[TheForge] Air hammer return stroke

Sun Feb 2 21:41:01 2003

Truly a terrible happening. Overall, the record has been pretty good for 
the US space program. Let's just hope this one wasn't due to poor risk 
management like the last one.

Jerry Frost wrote:
> Morning Steve:
> 
> I'm hoping this will take my mind off the smoking contrails of Columbia's
> wreckage on TV. Perhaps this will ease the numbness.
> 
> As already mentioned, an air cushion at either end of the ram cylinder's
> stroke is what I'm going to use. It's easier and "safer" than a mechanical
> stop.
> 
> How I'm going to do it is make the stroke of the compressor piston shorter
> than the ram piston so the compressor piston reverses stroke before the ram
> piston tops/bottoms out.

It seems like for this to work, what you're really describing is that 
the rear cylinder pushes too little air for the front one to do a full 
stroke. This doesn't seem like a good idea.

> 
> I would NOT use a spring. Fatigue could cause it to fail without warning and
> while I seriously doubt anybody would get hurt, the damage to the hammer
> could be catastrophic.

I like the Belleville springs. I could easily limit the spring 
compression within its long life limits. Also this would be on the 
cylinder rod, which is boxed in with 6" square tubing.

> 
> A rubber cushion would be safer but taking the kind of impacts it will,
> would probably degrade and fail pretty quickly.
> 
> I've looked through half a dozen drawings of hammers on the patent servers
> and have not seen a mechanical ram stop on one. They all appear to be air or
> hydraulic fluid cushioned/reversed. So far, the simplest hammer design I've
> seen is the Bates Hammer.
> 
> Something to consider as has been mentioned is excess air. Short stroking
> the compressor piston is going to spike the air pressure. Overpressuring the
> thing is easy to handle with a set of pressure relief valves. Looking at the
> drawings you see them in every one, usually in the valves. Putting relief
> valves in the spool valves I'm playing with was problematical on paper. They
> were causing me to include a bunch more ports and lines so I moved them to
> the source. On paper anyway.

I was figuring on a couple of relief valves in key places.

> 
> I've sketched in two relief valves through the compressor piston itself. No
> extra lines. Don't know if it'll work though. <grin>
> 
> I will post sketches as soon as I get a scanner operating, I was going to
> use my wife's but her computer's dead. We're taking it in to our favorite
> computer geek today. <sigh>

Very eagerly awaited.

Thanks,
Steve

> 
> 
> 
> Frosty
> ------------------------
> If it ain't forged
> it ain't real.
> Wrought iron is.
> The FrostWorks
> 
> Meadow Lakes, AK.
> 
> 
> ----- Original Message -----
> From: "Steve Smith" <[email protected]>
> To: "theforge" <[email protected]>
> Sent: Friday, January 31, 2003 5:08 PM
> Subject: [TheForge] Air hammer return stroke
> 
> 
> 
>>So I'm still working on a self contained air hammer, although my
>>question applies to other hammers as well.
>>
>>When the ram is on the return, headed upward, it reaches a hard stop so
>>that the air cylinder doesn't bung itself up. I'm trying to figure how
>>to cushion the hard stop.
>>
>>A spring seems like a good idea. Unfortunately, there is quite a bit of
>>energy to absorb. If I did it right, I could do it with a stack of
>>Belleville spring discs. This would run about $50 buying them from MSC.
>>I sized them based on stopping the hammer in less than 1" travel (which
>>makes for a lot of spring washers). The rod on the cylinder that the
>>discs would go around is 1 1/8" diameter. A large coil spring would also
>>work, but I don't have a source for one.
>>
>>Any other suggestions out there?
>>
>>Thanks,
>>Steve Smith
>>
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> 
> 
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