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Dana Smith 01-31-2020 09:30 AM

Bomma - melting recommendations?
 
We've decided to give Bomma Cullet a whirl.

Does anyone have any recommendations for melting it in a Stadelman-style 300 lb. moly furnace?

Bomma's datasheet recommends a melting temp of between 2282 to 2336.

I know each furnace is different, just seeking advice if anyone has a similar setup.

Thanks,

Dana Smith

Pete VanderLaan 01-31-2020 11:36 AM

That sounds good. Bomma is not a borax base cullet. It needs that heat.

Shawn Everette 01-31-2020 01:24 PM

I melt and use at 2100 in a wet dog natural. I've got 1.5-2 hours between charges and 12-16 hours after last charge before use. Doesn't fit everyone's schedule, but it can be done lower.

Pete VanderLaan 01-31-2020 02:11 PM

Quote:

Originally Posted by Shawn Everette (Post 146640)
I melt and use at 2100 in a wet dog natural. I've got 1.5-2 hours between charges and 12-16 hours after last charge before use. Doesn't fit everyone's schedule, but it can be done lower.

****
I thought you weren't using the Bomma yet.

Eric Trulson 01-31-2020 03:26 PM

Quote:

Originally Posted by Shawn Everette (Post 146640)
I melt and use at 2100 in a wet dog natural. I've got 1.5-2 hours between charges and 12-16 hours after last charge before use. Doesn't fit everyone's schedule, but it can be done lower.

Seconding this approximate schedule in a canned heat 200# furnace. My friend's shop has been using Bomma for much of the past year. He just charges at working temp (2080F), waits about an hour and a half between charges, and leaves it overnight after the last charge. Sometimes still has a few small bubbles left the next morning, but it generally fines out before the end of the day.

Pete VanderLaan 01-31-2020 05:45 PM

I've done this sort of schedule and agree that the fining goes well, but running a good deal hotter seems to yield up a different glass when it comes to cording. Is that being considered?
It seems OK on small work but not on deep dives.

Dana Smith 02-01-2020 11:17 AM

Pete,

Novice question - are you implying that you would expect more cords or less cords at the higher temps?

Pete VanderLaan 02-01-2020 01:18 PM

well, if you get way too hot, more cords as the pot dissolves. Then, looking at the other end, cords when melted way too cold as a glass not well stirred.

I'm more comfortable with the hotter melt than the cold one but it's clearly an economic consideration. With the Bomma, 2300F is not too hot if it has 8 hours to cook after the last charge. It would be more aggressive on the pot but would make bettter glass. It depends on whether you need better glass.

Shawn Everette 02-03-2020 09:46 AM

Nope I'm on it, have been since about October. Done a couple posts about it.

Shawn Everette 02-03-2020 09:49 AM

I'v tended to notice no cords until you are actually scraping the bottom with most cullets and my method. I've had pots sit for a considerable amount of time that were cord free. I tend to think that cooking it hotter promotes the cords as it bakes off some of the fluxes.

Dana Smith 02-03-2020 09:59 AM

Shawn - Are you using the whole tank before melting any additional glass or are you "topping off" the tank nightly/as needed?

The Bomma notes state:

"When using Bomma Cullet continuously, it is recommended to charge again when there is a minimum of 1/3 of the furnace capacity remaining."

If I am interpreting that correctly, that seems to be saying that they don't recommend letting your tank go below 1/3 full.

Shawn Everette 02-03-2020 10:21 AM

With our charging availability we're generally getting to about half a tank these days, charging about every 3-4 days. We used to charge once a week, and the only difference I noticed was the amount of complaining from people that don't want to gather out of a low tank.

Pete VanderLaan 02-03-2020 11:43 AM

Quote:

Originally Posted by Shawn Everette (Post 146662)
I'v tended to notice no cords until you are actually scraping the bottom with most cullets and my method. I've had pots sit for a considerable amount of time that were cord free. I tend to think that cooking it hotter promotes the cords as it bakes off some of the fluxes.

****
I tend to think differently. I think the glass feels a bit shorter because alumina is sloughing off into the melt and that makes a stiffer glass. It's a funny call with methodology. You can do something one way, and for a while it works great. Then it stops working. I don't know why that is.

In castings, there's always some difficult getting the glass to run down into the very thinnest spots. I think the glass rolls over the alumina mold and gets stiffer from it. Mark thinks I have a good point. In mine, I'm going to try painting a bit of lithium carb onto the thinnest spots to see if the skids can be greased with fluxes.

