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[machinist] OT Hydraulic forging press/ power hammer - Page 2
- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] OT Hydraulic forging press/ power hammer - Page 2
- Date: Tue, 31 Dec 2013 23:22:18 -0500
http://www.practicalmachinist.com/vb/general/ot-hydraulic-forging-press-power-hammer-277483/index2.html
Thread: OT Hydraulic forging press/ power hammer
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I, too, have wondered about a hydraulic breaker as a power hammer. I have a small one for my hoe. It weighs 700 lbs, and is classed as 750 ft*lb energy class. The tool is 3" diameter. It wants 12 to 18 gallons per minute at 1700 psi. This would be roughly 12-18 horsepower of hydraulic power, so 15 to 25 hp electric motor to drive. A nitrogen accumulator actually drives the impact piston, hydraulics don't move fast enough. Mine requires 380psi of precharge. Impact frequency is 500 to 700 beats per minute.
The hammer must be compressed to allow the hammering action. It requires about 2" of preload to get a good hammering action.
I suspect a power hammer could be sized to large as well as to small if used for steel. On concrete, a hammer really needs to be sized to the concrete at the job. To small of hammer and you pound without any progress. To large of hammer and you just drive the steel through the concrete without imparting sufficient energy to propagate cracking around the steel. After you get a proper sized hammer then you have to get a proper carrier. To small of carrier and the hammer breaks the carrier, to large and the carrier breaks the hammer.
The best thing about this theory is its easy to try. Go rent a skid steer with a breaker. You just have to supply a sow block, forge, and a tip for the breaker point that would be suitable for pounding steel.
I have the hammer and a 500# chunk of steel that might work as a sow block if someone wants to show up with a large enough forge.digger doug likes this. -
12-26-2013, 02:57 PM #22
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I'm way far away from being the expert on this, but have been studying this and related issues a lot. It may inform Kevin's question a little bit.
1. A hammer differs from a press, in some sense, because of kenetic energy - speed of the ram. And it's this difference combined with our talking about 20ton presses and 20ton hammers that yields the disconnect - a 20ton press is a mild mannered entity, a 20ton hammer shakes the Earth like a quake.
2. The aida servo presses, according to Aida straight from their rep to my ear at Fabtech, are presses, not hammers, and like any mechanical press depend on leverage to make tonnage - and so just like a conventional stamping press they only make full tonnage near the bottom of their stroke. So for some forging tasks, such as flattening thick stock, a servo press would be no better than a conventional stamping press (a poor choice)
Aida also pointed out to me, again, that tonnage and kinetic energy are different. And so a servo press can run (they showed it) very s-l-o-w-l-y and still makes, say 200tons at the bottom of the stroke. But the kinetic energy (1/2m*v^2) is of course much smaller when running very slowly. All of this makes them able to do various difficult and exotic stamping tasks, but they are in no way a substitute for forging hammer or forging press.
3. On the other hand, cnc turret punches can be either hydraulic or electric-servo, always strike quite fast (over a very short stroke) and there's apparently a huge debate about when to choose hydraulic or servo.
So it seems to me that Kevin is trying to develop his forming press into a forging tool, that is, to make it faster, both to work on things which are cooling, and to do tasks where the imparted kinetic energy matters along with pressure.
So, Kevin, if it were me, I'd try to find a way to make it go really fast - and things like gas accumulators seem like a fine idea. -
I was not proposing the Aida presses, as is, for forging- I am suggesting that the Direct Drive servo motor might be a possible approach to develop a forging hammer- but maybe I am wrong. It just seems like it could drive a flywheel, like a little giant, which would give you the mass and therefore kinetic energy. Since the DC motors are basically microprocessor controlled, it would seem the control would be much better than on an oily, slipping, leather belt.
I do know that hydraulic forging hammers have been made. So they can be made to work. I just think that the ones that worked, 100 years ago, were much bigger and heavier and more expensive than Kevin hopes they would be.
