Metal detection, X-rays – or both?

Metal Detection, X-Rays — Or Both?

Metal detection and x-ray inspection systems play a key role in product inspection for food and pharmaceutical companies. Choosing the right technology requires considering many factors, starting with the application.

Deciding whether a metal detector or x-ray system is the best choice for your product inspection needs isn’t as simple as it sounds. The app is the starting point, but several factors can complicate things. Consider this scenario, for example: you need to identify metal contaminants, but the product is wrapped in foil. A metal detector will see the foil itself as a detectable contaminant, while an x-ray system sees straight through the aluminum as it is a low density metal, allowing it to have a better view of any contaminants inside. X-rays will be the best choice, even if the potential contaminants are metal.

Both technologies have their strengths, as we will see, and a range of factors must be taken into account, including the nature of the product, the size of the product, the filling process, the types of potential contaminants, the packaging, financial constraints and physical space. , and the range of additional quality checks required.

metal detection

Modern metal detection systems can identify all metals, including ferrous metals (such as chrome and steel) and non-ferrous metals (such as brass and aluminum), as well as magnetic and non-magnetic stainless steels . They work through a system of coils, charged with an electric current, to create a balanced electromagnetic field. If a product passing through this field contains a metallic contaminant, the magnetic field is disturbed and this disturbance is interpreted by sophisticated electronic circuits and software algorithms.

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In order to operate as required, the detector must be stable and rigid enough to eliminate movement of the coil system, as even minute vibrations can cause undamaged products to be rejected. Airborne electrical noise can also be a problem, so it is essential that the metal detector can operate reliably in a factory environment.

The effect produced

The effect produced is a major consideration, which can lead to high false rejection rates. Products with a high moisture content, or those which are salty or acidic, are conductive, and when passing through the metal detector will emit a signal (i.e. “the product effect”) which disturbs the detection field. Other factors that contribute to product effect are temperature, format, consistency, size, shape and orientation of the product on the production line. Metal detection is particularly suitable for dry products, where the lack of moisture means that the product is non-conductive and therefore does not generate a significant “product effect”.

Manufacturers can eliminate the impact of product effect by installing a high quality metal detection system that uses a combination of simultaneous multiple frequency operation and software algorithms to optimize performance and reduce the possibility of costly false rejections. . This technology will also allow the system to have the right level of sensitivity to pick up signals from very small metal contaminants, whatever the application.

In addition to packaged products, other applications where metal detection can be used include bulk, unpackaged products, pumped products such as liquids, pastes and slurries, bulk powders or flowing solids free under gravity fall conditions. Additionally, large rigid containers such as bottles, jars and composite containers can also be inspected, although in these applications the inspection must take place before a metal cap or closure is applied.

Type of packaging

Metal detectors using multiple frequencies simultaneously or operating at a single low frequency can usually be used with products packaged in metallized film packaging, depending on the thickness of the film. If aluminum packaging, such as foil wrappers or product trays, is used, standard balanced coil metal detectors will not be suitable.

X-ray inspection

X-ray inspection systems have the ability to detect a wider range of contaminants than metal detectors, including metal, glass, stone, calcified bone, high density plastics and rubber. They can also perform a range of additional online quality checks on food and pharmaceutical products, including mass measurement, component counting, identification of missing or broken products, monitoring of fill levels, detection of products trapped in the seal and verification of damaged products and packaging.

The technology works by generating an X-ray beam that passes through a product for inspection and onto a detector. Some of the X-ray beam is absorbed by the product and any contaminants present, and since most contaminants are denser than the food and pharmaceutical products being inspected, the contaminants generally absorb more of the energy from the x-rays X. This difference in absorption becomes apparent in an image generated by the X-ray system, which is then compared to a predetermined acceptance standard for pass or fail.

However, while X-rays can easily detect these dense contaminants, with low-density contaminants such as aluminum, insects, wood, and polyethylene film, X-ray detection is not possible.

Nevertheless, x-ray systems are capable of inspecting a wide range of different product types, including pumped products such as slurries, fluids and semi-solids, bulk products, bulk products, jars, bottles and cans, and packaged products, including those wrapped in foil or foil.

What technology?

The process of choosing the right technology for product inspection means going back to the application and performing a Hazard Analysis and Critical Control Points (HACCP) or Hazard Analysis and Preventive Controls based on risks (HARPC). This will identify the contamination risks associated with your application and the likely types of contamination, as well as provide a better understanding of any customer requirements or compliance issues.

It’s rarely a clear decision, sometimes the right answer might be to deploy both.

Consider these examples:

Aluminum contaminants in non-metallic packaging: as a light, low-density metal, aluminum is difficult to detect by X-rays as a contaminant; metal detecting is usually the best solution.

Metal contaminants in aluminum packaging: metal detection will be unable to locate contaminants in the middle of the foil wrap unless it is metallized foil; x-rays are usually the best option.

Metal contaminants in gravity fed products: x-rays don’t work well with falling and accelerating objects that don’t have a uniform direction of travel; metal detecting is the only viable solution.

Metallic contaminants in non-metallic packaging: it can be complicated. Metal detection systems are more cost effective, but if the product is very large, a larger detector aperture will be required, which can reduce detector sensitivity. Multi- and high-frequency technology can help, but a larger metal detection system will be required. X-ray power can be increased for larger products, but installation cost increases as size increases. If it is necessary to protect against non-metallic contamination, the choice will go to X-rays.

Non-metallic contaminants in any packaging; perform additional quality control issues: X-ray inspection is the only solution, and the additional QC checks may justify the added cost of the technology.

Fast/variable line speeds; situations where space is limited: metal detection (at 400m/min) is able to inspect at faster speeds than X-ray (120m/min), which may have the advantage if other aspects of the application are more suitable to metal detection. Metal detectors are also less space intensive than X-rays, so depending on the application they may be more appropriate in factories with limited space.

keep it simple

Metal detection or X-rays? The flowchart below is a good starting point for identifying the correct answer. However, there is an area of ​​indecision where the application is not wrapped in foil, and metals other than aluminum are potential contaminants. Here, a more complex evaluation of options is required.

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There may also be situations where more than one type of product inspection system is desirable at different critical control points on the production line. For example, it may be a good idea to install a metal detector at the beginning of the processing chain to remove large metal contaminants which could, if left present, damage downstream machinery or break into smaller pieces and less easily detectable. Further down the production line, an X-ray machine could then check for non-metallic contaminants and perform other quality checks, while a second, more sensitive metal detection system at the end of the line could be used. to do a final inspection for smaller metal contaminants.

In conclusion, while factors such as space limitations, total cost of ownership and productivity goals are important, it is worth remembering that the first step in choosing a metal detector or system X-ray for product inspection is all about considering the application – this is where the evaluation begins.

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