For premium glass container producers anywhere in the world, the right refractory material for stirrers in
a colourant forehearth can eliminate streaky glass and increase plant efficiency and safety.
Picture 1. The red X indicates the Pyrotek stirrer compared to another supplier's stirrer.
Recently, a premium glass container producer in western Europe confronted the pain of repeated refractory stirrer change-outs every two weeks.
They also faced streaked glass and too many rejected containers. The stirrers they relied on were supplied by a well-known European manufacturer, but they degraded too rapidly.
At this manufacturing site, a colourant forehearth afforded the plant more flexibility and quicker turn-around times in their quest to offer a wider range of glass containers to their customers.
Colourant forehearths work by mixing colour frit granules in glass at elevated temperatures with a series of stirrers lined up in banks.
Glass depth in the colourant section of a forehearth is typically deeper than the rest of the forehearth, so double helix stirrers are usually used, but in this case the forehearth was designed to use paddle stirrers.
This feature in the design necessitated a higher-than-normal rotational speed of the stirrers. Stirrers work by lifting glass from the bottom of the forehearth and mixing it with colour frit, which is dropped onto the surface of the glass through the forehearth roof.
For melt and dispersal, colour frit must be heated higher than the ambient glass. Temperatures in this section of the forehearth are usually above 1320°C.
Paddle Design
All the stirrers used were a paddle design and had to be operated at up to 32 revolutions per minute to maintain glass
and colour mixing efficiency.
As they wore down, stirring speeds needed to increase to maintain efficiency, otherwise the colour frit would not mix homogenously with the base glass.
An increase in rotational speed is a double-edged sword in a colourant forehearth. The positive affect is that it will mix the glass better and reduce the potential of glass streaks. But it will negatively cause an increase in glass erosion to the refractory stirrers.
Also negative is the possibility of bubbles created by worn refractory, leading to lower quality glass and rejected containers.
The rapid degradation of the stirrers caused more frequent change-outs of stirrers. The long, labour-intensive change-out process hindered critical operational efficiency on the line.
Increased Service Life
Making matters worse and unacceptable, the work changing the stirrers was also dangerous for plant workers. The glass producer needed more service life from these stirrers. A change was needed immediately.
After meetings and delving into considerable detail on process and systems utilized, to fully understand the challenges faced by this glass producer, Pyrotek recommended a new refractory option for stirrers.
The advanced Pyrotek stirrers were made of Z30 refractory. Z30 is an aluminazirconia-silica formulation. The refractory exhibits low apparent porosity, high bulk density, high resistance to thermal shock and glass corrosion.
A small-scale trial of Z30 refractory stirrers was conducted with the glass producer to compare it with the old stirrers. After two weeks, all the stirrers were removed to compare the wear and condition.
The visual inspection and measurements showed that Pyrotek’s stirrers had less wear than those from the previous supplier.
Importantly, the tightly packed, dense structure of the Z30 refractory did not lead to bubble generation. The Pyrotek stirrers proved low porosity and better performance.
The glass producer was encouraged by the initial trial and decided to conduct a full-scale trial to find out how long the Pyrotek Z30 refractory stirrers could last effectively in this particularly challenging colourant line. This further trial showed a 50 percent service life increase compared with the stirrers supplied in the past.
They provided three weeks of service compared with two weeks, leading to substantial operational efficiency improvement. Importantly, this would also reduce the frequency of employee exposure to the dangerous conditions in stirrer change-outs.
After being impressed by the results of the trial stirrers, the container manufacturer now uses Z30 refractory stirrers in two other plants as well. The reduced downtime for change-outs and increase in overall efficiency have proved financially valuable.
The savings for the three plants is approximately EUR€100,000 annually, according to the glass producer.
The manufacturer is also very happy to reduce the number of rejected containers it was experiencing.
Other expendable refractories from Pyrotek are now extensively used in all the plants within the producer’s group.
For example, Pyrotek feeder tube expendable refractories have been another high-performance product. Pyrotek’s feeder tubes last 10 months, compared with a previous supplier’s tubes that lasted only four months.
Pyrotek has spent years developing refractories in multiple industries around the world for the most severe and challenging production environments.
Ongoing trials at other premium glass producers have shown similar encouraging results and Pyrotek will share those results in future articles.
The article was printed in Glass International magazine in September 2024.
Posted in Article, Feature, Product Spotlight, General News, Case Study.
Tags: Glass, container glass, Refractories, Europe, Sustainability, Expendable Refractories.