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  #76  
Old 01-12-2004, 10:08 AM
Dave Bross Dave Bross is offline
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I don't think it would hurt anything. There have been a number of posts about folks forgetting to turn up the furnace after batching and getting good glass anyway.

Personally I've always tried to get my cook time scheduled so that it happens while I'm asleep and I can then squeeze it in the morning and have glass that day.
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  #77  
Old 01-12-2004, 11:13 AM
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At 11pm last night, the most recent charge had not melted, so I just left it overnight.

This AM at 8:30, the glass had melted down flat again - to less than 3/4 of the pot. I did another charge, and will let that melt.

Once I'm over 3/4 of the pot "melted flat", I'm going to turn it up to 2250 for cooking. Probably around noon, unless another charge is required.

I see no need to fight for "a totally full" crucible on this first charge. Anything over 3/4 full will give me plenty of glass for this first run of the system.

Now all I need is a gas "bar-b-que" fitting installed in the house to use instead of those 20lb propane bottles, and I'd be set!

-Richard
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  #78  
Old 01-12-2004, 12:43 PM
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Congrats, Richard.

Sounds like you're up and running quite nicely again!
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  #79  
Old 01-12-2004, 01:03 PM
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It's not time to celebrate yet. I've been here before without incident.

Last time the problem came when I heated to 2400 because the cullet wasn't behaving as expected. I now know the real problem was "mass-temp lag". That is, the heating chamber said 2200, but the center mass of the cullet was nowhere near that.

This time I started with an empty crucible at 2150 (heated 100F per hour). Due to the way this furnace behaves (learmed while empying out after the disaster), using the ramp function pretty much guarantees accurate temp in the heating chamber and in the crucible.

I'm still melting down the charges at 2150. The batch is melting down very nicely to flat between charges. I'm not making the mistake of charging too soon, either (almost did that at 10:30 am today, but then I thought better of it). I still have at least one more charge before I cook the glass at 2250.

It looks like I'll start the cooking this evening, and let it go all night. I want to start early enough that I can monitor the cook to catch/avoid any problems.

Once it's cooked and I start the squeeze - THEN I can celebrate!!! I have a bottle of Guinnis waiting...



-Richard
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  #80  
Old 01-12-2004, 02:51 PM
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Vested interest!

Quote:
Originally posted by Richard Huntrods

Once it's cooked and I start the squeeze - THEN I can celebrate!!! I have a bottle of Guinnis waiting...



-Richard
I watch this with great anticipation! (or as Dr. Frank N. Furter said with "antici...pa...tion" ).
With a bit of luck I'll be invited over to see this rebirth! If all goes well, we won't even set each other on fire in the confines of the tin shack .
I've also discovered that if I bring beer into a studio I am made to feel very welcome.

- Randy
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  #81  
Old 01-12-2004, 03:09 PM
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Yes. Beer good. Cold bad.



-Richard
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  #82  
Old 01-12-2004, 05:39 PM
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Okay, then.

New pictures of the rebuilt furnace and current Spruce Pine batch charging are now up on my web site:

http://www.huntrods.com/

under the glassblowing link.

Yes, that's me in shorts - in January - in Calgary Alberta - in the snow! Thank goodness for Chinooks - it's currently -2 C or 17F here.

Thought I'd inlude that for all you "warmer weather" glassblowers. By the way, temps between -5 and +5 Celcius are perfect for glassblowing in my shack - the glory hole becomes a wonderful space heater! :-)

Cheers,

-Richard
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  #83  
Old 01-12-2004, 07:30 PM
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Sorry to get tangential, but to celebrate, try some of this:

http://www.vansteenberge.com/Bodypag...ldenDraak.html
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  #84  
Old 01-12-2004, 07:56 PM
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Quote:
Originally posted by Richard Huntrods
...Thank goodness for Chinooks - it's currently -2 C or 17F here...

Cheers,

-Richard
1. A Chinook is a warm wind (like a Santa Ana for you Californians; like a Sirocco for you Italians, etc.)
2. errrrr - check your math, Richard. Have you already been "celebrating"?

- Randy
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  #85  
Old 01-12-2004, 11:12 PM
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Darned conversion software.

-2C = 28.4F

Even warmer!

-R
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  #86  
Old 01-13-2004, 02:18 AM
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Apologies in advance for the long post, but I think this should prove interesting...

Current charging (SP batch):

It's just after midnight, January 13, 2004 and I *KNOW* what destroyed my last furnace.

