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  • baking painted items

    Often when I make metal parts like brackets, I paint then bake them. I don't have any test data to make sense of the time and temperature- usually I'll have something else lined up to do and just walk away for hours. Then it's usually too late and I'll leave them in the oven overnight to cool. But at times I need the parts and would like to carry on with the project as soon as practical. Anybody have bake times and temperatures that work for them? I've got these parts in the oven right now at 175F, the smell came up and is now dissipating at about the one hour mark. Ordinary rattle can spray paint is what I've been using lately, though I also use Rustoleum paint/primer a lot.

    For temperature I just try to keep it under 200F. I go with 150F if I know I'm going to leave them bake for a few hours or more, and crank it up a bit if I want them sooner. It's probably true that some paints bake well and others don't respond well enough to make it worthwhile- I don't really know. I do know that paint is much harder after a cool down period, and I know that some paints are just ****e to begin with and will flake off easily regardless of what you do. I also try not to handle the parts until they are fully cooled down- at which point I expect to be able to handle them normally.

    What are the good guidelines here?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Most likely, you are good if you remove them after the point that the smell of solvents has ceased to be noticeable.

    The paints you refer to are not "baking enamels", the baking does not "activate" them and enhance cross-linking, as happens with certain other types, so the baking is really to remove the solvents and perhaps more quickly reach the state that the paint would be in after a week or so.

    You want the paint to dry to a good extent before you bake, so the solvent is substantially gone, and will not cause bubbling. I think you can go higher than 200F, and it may be beneficial, but that is something which you may be able to find out from the manufacturer website, if you can get beyond the "consumer fluff" section and into real industrial data. Some of those paints are not industrial, and may have no further data beyond an "MSDS" (SDS).

    I have baked paints with good results as far as qicker drying. IIRC, I used about 250F, and pulled them out to cool based on time, not smells, giving them about 20 minutes or so in the heat, for 18 ga sheet metal parts.
    Last edited by J Tiers; 05-08-2018, 01:32 AM.
    2730

    Keep eye on ball.
    Hashim Khan

    Everything not impossible is compulsory

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    • #3
      Take great care with so-called "temperature". if you use a convection oven, all is good. If radiant, make sure there is no direct radiant path. If there is the dark surfaces will be way hotter than you may want.

      I use a convection microwave (no microwave) for small parts; big cardboard box and fan heater for larger.

      30 minutes to an hour is fine... don't touch until cold. Even then some paint (like Rustoleum industrial or pro) takes up to a week to get reasonably tough... and a year to fully harden. I use Seymour Engine enamels now; fast dry, fast cure, literally - "ready to use" in 24-48 hours.


      Where can you get the old fashioned "backing enamels " now?

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      • #4
        I have used gas grill.. straight to grill after painting. No idea of recommended temps, been using around 100-150c. No problems with solvent bubbles so far.
        Location: Helsinki, Finland, Europe

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        • #5
          Originally posted by lakeside53 View Post


          Where can you get the old fashioned "backing (baking ?) enamels " now?
          Not common for consumer use, but it is main stream for industrial production, I think.

          For coating steel strip, typically water based paints are used these days.
          The wet coated strip continuously passes into an induction coil ( typically rated 1000 to 1500 kW) where it is heated from ambient to just below nucleate boiiling in less than 2 seconds. Then into a holding oven few a few seconds followed by a cooling zone. It must be cured by then because the steel is recoiled.

          I don't know anything about automobile painting, but i think they use infra red baking?

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          • #6
            Baking enamels are not so uncommon.

            Had a prototype part a while back that had not been baked. A year later you could scrape paint off with your fingernail. Baking at about 250F hardened it.
            2730

            Keep eye on ball.
            Hashim Khan

            Everything not impossible is compulsory

            Comment


            • #7
              I also use my oven to speed cure small painted projects. I set the oven to 180 degrees. When things get hot I turn it off for a while, let the parts sit and maybe repeat the cycle a couple times.
              I have never compiled any technical data on doing this. Some paints may still be a bit soft even after a few hours of baking but once they cool the paint seems to harden up.
              I've done this with a variety of non catalyzed paints.
              I haven't noticed that this does anything for the durability or how well the paint adheres. That's all in the paint and primers used, and in my opinion nothing is as good as it used to be.

              JL................

