Air curtain blowing off powder paint

Letter 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
- White Rock, B.C. Canada

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
- 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. Everytime 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

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