Sand, Core and Shell Investment Casting Removal Using Caustic Leaching
Magnus Engineered Equipment (MEE) has supplied equipment to the investment casting industry for more than 50 years. Investment casting, or die casting, is a technique for forming metallic components having complex geometries, especially hollow components. Hollow cored super alloy airfoils and gas turbine engine components are examples of complex geometries produced with the investment casting process. MEE equipment is used with concentrated caustic solutions of NaOH (sodium hydroxide) or KOH (potassium hydroxide) to remove shell residues from ferrous and non-ferrous metal castings (including aluminum). Operating at just below the boiling point of the solution, the process breaks down the fused silica shell used in the investment casting process without damaging the metallic substrate. The process is faster, safer and more efficient than mechanical methods of shell removal and all surfaces within the substrate are cleaned.
MEE supplies equipment which uses heat, agitation and turbulation to quickly and effectively remove the shell residues from substrates including the complex geometries found in many castings. The effect of agitation and turbulation increases the dissolution rate by increasing chemical mass transfer at the shell interface. Agitation and turbulation act to quickly remove dissolved silica and spent chemistry from the substrate surface while bringing in fresh chemistry to continue the dissolution reaction at the fastest rate. MEE supplied equipment also continuously filters the bath thus removing dissolved silica and enhancing the dissolution rate of the remaining ceramic shell by returning clean chemistry to the part surface.
The temperature at which the caustic solution is operated is dictated by the concentration of the NaOH or KOH used. As a rule of thumb, it is advisable to operate at a temperature which is 20 oF below the boiling point of the solution being used so as to prevent cavitation in the pumps used to circulate the solution. (The lower pressure on the suction side of the pump lowers the boiling point of the solution). Most users of MEE equipment operate with a NaOH or KOH solution concentration of 35 to 50 wt%.
MEE supplies off-the-shelf or custom designed equipment for investment casting removal applications. Material handling, by-product removal, automation and post-processing needs can be addressed by MEE to make the overall process efficient and worry-free. Contact MEE today to discuss your investment casting application.