9. CLOSE-TOLERANCE PROCESS HUMIDIFICATION

A. Problem/Issue

An Implantable Telemetry Manufacturing Company used a vapor process to form a polymer on the end of a sensor inside a glovebox-style cabinet. This process had the requirements of 17% relative humidity with a window of only 2 percent. They were using dry nitrogen gas and mixing with a venturi valve. The cabinet also had to be vented because of the dangerous fumes inside. They had a very high scrap rate because the chamber was wandering outside the prescribed limits.

B. Analysis

We logged the humidity inside the chamber along with four other traceable events surrounding the process. We researched many other methods of controlling humidity and found that the range they were concerned with was unique when combined with the exhaust requirements. We separated each of four events and made further tests using a range of values with each event.

C. Solution/Results

A new ergonomic cabinet was designed with a novel plenum system that mixed the air using a modified static mixing system. We located a source of dry air that could be generated on-site with little or no maintenance. We installed the system and began to test with dry ice as the indicator gas. After flow testing, we modified the armhole gaskets and added more baffling to the intake plenum. We finally logged the humidity when subjected to the same four traceable events. The humidity maintained within the control limits and was validated. The system increased the yield to the point that it paid back all the engineering and installation costs in a matter of months and is still used today.