A Guide to Glass X-Ray Inspection for Food and Beverage
Advantages and Challenges of Glass for Food and Beverage Applications
No other packaging material has all the advantages of glass: unrivaled clarity; wide varieties; reusable, cost-effective, environmentally-friendly. According to a report by The Atlantic, “Glass has changed the world like no other substance….without glass, the world would be unrecognizable”. In the E.U. alone, a total of 20.9 million tonnes of glass was used for food and beverage packaging (a 2,9% increase from the year before).
All this to say: glass use is growing. And it will likely continue to grow as society becomes sick of the recycling challenges and environmental impact of plastic. According to a survey of over 4,000 consumers conducted by research group EcoFocus Worldwide, 37% of consumers said they were extremely or very concerned about the health of safety of plastic use in food and beverage packaging.
When it comes to manufacturers, there are two main reasons that glass is favored:
- The consumer assumption that things in glass are better products
- The perception from consumers that glass is inert – that is why you find baby food in glass
While glass has a host of consumer benefits, it also poses some real challenges in container manufacturing and food and beverage operations: defects. During manufacturing, glass containers can incur a host of defects that are serious food safety risks – including material cracks, chips, loose glass inside the container, wall inclusions and more esoteric defects like bird swings. Dangerous glass shards can be accidentally introduced to containers during operations.
Because of this risk, every glass container should be inspected.
Not inspecting, or insufficient inspection can result in contaminated or defective products, which can lead to recalls. Recalls are expensive, time-consuming, and damage brand trust between company and customer. But they can be avoided with glass X-ray inspection.
Basic Mechanics of Glass X-ray Inspection
The fact that X-ray inspection can find glass fragments within a glass container may be surprising – but it’s actually routine. Finding these glass fragments in glass bottles is possible because: :
- Glass has sufficient enough density that the added thickness in the image of the extra glass particles is material enough to be seen.
- The specific gravity of glass particles in the product differs materially from that of food or beverage products, which have a specific gravity close to 1.
- Soda-lime glass, which is the material most glass containers are made with, has a specific gravity of 2.48
Understanding the specific gravity of your glass containers is critical to ensuring that challenge samples used to testing will actually capture expected real-work inspection performance.
Modern glass inspection techniques use Empty Bottle Inspector (EBI) to inspect glass containers before filling. Then, a Full Bottle Inspector (FBI) will X-ray filled glass containers.
EBIs use ”vision technology” to ensure that there are no exterior finish defects in the container and to verify that the interior is free from foreign material.
FBIs focus solely on detecting foreign material. Ideally, FBIs are used immediately after the filling and closure process. This ensures that in the event of the filler or the capper damaging the containers, the least amount of defective containers are produced before the problem is resolved.
Specific Challenges of Glass Inspection
Depending on the physical design and software, an X-ray machine may face limitations in its ability to detect imperfections. Compared to other forms of food and beverage x-ray inspection, “glass container inspection” has a unique set of challenges:
- Detecting small contaminants in glass containers that are the same density of the container (e.g., detecting a glass shard in a glass bottle) requires significantly more inspection sensitivity than other applications
- Glass containers widely vary in container dimensions, which is directly attributed to the manufacturing process. Each mold used in the manufacturing process is unique, and so there are considerable mold-to-mold variations in the finished container.
- Glass shards are by definition asymmetric objects – one dimension of the shard is often very small. Reliably detecting these types of contaminants requires more sophisticated multi-beam imaging systems.
- “Punts” or “push-ups” are typical in glass containers, which can obstruct X-ray imaging.
- Thicker walls on glass bottles can also require high levels of X-ray power, risking the “image wash-out” of contaminants during an inspection.
- Speed: Glass lines can operate as fast as 1300 containers per minute; therefore, inspection and rejection equipment must be extremely fast (and yet not break the container during the inspection process).
Best Practices for Inspections
Developing Strong Image Resolution
Perhaps the most critical element of glass container inspection is to take extremely high contrast X-ray images that clearly show the defects of interest. Manufacturers use a variety of technical approaches to maximize image quality; including very high contrast X-ray sources and very short distances between the x-ray source and detector. The results of these efforts are very easy to see in an actual X-ray image – pieces of foreign glass material are clear.
Additionally, because glass containers are generally taller than they are wide, a side-view X-ray inspection architecture will produce the best inspection. Side-view glass systems also have more powerful imaging sources, which allows them to more properly expose glass containers.
Multiple Beam X-Ray Inspection for Glass
multiple-beam inspection systems are critical for inspection glass containers for three reasons:
- Asymmetric glass shards are best detected using multiple beam system. The container walls usually have a thin dimension, and the lengthwise dimension is slightly larger. This means that single-beam X-rays may not be able to detect a shard from every direction.
- They leverage various imaging geometries, which greatly increases the probability of finding asymmetric components.
- They are critical in imaging around the punt in the bottom of the container. The extra glass forming the push up reduces imaging and so special techniques are needed to address this shortcoming.
