- Created on Monday, 03 March 2003 03:16
- Written by Derek Longshore
BURBANK, CA – When Aramark Uniform Services began experiencing problems with metal contamination after laundering towels, they found that the cause of contamination emanated from areas such as machine shops and metalworking shops where metal chips and curls became embedded in the towels.Aramark Uniform Services, a uniform rental and industrial laundry service, markets its shop towels to machine and auto repair shops, and printing firms. They distribute these products through 65 market centers located throughout the United States.
The original towel inspection process was labor intensive. It involved employees visually inspecting each towel for tramp metal. Accepted towels were then folded, counted, bundled by hand and shipped to customers.
Still, Aramark felt that this tedious process did not fully protect their customers from injury due to metal lacerations. In addition, embedded metal would scratch paint on automobiles and plates and rolls used in the printing industry. An added problem was possible liability issues their customers could be exposed to.
Eriez Magnetics, Erie, PA, producer of a wide range of magnetic separation and metal detection equipment, was called in to provide a state-of-the-art towel inspection system. Eriez’ engineering team developed a metal detector/conveyor system that was to become an integral part of the Aramark Towel Management Systems (ATMS). The goal was to reduce labor costs, decrease the occurrence of tramp metal contamination in the towel laundering process, as well as to apprise the markets Aramark serves that the company was utilizing an advanced metal detection system.
The Inspection System
The metal detector and conveyor is a totally automated system. Together Eriez and Aramark developed an efficient and automatic reject device suited specifically for shop towels.
After the towels are laundered, they are inspected quickly for holes, epoxy, bondo, and anything that would make them defective. Towels are then placed on the Eriez conveyor where they pass through an Eriez E-Z Tec® Metal Detector and are automatically rejected upon the detection of metal. Below the discharge end of the conveyor are two bins, one for the rejects, the other for the accepted towels. Those that are rejected are either further inspected or sent for applications which do not demand metal free towels. The accepted towels are bagged and shipped to customers.
The Eriez E-Z Metal Detectors are located on an elevated six-foot mechanical conveyor, and are an integral part of the system. The system serves three functions: product scanning, accepting/rejecting if necessary and conveying to the bagging area. Everything is totally automatic.
Principle of Operation
The E-Z Tec® Metal Detector uses a balanced three-coil arrangement wound around the aperture to sense metal moving through it. The center (oscillator) coil emits an electromagnetic field throughout the space within the metal detector housing. Two receiver coils (placed equidistant on either side of the oscillator coil) are connected in series so that the energy coupled from the oscillator coil to either of the receiver coils exactly cancels the energy coupled to the other receiver coil; the net output of these pairs is essentially zero. Metal passing through this set of coils creates an imbalance which, if the signal’s amplitude is great enough, will result in a detection.
The oscillator and receiving coils are wound on a rigid frame and encapsulated in a stainless steel shell (USDA/FDS and CSA approved).
The controls are housed in a watertight, dust-tight and corrosion resistant stainless steel NEMA 4X enclosure. E-Z Tec circuitry is a high-quality system with easily removable printed circuit boards. An LED bar graph provides a continuous display of sensitivity and phase effect, invaluable for optimizing performance.
In addition to Aramark being pleased with the end result, customers receive added value: product purity, reduced opportunity for personal injury and virtual elimination of customer liability.
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