Perma-Code has developed and patented the system that uses sequentially encoded stencils to create permanent barcodes or machine-readable data symbols directly on individual castings.

Prior to use, the stencils can be pre-verified and submitted to the UID (unique identification) registry. For each casting, a stencil is applied to an interior surface in a sand mold before it is closed. When the mold is poured, the stencil creates a high-quality UID compliant barcode on the casting.

Perma-Code claims that the resulting identification marks are the most durable available, and points out that they will easily withstand the harshest shot-blast cleaning of the raw casting, as well as repeated overhaul cycles. A photo of the coding on a diesel-engine housing shows how it has survived blast cleaning.

The process begins when the pre-encoded stencil is produced, and then is applied to the mold surface by mechanical means, or with aerosol spray adhesive or hot-melt adhesive.

The first step in the application process is to designate an area in the mold for the stencil to be applied. The area must be clean, dry, free of loose sand particles, and smooth. In some cases, it is first necessary to apply a high temperature compound to smooth the area as necessary. In any case, the stencil to be applied should be as low in the mold as possible to maximize head pressure.

Regardless of the application method, the pre-encoded stencil should be placed on a contrasting surface and verified with a barcode reader.

A staple gun, brad gun, or nail gun may be used for mechanical fastening. Position the pre-encoded stencil onto the selected area of the sand mold. Staple, brad, or nail the barcode stencil about the perimeter as needed to conform tightly to the surface of the sand mold. Inspect for gaps between the stencil and mold surface. If any gaps exist, add additional fasteners as necessary.

To use an aerosol spray adhesive, place the stencil upside down on a paper surface. Spray it with the aerosol adhesive from a distance of about 14 in. Apply two coats to the stencil surface to ensure the stencil will adhere tightly to the sand mold. Allow the adhesive to become tacky prior to use. Place the stencil in the pre-determined location in the sand mold. Using a pressure pad, press the stencil tightly onto the mold surface. Inspect for gaps between the stencil and the mold. If there are any gaps, use the pressure pad to eliminate them.

To apply the stencil with hot-melt pressure-sensitive adhesives, the hot-melt glue dispensing machine should be set with a tank temperature of 350°F, hose temperature at 355°F, gun temperature at 360°F, pattern air at 20 PSI, feed screw at 50%, and shot timer at 50 ms. Position the extension arm and gun to spray the desired spot on the sand mold. Hold the tip 8 to 10 inches from the mold surface and spray the PSA over the desired location in the mold. Then, place the stencil onto the applied glue, then press it in place. Inspect for gaps between the stencil and the mold. If any gaps exist, use the pressure pad again to eliminate them.

If a problem develops during any of the three application processes, the stencil should be completely removed. Repeat the steps with a new stencil and cancel the scrapped stencil.

Perma-Code reports it has developed stencil materials to withstand 3,000°F, for use with any type of molten metal.

For permanent-mold operations, a heat-activated adhesive-backed stencil is encoded prior to use. A stencil is placed on the hot tooling in a location low in the mold for maximum head pressure. The permanent-mold surface is coated with a refractory mold coating prior to casting. A version of the same technology has been developed for investment casting operations, too.