali G., Dev S.J., Swathish R.S., Karthikeyan R., Vishaal K.E.V., Paramasivam V. Recent advancements in the field of Ni-based superalloys. Advances in Materials Science and Engineering. 2021;Dec.2021:9723450. https://doi.org/10.1155/2021/9723450

3. Kumar S., Karunakar D.B. Development of wax blend pattern and optimization of injection process parameters by grey-fuzzy logic in investment casting process. International Journal of Metalcasting. 2022;16: 962—972. https://doi.org/10.1007/s40962-021-00655-y

4. Pradyumna R., Sridhar S., Satyanarayana A., Chauhan A.S., Baig M.A.H. Wax patterns for integrally cast rotors/stators of aeroengine gas turbines. Materials Today: Proceedings. 2015;2(4—5):1714—1722. https://doi.org/10.1016/j.matpr.2015.07.005

5. Prokopchuk N.R., Gorshcharik N.D., Klyuev A.Yu., Kozlov N.G., Rozhkova E.I., Latyshevich I.A., Bakovich N.A. Pattern compounds for high precision casting. Izvestiya Natsional’noi akademii nauk Belarusi. Seriya khimicheskikh nauk. 2015;4:122—128. (In Russ.).

6. Дубровский В.А. Модельная композиция для выплавляемых моделей: Патент 2123902 (РФ). 1997.

7. Усков Д.И. Стержневой состав для получения прецизионных отливок. В сб: Молодежь и наука: Материалы Х Юбилейной Всеросс. науч.-техн. конференции студентов, аспирантов и молодых ученых с междунар. участием, посвященной 80-летию образования Красноярского края (15—25 апреля 2014 г.). Красноярск: СФУ, 2014. С. 1—4.

8. Громаков А.И., Михнев М.М., Усков Д.И. Смесь для изготовления водорастворимых стержней. В сб: Материалы Международной научной конференции «Решетневские чтения» (9—12 ноября 2016 г.). Красноярск: Сибирский государственный университет науки и технологий им. академика М.Ф. Решетнева, 2016. Т. 2. С. 332—333.

9. Fujitta T. Pattern material for making foundry patterns for use in investments casting process: Patent 4939187 (USA). 1990.

10. Стадничук В.И. Способ изготовления керамических форм по растворяемым моделям: Патент 2499651 (РФ). 2012.

11. Лакеев А.С., Щегловитов Л.А., Кузьмин Ю.Д. Прогрессивные способы изготовления точных отливок. Киев: Техника, 1984. 160 с.

12. Сумин Е.И., Андрианов Л.П. Композиция для изготовления водорастворимых моделей: Авт. св-во 602288 (СССР). 1976.

13. Seyedraoufi Z.S., Mirdamadi Sh. Synthesis, microstructure and mechanical properties of porous Mg—Zn scaffolds. Journal of the Mechanical Behavior of Biomedical Materials. 2013;21:1—8. https://doi.org/10.1016/j.jmbbm.2013.01.023

14. Wen C.E., Yamada Y., Shimojima K., Chino Y., Hosokawa H., Mabuchi M. Compressibility of porous magnesium foam: dependency on porosity and pore. Materials Letters. 2004;58(3—4):357—360. https://doi.org/10.1016/S0167-577X(03)00500-7

15. Hao G.L., Han F.S., Li W.D. Processing and mechanical properties of magnesium foams. Journal of Porous Materials. 2009;16:251—256. https://doi.org/10.1007/s10934-008-9194-y

16. Marutani Y., Kamitani T. Manufacturing sacrificial patterns for casting by salt powder lamination. Rapid Prototyping Journal. 2004;10(5):281—287. https://doi.org/10.1108/13552540410562313

17. Rutto H.K. Urea-based moulding compounds for investment casting: Thesis for the degree Philosophiae Doctor in Chemical Engineering. Pretoria: University of Pretoria, 2006.

18. Литье по выплавляемым моделями. Под ред. Я.И. Шкленника, В.А. Озерова. 2-е изд., перераб. и доп. М.: Машиностроение, 1971. 436 с.

19. Чуркин Б.С., Чуркин А.Б., Категоренко Ю.И. Специальные способы литья: Учеб.-метод. пос. Екатеринбург: Изд-во Рос. гос. проф.-пед. ун-та, 2012. 189 с.

20. Rutto H., Focke W. Thermomechanical properties of urea-based pattern molding compounds for investment casting. International Polymer Processing. 2010;25(1): 15—22. https://doi.org/10.3139/217.2256

21. Bazhenov V.E., Kovyshkina E.P., Nikitina A.A., Koltygin A.V. Influence of various additives on the properties of salt water-soluble carbamide-based pattern compounds. Tsvetnye metally. 2024;8:82—90. (In Russ.). https://doi.org/10.17580/tsm.2024.08.12

22. Bazhenov V.E., Kovyshkina E.P., Koltygin A.V., Belov V.D., Dmitriev D.N. Development of isolating composition for soluble salt models for investment casting. Liteinoe proizvodstvo. 2023;(6):30—37. (In Russ.).

23. Stadnichuk V.I., Bessmertnyi V.S. Formation of protective hydrophobic films on the working surface of foundry ceramic molds. Ogneupory i tekhnicheskaya keramika. 2011;(4—5):8—10. (In Russ.).

24. Караник Ю.А. Способ изготовления отливок из черных и цветных металлов: Патент 2048955 (РФ). 1995.

25. Васин Ю.П., Евсеева Т.М., Лонзингер В.А., Аверьянов Е.Ф., Сезганов А.Н., Розовский Л.Д., Хохлова Е.В. Способ изготовления форм при литье по выплавляемым моделям: Авт. св-во 1310098 (РФ). 1985.

26. Колтыгин А.В., Белов В.Д., Баженов В.Е., Ковышкина Е.П., Фадеев А.В. Раствор для улучшения смачивания поверхности восковых моделей для литья по выплавляемым моделям: Заявка на патент 2023110773 (РФ). 2023.

27. Bazhenov V.E., Kovyshkina E.P., Sannikov A.V., Koltygin A.V., Ten D.V., Rizhsky A.A., Belov V.D., Lazarev E.A. Analysis of the slurry and ceramic properties for investment casting obtained with domestic colloidal silica binders. Izvestiya. Non-Ferrous Metallurgy. 2023;29(2):15—28. (In Russ.). https://doi.org/10.17073/0021-3438-2023-2-15-28