Author Topic: Electric Heat Treating Oven  (Read 13764 times)

Offline unc1esteve

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Electric Heat Treating Oven
« on: November 08, 2013, 09:23:40 PM »
I have needed a small oven many times.  But for a project
I am working on I can not continue without heat treating some
parts.  I decided to make one.  I thought that I would just
make the smallest one that I could just to do the parts I needed.
That soon became the wrong approach.  They say you are to
learn from your mistakes so I started learning.

I thought I could get by with just nine refractory bricks and a
sheet metal cover as I was just going to harden and temper
several parts.  I ordered some nichrome wire and the bricks.
I was going to use only 110 VAC so I thought I could control
the temperature with just an on-off switch.  My flawed reasoning
was because I am on a fixed income.

The bricks arrived.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #1 on: November 08, 2013, 09:45:51 PM »
Before I continue I need help with the pictures.
How does one post a picture and then continue with text?

I am only able to see text.  When I click preview all I see is the
text without the picture.  I do not know if the picture attached
until I click post.  Then I have to start another reply.  Need help
with this.

Also is there a draft or save for the post so it may be edited at a later time?

I see others that post as I want to but I am confused.

Offline Brass_Machine

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Re: Electric Heat Treating Oven
« Reply #2 on: November 09, 2013, 12:11:54 AM »
Hi Steve,

What you want to do is embed your pictures. That is where they are hosted at another site and are inserted into the text with code.  You can read about that here.

What you are doing now is attaching the pictures. The forum software doesn't do inline inserts with attachments.

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #3 on: November 09, 2013, 01:21:27 AM »
Thanks.
See my post in this thread, second to last.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #4 on: November 09, 2013, 01:35:20 AM »
All nine bricks were damaged.  After receiving pictures of the damage
the seller replaced them.  I chose soft bricks as they were easier to cut
and  I would have more insulation.  I ordered a few more of the soft
ones and they arrived in two days.
http://www.ebay.com/itm/331060990306?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I used the table saw with a diamond blade to cut the groove
for the wire.  Opened the doors and pointed the saw to the
outside.  Got a fine white abrasive dust everywhere.  Trimmed
the bricks with the band saw.  Had to be careful as they cut
as if they were not there.  The yellow dust is from and
Osage Orange tree.  The people here call it a horse apple.
Was making carving mallets.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #5 on: November 09, 2013, 01:41:07 AM »
Assembled the one layer of soft brick with
a cut off hard brick as the bottom.  I thought
while putting it together that if I turned it
over I could use it as a furnace to melt aluminum.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #6 on: November 09, 2013, 01:53:10 AM »
After waiting for the proscribed period for the wire I
contacted them.  They told me the wire was out of stock
and they would ship it in a few days.  I told them this was not
acceptable.  After a few emails I received the wire.
http://www.ebay.com/itm/281091127057?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I estimated the length of the wire and wound it on the lathe
using a 7/16 bar.  It would have been easier to wind if I had
cut the wire in half but I did not think about that until I tried
to wind it from the roll.  I uncoiled it to about 3/8 between the
coils by mounting the bar in the vise and streaching the wire
over the bar.  This gave a much nicer finished coil.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #7 on: November 09, 2013, 05:28:28 PM »
Having trouble with my old cell phone camera.
Lost a few pictures

I fitted the coil around the bricks.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #8 on: November 09, 2013, 05:35:22 PM »
I finished the assembly and made a covering
from some sheet metal I salvaged from a
refrigerator.  I made the door.  I used a piece
of the broken hard brick to fit into the opening.
Tapered the edges with the table saw/  I did this
so I would have more insulation at the door.
Attached it to the soft brick with cement, then set
the oven on top of it to cure the cement.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #9 on: November 09, 2013, 05:57:07 PM »
I ordered this control.
http://www.budgetcastingsupply.com/Heating-Element-Control-Basic.php

While thinking about the door attachment I did a
test heating.  I set a large chisel in the oven and
prepared a coffee can of oil.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #10 on: November 09, 2013, 06:11:42 PM »
At this point I could see flaws in my theory.
Most instructions about tempering say to temper
right after the quelch.  How am I going to do that
while waiting for the oven to cool down to 400 deg.?
My idea of just a control defeats the purpose of the oven.
I thought that by watching it I could control the temperature.
So I concluded that I needed at least a pyrometer.  And two
ovens if your are going to temper soon after the heat.