I charged my rebuilt furnace at 2150 all day today. By 7:30 pm, I had a nice flat layer of melted glass sitting between 1 1/2 and 1 1/4 inches from the top of the crucible.

At 7:30 I started the cooking process by raising the temperature to 2250F. My plan was/is to cook the glass overnight, followed by a squeeze to 1900 tomorrow morning.

Being cautious (because of the past disaster), I decided to check the glass every hour or so. This is because the furnace will take 1 hour to rise from 2150 to 2250, but the "glass mass" will take longer to reach the new temperature.

At 9:30, I did my first check. The glass was now definitely higher in the crucible - about 3/4 inch below the top.

I checked again at 10pm. The glass was now 1/2 inch from the top.

Why? Thermal expansion. Checking with a punty, the layer of bubbles was not all that thick (and didn't increase in size between 9:30 and 10pm), but the glass had expanded due to the increased temperature.

Using the punty, I gathered some of the bubbles until the level was again 1" below top.

Between 10pm and now (midnight), I've checked every 15-30 minutes, and gathered bubbles three times more. Once (10:45) the glass was 1/4 inch from the top. Again, the thickness of bubbles was NOT the reason (I checked with the punty) - glass expansion was the cause.

The temperature now appears to be at equilibrium in the glass mass - recovery time after a gather has decreased from 5 minutes to about 30 seconds, and the temperature drop has lessened (at 9:30 a gather dropped the temp to 2239, at midnight a gather dropped the temp to only 2248). The level appears stable at 1 inch below the top of the crucible.

I'll check again in an hour, but it looks like I can let it cook overnight now.

SO what killed the first furnace?

SO - what destroyed the first furnace build? Same thing - thermal expansion. That time, I filled the crucible to the brim with cullet, let it melt, and filled it again. When I observed the "stiff foam" (my words from back then), it was about 1/2" to 3/4" below the lip of the crucible. SInce the cullet didn't seem to be very melted, I bumped the temp from 2200F (melting temp) to 2400 F, starting at noon. At 2pm, all was fine. At 5pm, the glass had overflowed. I know know that the expansion would easily have caused the glass to rise more than the 3/4 inch that I had, and so the glass simply had to overflow.

WHY? This is a straight-walled crucible, not a round crucible. Round bottom crucibles increase in diameter as you move up in height, so the expanding glass has "somewhere to go" (the extra diameter). In a cylindrical crucible, the glass can only rise.

In the final analysis, it wasn't a faulty thermocouple, or bad cullet, or foam or crap falling into the crucible - just plain old thermodynamics.

Anyway, this is what I have, and what I've found. I'll live with this crucible and furnace for the next little while, as that's what I have (and it's hot). Later, I might put a round pot into it.

So - if the furnace survives the night, I should have some nice glass by Wednesday morning!

-Richard

Last edited by Richard Huntrods; 01-13-2004 at 02:20 AM.
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  #87  
Old 01-13-2004, 08:33 AM
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I think it's worth noting that we normally talk about a glass having a linear expansion of 90 or 96. What never gets thought about is that this is in ten thousandths and is only measured up to 300C. The fact is that the expansion keeps on going when you pass 300C as Richard has observed. It actually really adds up. I find a pot that is brimfull at 2350 will shrink about 3/4 of an inch being brought back to 2050F.
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  #88  
Old 01-13-2004, 11:26 AM
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Quote:
Originally posted by Pete VanderLaan
I think it's worth noting that we normally talk about a glass having a linear expansion of 90 or 96. What never gets thought about is that this is in ten thousandths and is only measured up to 300C. The fact is that the expansion keeps on going when you pass 300C as Richard has observed. It actually really adds up. I find a pot that is brimfull at 2350 will shrink about 3/4 of an inch being brought back to 2050F.
Absolutley!

Also, some of the expansion is also due to the entrained air bubbles (seeds) in the melt expanding as you heat the glass from 2150 to 2250. I monitored the furnace during the night, and by 8:30 am the glass level had dropped 1/4 inch - and the bubbles were fewer and larger.

Pete - how do you tell when the glass is "cooked" and ready to squeeze?

When I started cooking, there was a stiff froth of bubbles about 1/4 to 1/2 inch thick on the surface. When I say froth I mean the bubbles were less than 1/8 inch in size, and plentiful.

