Heat treat oven

[stephenc]

Maybe someone can educate me .

Went to the monthly junk auction today and came home with a heat treat oven
Well sort of ... you can see what I got in the pictures .

The oven itself .. some sort of controller and a veriac, I know what the veriac is , or what they are normally used for , it was in the pile for the furnace at any rate

First pic is the oven opening

Second pic. Is the front of the pyrometer / controller thing a ma jig
Third is the guts of the thing a ma jig

Last is the veriac dc motor controller .


So... what does it take to make these things get hot ?
Everything is wired 110v. Including the oven coil

[jcfx]

Nice score, a Variac is a brand name for a rheostat, it lets you vary the voltage being fed to an appliance,
be it a light ( I used them a lot for set lighting ), or a motor ( probably not doing the motor any good if used that way ).
I'd use some caution before firing it up.
I see the variac has an on/off switch, then it's controlled by the Variac, where is the knob on it set to ?
If it's at zero there's little to no voltage going to the oven, dial it up and see if the coils in the oven start to
glow or get hot. If nothing happens then the either the heater coils are broken or the Variac is defective.

Easy check on the Variac is to use a incandescent light bulb hooked up to it, if it lights and you can dim it,
it works, checking the heater coils requires a VOM set to continuity to look for breaks in the circuit.
Of course, checking the heater coils is done unplugged.

[stephenc]

The veriac works just fine , I plugged a fan into it , speeds up and slows down just fine .
I guess my question would be is it something that would normally be used like this ?
Or is it something that just got lumped in with the furnace ?

In the first picture of the temperature tender thing you can see a what I am assuming is the temperature probe hanging under the dial .
It's not hooked up , but there is a corresponding hole in the top of the oven.

The heater coil ends in a normal 110v plug , and the temperature tender box also happens to have two 110v receptacles on one side .

I guess it couldn't hurt anything to just start plugging things together and see what happens if anything .

The veriac more then makes up for the $10 I payed for everything

[Russ Hanscom]

If the temp controller works, than the Variac is probably unnecessary unless you wanted to reduce the heat up rate significantly.

fyi, I think a Variac is a variable transformer and not a resistor.

[John Hasler]

If the temp controller works, than the Variac is probably unnecessary unless you wanted to reduce the heat up rate significantly.

fyi, I think a Variac is a variable transformer and not a resistor.

Correct.

[Bob D.]

I really don't think the Variac would be used with the oven. You will find a use for it.
Can't tell in your pics if the temp. Controller has two pointers and a needle or one pointer and the needle. Generally there is a process set point and an overtemp setpoint. Your elements are turned on and off with the power relay on the lower right of the backside photo. Your thermocouple has polarity. If wired correctly the needle will go up when the tip is heated with a match, if backwards it goes down. You really want overtemp protection, separate thermocouple preferred. The pot on the backside is a bias adjustment to calibrate the thermocouple.
Good score!
Bob D.

[SteveM]

I think, technically, a variac is not a rheostat (which is a variable resistor).

A variac is a variable transformer (I think it's sometimes called an autotransformer). I think the knob adjusts how many coils on the output side of the transformer are in play.

Many times ovens like that are called burnout ovens because they are used to burn out the wax in a lost-wax casting process. Dentists use them for that (I got mine from the estate sale of a guy that ran a dental lab out of his house).

My dad had one and used it with good success for heat treating.

Steve

[Harold_V]

If the temp controller works, than the Variac is probably unnecessary unless you wanted to reduce the heat up rate significantly.

fyi, I think a Variac is a variable transformer and not a resistor.

Yep! What Russ said. I've seen many of those small furnaces, commonly used for burn-out by jewelers (investment casting). I've never seen one used in conjunction with a Variac, which is, indeed, a variable transformer, not a resistor.

It's possible the amperage rating of the one in question isn't great enough to provide the amperage needed by the furnace. Try it without the Variac, as most of them have built in controls that allow you to regulate the heat. Heating by electrical resistance is generally a relatively heavy demand, depending on the size of the furnace, naturally.

H

[tornitore45]

Other have explained what a Variac is. Being an Autotransformer it provides NO isolation between input and output, therefore, for safety reasons is important to connect the cold wire of the load to the cold wire of the Variac (usually the white wire) Black input is hot all the time, the wiper is raising in voltage as one turns the knob CW.
Something to be avoided is to connect the load chassis (cold wire) to the wiper.

[stephenc]

Bob d.
The controller has one pointer and one needle .

My fridge gave up on me last night , luckily I found a pretty nice used one this morning
For a reasonable price , so once I get the old one out of the house and the new one home I'll give the oven a bit of electricity and see what happens .

Here's a question that ought to make some of you laugh ...

Any suggestions on how to determine where in the controller i need to plug in the temperature probe if this thing actualy starts to get hot when I turn on the juice

[Bob D.]

Steve,
Can you get a clear picture of the backside of the temperature controller? Generally the terminals are labeled T/C and maybe +, -. Might also state "type K". I doubt it plugs in. T-couples need a secure screw connection to reduce error.

Bob

[John Hasler]

Steve,
Can you get a clear picture of the backside of the temperature controller? Generally the terminals are labeled T/C and maybe +, -. Might also state "type K". I doubt it plugs in. T-couples need a secure screw connection to reduce error.

Bob

Often the thermocouple wires connect to a special two pin connector like this: http://www.omega.com/pptst/OSTW-CC.html