Hi Stuart,
I have a Lil Bertha furnace. and it will melt copper. It is a question of how much heat you put in compared to the surface area of the furnace and the quality of the insulation. I have two elements in parallel. Total about 3KW. The power and temperature from each element can be increased by shortening the length of the element. However it will have a shorter life. Other way is to add an extra element. In 2003 I put two tables in the group files titled wire resistance and wire temperature. From this you can design the length of wire in the element. I used 27 ft of 23 swg nichrome wire running at 240 V. It was close wound in the lathe on a 3/16" mandrel. then stretched to fit the inside diameter of the furnace. Each element went twice around the furnace. My controller is an old oven "Simerstat" i.e. it varies the time on to time off. Most controllers operate this way. So the elements take full voltage for a percentage of the time. I have had to replace two elements in 10 years. Hope this helps.
Colin
----- Original Message -----
From: confed2001
To: gingery_machines@yahoogroups.com
Sent: Monday, September 12, 2011 12:03 PM
Subject: [gingery_machines] Re: Electric furnace parts update
Stuart,
Thanks for the input I'll give that a try this weekend. When I first made this foundry I never tried to melt anything but aluminum. Over time I have had to make repairs to it, such as the lid, & it is possible I am losing a lot of heat from there. I have thought of hooking the heating element directly to the power source (220V with a 40 amp breaker), but I was not sure if the element could take direct power without some type of controller. Anyway, I'll check it out thanks.
Brian
--- In gingery_machines@yahoogroups.com, lists <Stuartlists@...> wrote:
>
> In article <j4js0t+p6p8@...>,
> confed2001 <confed2001@...> wrote:
> > It works & I have been using it for several years, but despite what the
> > plans say it does not get hot enough to melt copper much less brass. I
> > constructed the controller as described in the plans, and am using the
> > heating elements stated, but aluminum is the best I can get out of it.
> > If this controller will raise the temp of a small electric foundry than
> > I need to get one.
>
> I've not seen these particular plans but there are only two things that
> govern the achievable temperature of a furnace. 1) energy input 2) energy
> loss. The first is controlled by the resistance of the elements and the
> available voltage, the second by how well you insulate your furnace. For
> maximum energy input your controller must place no restriction on the
> current supplied.
>
> A simple way of testing the maximum achievable temperature is to bypass
> your controller and feed full supply voltage to your elements. This will
> tell you whether you need to look at improving 1, and 2 and whether there
> is a possible fault with your controller
>
> If you can get to the temperature you want with the controller bypassed,
> you have a faulty controller, if not you need to look at points 1 and 2
>
> --
> Stuart Winsor
>
[Non-text portions of this message have been removed]
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