Shawn Everette 02-03-2020 12:25 PM

How thin are you trying to go? You may have a solution with the added flux in the mold, pesky surface tension. Generic rule of thumb for most of the classroom situations was to not try and cast thinner than 1/8".

Pete VanderLaan 02-03-2020 01:32 PM

Coming out of Liuli Gongfang, Mr Bai was doing some stuff that defies all the conventions. Dan Clayman and I were talking about it as an issue but I think it can be done. What you can't do is to stick to the commercially available cullets.For casting, they pretty much all suck. The conventional mold materials contribute to the problem. Surface tension is one thing, viscosity is another. I'm learning fast. You need to make your own goop.

Shawn Everette 02-03-2020 01:48 PM

I'm curious about the Gaffer goop. It's anneal temp is so low that I'd think it have a low viscosity/surface tension in normal casting conditions. BE is really a fusers glass, but it gets real thin past a certain heat threshold. I think it'd sand cast beautifully, if it wasn't so yellow.

Normal molds really don't help things in terms of flow, and I don't really know of anyone doing anything that ground breaking. It's gotta stick to the mold, but not the glass, and that's a big order to fill. The boron nitride spray has been real hit or miss for me, but some people swear buy it.

Pete VanderLaan 02-03-2020 02:28 PM

Omce it gets to the terminal point in the mold, it will back up as long as the sprews are right. In China, I saw stuff as thin as the harvard flowers.

Shawn Everette 02-03-2020 03:09 PM

That is the theory, but most glasses I've used weren't ever brought to temperatures that would thin out enough to move up the sprew. When things when thermo nuke and the mold failed, it would flow into the thinnest flashing without fail.

Pete VanderLaan 02-03-2020 03:39 PM

the point of what I'm suggesting is to change the glass itself, midstream. If one uses the commercial glasses available, it won't happen.

Larry Cazes 02-03-2020 05:18 PM

Quote:

Originally Posted by Pete VanderLaan (Post 146668)
****
It's a funny call with methodology. You can do something one way, and for a while it works great. Then it stops working. I don't know why that is.

I tend to think thats just the world telling you that you really didn't understand why you were using a particular methodology over others.

Pete VanderLaan 02-03-2020 06:17 PM

or... something changed in the formula, or the mine run. They don't tell you that either.

Pringle Teetor 02-14-2020 11:36 AM

Nothing but seeds.

Pete VanderLaan 02-14-2020 11:49 AM

I am assuming you saw my PM to you.
Tell me how you melted, blah blah blah...

I've had a lot of conversations with a lot of people over the last few days on this and I'm hearing some doing fine, others having nothing but cords. One indicated they are doing fine melting at 2100F but topping up the pot when half full. Others, nothing helps at all.
What was most disquieting was the observation that sometimes it looked great, then a later load would actually be short and cordy. I think beginning to nail down batch runs from the pallets may suggest something new. Both SP and Olympic have had these issues. Charlie Parriot is substantially more distant from this process than I expected he would be. I am a lot less certain that the cullet wars/shortages are over. Cristalica continues to go down and from my understanding, the furnace is shot with no plans to rebuild. Writing a formula isn't really all that difficult but proper mixing and melting consistently require diligence. It would be ironic if Oceanside was left as last man standing with sys96, a cullet incompatible with a fair amount of color when last produced.

Spruce Pine 87 is looking far more attractive today than anything else at .81 lb. I don't really know why there are so many objections to a pelletized batch that is so reliable. It's not really dusty. Mine? Mine is more dusty and I just throw on a respirator.

Pringle Teetor 02-14-2020 05:39 PM

1 Attachment(s)
we've melted at 2100, 90 minutes between scoops - seeds. People said melt hotter and longer. Did that - waited 90 minutes between scoops (cooked @2285 for 9 hours), still seeds. trying a squeeze today and will check in the morning but not holding my breath. Only charging 1/2 pot. Stad moly furnace 250 lb crucible. I did blow a clear piece with a thick bottom and yes, there were cords.

has anyone seen seeds seeds this bad in bomma?

Shawn Everette 02-14-2020 09:39 PM

General rule of thumb is electric takes longer. When I was running electric, it was a minimum of 3 hours between charges, they just take longer to regenerate the heat. On my WD gas it's less than 20 minutes, on my old stad moly it was over an hour back to temp.


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