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View Full Version : Why won't this work? (sandblaster)



torker
07-24-2008, 12:39 PM
Hey guys.. I got the gun issue fixed.. it was plugged with the wet sand it had in it. Got that cleaned out.. put the sand out in the sun for a long time...stirred it around..it's dry as sugar.
Got over 100 psi to the gun.. it's blowing good but will NOT pick up any sand.
Can anyone see why?
The bottom "T".. the pipes are about 1/2" id. Is that too big...or is this thing just designed wrong? I think i see why the guy sold it to me now.. I don't think he ever got it to work.
http://img.photobucket.com/albums/v210/torker/DSC00001-72.jpg
I buried one end in the sand..even scooped some up with it first. The pipe/hose is clear...you can blow thru it easy..
http://img.photobucket.com/albums/v210/torker/DSC00002-49.jpg
Here's what the pickup looks like (homemade)
http://img.photobucket.com/albums/v210/torker/DSC00003-32.jpg
Thanks for your help!
Russ

RetiredFAE
07-24-2008, 12:46 PM
Russ, try capping off one end of that pickup with some duct tape, trigger the gun and put your finger over the other end of the pickup. Feel any suction at all? If not then there is something wrong with the venturi tube inside the gun would be my guess. That pipe is half the diameter of the one inside my cabinet, and mine works fine with 100 PSI and abour 8 CFM of flow.
The little venturi sube in mine once got turned partially around (its a small pipe with one end cut at a 45 degree angle, then threaded into its place inside the gun) and that stopped the vacuum production until I turned it back and Loc-Tited it in place.


Steve

oldtiffie
07-24-2008, 12:53 PM
Russ,
I'd suggest that at least part of the problem is at the "pick up" as the sand from either end has to "turn the corner" in the "T" at high speed. Further if either end comes out of the sand and sucks air you will lose vacuum - and sand.

Why not just remove the "T" and have a straight "lance". I'd also suggest having a look at the pick-ups in the commercial blasters next time you are in town.

What happens if you drop the pick-up into a bucket of water and turn the gun "on"? Does it pick up water and maintain vacuum?

Is there a pipe in the air flow (to create the vacuum) missing in the venturi in the gun?

Some "ready-for-use" sand that I've seen is in a self-feeding hopper with the "pick-up" well under the top surface of the sand.

From what I've seen previously here, there are plenty with lots of knowledge about these blasters.

How is the sore chest and ribs - OK and just bruising I hope. Best of luck.

Lynn Standish
07-24-2008, 01:09 PM
Have you checked the nozzle? If the size isn't right it affects performance. Also there are ceramic nozzles available to reduce the wear on the nozzle from the abrasive and make them last longer, but you could turn some different sizes up on the lathe to see what diameter works best for you.

torker
07-24-2008, 01:13 PM
Thanks guys! I'll try your suggestions. I was under the impression that the pickup needed to suck a bit of air in order to "pick up" the sand???
LOL! The ribs.. I'm a hurtin unit this morning. Walking around like an old crippled guy ;)

Dragons_fire
07-24-2008, 01:24 PM
you should be able to feel significant suction on the end of the hose..

ive got the same gun (i think, or at least the same design) and usually run it around 80psi and it can suck sand straight up through 10 feet of hose.

most of you guys are like me and enjoy trying to fix stuff, but if you get tired of playing around with it, you can buy those things for about $30

oldtiffie
07-24-2008, 01:26 PM
If the sand is dry there should be enough air in the sand between the grains to get and keep enough velocity to carry the sand. Exact opposite if it is wet - no go at all!! Just like sucking wheat (which has also been used a s blasting/cleaning medium at times). The sieve size of the sand may be important too. Re-cycled/re-used sand may not be sharp enough?

What's the diagnosis on the sore ribs - bruised (I hope), or cracked or broken (I hope not)?

torker
07-24-2008, 01:26 PM
Bingo! You got it tiffie! I just took the T off and stuck the hose right in the sand. It started spraying right away. The nozzle is 1/4"...seems a little big to me. It doesn't seem to blast very hard for the amount of air going thru it.
A smaller nozzle should increase the velocity right?
Didn't do much with it. This hamemade POS leaks dust like crazy. It's inside the shop so i didn't want dust everywhere. Needs more silicone for all the precision joints he made.
Thanks!
Russ
(Just got a call...my new motor is in for my ironworker!!!)

Oldbrock
07-24-2008, 01:33 PM
I have one of those and it does tend to get plugged up with damp sand but you say you have cleaned it out. Just pull the feed hose off the gun and see if there is any suction at that point, If not the venturi could be turned as previously stated. That's the only thing that can stop such a simple thing working. You probably did some rib separation when you fell if you didn't break one, just as painful. Go have a picture taken just to be sure, you don't want them setting bent. Being a limey I can't skate but got talked into playing hockey one time and got checked into the boards resulting in separated ribs and know what that feels like. You're not as young as you used to was. Peter

jamscal
07-24-2008, 01:35 PM
I have a pickup tube and then have another length of copper pipe attached to the side of it.

The end of the pickup and end of the copper are adjacent. The copper tube is a sort of snorkle that always allows some air to get down there, facilitating media pickup.

-James

Dawai
07-24-2008, 02:14 PM
I was playing with that toy sandblaster we had here.. I learned something..

http://www.youtube.com/watch?v=ZohlbjzzSFY

ANYWAYS what we learned.. take the quick connectors out of the air lines.. they are a small orifice.. screw the hose to the blaster..

aboard_epsilon
07-24-2008, 02:35 PM
the tube has to pick up air and sand at the same time ...
so the pick up tube should be chamfered at 45 degrees

all the best.markj

pcarpenter
07-24-2008, 05:44 PM
The end of the pickup and end of the copper are adjacent. The copper tube is a sort of snorkle that always allows some air to get down there, facilitating media pickup.

