January 27, 2022

X-ray inspection for comprehensive glass-in-glass detection

Whether it’s food, pharmaceutical or cosmetic products; the detection of glass-in-glass contaminants, i.e., glass foreign bodies in glass packaging, is still one of the supreme disciplines in product inspection. What can X-ray inspection systems do today to detect glass-in-glass contaminants – and what must be considered?

With food and drug safety regulations intensifying, compliance and traceability through every stage of a product’s life cycle are growing in importance. As a consequence, X-ray inspection is increasingly being adopted by manufacturers to detect and reject contaminated products from their production lines in order to protect the welfare of consumers, reduce the risk of product recalls and safeguard their reputations.

Made from all-natural, sustainable raw materials, glass is essential to modern life and the only packaging material rated ‘GRAS’ or ‘generally regarded as safe’ by the US Food and Drug Administration (FDA). With the retail sector striving to be eco-friendly, glass is rising in popularity as it is relatively inexpensive and 100 percent recyclable. No other packaging material matches the shelf impact of glass. The clarity, shape, and feel of glass containers contribute to the premium perception of products ranging from fine perfumes to liquor, foods to beverages. In addition, research from the British Glass Manufacturers’ Confederation (BGMC) demonstrates that 70% of consumers believe glass packaging suggests quality.

But, finding a shard of glass in a product is an emotive subject. Despite it having the potential to be an intrinsic contaminant, evidence shows customers are much more likely to lodge a complaint than if they discovered a chicken bone in a chicken-based product. All the more reason for manufacturers to have X-ray inspection systems that offer the most sensitive levels of contaminant detection. Also, some major retailers and the custodians of leading consumer brands have developed their own codes of practice that must be fulfilled and adhered to in order to satisfy supply agreements. Increasingly the implementation of a formal X-ray inspection program is expected before supplier approval is granted. In addition, X-ray inspection technology is widely acknowledged to provide an all-encompassing, reliable solution to help manufacturers comply with national and international legislative and regulatory standards such as the Global Food Safety Initiative (GFSI) and Hazard Analysis and Risk-Based Preventive Controls (HARPC), as well as meeting management systems such as Hazard Analysis and Critical Control Points (HACCP) and GMP (Good Manufacturing Practice).

Challenges in glass-in-glass detection

Nevertheless, glass-in-glass contaminations are particularly demanding when it comes to foreign body detection since the most likely foreign bodies and packaging are identical in terms of both material and density. This is exacerbated by factors such as the varying thickness of the outer walls and the concave bases of glass jars. Even if there are no anomalies in terms of total weight and external shape of the glass jars, fluctuations in glass thickness around the base of up to 20% are not unusual and have a direct impact on X-ray inspection. What is more, impurities in the glass itself, such as metallic inclusions that may have been introduced during the manufacturing or recycling process – metal residues from aluminium screw caps, for instance – influence X-ray absorption and thus detection sensitivity. Even the use of glass containers from different suppliers can affect X-ray absorption and detection sensitivity due to the varying density and chemical composition of the glass jars. In addition, embossing, the glass screw thread, and metal screw cap combined with fluctuations in glass thickness render the inspection of the cap and shoulder area of glass jars a particularly technical challenge.

As a rule of thumb: the more complex the shape of the container, the more challenging it is to inspect. Round containers are the easiest to inspect. This is because they have no sharp changes in vertical edge profile which could produce blind spots or hard, dark edges where detection would be reduced. Additionally, they can be constantly presented as they have no orientation effect. Square, rectangular, or hexagonal containers can also be presented well, but the side walls may require significant filtering, depending on the angle of inspection. Oval containers are difficult to guide and therefore not ideal for X-ray inspection as the image can constantly vary.

Furthermore, the viscosity of the product in the package has a significant influence on where in the jar foreign bodies or rather glass chips are deposited and needs to be taken into account at an early stage. The filling process of semi-solids or viscous products should be considered first since a contaminant could be in the container prior to filling. Quick, high-volume fillings can wash possible contaminants away from the base and higher into the container. While this makes it easier to discover them by means of X-ray inspection, it also makes it clear that not only the base should be inspected. Cold fillings of a semi-solid or viscous product can hold them in suspension, so the whole container should be inspected. In case of hot fillings with a lower viscosity, they will gravitate towards the base of the jar. In case of liquids, they are actually very likely to be there, so inspection should be concentrated in this area, too.

The silver bullet: Angled beam systems

The base, or crown, of glass jars has traditionally presented a challenge for X-ray inspection systems, because it varies greatly and is the densest area. However, innovations in technology mean systems are now available offering comprehensive glass-in-glass detection for a wide range of foods, beverages, and pharmaceutical products of various viscosities.

Current angled beam systems incorporate a single, perpendicular beam that shoots down through the base area while simultaneously inspecting through the side of containers. A top view of the base and lower body of the jar makes the crown appear flat in the X-ray image. The X-ray beam passes through level with the shoulder and upper area of the container, below the thread and cap. This removes traditional blind spots, reduces the complexity of the X-ray image, and optimises the probability of detection not only in the base and lower body area but also inside the jar. Dynamic filtering, changing to suit the profile of each and every single container, ensures that for products packaged in glass containers with dense edges, the high-absorption dark areas are filtered out, optimising detection sensitivity elsewhere in the image and minimising false rejects. As the belt absorbs a small amount of the X-ray and is part of the final captured image as well, its material must be low density and as thin as possible. However, angled beam X-ray systems incorporate adaptive software which allows the system to run with a durable belt. This prevents wear and tear, reducing downtime. Systems also provide exceptional full-height fill-level checking, with high accuracy at high speeds. Since the configuration of the X-ray beam allows for glass jars to touch, high-speed inspection of up to 1,200 containers per minute is possible. While a number of different automatic reject systems, such as side punch or pusher rejects, are available, for very high-speed applications, other more advanced reject systems can be used. These smoothly divert containers at high speed onto parallel, enclosed reject conveyors. The position of the X-ray generator is vertically adjustable so that the system can be tailored to a variety of different jar sizes.

Conclusion

Glass packaging is rising in popularity. Notwithstanding this, it poses a significant safety risk, and the effects of glass-in-glass contamination can be highly damaging. A tiny fragment of glass can cause serious injury to a consumer, and the subsequent adverse publicity – particularly if a baby or child was severely cut – combined with the high cost of product recalls, can have a devastating impact on business. Not only do product recalls mean lost revenue and a damaged reputation, but evidence also demonstrates that manufacturers’ greatest asset, their brand, may never recover. The risk of glass-in-glass contamination and its highly damaging effects, combined with increasingly stringent safety regulations worldwide, mean it is more important than ever for manufacturers to have X-ray systems that offer the most sensitive product inspection. That way, manufacturers can reliably detect glass-in-glass contaminations to protect consumers, product conformity, and brand reputation over the long term and stay ahead in the most challenging food and pharmaceutical industries.

For more information visit: www.mt.com/xr-glassinglass, while a link to the white paper can be found here.