Be careful how you go to full power. I did that when I first made my modified Hartman furnace and promptly developed a hot spot on the element. In no time it had burned through. I think it would be best to put something in the furnace to prevent too sudden a temperature rise. I would also raise the temperature slowly in, say, 60 minutes.
On my furnace, the largest heat loss seems to be through gaps. I fixed the one between the top of the body and the lid by casting it in place. The bottom of the lid is now a match to the top of the body. I do have an access hole where I put through my thermocouple and look at the melt. It has got to be the leading heat loss location now. Yet it is not so bad that I would want to close it off. Most of my delay in reaching full heat is with the first melt of the day. I have to bring the "hot face" up to temperature. After that the cycle time is cut in half.
I have only melted aluminum in mine and the max power setting is 80%.
Rick
Rick.Sparber.org
On Sep 12, 2011, at 1:48 AM, lists <Stuartlists@orpheusinternet.co.uk> wrote:
> In article <j4js0t+p6p8@eGroups.com>,
> confed2001 <confed2001@yahoo.com> 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
>
>
>
>
>
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>
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