TABLE OF CONTENTS Cryogenic operations use cryogenic (i.e., very low) temperatures and normal loose abrasive finishing processes to remove burrs. Most of the issues described in Chapters 8 and 10 apply to this process, except that no water or oil is ever used with the cryogens.
Cryogenic processes used include:
barrel tumbling
vibratory finishing.
Cryogenic deflashing of molded rubber or plastics products and aluminum or zinc die-castings is done in barrels and vibratory machines by freezing the workpieces with liquid nitrogen, carbon dioxide, or dry ice. Flash on the workpiece embrittles when its temperature is reduced, and mechanical means are used to remove the flash. When operators use liquid nitrogen, proper ventilation is essential and care is required in handling the cold parts and media. The cost of liquid nitrogen may be a limitation to the use of this process.
Barrels and vibratory machines used for cryogenic deflashing require special double-walled, insulated work chambers for conserving the liquid nitrogen. The chambers are fitted with multiple nozzles for spraying the nitrogen. It is general practice to cool the media in the work chamber prior to adding the workpieces, which must then also be cooled prior to starting the machine. Temperature control during processing is essential. Temperatures as low as ?320 F ( ?196 C) are used for some parts. Cryogenic barrels usually have 6 or 8 sides. The door is on one of the sides.
Equipment sizes range from 3 to 35 cu ft, although other sizes can be built.
Cryogenic tumbling...
