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The X-ray factor

11 July 2021

Sibtain Naqvi highlights some of the most important considerations when selecting an X-ray inspection solution. 

When compared to more traditional quality checks such as metal detectors, X-ray technology can offer greater versatility. 

X-ray inspection systems are able to look for a far wider array of foreign bodies, including metal, dense plastics, rubbers, glass, and stones, and can also carry out a variety of additional quality checks, such as detecting missing, undersized, and broken items, deformed product and packaging, under-filled compartments, the presence of cracks and fissures in products, and weight estimation.

With a wide choice of X-ray models offering different capabilities, it is important to take the time to assess the particular detection requirements of an application before making a purchasing decision.

Location, location, location!
Placement of the machine should be an early consideration. Unpacked products such as raw materials for further processing, or meat and poultry, salad, vegetables, and nuts may need screening at the start. Packed product will be inspected much later, where the placement of the X-ray may depend on whether the machine is required to assess primary packs or check for missing packs in a transit case. It may therefore sometimes be necessary to install two separate X-ray inspection systems at different points on the line.

X-ray technology produces X-ray wavelengths from a generator tube which traverse through the product onto a line sensor. The line sensor converts the X-ray wavelengths into visible light which creates the greyscale image that can be seen on the screen. The darker the area of the image, the higher the density. In this way foreign bodies which are denser than the product can be detected. 

Different X-ray models have different levels of sensitivity. Entry level systems are able to detect foreign bodies with a reasonably high density. Softer or less dense items such as glass or rubber, however, will require machines with greater sensitivity.
Generally speaking, the further down the line the inspection takes place, the more challenging the detection process becomes. The type of packaging therefore may also be a factor in the selection of the X-ray machine.

The size of the pack or product to be inspected will be critical. An X-ray inspection system with a much bigger chamber will be needed to check large items such as 25kg blocks of cheese, for example, than one for smaller retail packs.

Most X-ray systems operate from the top down, sending the X-ray wavelength through a product vertically. For tall or stand-up pack formats – such as bottles, cartons and tubes – side-beam X-ray models project the wavelength horizontally. As well as detecting foreign bodies, this gives them the ability to check for the correct fill level and that the closure is in place.

Some bulk and unpacked products also present inspection challenges. A typical quality inspection requirement for meat and poultry, for example, is the detection of unwanted bones or bone fragments in fillets. Because there is a relatively small difference in density between the bone and the meat, the bone can be particularly difficult to spot.  

Dual energy X-ray inspection systems feature two line sensors – one which takes images at high energy and one at low energy ¬– and this provides a better overall image of the product with a clearer contrast between the product and the bone or other foreign bodies.

Effective removal
The selection of the reject system will depend on the size and weight of the product and the speed of the line. Typical choices include arm, air, pusher and drop belts. Many retailers require confirmation that out-of-specification products have been effectively rejected and have not continued down the line.

In most applications, the X-ray inspection system will be part of a fully integrated line so it makes sense to look for suppliers with the relevant combination of technical and applications knowledge, who will have in-depth expertise in the supply and installation of other related packaging equipment, together with wide-ranging experience of handling many different product types.  

Finally, with any investment it is important to consider the cost of ownership in terms of the initial purchase price of the machine and ongoing running and servicing costs. One cost, however, that is almost impossible to put a value on is a company’s reputation – and quality issues can be extremely damaging. This underlines the importance of making the right decision when it comes to choosing an X-ray inspection system, and of consulting the experts early on in the selection process.

Sibtain Naqvi is X-ray product manager at Ishida Europe.

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