Challenge Test with Correct Density Test Pieces
It’s exceptionally important to ensure that test pieces used for challenge tests are the appropriate density. In the X-ray industry, there is wide use of test results using “high mineral glass”, which has a specific gravity much greater than soda-lime glass. While the detection of high mineral glass can be impressive, high mineral glass is not naturally occurring in any food and beverage production environment – and so test results from high mineral glass are meaningless.
Challenge testing for glass applications must be done using Type P or Type M soda-lime glass. These test pieces most accurately represent the type of glass used in glass container construction, and so test results will most closely replicate actual shard detection performance.
One of the inherent benefits of using X-ray inspection technology is traceability. An image of a container is generated and stored; if a contaminant is reported, the X-ray image can be reviewed – “traced back” – to determine if the contaminant was present at the time of inspection.
Mold to Mold Variations in Glass Inspection Performance
Glass bottles are created with molds; but variations in molds – small flaws or defects, at times nearly invisible – can impact inspection performance. Inspection refers to individual physical measurement systems that specialize in finding different defects; mold inspections require highly specialized data. This is another area where X-ray inspection for glass shines: it can catch the variations in molds and determine defects before the glass bottle is even made.
Sometimes, flaws or contaminants can create hairline fractures, compromising the glass. Even the smallest fracture must be identified during the molding process.
Minimizing False Rejects
Since there can be considerable variations in dimensions from container to container, sophisticated inspection software is required to ensure the variations do not cause false rejects.
In the most basic sense: the software needs to remove the container walls from the image and determine if any of the remaining images has contaminants in it. While conceptually simple, this is a complex process, requiring sophisticated software engineering.
Good false reject performance on glass containers is 4 false rejects per 10,000 inspected containers. Peco InspX is developing approaches that will reduce the false reject rate to 1 per 100,000 inspected containers.
Peco InspX offers two types of inspection systems
- SHIELD Trio Series
- SHIELD Glissando Services
Both systems are state-of-the-art X-ray tools for inspecting glass containers that are designed for specific applications.
The SHIELD Trio is a unique triple beam glass inspection system – it uses a single 600W X-ray tube to obtain 3 distinct X-ray beams, making the Trio much less expensive to own than competing X-ray designs.
The triple beam design offers superior detection of asymmetric glass shards as each container is imaged 3 times from distinct geometries. This design is fundamental to “seeing around the dimensions of the push up” in the bottom of the container.
Additionally, the Trio has a center beam that is perfectly perpendicular to the container, which allows for extremely accurate fill height and headspace measurement.
Because the Trio sits over the customer’s existing container, it is completer non-contact and requires no container transfers; which makes adding the Trio to existing plant operations easy. However, the Trio does require approximately 0.5 container diameter spacing between successive containers to prevent image overlapping during the inspection process.
The SHIELD Trio from Peco InspX
The SHIELD Glissando uses a different inspection architecture than the Trio that images from the top through the bottom of the container – this allows the machines to see directly over the container punt.
To provide multi-geometry inspection, the machine has approximately a 12-degree separation between the twin detectors imaging the bottom of the container, which are imaged using a single X-ray source.
Because the Glissando images through the bottom of the container (where there tends to be less container variation than in the sides), the Glissando series tends to achieve better inspection performance than the SHIELD Trio. However, this improvement does come with some operational expense.
Unlike the Trio, the Glissando requires that containers be transferred onto the machine’s internal conveyor (whereas the Trio sits directly over the customer’s conveyor). The Glissando conveyor uses a special high-tech belting material to aid in the container transfer and to ensure maximum imaging performance through the bottom of the container.
The Glissando architecture does not require spacing between adjacent containers. In fact, back-to-back containers can be literally touching.
SHIELD Glissando Plus
The Glissando series is also available in a large container format system called the “Glissando Plus”. The Glissando Plus is the only X-ray inspection system on the market that can completely image a U.S. gallon-sized glass container.
To image these containers, the Plus adds a secondary beam that is mounted on an electrically-adjustable track – so that the beam can be optimally positioned. The twin X-ray sources give the Glissando Plus 1200 watts of X-ray power, making it the most powerful food and beverage X-ray inspection system on the market.
Choosing the Right Glass Inspection Provider
Due to the complexities of glass inspection, working with a knowledgeable and experienced provider is critical to achieving the best results. So when purchasing a glass inspection system, it is important to understand:
- The design of the provider’s systems
- Their knowledge base of glass inspection
A good inspection provider can work with your glass supplier to improve the quality of your glass containers in addition to ensuring the root cause of any contamination that happens during the production process.
When deciding to invest in glass inspection X-ray technology, think of it as a partnership rather than a one-time purchase. If complications arise, your partner must confidently provide a solution.
Glass container inspection comes with a unique set of challenges, so it is critical to invest in a machine that is able to overcome them. Besides offering the highest probabilities for detecting contaminants and flaws, the ScanTrac Trio goes above and beyond by providing other precise inspection criteria such as lid presence and fill level. The Shield Glissando takes glass inspection performance even further by offering the best combination of speed and detection ability.
If you’re interested in a demo of how Peco Inspx can help your glass inspection process, watch our full product demo video and fill out the form on this page.
If you want more helpful resources from Peco InspX visit https://www.peco-inspx.com/lp/resources