Shell Room

The second step in the investment casting process is the building of a ceramic shell around the wax pattern.  This process is accomplished by first cleaning the parts in a three-step dip process, ten coating the wax part with a ceramic slurry, followed by broadcasting sand onto the wet surface.  Once a part is coated in this fashion, it must dry completely, a process that can take from a few hours to a few days (depending on the part geometry).  Once completely dry, the process of dipping/sanding is repeated.  This process normally builds up over five to fifteen coats of ceramic. Our ceramic department can build ceramic molds/shells for parts with finished metal weights of a few grams, as well as very large parts weighing over 150 kg.  These parts can be up to 42 inch diameter with a part height typically less than 30 inches.  For some specialized applications like boiler piping handcuff supports, we may cast up to 42” long sections.  This department is climate controlled and dehumidified to accelerate drying.  The facility utilizes redundant backup air conditioning and backup generators to insure optimal conditions even in the event of a machinery or power failure.

In order to promote the optimum in cost effective investment casting, EMP has worked with a Mexico based robot integration company to install an automated ceramic dipping process.  This system utilizes two ABB 7600 6 axis robots with a payload capacity of 325 kg.  The robots are integrated into a unique two tier stack drying system, featuring high velocity air movement and dehumidification.  The system is programmed to facilitate specialized processing requirements.

By using only ISO certified suppliers for our sand and ceramics, the customer is assured of optimum material quality.  The various process parameters necessary for robust part quality are stringently monitored by our engineering staff.

After the ceramic coating process is completed, the ceramic shells will be placed in a steam autoclave, and swiftly pressurized to 150 psi.  This puts pressure on the outside of the ceramic shell, helping to prevent cracking as the wax thermally expands.  Within a few seconds the wax becomes liquid and drains out of the ceramic shell.

At this point in the process, the ceramic shell is now hollow.  Before molten metal can be placed into the ceramic shell, the shell must be burned out to reduce any leftover wax into an insignificant amount of residual ash.  This burnout process also converts the green shell into a stronger “fired” ceramic shell.  Finally, the ceramics are held at a temperature typically around 1900F for one to four hours.    Once the ceramic shells have fully cured in the oven, they will be  very swiftly picked up with long metal tongs and placed on the melt deck.  The hot 1900F shell helps promote the ability to fill the very thin cross-sections found on many investment castings, with typical 2850F molten stainless steel.  EMP uses four primary induction melt units with output rates of up to 350kw, and a total output of 800kw.  The use of our lab resources with multiple spectrometers and other testing equipment, insure optimum metallurgy.

Once the parts have cooled, they are ready to remove the shell material, cutoff any gating/risers, and move the part into our in-house electric heat treating.  After heat treat, the parts will typically be sandblasted and forwarded to the next department for secondary operations such as machining, plating, welding, polishing, etc.

Shell room is 400 square meters (4000 sf)
Slurry tank capacity of 42 and 54 inch maximum part size
Air conditioned, with redundant backup
Dehumidification systems, with redundant backup
Use both fluidized beds and drums (rainfall) sand application systems
12 accelerated drying carts (240 Shell) based on Rolls Royce drying system.
Use shell drying standards based on each item’s process requirements, with infrared thermal measurement and conductivity measurement.
Process control charts for slurry consistency
Use chemical analysis from vendor (REMET-ISO Certified) to monitor slurry parameters
Suppliers of sand and stuccos are ISO Certified
Wax parts are cleaned with a 3 stage wash process prior to first dip
Generator backup
Shell room designed conveyor rails for large parts
High velocity stack drying conveyor with dehumidification
Two ABB 7600 325kg capacity robots for automated dipping and sanding