It took 5 hours in my furnace for the entire glass mass to heat from 2150 to 2250, so it cooked at 2250 from 1am to now (currently 9:30). At 8:30 the bubbles were fewer, a thinner layer (less than 1/4 inch) and larger (most between 1/8 inch and 1/4 inch).

I can happily cook till noon, supper, evening or midnight (or longer)- but there's no point cooking longer than necessary, IMO.

What are the key indicators that glass is ready for the squeeze?

-Richard
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  #89  
Old 01-13-2004, 04:50 PM
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I think I may have an answer to my own question. I cooked the spruce pine batch for 12 hours at 2250 last night (not including 5 hours to get the temperature at 2250 throughout the pot).

At noon today the glass was relatively clear on top (no significant bubbles), so II gathered a sample. It was full of bubbles (as expected), but they were uniformly distributed throughout the sample, and all were "pinhead" sized.

So - I started the squeeze. (it will be at 1920F).

Looks like this process worked almost perfectly!

The 40lb crucible took almost a full bag of Spruce Pine batch (50lbs), but since it's about 20% water, this is right. I could have put it all in the crucible - but then I'd have been scooping glass out last night. As it is, I had about 1/4 of a large peanut butter container left over. Next time I think I'll reserve a whole peanut butter container aside to prevent the expansion from getting near the lip.

One other thing abou SP batch - I added batch at room temp (-2 C or 28F) to the crucible which was at 2150F. There was an initial "foosh" as the batch hit the crucible (or melted glass), but no popping or any other unpleasant side effects. A VERY NICE batch to work with!

Now - tomorrow night - the big test. The first official "blow down" of the Tin Shack Studios!

I took some pictures of the first two gathers (at 2250, before the squeeze) to show how it looked. Again, on my web site.

-Richard
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  #90  
Old 01-13-2004, 04:51 PM
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The bubbles grow larger and are spaced further apart and there is good clarity between the bubbles. You described it perfectly.
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  #91  
Old 01-13-2004, 05:12 PM
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Thanks Pete. I do appreciate the encouragement.

Boy it sure feels good to have success!

This process was exceedingly rewarding. I can see why making your own batch is the next logical step!

-Richard
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  #92  
Old 01-15-2004, 05:05 PM
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The glass finished cooking and squeezing, so last night I had the first ever Tin Shack Invitational Blowdown...

Allan Gott, Randy Kaltenbach and I spent from about 7:30 to midnight blowing beer mugs and other vessles with the first glass from my furnace. If you're interested, pictures and blab are on the website...

http://www.huntrods.com/ under the glassblowing link.

As for the glass, it is *perfect*. Crystal clear, no bubbles, cords, seeds, etc. Came out of the annealer looking fantastic!

In keeping with the topic of this thread, my next post will be a detailed description of my process for making Spruce Pine batch in my wire furnace.

-Richard
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  #93  
Old 01-15-2004, 05:17 PM
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WARNING! LONG POST!

Also - I'm no expert (having only done one batch to date, but I figured "this is really fresh in my mind", so ...

Here are my batch cooking instructions for Spruce Pine (87) Batch using my 40lb wire furnace:

NOTE: since this was the first batch run since the rebuild, the crucible started totally empty at about 27F. Subsequent charges will start with a non-empty crucible at 1919F (my "squeeze and hold" temperature) A non-empty crucible will have anywhere from 1" of glass to 1/2 full depending on what I need and when.

1. The crucible is heated to 2150F. This was done using the ramp function (to preserve elements) of 100F/hour.

2. Once the crucible has equilibrated at 2150F (say 2-3 hours), batch charging begins.

Batch is added such that about 1/4 of the crucible volume is added at one time.

Temperature should initially drop almost 20F after an addition, but as the crucible fills this will change to a drop of maybe 2 degrees F (as the glass mass increases and equilibrates at 2150).

Temperature recovery times will also decrease as the crucible fills, from maybe 10 minutes to under 30 seconds.

Once a charge of batch has been added, the furnace is left for between 2 to 2 1/2 hours to allow the batch to melt flat. Under no circumstances should batch be added until the previous charge is melted totally flat. It should look like slightly foamy glass - it should NOT look like raw batch at all.

The crucible should be filled NOT FULL. I found for a cylindrical crucible that 1 1/2 inches below the rim is more than enough. Any higher and the cooking process (heat) will cause the glass to expand and overflow. This is, of course, very crucible dependant. Larger crucibles with non-vertical sides have much more leeway than the small vertical pots.

