Lost Wax Process

Effect of process parameters on roughness and hardness of surface and dimensional accuracy of lost wax process casting

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Abstract

We know different casting processes like sand casting, gravity die casting, low pressure die casting, pressure die casting, counter pressure die casting, and centrifugal casting, spin casting, lost wax and lost foam casting. But lost wax or lost foam casting process are going to be most acceptable way of castings to get the intricate and complex shaped castings. Lost wax process is generally known as “Investment casting process”. About 5000 years ago the Egyptians used this process in the time of Pharaohs to make gold jewellery, which was the way of their investment hence the names comes. Ancient “lost wax process”

We dip the tree into the secondary coating and then cover it up with molochite grains of grade 50/80 twice and then dip it into the secondary slurry and allow it to become dry. After dry give two coat of 30/80 and again dip it and dry it. Now give layer of 16/30 and after dry it dip it in the secondary slurry . times. Give sufficient time in between two coats of minimum 8-12hrs in controlled drying room with 20-22 degree C temperature and 55-60% humidity. The above temperature and humidity helps to dry the shell quickly without wax expansion and contraction. Air circulation helps to dry the shell quickly. The process of dipping the pattern tree, drain, and coat with refractory sand repeats with different fineness of sand for 7-8 times. Finally dry the shell for 48 hrs before de-waxing.

De waxing: Dried shell can be de-waxed mostly by dipping into the molten wax. Use of steam autoclave, dry hot air also used for dewaxing. Dewaxing by the use of microwave has been achieved in the past 10years in advance countries. Shell that is not fully dried prior to dewax or not have achieved sufficient strength to withstand the internal pressure of the expanding wax results in crack. Dried shell is dipped into molten wax which is at temperature about 150 deg C this will lead to de-waxing ie.wax in the shell will easily melt and slip from shell

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