-James

That helps me explain the theory behind a similar suggestion I got from somone here. My HF blast cabinet would not move much material. The suggestion was to braze a washer on the end of the tube such that the hole in the washer formed a smaller orifice for the tube end. My guess is that this has the same effect. It prevents it from pulling in so much sand that it binds up in the tube. While aluminum oxide is certainly not as "stackable" as salt grains, many here will remember the discussion about pouring tubing full of salt before bending to keep it from collapsing.

My guess is that the abraisive is pretty much doing the same thing by binding on itself inside the bore of the tube.

I really need to remember to grab that tube the next time I have the welder fired up and see if that doesn't fix the problem.

Paul

torker
07-24-2008, 07:35 PM
I played with this for a few more minutes. It's sorta "pulsing" after the first 30 seconds or so. I'm guessing it maybe should have a snorkel deal?

Paul Gauthier
07-24-2008, 07:54 PM
I use play sand in my homemade blaster, I think I have the same gun you have, looks the same. In my experience sand does not last long and must be replaced, breaks down, gets dusty, dosen't suck well at all. When I change the sand goes right back to good.

wierdscience
07-24-2008, 10:48 PM
I played with this for a few more minutes. It's sorta "pulsing" after the first 30 seconds or so. I'm guessing it maybe should have a snorkel deal?

Pulsing usually means the sand nozzle is too big,make one out of drill rod with a smaller hole,like 3/16" with a 60* cone machined (centerdrill) in the backside.Heat treat it and leave it glass hard.It will last for awhile.

dp
07-24-2008, 11:47 PM
I made a pickup tube from 1/2" electrical conduit. It's about 18" long. Near the base there is a 1/4" hole drilled in each tube and they are connected with a bit of plastic tubing. The bottom of one tube is flattened and sealed and the bottom of the other is open to allow sand to enter. Air enters the other end of the sealed tube and is passed to through the plastic tubing to the other tube. The extended tab prevents the pickup tube from sucking it's way to the bottom of the bin and getting blocked. A picture being worth lots of words,...

http://thevirtualbarandgrill.com/machinery/sandblasterpickup.jpg

J. Randall
07-24-2008, 11:59 PM
I agree with Weird, if you don't have any drillrod you could also use castiron to experiment with. After you form it heat it cherry red and quench it with a blast from an air nozzle, it will get pretty hard.
James

torker
07-25-2008, 08:02 AM
Dennis..Thanks for the pic!
Also.. I'll try a smaller nozzle. I have some O-1 looking to be sacrificed for something like this.
Thanks!
Russ

motomoron
07-25-2008, 01:54 PM
After fighting for a few years with a very nicely shop-built blast cabinet I'd been given, I finally gave up and went to TP Tools (http://www.tptools.com/)for a gun/suction tube/tips/gloves/window liner setup.

Immediate improvement. Actually works. I'd have saved 2 weeks of blasting on a car I restored.

At the spring Carlisle PA swap meet, where TP Tools has a retail store set up, I picked up their dedicated blast cabonet vacuum supply as a scratch and dent for about $200. It was the missing part of the puzzle. Having a depressurized cabinet dramatically improves media flow consistency and visibility.

GKman
07-25-2008, 06:41 PM
After solving suction problems with solutions like listed here, I still have feed problems due to condensation. High atmospheric humidity, compress, cool, then rapid expansion at the venturi are perfect conditions to get a LOT of moisture to condense out and mix with the sand in this area. Sometimes pulsating sometimes just clogging. Cold dry winter weather - no problem.

dp
07-25-2008, 07:07 PM
After solving suction problems with solutions like listed here, I still have feed problems due to condensation. High atmospheric humidity, compress, cool, then rapid expansion at the venturi are perfect conditions to get a LOT of moisture to condense out and mix with the sand in this area. Sometimes pulsating sometimes just clogging. Cold dry winter weather - no problem.

I think TP Tools sells vibrators for the bins to keep the sand moving. Also seems like they'd make a lot of noise. That got me to thinking a simple motor with a paint stirring wheel on it near the suction tube might keep the sand from compacting.

oldtiffie
07-26-2008, 11:37 PM
Thanks for the prompt Dennis.

"Angle of repose" is really what most granular loose material movement (or non-movement) relies on.

http://en.wikipedia.org/wiki/Angle_of_repose

http://www.google.com.au/search?hl=en&q=angle+of+repose&meta=

The AOR will change with the dryness - or lack of it - in sands etc. Hoppers on animal feed bins are a good case in point as are grain silos.

Vibration is a two-headed sword - too much and it will compact the material/sand and not enough will not move it.

Nozzles or apertures in an air flow stream work very well for venturi effects - up to a point. If the air flow gets too high the aperture will become "restricted" to the extent that it will pass little or no air (or any hydro-dynamic fluid - of which air is one). Try blowing down a drinking straw. While you are blowing slowly - all is well. As you increase the air-flow the aperture becomes more restricted until it seems to almost stop. Ask a local Structural Engineer about the effects of wind forces, gusting and "vortex shedding" etc. A "chain wire" fence can have the qualities approaching that of a solid sheet/wall at high wind velocities. This is also why small air hoses and apertures in tool-connectors cause such pressure drops in air lines.