Following his views on optimising forming process stability and reducing the weight of glass in general terms (Glass Worldwide issue 74), from issue 75 onwards Paul Schreuders explores the different (individual) steps to be taken towards optimising forming process stability and reducing the weight of glass containers. Here, the focus is on gob condition and how XPAR Vision’s solutions can help to stabilise this process.
As explained in issue 74, following the Paris Climate Change Conference (COP21) and taking their social responsibility seriously, many if not all food and beverage packing companies are actively working to reduce their carbon footprint. Since packaging is a substantial part of this carbon footprint, supply chain collaboration is a key for success. Knowing the competitive field of metal, plastics and bio-based packaging, for glass the keys to survival are to recycle and reduce weight (improving the content-to-glass ratio). Reducing weight requires further optimisation of the forming process stability.
Stable gob condition
The gob condition is an important input for the glass forming process. The creation of a ‘good’ gob is the first step or precondition to making a quality product that meets customers’ standards. To be able to do this, a number of parameters should be controlled: Temperature of the glass (viscosity); the homogeneity of the temperature distribution in the gob; the gob dimensions and weight; and last but not least, the glass condition. These parameters can be monitored by infrared and other sensors available to the industry.
The importance of a stable gob condition over time is obvious. When the gob condition starts to deviate from normal, it will also influence the stability of the forming process. No need to say it affects the quality of the container produced. Specifically, the loading of the gob into the blank mould will show changes (rg in speed, length, time of arrival and position). Variations in loading immediately leads to variations in glass distribution in the container.
Temperature of the glass (viscosity)
As all containers on the conveyor belt are measured by infrared (IR-D), changes in glass temperature can be easily identified by receiving an alert when infrared intensities are changing. In figure 1a, warnings are shown on the main overview screen, showing the front cavities (ie front gobs) deviating from the middle and back cavities. At cavity view (figure 1b), the IS machine operator can observe when the change in glass temperature started and that the trend is moving downwards.
When temperature changes are signaled by system warnings, IS machine operators would involve furnace and forehearth specialists to perform corrective actions. Knowing that, in order to make real-time corrective actions possible, suppliers of sensor systems (IR-D and/or dedicated gob monitoring systems) and feeder and forehearth (monitoring) suppliers would need to connect and interact for automatic adjustment and closed loop control of glass temperatures.
Homogeneity of temperature distribution
Where temperature measurements are provided by gob monitoring systems like GIA and GobWatch (by point measurement), these systems generally do not identify the homogeneity of temperature distribution correctly. Infrared can be a helpful tool determining changes in homogeneity of temperature homogeneity in the gobs. If circumferential temperature distribution in the gob(s) is bad, for example, it will result in uneven glass distribution in the bottom of the container. Again, alerts are given on the main overview screen (figure 2a), supported by the IS machine overview (bottom intensities from all cavities) in figure 2b.
Also database analyses from XPAR Vision’s XMIS can unveil the period in time where these events occurred (figure 3). Also with respect to warnings when temperature homogeneity is deviating, IS machine operators would involve furnace and forehearth specialists to perform corrective actions. Knowing that, in order to make real-time corrective actions possible, suppliers of sensor systems (IR-D and/or dedicated gob monitoring systems) and feeder and forehearth (monitoring) suppliers would need to connect and interact for automatic adjustment and closed loop control of glass temperatures.
Properly cutting the gob is an important conditional step for container forming. Each gob is ideally cut with identical dimensions (length, diameter and shape). However, glass condition variation (eg viscosity changes) and equipment wear and tear (eg shear blades) lead to changing gob dimensions. IS machine operators or specialists can only adjust shear mechanisms manually. Gob monitoring systems will identify these changes directly after the gob is cut but are not able to correct automatically and cannot relate the signaling to the root cause.
On the other hand, good gob dimensions at the shear cut are by definition changed by the delivery before loading into the blank. For good glass forming performance, the gob dimensions at the loading is critical.
A tool like GobAssist is on a near real-time basis taking measurements of the speed, length, shape and diameter of the gob. Any deviations from the defined tolerances are seen by warnings of the system. For the IS machine operator, it is easy to interpret and immediate remedial actions can be performed by him. Looking forward in time, these actions can be automated, for example, by robotic technology. For further details about GobAssist, refer to the ‘Amazing Discoveries’ series of articles in 2017.
An important condition for a controlled forming process is a stable and accurate weight of the gob. The necessity to control the gob weight has been explained in ‘Amazing discoveries part 12' (Glass Worldwide issue 74). Control over variations in gob weight open the way for production speed increases and reduced weight (lightweight containers), answering to future needs of customers and environmental demands (weight-volume ratio needs to improve) and leading to more profit.
Traditionally, the IS machine operator regulates the gob weight manually a few times every hour, logically with delayed correction leading to low accuracy and high variations in the weight of gobs. Automatic correction in closed loop (system control, eg by XPAR Vision’s IGC) has been available for many years and provides the accuracy and stability needed for above-described requirements. In figure 4, variations in the forming process (automatic control versus manual control) are visualised.
Glass condition (redox)
A very specific parameter that reflects the condition of the gob, or more precisely the condition of the glass is not identifiable by direct sensor measurement systems. Only from infrared intensity measurements and its trend information the changing glass condition can be visualised. Typically, monitoring the infrared intensity in the finish part of containers gives valuable information about redox changes. In figure 5, an example is given of this redox change (XMIS databases analysis).
A redox change observed often relates to a change in cullet quality. The task for an IS machine operator, when he notices a change in this condition, a notification/warning to the furnace specialist is the only action he can take, while the furnace specialist in return has few options to adjust, other than to control the cullet mix.
It is obvious that with the right use of infrared sensor systems and dedicated gob monitoring systems, the gob condition in all its aspects can be detected and controlled. Early or even real-time signals are presented to the IS machine operator to act upon. In more and more areas, direct steering (closed loop automation) is in place or will become available shortly. XPAR Vision is working actively to bring sensor solutions to the market or facilitates IS machine and other suppliers to develop in this respect.
The higher the level of control over the gob condition, the less variation and thus the more stability of the container forming process. Control and stability are prerequisite for performance improvement in such areas as the reduction of product weight, meeting future public (environmental) and customer requirements to reduce the carbon footprint of glass packaging.
In addition, a higher level of process control brings benefits to the glass manufacturer by the ability to speed up production, deliver better quality products and secure their competitiveness.