3. Crucible is filled and the glass is flat - time to cook. I heated the glass from 2150 F (charging temp) to 2250F, again using my 100F/hour ramp function on the controller (Watlow).

In my furnace, it takes about 4 to 4 1/2 hours for the entire 40lb pot of glass to fully equilibrate at the new temperature. This can be checked by peeking at the glass. If the temperature drops more that 2-3 degrees F and/or takes more than about 30 seconds to recover, you are not at equilibrium.

Once at equilibrium, I let the glass cook at 2250 for an additional 12 hours. After 10 hours, you can check the glass to see if it's "done". I use two tests to determine the "done-ness" of my glass. First, a visual inspection should show a very even glass mass, consisting of very fine bubbles (pinhead sized). Second, I take a gather of this glass - the glass should be easy to gather, and the gather should have an even distribution of many pinhead sized bubbles. Other than the bubbles, the glass should appear "clear".

NOTE: I cannot stress enough the value of SSR's and a good controller with a ramp function. Although you don't "blast" the temperature up as fast, you preserve the elements because you are always raising the temperature by small increments, allowing the controller and SSR to give small "bursts" of power to the elements instead of one large-amperage blast. This helps preserve the elements.

4. WHen the glass is done, I squeeze it by quickly cooling the furnace (ramp turned off) to 1919F and leaving it overnight (at least 12 hours). Resist the urge to peek at the glass once the temperature drops below 2200F, as this will chill the surface of the glass. Just leave it.

5. Once the glass has been at 1919F for 12 hours, you can bring it up to working temperature, or let it sit until you need it. For me, working temperature is 2070F. At that temp, the glass was easy to gather, but not "watery". This is somewhat of a personal choice - you want the glass at a temperature that produces nice gathers, but still hot enough that any trails quickly melt away from the punty (as you rotate it on the pipe stand near the crucible).

6. After your blowing session is complete, you can either heat the crucible to 2150F to start charging again, or cool it to 1919F to hold it for another day (depending on the amount left and what you need).

FINAL NOTES: If you are going to shut off the furnace, then you must gather as much glass out of the crucible as possible. I've found with the cylindrical crucibles you can get all but about 1/8 inch out of the pot with a small amount of care. This will cool and reheat without problems (again, I use the ramp at 100F/hr for shutdown and startup). When starting from room temp, I also stop the heating at 900F, 1000F and 1100F for 2 hours each temperature to ease through the quartz inversion.

I've also heard of people "idling" the furnace at 1600F without problems. For now, I'm going to stick with 1919F.

Cheers,

-Richard
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  #94  
Old 01-15-2004, 05:47 PM
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Quote:
Originally posted by Richard Huntrods
The glass finished cooking and squeezing, so last night I had the first ever Tin Shack Invitational Blowdown...

Allan Gott, Randy Kaltenbach and I spent from about 7:30 to midnight blowing beer mugs and other vessles with the first glass from my furnace.
For some reason, beer mugs just seemed so appropriate!

- Randy
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  #95  
Old 01-15-2004, 09:50 PM
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Richard, Congrats on your success. Looks like you boys had a real fun evening. Good company,good beer and good glass. I can't wait.
Jay.
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  #96  
Old 01-15-2004, 10:13 PM
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Quote:
Originally posted by Jay Holden
Richard, Congrats on your success. Looks like you boys had a real fun evening. Good company,good beer and good glass. I can't wait.
Jay.
Anytime you're in Calgary, Jay!

-Richard
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  #97  
Old 01-16-2004, 08:37 AM
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Do not idle your furnace at 1600 for any short periods. It's OK if you are just parking it for ten days, but it will cause devitrification. 1900F is fine.
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  #98  
Old 01-16-2004, 09:48 AM
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Quote:
Originally posted by Pete VanderLaan
[B... but it will cause devitrification...[/b]
Pardon my ignorance. devitrification?
- loss of glass
or
- loss of clarity?

Thanks
- Randy
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  #99  
Old 01-16-2004, 10:28 AM
Steve Stadelman Steve Stadelman is offline
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Devitrification is when the glassy matrix starts to come undone. Scummy stuff will start to form on the surface of the glass.
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  #100  
Old 01-16-2004, 03:12 PM
David Williams
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I have a degree in...science!

Literally, becoming not glass by crystal formation. If glass by definition has an amorphous structure, it can no longer be glass if it acquires a crystalline structure. So it de-vitrifies. Becomes not glass.
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