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  #26  
Old 02-15-2021, 08:31 AM
Josh Bernbaum Josh Bernbaum is offline
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Quote:
Originally Posted by Chris Lowry View Post
Still getting stones? Change the pot yet?
Sorry haven't been updating the status of this all that quickly. I'm far from a production shop, so I don't (or at least try not to) melt all that often. Maybe every two weeks on average. One of the pros to an electric vs. gas is that I feel like glass quality doesn't deteriorate as quickly as does sitting in a gas furnace. On the last melt, which I did last Monday, it was the first time since I started noticing the tiny stones that I did not scrape as much glass as I could out of the bottom/heel of the pot before refilling. So I just charged on top of about a 1/8 full pot, and didn't stir with potato as I habitually do normally (to try to avoid bringing up any offending material which might have still been at very bottom). So far, in the two days taking gathers last week, I'm seeing fairly clean glass. Did notice some small seeds randomly positioned in the larger gathers, which perhaps would have not been there after stirring. Maybe.. But I can live with small bubs, they don't bother me as much as solid material floating in the melt. Pot's about half full now, so I'll be keeping an eye out for what this week's gathers from the lower half show.

To answer your other question, I don't want to change this relatively new pot unless glass quality becomes unbearable. All these materials we use are just too expensive these days. I used to habitually change pots every summer shutdown, but I kept my last pot going for two years which was much more affordable of a decision (Sorry Pete). Again, not being a production shop, I still think I had less than 70 melts total on that pot at the end of the two years. And I'm only melting SP, so no borax or fluorine in there. Some people might have kept that pot going for a third year, but I wouldn't want to push my luck, and there was some noteworthy pitting on the inner face of crucible. But glass quality was still decent by the end. Added to wife's collection of outdoor planters.
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  #27  
Old 02-15-2021, 09:07 AM
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We see a lot of people trying to stretch their pot life beyond what the original performance intentions were. They then seem confused by the changing quality of the glass. To me, that's not rocket science. If they blame the quality of the pot, I do become irritable.

The other thing to keep in mind is that stones do dissolve.
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  #28  
Old 03-16-2021, 06:00 PM
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fast forward one month.. The stones?
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Old 03-16-2021, 07:25 PM
Josh Bernbaum Josh Bernbaum is offline
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I try not to melt clear too often, been about once every two weeks on average, so I don't have tons of feedback yet from the changes I made earlier. But things do look better than they did in January when I first reported the stones. I'm not sure I saw any in the last couple melts, just small seed bubs, which I can be okay with way more than I can with stones. After habitually potatoing (is that how Dan Quayle would approve of spelling it?) for 9 or 10 years with every melt, I haven't stirred the last 3 or 4 melts any. Maybe that's why I've seen some small bubs, maybe not. But things do seem to be homogenous enough without. I thought I'd try the potato again on the melt I put in yesterday, but when the time came I didn't feel like it. So I'll prob go back to that next time in 2 weeks just to see if any difference or not. I also haven't scraped out the heel in about 3 or 4 melts now (I had been doing that each time though when I first noticed the stones). I know that theoretically the best melts should come from completely emptying the pot between, but it's kind of nice to not have to fill it from dead-empty each time. Takes a while to fill a pot in this moly melting pelletized batch..
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Last edited by Josh Bernbaum; 03-16-2021 at 07:27 PM.
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  #30  
Old 03-17-2021, 07:13 AM
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"but when the time came I didn't feel like it. "

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excellent science.
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  #31  
Old 03-17-2021, 08:01 AM
Josh Bernbaum Josh Bernbaum is offline
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Well, jeez Pete, maybe you're saying that in jest but it makes me sound lazy the way you cherry picked that. I respect that physics and chemistry are all around us all the time, even in these super hot environments of our furnaces. But the decision to not stir this time was based on evidence that I hadn't been seeing much of a change yet in whether I stirred or not, which I have habitually done after every melt for years now. I know the physics of it can help promote homogeneity in the melt and bring some bubbles to the surface, but these last few cycles without stirring have looked ok enough. By the way, I'll never claim to have perfect glass (a claim even made sometimes by folks who melt cullet in invested pots and never raise their furnace temps). I think only those in industry with giant furnaces with less refractory-to-glass contact can accurately claim that.

