Hardening oven saga

[Ferrous Turner]

I gave it a test run last night. Initially it worked well, but then started struggling to maintain the increase in internal temperature at a reasonable pace. It was losing too much heat through lack of sufficient insulation. The exterior was hotter than I expected at that point in time.
I ordered some 2" ceramic fiber exterior insulation to cover the thing. I'll have to remove the control box and have it as a stand alone unit.
I'm also getting a small fan to cool the SSR heat sink. It got hot quick.
I'm getting an education in thermodynamics.

 

[Groundhog]

. . . I'm getting an education in thermodynamics.

Thanks to you I am too! When you get it all figured out I'm going to follow your experience and build one for myself.

 

[Ferrous Turner]

I grossly underestimated the thermal conductivity of the masonry. As well as the outside, I'm also going to line the inside of the oven with fiber board to further slow the egress of the heat.
The SSR is another issue. That thing eats a lot of power. For my purposes I think a simple mechanical relay would suffice, especially during warm up which can take an hour or so. An SSR is good if you have a lot of rapid switching of the power to the element i.e. during a long ramp up where the element is heating faster than you want it to. My oven heats slowly, so I could use a plain switch to power the element until it gets up to temperature.
Once I get it all re-insulated we'll have to see how fast it heats up. I still think it will be slow enough to dispense with the SSR during warm up.

 

[markba633csi]

This is why 220v would have made more sense- half the current for the same amount of watts to the element, less voltage drop
across the SSR, less loss there, but even so the heatsink you have is woefully too small even for 220v
Yes a mechanical relay would be better for 110v

 

[Ferrous Turner]

That's the heat sink that comes with the unit, although a small fan seems like it would keep things cool enough. It's a 40 amp SSR and running 13.5 amps, so well within it's power rating. As far as 220 being a lot more efficient... It's not going to be any more efficient across the element since it is a purely resistive load (voltage times current). That's also assuming you use the original element as one piece, and not as two halves wired in parallel.
The SSR would be more efficient since I'm pretty sure there is a set voltage drop across it, so half the current would mean half the power loss. I'll have to measure that to see what it is.
A simple switch or mechanical relay has no loss, so that seems like an obvious solution for my purposes. I just need to find a relay which activates at the voltage set by the controller.

 

[Ferrous Turner]

I bought some insulation for the outside of the oven. Think I got enough?

 

[FOMOGO]

I bought some insulation for the outside of the oven. Think I got enough?

I used that type insulation when I was in the heating business. It works well, but you don't want to breath the dust from it. Use a mask when working with it, and enclose it in something. Maybe some thin sheet alum. I've been enjoying your journey, and I believe in the end your persistence will carry the day. Cheers, Mike

 

[Ray C]

I made my kiln with that kind of insulation. It's great stuff! As Mike says, use a respirator and I will add, be careful handling it. It has shards of glass glass in it. I got a sliver of glass in my thumb that took 3 months to finally work itself out.

Ray

 

[ddickey]

You used this for the inside correct Ray? How did you attach the Kanthal wire?

 

[Ray C]

You used this for the inside correct Ray? How did you attach the Kanthal wire?

Yes, on the inside. The bottom of the chamber was lined with insulating brick. The coil is spaced-out (zig-zag) on the brick and pinned-down with some SS wire that can take the heat. Heat from the coils rises up. I have a frame of SS that sits above the coils on which to place the workpieces.

Hope that makes sense.

Ray