Metal detection or X-ray inspection in food?

The choice between between metal detection and X-ray inspection systems for food processing, ready meals, meat and poultry, bakery and dairy sector organisations

Making an informed choice of detector for your food manufacturing plant: this article considers the various issues facing many food processing, ready meals, meat and poultry, bakery and dairy sector organisations when choosing between metal detection and X-ray inspection systems and provides a few helpful pointers towards making the right choice.

There's little doubt that the task of choosing an inspection system for your production line can, at best, seem confusing and, at worst, appear daunting.

More often than not, there will be many factors to take into consideration.

On the one hand, you may need to assess the feasibility of different approaches based on detailed knowledge of the physical space available at the various locations in the process.

Then again, you may simply need to prepare a careful economic justification, based on up-front lifetime costs.

There may well be corporate guidelines regarding the contaminant size that must be detected - or growing pressures from customers who demand ever-increasing quality control standards.

You may need to review the various types of contaminant along with the defects that occur in your production processes, and how best to combat them.

To be certain of success, you should be aware that any contaminant or defect detection and rejection solution should only be part of an overall plan to prevent the contamination and the cause of defects.

NON-METALLIC CONTAMINATION.

Metal detectors are well established across the food industry, with thousands installed around the world.

Their reliability can be depended upon and the cost of installation, set-up and running is well understood.

But what do you do if you need to find non-metallic contamination? It's well known that X-ray systems are capable of much more than just detecting metal, but just how do you assess the risks in applying new methods for your application? X-ray can detect non-metallic contamination, for example stones, glass and PVC.

However, if these types of contaminants don't figure in your contamination log, what else can X-ray offer in terms of a viable quality control tool? X-ray is capable of defect detection, finding missing or misshapen parts, and checking the mass of food in individual compartments of a multi-compartment package.

So take time to consider if the greater cost implications associated with choosing X-ray is justified by these capabilities.

UNDERSTANDING THE TECHNOLOGIES.

As fully appreciating the significant differences between metal detection and X-ray solutions is a key step in making the right choice, we must first compare the technologies: Choosing between X-ray and metal detection technologies may require careful analysis of all factors, although in some cases the choice is simple.

For example, if you need to detect metal (included in this 'catch all' statement is the detection of small pieces of aluminium), then metal detection is probably your only option, as it is if your product is gravity fed.

However, if it is vital that you detect non-metallic dense contaminants - or that you check part counts, detect misshapen product or estimate mass of product - then X-ray is your most likely choice.

In other instances, however, the whole production operation needs to be considered, as - depending on your requirements - there may be a case for metal detection at one stage of the process and X-ray at other locations.

Another factor to consider will be your desire to equal or preferably exceed the quality requirements of your customer while minimising the total cost of ownership of the equipment.

* Metallic contamination detection in non-metallic packaging materials.

If your requirement is the detection of metallic-only contamination in product packaged in non-metallic materials, then in most cases, metal detection technology will offer the best alternative.

However, if your product is highly conductive - due to high moisture levels - then X-ray inspection should be investigated as it may well out-perform metal detection on a basic contaminant sensitivity specification, but the cost will be higher.

* Understanding the effects of aluminium.

As a contaminant and as a packaging material aluminium is a good electrical conductor, but has lower X-ray density than other commonly occurring metal contaminants.

This means that if aluminium is a contaminant threat, then metal detection will be best suited to identifying and rejecting aluminium contaminant.

A good example of where the use of X-ray in the food industry would be challenged is the detection of the ubiquitous 'blue plasters'.

Specifically designed to be metal detectable (and indeed they are), it is the use of aluminium that makes these plasters detectable and, therefore, undetectable by X-ray.

However, if aluminium is included in the packaging, either in the form of metallised film or as a foil tray, then its low X-ray density can be exploited - this is because the X-ray system will largely ignore it, and will do a superior job of inspecting the contained product therein for the metal contaminants.

* Challenging product characteristics.

Product effects are normally associated with metal detectors.

However, in the same way certain product characteristics limit metal detection performance, X-ray systems can equally suffer from "challenging product characteristics".

A good example being those products which contain a reasonably high level of salt and especially those with free salt crystals, as the salt crystals can appear as dense particles potentially limiting the X-ray's performance capabilities.

The above are just some of the issues to firstly be aware of, and secondly consider, before making the decision as to which technology best suits your application.

The one thing to remember in both cases, however, is that "ignorance isn't bliss", it can be extremely costly and if something sounds too good to be true, it probably is.

My advice to anyone considering either technology is to seek the help of a reputable supplier, someone without a vested interest in one particular solution.

The Mettler Toledo Product Inspection Division have produced a comprehensive guide covering all the issues above in far greater detail, as well as many other considerations, in order to assist you in making an informed choice.

To receive a copy of the guide, please contact Mettler Toledo.

Article provided by Mike Bradley, Business Manager of the Mettler Toledo Product Inspection Division,.

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