I had a potato in the fridge. It was something I was planning on getting back to after 3 or 4 melts without, but decided to put off for one more melt. Again, my results without stirring haven't been all that bad. It's still in the back of my mind, and yes, not scientifically corroborated yet, that I may be 'stirring' up little flecks that may be hanging out at the bottom of the pot. When I scraped the heel the last couple times, I saw more flecks in the ladle at the bottom of the pot than I did higher up. I know I wasn't able to scape all of them out with my ladle, which was why I asked earlier about 'swabbing' or another way to scrape the bottom of the pot. Maybe they've since dissolved, maybe not. Will know next time I ladle the heel out again soon.
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  #32  
Old 03-17-2021, 09:14 AM
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I was joking. It's part of my scientific method as well, like leaving a pot of glass in place for a year.

Stirring helps a lot with homogeneity since heavier glasses tend to sink and then get stirred by thermals in the pot. Stirring won't help with stones but again remember that stones do melt back into solution much of the time.

Approaching the problem you have is going to take a number of differing approaches. I would have mixed my basic clear first and not used SP87. That, if it yielded up the stones tells me it's unlikely the batch being put in the furnace and directs me to the pot. If one has a second furnace, then putting the batch in it and if that's good stuff also directs me back to the pot - or the crown area in the troublesome unit. But you have to do all of it and sometimes, it's easier to pick stones.

This stuff never stops, it just becomes easier to resolve. People didn't used to run their pots into the ground so we didn't see a lot of pot stones. Now, with two and three year old pots, we see more. They were never designed to do that.
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  #33  
Old 03-17-2021, 11:07 AM
Josh Bernbaum Josh Bernbaum is offline
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What's still curious to me about maybe the pot bing the culprit is that I started seeing the stones on the second melt of this brand new pot. I wouldn't be surprised if it were after a year or two of melting in it like you're saying. The inside wall still looks nice and smooth as far as I can tell. But there is an indented 'ring' on the interior surface about half way down that I haven't really seen before. Not implying that's contributing to anything, but perhaps it is, since I didn't notice it when installing the pot when it was cold. And if that's the case, I'm imagining that material had to go somewhere, like into the molten glass?

I like your idea about melting a different clear, but I'm just imagining other issues with getting this pot 'conditioned' to a new glass (and then back to SP again later). I'm turning my color furnace on in a month or so again, so I could try a melt of SP in there, but back to the previous sentence in that the 14" pot in there has been melting exclusively phosphates so far and still has life in it so I'm not changing it for this round. I think it's likely to expect issues when changing over to SP's soda lime, and then back again to the opal which I'd have to do because I still want to do more phosphates in there next. I did notice a bunch of snot in a transparent blue, which was the next melt after doing phosphates once, and then after going back to a phosphate formula which had fit previously, expansion was off the mark. Not surprisingly I suppose.
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  #34  
Old 03-17-2021, 12:21 PM
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when we look at potential pot defects at High Temp we have coding on the pot outside stamped indicating when the pot was made and the lot ID. We make up about 1500 lbs of the material at the time and it all gets accounted for. So, if I do have a pot with potential issues, we can go right back to that lot and see what was made from it and who it was indeed sold to.

So, if I have a potential problem with one pot, I expect to see that same problem in quite a few more , the quantity depending on how big the pots were from the batch, less if big, more if small.

So when I hear anything about a defect, I look to whether it's an isolated complaint, or if there is something to it. We can tell right away unless the pot was purchased and then stored new for years and that happens.

The worst time we ever had an issue was way back at the beginning and the crews simply didn't know as much as they know now. Way back, on one of the early mixes, the 1500 lbs was put in one of the rubber bags and was used up to make a mess of pots. I got this complaint that the glass would not fine out, ever. I knew it was multi source and even still, I couldn't pin it down until one day I asked Les if he had been using these things for a silicon carbide mix and he said "Yes, why." and I knew I had it. The pot mix goes only in brand new bags all set aside for the purpose. That was scary for me.

