painting inside of square steel tube

Concerning the preheating of parts to be coated, you'll probably like the results. The benefits are numerous, such as the heat driving off any surface
moisture from the air, faster product application and/or quicker time to reapply consecutive applications.
Portable electric panel heaters (typically quartz radiant lamp units) have become common in repair shops for partial area refinishing (on the car, or separate panels on a stand). These can be fairly costly to operate, but the heaters can drastically reduce normal air-drying times of numerous products. For small objects around the home shop, one can put the item out in the sun for free heat, both before and after applying the primers or paints.
The products applied to the lower sections of car bodies is commonly referred to as "chip guard", here. It's commonly available from autobody supply dealers, although I've never heard of anyone applying it by brush, and I never would've guessed that a car manufacturer (luxury or otherwise) would resort to brush application.. go figure. Many times chip guard is applied to cars as far as 8-12" up from the bottom edge on the sides, and below the bumper in the front. Most of the stuff I've seen is slightly cloudy, somewhat dull (flat-no gloss) and has been applied to a line where masking was done, making it even more unattractive.
Many of the current car models have so much thru-colored external plastic on them, that chipping doesn't result in a potential rust threat.
You had previously mentioned that the newer processes of applying corrosion-inhibiting coatings had been invented in 1963, so I don't know that '63 is much of a useful point, as far as when the process would have been widely adapted, then actually retrofitted or installed into manufacturing.
As the original topic concerned parts, I was commenting on parts in general, (car hoods, trunk lids, fenders, doors, with reinforcements welded into them) not entire car body shells, although I've seen the advertisements of dipping body shells that someone had mentioned. Many body panels can (and have) been "in primer" (or pretreated) before being assembled into body shells (including stocked replacement panels). I believe much of this was done by the dipping or flooding process, but I don't know when this process was replaced.
If I had 1 or 2 sections of 4" square tubing to paint, using a small roller would use up a lot more paint than the tubing required, although it's possible to recover a good deal of paint from the roller, if one would care to spend the time. Then comes the decision to throw away the roller, or clean it more, for reuse later. One would probably want to try to keep the side rod of the roller from removing paint from an adjacent side. For hundreds of tubes, airless spray would be better if the equipment was available (already paid for), since the equipment would be practical for many other uses. I've used automated airless spray in industrial production line applications (for coating interior surfaces), and it doesn't require much maintenance, and invloves almost zero wasted product.
Dipping parts has it's own set of complications, such as the tank, bulk materials, evaporation, draining and recycling, and more. Dipping pretty much also dictates that you want the same product on the outside of the part.
For a home shop project, pouring some liquid into a confined space and rotating the part is sure to get complete coverage with proper movement, and how much product is left over (drained out) depends upon how much was put in. If the product is reduced/thinned correctly, the coverage should be fairly uniform. Pour any leftover thru a strainer (or not) and use it later for something else (a project, not for a girlfriend's car, which might also be a project.. not the car).
Forced drying will definitely create problems if dipped parts don't drain properly (part of the designed-in drains and tilt-turn-parts-to-drain process). Excess primer (for example), trapped in a corner will tend to bubble when heated, creating a water trap maze, which is fairly common. If this occurs on the interior surface of a roof skin, it might not be a huge problem, but if it's in a lower section more directly exposed to weather conditions, it will most likely create an early rust-out problem. This may be the greatest benefit of the newer ED electrophoretic deposition process, aside from wasted/excess product being used. (ED not to be confused with erectile dysfunction, like race car drivers get, but ed as in my primer isn't getting hard properly).
WB ......... metalworking projects www.kwagmire.com/metal_proj.html

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Wild_Bill wrote:

Yes. They are used since long. Saves on heating up the drying chamber (or how you call that).

Sounds like I meant that.

That was not a joke. But it made me laugh. Really, a big round brush, maybe 80mm diameter and no masking tape. But the line was straight. He had enough samples to practice. :-)) When I asked, they told me that the automatic spraying of the chip guard didn't get good (enough) results. IIRC, it was a problem with the nozzle jamming from time to time or uneven application.

I've read that Ford switched to that process in the same year or the year after.
Nick
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I believe you about the chip gaurd being applied by brush. Hopefully, thay have the spraying equipment working by now, since it's likely that man has retired by now.
There are very talented painters that paint pinstripes and artsy stuff on very expensive cars, freehand, with the with about the same accuracy of a good laser printer.
That's talent far beyond any of my skills though (although I might still have 1 or 2 of those long tapered camel hair brushes around here somewhere).
There was a stripe masking tape, that was precut lengthwise into numerous strips. The tape was applied like regular masking tape (about 1" wide), then you could pick out separate strips, You'd spray a color over the tape, and when the remaining tape was removed, you'd have consistent-width parallel stripes. Kinda cheesy, but somewhat less cheesy than vinyl striping tape.
WB ......... metalworking projects www.kwagmire.com/metal_proj.html

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Put the tube on two saw horses. Put a clean bucket under one end. Raise the far end up a bit on something so paint will run down the tube and into the bucket. Pour paint into the raised up end. When all the paint has run out into the bucket, empty the bucket into the paint can. Rotate the tube 90 degrees and pour paint again.
This also will work to clean the tube with solvent before painting.
A bit messy, but you shouldn't have to buy any new tools!
Best regards, Paul Redmond, OR
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co snipped-for-privacy@yahoo.com wrote:

That sounds like it would work even with small tube, Paul. Very clever indeed. I might thin the paint a little, as your method may put on a very thick coat.
Also it would have some issues if the tube had holes drilled in it, but you could always paint first and drill the holes second.
Grant
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you
Or as they say, you could just put a cork in it.
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About the time I had mastered getting the toothpaste back in the tube, then
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On Monday, July 16, 2007 at 3:17:43 PM UTC-6, Grant Erwin wrote:

Tie a sponge to a wire. Put wire threw the tube Fill sponge with paint Pull sponge threw tube. Repeat until happy with the results. Same process for removing rust using the product of your choice Pulling a chimney brush threw a 4" tube works for me. Even wrap clumps steel wool and pull it threw. The options are endless
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On Wed, 4 Oct 2017 04:55:08 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

Fill the tube with paint. Pour out.
Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca
void _-void-_ in the obvious place
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