< INVESTING A WAX PATTERN IN CERAMIC SHELL 2
INVESTING A WAX PATTERN IN CERAMIC SHELL 3
5 FIRST STUCCO APPLICATION
After the wax assembly has been dipped for a second time and the excess slurry allowed to drain away, the assembly is removed from the vicinity of the tank to a clean area. This is where a fine powder grade of dry STUCCO can be dusted over the wetted surfaces. The fine refractory grit is best applied to the dipped assembly either through a graded MESH SCREEN, or else a mechanised RAIN MACHINE. The mesh prevents any oversize particles from penetrating the slurry coating and disturbing the wax. The dry refractory stucco adheres to the wet slurry, with excess stucco falling off the assembly into a collection tray. Once allowed to dry and harden, the applied slurry and stucco combine to make up the integral fabric of the shell’s wall.
These first coatings form the principal facing layers of a ceramic shell mould, these layers dictate the quality of surface reproduction in the metal cast. The first few layers of refractory are necessarily dense, enabling any fine texture and detail on the wax pattern to be accurately ‘imprinted’ on the shell mould’s internal surface. The subsequent stages of ceramic investment application have a relatively minimal influence on the quality of cast surfaces, and are instead mainly concerned with the building up the bulk of a strong, porous mould wall.
6 ONGOING SLURRY APPLICATIONS
After the second dip in a fine slurry/first stucco application and drying cycle, the assembly is ready for dipping in a coarse back-up slurry. The investment mould is first carefully checked to ensure it has been fully covered with fine investment, it is is also inspected to ensure it is completely dry before immersion. The assembly may be pre-wetted with a pure COLLOIDAL SOL prior to dipping in the back-up slurry, though this level of attention is by no means a requirement. The back-up slurry is usually distinguished from the premium grade slurry by being more fluid, it may also be somewhat different in colour (due to the different refractory flour component).
The assembly is coated with the second slurry using the same dip/paint/spray techniques previously described for first coats, ensuring any interior hollows and recess of undercut are fully wetted. Even though the secondary coat is less crucial than the first coat, and may be applied more quickly, coverage of the assembly should be none the less just as thorough. Once all surfaces have been wetted, the assembly is once again lifted clear of the tank and drained of excess slurry, paying particular attention to the emptying of the interior void in OPEN SHELL assemblies.
INVESTING A WAX PATTERN IN CERAMIC SHELL 4 >
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