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Dynisco eliminates mercury in sensors

By: By James Snodgrass
EUROPEAN PLASTICS NEWS

October 24, 2013

DÜSSELDORF, GERMANY — Walking around K, it’s all “green” this, “blue” that and “eco” the other. But when Franklin, Mass.-based Dynisco LLC introduced Vertex, its mercury-free melt-pressure sensor in October 2012, Matthew Carrara, vice president and general manager of Dynisco Plastics, didn’t intend the “green” connotations of the brand.

“We didn’t realize until afterwards that “vert” was French for “green.” I thought of the name “Vertex” meaning “apex,” the top of the pile. And the “ex” in the logo symbolizes the diaphragm flexing,” he said.

Whether or not the branding was intentional, the intention behind the product was green — getting rid of mercury.

Carrara explained: “If you go back historically, the typical melt-pressure sensor transmits flow by mercury. So inherently there’s a belief of toxicity with mercury in any product, even though it’s a very small amount.”

Several companies over the years have tried to perfect making a pressure sensor without mercury that still gives the features and benefits of mercury. Dynisco (Hall 10, G20) spent nearly 10 years researching different types of technology.

“Four years ago we nailed down a technology that’s a capacitance-based technology,” said Carrara, “Two plates move and measure the distance and capacitance, and that gives you a corresponding output through a voltage that you can convert to a signal.

“The beautiful thing is it’s simple. It really only has two moving parts. One of the benefits of it is that the diaphragm is about 7½ times thicker than a typical melt-pressure diaphragm, which are about the thickness of a piece of paper. So if you drop it, or nick it, or ding it, you can actually render the unit inoperable, because it’s so thin. The increased thickness provides protection not just on the bottom but up the sides as well.”

The ill-effects of mercury are obvious. “The waste stream was the big problem,” Carrara said. “If a unit fails, the plastic goes up and clogs it, so you don’t have much concern of [contaminated] plastic getting back in the process. But people never want to take the chance.”

Traditionally, Dynisco recalled sensors that failed in the field and reclaimed and refined the mercury, because “not many people are mining mercury in the United States these days.”

The advantage of Vertex, being mercury-free, is that it can be used in food extrusion, medical packaging and other applications where the possibility of mercury contamination would be unthinkable.

Carrara was keen to point out Vertex’s four-year warranty. In wear tests, Dynisco claims that Vertex will last three or four times longer than a normal pressure sensor.

He said that, in the field, sensors are used in really rugged applications, with temperatures up to 400° C, and materials that are sometimes corrosive and sometimes abrasive.