a Big regret in life is not being able to do "electronics" (hence the reason for joining here)
I have some ideas for upgrading some machines we are using in a new business venture...
basically modifying Sand Blast cabinets....
I could do what I want using relays pressure switches and electro pneumatic valves....
But I would like a more elegant way, and ultimately try to market the stuff to others...

Firstly is this the sort of forun where people would not only offer advice but perhaps if it involves circuitry someone make it (obviously such work would be rewarded and hopefully a small business arangement could be agreed shoul the idea proove sucessful)

I will draw up a sort of diagram and general principal of operation and post later...
the general idea is to control air in a pressure tank and shut off air and grit usinga foot pedal....
it is quite simple but i want to add a few extras to make it really nice

 

Welcome to AAC!

AAC forums provide a platform for discussing technical issues with fellow members from around the globe. Advice is provided at no charge. If two or more members wish to communicate in private they may do so under the private messaging facility after they have each reached ten posts.

Operating a sand blasting cabinet would appear to be relatively simple procedure requiring little electronics. We would be happy to assist you with your modifications. Looking forward to hear your requirements.

 

Welcome to AAC!

AAC forums provide a platform for discussing technical issues with fellow members from around the globe. Advice is provided at no charge. If two or more members wish to communicate in private they may do so under the private messaging facility after they have each reached ten posts.

Operating a sand blasting cabinet would appear to be relatively simple procedure requiring little electronics. We would be happy to assist you with your modifications. Looking forward to hear your requirements.

Yes a sand blast cabinet is a simple operation, but it has been done the same way for years and that may not be the most efficent just "done that way"...
the majority operate as "Suction feed" this means that media is sucked into the blast gun and projected out.. however this is very inefficient and slow, as it is hard to creat a large vaccum to suck suffient media a a constant flow rate.
an alternative is to put the media in a presurised tank and thus more media can be fed under pressure, however these tanks are usually external addons and require refilling when empty...
Expensive professional systems utilise a tank that the media is recirculated into, but this requires depressurisation to refill, and often this depressurisation is every time you stop blasting, so even if for 5 seconds to turn something then requires a 1-2 minute represurisation.. so my thopughts are to control this refilling and depresurisation....
Also the media has to be fed at a certain rate controled by a valve (manually) an set differently for different media or nozzle size, again I visulise a means of beinag able to control this and change at will...
I have the general ideas of what can be used to achieve these things bu there are improvements and "nice to haves" that would make it better.... In adition my view is that this system could be self contained and thus used with any machine and tus allowing peopel to change te mai cabinet to a larger one and keep the pressure b;last sytem which woul be an investment...

 

I don’t know the jargon you are using, I am assuming that “media” is the “sand” used in sandblasting.

If I understand you correctly, the media was traditionally moved by suction, but an improved add on has a pressurized tank that pushes the air and media instead of pulling.

The problem is that this pressurized tank only holds so much, and must occasionally be de-pressurized and reloaded. This takes time. Let’s say 3 minutes to reload every 12 minutes, so the system is down 20% of the time (3/15).

The obvious solution is to make it bigger. Hopefully, the run time would double and the reload time would not, hence the percentage of up time would increase. Since it is the obvious solution I assume it has been tried and failed.

 

I don’t know the jargon you are using, I am assuming that “media” is the “sand” used in sandblasting.

If I understand you correctly, the media was traditionally moved by suction, but an improved add on has a pressurized tank that pushes the air and media instead of pulling.

The problem is that this pressurized tank only holds so much, and must occasionally be de-pressurized and reloaded. This takes time. Let’s say 3 minutes to reload every 12 minutes, so the system is down 20% of the time (3/15).

The obvious solution is to make it bigger. Hopefully, the run time would double and the reload time would not, hence the percentage of up time would increase. Since it is the obvious solution I assume it has been tried and failed.

Hi yes media is "Sand" but sand is not used can be anything from Walnut shell to Aluminium oxide...

