Steve Smith wrote:
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So why won't the HF press do the job?--speed of travel during forging.
It does have a means to move the press tooling up and down rapidly when
under no load (via air). The problem is that air can't give you a lot of
pressure in the dies. The manual on your press says air at 100 psi; my
press is at an internal pressure of about 2000psi when the dies are at
30 tons pressure. Quite a difference. How the HF press works is you use
air to move the dies into contact with the work, then switch to the hand
pump, like with most shop hydraulic presses. This is *very* slow, way
too slow for forging.
I agree that the press speed is probably way too slow for the work in
question, but I think you misunderstand how the air/hydraulic presses
work. The 100 psi air does not directly act on the press piston, it
operates a reciprocating air motor that operates a small pump cylinder
for the oil, same as the manual pump cylinder works. Given proper air
line pressure, the air operated pump will build pressure up to the
hydraulic relief valve setting just as the manual pump will.
Here's an example. My press has a hydraulic cylinder with a 6" diameter
piston. The area of the piston times the pump pressure gives you the
amount of tonnage the cylinder will put on the dies. In this case, a 6"
diameter piston has 28 square inches of area. Multiply this by 2000psi
and you get 56,000 pounds pressure, 28 tons (I guess my press is
'almost' 30 tons). The issue is how fast you can move at this pressure.
My press moves 1/4" per second at 30 (alright, 28) tons pressure. This
takes a pump driven by a 3HP motor, not something you can contemplate
doing with a hand pump. Maybe you could motorize the pump, but it isn't
designed to work at this kind of speed and I'd expect it would fall
apart quickly.
You have a direct acting powered hydraulic press, more or less the same
as a log splitter, this is quite different from the basic hydraulic jack
powered H press.
This also means that modifying a 20 ton shop press (hand pump) won't get
you where you want to go. You could imagine adding a motorized pump to
such a press, but the cylinder has no provision for the high pressure
plumbing. You could replace cyinder and pump, but you might as well
build the whole thing at that point.
I disagree, the commercially available 20T H presses are quite
inexpensive and will save a lot of time and effort tracking down the
steel, welding and trying to keep things square. My recommendation would
be to use a commercial 20T press frame as a starting point. The 20T jack
can readily be used separately as a normal jack.
You should be able to find a suitable hydraulic cylinder, valves and
pump unit from a place like
http://www.surpluscenter.com and have a fast
powered unit operating in short order.
more snipped
Pete C.