Idling a moly furnace

[John Riepma]

We are coming up to about a 1-1/2 - 2 week period when we will not be able to work in the studio. The furnace is a Moly-D Stadelman design/ripoff with an EC crucible, and we use SP87. We've got it all mopped out, but wondered if it makes sense to turn it all the way off or could we safely idle it down at 1300F or some other temp that will be kind to the crucible and at the same time use less energy? It seems to me that it will be cheaper to turn it down for that time period than to turn it off and then back on. Does anyone have any experience with this, and does it make sense? And am I needlessly torturing the crucible? My main concern is the crucible, and if that's not a problem I'm just about curious enough to just do it and watch the electric consumption and post results here.

[Steve Stadelman]

1400-1500, just to be sure, scoop most of the glass.

[John Riepma]

Thanks for the reply Steve. We'll try it and I'll post the difference in consumption here as nearly as we can calculate it for others who may want to try the same thing.

[Richard Huntrods]

Steve,

I'm curious. Why not 1300? 1300 is above the trouble point for a crucible, and low enough so any glass residue is pretty much inert.

I'm asking because I have been turning my wire melter down to 1300 when I'm not blowing for a length of time, and it seems OK.

I was idling at 1850, but glass is too reactive at that temp, and any remaining can still eat into the crucible.

Thanks,

-Richard

[Steve Stadelman]

I was just thinking about the power going out for a little while when John is gone, at a low temp like that it would take many hours for the furnace to drop very far and get down to be a concern.

[Eben Horton]

Id turn it off. electric furnaces are so easy to control, why not?

As a rule for me, if I am not going to use it for more than 10 days i shut her down and she's gas.

I really enjoy getting back from a trip and knowing that I dont have to blow glass right away- having to turn it on and charge gives me a few days to get back ino my rutines and I also can sleep at night when i am away knowing that I wont read about a gas explosion at my studio.

[Pete VanderLaan]

It draws close to nothing at 1300F and you remove the risk of the thermal expansion that occurs at quartz inversion. If I don't have to turn one off, I don't. 1300F was my temp of choice. You just set the controller and walk out the door.

[Scott Novota]

Is that a universal statement or pinned to Moly. If you set a wire or SiC at that could you expect that same level of power usage?


Scott.
.

[John Riepma]

Thanks for your replies, everyone. The only reason I mentioned that it was a moly, as well as the design, was that I wanted the responders to know what the castings and insulation were like in case of a power failure. That was one of my biggest concerns when we started up, since we are in an area where power outages are fairly common. My mind was put at ease the first time we shut down when we watched closely as the temp dropped when turned down. It seemed to drop like a rock through 1700F, then slowed down considerably. When it was at 1300F it dropped at less than 25 degrees an hour, so I just figured we were safe and shut the power off. It dropped even more slowly after that. This was all with a very empty crucible, so much less mass for a thermal flywheel effect.
I thought that we can't be the only ones that want to take a break from time to time, and this one is only going to be about 10 days. It seemed a wasted to keep it at temp or to shut all the way down, so we'll try this and get some numbers to compare a week at 1300 to a week at 2050, and also add in the kW usage to come up from dead cold which we have from previous startups. This should help us to calculate the break-even point between idling vs shutdown in terms of days. Unless someone else already knows all this and is willing to post it. (or has, and I'm too lazy/incompetant to search for it)

[Randy Kaltenbach]

Originally posted by John Riepma
thermal flywheel effect. Wait a minute, isn't that a trademark or sumptin'? :confused: :D

[Charles Friedman]

Originally posted by Scott Novota
Is that a universal statement or pinned to Moly. If you set a wire or SiC at that could you expect that same level of power usage?


Scott.
.

Thats' a good question Scott. I'm also wondering?
If there is much, of any, aging deference between Moly and SiC, The heaters them selves, at hold, at that temp. 1300?

But heating back up, from cold, does a lot of ware and tare to them, cuts down on their life. That will have to be factored into the future cost, as well.

I have been bitting the bullet and turn down to 1850 and having a good house and shop setter, works good for me.

Much longer than that, off.


I have not seen much of the pot getting eaten, at 1800.

Nor have I seen much of a glass problem , but I do stay away from any iffy colors for the fist charge.



I figure that the extra 500 degrees will add to the hold temp. time thing, if there is power outage, a little extra time insurance, couldn't hurt for the setter.

[Pete VanderLaan]

I can only speak for moly's.