Making the tank bigger is not really a great solution, in the vac system the media recirculates so you only top up probably once per day, and if you have 25kg an double that .. then decide to swap media you have a lot of media to take out..
In adition not only does teh tank have to be bigger bu the blast cabinet has to have a hopper that can store that much media, often 25kg is about the norm....
I have tried the seperate external tank, and if you had large enough tank and blaster, 50kg of media could last 30mins, so you woul be constantly stopping, emptying and refilling, and no matter how good you are media always ends up all over the floor..

the best presurised solution recirculates the media but they are either very expensive, machine specific or depresurise the second you stop blasting, so if you could prevent depresurisation (easy with valve) and only depresurise when the tank is low on media than as you rightly point out the system becomes much more efficient... simply if lasting a complicated object you may stop and turn/reposition every 30-60 seconds...

the media useage is directly related to the flow rate, ofte controlled by a manual ball valve, I know there are various electrically controlled valves that could be remotly operaed to allow this flow to be altered, e.g if the flow was zero and teh air supply cut off then the tank would remain presurised, if you wanted to depresurise simply applying power to a solenoid valve to open would do that....
My initial thoughts are what I would call "Heath Robinson" clunky but would proove the idea..
e.g two buttons to control the flow valve, but to shut off the flow would require pressing "close" everytime you paused, it would not be hard to detect when the blasting was paused an instantly close this, and upon starting press "open" but wouldn't it be better to automatically detect the pause an close the valve, then open at the same position when blasting resumed...
pressure switches could detect blasting pause/restart..

There are other "nice to haves"
Some sort of scale to indicate "Flow Rate" (probably an arbitary value but in relation to teh valve opening flow rate 0= valve close, flow rate 10 valve fully upen)
That would alow a simple table Aluminium Oxide medium, Flow rate 3, Walut shell Flow rate 8, Medium Crushed Glass Flow rate 6...
that would allow you to change media and not have to test to get the best performance again....

Control pressure electronically rather than a manual pressure regulator....
Differen media and things being blasted require different pressures...
(and we have not added Nozzle size into the mix)
there are a lot of variables to achive the best performance, sure it woul be great to have 1 cabinet 1 media, but that isn't always possible, nor 1 cabinet 1 media that does for everything....
but being able to reproduce the ideal setings quickly and repeatedly are again my thoughts...

Perhaps I am looking at a Rolls Royce solution to what is basically a Grey Furgie.

 

I wonder if you could use two tanks, and have them switch source and sink (recovery) roles periodically.

What I have in mind is something like this:

As the blasting is being done, the source tank is always pressurized. Even if the operator stops, the tank remains pressurized waiting for a restart by the operator.

The sink tank is continuously being filled by the recovery mechanism. Once the tank is full, or the source tank is nearing empty, the recovery pauses (though the operation of the blaster doesn’t) and the sink tank is pressurized.

Once pressurized, the source and sink roles are swapped on the fly, and what was the sink tank is now source, source is de pressurized to allow it to become sink, and recovery resumes to the “new” sink tank. This would possibly include some sort of make-up high flow pressurization to avoid a race condition.

The same sequence is repeated. For changeover to a new medium perhaps there could be a two hoppers: one for the new media and one for the currently loaded. The new hopper would be filled with a specific amount of the new media. The blasting system would pump the current media from both source and sink tanks into the old hopper, then pump the new hopper contents into the current source tank.

The source tank would be pressurized and you are ready to go. The old hopper would have a bottom mounted gate and use gravity to empty the contents. Alternatively, the hoppers could be removable and used to store various media. Once the new media is loaded, that hopper becomes the old hopper for subsequent changeovers and the roles alternate, much like the tanks.

 

Perhaps I am looking at a Rolls Royce solution to what is basically a Grey Furgie.

I think you have got it.

You said it can operate for 30 minutes then shut down for 3 to reload. The is 30/33 = 91% time efficient.

