CraftWEB Hot Glass Talk  

Go Back   CraftWEB Hot Glass Talk > Hot Glass > General Hot Glass Discussion

Reply
 
Thread Tools Display Modes
  #1  
Old 03-01-2018, 12:58 PM
Jack Abner Jack Abner is offline
Registered User
 
Join Date: Feb 2018
Location: Ohio
Posts: 7
Jack Abner is on a distinguished road
Preheating Furnace To Reduce Thermal Shock

In our new gas fired free standing pot furnace we have incorporated a removable electric element for overnight preheating. Reducing thermal shock to the refractories and crucible by preheating the furnace to 600 degrees Fahrenheit and also reducing start-up times. The furnace has been operating four months and cycled to temperature 16 times (weekend warriors) with no apparent damage to refractories or crucible. We typically charge 50 pounds of cullet in the 100 pound pot reaching temperature (2060) in 3.5 hours. We slowly bring the temperature from 600 to 1200 over 1.5 hours then from 1200 to 2060 over 2 hours.
Any thoughts or experience with preheating would be appreciated...
Reply With Quote
  #2  
Old 03-01-2018, 01:28 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,505
Pete VanderLaan is on a distinguished road
going from 600 to 1200 in 1.5 hours is really really fast. I'm inclined to congratulate you on being quite lucky
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #3  
Old 03-01-2018, 01:47 PM
David Patchen's Avatar
David Patchen David Patchen is offline
Registered User
 
Join Date: Sep 2005
Location: San Francisco, CA
Posts: 1,861
David Patchen is on a distinguished road
Quote:
Originally Posted by Jack Abner View Post
We slowly bring the temperature from 600 to 1200 over 1.5 hours then from 1200 to 2060 over 2 hours.
Any thoughts or experience with preheating would be appreciated...
Best quote ever!
Reply With Quote
  #4  
Old 03-01-2018, 02:13 PM
Mark Rosenbaum's Avatar
Mark Rosenbaum Mark Rosenbaum is offline
Registered User
 
Join Date: Apr 2002
Location: New Orleans, LA
Posts: 977
Mark Rosenbaum is on a distinguished road
Search "quartz inversion" on this site.... you will have an eye-opener....
Reply With Quote
  #5  
Old 03-01-2018, 02:54 PM
Ed Pennebaker's Avatar
Ed Pennebaker Ed Pennebaker is offline
Registered User
 
Join Date: Apr 2002
Location: Red Fern Glass near Green Forest, AR
Posts: 192
Ed Pennebaker is on a distinguished road
I have used outdoor halogen lightbulbs in the furnace for preheating. Up to 400-500 degrees F over several days. 140 lb. Natural gas fired furnace, venturi burner, freestanding crucible. After that preheat I take another three days to heat up to 2250 before I start a melt.
Reply With Quote
  #6  
Old 03-01-2018, 03:18 PM
James Ennis James Ennis is offline
Registered User
 
Join Date: Oct 2004
Location: seattle
Posts: 328
James Ennis is on a distinguished road
we have used space heaters, bbq lighters(electric) and light bulbs.....but your
ramp up to temp is way too fast. you will have an EPIC fail, a free standing
pot wont take this.
Reply With Quote
  #7  
Old 03-01-2018, 04:11 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,505
Pete VanderLaan is on a distinguished road
moisture is totally separate from thermal shock but does need attention. When water is chemically bound which is the case in most castables, it needs to be driven off under 212F so it doesn't turn to steam since steam is water expanded by about 200 fold. That expansion will crack any casting, so, a new furnace needs to be candled at under 212/ Kenny Pieper used to suggest holding a mirror up in the door port and if it fogs, there's still moisture.

The pot doesn't have any moisture, it has been fired to 2380F. It is still totally susceptible to cracking from expanding too fast. Do what Mark suggested about looking in the archives for quartz inversion. It can be deadly between 980 and 1100F when the silicon atom flips. I bring pots up at 50F per hour with a major slowdown at 980-1100F. It's all in the archives and it's just as important for your furnace as it is for your pot. While I recognize your eagerness to be up and running, you are asking for disaster. The fact that the pot has not failed at this point is surprising to me. It could at any time. Pots don't respond well to being shut off even once. They put up with it, no more. but it does shorten its life.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #8  
Old 03-01-2018, 03:02 PM
Jack Abner Jack Abner is offline
Registered User
 
Join Date: Feb 2018
Location: Ohio
Posts: 7
Jack Abner is on a distinguished road
Thanks Pete 😉 I love this 16 pot it has the perfect dimensions for my needs... I decided on the preheating based on some reading on the effects of moisture on thermal shock... Im amazed at how much moisture is driven out of the furnace during the preheating process.
Reply With Quote
  #9  
Old 03-07-2018, 04:48 PM
Josh Bernbaum Josh Bernbaum is offline
Registered User
 
Join Date: Feb 2009
Location: Brattleboro, VT
Posts: 577
Josh Bernbaum is on a distinguished road
Quote:
Originally Posted by Jack Abner View Post
In our new gas fired free standing pot furnace we have incorporated a removable electric element for overnight preheating. Reducing thermal shock to the refractories and crucible by preheating the furnace to 600 degrees Fahrenheit and also reducing start-up times. The furnace has been operating four months and cycled to temperature 16 times (weekend warriors) with no apparent damage to refractories or crucible. We typically charge 50 pounds of cullet in the 100 pound pot reaching temperature (2060) in 3.5 hours. We slowly bring the temperature from 600 to 1200 over 1.5 hours then from 1200 to 2060 over 2 hours.
Any thoughts or experience with preheating would be appreciated...
I'd be curious about a comparison between your current fuel consumption with this gas furnace going up from room temp once a week it sounds like, versus what your fuel consumption would be if you just let the thing idle midweek at a lower temp (something above quartz inversion). Perhaps your furnace is made with just lightweight materials like lots of fiber frax but typically it takes more energy to heat up harder materials (which have more longevity) from room temp than it takes to have the furnace material's thermal mass do some of the work in maintaining a set-point at higher temperature. I'm really surprised your 16"er hasn't cracked yet, that's got to be luck more than physics from what little I know about these pots that we use.
__________________
www.jmbglass.com
instagram.com/joshbernbaum_glass
Reply With Quote
  #10  
Old 03-07-2018, 04:51 PM
Eben Horton Eben Horton is offline
Registered User
 
Join Date: Apr 2002
Location: Wakefield, RI
Posts: 4,378
Eben Horton is on a distinguished road
MR T says... Say no to crack. Take it slow sucka
__________________
<eben epoiese>
Reply With Quote
  #11  
Old 03-07-2018, 05:28 PM
Mark Rosenbaum's Avatar
Mark Rosenbaum Mark Rosenbaum is offline
Registered User
 
Join Date: Apr 2002
Location: New Orleans, LA
Posts: 977
Mark Rosenbaum is on a distinguished road
You have asked a question, and you have been answered by people who have decades of practical experience in studio situations. There are pages of discussion on heating up crucibles from room temperature, for the first time, and then subsequent times. You can take the suggestions offered here as you may, but in my opinion, this group is the best source of knowledge that you will ever find. Keep us updated on your journey. Good luck....
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 05:34 AM.


All published comments within these message boards are the opinions of its contributor and does not represent
the opinion(s) of the owner(s) of this website. Please see the Terms of Use file for more details.

Books to Help Artists Avoid Online Scams: Top 10 Email Scams | Social Media Scams

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
CraftWEB.com. Opportunity Network. 2008. All Rights Reserved.