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Baking Oven

Discussion in 'Amplitude Modulation' started by K4KYV, Sep 29, 2019.

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  1. K4KYV

    K4KYV Subscriber QRZ Page

    From another thread:
    I don't think a toaster oven would do the job. I have located a used "barbecue oven" and thought about using that for the purpose after removing the rotating split, but probably won't go that route either. The problem with those types of ovens is that they depend on direct infra-red radiation from the heating coils to singe or toast the food, and the rotator keeps it from burning by preventing each part from basking in the radiant heat for too long. If the transformer stank up the place, the temperature was probably too high and may have caused permanent damage. That happened to me once, when the paper insulation on the windings of a transformer turned brown and brittle after it was baked for several hours.

    An immediate use I would have for such an oven is to bake out a Collins PTO after making necessary repairs, before replacing the hermetically sealed cover. The problem is, you don't want to heat the object by direct IR radiation, but by placing it in a pre-heated chamber where the walls of the enclosure and the air inside are already at temperature. Toaster and barbecue ovens don't even have insulation on the walls of the enclosure; on the contrary, they have ventilation louvres instead.

    In the past I have baked small transformers and coils in a regular baking oven, but that was back when we had an electric stove. Now, we have a gas kitchen stove, and I don't trust gas heat because one of the products of combustion process is water, just the opposite of what this baking process is intended to do. An electric oven produces dry heat.

    A quick on-line search for a compact portable baking oven showed them to be very expensive, hundreds of $$$, except for toaster ovens, although cheaper ones may exist. This oven needs robust walls with plenty of thermal inertia to hold the heat, and the heating element must be placed so that direct IR radiation from the coils won't toast the surface of whatever is being heated. This probably calls for something home-made. A concrete or ceramic enclosure would work.

    I have an old electric hot plate, and one thought is to find or make a small box out of concrete or fired clay and set that on top of the hot plate, which would be controlled by a variac until the chamber reaches a measured temperature. I could even buy the used barbecue oven and modify it in similar fashion.

    I am open to other suggestions, since this is planned to be an upcoming winter project.
     
  2. K7JEM

    K7JEM Ham Member QRZ Page

    I think you could make a small concrete box from "pavers" available at Home Depot or Lowe's. They are around a buck each, and a complete cube could be built from 6 of them. Add a temperature probe so you can look at the internal temp, and adjust your variac. If you wanted to get real fancy, you could have the probe control a relay to cycle power on and off. 185 degrees isn't really that warm, about like a car parked all day in the July sun in Phoenix (or so it seems).
     
  3. N1OOQ

    N1OOQ Ham Member QRZ Page

    Well, my favorite trick, and this depends a little bit on where you live... Put the item in your car/truck, close all the windows, park in the Sun.
     
  4. KL7AJ

    KL7AJ Ham Member QRZ Page

    When I worked in an R&D lab, we had a commercial grade "Shake n Bake" for life testing circuit boards. It was about the size of a pizza oven...had refractory "foam" on all the inside surfaces, so was quite heat-tight. It shouldn't be too hard to build something like that. ALSO....I'm an inveterate auction junkie. Check out industrial auctions in your bailiwick....some of this kind of stuff they almost give away (at least near the end of the day). You might even look at a defunct ceramic kiln....you don't have to run the thing up to 4000 degrees...you can replace the heating elements with a few heat lamps.
     
    WZ5Q likes this.
  5. KL7AJ

    KL7AJ Ham Member QRZ Page

  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Collins sealed the PTOs at the factory. However, they were not really sealed all that well. Within a short period of time the seal just wasn't there anymore.

    Sounds good "on paper" but, really, not all that effective.

    Glen, K9STH
     
  7. KC2ZFA

    KC2ZFA Ham Member QRZ Page

    some PTOs come with an oven....turning it on for a few days may do the job ?
     
  8. K5UJ

    K5UJ Ham Member QRZ Page

    Water produced by natural gas combustion isn't that big of a problem because only 12% of the combustion product is water. The bigger problem is how most gas ovens work. There's no forced air but there is air brought in via convection from the bottom where the burner is located, up as heated air into the oven, and then out via a chimney opening usually at the back of the oven at the top of the enclosure. This means that if the outdoor air is humid, as is usually the case where you are Don, you'll be heating damp air in the oven. I'd just watch the relative humidity for your area and bake the iron outside when it is down below 50%. That is probably good enough.
     
  9. WB2GCR

    WB2GCR Ham Member QRZ Page

    Well... go to the "dump" or to the throw out place for a local appliance store and get thee
    an old electric stove w/oven... for most folks a small one is best. Then store it until you
    need it and run an appropriate 240vAC line to run it outside. Could be an "extension
    cord" off the dryer plug (etc.). Most of the throwouts are there for either cosmetic
    reasons or broken features. The ovens usually work fine.

    I've baked paint finishes, bitumen out of transformer cans, and transformers.

    Don't care about "messing up" the innards... :D

    Worst case get one for this job, then chuck it until you get one for the next! :D
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    I use my house in the wall oven and monitor temperature Overshoot, Then adjust the T-Stat to compensate.

    As long as the smoke detector don't go off all is good.

    Just leaving the oven light on works great to dry electronics at about 120F.

    The smell of a transformer is only bad if you smell the Fish paper.
     

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