Choice of grit and gun size?

[steve_d]

Hi
Will be setting up a grit blast room to strip rusty tubular steel car chassis.
Can someone advise:-
Type of grit and grade to use?
Size of gun to use?

When I know the gun to use I will have the required CFM.
So any ideas on how to find out what my existing compressor produces as there is nothing marked on it?
As a general guide the tank is about 2' dia. by 5' long with a 2 cylinder 3 phase pump on top. the whole lot stands about 4' high.

Many thanks
Steve

 

[brightspark]

what hp motor is fitted . u realy need a pressure pot . jet size depends on cfm output

 

[steve_d]

Already had the pressure pot in mind.
Will find the motor spec in the morning.

Thanks

 

[frank horton]

been there done that to a 1928 Citroen C4 chassis...(amongst others)..rebuilding the vehicle (Pick up)........
had 2 large worshop compressors running side by side, blew 1 motor then wrecked the comp pump on the other cos they were running full time....using a largish press pot from ebay £100'ish...size of a dustbin....bough kiln dried sand in 25kilo bags, diff grades......
anyway, so, luckily adverised in the local rag a tow along with a rotary/screw pump ???? and a rebuilt engine .....cost a grand but as it's cleaned several chassis now have got me money back.....

unless u have a huge comp and can afford the elec don't bother, just get a firm to do it......it's not mad dear and as soon as it's cleaned they can/will paint it in primer......otherwise it starts to rust before ur very eyes........
most 2 cylinder workshop compressors are only just man enough to run a sand blast cabinet........they don't like to run full time and then u have to stop the dust getting into the inlet and standard comp filters are not up to it and then there's the condensate......
incidentaly my tow along is always 50m away from the work in progeress.........
got a quote for doing my chassis and body panels, dry sand blast and paint in special Zinc primer was £800 from a firm in Brum.......was happy to do it but transport cost's made me think again.......
YES I have a very understanding wife........hahaha.........when I pop me clogs she's gonna have some sxxt to clear out ....hahaha.........Frank

 

[steve_d]

Been using a number of blasting companies over the years and they basically don't want to know.
The chassis are powder coated (albeit 20 years ago), have flaking rust, waxoil, grease and oil all of which contaminate the grit at the blasters causing problems on their next job. All the time they have piles of newly welded railings or equipment cabinets to do they are not interested in our one chassis per month.

 

[steve_d]

Decided not to even look at existing compressor as research would suggest it is never going to be big enough. Also it is in a sound deadening enclosure with loads of stuff dumped on it which I could not justify moving.
Looks like a road drill compressor will be called for.

Steve

 

[brightspark]

if u go down diesel screw compressor route the mimimum cfm would be a 80 cfm pump . at that the jet size would be a 6mm jet

 

[henry Kadzielski]

^^^ That would be at best. A 6mm jet will still take quit long time. There is no substitute for air volume and grit being thrown around to get the job done faster. A 3/8 nozzel with a air fed blasting helmet will require about 250cfm at 100psi at the nozzle. Then you have the condensate to deal with and you will have to deal with it. Garnet is the most freindly to use and can be reused if it can be contained. A grit recovery system is then a great advantage.

 

[sasquar]

road compressors kick out lot and lots of water, bad idea, trust me on that one unless you have a big chiller.

I would seriously reasses getting someone to blast it for you, but then i work for a blast company, so i would wouldnt i!!
Get it blasted, hot zinc sprayed and primed. Yes it will cost you a few hundred quid, but it will save you tonnes of time and messing around, and be a far better job.......

MOD edit language

 

[brightspark]

dunno what I have been doing for the last 35 years after blasting loads of wheels motorbike frames and other parts along with sandblasting 3 houses and never had a problem with water on my diesel screw pump. once the gears hot there is no water and u can run all day without having to touch the grit valve or anything else

 

[steve_d]

Sasquar
We have used a number of different blasting companies but they are not interested and just mess us about which is why we are going down this route.
As you say it would seem to be more cost effective to outsource but only if they perform which up to now they have failed to do.
We have one chassis away for blasting at the moment, it took them over 3 weeks to come and collect it.

Steve

 

[sasquar]

fair enough, if youre not getting the service that you need, then as you say, the only option is to look after it yourself. I would strongly suggest using crushed glass as a media unless you have a dedicated room to do the blasting in. Its cheap enough to not worry too much about reusing it (although youll normally be able to recover and reuse it a few times anyway). If you do have a dedicated room for it, then you could look at using chilled iron. Its more money, but it will last a lot longer that the glass and remains sharp for a lot longer meaning youll get a lot more done. Does need to be kept really dry though, otherwise itll just rust up and cause you no end of issues.....

 

[fizzy]

Whilst a huge compressor is a Godsend for blasting I have managed a few LR chassis using a 14cfm Clarke with a 10 gallon pressure pot blaster. Yes it takes a while but it does the job. I use black grit which works really well - think it is reclaimed slag from a steelworks.

 

[sasquar]

close on the black grit, its called 'J blast' and the leftovers from making copper i believe. also, relatively expensive and hard to get compared with glass. When i say 'hard to get' im working on the assumption that people dont want to buy a pallet (1T) at a time.......

J blast also leaves horrible black dust everywhere, think coal mine type effect..... it is good though!!

 

[rtbcomp]

One thing I did find with J-Blast is that being black it absorbed all the light in my blast room. Glass is much lighter and reflected the light, making it easier to see.

 

[fizzy]

I did try normal sand once. Forget the health and safety stuff - it looked like the sort of sand storms I used to get caught up in the Middle East!

 

[brightspark]

I did try normal sand once. Forget the health and safety stuff - it looked like the sort of sand storms I used to get caught up in the Middle East!

kiln dried used in the correct proportion on any size pot 80 percent air 20 percent sand @ 90 psi is very efficient and not a lot of stray sand flying all over