Shell moulding process
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The shell moulding process involves making a mould by applying a mixture of sand and thermosetting resin to a heated metal pattern. This forms a hardened shell around the pattern that can be removed. The shell mould allows for casting of complex parts with a smooth surface finish, high precision, and thin walls down to 2-2.5mm. Examples of parts made using shell moulding include brake drums, bushings, pistons and other automotive and machine components.
Shell moulding process
- 2. INTRODUCTION Pattern – made of copper alloys, Cast iron, Aluminum or Steel Shell – dry, fine silica 5-10% thermosetting phenolic resin (phenol formaldehyde) Heated: 200 - 300 C Curing of shell for 1 - 3 min at 250 C – 450 C
- 3. high precision / accurate castings / smooth surface finish complex parts cleaning of casting is reduced /eliminated size of casting is 10 - 13.5 kg minimum wall thickness 2 - 2.5mm is possible. Examples: Brake drum, bushing, cam/cam shaft, piston, piston rings, pinions, pipe bends, air compressor crank cases, etc.,
- 4. SHELL MOULDING PROCESS It is a process in which, the sand mixed with a thermosetting resin is allowed to come in contact with a heated pattern plate (200 degC), Skin (Shell) of about 3.5 mm of sand/plastic mixture to adhere to the pattern Then the shell is removed from the pattern This process can produce complex parts with good surface finish 1.25 µm to 3.75 µm, and dimensional tolerance of 0.5 % A good surface finish and good size tolerance reduce the need for machining. The process overall is quite cost effective due to reduced machining and cleanup costs. The materials that can be used with this process are cast irons, and aluminum and copper alloys.