[TheForge] Power hammer questions/Frosty

Fri Apr 11 02:25:00 2003

Frosty,
Thanks for the comments.I now understand your comment re knocking out the
end of the cylinder. You were talking about the up stroke.
I like the idea of shortening the stroke to equalize the displacement ratio.
This will cause less side pressure on the power cylinder piston rod, less
vibration,less work for the crank and motor.
I should correct my description of the "balance valve"I am using. These are
flats, not grooves. They are ,as you said, like flats on a wrench.
I will try a check valve next. The valve at the hydraulic shop is pretty
large and there is a threshold pressure to overcome before it opens. I dont
know if the pressure generated in my set up will overcome that pressure. Any
homemade check valve or alternative suggestions?
Any way you can e-mail  me a copy of the Massey drawings or can you explain
how to get to the patent?
I have gone to the uspto site and can never figure out how to access older
patent drawings.
Thanks again,
Bob S

----- Original Message -----
From: "Jerry Frost" <[email protected]>
To: <[email protected]>
Sent: Thursday, April 10, 2003 12:45 PM
Subject: Re: [TheForge] Power hammer questions/Frosty

>
>
> ----- Original Message -----
> From: "Bob Smolen" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, April 09, 2003 10:10 PM
> Subject: Re: [TheForge] Power hammer questions/Frosty
>
>
> > Frosty,
> > I have a semi complete Krause type hamer. Last weekend I mounted a
larger
> > power cylinder and had to replumb the Krause style valve for the larger
> hose
> > required by the new cylinder. As an experiment before I redo the valve,
I
> > thought I would try the Massey circuit and valve you described.
> > I connected top to top and bottom to botom ports. I then tee'd into
these
> > two lines and inserted a ball valve. Just as you said, when the valve is
> > open, the ram or slave cylinder does nothing. When I close off the ball
> > valve, the ram rises and falls in the opposite direction of the power
> > cylinder.I dont have a check valve so the ram stays on the bottom die
when
> > the valve is reopened.All as you described and pretty predictable.
> > I should now celebrate or brag(?), but all is not well just yet.
>
> Celebrate/brag away, what you describe below are just tuning and
debugging,
> not real problems. <grin>
>
> > After a few
> > good hits, the ram started to "short stroke". The ram stroke shortened
and
> > did not come down or go up completely.I believe this is due to the fact
> that
> > my balance valves -the kind described in  Mark Krause's pamphlet, are
not
> > large enough. I have grooves ground on the piston rods(double ended
> > cylinder) at the point where when the piston is at top and bottom dead
> > center, these grooves  will extend past the  seal   to allow air in or
out
> > of the circuit.  Because the rod is moving up and down so quickly ,
these
> > grooves are not in position very long and I believe the "excess air"
from
> > the larger power cylinder binds up the slave cylinder.
>
> > My question to you /and or the group is does this make sense?
>
> Yes. This makes perfect sense.
>
> > Can someone tell me the approx.
> > size of groove needed? My power cyl. is 5" dia and 6 in. stroke. The
slave
> > is 2.5 in. dia. and 10 in. stroke. The displacement ratio is about 2/1,
I
> > believe.The gear reduced speed is about 275 strokes per min.
>
> I have no idea how much groove you need. However, in the few drawings I've
> seen nobody used grooves for balance valves/ports. Most have flat sections
> in the piston rods where you have grooves, they look like wrench flats. If
> you don't think you can make the grooves larger make them longer so they
> stay open longer, at 2:1 you have more than enough air.
>
> Or you might be able to grind flat sections in the rods you have. You
should
> be able to make the depth of the flats about 10% of the rod diameter
(each)
> without weakening the rod appreciably. For example you could grind 1/8"
deep
> flat sections on opposite sides of a 1 1/4" diameter rod and not weaken it
> appreciably.
>
> Shortening the stroke on your compressor piston so your ratio is closer to
> 1:1 might make the problem go away altogether.
>
> > I tried  to follow your response to Bob Schade below. If the ram
cylinder
