CraftWEB Hot Glass Talk  

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

Reply
 
Thread Tools Display Modes
  #1  
Old 08-30-2020, 08:11 PM
Peter Bowles Peter Bowles is offline
Registered User
 
Join Date: Sep 2002
Location: Breadalbane, Tasmania
Posts: 639
Peter Bowles is on a distinguished road
Gas Furnace to Moly Conversion

Hi All

I'm trying to scope out the practicality and feasibility of converting my existing gas furnace to a moly. I'm moving studio and the move is giving me the impetus to make these changes for the next venture.

I'm doing as much of the background reading around moly and control systems here and a couple of other places and everything gets pretty murky pretty quickly in my limited electrical knowledge.

What I do know is that I can't afford to get the sizing of the control system wrong, everything in Tasmania comes in from afar with additional cost and often delay so I'm going to need some expert input and I'm not quite ready to have a conversation with Cheyenne till I'm not so in the dark and don't look such an idiot.

What I do know:

I've got an internal chamber of 19.5 of your cubic feet, which once the crown is modified will come to 16.3 cubic feet. The furnace takes a 24 inch diameter pot of approx 300lb. There is an additional space at the back of the furnace where I was once going to put a couple of small colour pots, I could modify the build and get the volume down to around 13.5 Cubic feet if needed.

At a recommended 2000 - 2200 watts per cubic feet that comes out to 32 - 35.8 kw which seems high for a 300lb furnace which I've seen as needing 22-24kw.

I've got 3 phase distribution board with a 63A mains breaker and Australian voltage is 240v single phase 400v 3 phase.

The furnace is lined with 2 inch dense refractory castables and backed up with 4-6 inches of insulation castables / fibre. It's probably a little heavy in thermal mass and a bit light on insulation in comparison to other furnaces out there.

I'll be melting batch once a week to once a fortnight.

First off, I'm having trouble making any sense of how many KW I've got available - there seems to be so much conflicting information regarding 3 phase and how much power it can actually deliver, so maybe that's where I need to start.

I'll be running a small kiln as a hot box - single phase (240v 3.6kw) and an annealer rated at 3 phase 3x240v, 3 x 3.6kw. Plus lights etc.

An upgrade to a 100A supply is possible, anything over 100A gets very expensive here and probably prohibitive - especially in these times.

Any thoughts please? I just need to know at this point how this is looking.

Thanks

Peter
Reply With Quote
  #2  
Old 08-31-2020, 07:41 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 22,199
Pete VanderLaan is on a distinguished road
the refractory brick interior is not dissimilar to the castings Steve had in his. What is critical is no unnecessary dead air space. That means no combustion chamber essentially. Having the extra AMPS (2200) means it will respond better when you are preparing to turn it up to charge. The chamber height is really going to be determined by the length of the elements. Mine was larger and accommodated a 28 inch pot if I wanted and it ran on 22KW. It did have a 120 AMP breaker. It was also sluggish and I turned it up the night before to get a head start. I only used my own fine powder batch.

I don't know how anyone can do this with a 100 AMP Service. Scott Benefield has the same problem in Northern Ireland and he doesn't have a moly. Something about former colonies getting what they deserve.

When I ran mine with the color pots, I did have three 75lb pots in there. I never ran it the way it was intended. The KW usage you cite seems ridiculously high. I can't recall any of the big moly's using more than 22.5 unless you're talking the 34 inch units. That's a big pot.

I had a 30KVA Transformer with six 9/18 312/500 elements.

I went back to gas and vastly prefer it.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #3  
Old 08-31-2020, 08:53 AM
Antti Torstensson Antti Torstensson is offline
Registered User
 
Join Date: Jan 2013
Location: Finland
Posts: 33
Antti Torstensson is on a distinguished road
400 V and 24 kW in a three-phase circuit draws only 20 A per phase. So I think it can be done easily with a 100 A main fuse. As that's 100 A for each phase.

Your hotbox and annealer together draw 30 A.
Reply With Quote
  #4  
Old 08-31-2020, 09:33 AM
Josh Bernbaum Josh Bernbaum is offline
Registered User
 
Join Date: Feb 2009
Location: Brattleboro, VT
Posts: 719
Josh Bernbaum is on a distinguished road
I don't know enough about 3 phase, but I can maybe add to the discussion at least a little bit based on my single phase setup. I have a moly with a 22" pot/200# rating, 15kW transformer, and it's hooked to an 80A circuit breaker. I have a 400A single phase service/main breaker, but I know that's a bit overkill although I do also run an air compressor motor, an O2 generator, my welder, other ovens, etc. My guess is that I'd have some issues if I had anything less than 200A service to the building.
__________________
www.jmbglass.com
instagram.com/joshbernbaum_glass
Reply With Quote
  #5  
Old 08-31-2020, 11:12 AM
Shawn Everette Shawn Everette is offline
Registered User
 
Join Date: Mar 2013
Location: Indianapolis, IN
Posts: 696
Shawn Everette is on a distinguished road
Always get as many amps as you can. Always. 10 amps is not much in the way of overhead, and wouldn't follow the 80% rule. The small things can add up quick, and a motor with a high start pull, think ac, is a surefire way to trip the main when everything's humming.

I'm curious why your 3 phase annealer is running on a different voltage than the furnace?
Reply With Quote
  #6  
Old 08-31-2020, 02:42 PM
Antti Torstensson Antti Torstensson is offline
Registered User
 
Join Date: Jan 2013
Location: Finland
Posts: 33
Antti Torstensson is on a distinguished road
Quote:
Originally Posted by Shawn Everette View Post
I'm curious why your 3 phase annealer is running on a different voltage than the furnace?
It's just a matter of connecting the neutral wire or not. If you were to wire the annealer for line voltage (400 V) it would require almost three times the amount of heating wire compared to wiring it for phase voltage (240 V). In this case it would only save you few amps.
Reply With Quote
  #7  
Old 09-01-2020, 08:48 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 22,199
Pete VanderLaan is on a distinguished road
Quote:
Originally Posted by Shawn Everette View Post
Always get as many amps as you can. Always.
*****
I would have agreed with this most of my life but then came the sale of NH public service to Eversource and the deal that followed from the utilities commission.

I have a 400 AMP Service, more than I would ever need but we did have the moly and a lot of big grinders- never enough to dent our potential. However, Eversource bills us at a far higher rate because we have the potential to use 400 AMPS. It's not on the electricity side, it's the delivery side of the bill and delivery is always higher than the power cost. It's Pure BS no lines have been changed or upgraded. I have never been able to get the monthly bill below $200 bucks with no draw. If it actually gets run, with no moly mind you, the usage delivery cost goes up to as high as $400. with the power- $600.00

We're considering one of two scenarios. First, rewire the house and run a line out to the shop and to then disconnect the shop entirely, or to fire up the 30KVA generator and to run the shop off of it. It's propane powered.
__________________
Where are we going and why am I in this basket?
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 03:37 PM.


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 - 2020, Jelsoft Enterprises Ltd.
CraftWEB.com. Opportunity Network. 2008. All Rights Reserved.