Solution To Limit The Torque Of “Baling Press”

Every positive displacement pump that I have ever worked with has a pressure relief valve built into it. The valve is necessary to keep the pump from self destructing if pumping against a dead head. In most cases the valve is adjustable, the adjustment screw may just be hidden under a cover. In the case where there is no adjustment, a separate relief valve can be added to the circuit between the pump and the directional control valve.

One caveat, prolonged operation with the relief valve open will overheat the hydraulic fluid so some operator training might be in order.

That's right,.... with a PD pump on a hydraulic unit, it should have a relief valve... (I have seen PD pumps with out one because of the product pumping, but they were not on hydraulic units, but to pump high viscous fluids..... should add, that because of it I saw the screws snapped on them)

I don't think it would have a cooler on it, but if the reservoir size is 'big enough' to handle the heat load then it should be ok. now all that has to be done is define 'big enough'.

One other thing, if the relief valve is constantly going off due to over loading.... the operator needs training.

How about some sort of "warning" when the valve opens - Klaxon?

Warning for what?......other than stopping...

Well leaving it running on "bypass" will heat up the oil and waste power.

If you have a simpleton operating it as some mention, make it so they cannot miss that the torque limit is achieved is a good safe move....

True, problem is when do you say when and transfer the responsibility.

Working in PRESS mode will heat the oil a lot more than in bypass.

The motor and mechanical parts (vibration intensity) will alert you well enough if the press is going from work to idle. You'll need a bell for the deaf and a light for the blind.

A simpleton should just not operate such a press.

I agree entirely that having a simpleton operating it is a bad idea, but are people who handle rubbish likely to be overly intelligent......? It needs to be made "idiot" proof.....

Passing at full pressure through a pressure relief valve, will warm up hydraulic oil faster than just being under pressure, but relatively static....

Also, the length of time the relief valve is lifting will also play a role.....as already mentioned somewhere here....

Are you saying that Sanford and Son are not overly intelligent?

I have no idea who they are!

I would guess that you refer to a company that operates where you live, not where I live!!

Maybe a more detailed question might be better. Just a thought!!

Certainly in Europe, a cardboard crushing machine as described would need safety devices to suite the dangers to anyone (and it!!), not just a simpleton.....it would be required by law!!!

If it shows up on the schematic(it should have one) or not, you can always get a adjustable relief valve which can be used to replace/install new which would let you set the desired pressure based on physical conditions. Just make sure that it is "out of sight" so operators will not tend to play with it.

A machine that can be damaged by an operator pressing the GO button for too long, without some kind of overload indication to tell him to stop pressing it, sounds like a badly designed machine to me.

You realize you are describing most automobiles today. The "Check Engine" light more often than not means replace engine and not perform maintenance.

In the immortal words spoken by DeForest Kelley, "He's dead Jim."

If automobiles had to conform to the same standards as machine tools, they'd never get as far as the showroom (much less be allowed on the road).

The machine is just not idiot proof.

Sounds like it's also a case of poor, or no, operator training.

Idiots are very creative and machines they operate will require positive limits/stops/pressure controls.

Operators can be trained.

There is another thread running here where the OP was told to reset the motor overload to lower than required for motor protection. I don't think this is good practice, but it would limit motor power output.

How about installing a motor current sensor, with adjustable trip point? That would limit torque, and much more sensitive than the usual motor overloads.

Starting might become difficult.

High current could be ignored via a timer for a few seconds on starting.

How many seconds does it take to mangle metal? With this being a 400 VAC motor this sounds to me to be a three phase motor. There probably are not starter windings, too. My comment about starting time might then be moot.

I like much better either the hydraulic pressure relief solution or the active current trip that measures real electric power applied. Just measuring the current without knowing anything about the phase angle could easily produce either many false trips or no trips as the machine rips itself again apart.

It's not unusual to have protection devices which are bypassed for a short time during start-up etc. E.g. using a pressure switch to stop a pump on low discharge pressure (indicating something has failed) it's essential or it would be impossible to start it.

Also the baling press is manually controlled. He's not going to start the motor and get it into an overload situation before the timer has expired.

Worked for a manufacture of cardboard balers and compactors for a few years. Don't know of one that didn't have limit switches for to limit the stroke. If the there is no trash or cardboard for it compress. You don't want the swab to slap up against the gland nut at the rod end. Or at the other end on return. Nor have I seen any motor driven hydraulic device that didn't have a pressure relief valve to control the high pressure output from the pump. Which is placed on the system for just what you discribe damage to the baler.