Lets say you could double the run time with the reload time staying the same. That would get it up to 95% efficient. So a 4% increase in production. But at what cost?

I think you are well into the territory of diminishing returns for any improvement, which is why no one is working to improve it.

 

I have on occasion used the sand blaster in our shop. I do not recall having to wait for the sand (aluminum oxide) to recharge.
The unit is operated by pressing the trigger on the nozzle of the pressure hose if I can recall correctly. I think the abrasive was automatically recycled, but I could be wrong.

 

I think you have got it.

You said it can operate for 30 minutes then shut down for 3 to reload. The is 30/33 = 91% time efficient.

Lets say you could double the run time with the reload time staying the same. That would get it up to 95% efficient. So a 4% increase in production. But at what cost?

I think you are well into the territory of diminishing returns for any improvement, which is why no one is working to improve it.

it takes 3 mins to represurise immaterial of refilling or not, you could use 100g of media but if you pause it depresurises, so if you blast for 5 seconds, pause you must wait 2-3 mins to represurise, so if blasting something than needs turning every 5-10 seconds and you have to turn 10 times...
for 1 minute of actual blasting you have 30mins of down time waiting for represurisation between pauses...
you cannot simply say "blast for 30mins" if you have to let the gun go and media fly about everywhere while you use both hands to turn something....

with a presurised system where you can stop the depresurisation till you need to refill you can blast till all the media is used that could be 30mins then have a 3min refill and presurisation so then you get your efficiency values...

you need to really have used a blast machine to understand the problems....
2 tanks are not really viable, as that creates other complications....
then you would have to have to double up on other things...

the Rolls Royce is't unobtainable and I believe woul make things much more efficient...
as I have said I have the system in "development" just I believe it can be improved...
Basically buttons relays, solenoid valves pressure switches etc will do the job, but I am seeking to improve that...
to maintain pressure simply close the media valve, at the moment that consists of pushing close media, it would be nice for that to be automatic when you stop blasing and delay cutting off the air till that happens (probably could do with a relay with a delay)
when blasting stops air supply is cut, using a simple solenoid valve normall closed - cut power valves closes, tank remains presurised...
start blasing, air solenoid opens, and press open media button.... the nice bit would be to be able to have the media open and close position "remembered", should you require to refill, stop blasting and automatically close when you stop blasting.. then press a refill button that simply vents the tank, there is a musroom valve inside the tank that drops allowing recycled media to refil the tank, release the button valve closes, start blasting, air valve opens tank represurises, press open media valve..

The tank sits below a media recycler that sucks media/dust from the bottom of the blaster an removes the dust, the media falls to the bottom above the blast tank waiting to refill when needed...

i is a working system that just needs some automation improvement..

 

the Rolls Royce is't unobtainable and I believe woul make things much more efficient...

Of course not, but if you operate a taxi service do you choose the Rolls as your vehicle? Why not?

 

Of course not, but if you operate a taxi service do you choose the Rolls as your vehicle? Why not?

depends on the clientele....
I know a guy who runs a car hire business.. he only hires out Aston Martins..
His friend runs a taxi business you may call it executive limo hire he uses Rolls Royces

I run our business and it takes some skill not to damage rare car parts.. and to set up the equipment epending on what you are working on..
but I cannot do everything, so I need to take someone else on.... no matter how hard I train them it will take years to gain the experiance and knowlege.. I want to automate settings etc so they can just look up a table that shows them what to turn on dials....

And remove downtime as much as I can...
I am just looking to automate an improve what I have developed.... to a point where it could possibly be sold on as well....

 

It might be cheaper to just get a second unit.

I don’t see how we can help you unless you can get it down to an electronics problem.

