Armstrong Mold Corporation

Precision Air-Set Sand Casting Process

Armstrong utilizes the no-bake sand molding process.  This produces metallurgical quality and finish that is superior to that of industry standard oil or green sand methods.  Armstrong utilizes only much finer grain silica than most foundries, taking this extra step to produce a better finished casting.

Another reason we produce castings more precise than others, even those who use this process, is the engineering work we put into the pattern before making the molds, and the checks and processes to which we subject the casting after it is poured.  These steps include:

• The initial design of the datum points and parting of the mold is selected for ease of machining and to achieve dimensional quality.
• The mold material used (cores of no-bake sand, shell sand or plaster) and gating is created to give the customer the best metallurgical quality and the best surface finish achievable.
• Required fixturing is designed to insure dimensional quality through the straightening and final inspection process.

On the shop floor, the tests that are done on the melt before it is poured are:

·       A spectrometer check that will give us a chemical analysis to confirm the alloy is within specification.

·       An Alu-delta check, giving us the grain size and the silicon eutectic phase of the melt.  Both the grain size and eutectic phase can be adjusted with additions to the melt. 

·       Purging the melt with an inert gas to drive off the hydrogen level of the melt, to finely control porosity in the casting. 

·       Test bars are poured from the melt and follow the casting through heat treatment to check tensile strength, yield point, and percent of elongation.

·       When required, a sample of the melt is polished and a metallographic inspection is performed  under microscope, checking grain structure and the silicone phase

After the casting is poured and goes through knockout, the new casting:

·       Undergoes First inspection.

·       Is serialized.

·       Is x-rayed to prove internal integrity, the gating system design, as well as to check for melt temperature problems, porosity and internal flaws.

·       Is processed to improve the finish quality.

·       Goes through the straightening department.  In straightening, the casting will be put through a solution cycle of 1000 degrees F for 12 hours (time and temperature dependent upon the alloy) which puts them in a T-4 or soft state for several hours.  During this time the castings are straightened to templates and fixtures to confirm dimensions critical to function are obtained, the machined surfaces are properly located and the geometry is correct. 

·       Put through an aging heat treatment cycle of 310 degrees for 3 to 5 hours (depending on alloy) which hardens the casting to a T-6 state to improve the machined surface.

·       Goes through a final inspection process to check DTF dimensions and to make sure that all steps in the process have been completed.

·       Where required and for additional cost, the casting can also be put through pressure testing, dye-penetrant testing and a final x-ray,

Foundries that skip some of these critical steps may be able to make a casting cheaply.  However, they will not be certain of the metallurgical quality, internal integrity or dimension stability of that casting let alone be able to provide traceable information,