Cryogenic Deflashing Process

Cryogenic high-speed shot blast deflashing is a process for removing flash from molded rubber parts. We use liquid nitrogen, high-speed rotation and shot blasted plastic deflashing media in varying combinations to remove the flash in a highly precise, economical and expedient manner.

Parts that have thin flash can be quickly and thoroughly cryogenically deflashed. This process is exceptionally good at removing the inner dimensional and complex flash that cannot be removed by any other method. Deflashing plastic parts and rubber parts is an easy way to remove leftover particles.

Cryogenic Systems Parts before and after deflashing

Molding for Best Results

The old saying “garbage in, garbage out” is very appropriate. To consistently get a quality finished part, you have to consistently put in a quality unfinished part.

Everyone who molds rubber parts feels that the ideal flash configuration is no flash at all. Flashless molding is being developed and will have a future, but given the vast quantities of existing molds, cryogenic deflashing will be around for quite a while. So what is the ideal flash configuration? Make the flash as thin as possible, with as good a flash base as possible, or in the case where sealing surfaces are involved, try to move the flash away from the critical areas.
The location of overflow in reference to the part has an impact on the cycle time and deflashing temperature, as well as general deflashability of the part. Overflows should, if they are necessary for the molding process, be moved as far away from the part as possible (X* > plastic shot size).

The closer the overflow gets to the part, the more difficult it is to remove; the plastic shot cannot penetrate between part and overflows to remove the flash. If enough room is left between the part and the overflow, the following advantages are usually achieved:

  • Shorter deflashing cycle
  • Better deflashing quality

*X = distance between outer edge of part and inner edge of overflow. Plastic media must be smaller than X in order to get inside this area and deflash properly.

Tear trim design was developed to eliminate the cryogenic deflashing operation. The overflow is placed extremely close to the part (X = zero)** so that, when this overflow is removed by hand, no flash remains.

This design usually works well until the mold starts to wear, and this usually does not take very long because of the knife edge required between the part cavity and the overflow cavity. Trying to cryogenically deflash these parts is very difficult. When the part is cooled down and becomes hard, the overflow essentially becomes part of the part, and the shot media cannot penetrate the minuscule area between part and overflow. A solution to permit cryogenic deflashing of this part design is to fill in the overflow cavity, thereby leaving only a skin (thin flash) to remove. This improves the deflashability and quality of the part and also results in a mold that has far superior wear properties.

**(actually, x approaches zero – there is virtually no thin area between part and overflow).

Everyone knows that the parting line and flash base configuration determine the overall deflashing quality. If there is no difference between the thickness of the flash and the part, the deflashing unit will remove both. No cryogenic deflashing unit will eliminate molding problems.

In these cases, if part quality needs to be improved, mold rework is necessary.

When qualifying your part:

  • Best results can be achieved when the parting line does not exceed 0.005 inches, or 0.127 mm thickness
  • Parts need a clear, consistent demarcation of flash

The Process

To begin the rubber deflashing process, liquid nitrogen (LN2) is injected into a highly insulated chamber in which molded rubber parts are tumbled and blasted. The flash, which should be significantly thinner than the parts themselves, is embrittled by the low temperature.

At the same time, a precision throwing wheel, turning at high speeds (up to 8,000 rpm), throws plastic shot at the tumbling parts, and the plastic shot breaks off the brittle flash on impact. The deflashed parts remain in the chamber, and the machine separates reusable media from debris (flash and dust).

There must be room within the blasting chamber for the parts to tumble. The tumbling action exposed the parts to both the LN2 and the media stream. The actual size of the chamber should be at least twice the size of your load. Average load sizes are from 3/4 cu. ft. of parts to 4 cu. ft. of parts.
Average cycle time in most cases is three to five minutes.

Ultimately, the best way to qualify your parts as candidates for the cryogenic deflashing process is to have a sampling of your parts processed (tested) in a cryogenic deflashing machine.

The new generation of cryogenic deflashing machines uses the latest in technology – offering options including programmable controllers with numerous deflashing “recipes” for automatic operation, networking capabilities, bar coding abilities, message centers, SPC reporting, and remote access via VPN for trouble shooting. Learn more about the cryogenic deflashing process and the machines involved here at Cryogenic Systems & Parts.