Multitasking can be as useful for inspection equipment as it is for humans.
Equipment now is available that can both weigh packages and examine them for metal or other contaminants. These combo units can expedite initial line integration, save space and simplify maintenance and other functions.
“Traditionally it helps [end users] in terms of not only line integration, but it usually also helps them from a mechanical perspective-ease of installation, getting things up and running faster,” says Kyle Thomas, marketing manager for Mettler-Toledo Hi-Speed. “And in general, you can also save some space, too.”
Putting metal detection and checkweighing into a single unit is one of the most popular forms of combination quality-control inspection. Some machinery suppliers, like Hi-Speed, integrate the two functions when they custom-build such units.
Custom building of combo units allows Hi-Speed flexibility in specifying the components. Usually, the metal detector will be from Safeline, a sister Mettler-Toledo company, but Hi-Speed is able to use competitors’ detectors if the customer wants, Thomas says.
Thermo-Fisher Scientific, on the other hand, offers a standard frame that can pair a variety of its checkweighers and metal detectors. These include any Thermo-Fisher checkweigher (except the Teorema high rate can weigher) together with either the small-footprint IP69K-rated DSP-IP+ metal detector or the newer high-technology APEX models. This setup gives Thermo-Fisher the flexibility to match crucial components, such as the aperture size of the metal detector or the area of the checkweigher table, to the customer’s needs.
Metal-free zonesWith combination metal detector/checkweigher units, designers have to take into account the “metal-free zone” required by metal detectors. Because they use electromagnetic fields to find metal particles, they can’t have metal components within a certain distance on either side (the distance varies due to different factors, principally the size of the aperture through which the packages pass).
The need for a metal-free zone lessens but does not eliminate the space savings afforded by a combination unit, Thomas says. A combination unit can operate without some of the components that would be required by two separate units. For example, if a metal detector and a checkweigher were separate, they would each need drive and idler pulleys; a combo unit can eliminate one set of these pulleys.
“Where we save space is in getting rid of the transition pulleys that are between those two units,” Thomas says. “We have a rejecter traditionally there as well, so there is some space required for that. But you’re able to optimize that zero-metal zone.”
The Thermo Fisher combination unit eliminates a conveyor that would be needed by two standalone units, says Paul Thronson, checkweigher product manager. That can save up to $15,000 in initial costs, Thronson says.
Eliminating a conveyor can save space as well as money. That’s why Little Lady Foods, a manufacturer of pizza and other frozen foods for private label located in Elk Grove Village, Ill., bought a combined APEX metal detector and FR8120/AC4000i checkweigher from Thermo-Fisher.
“In our application, with space availability on the line, the combination unit makes more sense,” says company manager John Glidic. The combo unit saved about 3.5 feet over what would be needed for separate units, Glidic says.
Multiple rejectsRejection mechanisms, however, are one aspect of inspection that combo units can’t reduce. Even packagers who use one unit for two inspection functions probably will want to have at least two reject mechanisms.
In theory, it’s possible to use just one rejecter for a multi-purpose unit. But most packagers will want to keep product that was rejected as possibly contaminated, with metal or other substances, separate from under- or over-weight product, because the latter can be reworked. Many of Hi-Speed’s customers locate the metal detector and its rejecter before the checkweigher component, Thomas says.
Some end users also have separate rejects for under- and overweight product, but many use a single one, Thomas says. Some just reject underweight product; they collect data on overweights but don’t take them out of the line because consumers won’t mind getting a little extra product.
Dual-use X-rayX-ray equipment can form the basis for another type of dual-function inspection machinery. With the right software and other tools, it can both inspect packages for contaminants and weigh them.
Unlike metal detector/checkweigher combos, which basically are two attached machines, an X-ray inspector/weigher is a single machine that performs two functions. The X-ray determines a product’s density and the rate at which it absorbs the radiation; an attached computer uses software logarithms to extrapolate its weight. (X-ray systems, like metal detector/checkweigher combos, typically will have separate rejects for contaminated and off-weight products.)
X-ray inspection is especially useful for multi-component products, such as ready meals with several courses on a divided tray, or refrigerated lunches that comprise a sandwich and other elements like chips and a juice box. For such products, X-ray systems can be set up to inspect by zones. A checkweigher with a loadcell can only determine that such a package is over- or underweight; an X-ray system can pinpoint the component that’s off-weight, which makes it easier for the problem to be corrected at the filling point.
X-ray weighing can also be used as an intermediate quality control step, says Chris Young, X-ray product manager for Smiths Detection. For example, canned soup is often filled with the solid components, such as meat and vegetables, first, with broth added downstream. An X-ray system could examine the cans after the solids are added, to make sure they were filled in the right amount and proportion.
X-ray drawbacksOn the other hand, using X-ray equipment to weigh packages has some drawbacks. For one thing, extrapolated X-ray weights are not legal for trade in many states; to meet regulations about declared weights, the packager may have to incorporate a standard checkweigher before case packing.
“It may well be that a customer who’s manufacturing a product for sale in many states, if you have a declared weight on that package, you still would want to have the ability to say, this was run across a checkweigher with captured data, usually a loadcell, which is an accepted device for weights and measures,” says Gary Wilson, president of Loma Systems.
This is by no means universal, however. Young estimates that about half of the food customers who use X-ray weighing do without a checkweigher; some of them use both at first but then retire the checkweigher as they get more comfortable with the new technology.
Another problem is that certain kinds of products give X-ray systems a hard time when it comes to weight reading. These include products with inconsistent density, such as ice cream with nuts or fruit, or products with high salt content, because chlorine has a tendency to absorb X-rays.The only way to accommodate such products is to determine what the accuracy range will be with an X-ray system, and see if that range is acceptable to the customer, Wilson says: “It comes down to your target weight. Are you inspecting a 10-pound package and you want to see plus or minus a couple of grams, or are you inspecting a 10-ounce package and you want to see plus or minus one gram?”
X-ray combination contamination/weight units tend to be more expensive than the alternative. Young estimates that a conventional metal detector would cost about $15,000, and a conventional checkweigher from $10,000 to $15,000. An X-ray unit with weighing capability would go for about $50,000, or roughly twice as much as the two separate units combined. The extra cost comes, not only from the expense of the X-ray tube and ancillary equipment, but from the high-speed computer and sophisticated software needed to interpret the images.
But X-ray units have important advantages. They can look through metal packaging and can find nonferrous contaminants, both of which present problems for electromagnetic metal detectors. And, according to Chris Young, X-ray product manager at Smiths Detection, they can weigh cans in high-speed operations at up to 1,000 cans a minute-a speed that would require two loadcell-based checkweighers.
The bottom line is that combo units cut down on the amount of equipment in a plant, which means cutting down on the number of things that can go wrong.
“The advantage is that you are using simply one technology, one machine, one footprint, and in today’s industry, line space and transfer points become critical,” Wilson says. “The more stations you have, the more calibrations and things that can go wrong. If you can eliminate the number of inspection stations but still perform the same number of functions, that’s pretty much a win-win for everyone.” F&BP
Thermo Fisher Scientific