Which inspection technology should you use? Metal detection or X-ray?

Posted by AFN Staff Writers on 9th November 2015

Metal detection and X-ray inspection are an excellent first line of defence to check products for foreign contaminants before they leave your processing plant.

In food and beverage applications, both systems must be extremely sensitive, easy-to-use, fast, fully automatic, robust, reliable and cost effective — often they need to be able to pick up the smallest contaminants from thousands of products in challenging processing environments.Metal detect or xray_Matthews Nov15

But which inspection technology do you need? Metal detection or an X-ray system? Does the old generalisation still stand of metal detectors not coping with wet, salty products and X-ray not doing well around dense products with lots of texture?

What you need depends on several factors, but often the real challenge isn’t finding the contaminant, rather it’s ignoring the packaging, product and environment. False detections can quickly add up both in terms of time and costs.

Metal detection and X-ray inspection have both have undergone large improvements in engineering and software, making them even more useful to food and beverage manufacturers.

To help you make your decision, consider the following seven questions:

  1. How is performance measured?

The performance of a foreign-object detection system is determined in three ways:

  • Detectable contaminant types: There are lots of contaminant types, including glass, rocks, bones, plastic, pieces of metal and so on. This is a classic case of the challenge being in ignoring the packaging, product and environment rather than finding the contaminant.
  • Minimum contaminant size: This depends on the system design and technology as well as the “product effect”; this is the degree to which the food looks like a contaminant to the detection system.
  • Probability of detection: What is the chance of the system missing a contaminant in real production, with real products running at real speeds? As a general rule, the larger the contaminant, the higher the probability of detection. However, you also need to build in a margin for error, with periodic audits and doing preventative maintenance.
  1. What contaminants do you want to detect?

Traditionally, metal detection systems were used to detect metal (including aluminium and wires), while X-ray inspection detects all metals, as well as many other solid contaminants (think glass, stones, bones and some plastic). However, today’s technology means metal detection systems, such as Matthews’ systems by Bizerba, can also detect non-ferrous metals.

Typically, X-ray inspection systems can find smaller contaminants than metal detectors and can check a wider range of materials, including large packaged products, cases, cans and bottles. However, there are challenges for both systems. As a rule, metal detection systems find it difficult to ignore wet and salty products, as they are conductive. While X-ray inspection systems have limited success when it comes to dense products with lots of texture. That said, there are examples of advanced systems that can overcome both these issues.

  1. What is the packaging type?

In the food and beverage industry, many brand owners are switching to metallised film or foil-based packaging to enhance products’ appearance or shelf life. This instantly rules out metal detectors, because they can’t get past the packaging to see any contaminants inside. X-ray inspection systems however, can see right through into foil-based packaging to detect extremely small foreign objects. Make sure you take into account how you might change your packaging down the track, as this will determine the best investment for your inspection processes.

  1. What’s the optimum detection point? 

The optimum detection point is the stage in your processing line that has the most chance of finding contaminants. This influences which technology should be employed for the best performance.

Metal detectors can be installed almost anywhere along the line, but their success largely depends on the size of the opening in the metal detector that the product passes through. So that means they tend to work best for products in small packages and bulk conveyed products. By contrast, X-ray systems have greater sensitivity with large products. In both cases, processors and packers can often derive the best value by placing the unit at the end of the line, examining finished (i.e. packaged) products.

  1. What’s the speed of application?

One of the biggest challenges for manufacturers and processors is finding a system that will perform at the rapid speeds. This is where many X-ray systems come up short. Because of the scanning rate, their speed range may be limited. Also, X-ray systems need a constant, known speed to construct images. So they cannot be used in gravity-flow applications, unlike metal detection systems, which can be used almost anywhere in the process.

  1. What else can the technology do?

When investing in any technology, it’s worth thinking about how you can get the most value for your business. In this case, you want to look at what the systems can do in addition to detecting contaminants. For example, X-ray inspection systems can see inside a container to detect missing products in a pack — something that’s not possible with a metal detector. X-ray systems can also inspect a product by measuring the shape, counting objects or using the density of the image to estimate weight. Each of these processes helps to ensure that only the highest quality products are leaving your factory doors.

  1. What’s the total cost of ownership (TCO)?

As with all processing equipment, it’s worth weighing up the upfront cost against the total cost of ownership (or TCO) over its lifetime. This includes training, maintenance, repair, parts and so on. In general, X-ray systems are more expensive up front than metal detection systems. Metal detectors also last up to five times longer. So if you only need to examine small, dry products the extra functions of an X-ray system won’t add any value to your business, so opt for a metal detector. But if you need to go beyond the basics, the X-ray system could prove a worthy investment over the long term.

(You may find these articles explaining TCO and how reducing TCO can help improve your bottom line interesting.)

The Result

So what’s the answer for metal detection versus X-ray inspection? Well, the bottom line is, one solution does not fit all. Because there are so many different factors that affect performance, the best way to choose your ideal inspection system is to look at your exact application, product and industry needs. Speak to the experts at Matthews for information about the different systems on offer and how they can be configured to meet your requirements.

And while we’re talking inspection, did you know there are 5 different types of inspection equipment manufacturers can use? Of course, by implementing a system to detect any foreign contaminants in your product before they leave your doors, you will greatly reduce your risk of product recall due to contaminants. You can access our free whitepaper on avoiding recalls, and find our other whitepapers here.

* Andrew Key has over 25 years’ experience with packaging machinery, inspection technologies and identification technologies. His career spans across several organisations, including Alfa Laval and TNA, helping manufacturers to effect process improvement using the latest technology from around the globe. In his Business Development Manager role for Inspection Technologies at Matthews Australasia, he is constantly looking at cutting-edge technologies for our customers to improve quality control. Andrew grew up in the country and loves the outdoors. In his spare time he enjoys sailing, snow skiing, water skiing, bushwalking and camping.