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  • #31
    Re: Planebuilder Big Propane Oven

    Sorry on misunderstanding, I was not clear if it is duct or double wall, but I get that fan is from floor.
    I will do some drawings in google. Every picture is welcome.

    I try to make 2D drawing in 3D model like simulation.

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    • #32
      Re: Planebuilder Big Propane Oven

      Click image for larger version

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      I traying to made visualisation for manufacturing oven form 2D drawing, I use for circulation
      double walls but I am not sure if I am no right track, my be to use classic duct? Fan is down under trailer. Please correct me.

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      • #33
        Re: Planebuilder Big Propane Oven

        Originally posted by planebuilder View Post
        The big housing tube is 19" long, and the orifice is 8" inside this tube, measured from the intake
        (outside) end. This is not a critical dimension, and if you are building a smaller burner it can be
        a shorter distance. In fact , look at how your BBQ is built, you could have the orifice just out of
        the tube, pointing into it. I have found however that putting the orifice up inside the tube a little
        makes it a little more stable, less likely to be disturbed by outside breezes. Be CAREFUL, and
        do this outside, but you can mount the burner tube, on cement blocks or something solid, and
        hold the orifice tube in position and light it up. Then you can move the orifice tube farther in or
        out of the burner tube by hand to find the ?sweet spot? (usually a range) . The 3 leg supports, as I
        used, are not necessarily needed. On some smaller burners, once I found the position I wanted
        for the orifice, I tack welded a small angle iron onto the bottom outside of the tube, parallel with
        the tube, and hanging out past the intake end about 8". Then I laid the orifice tube in the angle
        and bent the tube so it pointed along the center line of the burner tube, I then hose clamped ,
        with a few clamps, the tube to the angle.
        Hi planebuilder
        Another question if you don't mind. Do you think a burner the same size as yours would be to much for a oven that's 5' w X 6' d X 8' t ? Could I just turn down the pressure from the regulator would I need to go with a smaller burner? I have decided to build my oven on an old trailer like yours only smaller and back it up to my shop and cut a 5' door in the back wall to access the oven. To gain space in the shop.
        Thanks
        bikerdad46

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        • #34
          Re: Planebuilder Big Propane Oven

          Bikerdad46:

          Yours is 5x6x8=240 cu.ft.
          My ? oven is 8x12x8=768 cu.ft.
          2 burners in mine are a little overkill, but might be good in the cold Canadian winter.
          Therefore 1 burner would be overkill in a 768/2=384 cu.ft. oven, so would definitely be big for
          your 240ft. Oven.
          I have found that if you turn the burner down too much it can “flame out” more easily. If you
          have to run it at 50% to heat up, then turn it down to 25% of that to maintain temp, that’s about
          12% of the burners capacity, I would worry about flame stability. If you build a smaller burner,
          run it at 100% to heat up, then turn it down to 25%, I think it would be safer.

          As a side note: If anyone is running 2 or more burners, monitor them closely, they should EACH
          really have their own flame sensor. I was running 2 burners the other day and turned one down
          just to maintain cooking temp. The low one went out, But propane was still flowing! Into a
          container (oven) with a live flame in it! I was there and shut the gas off immediately, but if I
          hadn’t, and the oven filled with propane, and got to a good concentration, you might have heard
          the explosion from your house!
          When the one went out the noise from the other prevented me from hearing the problem. The
          flame out happened within seconds of me turning it down. I always watch the burners closely.
          When I have a small job I just use the 5x4x7 electric oven. Sure is nice just to let the PID worry
          about running it. I really need to get the monitor/control system done for the big gas one, I would
          still watch it closely, guess I’m too old to trust electronics 100%.

          Comment


          • #35
            Re: Planebuilder Big Propane Oven

            Originally posted by planebuilder View Post
            Bikerdad46:

            Yours is 5x6x8=240 cu.ft.
            My ? oven is 8x12x8=768 cu.ft.
            2 burners in mine are a little overkill, but might be good in the cold Canadian winter.
            Therefore 1 burner would be overkill in a 768/2=384 cu.ft. oven, so would definitely be big for
            your 240ft. Oven.
            I have found that if you turn the burner down too much it can “flame out” more easily. If you
            have to run it at 50% to heat up, then turn it down to 25% of that to maintain temp, that’s about
            12% of the burners capacity, I would worry about flame stability. If you build a smaller burner,
            run it at 100% to heat up, then turn it down to 25%, I think it would be safer.

