Investigation of field temperature in moulds of foamed plaster

• Autorzy: Pawlak M. , Niedźwiedzki Z.
• Języki publikacji: EN

Abstrakty

EN

Plaster moulds used in precision foundry are characterized by a very low permeability which, in the case of classic plaster moulds, equals to about 0,01- 0,02 m2/(MPaxEs). One of the most effective methods for increasing the permeability is a foaming treatment. Another characteristic feature of plaster is its very good insulating power which has influence on the process of solidification and cooling of a cast and also on a knock-out property. This insulating power is a function of thermophysical properties of plaster which, in turn, depend mainly on the mineralogical composition of the mould material, its bulk density as well as on the temperature of the pouring alloy. In the case of a foamed plaster mould an increase of the degree of foaming increases its porosity which causes a change in its thermophysical properties, thereby increasing susceptibility of the mass to overheating. The susceptibility of the plaster layer surrounding the cast to overheating is favorable because it makes it easier to knock-out of the cast by immersing the hot mould in cold water. Thermal and phase tensions that are created during this process cause fast destruction of plaster. This paper describes our investigations aimed at the determination of the dependence of the mould temperature field on the time of the cast stay in the mould, as recorded in a process of an unsteady heat flow. The determined data were planned to be used for estimation of the technological properties of the plaster mould. The tests were carried out using the plaster [alpha]-Supraduro and Alkanol XC (foaming agent). The test mould had a diameter of [...] 120 mm with centrally situated mould cavity of [...] 30 mm. Plaster moulds with a degree of foaming 20; 32,5 and 45% and comparatively from non-foaming plaster were tested and their temperatures were measured at the distance x=2; 9; 21; 25; 27; 30 mm from the mould cavity within 25 min. Analysis of the results leads to the conclusion, that the highest effectiveness of heating and overheating of a mould made of a foamed plaster occurs at the degree of the plaster foaming equal to S_S=45%. The results obtained can provide the basis for the elaboration of the best plaster mould properties, and thus to increase the technology effectiveness.

Słowa kluczowe

EN

innovative foundry materials; innovative foundry technologies; precision casting; foamed plaster process; foamed plaster mould

PL

innowacyjne technologie odlewnicze; innowacyjne materiały odlewnicze; odlewnictwo precyzyjne

• Wydawca: Komisja Odlewnictwa Polskiej Akademii Nauk Oddział w Katowicach
• Czasopismo: Archives of Foundry Engineering
• Rocznik: 2007
• Tom: Vol. 7, iss. 4
• Strony: 141--146
• Opis fizyczny: Bibliogr. 8 poz., rys., tab., wykr.

Twórcy

autor

Pawlak M.

autor

Niedźwiedzki Z.

• Technical University of Łódź, Department of Materials Engineering and Production Systems, Stefanowskiego St 1/15, 90-924 Łódź, Poland,

Bibliografia

• [1] Lewandowski L.: Moulding materials, Akapit, Warsaw 1997 (in Polish).
• [2] Nelson C. D.: Plaster Molding, Metal Handbook (1998), Vol. 15, Casting, p. 242÷247.
• [3] Clegg A. J.: Precision Casting Processes, Pergamon Press 1991.
• [4] Pawlak M.: The firing gypsum moulds for artistic casting, Archives of Foundry, Polish Academy of Science 2006, no. 19, p. 213÷230 (in Polish).
• [5] Pawlak M.: Influence of conditions of preparing the foamed plaster on its degree of foaming, Archives of Foundry Engineering, Polish Academy of Science, Vol. 7, Issue 3, July-September 2007.
• [6] Koch R., Noworyta A.: Mechanical processes in chemical engineering, WNT, Warsaw 1995 (in Polish).
• [7] Wiktorski M., Pawlak M., Niedźwiedzki Z.: A stand to search coefficient of thermal conductivity for materials applied on plaster moulds in precision casting, Archives of Foundry, Polish Academy of Science 2004, no. 13, p. 232÷240 (in Polish).
• [8] Pawlak M., Influence of temperature and time of firing on the properties of gypsum, Reserch in Polish Metallurgy at the Beginning of XXI Century, Committee of Metallurgy of the Polish Academy of Science, Publishing House AKAPIT, Cracow 2006, p. 287-293 (in Polish).