??? - atomizing holes in air cap - number/pattern

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PostPosted: Sun Jul 08, 2018 4:48 pm
hello - noob, first post, and hope this isn't any kind of dupe question. getting back into painting after 25+ years - last paint work was 1991, lacquer, with an old devilbiss jga-502 suction gun, so it's been awhile. never done BC/CC. anyway, back to my question. on air caps (various hvlp guns) - does the atomizing hole pattern and number of holes, in the air cap make any difference in spray patterns? do more holes atomize better? any relation between number of holes and material's viscosity? anything in relation to BC and clears - more holes better for clears? is it just a relationship between the air cap profile and the fluid nozzle profile? I've seen the number of holes from one hole on each side of the fluid port, two holes each side, either horizontally or vertically, three holes, each side, in a triangular pattern, and four or five holes, each side in a circular pattern around the fluid port. i'm assuming the number and hole pattern have some effect on the fan pattern, but what about the overall atomizing? confusing as hell, and can't seem to find anything on-line! as I said, just getting back into this. thanks for any reply comments....



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PostPosted: Mon Jul 09, 2018 2:57 am
Hello and welcome to the forum.

I posted up this link recently and it applies here too.

Watch the video and the other videos he's linked - should explain most of your questions.

https://www.youtube.com/watch?v=8-3re8Z_NLw
Chris



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PostPosted: Mon Jul 09, 2018 6:50 am
thanks for the reply. I've watched a bunch of the gunman's videos - learned a lot. that guy's got some serious talent. in your posted link, he's leaning toward a non-hvlp or conventional gun. this is all good, and I fully understand what he's talking about. I would still like to give the hvlp thing a shot - I ran some "cfm" tests on my compressor using an old star hvlp (1.9) gun. and my old 7 HP/60 gallon tank didn't miss a beat, so i'm fairly sure i'm good in that department. I've also plumbed a hvlp dedicated air line with hvlp disconnects and a 3/8 hose. again, I think i'm OK.

as for guns, I came across a binks m1-g, new in the box, and this is what's driving this effort. from what i'm reading, it's not the best for "clear" so i'm looking at the sharpe finex fx3000 (1.3) hvlp. what's interesting now, the sharpe fx2000 is the conventional equivalent. most likely the basic guns are the same with only the air/fluid nozzles and needle differ. this might be an option. I need more of the middle of the road gun - not high dollar, and not harbor freight.

anyway, i'll be taking baby steps here and will be doing some panel repaint on my old 85 corvette. still curious about the atomizing holes/pattern in the air caps.

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PostPosted: Mon Jul 09, 2018 9:34 am
I might be able to answer a little of the tech. on the holes thing.....I was a former Capspray dealer (this is turbine systems I am talking about) and also eventually built/sold my own turbine gun systems. When I could, I went to rep. tech. meetings about gun types (again turbine talk here) and needle/air cap combos. It was a real snoozeathon but I tried to stay awake..... There is kind of a correlation between guns going from low fluid transfer efficiency ( more fluid throughput and a few holes) to higher efficiency (less fluid throughput and more holes). Our early turbine guns had the two standard "air horn" holes like most guns and two tiny holes on the air cap close to the fluid nozzle. Simple air horn holes establish the pattern and the small holes "smoothed" the pattern making for less of a"sandy" outer edge to the pattern. What started driving the more holes things with our guns was the heated air supply, high cfm, and low pressure. It was found that doing a ring of laser drilled small holes would soften the outer part of our pattern. I can't really comment too much on regular HVLP, LVLP, RP guns but I would think the same principles apply. As the guns have become more efficient they have needed more refinement in the air cap.
Just an opinion....but I wouldn't get too hung up on the holes issue. You can do more to control how the shoot goes by reading your p. sheets, observing viscosity rec.s from your gun maker using a viscosity cup, having plenty of pressure/cfm for the shoot and as Paint Dave has pointed out recently, watching TEMPERATURES (ambient air, the car itself, temp.s over the cure period, etc.)
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!

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