> is
> > mounted so that  the cylinder cannot fully extend before the top die
meets
> > the bottom die, should you be concerned about knocking out the bottom
end
> of
> > the cylinder?
>
> What I was trying to say is the ram is controlled totally by the
compressor
> piston so it should just be a matter of stroke length to keep the ram
piston
> from bottoming (topping?) out on the return stroke. The ram piston hitting
> the end of the cylinder WILL eventually hammer it to pieces.
>
> Massey extended the ram cylinder bore into the head, past the top port so
> there was a dead space. When the piston entered the dead space on the up
> stroke the air trapped there compressed and cushioned it. When the
> compressor piston reversed direction (slightly before the ram piston
reached
> the top) it put the bottom of the ram piston under a vacuum. The vacuum,
> coupled with the compressed air in the dead space not only stopped the ram
> piston cold but reversed it quickly.
>
> > I believe it is a good idea, as you said, to have more rather than an
> > inadequate amount of displacemnet . If this is done, you should be sure
> the
> > balance valves are of adequate size.
> >
>
> I must've been unclear. It's not surprising, this is a difficult way to
talk
> about machinery. I MUCH prefer face to face, coffee, pencil, paper and
maybe
> the actual machinery.
>
> What I was trying to say is: oversizing the pistons is better than
> undersizing or even guessing. The displacements MUST be balanced properly
> though.
>
> If you're pushing a conbined 100 lbs of ram weight and a commercial hammer
> uses a 4.5" dia ram piston pushed by a 6" compressor piston. (I'm using
> piston rods of 1.25" dia. for the purpose of discussion only) Diameters
> alone have a ratio of 1.84:1 compressor to ram. I don't know what the
> compressor piston stroke is but assume it yields a displacement close to
the
> 1.2:1 - 1:1 I've inferred from drawings. This hammer also produces
pressure
> peaks of 15 psi.
>
> So, from the example we know a 4.5" ram piston under 15 psi is enough to
> operate a 100 lb. hammer. Assuming a 1.25" rod, the ram piston has 14.7
> sq/in area. At 15 psi. this is 220 lbs. of force.
>
> The compressor displacement can be adjusted by changing it's stroke length
> so for the purpose of discussion let's just assume it's balanced to the
ram.
> In what I call an oversized system, the ram piston(s) have larger area(s)
> but balanced displacements. This means lower operating pressure or greater
> ram force.
>
> For example a 6" ram piston with a 1.25" rod have an area of 27 sq/in. To
> produce 220 lbs of force it needs 8.2 psi. Or at 15 psi. developes 406
lbs.
> of force.
>
> Looking at the example of the commercial hammer though we don't see the 4
or
> 5:1 force to weight ratio. This is because I've ignored the effects of the
> vacuum acting on the opposite side of the ram piston. I've left it out
> simply because I have no idea what kind of partial vacuum to expect but
for
> my own guestimating I've been using -10psi.
>
> > I did not try using holes at the equator of the ram cylinder for
balancing
> > the system(ala Massey) but I like that idea as well because I believe
you
> > can move more air that way without making grooves in the cylinder rod
> which
> > could weaken the rod.
> > I really appreciate your info on Masseys. This valve  circuitry may
really
> > simplify the home built self contained  hammer.
> > As a post script to my speculation that the balance valve son my hammer
> are
> > inadequate, I did enlarge the grooves and the hammer seemed to be
working
> > much better . I only ran it a short while before one of my welds broke,
so
> I
> > dont want to say I am sure this is the fix. After some repairs this
> weekend,
> > I hope to give it another try.
> > Thanks for any comments. Do we have a fluid power technician in the
group?
> > Regards,
> > Bob S.
> >
> >
>
> Thanks for the report, it made my day. <grin>
>
> Frosty
> ------------------------
> If it ain't forged
> it ain't real.
> Wrought iron is.
> The FrostWorks
>
> Meadow Lakes, AK.
>
> _______________________________________________
> http://mailman.qth.net/mailman/listinfo/theforge
> theforge mail list group photo site is
> http://www.photoaccess.com
> Login:  [email protected]
> password:  anvil
> ___________
>
>