There are conditions which can make a pot go bad really quickly and they have to do with reactions that occur when one glass type is put in the pot right after another It's catalytic and the wear overnight is amazing. People firing without temperature controls can do remarkable things. Firing from stone cold is often interesting. Fluorine does great stuff. Normally, when I see a faint, or not so faint ring around the inner part of a pot, its a great demonstration that glass is a universal solvent. Again if it was made with a defect, the shop staff is pretty fussy about it. Off center castings are my greatest irritant.
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  #35  
Old 03-17-2021, 06:40 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is online now
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That your first melt was fine could be attributed to the common fluke, or it could be that your furnace was not completely heated through after taking it up after the pot change, so some of the energy was spent in the walls and crown.
That resulted in exactly what the first thing Pete told you to do, it lowered the temperature, and you got good glass
You seem reluctant to follow his advice, because you wont get done in time?
But you cant sell glass with stones in it, so its absolutely necessary to solve the stone issue first, then you take step two and work on the seed problem, as it is youíre just wasting time, fumbling in the dark, and wasting money..
You can if necessary blow glass with seeds- its a design question, you can hide it or utilize the as part of the design, but it can be sold.
Not that it has anything to do with the stones, but I donít understand why charge at a lower temp than your melting cycle?
One thing you could try instead of scraping your pot (ouch!) is ladle out the pot and turn up to your new found proper melting temp in the evening , overnight. This is to let all the stones on the walls slide down into the bottom glass. And then put in batch, three times the volume of the glass left there, and leave it until evening. The batch will melt the stones and you ladle that out, and you should be rid of the stones.
Its always a good idea to be on the right side with your hot shop Gnome- hes a nasty b#stard
So you put a shot of vodka or scotch in a glass behind the furnace at night, If its gone in the morning youíre making progress with him, and things should improve
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  #36  
Old 03-17-2021, 07:15 PM
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A gnome I'm not but I like the concept, travelling in the night to curse studios everywhere.

Smyers had it right. "You do this, you do that. You tear your hair out and eventually the problem goes away by itself."

That nails it sadly.
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  #37  
Old 03-18-2021, 09:15 AM
Josh Bernbaum Josh Bernbaum is offline
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Quote:
Originally Posted by Michael Ahlefeldt-Laurvig View Post
One thing you could try instead of scraping your pot (ouch!) is ladle out the pot and turn up to your new found proper melting temp in the evening , overnight. This is to let all the stones on the walls slide down into the bottom glass. And then put in batch, three times the volume of the glass left there, and leave it until evening. The batch will melt the stones and you ladle that out, and you should be rid of the stones.
I like this idea, thanks. I may try this soon if I still need to. As far as the initial heat up after changing the pot last, yes, I'm certain I gave all the materials plenty of time to preheat, it was a few days at my regular working temp before turning it up for that first charge cycle.
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  #38  
Old 03-19-2021, 07:34 AM
Eben Horton Eben Horton is offline
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Years ago I was having problems with stones. It was very confounding to me because I hadnít changed anything. I figured my thermocouple was decaying so I bumped up my charge temp. Still ... in a 300 lb pot I would occasionally have to dig a stone out of a gather.
Then one day I noticed that the person helping me blow glass would flop their clear bit of glass onto the floor on the way to the cullet bucket after I took a bit.
Mystery solved. He was picking up crap off the floor and it would end up in my remelt bucket.
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  #39  
Old 03-19-2021, 08:54 AM
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I have this book called ( A racy title) Refractory stones in glass) published by Corning years before the sermon on the mount and the very last slide with comment indicated that :

"An employee was found to be throwing his asbestos glove into the furnace at the end of the evening shift. Once the practice was discontinued, the issue was resolved."
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  #40  
Old 03-19-2021, 09:16 AM
Eben Horton Eben Horton is offline
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Wow!!!!!! That is astounding !
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  #41  
Old 03-19-2021, 02:30 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is online now
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Yes bumping a punty or a pipe off the floor is absolut forbidden
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