Food Engineering

If you use metal detectors, don't go it alone

September 20, 2005
Understanding your equipment's capabilities up front keeps food safe and makes manufacturing easier.

Richard F. Stier
In the last few years, I've been in many plants and have seen staff fighting more than one battle with the facility's metal detectors. In each of these cases, the problems stemmed from the plant trying to commission and/or operate the metal detector on its own. But the time, effort and aggravation experienced by plant staff could have been alleviated with a single call to the equipment vendor.



Metal detection has become an integral part of most food processing operations. In fact, many companies mandate every ingredient they buy must be run through a metal detection system. This business practice can protect raw materials, finished goods and your brand.

But how do you choose the right metal detector? They may be used to detect metal in liquid systems, powders that flow, pieces of meat, fruit or vegetables and packaged products. To select the right tool for the right application, processors must understand not only their products but also the capabilities of metal detection technology.

The very nature of some products can cause a metal detector to reject them and interfere with the detector's sensitivity. Products that may cause this kind of reaction-known as a "product effect"-are those with high moisture content such as meat, cheese, warm bread, fresh produce and most liquids. The detector can be adjusted to minimize this effect, but its achievable sensitivity will be reduced.

Low-moisture products such as cookies, fried snacks, sugars and cereals have little product effect and can operate at greater sensitivities. Frozen foods also have little product effect since their moisture is bound up.



To select the right tool for the right application, processors must understand not only their products but also the capabilities of metal detection technology. Source: Thermo Electron.
Processors can come up against challenges when they try to install detectors on their own. For example, one company decided to run all of its finished products through a metal detector. This processor manufactured a wide range of products (300 SKUs) and decided to pass cased goods through the detector prior to palletizing. The processor's client had standards of 1.0 mm for ferrous and 1.5 mm for non-ferrous. The processor unsuccessfully tried to make the unit work for the standards. When the processor finally called the metal detector company, the service representative said the unit simply could not run at the desired sensitivities. The rep sent a letter describing the minimum operating parameters for the unit given the products the processor was running. The processor shared the letter with its client, who granted a waiver to operate at lower sensitivities for its products.

In another example, a processor decided to install a metal detector on a line handling sauces with particulates. The processor did the set-up on its own and adjusted the sensitivities to the lowest possible detection limit. This operation also had problems. With the supplier's help, the processor adjusted the sensitivity upward and made changes to the software, solving the problems.

With metal detection becoming mandatory, processors must do everything they can to get their systems working properly from the very beginning. This means understanding products and the basic principles of metal detection and taking advantage of the expertise offered by suppliers. Remember one of the primary corollaries to Murphy's Law: "There is never time to do it right, but there is always time to do it again."