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Why Medical Injection Molding Uses Cryogenic Deflashing


Medical injection molding supports the use of a wide variety of plastic and rubber materials. Examples include PEEK, polycarbonate, and LSR – just to name a few. During the injection molding process, excess material known as flash can escape the mold and mar part surfaces. The causes of flash are numerous and include parting line mismatches from worn tools, improper venting, problems with clamping pressure, inadequate sprue bushing support, and processing issues that lower viscosity.

Flashless molding that uses precision tooling can produce parts with only small amounts of flash, but this type of tooling is relatively expensive – and the injection molded parts still aren’t completely flash-free. Plus, in many medical applications, injection molded parts need tight tolerances and a fine surface finish. Otherwise, the parts won’t align during assembly or, in the cases of molded medical gaskets, provide proper sealing. Mold flashing can also affect ergonomics and perceptions of quality.

Comparing Cryogenic Flash Removal Methods

Nitrofreeze® cryogenic deflashing removes flash from injection molded parts by cooling them near their glass transition temperature (Tg) so that the residual plastic or rubber flash can be removed. The parts are then blasted with a cryogenic-grade polycarbonate media to remove unwanted flash.

Nitrofreeze® dry ice deflashing combines the advantages of cryogenic deflashing with dry ice as a media. It is a safe and clean process that’s effectively media-less because dry ice sublimates, or changes state from a solid to a gas. Dry ice blasting is approved by the U.S. Food and Drug Administration (FDA), which has regulatory authority over medical devices, and is used typically for individual parts instead of batches. By contrast, both cryogenic deflashing and dry ice deflashing are ideal for batches of parts.

Cryogenic Deflashing vs. Other Flash Removal Methods 

Cryogenic deflashing and cryogenic tumble deflashing won’t affect the surface finish or part tolerances, but how do other types of flash removal compare? Thermal energy deflashing burns a mixture of O2 and H2 (or O2 and CH4) with combustion temperatures that can reach 3000°C (5323°F). With plastic and rubber parts, that’s hot enough to mar the surface finish. Magnetic abrasive deflashing, a flash removal method that uses tiny steel pins, water, and magnetic force, isn’t the best choice for rubber or plastic either.

During blast deflashing, a metal powder (usually alumina) is sprayed on part surfaces under high pressure and speed. That’s not ideal for injection molded medical parts because of the cleanup that’s required to remove residual powder, and the rough surface finish that results. Ultrasonic vibration is a cleaner process but it is not always strong enough to remove injection mold flash. Plus, it doesn’t work well with rubber. Manual deflashing, the most common option, is time-consuming. It’s also labor-intensive and often yields inconsistent results.

Nitrofreeze® Deflashes Medical Injection Molded Parts

What’s the best way to remove flash from medical injection molded parts? Contact the experts at Nitrofreeze® to review your requirements. If your molded part is a viable candidate for our batch deflashing techniques, we can perform sampling to demonstrate our process. The consultation is free of charge. Nitrofreeze® also sells cryogenic machines and dry ice blasters so that medical injection molders can use this equipment in-house and provide their customers with even greater value.

To learn more, contact us at the phone number and email listed below.

(508) 459-7447 x105 |