Recommendation? KILN PID

NickHFSS said:
Hello everyone , I’ve been forging and heat treating in coals since day one and I want to up my game and get a kiln , I am buying it from a local but he said that the chinease pid that it has can have 20-30degree C off from what it shows (...)
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Good thermocouple wire (more expensive) will have 5C of *initial* accuracy. A good controller will add 2C of error on linearity, plus 1C in the cold junction compensation.
Over that, you need to consider gradients both espacial in different parts of the oven, and temporal (with the different parts of the system having different time constants).

But then TC ages, with naked thermocouples aging the fastest, and depending a lot on the atmosphere during firing.

It's best to have multiple devices to cross check. Still, even with good repeatability you should not trust your absolute values too much.
 
I think I’ll go with the old Soviet spiral , as for cover for thermocouple do I need it ?
 
NickHFSS said:
so do I need the sheath?
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NickHFSS said:
as for cover for thermocouple do I need it ?
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Sorry for the delay, didn't see the question earlier.
I'm not sure I have the answer, I'd ask the manufacturer or seller of the TC you are going to use and what temps you are planning on running. If you're going to use this solely for a tempering oven, where your temps won't exceed 200C, then you're probably OK without one. But if you're going to be using it for normalizing, thermal cycling and quenching, even if you're staying under the max temp rating, as others have stated above, it'll last longer with the ceramic sheath.

NickHFSS said:
the ssr needs cooling
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Yes, especially if your system will be continuously or regularly running near 80% amperage capacity of the SSR (IIRC). But this can be accomplished a number of ways. One way (which is what I did on my system), is to use a metal box to house everything and have the box act as a heat sink by attaching the SSR directly to the metal wall of the enclosure. If this isn't an option, due to space or if you are using wood or plastic for your case, then a dedicated heat sink will be needed.
 
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A TC sheath is not needed in a normal electric HT oven. It can slow the response time for the PID controller down.

In a forge, a TC sheath is a must or the hot gasses will corrode the TC quickly leading to failure.

The reason you use 40 amp SSRs is that they are more robust than the 20 amp units and generally cost the same or less.
Just being capable of handling much more current than needed doesn't meant the will run cooler. Despite what the paperwork says, they will not last as long in a HT oven without some sort of heat sink. Even a 6"X6" piece of 1/4" aluminum plate will help as a heat sink.
It is best to use some Heat Sink Compound (white greasy stuff) when mounting the SSR to the heat sink.
I like to use a small fan (computer type pancake fan) to gently blow air across the SSR and heat sink.
 
On the SSR and heat sinks. Just by way of example, my son was building a robot which used an SSR. It was operating well within its current bounds, and yet consistently failed (burned out) within a few minutes. He put a heat sink on it with a small computer fan blowing across it, and the thing would run for hours.

using a heat sink is a good idea and cheap insurance
 
weo said:
IIRC Auberins has a silicone pad that goes with their SSRs you can add for $1 that's supposed to do the same thing
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Yes I got that as well , Received everything , looks good.


Another question I have is where should I get good insulating blanket?
 
I don't really know... I've never made a kiln.

I think I'd probably make a frame out of angle iron, a thinner piece of hard firebrick for the outside surface and then koawool/inswool for the inside surface maybe coated with satanite, and a headed fiber "washer" around the edge.

But like I said, I've never made one. I'm sure the guys who have will have better advice than I can give!!
 
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