Choosing a cylinder - air hammer build

[Astro_Al]

Hi guys, slowly gathering bits for the hammer build.

I want to have as solid a hit as possible, so I'm trying to go with as big a ram as realistically possible. The only downside to a bigger ram, as I see it, is more air requirement. Shout if I missed something.

Standard cylinder bores seem to be 50mm, 63mm, 80mm and 100mm (and up). I have about 23 cfm of air to play with, more if its not 'free air delivery' and can recharge tank capacity between heats, which is realistic. I would consider adding more air if needed.

Does anyone know how to equate these figures? Is 80mm bore asking too much of this air supply? Anyone built a hammer with an 80mm cylinder bore?

My anvil will be around 1350 lbs, and the base plate about the same again, so I figure there is enough mass to absorb a fair size punch.

Other things to look out for on the cylinder are:
1. Largest port size I can find.
2. Largest haft diameter I can find.

...Anything else?

If I increase bore size, presumably I shouldn't play with the stroke, I need what I need, right? What would, in your experiences, be a good size ram?

Cheers, Al.

[PeterDE4]

I have a 50mm (2") bore on my cylinder, and I use about 11CFM. A 63mm bore is 58% larger in area than the 50mm, and the 80mm bore is 156% larger than the 50mm. I think the 80mm bore would be pushing it. Good luck with your build!

[Astro_Al]

Hi, thanks for your reply. I found some interesting info on the 'Iron Kiss' hammer website:

"You do NOT need 3-phase power to run a large Iron Kiss power hammer in a production setting. The 100, 125, and 150 pound Iron Kiss hammers will run with "one iron in the fire" with 5, 7 1/2, and 10 hp 2-stage air compressors. These are available in single-phase electricity versions. This is intermittent forging--while the iron is back in the fire the compressor recharges the tank for the next bout of hammering. For "multiple irons in the fire" --continuous forging--the compressors are larger: 7 1/2, 10, and 15 hp. To get these numbers when you have already installed a compressor that is proving to be too small, you can buy a second machine and place it on a separate circuit breaker and then unite the air lines to feed the hammer. You only need to run the second compressor when doing the heavy production, saving on wear and tear. Blacksmiths can often find used compressors at equipment auctions to save money."

Power Hammer FAQ - Iron Kiss Hammers, LLC.

Along with some comments on their cylinders:

"Cylinders used in standard Iron Kiss hammers are premium steel tube Norgren units made in the USA with 3.25" and 4" diameters. Each cylinder uses air cushions on the top and bottom caps. These diameters permit the hammers to run effectively at pressures as low as 80 psi. As a forging session is using up the air in the compressor's tank, Iron Kiss power hammers will run longer than competitive brands that need as much as 120 psi to function. Iron Kiss power air hammers are very snappy performers in the 80 to 150 psi pressure range and can be tuned to run at least four blows per second at short strokes or tuned to run slower with longer strokes."

So I guess they are saying roughly that a 10 HP with a 3.25" (roughly 80mm) bore is a workable combination for continuous forging. Seems like I have enough air to get me started at least, if I go for 80mm, which I can always add to if needed.

As they say, a larger bore requires a lower pressure to exert the same force, so you can run at lower pressure for the same effect, helping with air requirements.

I'm figuring on an anvil to ram mass ratio of 16.66:1 if I go with a 150 lb ram. That seems like a decent ratio.

Incidentally, some nice p/hammers here (I guess you guys have seen them): Phoenix Forginghammers : Pneumatic Air power hammers for the forging industry

Both sites have some useful data to help size things. Good one here on anvil mass ratio: Phoenix Forginghammers : Pneumatic Air Power Hammer Effectiveness

Cheers, Al.

[monstermetal]

I think I still have a 3.25" bore 12" stroke parker air cylinder with air cushions top and bottom I bought for a hammer project that Im not going to use..

If you want it Id sell it for what I paid ( I think about $140) It looks good as new..

[Astro_Al]

Thanks for the offer, I think I can probably beat that after shipping to the UK, but thanks anyway.

Having said that, I just got quoted about $3000 USD for a heavy duty Norgren M1031 cylinder (3" x 350mm stroke) Ouch, won't be buying that then!

Al.

[Astro_Al]

Hi guys, right well, I have accumulated some pneumatic paraphernalia!

I have found a suitably large ram - bore 80mm, stroke (about) 45cm (18") - leaving a bit of room at the ends (cylinder length is 500mm I think).

Hopefully you can see them in the pics, plus a couple of 63mm rams I found along the way.

The issues are that - a. it doesn't have air cushions at each end, but that won't matter so long as I control the stroke to not go near the ends, right? - b. the ports measure very crudely about 5/8", but seem to be almost blanked off at the end down to a roughly 1/8" hole. I'm thinking I can just drill this out to get the air flowing, any thoughts? I can't think why they'd make it like this!

There seem to be lots of different mounting options. Does it matter?

Cheers, Al.

[John Larson]

The constricted port that you've shown is bad for hammer performance. An air cushion on the rod end is not needed with the stroke not fully used with dies touching, but it is very sensible to use some means to prevent metal-to-metal contact at the other end. The advice I give on my web site comes from 14 years of experience with air hammers in quite a few configurations and lots of investigation. The 16 to 1 weight ratio is plenty adequate.

[Astro_Al]

Hi John, many thanks for your input.

Yes, I dismantled the cylinder and I'll be drilling out the end of the port. The restriction seems totally pointless. I am also intending to drill a second port at each end of the cylinder to aid flow (by the time the fittings are screwed in, its not too large of a bore, so I figured doubling the flow capacity with a second one is a good plan).

