Process control for cryogenic decoating

Claim 1

In a process for removal of bonded coatings from articles by chilling the articles in a closed treating chamber to effect embrittlement of the coatings thereon and subjecting the chilled articles in said chamber to high velocity impact by blasting media centrifugally hurled thereon by a rotating bladed impeller, the improvement which comprises the cycle sequence: (a) initiating the process cycle by subjecting the coated articles to a cooldown stage in an initial environment of cryogenic fluid until a preset lowest temperature level is attained within said initial environment; (b) continuing exposure of said articles at said first preset temperature level for a fixed present time period to assure pre-chilling of said articles to below embrittlement temperature of the coatings thereon; (c) at the expiration of said pre-chilling time period, initiating impact of the articles with the blasting media; (d) while continuing said impact, subjecting said articles to a controlled warming temperature environment until the warming environment reaches a second preset temperature level and when the second preset temperature level is attained continuing said impact at substantially said second preset temperature level for the remainder of a fixed time period measured from the time of initiation of impact with the blasting media; (e) at the expiration of the remainder of said last-mentioned fixed time period, discontinuing continuous injection of cryogenic fluid into said cryogenic environment while maintaining exposure of said articles to temperatures proximate that of said second preset temperature while continuing impact with blasting media to the end of said treating cycle; (f) and thereafter discharging the thus treated decoated articles from the treating chamber.