 

ok the electonic problems are:
At power up all valves are closed
When blasting starts one air valve opens and allows the tank to presurise, when at full pressure a pressure switch operates a relay to open another air valve to allow air to flow to the blast gun, after that valve opens the Media Ballvalve is opened using a push button till the desired flow is achieved (this flow is down to experiance, it would be nice to have a scaled knob to select precicely the flow)

When blasting stops then automatically main air flow valves and ball valve close using the relays but when I start blasting again start process is repeated open the air flow valve to permit the tank to be at full presure again incase of leakages, the pressure switch operate and opens the second air flow valve then manually open the ball valve to the exact position it was before I stopped blasting.
The ball valve is manually opened or closed to regulate the media flow using 2 buttons.. at the moment I am using a 3 wire valve +ve +ve and -ve so when power is applied to either +ve it either opens or closes... I am assuming a stepper motor controlled valve would allow some precise control and positioning!! that is there the Electronics I believe starts to come in... then instead of using 2 butons to control the manual positioning say a knob 0-10: 0 being closed 10 being fully open... so the position could be adjusted but if blasting stops it closes and returns to that exact position when starting again...
a delay (variable) on opening that valve opening would also be useful...

I said I would upload further details but everyone started to suggest alternative working practices....
We have 6 blast cabinets, and this solution would be applied to 4 it would be impossible to use specific cabinets for specific media types etc as different things require different media so there is a need to change media... we would need 20+ cabinets plus it does not solve teh stop start blasting problem with presurised cabinets...
a vaccum system can operate stop start but it is very inefficient as presure cabinets are up to 400% more efficient
a lot of the work is small components so lots of stop start rather than something big that can be put on a turntable and blasted while rotating for 20 minutes..
something small may take 20-30 minutes in a vacum cabinet but between 5-10 mins in a pressure system.... hence why I tried a simple external pressure tank, but there are additional issues using a simple extrernal pot and refilling...

 

To be honest, I don't see how changing from relays to electronic actuators would change much of anything. For my limited knowledge and experience with sand blasting the most efficient method is the one that has been around for a very long time. I can think of one possible change that might make a difference and that would be to have a hopper above the chamber. Let gravity feed media into the blast nozzle. When the air is triggered it can also open a baffle and allow media to flow into the gun. But adding a microcontroller doesn't make sense to me. Well enough is well enough. To spend a whole lot of money just to make it a little better doesn't make sense.

I've not heard of media in a pressure tank before. And if as you say, you spray for five seconds then pause for a moment you lose all the pressure in the tank and have to wait for it to repressurize. That sounds as if it has a blow down valve that relieves the pressure in the tank when you're not spraying. That sounds like a terrible design. Which calls into question the effectiveness of the unit(s) you have on hand.

I've made vacuum venturi's before. High velocity air moving past a choke point creates a vacuum. Media is sucked through a tube into the venturi and blasted against the target. I see no place for improvement except for possibly a gravity fed system that feeds into the venturi. My only concern with a gravity fed system it might be possible for media to get stuck in the tube and fail to flow. There's gains and drawbacks to every system out there. Nothing is 100%.

 

I have on occasion used the sand blaster in our shop. I do not recall having to wait for the sand (aluminum oxide) to recharge.
The unit is operated by pressing the trigger on the nozzle of the pressure hose if I can recall correctly. I think the abrasive was automatically recycled, but I could be wrong.

View attachment 300946

no disrespect... but that is something that Machine Mart or similar sells, suitable for the odd bit if you are not using it to make money....
it is a simple suction feed, a guy opposite has one... he now gives his stuff to us to do....
We have a contract for a company... in our machines 1 part takes less than 30 seconds, in a machine like that probably 4-5 minutes.... we charge them 25p per part, as it is simple repetative work 300-500 parts per go... and can usually do 40 at a time in one blaster..

 

no disrespect... but

Did not feel any disrespect. I DID say I have limited exposure to such equipment. Perhaps if you could link a page that shows what you have so we can get specs on it and learn how it operates. Maybe then we can come up with a workable plan.

