Air valve

AIman

Greetings,

I am working on a project that uses electromagnets and air pressure and need to create an electro-magnet that will either have several coils or one long coil to move a metal piece from one end to the other through the center of the magnet and before entering the magnet will use·air pressure·(released very quickly) to start the movment.

High level overview - this will be Propeller driven. The air pressure forces the parts forward before the next piece comes and then the electro-magnet grabs the part and pushes it the rest of the way. This combination is used because of the processess involved. Most parts are rod shaped or spherical and weigh less then 1/4 oz.

Obviously making electro-magnets is not that hard, however I am after any ideas offered. I have looked at coil guns but that system takes to long·to charge the electro-magnet and the magnet needs to be able to go on and off to move parts rapidly. Currently the magnet is manually tripped when the air pressure forces the new pieces forward. Ick.

For air pressure no manual triggers I have found work and I can't find any electric ones that can be hooked in.· I have explored everything from triggers in air guns to diaphram pilot valves but the question as to what is best still remains.

Any ideas on what to use for fast air release with high PSI?
Any suggestions on how to do the electro-magnet?
Would·a QTI work to synch the movment of the pieces between the air chute and the magnet?
·

ElectricAye

AI,

a lot probably depends on what you want to spend on your pneumatics. See link for aircraft fast acting valve, about 15 ms response time, handles about 4000 psi. Probably costs a mint, though. Also, when you say "manual" trigger, I presume you mean mechanical and not "done by human hand"? Details on actual movement velocity requirements might help the forum.


www.marotta.com/DataSheets/MV604C.htm

hope that helps a little,
Mark

kwinn

Not sure what you mean by "high psi". If it is under 100psi try a solenoid valve.

Check with a pneumatic supplier such as FESTO for solenoid operated air valves, and if the parts are small enough you may be able to use multiple coils from solenoid valves to move the parts along.

mctrivia

Paintball gun solinoids are fast and can take 300 psi

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
propmod_us and propmod_1x1 are in stock. Only $30. PCB available for $5

Want to make projects and have Gadget Gangster sell them for you? propmod-us_ps_sd and propmod-1x1 are now available for use in your Gadget Gangster Projects.

Need to upload large images or movies for use in the forum. you can do so at uploader.propmodule.com for free.

AIman

Yes I mean triggered by the device and not by hand.

The speed of the air needs to equal 2000 FPS or greater and the magnet needs to match.

·Not sure entirely how to calculate the PSI needed to move a small object at that speed. Anyone know how to calculate that?




Post Edited (AIman) : 7/13/2009 2:37:26 PM GMT

ElectricAye

If you neglect friction on the walls of whatever is containing the pellet, then you use Newton's 2nd law. Force = Mass x Acceleration. Acceleration integrated over time gives you the resulting speed.
Force will equal cross sectional area of pellet that is facing the air pressure, presuming that the air isn't leaking substantially around the sides where it should "seal" against the chamber walls.

This would give you a ballpark number, provided the geometry isn't too far out of ideal conditions. Also, depending on the design of your pneumatics, the air pressure might plunge once the pellet starts to move. To prevent that sort of plunge in air pressure, you might need a hefty capacitance, a reservoir of pressurized air, to maintain the pressure and keep the acceleration constant.

Bear in mind, however, that the friction on the walls might NOT be negligible AND might not be linear (it might change with respect to velocity, temperature, dirt, etc.). In which case, you'll need to do lots of testing.

hope that helps get you in the ballpark at least.... somewhat,
Mark



Oops,

sorry about this, up above, where I said:

"Force will equal cross sectional area of pellet that is facing the air pressure, presuming that the air isn't leaking substantially around the sides where it should "seal" against the chamber walls."

I should have stated:


"Force will equal AIR PRESSURE X cross sectional area of pellet that is facing the air pressure, presuming that the air isn't leaking substantially around the sides where it should "seal" against the chamber walls."

my apologies for the omission,
Mark



PS. Also, where I said "Acceleration integrated over time gives you the resulting speed." If the acceleration is constant, then "integration over time" turns out to be a fancy way of saying "just multiply acceleration by time."

(I've got to remember not to answer these questions until my coffee kicks in...)

Post Edited (ElectricAye) : 7/14/2009 2:15:25 PM GMT

Jay Kickliter

Mark is right about friction. In high-pressure steam lines, the steam in the center of the line may be moving fast, yet the velocity at the walls is almost zero. Same thing applies to any fluid flow.

AIman

Thanks guys.

We re-bored the cylinder to fit the size of the pellets and rods. There has been a drop in air pressure which was supsected to be due to the air reserve tank which basically didn't exist, litterally it was 1/4 in x 1/4 in. The parts were running in a make shift plastic tube that were cut by hand, pounded in place with a rubber hammer and then litterally taped down with duct tape. I really am floored that such rickety stuff was used to start.

The new set up is milled out of a piece of metal making the air tube one piece of metal·instead of 3 plastic tubes, fits to within 1/64 in instead of 1/32 and·has 1/8 thick walls instead of 1/16. Externally its the same size.

The magnet was hand wound and is being rebuilt using things designed for making magnets that have much more specific standards. The trigger to activate the magnet was simply a spring loaded lever that was tripped as the pellet or rod moved through the air tube.

The tolerance changes have been·remarkable.·The total power consumption·has dropped about 40% already. So far the changes have resulted in a much smoother transition, much lower use of air pressure and much quiter equipment. When the changes are complete (the Propeller version being discussed) the anticipated change in production will be close to 80% less power being used to move things and·increase production to 50·or 60 percent faster.

I am not sure if I should laugh or cry...

ElectricAye

AIman said...
...
I am not sure if I should laugh or cry...

Try both at the same time. It's the human condition.