Continuous-flow conveyors processing operations

Process industries frequently need to weigh and control the flow rate of bulk material for optimum performance of such devices as grinders or pulverizers, or for controlling additives, eg, to water suppHes. A scale can be installed in a belt conveyor, or a short belt feeder can be mounted on a platform scale. Either can be equipped with controls to maintain the feed rate within limits by controlling the operation of the device feeding the material to the conveyor. Direct mass measurement with a nuclear scale can also be used to measure and control such a continuous stream of material. 

The first series of products developed and commercialized were the solvent processable resists called RISTON I. A 24" wide conveyorized spray developer was fabricated that used 1,1,1-trichloroethane (methyl chloroform) as the developing solvent. After development, the PWB panel was then ready for etching or electroplating. Following that, it was necessary to strip away the polymerized resist. Methylene chloride or azeotropes with methanol were the iiutial stripper chemistries and DuPont fabricated 24" conveyorized equipment to perform that operation. The developer and stripper equipment both fabricated from stainless steel, required in-line solvent stills that would continuously feed a fresh supply of clean distillate solvent through a series of spray chambers and in a counter flow direction to that in which the boards were traveling. Smaller fabricators often stripped using a series of dip tanks. 

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