Glass Level Control... The Question is: Should you have 1 or 2 Glass Level Measuring Systems per Furnace?

Hello and Welcome to the April 2023 Newsletter.

So it comes just in time before we flip over to the next month (Yet Again!)... this year is flying by!

For those who don't know about the topics I present in this newsletter series, then those topics might as well have been a well-kept secret. That is because you may go through your glass-working-life and were never aware of the information, not to mention the value it can bring to your part in the glass container-making process.

What I am about to present here in this Newsletter is something I touched on in the last news letter regarding the accuracy of the level probe. However there is another crucial debate I think that is often not talked about.

The question is whether to use two level probes or just one. You might wonder why there is a need to consider a second monitoring-only glass level probe. After all, we only need one glass level probe to control the batch charging rate to maintain the set point glass level.

I am a big supporter of the idea to have two glass level probes. I have worked with two level probes in the past and found it of immense value. If you don't have a second glass level probe then you probably won't even know what you are missing. Quite literally.

Perhaps this is more relating to the dipping probe as illustrated, but also could be any measuring device for that matter. The need for a second glass level probe in my experience is to keep a check on the reading measured by the 'duty' level probe and check there is no deviation or error being incurred.

If this was to be the case, the glass level would take up another 'real' glass level and nobody would be aware of except maybe for the Production department, where there could be an effect upon the change in gob weight.

Even when there is a change in gob weight the automatic systems or manual procedures (depending how gob weight is controlled) will mean that this is managed and the tube height set up to accommodate the change in glass level. Hence it continues to go undetected.

However, maintaining steady glass level is very important especially in coloured glasses where any change in glass level can result in streak occurring from 'cold glass' on that might be left on the side of the forehearth channels. This could happed during the erroneous glass level change or after it.

If the glass level in reality goes down then the glass at the sides of the forehearth channels will turn to 'cold glass' and give a problem with streak and blister when the level is return to the correct level. If the glass level in reality rises, then when it is brought back to the correct level there will be cold glass left on the sides of the channel which could then later drip feed into the main stream of glass.

Amber glass I find is particularly sensitive to glass level change and creating of so-called 'flint streak' in the bottle. This can also lead to blister as well as the streak, again mostly in amber or any other reduced glass. My main experience however is with Amber, a very common glass colour for beer bottles.

In practice, I rarely see furnace departments monitoring the glass level with two level systems. Then they wonder why they get streak and blister that seems to come from nowhere!

When you have two glass level systems, then you can check one against the other and when there is a difference you can set an alarm to get the attention on the matter before it becomes a problem.

In the case of a dipping probe, it is often common for a small 'string' of glass to be left on the tip of the probe and that makes the level appear higher than it actually is. That would result in a lowering of the actual glass level and giving the effects as described above.

There is no need to have the same kind of glass level system as the backup glass level monitoring device. It can be totally different technology. For example, you could have a dipping probe as illustrated here together with one as illustrated in the last newsletter by Ganty, which works on the movement of a reflection inside the foreheath as the glass level changes.

The other thing is that once you know which glass level measurement system is not telling the truth, you can immediately switch to the other level measuring device and then work on fixing the problem without significantly affecting glass quality.

When it comes to good glass production it is all about stability and glass level is one of those processes that needs to be kept stable. This in turn keeps better glass weight stability as well as preventing the problems described with possible streak and blister.

This particular 'Secret' to great production is often overlooked in my experience as the furnace project team don't know the benefits of a second glass level measuring system. Or it is taken out as a cost saving exercise. Believe me, the price will be paid later, and maybe on many occasions during the life of the furnace.

The ultimate cost paid might not be so obvious but unhappy customers for streak and blister in their glass can be very costly as these can result in loss of business. That is not to mention the commercial ware loss that can occur as the streak (in the base) and blister (body and base) cause rejects from the automatic inspection equipment.

Finally, to lay the foundation for future support of the offerings of new technology from other great companies, I am reminding you that I have created a place where my equipment reviews can be accessed easily. Even though these are still on LinkedIn, I have added a domain name to the link so it is easy to remember whenever you might want to go there and see who has been added.

The domain name for the link is?www.Meet-The-GUYS.com

If you go to this domain name link right now, you will see Konatic and SEI Inc. featured, but in the coming months, other GUYS will be added. On the links provided, you can check out some of their other products that offer glass plants some distinct advantages.

If you don't know the background to 'Meet The GUYS' (and would like to know about it), here is a link to the Glass International article I wrote on the topic:

LINK to The GUYS and the GIANTS of the Glass Industry Article

I hope you enjoyed reading this newsletter and look forward to seeing you in the next edition.

• Peter J Firth M.Sc.