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Old 08-04-2018, 08:32 PM
Chris Lowry Chris Lowry is offline
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Crucibles

So what other crucibles are out there, what do you use?

We have been using High-temp's crucibles for years but wondering if there is something better. I have no way of confirming but we just put a new crucible in and I've never had so much trouble with bubbles in the glass. Of course it might have nothing to do with the crucible but that is the only thing that has changed.

Does anyone out there use gathering rings, or even know where to buy one?

Aloha
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Old 08-05-2018, 07:20 AM
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You have a choice also of Engineered Ceramics and LaClede Christy for crucibles. In my experience, just as many people swear by, or swear at their crucible supplier.
There are lots of reasons for getting bubbles in the glass and you simply don't supply any other information. Something falling in the pot, changing cullets or batch types, failing inaccurate thermocouple , all come to mind.
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Old 08-05-2018, 07:46 AM
Eben Horton Eben Horton is offline
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Iím going with immaculate thermocouple. Or is it inaccurate? 😂
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Old 08-05-2018, 08:04 AM
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In the radar in my world, I always am looking for recurring trends. If someone seems to have an isolated problem, I tend to discount the notion that the crucible maker has failed. If I'm suddenly swamped I see it quite differently and most of the quality control decisions are between Jeff and I and it's rare that we disagree. In this case, I look for in house issues and I would say right now that I'm not seeing any recurring complaints over issues like the one Chris mentions, so, I'd keep digging.

I do believe in Karma and go out of my way to not dis the competition and see no reason to be inclined to do so here. Making pots is as much an art as it is a science.
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Old 08-05-2018, 12:07 PM
Chris Lowry Chris Lowry is offline
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I would love to figure out my bubble problem and can only assume a few possible reasons I get them. My bubbles are large and I tend to get them on third or bigger gather. I can see them in the glass as they wind up around my gather. Not a glass, melting, thermocouple problem.

Of course my first guess would be Iím not gathering correct.
Second would be Iím too picky.
Third would be Crucible.
Maybe circulation and furnace related.

And of course these are just an opinion. Iím not blaming anyone just wanting to know what types of crucibles people use.

And want to know what other people do to get rid of gather bubbles. Like gathering rings, raking the surface, furnace types.
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Old 08-05-2018, 12:24 PM
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I don't recall your crucible size but bubbles deep in the glass are not usually pulled in from the pot wall or if they are, your wall has enough honeycombing to trap bubbles. How you gather and strip off, intentionally or not is a cumulative issue during a day.

You don't say what you're melting or how hot and long and that's worth looking at.

It can also be from an inadequate squeeze. It can actually be from cullet itself. I do find that I get far better glass if I stir the pot before turning it down from a melt. Potatoes are really good stirring agents. You can go to the floor, smooze it around and really disconnect any gunk from the pot wall. Experience tells me that it's almost always three things coming together to create an issue, but if I was hearing from lots of people over this suddenly becoming an issue, I'd be digging in. With the new cullet now available, I had a terrible time fining that stuff out.
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Old 08-05-2018, 01:17 PM
Chris Lowry Chris Lowry is offline
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We have a 400lb pot itís brand new on its third melt. We melt Spruce Pine batch, canít remember exact program right now, but we throw in 50lbs every two hours with the furnace 200 degrees over idle. Melt for 9 hrs around 2300 and really do no squeeze just wait for it to get back to idle. Charge starts Saturday night ready Monday.


I would usually and maybe still do guess itís drip off bubbles and furnace circulation although I have two weird issues.

One is we usually get 60 or so charges before we change a pot and that is before it cracks. This last crucible lasted 30 charges and had a pin hole bottom side. Then this new crucible has intensified my bubble problem.

Two is I always gather on one side and drip to the other. Maybe after many pieces the bubbles would travel to the middle but Iím getting big groups of 4-5 bubbles on the first piece. Some days threw the melt are better than others but can be any day of the week. Iíve been trying to shadow for bubbles before I gather but they are hard to see as they are not right on the surface.

If it is drip off bubbles how do I avoid? Gathering ring, rake the surface, gas furnace to pop them more???
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Old 08-05-2018, 01:20 PM
Josh Bernbaum Josh Bernbaum is offline
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Quote:
Originally Posted by Chris Lowry View Post

And want to know what other people do to get rid of gather bubbles.
Cut them out.
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Old 08-05-2018, 02:20 PM
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the primary function of a gathering ring is preventing cording. Essemce was selling them at one point, I don't know of an american manufacturer. Possibly LaClede.
The way I view a crucible peak performance is that the first melt is never very good but the second melt should probably be the best glass you will see from the pot. I would still stir it.
That however is based on the way I melted and not on the way that you're doing it. I think that the melt schedule you have is not unreasonable but only going to 2300F in such a large pot and then not squeezing is likely not allowing the valence shift to be total which could account for bubbles remaining at the core. As to the life span, I like to see 60 melts as well but it doesn't always work out and that's true of all pots made.
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Old 08-05-2018, 04:07 PM
Chris Lowry Chris Lowry is offline
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Yes I do know life of the crucible is relative and I wouldnít worry unless it happened all the time.

Can larger bubbles just sit under the surface for a long time? Seems like they would work their way up and pop.
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Old 08-05-2018, 05:38 PM
Eben Horton Eben Horton is offline
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Quote:
Originally Posted by Chris Lowry View Post
Yes I do know life of the crucible is relative and I wouldnít worry unless it happened all the time.