I am in Argentina, but I brought along a hard drive with a backup of my main computer, and, after much searching, finally found the old article that Grant sent me- lets see if I can attach it.
It appears they used steam accumulators, at 30psi- a bit dodgy, if you ask me, but that was before workplace safety regulations. Also, note the entire hammers were built to the same degree of stoutness as equivalent air hammers- a 100lb ram requires an anvil block of close to 1500lbs, to be very useful. My 88lb ram air hammer has a 1350lb anvil block, the entire hammer weighs about 3500. I would like a 100lb hammer to weigh 4500 or more. Mass is essential when forging fast. Elsewise you lose all your force, and hardly any of it goes into the actual moving of metal.bryan_machine likes this. -
12-26-2013, 07:42 PM #24
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Thanks for all the replys. I was messing with my forging press this morning and was able to get great response and controll even in mid stroke. I am running a 16 gallon per minute pump `with 5hp and it generates 20 tons, the pump has a high and low side. What I am imaginining is a pump that runs at low pressure and treats the oil as if it was air. Meaning that I would be running under 200 psi and using the oil to lift the ram and drop the ram. My air hammer ran at 100psi with a 2.5 inch cylinder and lifted a 100 lb ram. I am going to run oversized lines keep the pressure low just like some of the self contained power hammers. I am talking with a shop that rebuilds hydraulic hammers for demolition the kind that go on excavators, they have never seen anything like what I want to do. I have seen big hydraulic hammers as in 2000lbs stuff but never anything in the 100-200 lbs range. What I am hoping for is a combo press hammer but most combo machines give you the worst of both, I will test out the new cylinder and see what kind of speed I can get. I have been using an online calculator for hydraulic systems and it gives numbers that look doable.
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I think if you just want oil to raise the ram like the old time steam hammers you will need a mechanical release like a pile driver. I don't think you can get the oil out of the way fast enough to get enough drop out of your hammer.
I wonder how it would work if you used your hydraulics to lift a hammer that had a pneumatic cylinder on the top? The pneumatic pressure could be varied depending on how much more hit you wanted over the weight of your ram. -
Being around hydraulic CNC turret punches I'd think hydraulics can work pretty damn fast if you get it right.
A turret punch blowing 3" blanks from 1/4 plate is pretty much a quake. -
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12-31-2013, 03:41 PM #29
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I m just speculating, but I would start with the job I wanted the tool to do.
I have observed that pressing and hammering act very differently. A steady pressure, wherther from a screw, air or hydraulic cylinder, as long as it is maintained as the tool advances into the work, works the entire thickness of the work, that is, if you are flattening a piece, the width will increase slightly more at the middle of the thickness, because the surfaces are constrained by friction with the tool and anvil.
Calculate the total work done/energy expended as decrease in thickness (ram advance) times force.
If you want to use a hammer, the energy is put into it by accelerating it .Long swing or fall gives a lot of time to put energy in. Easiest to calculate with a drop-hammer, since the energy out equals the energy used to lift, i.e. weight times height to which you lift it.
So you can put same emergy into a small hammer lifted to great height or a heavier hammer lifted to lower height. And can put in same energy as you expect to get with slow hydraulic press.
But the action is VERY different.
Small hammer will be moving very fast at impact, and you will find that all the energy is dumped near the surface of the work. It will "mushroom". The larger hammer carrying the same energy, moving slower, will distribute its energy deeper into the thickness of the work.
You can end up with a workpiece cracked into two at some level by too-light hammer use, because the deformation ends as some depth and that creates a shear zone.
I am sure some great engineers (or smart blacksmiths) in late 19th or early 20th century mada a table or rule of thumb for proper weight of hammers for a given thickness of work.
But you will see on various videos of large-scale forging that it is done with presses, not hammers. Hammer will create great peak, instantaneous tonnage relatively cheaply, but what you need to work thick stuff is to work it all the way through the thickness, and at some point a hyd press will do that cheaper than a enormous hammer.
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- [machinist] OT Hydraulic forging press/ power hammer - Page 2, Lawrence London, 12/31/2013
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