Cryo Central - Deflashing

Robin A. Rhodes
Cryogenic Institute of New England, Inc.
rrhodes@nitrofreeze.com

Cryogenic Deflashing is employed to remove undesired residual mold flash that remains on molded parts after they are removed or ejected from the mold cavity. Typically, this flash occurs in areas where different sections of the mold come together (and apart) and is known as "parting line flash". The remaining mold flash typically traces around where the different mold sections "mate" and is created when the liquid mold material escapes out of the mold cavity into the tight area where the mold sections press against one another.

Mold flash can be caused from old or worn mold cavities that no longer fit tightly together. Other times, the complexity of the part requires so many mating pieces with such precise geometries that it is almost impossible to create a perfect fit on every impression. Most often, the type of material being molded, and its attendant viscosity in its liquid form, is the primary factor that leads to the creation of the unwanted mold flash.

To remove flash, manufacturers can turn to a cryogenic deflashing process. This is often performed by an outside specialty finishing contract shop. By processing the parts in a frozen state, the flash becomes stiff or brittle and breaks away cleanly during its processing.

The process typically works as follows: Parts are loaded into a basket that is placed into an insulated chamber. Using liquid nitrogen, the temperature of the chamber (and the parts) is lowered to a programmable point, typically between minus 50°F and minus 200°F. The parts are tumbled at a predetermined rate (5 to 50 RPM) and blasted with a cryogenic grade polycarbonate media that is sized at between 0.015" and 0.060". The temperature, tumble rate, size of the blast media and process time varies widely depending on the part size and geometry as well as the type of material being processed.

Cryogenic deflashing offers the advantage of not degrading or otherwise affecting the finish of the parts. In addition, only the undesired flash is removed and the integrity of the part shape is fully maintained. Sharp edges are not rounded from the process and the media can penetrate into recessed sections and clean blind and through holes with remarkable precision.

A wide range of molded materials can utilize cryogenic deflashing with proven results. These include:

• Silicones
• Plastics — (both thermoset & thermoplastic)
• Rubbers — (including Neoprene & Urethane)
• Liquid Crystal Polymers
• Glass Filled Nylons
• Aluminum Zinc Die Cast

Typical examples of applications that use cryogenic deflashing include:

• O-Rings & Gaskets
• Catheters and other in-vitro medical
• Insulators and other electric / electronic
• Valve stems, washers and fittings
• Tubes and flexible boots
• Face masks & goggles

In some instances, cryogenic deflashing does not utilize a blasting action, relying instead only on the tumbling of the parts to remove flash on the outer edges. This early technique, still in use today, was widely employed in the rubber molding industry for automotive components.

Once developed, cryogenic deflashing process recipes offer consistent results from batch to batch. Cost per part is generally well below any alternative technique.

Today, many molding operations are using cryogenic deflashing instead of rebuilding or repairing molds on products that are approaching their "end-of-life". It is often more prudent and economical to add a few cents of production cost for a part than invest in a new molding tool that can cost hundreds of thousand of dollars and has a limited service life due to declining production forecasts.

In other cases, cryogenic deflashing has proven to be an enabling technology, permitting the economical manufacture of high quality, high precision parts fabricated with cutting edge materials and compounds.