hello everybody,
We make spms and hydraulic powerpacks. Recently we started manufacturing hydraulic cylinders. During our first experiment we found lot's vibrations in our cylinder in feed(not in rapid though)! Not just that it doesn't move at very low feeds. Our cylinder is for machine tool application and one DA and two wear rings have been used. Can any one plz suggest me the possible reasons and sollutions for that? so i can go ahead. And i found there are no mechanincal vibrations. So plz reply with your valuable sudgetions.

How are you controlling the cylinder speed...metering the fluid in or out?

Try Googling Hydraulic Cylinder Lunge.

"Fluid compressibility has a great effect on cylinder performance. Especially when the fluid type is
changed, such as changing from a mineral oil to a water-based or synthetic fluid. Hydraulic cylinders
are especially sensitive to changes in bulk modulus. In critical operations it is often necessary to extend the
cylinder smoothly and at a very constant velocity. If the load changes, the compressibility of the hydraulic
fluid will have a negative influence on the constant velocity. Also, any change in the volume ( Delta V ) of
the fluid under compression will translate into a change in cylinder stroke ( Delta S) defined as “lunge.” The
following expressions can be used to calculate “lunge” ( Delta S) and the resultant velocity change ( Delta v):"

"The degree of “lunge” is directly proportional to the load
change and inversely proportional to the bulk modulus of the fluid. In addition, cylinder lunge is greater
in the meter-out mode than in the meter-in mode. This is due to pressure intensification in the rod-end
of the cylinder"


Regards Woody

This message has been edited. Last edited by: Woodygb,

You may have stiction problems. Stiction comes from STactic frICTION and deals with seals and valves sticking at low speeds. A google shows several patents for low stiction cylinders and most manufactures of pneumatic and hydraulic cylinders make mention of it.

Ditto what NA said. In addition, the ratio of the static friction to the dynamic friction is too high.

Thanks everybody,
Yes i also found it must be stiction problem. I also found wear rings are sticking with cylinder tube. Thanks for your replies. And NA What do you mean by low stiction cylinder what is the difference can u plz explain?

Humnnn...I guess your systems natural frequency is low... .

Hello.
Well, when the cylinder is manufactured and assembled for the first time, during the first test some vibration may occur but, after the air inside the cylinder is bled out the only one that you can see is caused by the roughness of the tube. This is polished by the seals and after some strokes it will disappear. If after some time the vibration remains, then you need to check for misalignment, bushings or wear rings too tight. Double acting PTFE composite seals are good for that application.

Regards

KamilRhu

Hydraulic Cylinder video