Go back and inspect that these device are not there. The pressure relief in must applications should be on the pump. There sould be lever actuated switch that would be engaged by the ram or platen.

Given the location of the OP, I think it may be safe to assume that all that extra, unnecessary stuff was taken off the machine and not replaced as they failed or slowed production.

You could be right. And now they are finding out it's damaging the baler. Now we get

How slow is it going to get if they have to have someone jump up and down on the waste to compact it.

When I was a student - many years ago- I had a job in a supermarket. Part of my duties included compacting the waste packaging using a manual screw-press (a bit like a cider press). Only took a couple of minutes and was very little effort. Must be a LOT of waste if they need a hydraulic press.

Yes, and I'll bet you weren't putting out 37kW

Yes, they do much larger batches now. I had a similar experience as you as a child working at the local grocer on weekends baling the cardboard with a manual baler. My pay was whatever I got fro recycling the cardboard (not realizing that my Father was subsidizing me with the gas for his truck...) But as I learned later, those manual presses went by the wayside some time later.

My rude awakening came when I received my first assignment as a new Engineer in 1979, to investigate what my company had provided and what went wrong on a cardboard baler that injured a worker. I remember thinking about my experiences with the manual screw press balers and wondering how someone could hurt themselves on that, and why it involved electrical controls.

For some godforsaken reason, people who make these machines have somehow gotten away with woefully inadequate safety procedures. My company (Klockner Moeller at the time) had provided components to an OEM hydraulic baler mfr, who wired it himself. He made a major mistake in how he powered the auger that pushed the scraps into the press. The worker got his sleeve caught in the auger and it started pulling him in. A co-worker was right there and threw the main disconnect handle of the control panel, but although it killed power to the hydraulic ram, it did not kill power to the auger because the tap-off point for the auger power was on the LINE side of the main disconnect. By the time they found the separate starter for the auger, it had ripped the man's arm out at the shoulder.

We were sued because our name was on the components and we had the deepest pockets. We "won" the lawsuit because we had not designed or wired the equipment, but "winning" involved almost $200,000 in legal fees as I recall.

As part of that investigation, our lawyers had me look over the safety system designs for the entire machine, likely to forward the notion that the OEM was negligent on more than one front. I had some experience with hydraulically driven conveyors from a previous job, so I noticed that there was no bypass on the hydraulics either, which is another serious safety concern. The concern I raised was that of a hose bursting under extreme duress because a worker could, in his zeal to get done faster, over power the system. The way the hoses were laid out, a burst fitting could have easily made the hose whip around and injure the worker as well.

A related point is that high-pressure hydraulic leaks can cut into the skin, with nasty effects, to say nothing of spraying into an eye.

Assuming that the hydraulic solutions are for some reason impossible to implement, then yes, you can get a "smart overload relay" from several of the larger suppliers which can give you what's called an "Active Current" or kW trip function. active Current or kW is a much better indicator of actual shaft torque on the motor. Just reading curren alone means it is subject to fluctuations based on supply voltage, which makes it inaccurate as far as shaft loading. KW or Active Current must use power factor, which means the device must measure the voltage as well as the current, so it will inherently account for voltage variations. You can get this feature in a Siemens Simocode or Allen Bradley E300 smart overload relay.

That said, keep this in mind. There's and old saying:

"You can't make something to be idiot proof, because we humans just keep making better idiots."

Just remember that " If " you train the untrained operator, then the unskilled will become the skilled and an increase in wages will be necessary.

A closed hydraulic circuit press without relief valves doesn't make it through the EU and if it passes, the safety engineer will reject it on the spot.

All companies in the European Union must have that machine checked:

By a Safety engineer when ordered.

By a Safety engineer, who signs it "safe to work" with.

Each Engineer will request 2 valves when the machine is "pressure stopped" . One to set the working pressure and one to serve as absolute safety to safeguard the machine.

Depending on frequency of application he will use one that also operates the pump.

It sounds like the baler was cobbled together with "extra" parts laying around the shop. I've seen that before, a custom machine designed and assembled on the CHEAP.

Have a competent engineer look at the machine and give you a recommendation on the workings.

1. Hydraulics / pneumatics must have over-pressure protection!
2. Electrical must have short or overload protection!

Be careful and good luck!

I agree with the idea of hydraulic solutions put forward so far. I would also fit a pressure gauge with a red line on it. Also a hydraulic solution! As mentioned, these should already be there.
Jim

Hi friends;

Thanks for your inputs. We are going to install hydraulic pressure relief valve.