wiring controls for a hydraulic press - opinion?

I have an old 60-ton press which I got cheap because it was
damaged by a forklift while being moved. The electrical controls
were completely destroyed. Basically, there is a 3-phase motor
which when you turn it on, pumps more fluid. As long as you don't
turn the release valve in the piping, the pressure will stay.
I'd thought I'd use an on/off/jog setup. Now I realize these need
an auxiliary relay which is some complexity I don't necessarily
want. I'm wondering if it would make sense to just wire a simple
one-button setup. Push the button and hold it and the motor runs,
let go and it stops. What do you guys think?
Grant
Reply to
Grant Erwin
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Oh, no--I'm not touching the plumbing! That's all special stuff, and it doesn't leak. No way I'm going to monkey with it. This is strictly an electrical issue.
Grant
williamhenry wrote:
Reply to
Grant Erwin
Sounds good to me. Mine has a manual switch which you throw in or out and I'm always jogging. My hand rarely leaves the switch when I'm pressing anyway.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
the press we have in our shop has a control handle, one way releases presure, the other direction pushes on a microswitch which causes the pump to run, very natural to use
push the handle, it presses, pull the handle and it releases
Reply to
Jon Grimm
Why would you want to increase the force? Are we trying to wreck a press, or use it? They are very capable of mucking themselves up as they come "out of the box."
Regards,
Robin
Reply to
Robin S.
Is this a power press for stamping for a "shop press"?
If a power press, have you calculated the ram speed for the press? We have a 2500T hydraulic tryout press at work (and a dozen more at 1000T+). When they run in cycle mode, they go fast. Fast enough that anything more than an arm in the die probably wouldn't have time to get out before becoming pea soup. A 60T press would be just as capable of stumping your arm...
Perhaps you can wire in the double palm buttons for your safety? It's easy to forget where one hand is when you're doing a batch run and something happens differently during one cycle. Your left hand is ready to cycle the press but your right hand is in the danger zone fiddling with the part....
Just a thought...
Regards,
Robin
Reply to
Robin S.
Shouldn't be a problem but consider a couple of points. As Robin says, high speed presses are nasty things. I'm assuming that yours is a low speed workshop press. Manual control as you describe will mean that there will be a lot of starts and stops. Make sure that the switch contacts are rated for the current, preferably over rated. Some switches are manually dependant. That means that the speed the contacts move is determined by how fast the operator pushes the button. These are bad for regular use as they are more prone to arcing. Use the sort that click positively regardless of how slowly you push the button. Finally, don't forget safety gear. Things in presses shatter so wear eye protection at least. Also, make sure that your work or push rod isn't going to kick out. I had a 5/8 cap head kick out once at head height. Fortunately, it went away from me or it would have killed me. Even Russian roulette has better odds than 50/50. When we found the cap head, it had been bent by 45 deg and the end was blue where it skidded out of the press. These things look safe because they are slow and ponderous. Don't be fooled.
John
Reply to
John Manders
I'd use a contactor, wired to a button. The contactor will make and break fast and last a long time. An improper switch could possibly weld itself on and that could be trouble. An E-STOP switch might also be a good idea. Eric
Reply to
Eric R Snow
I am certainly planning to use a contactor. I have a nice Square D one already bolted on and wired in. Only question is how to wire the control buttons. I've about decided to go with a one-button design. I'll probably use one of my "start/stop" buttons and just not do anything with the stop button. This press is old and is an unusual design. It has a hydraulic tank with a little actuating arm which is run by an eccentric shaft belted to the motor. It's actually very similar to a hand hydraulic jack where you run the same kind of actuating arm but by a lever with your arm. I'll cobble it all together today and see what kind of shape it's in hydraulic-wise before I spend any more money on it at all.
Everyone's issues with speed and safety are very well founded indeed.
Grant
Eric R Snow wrote:
Reply to
Grant Erwin
Hey Grant,
I my former business, we wouldn't allow anything to move using just "one" contactor. We would have a safety circuit that pulled in one, and then a separate one for the motor run. With only a single one, too much scary stuff can happen. And no single push-button should pull in both relays either. Best if one is in constantly so that it never "arcs" and is used only to open as a safety, and a second to do the actual motor control.
Take care.
Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXXXX
Reply to
Brian Lawson
Well, in my shop I have 30A 3-phase disconnects within a few feet of every machine. That does the same function as your first contactor, only cheaper. If the button malfunctioned and stuck on or something, it would take only seconds to kill the power at the wall. Maybe I should wire in the "stop" button just in case the "start" button sticks on.
Grant
Brian Laws> Hey Grant,
Reply to
Grant Erwin
I'll post pics when it's done. It isn't much to look at, just an old press. Says Westinghouse on it. I'll get a lot more excited if it tops out my load cell the way I hope it will.
Grant
Rob>
Reply to
Grant Erwin
I think you'd get better control through valving.
Won't the motor be starting under a very high load if you're in the middle of a press job using high tonnage? Or does the pump have some sort of pressure relief when starting similar to an air compressor?
Reply to
DougR
I take Brians point and it's a good one. However, wiring in your stop button won't solve the problem. The danger is if the contacts in the only contactor weld closed. Then the thing keeps moving. By having a second set of contacts, This risk is eliminated. If you have a number of machines, you could have a shop emergency stop. A single contactor switching the whole shop and emergency stop buttons by every machine (and exit for when things go REALLY wrong).
John
Reply to
John Manders
Unless you have more than one person in a shop, there's really no need for this (unless you're foolish enough to walk away from a running machine). The only place I've seen such a setup is in school. Both shops (college and high school) had emergency stop buttons all over the shop that would shut the shop down. Kind of annoying really.
I've never seen such a setup in a real shop before, however. Not really surprising. Could cause a host of problems.
Regards,
Robin
Reply to
Robin S.
I agree with Doug about using valving. We have a motor powered universal press where I worked. There is a hand valve set/release and a bypass valve that when closed builds pressure in the ram. A check valve between maintains ram pressure until the release valve is opened. There is a ram pressure gauge in plain site. A maximum pressure bypass is part of the pump. Allows for a smooth controllable operation.
Reply to
Chipper Wood
I have seen a few here in UK. They are not common though, I will admit. Our theory is that if someone sees a problem on another machine, a local stop button will shut it down without them having to go towards the point of danger. The other argument is that if a machine has a problem, the operator has the option of moving away from it and shutting it down from a safe distance. I agree it's a long shot but I can't see any downside to having remote stop buttons. We have that facility at work here and it gets used most nights as a simple way to ensure that all machines are off. As always, the choice is yours.
John
Reply to
John Manders

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