brightspark
Member
- Messages
- 40,165
- Location
- yarm stockton on tees
ive just showed the pot and choke valve fitted on the air pipe half way down
- Thread starter fizzy
- Start date
henry Kadzielski
Member
- Messages
- 1,208
- Location
- Australia Wollongong
My two cents worth.
I have used a 3/16" nozzle with a 10hp compressor (rotary screw) and a air fed helmet and no good, too little air and the blast pressure dropped, thus the blasting speed dropped. With no helmet I could see that you can get away with that, but that's the limit. I upped my 10hp to a 15 and now no trouble with the air fed helmet and 3/16" nozzle. I can almost get away with a 1/4" nozzle for short bursts. I have done blasting for a crust so you do notice the speed differences and no customer wants to wait. If you are faster you can charge more anyway.
I don't as much blasting anymore, I prefer to do the repairs / upgrades on pots, blast rooms and paint equipment, in the workshop it is environmentally much better
That is about right, however that is also the min size compressor capacity for that nozzle size. The other thing that you may or may not know, blasting speed measured as a % is determined at 100psi at the nozzle. 1psi over 100psi at the nozzle will give you 1.5% increase in blasting speed at the same grit consumption, with the converse also true, for every psi under 100psi at the nozzle will result in 1.5% reduction in blasting speed. Thus at 150psi at the nozzle will result in a 75% speed increase for the same grit consumption. That is very noticeable. Grit control is also very important, there is a sweet spot for the amount of grit being thrown at the job, when you look through the blast stream you should not see the hue of the grit being used, only the like mist out of the nozzle. I generally use 30/60 grit for most jobs to knock of larger chunks of rust, old paint and other stuck on crap. However on clean jobs I have used 80 mesh grit (normally garnet) as it cleans faster and gets into smaller areas with it's smaller particle size.
I have used a 3/16" nozzle with a 10hp compressor (rotary screw) and a air fed helmet and no good, too little air and the blast pressure dropped, thus the blasting speed dropped. With no helmet I could see that you can get away with that, but that's the limit. I upped my 10hp to a 15 and now no trouble with the air fed helmet and 3/16" nozzle. I can almost get away with a 1/4" nozzle for short bursts. I have done blasting for a crust so you do notice the speed differences and no customer wants to wait. If you are faster you can charge more anyway.
I don't as much blasting anymore, I prefer to do the repairs / upgrades on pots, blast rooms and paint equipment, in the workshop it is environmentally much better
Ahh I just thought it was called the air valve. Yes that one is wide open it is only the grit valve that is opened a crack.
Erie Fred
Member
- Messages
- 4,824
- Location
- Erie, Pa USofA
Are you using some form of valve at the nozzle ?
Erie Fred
Member
- Messages
- 4,824
- Location
- Erie, Pa USofA
Yes, I see that, we were typing at the same time.ive just showed the pot and choke valve fitted on the air pipe half way down
Thank you for posting it, saved me some work.
Yes but I always leave that wide open.
And talking of nozzles can anyone recommend the best type to use? My ceramic ones are only lasting 2 hours or so.
Erie Fred
Member
- Messages
- 4,824
- Location
- Erie, Pa USofA
Just remove it.
I don't seem to get that fast of nozzle wear.
How do you start up each time ?
Walk me thru each step, I'm sure we can spot a problem that's causing your troubles.
Dcal
Member
- Messages
- 3,958
- Location
- Antrim Northern Ireland
I use these on a similar blast pot.
I've put tons of grit through it and it hasn't worn appreciably.
I installed it in a straight compression fitting so I can just unscrew it if there a blockage.
I've put tons of grit through it and it hasn't worn appreciably.
I installed it in a straight compression fitting so I can just unscrew it if there a blockage.
I am not really having trouble with the finer stuff. It was just the glass grit was far too coarse for my nozzle.
Metering valve a bit hit and miss so will replace with the Clemco style
Nozzles wearing out too fast.
That is all really.
Erie Fred
Member
- Messages
- 4,824
- Location
- Erie, Pa USofA
I thought you indicated having trouble with the sand air ratio & clogging ?.....
What CFM? My compressor is a 7.5hp 3 phase I think about 28 - 30cfm. Will I be able to run a 4mm or even a 5mm which is around 3/16"?
No it was fine when I switched - got a few problems towards the end but I am sure that was down to the mixing valve. Give the unit a few shakes and it would run again - material may have been a bit damp which wouldn't have helped.
Erie Fred
Member
- Messages
- 4,824
- Location
- Erie, Pa USofA
Just consult the charts.
Dcal
Member
- Messages
- 3,958
- Location
- Antrim Northern Ireland
A 3mm is too big for a 3hp compressor, but just about ok for what I normally do.
I've another 3hp that I can use when I need more umph.
A huge nozzle is all well and good (I know 4mm isn't big) if you have lots of rusty steel plate to derust, but it can destroy flat body panels, alloy or other delicate parts.
I've another 3hp that I can use when I need more umph.
A huge nozzle is all well and good (I know 4mm isn't big) if you have lots of rusty steel plate to derust, but it can destroy flat body panels, alloy or other delicate parts.
1/8th in or 3.2mm is about 28 to 30cfm. 3/16" they suggest 45 to 60cfm
I don't do delicate
I do have some thick aluminium lathe covers etc to do but I suspect a softer/finer media would be advisable?
When the glass grit did manage to flow the surface roughness was incredible!
brightspark
Member
- Messages
- 40,165
- Location
- yarm stockton on tees
a 28cfm compressor runs a 3.0mm jet just fine at 90psi a 14cfm peters out after a couple of minutes which is useless as the ratio of air and grit alters . 
a constant pressure is required or you waste grit and time
a constant pressure is required or you waste grit and timehenry Kadzielski
Member
- Messages
- 1,208
- Location
- Australia Wollongong
That's about right for continuous operation to maintain the pressure at the nozzle, sorry no if's or buts.3/16" they suggest 45 to 60cfm
Dcal
Member
- Messages
- 3,958
- Location
- Antrim Northern Ireland
a 28cfm compressor runs a 3.0mm jet just fine at 90psi a 14cfm peters out after a couple of minutes which is useless as the ratio of air and grit alters .
I agree, but if you have a compressor running at 150psi and have a pressure regulator set to 90psi just before the pot you have more than a few minutes.
For industrial blasting it's hopeless, but for cleaning up small parts it's certainly workable.
I tend to line up a few other jobs to do while I'm blasting because it gives the compressor a chance to catch up and because, if I'm honest, I don't like blasting so the break is welcome.
When I do have serious blasting to do, I get the lend of a road compressor.
What I'm trying to say is, just because you don't have access to a monster compressor and a Cemco pot, doesn't mean you can't blast.
However, don't expect to make a living at it.
I was running at 110psi - is that a bit too high?
