Impact mechanism possibilities??

[coneboy]

I am a Geotech Engineer and have become invloved in the design of a hammer impact unit.

We need to build a mechnanical device that will push a rod horizonatlly and hit a
plate horizontally. The striker rod will be activated by a switch and upon activation it will shoot out and strike an anvil. We are hoping the impact rod will achieve at least a velocity of 4 m/sec. We need the rod to strike the anvil with at least 50 Juoules of energy. After impact we will measure the waves this device causes in the earth. The device then needs to be able to repeat the striking procedure for 1000's of hits. Approx 30 seconds between strikes is the time frame we are hoping for, or less. We are going to enclose this device inside a sealed chamber.

My question: What kind of device would use to create the desired impact?
The two items impacting need to be steel, and the impact needs to be steel on steel.
(Similar to gently swinging a 8 kg sledge against a steel block)
As far as I can see hydraulic power would be to slow to push a striker rod out at 5 m/s.
Also hydraulic power supply issues eliminates this possibility. Would an air actuated pneumatic cylinder work? Do pneumatic cylinders stand up to repeated impacts?
What do you think about linear thrust actuators? I did not see any that achieved the desired speed. Would you recommend the use of simple tension or compression springs for propelling the striker against the anvil for a design?
Any ideas or simple solutions that you have are greatly appreciated. Feel free to shoot down any of my comments as un-acceptable or expand on them as you see fit.

Coneboy
Geotech Pro Eng

 

[Sparweb]

KISS...
Doesn't gravity work well enough? Two strikes per minute gives lots of time for the hired-hand to line up the sledge for each shot. I can keep up sledge-hammering once per 5-10 seconds for several minutes at a time, but I'm sure you could find a burly guy who can swing a sledge once every 30 seconds and not get tired all day.

But I get that you want a higher level of control than this, so set aside the old-fashioned way for a minute. Would a pile-driver work? Lifts a fixed mass and drops it at regular intervals. In your case, the mass swings around a pivot and strikes the target at the bottom of the arc, rather than dropping straight down. If there really is 30 seconds between hits, the average power requirement is pretty small. Still within the human-power potential, BTW. If this has to run unattended by people, then a small electric motor can lift the mass. You then need a mechanism to hold it up and drop it at the correct time. Still less complicated than ramming it down with hydraulics or springs.


STF

 

[MikeHalloran]

Ever see a Charpy impact test?
A big ol' gravity powered swinging hammer should work just fine.
Now all you need to worry about is the hoisting mechanism.


Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Why not just do a literal hammer? The math says that something dropping through a 0.8-m height will achieve 45 m/s . Your 50 J requirement means that impactor must have at least 6.3 kg mass, so that's not exactly a "rod" in the normal parlance, unless it were tungsten or uranium.

You can look up MIL-S-901 and related documentation to see what's done for ballistic shock testing:

http://en.wikipedia.org/wiki/MIL-S-901

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[GregLocock]

IRstuff has done the maths and left out a crucial decimal point ( 4.5), and to reset the striker to its height a pneumatic cylinder a piece of rope and a pulley is a simple and robust solution. You can do all the control and programming you need in pneumatics, none of that nasty electrickery required.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[IRstuff]

Sorry, meant to delete the 5 altogether

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[rb1957]

"at least a velocity of 4 m/sec" ... why?
"at least 50 Juoules of energy" ... ok, this is the requirement ... why define the mass of the impactor as 6.4kg (using the 4m/s) ?
"We are going to enclose this device inside a sealed chamber." ... how big is the box ? how portable ? how heavy ?

i think your (steel) impactor is going to be something like 4in3 (if i've done the conversion properly).
you say hydraulics are out, by possibly pnuematics. sure air pressure could create the force needed, but recharging in 30sec ? maybe you need a reserviour system (rather than a "direct drive" type of pump) ... a regulator on the outlet of the reserviour, a separate means to refill.

Quando Omni Flunkus Moritati

 

[Compositepro]

When you factor-in the need for calibration and consistency over time, a gravity pendulum is the best solution.

 

[rb1957]

you'll also need to think of a way to "re-cock" the firing mechanism ... grab (control) the mass after rebound, pull it back to the firing point, ...

