Machine Design

Cooling is key to better molding

Kokomo, Ind.-based analytical lab Foresite Inc.'s overseas supplier designed production molds for a new plastic assembly.

Foresite's C3 cleanliness test system directs microbursts of steam through a 1.6-mm-diameter flow-path to the opening in the end seal. Then, the vacuum draws the sample into the test chamber through another 1.6-mm-diameter path. The sample is analyzed electrically in the test chamber for corrosive residues and the information is transmitted to the system computer to determine the sample's cleanliness.

The C3 test cell combines a hollow body, snap-fit cap, electrode, and end seal. The red arrow shows the path of the steam onto the test surface. It condenses and soaks at the opening in the end seal briefly. The blue arrow shows the path the sample then takes when drawn into the testing chamber by vacuum.

"Molds didn't cool properly so components wouldn't snap together right. And despite secondary cleaning by the molder, parts did not meet our cleanliness specifications," says Steve Ring, director of new product development.

So Foresite turned to Minnesota Rubber and QMR Plastics in Minneapolis, which provided the know-how to successfully manufacture the parts for the test cell — the heart of Foresite's C3 system. The C3 is used by electronics manufacturers for realtime analysis of printed-circuit boards and assemblies for cleanliness.

Intended for one-time use, the test cell combines a molded hollow body and cap, electrode, and end seal. The electrode slides into two slots inside the cell body. The cap and body snap together, retaining the electrode and forming a vacuum seal. Vacuum is applied, drawing the sample up into the testing area of the body.

"When components don't fit together right, the vacuum is too low and varies too much," says Dwight Bruellman, technical sales at QMR. "However, readings must be consistent and at a certain level for C3s to operate reliably," he says.

QMR first improved mold cooling with additional cooling lines in the molds. This made part dimensions more exact, increased dimensional stability, and shortened the molding cycle. The next step was to use a medical-grade polypropylene to mold components because such high-grade resin help ensure cleanliness. The firm also used a recirculating, filtered cleaning tank and a parts-drying oven after molding and before assembly and packing.

"The cell vacuum-seal has improved 50%, with vacuum tests reading consistently 24-in. Hg. And Foresite lab tests continue to verify cell cleanliness," says Bruellman.

Foresite Inc.,
Minnesota Rubber and QMR Plastics,





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