Can larger bubbles just sit under the surface for a long time? Seems like they would work their way up and pop.
Howís the viscosity feel of your glasses at your normal working temperature? I have a hunch that during your crucible change something happen to your thermalcouple
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Old 08-06-2018, 12:12 AM
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Good thought but no... every time itís a little different but not more than 10 degrees. I feel like we get good melts just have random bubbles. Maybe Iím wrong but ???
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Old 08-06-2018, 01:54 AM
Peter Bowles Peter Bowles is online now
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Just curious, does the grouping of 4-5 bubbles tend to occur half way to two thirds down your gather?
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Old 08-06-2018, 10:41 AM
David Hopman David Hopman is offline
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Try squeezing at 1950 for an hour.
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Old 08-06-2018, 10:58 AM
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In a 28 inch pot, I'd go longer. It takes time to penetrate that much glass but the temp suggested is very good.

I'm thinking Peter Bowles is thinking about thermal layers. That's real.
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Old 08-06-2018, 11:22 AM
Chris Lowry Chris Lowry is offline
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I would say yes... bubbles tend to be right in the center of my gather but not 100%

Can you squeeze later, we do turn the furnace down 50 degrees at night. Would that give it a squeeze each day?
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Old 08-06-2018, 01:26 PM
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The Squeeze:

Antimony trioxide is an essential additive to most soda lime glasses and SP87 certainly is one. Without having the specific numbers for you, I will tell you this. When Antimony is added to a glass it nominally is in a monovalent mode during the high temps in your melt. That means it has one space on its outer electron ring. It will not accept anything onto that ring.
BUT when you drop the temperature of it below about 2100F it flips valence agoes into a pentavalent state meaning there are now five spaces on that outer ring. When you are watching the bubbles in your glass getting smaller, the glass is shrinking ( Expansion/plus and minus goes on forever!) and at the same time those gases are being drawn back into solution and engage the outer antimony electron ring.
Reboil, another deceptive and charming term:

That's when you over heat the glass and the antimony reverts to the monovalent state and lets everything off of that outer ring.

If you don't believe that your glass is full of gas, try this: Take a gather of glass on the end of a punty and hit it hard with compressed air for about 40 seconds. Now Stop and watch all thee bubbles form in the gather. As the glass begins to adjust to not having cold air blown at it, those bubbles go back into solution.
If you never really switched valences in the first place, that central core of your pot is a happy place for gas looking for a home. The 1950 number is a good one. The bigger the mass of glass, the longer it takes to flip.
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Old 08-06-2018, 02:00 PM
James Ennis James Ennis is online now
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I have had excellent results using the potato, it has helped clear up problems like these in our free standing pots(high temps pots)
I like to bubble about 1/2 way thru the melt, when everything is nice and hot,
stick the spudd on a punty rod and shove that sucker down to the bottom
and stir a few times. we are melting spruce pine, not pellets, but raw, in 12 lb beer bags.
you might not be getting your furnace as hot as you used to before your
pot change, 20 or 30 degrees can make a huge difference at high fire,
and a bad thermocouple can and will act different at different temps,
you might be right in at 2100 but as you get hot it may then start to
fail and cause all sorts of issues.
if it is not equipment, then its all about time and temperature.
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Old 08-06-2018, 02:07 PM
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and I thought the Hokey Pokey was what it's all about. ..
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Old 08-06-2018, 02:15 PM
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Quote:
Originally Posted by James Ennis View Post
we are melting spruce pine, not pellets, but raw, in 12 lb beer bags.
********
Hi James, Lately I find myself pushing the notion of SP"Snowflake" 87, particularly to the wire melters. Do you find it melts faster than the pelletized stuff.

Disclaimer: This is far dustier stuff for those of you who already think SP87 is dusty.
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Old 08-06-2018, 02:59 PM
Art Freas Art Freas is offline
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We batch sunday night, let it come down overnight and next day to 2100, then drop to 1960 for Tuesday and then bring it back to working temp Wednesday morning. Seems to work for us in spite of our aged crucible like object. Currently using Cristalica.

Art
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Old 08-06-2018, 05:33 PM
Chris Lowry Chris Lowry is offline
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Ok... so if I turn the furnace down every night am I getting a good squeeze to absorb bubbles or is it too late? Is 1930 too low, can it be too low to squeeze?
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Old 08-06-2018, 06:06 PM
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1950 would be good
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Old 08-06-2018, 06:45 PM
Chris Lowry Chris Lowry is offline
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Thanks but not totally my question.

We do turn down to 1930 every night.

Is that too low?

Is it still effective to squeeze the second day?

I know it wouldn’t help the first day but does it help remove bubbles for the second day?
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Old 08-06-2018, 06:57 PM
Peter Bowles Peter Bowles is online now
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It might be that you're getting touch down bubbles.
Particularly if your parison is quite cold when you go in to gather, and especially if they occur when the pot is fuller.
If they are happening as a cluster its likely a function of the way you gather.
I've had similar issues and a combination of the following cleared them up..certainly on 3rd, 4th and 5th gathers..
Briefly fire polishing the outside after blocking / papering.
Making the parison slightly more pointy, or at least less round.
Entering the glass at a higher angle to start and then drop the iron onto the sill to gather.
Going into the glass a little slower and not turning (or turning slower) until your a good 3/4 way into the glass.
Running the glass a little hotter.

It could also be that you are coming out of the glass after gathering too quickly and making bubbles from the run off, that you get to collect on your next gather. If you have other people gathering from the same furnace it could also be them leaving the bubbles behind.

If there is any kind of consistency in how the bubbles cluster, or where they are on the piece its less likely that its part of the melt.

Last edited by Peter Bowles; 08-06-2018 at 07:02 PM.
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