Metal Detectors or X-rays?

Metal detection, x-rays, or both? Manufacturers need to assess what the risk is and which method will best minimize that risk when choosing inspection technology. For maximum due diligence, multiple solutions are often used.

“In some applications, customers have chosen all three of our solutions,” says Robert Scott, product manager, x-ray inspection. Mettler-Toledo Safeline (Tampa, FL). “We are doing a factory acceptance test now on a system using x-ray, metal detection, and check-weighing.”

When considering the true life time cost of inspection systems, companies need to keep in mind the impact of indirect costs such as scrapped materials, recalls, and brand image. Ultimately, inspection is a consumer quality as well as a consumer safety issue, presenters advised in a recent Mettler-Toledo Safeline webinar on x-ray and metal detection.

X-ray and metal detection systems address different inspection requirements. Metal detectors can detect only magnetic or electrically conductive metals. When used for contaminant inspection, x-rays will discover metal and nonmetal contaminants, such as glass and stone. A contaminant is visible to x-ray detection as long as it is denser than the product being inspected.

X-ray systems can also simultaneously check for fill levels, missing or damaged components, and product mass. X-ray can inspect fill levels when opaque packaging or labels mask the product, thus making vision systems unusable, Scott says.

Mettler-Toledo�s Tablex unit detects metal in pressed tabs.

“For weight measurement, we do a mass calculation using an x-ray image, stating the mass in the same units of measure as you would weight. A different algorithm is used to determine contamination,” Scott says.

“X-ray energy is converted to visible light to form a bit map image divided into 0.8 mm sections. Shapes in the cells are compared to surrounding cells to detect differences caused by contaminants. The image analysis is identical to that used in a vision system, except we can’t detect colors,” he says.

“If a contaminant is embedded in the product, you can’t use a vision system. The only alternative is x-ray,” he adds.

Metal detectors are widely deployed by pharma for inspecting bulk product and finished pills. X-rays, although used in the food industry for 20 years, have gained a far smaller market segment in pharma, says Oscar Jeter, national sales manager.

“There are thousands of metal detector units used in the drug industry mainly for inspecting tablets and capsules coming from the presses. CGMPs require metal detection on tablet lines. But it doesn’t specify electronic metal detection. A magnet could be conceived as a metal detector, but it won’t detect aluminum, brass, or stainless steel,” Jeter says.

“We have seen major interest from nutraceutical companies in metal detectors, with FDA’s requirement for CGMPs in that industry,” Jeter adds.

Metal detector performance, however, is limited by metalized packaging. Vision systems are hampered by foil’s reflectivity. X-rays provide the only option for inspection of finished packaging.

“We are a little bit baffled as to why pharma hasn’t moved forward more in x-ray inspection,” he says. “There is no other system that can inspect inside a closed carton of blister packs. X-rays can be used to inspect for glass contamination in liquids. But there has been little interest.”

“Even if product is inspected by a metal detector coming off the press, tablets are then handled multiple times before going into the blister. In final package inspection, x-ray systems can confirm crushed, broken, or absent product, identify multiple different tabs in the pack, the presence of leaflets, and examine for the presence and condition of multiple layers of blister cards,” Jeter says.

“Inspection of the final package allows you to know the consumer is getting what they are paying for,” he adds.