Why A Side-Shoot X-ray Inspection System Is Optimal For Inspecting Bottles, Vials And Cans
Friday, April 20th, 2018 | 1488 Views
Bottles, vials and cans are more challenging to inspect than flat packages because of the thickness and density of both the containers and their typical contents, as well as the wide variety of bottle thicknesses, sizes and shapes says Michelle Schultz, applications manager, product inspection equipment, Thermo Fisher Scientific.
Food and pharmaceutical manufacturers are constantly under pressure to prevent contaminants from being introduced into their products and reaching the consumer. The type and orientation of the containers affect decisions about the optimal X-ray inspection system for this purpose. When choosing an X-ray inspection system for products packaged in these types of containers, the location and number of X-ray sources and detectors will significantly affect the accuracy of the system’s detection capability.
Further, special attention must be paid to software, which is system-specific and must be able to ignore the package and utilise the most applicable algorithms in each area of the product to detect contaminants.
Vertical-Beam Versus Horizontal-Beam (Side-Shoot) Systems
Standard X-ray inspection systems are designed primarily for inspecting flat-packaged goods. In these systems, the X-ray beam is directed vertically, from the top of the container to the bottom or vice versa. Using them to inspect bottles, vials and cans present challenges. Shooting through tall upright containers vertically means the X-ray beam must penetrate the entire height of the container, which is often the densest path.
In a side-shoot X-ray inspection system, the source is located in front of or to the rear of the machine, shooting a horizontal beam through the containers during inspection. The horizontal X-ray beam is positioned to go through the side of an upright can, bottle or vial, optimising detection performance by reducing the thickness through which the X-ray beam travels.
Another issue with vertical-beam X-ray inspection systems is that they have radiation-blocking curtains. These curtains often cause upright containers to shift or tip as they come into contact with them, and metal cans can cause extra wear on the curtain material over time. Since X-rays travel in straight lines and do not turn corners, a chicane-style side-shoot system with a curved shape eliminates the need for the curtains, so upright containers can transfer through the system smoothly, without interference.
Single-Beam Versus Dual- and Multiple-Beam Side-Shoot X-ray Systems
Side-shoot X-ray inspection systems can have either a single beam and detector or two or more X-ray beams and detectors (some systems use split beams). These systems are designed to inspect the contents of a container while ignoring the container itself. Systems that use more than one X-ray source and detector are better at ignoring a product’s container than systems that use only one source and detector.
Single-beam units sometimes have a “blind area” at the bottom of the container, directly in front of the beam. In side-shoot systems with two or more sources and detectors (dual- and multiple-beam systems), those sources and detectors can be at different angles to focus on different regions of the containers to minimise or eliminate blind areas. Having more than a single view increases the probability of detecting foreign materials that could be hidden or lost in a blind area using a single-beam unit, especially in the bottom of a container, as shown in Figure 1. The more beams, the more views and the better the detection.
Consider the following when evaluating single-beam versus dual- and multiple-beam side-shoot systems.
Container type, material, shape and thickness
Some packaging materials allow X-rays to pass through them more than others, and thinner containers allow the beams to pass through more while thicker containers absorb the beams more. The less the X-rays can pass through the containers, the greater the negative impact on detection sensitivity.
If the bottom of the container is thin and flat, this blind area usually isn’t a problem because any contaminants would be higher than the container’s bottom profile. However, the blind area at the bottom is significantly larger when inspecting containers with thick or domed bottoms, reducing detection sensitivity.
A dual- or multi-beam system should be used for inspecting pharmaceutical vials as well as for glass bottles, especially those with domed bottoms.
Detecting glass-in-glass contaminants—glass contaminants inside glass containers, especially thick ones—is the most challenging inspection scenario because the container and the contaminant have the same density. For that reason, accurate glass-in-glass X-ray inspection requires a dual- or multi-beam system.
The smaller the potential contaminant, the greater the chance that it could be hidden in a blind area of the container. Therefore, the smaller the contaminants you need to detect, the greater the need for a system with two or more views. Further, providing additional data to the X-ray system enables better analysis.
The consistency and homogeneity of the product inside the container also can influence the choice of a single-beam versus a dual- or multiple-beam X-ray inspection system. When inspecting liquid products, for example, gravity causes foreign materials to sink to the bottom of the container, so that is the area of greatest risk. If the liquid is packaged in a thick- or domed-bottom container, the area of greatest risk will be in the blind area of a single-beam inspection system. The density of powders or solid products is fairly consistent, so a single-beam system will generally have the same detection capability throughout the container, although blind areas still may be a concern depending on the shape of the bottom of the container.
