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Houston, TX -- Melfi Technologies has completed a gravimetric feeder control retrofit at a major polyethylene resins producer. Each of the two compounding lines consists of a single main powder resin LIW screw feeder running at 30,000 pounds/hour, with four powder additive LIW feeders running at 10-150 pounds/hour.
The existing feeders were the conventional LIW-screw and weighbelt type using digital vibrating wire loadcells.
Maintenance for the proprietary electronics was becoming increasingly difficult, as parts and service was only available from the feeder manufacturer. The maintenance manager began searching for a replacement control system that specified components readily available from local stocking distributors.
Melfi Technologies was contacted and their applications engineer visited with a PLC demonstration control system. The gravimetric controller has been developed around the Rockwell Automation
ControlLogix and CompactLogix hardware platforms, using standard RSLogix5000 programming software with RSView32 HMI. The field communications to the motor drives and loadcell amplifiers are open standard DeviceNet components. After reviewing both their capabilities and previous installations, Melfi Technologies was awarded the project to convert two compounding lines.
The entire proprietary microprocessor-based control system was removed and replaced with an Allen-Bradley ControlLogix PLC performing the LIW algorithms, using and Hardy Instruments Devicenet weighing modules mounted on the individual feeder to read the loadcell weight. Keeping all the field equipment on a Devicenet network ensured only a single new field cable needed to be pulled for the entire retrofit.
Downstream of the pelletizer there is weighbelt feeder to totalize the finished pellet stream. An analog level indicator in the prefeed hopper controls the belt feed rate. The operator enters a level setpoint, and the PLC will control the belt speed to maintain the hopper volume.
The operator interface consists of an RSView32 local touchscreen monitor located in the control room, with a remote redundant touchscreen monitor located in the extruder panel for easy field access.
Both lines were retrofitted, commissioned and operational within a two-week time span. The feeders continue to perform well, with greatly reduced downtime due to electronics failures. Since the initial commissioning there have been no additional service or repair return visits by a Melfi Technologies field engineer.
About Melfi Technologies
Melfi Technologies is a process control company that specializes in bulk solids manufacturing automation and systems integration. The corporate office is located in Toronto, Ontario with a regional sales office in Houston, Texas.
For more information about Melfi Technologies visit
www.melfitechnologies.com.
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