            As a side note: If anyone is running 2 or more burners, monitor them closely, they should EACH
            really have their own flame sensor. I was running 2 burners the other day and turned one down
            just to maintain cooking temp. The low one went out, But propane was still flowing! Into a
            container (oven) with a live flame in it! I was there and shut the gas off immediately, but if I
            hadn’t, and the oven filled with propane, and got to a good concentration, you might have heard
            the explosion from your house!
            When the one went out the noise from the other prevented me from hearing the problem. The
            flame out happened within seconds of me turning it down. I always watch the burners closely.
            When I have a small job I just use the 5x4x7 electric oven. Sure is nice just to let the PID worry
            about running it. I really need to get the monitor/control system done for the big gas one, I would
            still watch it closely, guess I’m too old to trust electronics 100%.
            Hello planebuilder
            Another question if you don't mind. When running the burner, do you want the flame to be completely outside of the burner tube or inside? I have been reading on the links (web sites) you listed and some burners are using a flair on the end of the burner tube anmd the flame is burning in it and some are not using a flair. Are you using a flair or is the flame burning in just the end of the burner tube? Does your burner tube get hot where you have your orifice located?
            Thanks
            bikerdad46

            Comment


            • #36
              Re: Planebuilder Big Propane Oven

              Hello planebuilder
              Are you using a gauge on you regulator?
              Thanks for the info.
              bikerdad46

              Comment


              • #37
                Re: Planebuilder Big Propane Oven

                Bikerdad46:
                I don?t have a flare on my burner tube, the whole tube is Stainless Steel.
                The tube is 19" long, the orifice is about 8" inside the intake end. The flame burns inside the last
                7" of tube and about 20" outside the tube for a total flame length of 27". I pulled one burner from
                the oven and fired it in the dark to get a good picture for you. You can clearly see the 7" of red
                hot tube. I then took a similar pic in daylight with the burner firing at the same setting (full
                blast). You can still see red in daylight but it?s not so vivid, even though the temp is the same as
                the night shots. It?s interesting that the flame is almost invisible to the camera in daylight but it?s
                there if you look close. It was more visible to me, probably means I need to learn some new
                camera settings, in my spare time, yea right....
                This brings up an important point. The tube, or at least the heat affected part (red), should be
                stainless. If it?s not stainless it will burn, eroding away, and contaminate your oven. I do see a
                small amount of deposit on the inside of the tube in the hot section, this deposit sparks and burns
                off on the next light. It?s very little and I don?t think it contaminates the finish but I?m not sure.
                It might be a good argument for having the flame out of the tube, but I?m not going to worry
                about it right now. The flame starts a few inches away from the orifice and due to the airflow
                into the tube the non red part of the tube and the orifice and it?s supply tube stay cool.
                No I don?t have a gage on the regulator, another spare time job on the to do list.
                Attached Files

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                • #38
                  Re: Planebuilder Big Propane Oven

                  Here is the daylight pic of the burner firing.
                  Attached Files

                  Comment


                  • #39
                    Re: Planebuilder Big Propane Oven

                    Originally posted by planebuilder View Post
                    Bikerdad46:
                    I don’t have a flare on my burner tube, the whole tube is Stainless Steel.
                    The tube is 19" long, the orifice is about 8" inside the intake end. The flame burns inside the last
                    7" of tube and about 20" outside the tube for a total flame length of 27". I pulled one burner from
                    the oven and fired it in the dark to get a good picture for you. You can clearly see the 7" of red
                    hot tube. I then took a similar pic in daylight with the burner firing at the same setting (full
                    blast). You can still see red in daylight but it’s not so vivid, even though the temp is the same as
                    the night shots. It’s interesting that the flame is almost invisible to the camera in daylight but it’s
                    there if you look close. It was more visible to me, probably means I need to learn some new
                    camera settings, in my spare time, yea right....
                    This brings up an important point. The tube, or at least the heat affected part (red), should be
                    stainless. If it’s not stainless it will burn, eroding away, and contaminate your oven. I do see a
                    small amount of deposit on the inside of the tube in the hot section, this deposit sparks and burns
                    off on the next light. It’s very little and I don’t think it contaminates the finish but I’m not sure.
                    It might be a good argument for having the flame out of the tube, but I’m not going to worry
                    about it right now. The flame starts a few inches away from the orifice and due to the airflow
                    into the tube the non red part of the tube and the orifice and it’s supply tube stay cool.
                    No I don’t have a gage on the regulator, another spare time job on the to do list.
                    Hello planebuilder
                    Thanks for the info. That sucker is hot. I'm getting some yellow flames out the end of the tube without a flare and that is why I was asking. I think my main problem is the low pressure reg. I have a cutting torch reg. on it's way. With It I can run more pressure and see it that helps. It seems that I was reading somewhere the other day that the low pressure reg was only around 2 or 3 psi.
                    Thanks
                    bikerdad46

                    Comment


                    • #40
                      Re: Planebuilder Big Propane Oven

                      Plainbuilder, I am in the process of designing a 7'W x 7'T x 12'L propane powered oven following your design for the most part. What CFM is your blower pushing? Just wondering because I don't want to have too much air moving around to possibly distrub the powder, but still need enough moving air to do a good job circulating the heat. Also can you post a picture of your circulation sysem with a view from the front sooting toward the back of the oven. Thanks. Frankle8.