Additional Challenges and Considerations
A side-shoot X-ray system’s software is inherently complex. First, the software must identify the shape of the container. To enable it to find the smallest foreign material, regardless of its location within the container, the software also must be able to optimise inspection in specific regions. Increased density around lids/caps and bottom domes creates naturally dark areas in the X-ray images, and those areas of added density must be either ignored or compensated for by the software to focus inspection on the remainder of the container.
Software is system-specific and varies based on the number and position of the source(s) and detector(s). A beam may be angled slightly up or downward at the container bottom to reduce the natural dark areas in the bottom area directly in front of the beam, though it may still leave a smaller blind area near the edges, as shown in Figure 2. This also eliminates the added density in the dome area of the container, making foreign materials easier to detect.
In some side-shoot X-ray inspection systems, special software is available that can identify missing or cocked metal caps or lids.
Most models have a configurable parameter for fill level detection that can be set to determine when containers are significantly underfilled. This parameter is appropriate for homogenous, solid products where there is a distinct line between the product and the “head space” above it. Typically, there is a distinct line between a liquid or gel product and the head space, while powders have an inconsistent/moving fill level that prevents accurate fill level detection.
Side-shoot units may not be suitable for mass estimation because the weight of the containers (especially glass containers) can vary significantly. Also, the view of the container is distorted as a result of the beam location and focal point, and this distorted view makes mass conversion difficult. Fill level can be used for gross underweight detection.
Pharmaceutical vials, while typically small, can vary considerably in size, shape and required rate of inspection. A complex product handling system including a timing device is required to properly transfer and space the vials during inspection. Because of the rigorous inspection and detection requirements of this industry, a dual-or multi-beam design should be used for inspecting vials. For vials sealed with rubber stoppers, some systems can be set up to detect whether the stopper is missing. Some manufacturers will also help you with IQ/OQ/PQ validation documentation.
Some side-shoot systems offer integrated product handling, X-ray inspection and product rejection for increased efficiency and faster throughput.
Single-beam side-shoot X-ray inspection units are significantly less expensive than the more complex dual- and multiple-beam systems. However, detection levels diminish as the thickness, density, and rate of inspection increase. A single-beam machine is best suited to containers that have simple shapes and flat bottoms and are made from a low-density material, such as plastic. A dual-beam (or split-beam) system is recommended for medium-density containers, such as metal cans, or containers with more complex shapes, such as domed bottoms, that create blind areas. Glass or other high-density containers, especially those with domed bottoms, are by far the most challenging to inspect, so a dual- or multi-beam system is your best bet.
Curtain-less, curved side-shoot systems are longer than curtained, straight horizontal-beam systems. Yet, single-beam side-shoot systems typically have smaller footprints than more complex dual- or multi-beam systems.
Choosing the Right Solution for Your Application
Choosing the optimised detection capability of a side-shoot system over a vertical-beam system for inspecting bottles, vials and cans is often an easy decision. Determining the best system type and model for your application, however, involves many considerations, such as the size, shape, density and variety of the containers to be inspected; the highest risk area(s) of each container; the form/consistency (solid, powder, liquid, gel), density and thickness of the product inside the container; the size and density of potential contaminants; the speed/rate of inspection; the X-ray power; the space available to accommodate the system’s footprint; the range of features and capabilities (e.g., integrated product handling and rejection); your sensitivity requirements; validation documentation requirements, if applicable; and cost.
Ask the manufacturer or vendor to help you identify which systems and models meet your application requirements and to explain the differences between models. A knowledgeable representative can advise you, for example, on whether a dual-beam system has the detection sensitivity you require for inspecting your glass-bottled products or whether only a multi-beam system can deliver that level of performance. Be sure to ask about differences in warranties and service and support options that might influence your choice of model or brand.
Once you have narrowed your choices to two or three models, ask the vendor(s) to inspect a selection of your product samples on those system(s), then compare the results. A valid comparison can be made only when identical sample sets are sent to multiple vendors.
Prioritising your requirements and taking advantage of the vendor’s expertise can help you choose a system whose features and capabilities can best serve your needs.
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