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              • #8
                Originally posted by wombat2go View Post

                I don't know anything about automobile painting, but i think they use infra red baking?

                Those are typically two part urethane paints. The IR simply speeds up the process.

                I searched a couple of years ago and could not find any "baking enamels". But I still want to

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                • #9
                  I just use my heat gun . Heat-cool, heat cool, done. I forgot last step Clearcoat .

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                  • #10
                    Hey Group,

                    I too use the heat gun (not the hair dryer) to dry painted small items with rustoleum paints. The problem I had just this last weekend was the first top coat went on fine after a primer I did last week. I came back after 4-5 hrs and put a second coat of the same paint and used the sun as the drying tool for the first coat, I got alligator on a couple of spots when the second coat went on. I thought this was usually from lacquer and miss matched paints.
                    Anyone experience the same? I'm going to wait longer and wet sand to remove the defects, then another coat to see what happens.

                    TX
                    Mr fixit for the family
                    Chris

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                    • #11
                      Chris, Many of the paints I've seen recently specify a window for applying the second coat. Might be that the heating accelerated the curing to the point where the second coat could not bond properly.

                      Dan
                      At the end of the project, there is a profound difference between spare parts and left over parts.

                      Location: SF East Bay.

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                      • #12
                        Originally posted by danlb View Post
                        Chris, Many of the paints I've seen recently specify a window for applying the second coat. Might be that the heating accelerated the curing to the point where the second coat could not bond properly.

                        Dan
                        yes. Some even say things like "re-coat in one hour, or after 48 hours cure time". Sometimes the early re-coat time is even shorter. Apparently there is a time in which things are going on that will affect the bonding or the cure.

                        Often, the paint skins over solidly in an hour or so, and if you put a second coat on, the solvents will not escape from the first coat effectively because they have to go through the "skinned over" part of both coats.

                        So if you re-coat quickly, the first coat has not "skinned over", and the two coats become one thicker coat.

                        But, if you wait for the 48 or whatever hours, the first coat has cured enough and the second will not affect it.
                        2730

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        Comment


                        • #13
                          Worked at a company many moons ago that did coating /painting of steel and baked it in a oven
                          Lacquers and enamels were treated slightly different based on Mfg's suggestion.
                          However, they did it all in 10 minutes
                          First minute was at 150 (F) to flash off solvents ( EPA Afterburners of course ) then 300 to 325 for 8 to 9 minutes.
                          As Jerry said earlier, the heated paint cross-links the molecules and becomes very hard in a short time.
                          SO it is a time/temperature correlation
                          I would think that a 150 temperature would require 45 minutes to an hour..just my estimate.
                          Rich

                          Oh, One other factor, the "mass" of the part
                          Painting a solid iron part causes a delay in achieving proper temp levels
                          Last edited by Rich Carlstedt; 05-08-2018, 05:18 PM.
                          Green Bay, WI

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                          • #14
                            Try a catalizer.

                            Heating the part pre paint needs to be round 100*.Mix up the catalyzed enamel let it go about 10-20 minutes depending on your shops ambient. Shoot the part right off the hot plate.Chill,let the part sit whilst either dumping the guns load,and shooting some lac thinner through or,depending on pot life.... take a 20 minute break,and shoot another coat.Then park the part over the hot plate at around 150/75.Clean the gun.... done.Come back in a cpl hrs to a pert near finished part.From here adding or continuing heat is just a waste of electricity IMO.Let it sit for 12 hrs,assemble if you must.After a day you can try to scratch it,good luck.After a cpl days you can beat on it with a hammer.

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                            • #15
                              The parts I painted last night are durable today- the paint doesn't take fingerprints or dent from a fingernail. That's the goal of course- painted parts that can be handled without having to wait a week or more. I actually got to work with the parts last night and installed them today. Now our stage has a cross bar to which you can affix banners, then raise them to height.

                              Because most paints I'd use are not 'baking paints', I have used the technique of sensing when the solvents have gone to say when it's been in the heat long enough. I guess that's pretty much the method I'll continue to use. I'll keep in mind the mass of the part and allow enough time for the temperature to come up. What I've learned is that extended time under heat does nothing for the end result unless the paint actually has that requirement. Beyond evaporating the solvents, nothing is gained- that's probably the truth of it.
                              Last edited by darryl; 05-08-2018, 09:02 PM.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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