                      Comment


                      • #41
                        Re: Planebuilder Big Propane Oven

                        Frankle8:
                        The first pic ( if they loaded in order) shows the ceiling of the oven standing on edge during flipping. You can see the round hole where the fan will suck air from the oven and the two rectangular slots for the return air. I removed the roof from the container and laid it upside down on the floor and installed the sheet metal with tapping screws. Then as shown in this pic I flipped it and laid it down right side up to work on the top.
                        On the first page of this thread, post 10, you can see the fan installed and the bottom and sides of the duct work. I don?t know the CFM of the fan, it?s big. The fan housing is about 40" dia. You can?t have too big a fan. Within reason? I recommend to anyone building an oven that they apply powder to a piece of metal, don?t cook it, just play with it in front of a fan, maybe test
                        the fan they might use. You will be surprised how hard it is for a fan to blow the powder off. I have a lot of fast air coming out the side ducts and intended to extend duct panels down the inside of the oven to diffuse the airflow and get it to the bottom of the oven. I had to get some coating jobs done before I got that done. I found it unnecessary to extend the ducts even with big parts near or in the fast airflow. I went in the oven, with no heat, and turned on the fan, I made some confetti from Kleenex and threw it into the fan intake to watch the airflow, it circulated EVERYWHERE a number of times. In the past I have built ovens with inferior ducting that didn?t do that, and I had inconsistent temp. problems, but not this time. I am still using the ? oven, 8x8x12, but hope/need to finish insulating to 24' and then will probably finish and extend
                        the interior ducts to get the heat to the far end. There is an interesting detail about fans that few understand. If a fan blows too much air you can restrict the intake or output side with a baffle to reduce the airflow. This will NOT hurt the fan. You might think it would make the fan work harder and overload the motor but the opposite happens. Fans are lazy, if you don?t let them have air they don?t care, the load will be less and they cost less to run. You can demonstrate this with a vacuum or dust-collector. Block the opening when it is running and you will hear the RPM
                        increase due to less load. It?s not more noisy because its working harder, it?s because it?s not working hard and the RPM rises. Just a word of caution, there is no problem doing that with a ?fan? but a vacuum can be a problem if done for a longer time. Many vacuums use the air they ?suck? to cool the motor, if it is restricted the motor can over heat. Bottom line, you probably wont have a ?too big fan?. If you think it?s too big, don?t panic, wait until ALL the ductwork is done and then test and decide. There will be significant losses in flow in the ducts. Notice the smooth curves in the ducts, no square corners. Air is not only lazy, it?s dumb, it doesn?t know how to go around a square corner. A huge percentage of your oven build time will be spent on the ductwork, but it will be worth it! Next (on P1, post 10) you can see the closed in ducts ready to start insulating. And finally on this page the ductwork buried in fiberglass. You can also see the start of the framework to build the peak roof over the oven because it will live outside. When the top was done I lifted it onto the container and started insulating the walls and floor.
                        Hope this was the info you needed.
                        Attached Files

                        Comment


                        • #42
                          Re: Planebuilder Big Propane Oven

                          Planebuilder,

                          First off all thanks for all the great info!! I have constructed a similar oven 4x8x16ft (with plans to go a little bigger) using 2 weed burner torches. I am wonder how much temperature difference you get from the top to the bottom of your oven? with my current setup i get about 75 degrees F difference, is this normal? Do I not have enough air flow? I used a modified furnace blower for air circulation probably about half the size of your blower. The oven get up to temp quick but the temp differential worries me and i tend to overbake and have actually burned a few parts and had to redo them. Any thoughts on this?

                          Jim

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                          • #43
                            Hi Guys, if you're still here? Can't believe it's been 10 years! Short update,,,, to Chevota's post, you don't have enough airflow, I have only a few degrees difference top to bottom.
                            I have done almost no changes to the oven, it just keeps working well. One thing I learned is that heating too quick, like 10 minutes, doesn't give the powder time to flow before curing. Heating up slower, like 20 minutes to 400 deg. gives less orange peel and a better finish. Also I had a partition to cut the oven in half for small loads. I found the propane $ savings were not enough to bother with the partition. I put 2- 3" channels on the floor and made a rack with steel wheels. The oven is ~18" off the shop floor so I pin 2- 3" channel ramps to the oven. I have a pulley with a cable in the back of the oven, and use a winch in the shop to pull the rack up into the oven, then remove the ramps and close the door. Anyway, just thought I would update that it still works great.

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