I found this pyrometer but did not order it.
http://www.clay-king.com/pyrometer.htm

I looked at PID controls.
http://www.ebay.com/itm/3-IN-1-PID-Digital-Temperature-controller-40A-SSR-Thermocouple-JT1-/400603021461?pt=LH_DefaultDomain_0&hash=item5d45cd0095
When buying a PID you will probably have to purchase a separate thermocouple of the proper range.

It should be obvious to the casual observer that I was fast
approaching my fixed income budget.


Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #11 on: November 09, 2013, 06:32:34 PM »
It did not take long to heat up the chisel.
I decided not to quelch it as the epoxy I used
on the handle was melting.

And how was I going to correctly temper it?

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #12 on: November 10, 2013, 01:14:37 PM »

Safety
The placement of the oil next to the oven was
for illustration only.
The correct way to quelch the chisel would be to
place the oil container in front and below the oven.
This would allow one movement from the oven to the can.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #13 on: November 10, 2013, 01:28:51 PM »
The oven heated well, too well.
The outside was hot, too hot to touch.
I had viewed videos where the builder
said his oven was cool with only 2 1/2"
of insulation.

So instead of burning my shop down
I ordered more insulation.  I felt it was
better to make a new sheet metal skin
than to take the chance of a fire.  I ordered
ceramic board as I wanted to view the material.
http://www.skylinecomponents.com/In-Stock_CeramicFiber.html

I had thought about just starting over but the
original design was still valid with some refinements
in the budget.  I decided to stay with the switch and
add a pyrometer.  I liked the analog one but found this
http://www.amazon.com/AGPtek-Digital-Thermometer-Thermocouples-50~1300%C2%B0C/dp/B0084JQLRU/ref=pd_cp_hi_3
It requires a high temperature thermocouple.


Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #14 on: November 20, 2013, 10:56:16 AM »

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #15 on: November 20, 2013, 11:17:38 AM »
The ceramic board arrived.
I removed the sheet metal skin and
applied the board.  I ran the element wires
between the insulation brick and the board.
I connected the leads to the power supply with
small bolts and washers after testing the wire and bolts.
I re-used the sheet metal
by bending the corners back flat. 
I made a ridged frame of an old bed frame.
I added legs to the back so the oven could be
used as a furnace.  Then did a test run to see
how hot the metal sides would get.  Let it heat for
about 45 minutes.  The sides were again too hot to
lay your hand upon.  But I am satisfied that no fire
will ensue.
The PID control I showed earlier was for demonstration.
It does not have the needed heat range for this oven.
Still looking for the correct controller.
As the heating coils are exposed and are electrically hot
when in use it is always a good idea to turn off the power
before entering the chamber.  As I plan on using the oven
with the door open at times I have not installed an
automatic shut off switch.
I attached the door with a removable hinge.  I also ordered
a small piece of glass for a site hole.
http://www.skylinecomponents.com/In-Stock_FusedQuartzDiscPlate.html


Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #16 on: November 20, 2013, 11:52:00 AM »
I need to get high temperature paint.
I added a high temperature thermocouple.
I made a mock up of a door latch.
While I was doing this I thought a test firing
of aluminum would be in order.
I made a crucible of 1/4 steel pipe and a few
tools.  I collected safety equipment.  This oven
can be deceiving.  There is no harsh bellowing
noise.  There are no flames issuing forth.  It is
easy to forget how dangerous it is. 
That picture of doubleboost's mate's face shield
with the brass splash on it scares me.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #17 on: November 20, 2013, 12:12:16 PM »
I made an ingot mold.
I purchased some bentonite clay for greensand
as I did not want to deal with oil.
http://www.ebay.com/itm/15-pounds-BENTONITE-HEALING-CLAY-Best-internal-external-DETOX-Guaranteed-/221310369189?pt=LH_DefaultDomain_0&hash=item3387203da5
I used the recommended play sand.
http://www.quikrete.com/productlines/SandPremiumPlay.asp
I used 4% water by weight.
Mixed together in small containers first.
I made a pair of small flasks of wood and two ingot patterns.
I figured that this would be a good time to test things
and get used to the feel of casting as I had not done this before.



Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #18 on: November 22, 2013, 04:10:36 AM »
While waiting for the PID controller I made some test
ingots.  I made one change at a time to see the
difference, such as no vents or vents. 
A peek through the site hole.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #19 on: November 22, 2013, 04:21:06 AM »
This is the PID I ordered.
http://www.ebay.com/itm/161111236826?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
The thermocoupler.
http://www.ebay.com/itm/181187310615?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
And the SSR relay.
http://www.ebay.com/itm/Solid-State-Relay-SSR-25DA-25A-3-32VDC-Output-24-380V-AC-Solid-State-Module-USA-/161111607581?pt=LH_DefaultDomain_0&hash=item258300091d
I painted the oven and made a box for the controls.
I added a cut off switch for the coil so I could set the
PID without the heat on, and to open the door without
turning the power to the PID off.
The PID instructions are a little confusing.
I have it wired for 110 VAC but it could also control 220 VAC to
the coil by adding another relay.

I decided to behave like our government and pass the cost of
this project to the third and fourth generations.

Offline Meldonmech

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Re: Electric Heat Treating Oven
« Reply #20 on: November 23, 2013, 06:57:53 AM »
Hi
          A very interesting project, detailing all the equipment and where you sourced it. Have you a total cost for the build, and have you any heating costs compared with propane.
                                                                                      Well Done  David

Offline DavidA

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Re: Electric Heat Treating Oven
« Reply #21 on: November 23, 2013, 09:37:18 AM »
It looks as if you can run the oven with the door open and the power turned on;  even if by accident.

Is this so ?

Dave.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #22 on: November 23, 2013, 12:48:28 PM »
A final coat of paint and this project is complete.
I am satisfied, more than satisfied,  I started out
wanting a simple heat treating oven for a few small
parts.  Now I have that and more.  I did not intend
to use this as a foundry but it works well.  Precise
control over temperature if I can figure out how to
set the PID.  I have searched for pid terminology
but can not find a clear explanation of the settings.

Conclusions.
1.  I used 16 ga wire as I first wanted to use 220 VAC.  But
this works good on 110 VAC.
2.  I made the coil as long as possible.  I put the coil on all four
sides.  I wanted as much resistance as possible, more heat.
3.  The coil expands when hot.  The top coil may slip out of
position when hot.  A nichrome wire across it holds it in place.
4.  The coils are electrically charged when in use.  The expensive
ovens use glass tubes to enclose the coils.  Also safety switches.
I did not put an automatic off switch on the door.
5.  The lack of noise and great heat when being used as a furnace
makes this deceptive.  Hot and molten metal are very dangerous.
6.  My first idea of a simple switch control is not a good idea for
heat treating.  But it will work well for the furnace with a pyrometer.
7.  With the damage in shipping and a few mistakes I have almost enough
material to make a second oven. 
8.  Use hard brick for the exposed areas as they will get damaged.  They
can be cut with masonry blades.
9.  PID control is good.  Make sure to match the correct temperature range
on the controller and the thermocouple.
10.  Casting Is Fun.


Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #23 on: November 23, 2013, 12:54:40 PM »
Meldonmech,
Once I realized that my first ideas were not very good I did not keep track of costs.
I do not have an ammeter in the range for this oven.
I will do some math.

Offline unc1esteve

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Re: Electric Heat Treating Oven
« Reply #24 on: November 23, 2013, 01:02:05 PM »
DavidA,
Yes, the power can be left on by accident.
I put a switch in line with the ssr relay so I could
have power to the PID for setting.
One of the heat treating projects I have is a set of
12" mortise chisels with the handles attached.  I saw
a need to use the oven with the door open or detached.
I made a temporary label for the control panel.  It shows
the coil switch and the indicator light.
It would be a simple matter to add safety switches and alarms.