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Problem with getting even heat in oven

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  • Problem with getting even heat in oven

    I built the oven from the caswell powder coating oven information. Got everything working but am having some problem with getting even heat in oven. It has been mentioned that maybe my blower is to strong but I used the 310 cfm blower as recommended. My specific problem is that if I put my parts in oven and then heat up oven the lower part of the oven gets about my specified temperature. Say I set the oven on 400 and while the oven is coming to temperature the part overheats on the lower end. Like 30 to 40 degrees. I think it is an airflow problem but don't really know where to start to fix it. The reason I hang my parts before preheating the oven is the difficulty involved in trying to hang large items in a hot oven. Anyone got any solutions? I am using an auber PID and have run the autotune function. I am hotter on bottom of my oven than on the top!

  • #2
    The oven temps should even out as the oven heats up. It may also be possible that your lower hanging parts are seeing radiant heat reflected from the elements. You can build shields around the elements, just punch a lot of holes in them or you risk overheating and destroying the elements. I added these to my oven which are made from thin gauge aluminum sheet. Yet another possibility is to place a diffuser at the outlet of the fan to disperse the air more evenly around the oven.

    Lastly most powder is somewhat over temp stable so some temperature differences should not be a problem. Building a roll-in rack is another option for getting larger heavier parts into an oven, regardless of the ovens temperature. .

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    • #3
      Have worked all day building shields for the elements. Got the rear two elements done and the two side elements made but have to finish mounting brackets and install them. Will take a couple pictures and post them later this evening. You are right lots of holes. I think I counted and I cut 306 one inch holes total. Better to just see what I have done than trying to explain it. I am mounting them with a 3/4 inch offset from the oven wall rather than attaching them directly over the elements. I think I got this right but will let you take a look as soon as I get the pictures. Worked all day and I hope it will pay off. Thanks for the info. Watch later this evening for me to post the pictures and would appreciate your reply. Thanks Again!

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      • #4
        Pic of element shields in my powder coating oven

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        • #5
          Those look almost identical to what I have in my oven. Nice job. They should help eliminate any radiant heat issue you may be seeing.

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          • #6
            Thanks for taking a look a my progress, I have another question about my PID. I have an auber syl-2362. I use basically two temps in my oven.350 and 400 degrees. Can I autotune for each of these temperatures and when I set the SV to one or the other will the parameters for that temperature be used. What I guess I am really asking is there a way to setup two you might say modes like 350 and 400. It is kind of hard to put into words but hopefully you get what I am saying. Any help with this or guidance where to find help. The manual as far as I can tell doesn't cover setting up multiple temps. Thanks Again!

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            • #7
              There is only one mode... Controlled. The oven "tune" is the only tune needed. Changing the set point is all you need do. The PID knows the oven, not the temp... it adjusts things per the oven, not the settings... the temp setting just gives it a goal to reach/maintain...I hope that makes some sense. Autotune does it's job at whatever temp the set point is set at. The autotune feature is to allow it to learn the "space" and characteristics of the oven so it can achieve those desired results... it will work the same at 350 as it does at 400... the only difference being "initial time to temp" on turning it on each day or cycle of use. It just takes longer to reach 400 than it does 350 using the same oven. Period.
              sigpic

              See photos of my work on Facebook "Scottrods Powder Coating"

              EMAIL [email protected]

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              • #8
                In the simplest of terms the autotune allows the oven to overshoot the set point, cool down and then fires the elements several times again to gauge how quickly the oven reacts once the set point approaches and/or has been exceeded. The autotune then adjusts the P, I and D parameters based on the oven heat up characteristics as Scott mentions. Then when you start a cure cycle the elements will be full on until the set point is approached. Based on the parameter settings the pid then begins to cycle the elements on/off to slow the heat up process and slowly move up to the set point. Once set point is achieved the pid continues to cycle the elements to maintain that temperature.

                IMO it doesn't hurt to re-run the autotune if you make changes to the oven configuration such as installing the element shields. If you're curious about changes the autotune function makes, if any, note the P, I and D settings prior to starting the autotune and review them once the process has completed.

                The Auber does have 4 modes of operation, PID, on/off, Limit and Manual. On/off will work for PC ovens but generally not with as much accuracy as PID based control. Other more robust controllers than the Aubers will also have ramp and soak capability and the ability to create and save multiple programs which is what I believe you are inquiring about. This generally isn't necessary in PC applications as has been mentioned.
                Last edited by ed_denu; 10-02-2017, 09:58 AM.

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