Eleonora Bordini, Marposs International Industry Manager, Glass Packaging
Glass is one of the oldest materials dating back to 3500 BC. Egyptians manufactured the first hollow glass container in 1500 BC, and the invention of the blowpipe in the first century BC was considered a technological revolution. The true revolution, however, was the automatic bottle blowing machine invented in the USA by Michael Owens at the beginning of the 20th century. Its ability to manufacture 2,500 containers per hour made glass container production possible on an industrial scale.
The technology continued to be improved over time, and in 1925, the first Individual Section (IS) machine was developed enabling each section to produce one or more containers independently. The IS style machines used ‘blow and blow’’ or press and blow’ techniques that are still applied today. Using these processes, a specific amount of melted glass—or a “gob”—falls in a blank mold where it is either pre-blown or pressed with a plunger. The pre-shaped gob—known as a parison—is then deposited into a finish mold where blowing is completed.
Nowadays, forming machines can have up to 20 individual sections each producing one to four containers simultaneously. This means that one to four gobs of melted glass fall in one to four molds present in each section, which occurs in parallel in each section. Depending on the container’s size and shape, the production speed can be as fast as 700 containers per minute.
Glass containers are used as packaging for different industries including food and beverage, perfumery and cosmetics and pharmaceuticals. Glass is inert in that nothing passes from the glass into the product and nothing penetrates the glass from the outside and into the product. It is sustainable and 100% recyclable. When compared to other packaging materials like plastic and aluminium, glass is beautiful and enhances the perceived value and quality of the product.
In respect to other materials, however, glass is much heavier, although the manufacturing process has recently improved to enable production of lightweight containers. Today’s glass containers are up to 40% lighter as compared to 20 years ago. This weight reduction is a necessity, not only to reduce transportation costs but, above all, to save raw materials and energy. With this in mind, significant technological improvements have been done on melting furnaces to reduce energy consumption and CO2 emissions.
Glass containers have become more and more complex in shape. Unique shapes increase premiumization—or product value—and brand awareness. Consider, for example, how easy it is to recognize a Coca Cola bottle or a Nutella jar, even if the container is empty or without the label.
Controlling Glass Quality
Glass container manufacturers have become more and more concerned with the quality of their production, aiming to reduce scrap and avoid customer complaints. Quality control is implemented at the earliest possible stages of the glassmaking process in order to immediately take the necessary actions. Inspection for defect detection – on the bottom, body, neck and finish of the containers – occurs along the entire production with in-line inspection machines, mainly using contactless techology with cameras and sensors. Other types of controls and tests carried out on glass containers on a sample basis in the quality control lab include:
– impact test
– vertical load
– internal pressure test
– internal volume measurement
– residual stress
With respect to dimensional control, it is carried out, on a sample basis, near the production line, with go/no-go gauges or, alternatively, with manual gauges or semi-automatic/automatic gauging systems in the quality control lab. Dimensional controls required on glass containers include:
- total height
- mouth parallelism
- external diameters, or long/short sides, and diagonals on the body
- external diameters on the neck
various parameters on any kind of finish (e.g. diameters, heights, radiuses, angles…)
Control with go/no-go gauges presents a whole set of issues: it does not provide any quantitative information, and it relies on the operator’s skills. Moreover, it implies high costs, since a set of dedicated go/no-go gauges is required for each article produced, and these hard gauges have to be managed and periodically re-calibrated. Furthermore, it is also not possible to collect any data and perform statistical analysis to improve the process using this method.
Semiautomatic gauging systems can be based on contact or optical technology. The container to be measured is manually loaded/unloaded and the measuring cycle is carried out automatically. Systems based on optical technology are flexible and can measure many different articles regardless of their size, shape and colour without any job change.
In automatic gauging systems, container handling and measurements are fully automatic without any human intervention. They are mainly based on contactless technology and, in addition to external dimensions, they can also measure other features like the inside of the mouth diameter and profile, wall thickness, weight, push-up and labelling area profile.
The advantage of automatic gauging systems over semi-automatic ones is they dramatically reduce manpower.
The results of the acquired measurements from semi-automatic and automatic gauging systems are sent to Manufacturing Execution Software (MES) and are used by decision makers to fine-tune and monitor the manufacturing process in real-time.
Glass manufacturing has greatly improved since Owens’ automatic blowing bottle machine. Its uses in various industries provide strong brand recognition and product value. With various forms of inspection control and gauges, the quality and manufacturing of glass will only continue to improve.