[Technology Spotlight] The Detection Evolution

The basic design of metal detection and separation equipment has not changed much in the last few decades, however, improvements to the electronics, filtering and user-friendly aspects of the equipment has reduced the intervention required by the quality assurance department.

In the past, metal detectors often had false positives, causing constant intervention, said Gary Wilson, president of Loma Systems, but the evolution of the equipment has seen improvements in solid-state technologies, auto-balance controls and microprocessor controls, so the equipment is able to do more adjustments, calibration and other controls on its own. "As the equipment becomes more reliable, it has freed up the quality control department," Wilson said, with the quality control officer now able to monitor the equipment’s performance using software programs. The data can be downloaded then accessed at any computer. "It takes out the requirement of always needing to be there."

There are, however, still limitations with detection equipment. "Metal detectors are affected by the product itself," he said, explaining, "Any change in conduct of the product or packaging affects results." For this reason, newer detection equipment generally has multi-frequency options, from dual (high/low) to variable, with specific settings able to be set. "Having the ability to utilize different frequencies gives you the ability to deal with different products," he explained. Take, for example, a plant that produces hot dogs, packaging them in plastic-wrap 8-packs as well as individual microwavable material and producing standard, foot-long and bite-sized dogs. Any of these variances would affect the readings of the metal detector placed at that stage, but with frequency options, the equipment can be set for each.

Most of today’s detectors also have a self-learn feature, by which the equipment is calibrated as a sample of the product is run through it. Then the settings are saved to memory, so that a push of a button telling the equipment which product is being run sets it to the proper variance.

Most manufacturers offer individual equipment pieces as well as complete systems – including magnetic separators and detectors with rejection devices – with some also providing on-site consultation for proper equipment selection and placement. This is important, Wilson says, because "it is not a cookie-cutter product. Each one is pretty much tailored to the application."

Because every metal contamination problem is unique, the appropriate equipment for detection (and rejection) is not always apparent, explains Eriez Magnetics in its booklet, How to Choose and Use Industrial Metal Detectors (available from its Web site www.eriez.com with free registration). Metal detectors should be used wherever there is a chance that metal particles may contaminate a product stream.

Historically, detection equipment has been used at the point of product output, which does prevent the release of contaminated product, however, it can be just as vital to incorporate equipment at the input to reduce or eliminate the potential of equipment damage and processing of a product which would then be rejected at output. "A single metal object in the [food], one that could be detected at the feed point and rejected at negligible cost, might be spread by processing so that an entire batch of product is ruined," the booklet explains.

In addition, explains Don Bina of Thermo Electron, "We typically like to put [magnetic separators] in front of pumps to avoid damage." He also recommends that separators be placed in front of metal detectors, so that ferrous metals can be removed from the product before a detector’s rejection device would kick out the fragment – along with processed product.

Once equipment is installed and calibrated, it is important for the quality assurance department to regularly test the equipment, although "regularly" can vary based on the industry, the sensitivity of the product and hazard potential. Hi-risk product lines, such as meats, should be checked once an hour, Wilson says, while it can be sufficient to test equipment for low-risk products at the start of the shift. And in actuality, he says, some plants check the equipment every 15 minutes, while others never test the equipment at all.

Because each operation has unique characteristics, it is important to ensure that the metal detection and magnetic separation equipment you choose is right for your line. On the facing page is a guide to some of the leading manufacturers in the industry, along with contact information for each. QA