Simple balance circuit needed hydraulic

MwTech Inc · Apr 18, 2008

Ok I can't do it anymore, back is hurting as I write.

2 years ago bought a new 6" 12 ga National box/pan brake, manual operation.

My back will no longer take the pressure pulling up on the levers.

No problem to place two hydraulic cylinders to push, already have a self contained pump unit.

Doing research I found flow dividers, standard units. The info says you cannot sync two cylinders precisely. Over a 10" stroke just how far will they be off?

I can't see much difference with two people pulling on two levers being in sync either.

The cylinders will need to be fully retracted after every "push" anyway to re position the sheet metal, so they will always be starting from an absolute zero.

Suggestions otherwise, are there other controls usuable without going to encoders etc?

matt_isserstedt · Apr 18, 2008

I think you need the balancing device used on a shear or hyd press brake.

Funny things happen if these aren't equalized as you state.

One simple concept I can think of is a hydraulic motor. Suppose the flow to cylinder "A" has to go thru a hydraulic motor. Suppose Cyl "B" is the same.

Now couple the drive-shafts of both motors together.

Being a positive displacement device, the motors cannot "overspeed" each other, and as such with every revolution output a very similar volume of fluid.

Can't say what will happen with torque and such or if one motor has a grossly lower restriction than the other one due to something unexpected like blowing a hose or a seal, there would have to be some more engineering than that to avoid some kind of impressive failure.

Edit: motors have to rotate same direction when coupled...can't "fight" each other with equal and opposite torques...

boslab · Apr 18, 2008

you cant perfectly sync but you can get a fair approximation, speak to your hydraulic supplier there are proportional control valves and such like they can recomend and supply
i'm sure it can be done.
mark

gbent · Apr 18, 2008

My 8' electric brake has a curved rack in the center to fold the apron. No equalizing necessary.

matt_isserstedt · Apr 18, 2008

I think I'd also consider using air cylinders unless you use this thing on the order of every day and could not stand the cost of the air.

Reasons: air cylinders and controls are 10x cheaper than equivalent hydraulics in general principle. Also if you can do this personally by hand now, this is easily within the realm of a single 2" air cylinder.

MwTech Inc · Apr 18, 2008

Well the only reason to use two cylinders was ease of mounting on the frames at the end.
I guess if equalization is a big issue then I'll just have to fab a framework for a center mounted cylinder. Also add a framework on the leaf to distribute the pressure more even than one center point.

It takes two to pull a full 6' of 16 ga ,14 is tougher yet, and two the of us can't pull 12ga at all.

Would not hydraulics provide a better "feel-response" than pnuematics?
Not to worried about cost( within reason,so using hydraulics is fine)

Rotary flow divider, that's an option, already have one new good sized motor on the shelf.

I know some may think just get a press brake, but for now that's not an option.

Good help so far- Thanks

matt_isserstedt · Apr 18, 2008

Hydraulics are definitely stiffer than pneumatic, especially if you are "jogging".

One possibility of air is a "pneumatic-assist" which isn't enough load to bend the part but enough to take most of the strain off you, but allow you to fully control the bend.

Two things to think thru are the changing force vectors as the moving arm cycles, and having a simple table of where to set a regulator. I also expect most materials work-harden somewhat as they are bent and so there might be that variable too.

SteveF · Apr 19, 2008

On my front end loader everything runs off double cylinders. The fluid flows from the control valve to a T fitting then to each pair on left and right. This guarantees equal pressure to each cylinder and equal movement. Maybe someone can clearly explain how this application is different and needs balancing valves or proportional control, etc.

Steve.

Mud · Apr 19, 2008

The Surplus Center has rotary dividers - http://surpluscenter.com/item.asp?UID=2008041821353884&item=9-5120-10&catname=hydraulic .

I would think that a pair of cylinders mounted 2 to 3 feet apart in the center would work without a divider as long as you kept heavy work reasonably centered in the brake.

js412000 · Apr 19, 2008

You don't need a balancing device, because the mechanical design of the brake will keep them even, the same as on a tractor front end loader. The workpiece should be kept in the approximate center to put less twisting force on the equipment.

boslab · Apr 19, 2008

of course, i b an ahole, its so obveous

SteveF · Apr 19, 2008

I was thinking about Matt's point on the changing direction of force to the handles and offer up this. Put gears on each end, concentric with the shaft driven by the handles. (Hard to tell in the pictures but it looks like the handles can be removed and those bolt holes used to mount a plate with a gear welded to it) Next run a shaft behind the pan brake with a gear at each end. Connect the gears either directly or with a toothed belt or chain. Now one shaft can be turned with a cylinder (arbor press type drive to change from linear to rotary motion) or mount a small elec 3 phase motor geared down so full range of motion on the brake takes maybe 5 seconds and a forward/reverse switch.

Just a thought.

Steve.

MwTech Inc · Apr 20, 2008

Ok after doing research after getting ideas from posters I have another question.
Seems a rotary flow divider has a operating rpm area for best efficency.
What happens when you are slowly giving pressure/fluid to the cylinder/s?

Does the unit still function as described?

Thinking that while starting to bend the metal full flow could be given to the cylinders, however when getting close to the required angle i would be slowing the cylinders down as to not overbend.

surplusjohn · Apr 20, 2008

try to find a hyd circuit diagram for a Samco hyd die cutting press Model 60, these used two cylinders and had to keep pretty equal pressure under widely varying loads. I remember them using two pumps and two valves with a clever cross over arrangment, the details of which escape me right now. but it worked well.

Robert Campbell Jr. · Apr 20, 2008

K.i.s.s.

I'd sure be tempted to build it with a simple Tee splitter, eyeball-center the work and live happily ever after. It's not like you can't easily replace the Tee with an equalizer should need be. Bet 'cha don't need it. The output of split hydraulic pressure equalizes in any system that is reasonably symmetrical.

How many of us have jammed the corner of the bucket of a loader into tough stuff, (clay, hidden rock out-crop etc.), just rared back on the valve, made the pressure pop-off squeal, reduced the bite and jammed it again? Can't imagine that a loader bucket, (the only structure between the cylinders) is substantially more rigid than a brake. Some John Deeres make it with only a single cylinder in the middle, no warning labels to center load pressure.

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