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Cylinder Piston Rod Breakage

01/16/2012 10:16 AM

We had a pneumatic cylinder used to move rubber from one idle roller conveyor to other idle roller conveyor . Frequently we are facing piston rod breakage at rod threading portion.

Cylinder dia is 100 mm and stroke length is 1200mm.

what would be the possible reason for the breakage and parameters to be checked.

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Guru

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#1

Re: Cylinder Piston rod breakage

01/16/2012 10:20 AM

Sounds like something is mis-aligned and the rod is failing at its weakest point.

Or, it's too small for the applied load.

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#2

Re: Cylinder Piston rod breakage

01/16/2012 10:26 AM

You wrote, "what would be the possible reason for the breakage and parameters to be checked."

Obviously, the weak link is breaking.

Either the system is under rated for the task at hand or...

The system is incorrectly deployed.

That is about the best anyone here can do to help you because there is so much information missing here that it is impossible to narrow down the problem and then recommend a fix. As they say, god knows, but he isn't telling.

Who made and installed the device? You should consult with them to see what they recommend for a fix. You may need to simply use a more robust pneumatic cylinder assembly or it may be the way it is implemented that needs to be changed.

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#3

Re: Cylinder Piston rod breakage

01/16/2012 10:35 AM

Hi,

Difficult to give an opinion without drawing or preferably photo of the application.

The root of the rod thread is a weak point, (I would think the rod is 25mm diameter and the thread M20 x 1.5).

In my experience, the usual cause of that type of rod failure, is the piston rod fork end mounting (I assume that the cylinder is flexibly mounted at both ends) cannot move fully through it's arc of movement and causes the rod to snap off "like a carrot". Also if the cylinder is mounted with a rear hinge assembly and a piston rod fork, the extended length of a 1200mm stroke cylinder will be over 2500mm and the assembly will sag causing high stress at the rod thread junction.

The above is all a bit speculative without a drawing or preferably photo of the application.

Look forward to hearing your thoughts.

Best regards,

John

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#12
In reply to #3

Re: Cylinder Piston rod breakage

01/17/2012 5:29 AM

all rod loads should be compressive so no way things will snap while extending

loads while retracting can will lead to either the piston extruding the shaft at either end until the nut end or clevis end snaps off ,another cause if air pressure does not exceed the maximum rating plus 50% is lack of cushioning at the end of stoke causing a shock load usually if not always at the clevis end

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#14
In reply to #12

Re: Cylinder Piston rod breakage

01/17/2012 1:30 PM

You've obviously never watched an out of line cylinder operating!

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#4

Re: Cylinder Piston Rod Breakage

01/16/2012 11:05 AM

When was the original equipment manufacturer contacted for advice and why has that advice been disregarded?

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#5
In reply to #4

Re: Cylinder Piston Rod Breakage

01/16/2012 12:51 PM

Probably because they still want to be paid for the installation. It could also just be that they insist on being paid for "out of warranty" repairs.

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#11
In reply to #5

Re: Cylinder Piston Rod Breakage

01/17/2012 3:26 AM

Then perhaps the original poster will say so.

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#6

Re: Cylinder Piston Rod Breakage

01/16/2012 5:20 PM

Is this a case where the cylinder is being used as a linear actuator meaning all side and moment loads are being transmitted to the cylinder rod? If this is the case, proper linear guides are needed in addition to the cylinder.

Another possibility is inadequate cylinder/rod float in some axis that puts load on the rod instead of allowing float. I have seen this mistake such as the cylinder is mounted rigidly when it should be trunnion mounted.

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#7

Re: Cylinder Piston Rod Breakage

01/16/2012 6:30 PM

If the rod packing is or has not been damaged, I would suspect that the rod end is of the wrong design. When ordering cylinders the rod end can be ordered in several different sizes. I would check with the OEM to see what they have to say 1st. If you do not get a satisfactory answer, I would suggest going to the cylinder manufacture. They will be able to tell you why it failed and how to effectively make repairs.

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#8

Re: Cylinder Piston Rod Breakage

01/16/2012 11:06 PM

This is your third successive post about some breakage. Do you have anything that is not broken yet?

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#9
In reply to #8

Re: Cylinder Piston Rod Breakage

01/16/2012 11:29 PM

Yes, but we're working on it....

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#13
In reply to #8

Re: Cylinder Piston Rod Breakage

01/17/2012 9:34 AM

Sounds more like they are trying to push equipment past there design limits. Too much weight on conveyors could cause the axle and pusher failures.

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#10

Re: Cylinder Piston Rod Breakage

01/17/2012 12:26 AM

That's 3 breakages you've reported.

Have you inherited this legacy and are now trying to sort out the problems and eliminate recurrences?

With every additional post of yours it is looking allot like a facility wide alignment practice or flimsy design problem.

Share your pain not just your problems.

Good luck!

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#15

Re: Cylinder Piston Rod Breakage

01/17/2012 6:07 PM

Is the rubber being pushed sideways off the first rollers? This will have a massive additional friction load. Can the final section of the first conveyor be replaced by balls, so the change of direction will not have such a large load?

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#18
In reply to #15

Re: Cylinder Piston Rod Breakage

01/18/2012 4:59 PM

I'd agree with that - GA

I have a picture of a big plate threaded to the rod end to do the pushing and the load is cranking the plate. Hence the breakage.

What this usually means is the cylinder is mounted too high as the designer has not considered friction (i.e your fix applies) or offset/off centre forces.

But such a long stroke for the diameters, should be gimbal mounted and the plate fully guided

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#20
In reply to #15

Re: Cylinder Piston Rod Breakage

01/19/2012 6:22 AM

This weeks movie review by Major Elkie.

I recently watched, in the privacy of my dacha, the movie, "Sideways Friction Load", starring Rod Packing.

It was not what I had expected, given the promising cover blurbs: " rubbers being pushed sideways,,, large loads,,,replaced by balls,,, massive additional ,,,load",

Was not expecting film strip presented by my 9th grade shop teacher.

Much disappointed by deceptive advertising, cannot recommend this movie.

Major Elkie, out

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#21
In reply to #20

Re: Cylinder Piston Rod Film Review

01/19/2012 7:50 AM

Thank you, Major. I shall make a note to avoid this movie.

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#16

Re: Cylinder Piston Rod Breakage

01/17/2012 9:20 PM

O

I see now, you owners manual is Chinese you need Chinese man translator

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#17

Re: Cylinder Piston Rod Breakage

01/18/2012 2:29 PM

In general, a piston rod breaking near the piston is from overspeed and at the crankshaft end is from insufficient lubrication.

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#19

Re: Cylinder Piston Rod Breakage

01/18/2012 9:23 PM

What is the size and type of threads and MOC of piston rod. For 1200 mm stroke, how much (length)portion of the piston rod remains inside the cylinder when full length of movement is achieved?

To achive 1200 mm movement from the cylinder, stroke length selected should be at least 15 to 20% more so that in full extension, threaded portion of the rod is not loaded transversally due to sagging or self weight.

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