 

I think what you want is called a "Deadman Valve". They now make them that use air or electric to shut off the air stream. But my old pressure tank blaster just had a neoprene block to cover the nozzle when you stopped blasting, no depressurizing the tank needed it just blocked the end of the nozzle.
https://www.google.com/search?q=san...1gQYsAPiAwQYACBBiAYBkAYI&sclient=gws-wiz-serp

 

I think what you want is called a "Deadman Valve". They now make them that use air or electric to shut off the air stream. But my old pressure tank blaster just had a neoprene block to cover the nozzle when you stopped blasting, no depressurizing the tank needed it just blocked the end of the nozzle.
https://www.google.com/search?q=sandblaster+deadman+valve&client=firefox-b-1-d&sca_esv=558882007&sxsrf=AB5stBgLOXtYUt5SdTiTPWQCHc1yUfyoSA:1692654328363&ei=-NrjZNvuFaSfptQP-KS-uA0&oq=sand+blasterDeadman+Valve&gs_lp=Egxnd3Mtd2l6LXNlcnAiGXNhbmQgYmxhc3RlckRlYWRtYW4gVmFsdmUqAggAMgcQABgNGIAEMggQABgFGB4YDTIIEAAYigUYhgMyCBAAGIoFGIYDMggQABiKBRiGA0jbVVCcE1jyN3ABeAGQAQCYAbUNoAHRM6oBDzItMS4yLjAuNC4yLjAuMbgBAcgBAPgBAcICChAAGEcY1gQYsAPiAwQYACBBiAYBkAYI&sclient=gws-wiz-serp

I know what a deadmans valve is.. yes we have 2 large pressure pots that use them.....
the system is designed specifically for use with a Pot for blasing large objects outside of a cabinet, the hose for blasting is about 2" across and you hold the deamans closed and if you fall or stop blasting the deadmans is released they are about 10-12" long and not suitabe for use within a cabinet....

Whilst offering soilutions is great we have been doing this for a while an have tried an tested mosst of what is available....
Most of which has not chaned for years, we are simply lookig to updae and improve using modern electronics...
there are solutions similar to wha we are looking to do but with a price tag of £10k+ and very machie specifc...
We have a generic solution that works and are looking to improve it not change it for something else (that we have probably tried or does not cure the exact problems encountered).

Many poeople simply "Blast" they have a one shoe fits all aproach, an they ruin stuff with teh "Ahh well mate thas what happens" caveat "at your own risk". This pressure this media and thats it, I have seen irreplacable carburettors ruined because the surface was etched away giving a shiney finish because "thats how we do it", every man an his dog is trying to get in on the act, and without kowlege an appreciation for the parts they are handling, hence efficiency an being able to reset to specific parameters every time if you need to change...

so the main issue is how is it possible to open an close a ball valve (3 wire currently used but stepper motor valves available) to the same position when powering back on each time, an able to alter that position (using a knob with a sale form fully open to fully closed) also can be shut off to fiully close without altering the knob position, so if switched off/on returns to the same new position. we do not nee new tanks, new solutions new operating proceeures, we have a working prototype that needs some improvement.

 

so the main issue is how is it possible to open an close a ball valve (3 wire currently used but stepper motor valves available) to the same position when powering back on each time, an able to alter that position (using a knob with a sale form fully open to fully closed) also can be shut off to fiully close without altering the knob position, so if switched off/on returns to the same new position. we do not nee new tanks, new solutions new operating proceeures, we have a working prototype that needs some improvement.

Why limit yourself to one valve? Have a few valves(3?), each set at a known opening that can be selected for a certain task. With a main valve on the pressure pot to shut down flow when needed to turn the work or what ever, A switch to turn on the main valve and a selected flow valve and start blasting again.

 

set valves would not work, sometimes it would be nice to vary the media a tiny bit while blasting....
and here are that many variables a simple simgle adjustable would be less complicated....

Is it possible to accurately control and position a normal motor in either direction or is a stepper motor the best solution....?