Dry ice blasting

[MintJulep]

Does anyone out there have actual experience with dry ice blasting?

There is no shortage of information from equipment suppliers, which not surprisingly touts it as the best thing since sliced bread. I'm hoping for some actual user input.

My specific current possible application is copper fin HVAC coils, but I'd be interested in any uses.

 

[kepharda]

I have used this before for pre cleaning some metal before welding, previously we had a horrible system of using water ice to clean the parts.

The dry ice for us was way better, the old system was a maintenance headache, causing lots of downtime.

The new system was better, but you have to be ready to buy the feedstock and ensure you always have it on hand, but for us it was a HUGE improvement not only in downtime, but also we had less contamination overall because the production operators and maintenance personnel where not constantly getting in to "fix" freeze ups .

And not having to deal with the subsequent liquid water was nice.

this message has been approved for citizen to elect kepharda 2008

 

[unclesyd]

I have used CO2 blasting for numerous jobs and have been quite successful with some and complete failures with others. It would work quite well on most soils seen by HVAC coils, it is only the harder stuff that doesn't work.
I've never tried it on HVAC coil fins and don't believe that it would work due to the mass effect of CO2 pellets bending the fins. It was the same with soda blasting (wet and dry}, walnut shells,
and corn cobs.

I've tried water pressure from 90 psig to 35,000 psig. It is strange to say the 35K caused less damage with the proper angle of attack. It was so critical that it would have to be machine guided.
I have a system in effect on several coil banks where I use 2000-2200 psig water +additives to wash the coils. Again the secret is the angle of attack which has to straight on or parallel to the fin as any other angle will bend the fins. The tracking system work in vertical direction with the tubes being horizontal.

 

[MintJulep]

The particular coils in question are located in the ceiling of subway cars.

Removing the coils is an unattractive option due to the amount of disassembly that would be required - so an in-situ method of cleaning is highly desirable.

Any form of "wet" cleaning would certainly create a horrible mess.

 

[unclesyd]

MintJulep,
I hate to say it but you have a problem.

Back to the OP. All my work was with fairly large pellets, mostly around 9 to 12 mm in cross section. I understand that they make smaller pellets that may work in you case if the the spacing on the fins is wide enough. This assumes that the blasting stream is straight on parallel to the fins face. I would check around and see who offers the smaller pellets. If you have a scrap or spare coil I would ask for a demonstration with you watching.

What are the tubes/fins?

what is the fin spacing?

Do you have access to both sides of the coil?

We cleaned some vent fans while they were running with very fine corn cobs as the fans actually exhausted the grit and soil outside. We also cleaned some of the very dirty vent fans by shutting them down and enclosing the fan inlet with cotton sock that dropped into a drum and we blasted from the discharge side of fan toward the drum. Taking a similar approach with the sock and drum you may be able to generate a workaround to the messy part.

HVAC fins can generate some nasty soils to clean.

 

[MintJulep]

Yeah, it's a challenge.

Fins and tubes are both copper. Fin spacing is either 10 or 12 fins/inch, I'll need to count that some time.

There is ok access to the air entering side, but not enough to get straight-on access to any kind of "wand" without a 90-degree head. The air leaving side is obstructed by electric resistance heating elements. The coil is 6ish inches deep.

 

[zekeman]

Why don't you post this on some of the HVAC forums where the pros have mucho experience cleaning coils with other agents that may not leave residue.e.g.

http://hvac-talk.com/vbb/