Heat treatment oven?

[SwissTony]

After messing up 4 blades I now want to either buy or make a heat treatment oven.
I have found the pdf guide on here, but it doesn't show what controller to use other than one bought in from the states.
I am hoping to be able to do various types of steel, not just O1, so I will need a programmable controller.
What controller should I buy? UK source so I don't get clobbered for customs e.t.c.

I want to be able to use this on a standard 3 pin UK plug, is that possible or will I have to get it wired in to the fuse box?
My fuse box is an old style which you wind fuse wire onto 2 pronged blocks, I am also pretty sure there isnt any space left to add extra fuses/wires.

[timgunn1962]

I've built 4 HT ovens so far, and I'm working on a fifth. I think I'm getting them pretty close to right now.

They all run off a 13A socket with no problems, so far at least, though I fit an RCD plug for additional safety.

The last 3 have used AutomationDirect Solo controllers, which seemed to offer the best combination of features and price I could find.

It is ramp-and-soak programmable. The 4848VR will do the job when coupled with a cheap SSR from ebay.

http://www.lamonde.com/acatalog/16DI...ntrollers.html

[rojaz]

I've built 4 HT ovens so far, and I'm working on a fifth. I think I'm getting them pretty close

Any pics Tim?

[timgunn1962]

None recently. Thread on the first one is at http://www.britishblades.com/forums/...eat-Treat-Oven

It's one of these "I'll do a proper write-up once I'm happy with it" things. I keep coming up with little improvements and moving the goalposts.

[Colin KC]

...and moving the goalposts.

further apart

[SwissTony]

That solo controller looks just the jobby although the manual looks like a fun read
Got some 1mm mild steel sheet for the box already, and can probably knock some angle up from some flat stock I have laying around.
Everything for under £250 looks a possibility.

[SwissTony]

Pretty much decided on the SL9696-VRE for the extra size buttons e.t.c.
Which thermocouple do I need to go with it?
I was thinking NB11-NNXL-IM60U-300 (N thermocouple probe with NB11 style head, 6 mm diameter, insulated junction, 300mm length) from here http://www.omega.co.uk/ppt/pptsc.asp...NXL&Nav=tema06

[xbow]

Maybe this one?

http://www.omega.co.uk/ppt/pptsc.asp...-CP&Nav=tema06

[SwissTony]

Would I need one as higher spec as that for heat treating?
The one in the link I posted in my last reply appears to be suitable up to 1335oC and I dont think I will be going over 1200oC.
Could do without the extra £25 on the bill also

[timgunn1962]

The ceramic sheaths are only really necessary for silly temperatures and need to be used in conjunction with precious metal thermocouples to gain the benefit. You really don't need them.

I've only needed to buy one thermocouple so far, as all my others have been salvaged. The one I bought was an Omega NQXL-IM60G-450.

I used 6mm diameter and 450mm long, because the salvaged ones were that size, but if you don't need the insertion depth, you'd get away with a 3mm diameter, no problem. If you can go smaller diameter and shorter, the option of a transition junction thermocouple presents itself, saving another few quid on cable, etc.; NMTXL-IM300G-300 is £18.75, though the carriage hurt quite a bit when I bought mine.

I like type N a lot and would take it over type K even if it carried a significant price premium.

On my second oven, I did some testing with a datalogger and various thermocouples and came to the conclusion that thermocouple response time can have a much larger effect on the effectiveness of an oven than even I suspected. I'd certainly go with a grounded junction for fast response.

I've not actually used the Omega one yet. The salvaged ones have type 310 stainless sheaths, which form a stable black oxide layer and this probably helps with the response time issue. I'm not sure how readily the fancy Omega sheath oxidises at around 800 degC. It might need a run up to a higher temperature to blacken it.

[SwissTony]

My order list so far

Solo SL4848-VR PID (£106 + post)

TJ1-NNXL-IM30G-450 N thermocouple with 1m wires
HTTG-1CU-322S High temp wire ( for this and thermocouple £37ish inc postage)

Fotek SSR-25DA Solid State Relay 3-32V DC / 24-380V AC / 25A (£8.99 delivered)

Kanthal wire from budget castings (I assume I want just under 13amps worth?) (£18.95 delivered)

Tufnol for mounting the terminals on the back of the oven.(£5)

Some kind of case to pack all the electrics in (£15 at most)

Lots of bricks, 30ish depending on the design. (Probably £100 with the shipping )

Assuming that the bricks will cost £100, the above should cost me about £300

Do I need different, more wear resistant blocks for the flooring or do I use some kind of kiln furniture rack?
Anything obvious that I have forgotten?


