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  • #16
    I bought a delta pid type temperature controller and had a ssr in my garage . I battle with electronic things but it seems my controller will only go up to 999 degrees celcius.However it takes a long time to get there. This oven is rated at 7 amps .Does an oven like this utilize a lot of power over 4 hours. I am trying to figure out the maths to wortk out how much it would cost to heat treat a small item .
    My second dilema is that I set the oven at 780 celcius and it holds the temp accurately to about 2 degrees. It battles at anything below 180 celcius and fluctuates as much as 15 celcius above or below. But at higher temp it is very stable. However my part was a dull cherry colour. I was expecting it to be a bit brighter. It also never lost its magnetism and I understand that at that temp it should .I used my multimeter and on converting the mv to temp I get the temp 30 celcius lower than the controller reading. Any suggestions as to how I could accurately assess what temp it is at . Could I try and see if aluminium would melt and then I know if I am in the range?
    I am hoping that for most hobby type heat treating of metals that 850celcius is enough. I read that it is as bad to shoot over the critical heat as it is to be under it.

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    • #17
      Hi plunger
      This oven is rated at 7 amps .Does an oven like this utilize a lot of power over 4 hours. I am trying to figure out the maths to wortk out how much it would cost to heat treat a small item .
      That works out to 7 Amps x 230 Volts = 1.61 kilo Watts. Multiply by 4 hours and you get 6.44 kilo Watt hours. Take your electric bill and divide the amount to
      pay by the number of kilo Watt hours billed. That will give you the cost per kilo Watt hour.
      Last edited by RichR; 08-21-2014, 10:17 AM. Reason: Changed calculation from 120V to 230V
      Location: Long Island, N.Y.

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      • #18
        Originally posted by RichR View Post
        Hi plunger

        That works out to 7 Amps x 120 Volts = 0.84 kilo Watts. Multiply by 4 hours and you get 3.36 kilo Watt hours. Take your electric bill and divide the amount to
        pay by the number of kilo Watt hours billed. That will give you the cost per kilo Watt hour.
        Rich,
        I believe that South Africa uses the 15 amp BS546 plug system still, which implies that the supply voltage is 240 volt. (Or 220, or 230...) If so, Plunger's power consumption will be twice your estimate, and the cost likewise.

        George

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        • #19
          Originally posted by J Tiers View Post
          That thing has two uses...... first, hardening, and second, tempering....
          JMHO, but the best uses for an oven have nothing to do with heat treating but rather assembling/unassembling shrinik fit assemblies, and a bit of homebrew branding.
          "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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          • #20
            Originally posted by Georgineer View Post
            Rich,
            I believe that South Africa uses the 15 amp BS546 plug system still, which implies that the supply voltage is 240 volt. (Or 220, or 230...) If so, Plunger's power consumption will be twice your estimate, and the cost likewise.

            George
            Thanks George, you are correct. I've updated my post to reflect 230 Volt operation.
            Location: Long Island, N.Y.

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            • #21
              Originally posted by plunger View Post
              It battles at anything below 180 celcius and fluctuates as much as 15 celcius above or below.
              Check the instructions, the terms you are looking for are undershoot and overshoot.
              Location: Long Island, N.Y.

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              • #22
                Originally posted by justanengineer View Post
                JMHO, but the best uses for an oven have nothing to do with heat treating but rather assembling/unassembling shrinik fit assemblies, and a bit of homebrew branding.
                probably does assembling nicely, but the "unassembling" has me puzzled, as all the parts will heat the same, and expand the same unless of different materials.

                I probably do twice as much hardening as I do shrink fitting, and it might be much more different than that. But I tend to torch harden.

                What would be SUPER good is tempering..... a nice even tempering oven is a lot better for springs and the like.... which tend to develop softer and harder spots even with "plate tempering" where a plate is heated with the part on it.

                Actual temperature control should beat the dickens out of "color tempering", especially when the entire part can be heated to the same even temp, ensuring a good job with no left-over hard/brittle spots.
                CNC machines only go through the motions

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                • #23
                  Originally posted by plunger View Post
                  I bought a delta pid type temperature controller and had a ssr in my garage . I battle with electronic things but it seems my controller will only go up to 999 degrees celcius.However it takes a long time to get there. This oven is rated at 7 amps .Does an oven like this utilize a lot of power over 4 hours. I am trying to figure out the maths to wortk out how much it would cost to heat treat a small item .
                  My second dilema is that I set the oven at 780 celcius and it holds the temp accurately to about 2 degrees. It battles at anything below 180 celcius and fluctuates as much as 15 celcius above or below. But at higher temp it is very stable. However my part was a dull cherry colour. I was expecting it to be a bit brighter. It also never lost its magnetism and I understand that at that temp it should .I used my multimeter and on converting the mv to temp I get the temp 30 celcius lower than the controller reading. Any suggestions as to how I could accurately assess what temp it is at . Could I try and see if aluminium would melt and then I know if I am in the range?
                  I am hoping that for most hobby type heat treating of metals that 850celcius is enough. I read that it is as bad to shoot over the critical heat as it is to be under it.
                  You need to tune the controller. Look in the manual and see if there is an auto-tune mode. It will ramp up the temp and figure out the right settings to maintain a steady temp without overshoot. If not you will have to set the PID settings manually. It will probably just be PI, proportional and integral. If it is overshooting now you will want to lower proportional to start and possibly increase the integral to lower the settling time. It is a bit of trial and error, if you have another thermocouple and a digital o-scope you can set it to very slow sweep and watch the trend.

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                  • #24
                    Originally posted by macona View Post
                    You need to tune the controller. Look in the manual and see if there is an auto-tune mode. It will ramp up the temp and figure out the right settings to maintain a steady temp without overshoot. If not you will have to set the PID settings manually. It will probably just be PI, proportional and integral. If it is overshooting now you will want to lower proportional to start and possibly increase the integral to lower the settling time. It is a bit of trial and error, if you have another thermocouple and a digital o-scope you can set it to very slow sweep and watch the trend.
                    Macona, I have decided that you are a very smart man! How do you know all this stuff that you know? Real question!
                    Location: The Black Forest in Germany

                    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                    • #25
                      Originally posted by plunger
                      I used my multimeter and on converting the mv to temp I get the temp 30 celcius lower than the controller reading.
                      Thermocouples generate a voltage dependent on a temperature difference. When using a meter to measure the voltage, the temperature of the thermocouple leads at the position they connect to the meter leads needs to be taken into account.

                      Thermocouple tables assume a reference ('cold') junction at 0°C. If the meter connections are not at 0°C the thermocouple table does not apply directly.

                      The relationship between thermocouple voltage and temperature is not linear over wide ranges, and the correct way to compensate for the 'measuring point' temperature is to use the table to convert this temperature to a voltage, add this to the measured voltage and then convert this total back to temperature...

                      However in this case, for simplicity, adding the 'measuring point' temperature to the value derived from the (0°C reference) table will give very close result.

                      I'm guessing Durban is a pretty warm location and that much of the 30°C deviation from the (compensated) controller mentioned above can be attributed to this.

                      Given the unknown history of the oven it might be worth obtaining a fresh 'K' type for comparison if you can. You may be surprised at the difference. On the other hand, if it compares well so much the better.

                      Cheers

                      .

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