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Dale
06-03-2010, 05:28 PM
I submitted a post awhile back about buying or building a 50 ton shop press. I am in the process of building one and have need of a hydraulic cylinder. I will need a 6*6 - 6*12 cylinder rated at 3500 psi. The cylinder should have a bearing surface on either side or some way of mounting it to the upper part of the press. I contacted a local manufacturer and for a 6*6 they charge \$950.00 Is this reasonable? Does someone know of a good supplier, or maybe a used cylinder? The press will not be used a lot.
Thank You, Dale

duckman
06-03-2010, 05:34 PM
Surpluscenter.com I've always had good luck with them, for what its worth get more cylinder than you need and the largest rod you can get.

oldtiffie
06-03-2010, 07:46 PM
I'm a bit curious as regards the 3,500 psi pressure limit in a cylinder delivering 50 tons of axial pressure.

The figures I get (not allowing for any inefficiencies or pressure loss or drop) for 50 tons pressure at 3,500 psi are:

50 ton x 2,240 # per ton = 50 x 2,240 = 112,000#

Piston pressure area = axial pressure/3,500 psi = 112,000/3,500 = 32 sq ins

Piston pressure are diameter = piston pressure area/pi = 32/3.1416 = 10.189 inch diameter.

Volume of oil per inch stroke of the piston is: 32 cubic inches per inch of pressure piston or ram stroke.

That is a lot of pumping by hand.

The return spring/s will need to be pretty substantial to force the oil back from the pressure piston to the oil reservoir.

"Losses" to be allowed for to assure 50 tons force at the point of application to the item to be forced/pushed/bent etc. should include but may not necessarily be limited to piston friction, pressure line losses and return spring pressure etc.

My 20T press operates at 10,000 psi ~ 700 Bar:

http://i200.photobucket.com/albums/aa294/oldtiffie/Hydraulics/Hydpresspressure2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Hydraulics/Hydpresspressure1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Hydraulics/Hydraulics1.jpg

It is a clone "Porta-power" pressure unit and gets very hard to pump up to 20 tons of pressure - but it does it.

The pressure and piston area required may need to be re-addressed.

It is quite possible that I've got my figures wrong so please check and confirm them before using them.

Check these items out for size and pressure comparisons:
https://www.machineryhouse.com.au/Hydraulic-Press-Manual

dr pepper
06-03-2010, 08:01 PM
Enerpac make a range of cylinders for the purpose, but the price would be similar.

Michael Hall
06-03-2010, 08:12 PM
Dale

I have a cylinder that is about 4-5" outside diameter and about 12-14" long. I think the shaft is 2" dia. It has a plate attached to the shaft end that is about 9 1/2" square. I may also have a 10k psi pump.

Michael

duckman
06-03-2010, 11:42 PM
Oldtiffie here in the colony's we use 2,000# when figuring tonnage. Michael Hall if your cylinder is not rated for 10,000# you need to find out what the operating pressure is other wise you could expand the barrel (blow up like a balloon) then you have a very large paper weight, if the plate that is mounted on the rod end of your cylinder is not 1 1/2" or more in thickness when you start to press the plate will start to bend because of where the studs are threaded to it, JM\$.02W. I just like to share what little knowledge that I have to keep people from making expensive mistakes, been machining and repairing machinery for the last 4 decades. :D

wierdscience
06-04-2010, 12:23 AM
I buy a lot of cylinders and hoses from these guys-

http://baileynet.com/index.php?dnfwd=1&id=38&page=Details&line=WHP&baileyno=216-420

They will also build you a custom cylinder per your specs.

http://baileynet.com/index.php?id=21

hardtail
06-04-2010, 12:31 AM
Surplus center sounds like a great place for the US to shop..........

Up here this is one of the most economical.........

http://www.princessauto.com/hydraulics/cylinders/specialty/1200060-6-bore-x-5-1/2-stroke-power-pack-cylinder

I would design your own trolley.......don't need much as once the pressing starts it will push up and secure itself if everythings in relative alignment.

JS
06-04-2010, 12:57 AM
If I was going to build a press I would put a cylinder in it with enough travel to broach without resetting .

diameter of rod squared X PSI X .00039

so a cylinder rod of 6" at 3500 PSI is 49.14 tons

Fasttrack
06-04-2010, 02:13 AM
OT - Your math is wrong. If we use your figure for a ton, we need 32 square inches like you've calculated. To calculate the diameter, you need to use the correct formula for the area of a disc ;)

A = pi*r^2

32 = pi * r^2 => r^2 = ~10 => r = ~ 3.2 and the diameter would be about 6.4 inches. ;) These are just round figures I did in my head. Not sure what the actual values are.

Dale
06-04-2010, 02:46 AM
Dale

I have a cylinder that is about 4-5" outside diameter and about 12-14" long. I think the shaft is 2" dia. It has a plate attached to the shaft end that is about 9 1/2" square. I may also have a 10k psi pump.

Michael
Are you saying the cylinder and pump are for sale? And if so, how much?

oldtiffie
06-04-2010, 04:51 AM
OT - Your math is wrong. If we use your figure for a ton, we need 32 square inches like you've calculated. To calculate the diameter, you need to use the correct formula for the area of a disc ;)

A = pi*r^2

32 = pi * r^2 => r^2 = ~10 => r = ~ 3.2 and the diameter would be about 6.4 inches. ;) These are just round figures I did in my head. Not sure what the actual values are.

Thanks FT - appreciated.

It was a silly mistake as I calculated circumference and not area as you did.

Thanks for riding shot-gun and for the heads up.

DR
06-04-2010, 08:01 AM
A few thoughts.....

Use a large cylinder with as low pressure as possible. Enerpac (10K psi) and equivalent are fine except very expensive when you get into the pump, fittings, valves, hoses, etc.

Double acting, power down and up, is very nice. My 50 ton press is that way. We broach blind holes and punch, both needing a fair amount of force on the return stroke.

Dale
06-04-2010, 10:59 PM
Thanks, I appreciate all the suggestions. I did go and talk with another local manufacturer and he is less expensive, and he will let me make the mounting block which should save some. He is going to make a drawing of a 6*8 with a 3" shaft, 3500 psi and e-mail it to me for my approval.

Dale
06-05-2010, 09:21 PM
Are these figures correct for figuring the requirements for a power unit for the press I am building? I was looking int the Surlus Center catalog. They have a pump which displaces .07 cu in . I am slso figuring 3500 psi. using a 1725 RPM motor. 6 inch diamerter cylinder. GPM=1725*.07/ 231( cu in/gal) which equals .5227 GPM. I saw a formula on the web, HP=GPH * PSI / 1714. So I need about an 1.07 HP motor. Is this correct?