Wiring diagram so far, using terminal numbers for the Solo PID
Click for full size

[timgunn1962]

My order list so far

Solo SL4848-VR PID (£106 + post)

TJ1-NNXL-IM30G-450 N thermocouple with 1m wires
HTTG-1CU-322S High temp wire ( for this and thermocouple £37ish inc postage)

Fotek SSR-25DA Solid State Relay 3-32V DC / 24-380V AC / 25A (£8.99 delivered)

Kanthal wire from budget castings (I assume I want just under 13amps worth?) (£18.95 delivered)

Tufnol for mounting the terminals on the back of the oven.(£5)

Some kind of case to pack all the electrics in (£15 at most)

Lots of bricks, 30ish depending on the design. (Probably £100 with the shipping )

Assuming that the bricks will cost £100, the above should cost me about £300

Do I need different, more wear resistant blocks for the flooring or do I use some kind of kiln furniture rack?
Anything obvious that I have forgotten?


Wiring diagram so far, using terminal numbers for the Solo PID
Click for full size

I really must get a write-up done.

Controller is fine. Thermocouple is fine. I use fairly long lengths of stainless M6 studding for my terminals, with enough stand-off at the back of the oven to obviate the need for the high-temperature cable. It makes the oven longer, but I have an extended frame anyway so I can stand it on end and use it with a salt pot. You obviously need to work out what's best for you. I don't use the Tufnol.

The Fotek SSR is fine, but needs a heatsink and a fingerproof cover. My first one came with the cover. Then I bought 6 with heatsinks and they came without covers.

I get my elements from jrider12 on ebay.

http://www.ebay.co.uk/itm/Kiln-Furna...item27bb0e1d96

I use 2 of these elements wired in series, rather than a single 240V element, as it means there are straight element wires across the back of the oven instead of coiled, giving almost all the heat from the sidewalls. I get the tails untwisted and last time I asked him to bear in mind that UK domestic supplies are fused at 13 Amps, so he adjusted the length accordingly. I'd had no problems with the "standard" elements, but wanted to cover the risk.

I went for a "proper" control panel, which is pretty expensive but gives quite a lot of extra versatility. The control panel has a 13A RCD plug on a trailing cable for the power in. Power out to the oven is via a 16A industrial socket and the thermocouple plugs into a miniature panel socket on the front of the panel next to the controller.

This allows the control box to be used for other stuff as well; I've built a crucible furnace already and my next project is a tempering oven.

I don't trust the SSR to provide full isolation on its own, and use a contactor in a No-Volt-Release circuit that includes a door switch (also on a plug/socket arrangement).

Don't worry about the floor bricks. The easiest ones to cut with hand tools are the expensive branded JM23 ones, because they are the softest. The cheaper ones are harder. I've been using a router to cut the grooves on my latest ovens. It's much faster and it doesn't seem to make any difference whether you use the cheap bricks or the expensive ones. As the cost of a 10mm router bit from Toolstation is about the same as the difference between one branded and one unbranded brick, it's a bit of a no-brainer. I use 30 bricks for an 18"D x 7"W x 6"H (internal) oven. I'm sure you'll also be using the cheap ones.

[SwissTony]

Thanks for all your help Tim
Good idea with the longer studding. My work bench is pretty deep so should easily be about to accommodate an extra few inches of studding.

Found a Fotek ssr with heatsink already attached for about £9.50, no cover though, but as everything will be sealed in a box, hopefully I wont need a finger guard. I have some perspex laying around which I could knock a guard up if needed.
Had looked some project boxes, but it looked like they all had sloping sides, which might make mounting the PID a bit of a pain.
There are a few metal enclosures on ebay which I am keeping my eye on, all square sided.

Have found a couple of places in the UK that sell kanthal wire, but knowing the quality pricing in the UK, they will probably end up double the price.
http://www.kilns.co.uk/product-category.aspx?id=180
http://www.claymansupplies.co.uk/PRO...ILNSPARES.html


For the door switch:
I am not sure how to go about wiring in a contactor and nvr switch, so was just going to mount either a rocker or rotary switch that shuts off the positive and negative to the elements, but leaves power to the PID. So I always remember to switch off the power, I could mount the switch in such a way, that it needs to be switched off for the door to pass it.

Not got a router unfortunately, so will go the handsaw and studding route to cut the groves.
I assume that as you are using a router, the holes are cut straight into the bricks rather than at an angle like one of your previous ovens?

[rojaz]

my next project is a tempering oven.

Out of curiosity Tim, why can't you use the same heat treat oven as you can with such as an Evenheat?

[timgunn1962]

It's really just a case of avoiding the wait while the oven cools down. It takes a few hours to get from 800 degC down to 200 degC and my test driver complained that he couldn't fully treat a blade in an evening.

I'm pretty sure I can make a rockwool-insulated low temperature oven, for not much money, that'll run off the control box.