Hydraulic Cylinder Rotation

[kklinger]

Group,
I am looking for ideas. We are trying to qualify a replacement hydraulic cylinder from a new cylinder manufacturer. During cycling of the new cylinder, the cylinder rod rotates which leads to loosening of threaded connections. The new cylinder manufacturer does not have a much, if any, engineering support. Our current cylinder does not have this rotation problem.
My first guess is that there is a "rifling" effect where there are small groves introduced during the machining causing the cylinder rod to rotate. But I am looking for other ideas which could cause the cylinder rod to rotate.

Thanks,

Kirk

 

[maytag]

Its been my experience in heavy industry that all cylinders want to rotate-thats why the piston will be mechanically
(grub screw) and sometimes chemically fixed to the rod-also the clevis or rod eye will be fixed chemically or mechanically by some means. Some design as far as mounting and rod attachment can hide this rotation force but I would never put a cylinder in service without addressing this issue. Bud T, that frequents these forums, worked for Miller Cylinders for years may have some better advise along with some other regulars. Good luck,
Maytag

 

[hydtools]

The threaded connections may have not been tight enough to prevent the rotation.

Was the new cylinder connected differently than the old?

Ted

 

[kklinger]

The cylinder is a single acting cylinder with the hydraulic pressure coming in at the end of a hollow rod and the pressure pushing the cylinder casing away from the rod. At the end of the hollow rod is a block with the fitting port, which is threaded into the hollow rod. After torquing and applying red loctite, this block still works itself loose with cycling of the cylinder.

The new cylinder and old cylinder were connected identically.

Thanks,

Kirk

 

[maytag]

I have the same mounting arrangement with a vertical mounted, rod down, single acting cylinder(arc furnace regulation)-in this application the rod is locked in place with a mechanical lock to keep it from rotating. Maytag

 

[zeusfaber]

We had a similar problem a few years ago when somebody started doing non-oem overhauls on one of our main assemblies.

In our case, all it took was getting the end fittings torqued up to the manufacturer's spec instead of "matey boy's" "feels about right".

A.

 

[hydromech]

When a hydraulic piston begins to move the hydro dynamic support is near perfect and it becomes very easy to rotate the rod/cylinder.

The difference between the two cylinders may be in the piston/rod seals. Have the seals been checked are they identical in the two cylinders?

One set of seals may have a higher contact ratio with the cylinder wall or rod surface.

Adrian

 

[kklinger]

The required torque to turn the cylinder rod while the cylinder is loaded for the new cylinder is twice that of the old cylinder. We are going to inspect the seals and guides between the old and new cylinders.

Thanks,

Kirk

 

[SincoTC]

If the new cylinder requires a lot more torque to rotate it, is it possible that it is bent slightly or somthing has got misaligned, resulting in a slight "kick" during the stroke which is loosening the screwes block?

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

SW2007x64 SP3.0 Pentium P4 3.6Ghz, 4Gb Ram ATI FireGL V7100 Driver: 8.323.0.0
SW2007x32 SP4.0 Pentium P4 3.6Ghz, 2Gb Ram NVIDIA Quadro FX 500 Driver: 6.14.10.7756

 

[gerhardl]

If two, seemingly equal, mechanical components behave differently, there must be either some difference in working conditions (which seems here to be excluded) or in the components themselves.

The posts above have pinpointed some possibillities, and sealings are also in my mind an important checkpoints.

But there might also be another difference: one cylinder better or more precise machined, constructed and mounted (better quality) than the other.

 

[btrueblood]

Uh, wait - you say this is a single-acting cylinder? Is it a spring-return type? Most coil springs will twist slightly as they are deflected, unless they are restrained from doing so. Sometimes two nested springs of opposite wind can be used to balance or negate any twist.

 

[budt]

Kirk wrote:

"The cylinder is a single acting cylinder with the hydraulic pressure coming in at the end of a hollow rod and the pressure pushing the cylinder casing away from the rod."

The only possible time for the Rod (RAM it is normally called in this type Single Acting construction) to come unscrewed is when it is being pulled out by an external force. The only forces restricting that movement is Seal friction at the Ram, VACUUM of One Atmosphere or other mechanical stiction such as the design of the internal Ram Guide/Guides. That is, UNLESS THE ITEM TH RAM IS SCREWED INTO IS ALSO FREE TO TURN.

Vacuum at maximum would be 14.5 PSI on an average day at Sea Level and would have little consequence umless the Ram is a large size.

Vacuum would be high if movement of the Ram Body was very rapid and/or the drilled hole in the Ram was undersize or Orificed for some reason.

Sloppy thread fit giving less surface contact could account for the problem also. After all a Thread is an Inclined Plane that can always allow movement when acted on by external forces.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[kklinger]

The cylinder is rod side down and the return stroke is powered by gravity. Therefore, there are no springs or external forces pulling on the cylinder (good points, though).
I have investigated the seals and rod guides, and the only differences are the old cylinder gland has only one rod guide vs. two rod guides for the new cylinder; and the rod seal on the new cylinder has two sealing edges vs. one sealing edge on the old cylinder.
Our next step is to try to isolate if the problem comes from the machining of the cylinder rod.
I am also suspect of the thread quality of the new cylinder.

Thanks,

Kirk

 

[jetmaker]

Don't know if you can try this at this stage, but how about reversing the thread direction. i.e. right hand thread now... make left hand, and see if problem continues.

jetmaker

 

[EdDanzer]

The rotation is usually caused by the honing marks in the barrel. Your piston seal material can cause greater friction against the barrel hone marks causing more rotational force. The unscrewing can be caused by poor design in the piston to rod interface. thread725-217378 has more information about your problem.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[budt]

Kirk wrote:

"The cylinder is rod side down and the return stroke is powered by gravity."

Remove the threads from the Ram or what it is screwed into since the unit is always in compression. That would eliminate any unscrewing possibility.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[SincoTC]

I don't know what grade of Loctite you're using, but you said that you torqued the joint then applied the Loctite; was it the type that will "wick" in and was the thread fit too good to allow this? I prefer to apply prior to assembly to ensure adequate coverage, even then, some combinations of material/surface finish (or oily contaminents) can prevent proper curing. A primer/activator is required on some grades, especially with steels. In the absence of this, you can try rubbing the components with a brass bristled brush or using a piece of brass or copper in a file like action the threads, even applying some very fine dust obtained by rubbing a bit of brass on some clean dry abrasive paper to the loctite just before assembly. The presence of copper ions will trigger the curing process and result in a much stronger bond.

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

SW2007x64 SP3.0 Pentium P4 3.6Ghz, 4Gb Ram ATI FireGL V7100 Driver: 8.323.0.0
SW2007x32 SP4.0 Pentium P4 3.6Ghz, 2Gb Ram NVIDIA Quadro FX 500 Driver: 6.14.10.7756