Cylinder Piston Rod Breakage

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

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

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.

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

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

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

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

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.

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.

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

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

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.

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!

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?

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

O

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

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

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.