1 March 2002
Gauge design saves replacement costs
Chester, Va.—At Honeywell's Performance Polymers plant in Chester, technicians charged with making Nylon 6 faced a daunting challenge.
To process Nylon 6-a material widely used in carpets, car parts, wiring, and other consumer goods-a polycondensation chemical reaction must occur that increases the temperature and pressure of caprolactam (lactam), a monomer, in an inert atmosphere. When the correct viscosity is achieved, it moves to an extrusion process, where it is converted into a polymer.
After extrusion, the product is spun into yarn or cut into pellets, then washed. Once the polymer is washed and dried, it's packaged and shipped to other facilities, or end users, for fabrication.
Unfortunately, the highly volatile, molten 300°C (572°F) lactam sometimes cools down and solidifies in gauges' bourdon tubes, preventing readings and making the gauges useless.
Honeywell designed the continuous process to run 24/7 and annually turn millions of pounds of lactam, made at a neighboring Honeywell chemical plant, into Nylon 6. Unplanned shutdowns are extremely costly.
Controlling consistent temperature, pressure, and product movement throughout the plant is key to profitability. However, Honeywell instrument technician David Edwards said the Nylon 6 process's extreme conditions "can play havoc with ordinary instrumentation."
Keeping gauges from clogging made Honeywell's operation even more challenging, he said. When that occurred, technicians needed to install a new gauge before engineers could make routine pressure readings. Sometimes, less than 24 hours later, the new gauge would clog and also become inoperable.
About three years ago, during a plant review meeting with Commonwealth Industrial Specialties, a local processing instrument distributor, the Honeywell team learned about a gauge that had a diaphragm to separate the instrument from the process media.
Called Sealgauge, the WIKA Instrument Corp. diaphragm prevented the lactam from getting into the instrument and clogging it. Honeywell reported it saves thousands of dollars annually because technicians no longer need to replace clogged and broken gauges.
The product's design combines a chemical seal and a pressure gauge into one unit. A mechanical link between the diaphragm and gauge does not require a system fill to transfer pressure readings. Traditional gauge and seal combinations, which require a system fill, encounter problems in high-temperature applications.
In addition, in processes where pulsation and/or vibration is severe, users can fill the Sealgauge with glycerin to dampen movement, reduce pointer oscillation, and extend gauge life (silicon and halocarbon are also available for specific applications). The mechanical design also allows the gauge to mount in any position, easing readouts and eliminating pressure reading errors caused by head pressure effect.
Most Sealguages at Honeywell have continued to operate within accuracy specifications since they were first installed more than three years ago, Edwards said.
Besides the diaphragm, the gauge has other features technicians like. For example, it uses a mechanical link unaffected by mounting positions or temperature. It also features a one-piece upper housing construction durable against shock and vibration.
—Edited by Jim Strothman
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