I'm definitely going with the 80mm bore cylinder, confidence boosted by the comments on your site!

Cheers, Al.

[John Larson]

The constricted port may have been a factory machining error. If there is a second port in that cap maybe the constricted one is related to an air cushion and some parts are missing. Big Blu uses two small air lines to the caps on their 155 trying to perk it up by doubling air flow. Not a bad idea, but their lines are so small that the 155 needs more than that. But that's their bizziness. Double big air ports may not help you Al if the port from the cap into the cylinder is the bottleneck. If the cap is not related to an air cushion, then that cap center hole can be any size you want it to be. My 3.25" cylinders have a 5/8" center hole and spear related to the air cushion on the none-rod end. That is adequate. But at high pressures (150 psi) and cfm, like with a 160 pound hammer head at 3 to 4 blows per second, bigger ports will be beneficial. I've run 160 pound hammers at 150 psi with a 3.25" Norgren cylinder very effectively, but at that weight it wants 100 to 120 psi to get it running in a snappy way. Utility hammers need to be snappy to perform well. By the way, Al, Norgren sells world wide and like many manufacturers they tend to have cylinder critical dimensions that conform to the (USA)National Fluid Power Association guidelines that let stuff from different manufacturers interchange to some degree. For example, the bore size progression seems to be the same for all NFPA-conforming cylinders. Ditto cylinder wall thicknesses. But air cushion designs do not seem to be an NFPA item. In your case, like a lot of fellows do, you may want to use an external coil compression spring to decelerate the upward moving assembly so that it doesn't slam the piston into the cap. A rubber bumper from a truck suspension stop can also work--or a pair to keep the load balanced on each side of the rod.

[Astro_Al]

John, thanks I really appreciate your thoughts, I'm totally new to pneumatics - aside from the odd air tool.

I was actually thinking of a rubber bumper (shock absorber bump-stop style) for the end stop. A spring sounds like a good idea also, I'll have a look around... You just mount that directly to the piston so that it contacts the end plate towards the end of the stroke, right? I think a spring would give a nicer deceleration than a solid rubber bump.

Yes, I encountered these standard dimensions while getting quotes for cylinders. They are a pain! It seems most specs are related to cylinder bore size (piston rod diameter and port diameter for example), which makes little sense when the rams can be used in all manner of ways - particularly at very different rates. The superior method would be to have a set of stock sizes from which a person (customer) could choose the required combination of variables. Sadly, it seems everything is locked together as a set of specs. Over here in the UK we have different codes for the 'standardization', but it all amounts to the same thing - a PITA. I'd like to select a fat piston rod, and some large ports with the cylinder dimensions I already have, but...

I will drill out the narrowed port (it is literally a narrow web at the end of a wide 'hole'), and add another port at both ends. Its almost zero cost for the extra flow, I'd be mad not to. I will endeavor to fit the largest fittings I can, and not to restrict flow at any point (including into the cyl). I was planning to use the largest bore pipework I can reasonably use.

The specs you quote sound similar to mine - (roughly/estimate) 150lb ram, 3.25" cyl bore. So its interesting to hear that I'll need maybe 100 to 120 psi to getting it running well. Any idea on the CFM for that (at a given stroke?), also I'd be interested to hear your experience of how varying the stroke, by an inch - say, affects cfm requirements?

Many thanks again for your input & experience, its great that you share this info despite being a supplier. Al.

[John Larson]

Noooooooooo, the spring goes on the outside, over the rod, contacting the bottom outside of the cylinder cap as the object on the rod's threads (typically a clevise) approaches the cylinder. If the spring is put inside damage is quite likely as a consequence. On the outside you can keep an eye on wear. If you think you really want to use an internal spring, use a rubber donut of some kind about the same outside diameter as the cylinder bore. But it can bounce around and lose its original flat-to-the-piston position. Norgren makes an "ecology" (E type) cylinder that uses piston rings that overlap the piston's top and bottom so that these overlaps prevent metal-to-metal contact. I have one such cylinder and it seems to work. I almost exclusively use the EJ type cylinders with standard pneumatic piston rings and spear-into-a-hole type of air cushion where the hole has an O-ring that seals the spear as the piston approaches the top of its stroke. The captured air serves as an air spring. Most air cushions work similarly. Any kind of cushion other than that probably should be outside the cylinder like the coil spring-over-rod idea.

Edited November 29, 2009 by John Larson

[John Larson]

My post above was not destroyed as I suspected.

Edited November 29, 2009 by John Larson

[Astro_Al]

Hi John, thanks again, no, you're coming through loud and clear. Ok got it - spring on the outside. Makes sense, will need a pretty stiff spring though - quite a bit of weight behind it, maybe an engine valve spring or two...? Yes I have a couple of cylinders with air cushions (piston into hole type) which I took apart to see how they work.

With these larger diameter cylinders, what are your thoughts on plumbing dimensions - general pipe size, and port sizes for the valves? Do the larger cylinders demand higher flow all round (so larger bore everywhere?)?

There are dizzying numbers of valves in the catalogues, so clues would be good - especially bearing in mind the large cyl bore. Cheers, Al.

[John Larson]

The valve spring idea is one I've seen, something pretty stiff. The Iron Kiss hammers use 3/4" i.d. hoses though the hose barbs have a 5/8 hole. I'm going to increase the one's on the 4" cylinders to 1" hose, but that is more than you need. Try to determine how you are going to throttle the hammer. A simple ball valve will not give you the control you need. Without control you'll not get a fun hammer. I use a proprietary design. One resourceful guy used a truck air brake valve. The trick is to get a "linear" progression in the air opening as the treadle is depressed.