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topic 11108

Air curtain blowing off powder paint


 

At the moment we have a line of powder pained panels going along a conveyor belt into a curing oven. There is an air curtain at the entrance to the oven to reduce heat lose but at the moment the powder is being blown off the panels by the air curtain before they reach the inside of the oven. Any suggestions on how to cut down lose without turning down air curtain velocity?

Sarah O'Hare
- N. Ireland


 

Sarah,

Having designed air wipes (radiator mfg) and seen others, the only idea that comes to mind is

l. Before the oven (where, naturally, you want to prevent heat loss), have not ONE air wipe but 2 or 3 'boxes' each having a LOWER airflow velocity air wipe.

2. Reduce, if you can, the 'aperture' size of the oven opening ... but if you can do this, then the air wipe speed/cfm must also be reduced.

3. These 'boxes' is just what I'd call an extension of the inlet to the oven. They can fairly large BUT in the centre you'd need a baffle arrangement to fit the size of your parts and the conveyor rail.

4. Lastly, you didn't say/mention just HOW the air wipes are constructed? A manifold with jets? A manifold with a slot? ... If the latter, I'd opt for an ajustable slot and have the plant engineer play around with airflows and the slot sizing. But first of all, measure the slot velocity for future calculations. If over 3,000 fpm, that's far too high for you. The other consideration is the distance from the 'slot' to the parts.

Just some thoughts. I hope this will help somewhat.

Cheers!

P.S. Some afterthoughts It's not fair to you if you don't have the right equipment. The Company should go & buy a velometer ... a thing for measuring air speed. An electronic one is best! The supplier should know what you are trying to do so that the 'best' one for the purpose is provided ... probably with a pitot tube.

freeman newton portrait
Freeman Newton
White Rock, British Columbia, Canada

(It is our sad duty to
advise that Freeman passed away
April 21, 2012. R.I.P. old friend).



 

Sarah,

Some amendments to the answers you've already got (by the way; these answers are basically correct)

1. There are different types of air curtains. I develop and build powder(and liquid)paint-ovens for over 25 years now. Principally, increasing the length of the air-curtain is a possibility, but often there is no space available. I had good results in re-designing and changing the existing curtain in such a way that the effectivity increases. One of the basic rules in this dre-designing is taking into account that hot air tends to come out of the oven at the top-third of the opening (normally there where the conveyor and the jigging is), whilst cold air from the workshop enters the oven at the downward third of the opening. The airflow in the curtain must be directed in a way that the natural airflows are stopped. In this case obviously the overall air-speed has to come down. A side-effect of such a change is that your oven-curve will be better looking and overall energy consumption will go down.

2. Install an IR-preheating section in such a way that the powder is just melting before entering the actual oven. Advantages:
- No contamination of the oven (and the parts) with powder particles flying around
- Better flow of the powder (less orangepeel)
- Convectional part of the existing oven can be altered to higher air-flows, thus faster heating up, therefore shorter oven necessary (or in production terms: higher conveyor speed possible).

Best regards,

Remmelt Bosklopper
Remmelt Bosklopper
- Enschede, The Netherlands


July 22, 2009

We have a 28 mtrs PCO with Vertical air curtain at both the ends. The oven temp is 230 Degrees. every time the door opens, considerable amount of heat loss takes place , though the air curtains are there in place. Seems as if the air curtain is ineffective.

What should I do to prevent heat loss.

Regards,
Khushal
India

Khushal kalra
Employee - India



May 15, 2012

Q. Hi we have a powder coating Line (conveyor type) about 35 years old, and we always add problem with the original air curtain, we are not able to add some vestibule at the openings so we tried to change the air pressure without good result , a have made some research on google but nobody seems to have the qualification to help us,

can somebody give me some advice or reference

can we have something to fix the problem for ever

thanks in advance for your help

Stephane Key
- Canada


May 18, 2012

A. Well the headline on this question was:
Air Curtain blowing off Powder.
The answer to this is a very positive reinforcement of the advice provided by the original respondent to this thread.
Stick an IR Bank at the oven entrance.
Not only will you have no more trouble with Powder displacement and the mess that is associated with it.
You will almost certainly have created the ability to increase line speed if your guns can handle it.
Hope this helps.
Regards,
Bill

William Doherty
Trainer - Salamander Bay, Australia



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