Quando Omni Flunkus Moritati

 

[hydtools]

Look at a drop hammer concrete breaker. Hydraulic motor drives a roller chain that has a tabbed link that engages the impactor mass and lifts it. At the top of the lift the chain tab disengages the impactor which then free falls. Use a pendulum impactor and run the roller chain horizontal which engages the pendulum rod to pull the pendulum to a release position and pendulum free falls.

Ted

 

[coneboy]

Thanks everyone for guidance and comments.
Please provide additional comments or thoughts if you can see an alternate idea.
We are really trying to keep it KISS.

hydtools: Yes, I am looking at rock breaker type hammer. They tend to have very fast and hard impacts which is good, but they are hard to control so that a single strike occurs. A chain driven swinging pendulum arm is also being considered.

Rb1957: Yes, recocking the impact hammer after each strike also needs to be assessed.

Compositepro: A gravity driven pendulum swing arm works great when you have lots of room. If space is limited then there might not be sufficiet room for a full swing of the arm as we will need a fair amount of impact energy.

Greglocock: A rope actuated pull system works great in other scenarios. Inside a sealed box there are some more challenges.

MikeHalloran: Yes, a charpy impact swing arm would work great, but I need it much smaller. What would you use for pulling the swing arm back?

Coneboy

 

[rb1957]

"We are going to enclose this device inside a sealed chamber." ... how big is the box ? how portable ? how heavy ?

Quando Omni Flunkus Moritati

 

[btrueblood]

The impact and rebound should be fairly repeatable events, so "catching" the impactor on the rebound should be just a matter of timing, i.e. hold the trigger release for a certain duration, then let it re-engage the impactor for resetting.

Agree that a gravity pendulum will be more reliable/repeatable than a spring or pneumatic driven device. But spalling of the impactor/impactee and changes in their mass over time will need to be considered, as these will/may affect the delivered energy. Your sealed box will need to be opened occasionally to check for such damage.

"What would you use for pulling the swing arm back?"

Any of a thousand different mechanisms, actuated by pneumatic or hydraulic cylinders, or electric motors with gear or worm drives, or a big whomping electromagnet (e.g. solenoid). Why not use a semi-automatic rifle bullet as the impactor, then all of the mechanics will have been figured out already. You'd just need to purchase large-capacity magazines for the rifle...which will be a problem in the US.

 

[rb1957]

"Why not use a semi-automatic rifle bullet as the impactor" ... good idea, but how'd you get the texan (holding the gun) into the box ?

c'mon smile, we know how much you guys south of the border Love your guns

Quando Omni Flunkus Moritati

 

[MintJulep]

Yes, gravity. Cheap, reliable, repeatable.

Swing hammer. Lift with a simple disk cam.

 

[IRstuff]

You've stated a volume limitation, but not the actual numbers. The calculation I had was 0.8m drop, and that can be done as a pendulum, or a simple drop into a rocker, i.e., something that resembles a quarter circle with straight faces at -90° and 0°, with a pivot at the center of the circle. The weight hits the 0° face and the force is propagated to the -90° face, where the -90° face is in contact with the vertical surface you are trying to hit..

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[coneboy]

btrueblood
Yes we are considering the lever arm pendulum design as our most likely option.
The anvil and striker on the pendulum would be sizable so I am not worried about spalling over time and related changes in mass.
Yes, we will make the sealed box with a bolted cover so that we can check the contents periodically.
This box it will be mounted in will be about 0.5 meter wide, 2 meter long and about 1 meter high.
Estimating the weight of the box and enclosed impact unit at approx. 200 lbs.

Use of any kind of bullets is out of the question as it will be used in a sensitive area.

Minjulep
Diskcam device is being looked at.
Trying to adhere to KISS.

Thanks
Coneboy

 

[3DDave]

How does the trigger signal get in?
If the chamber is sealed how does the energy get out?

What mechanism is typically used in this application?

 

[MKIX]

this thing

http://www.giscogeo.com/pages/seixwsn.html

 

[MKIX]

or this

http://www.passcal.nmt.edu/content/passcal-obtains-new-automated-seismic-source