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.

quote:

Originally posted by keyur trivedi:
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.

Are you sure there is no air in your cylinder, this is a problem especially when your hose volum exceeds the volume of the cylinder. Send me a drawing of your cylinder and seal arrangement and maybe I can help. You can get my email off my webpage.

http://hansonhydraulics.com/contact.html

thank you,
I don't think there is air inside it. Let me give you some datas regarding our cylinder.
Bore dia. : 32 mm
Piston dia. : 30 mm
Rod dia. : 18 mm
Bore length(stroke length) : 120 mm
Hose pipes : 3/8" and about 1.5 mtrs long.
Sealing : One glydring(T-type) in the center and two wear rings around it.
Another cylinder of 63 mm bore and 1300 mm stroke with same types of hoses and power pack is working very nicely. I hope the above datas are helpful to you to guide me to go ahead.

Regard,

keyur v. trivedi

quote:

During our first experiment we found lot's vibrations in our cylinder in feed(not in rapid though)!

Sorry keyour, I might have misunderstood your first post. I was thinking that you were just testing a newly designed cylinder and it was chattering with no load on it. It is actually installed on a machine with a load on it? Does it chatter with no load just extending on its own?

quote:

I don't think there is air inside it.

Try purging the lines to be sure there is no air. The retract volume of your cylinder is 65,973.6mm^3. The extend volume is 96,510mm^3. Both are smaller than the volume of the pipe you listed - 106771.67mm^3. In such a case, the cylinder will not purge itself of air, it will keep traveling back and forth between the cylinder and the control valve, if in fact the valve is 1.5 meters away.
What kind of control valve is being used? Is there any form of feedback?
As far as cylinder design goes: is it true that the od of your piston has 2mm diametrical clearance to the bore? Pay special attention to the wear band grooves on the piston, radiuses in the corners of the grooves often make the fit tighter than it should be, if you can, undercut the corners. As far as piston seals go, TFE's are the way to go, but tighten up on the diametrical clearance on the od of the piston .015" (.381mm), assuming it's not a steel piston, .005" (.127) diametrical clearance on the od of the wearbands

thank you mr. doug,
My cylinder was vibrating itself it was not attached to the machine. But because of your help the no load vibrations have been stoped. I have done the following two things.
(1) shortened the hose lengths.
(2) Removed the wear rings.
Though i haven't checked it onload. But i think it will work. I have used 4/3 position directional control valve(rexroth made) and yes i have visited your website and opened an accnt. in it. It's really nice and weldesigned. Now as i have removed the wear rings, will it affect the life of cylinder?

Removing the wearbands may very well destroy your cylinder. Depends what the clearance on the od of the piston to the bore is and what the piston and barrell material are. Send me a drawing and I can give you some ideas.
You had the right idea with two wearbands, narrow and one at each end, I prefer glass filled nylon. Machine the grooves so there will be .005" of diametrical clearance from the od of the wearband to the bore. Machine the od of the piston so there is .015" diametrical clearance to the bore. Make sure the radius in the corners of the wearband grooves don't interfere. You can either undercut the corners in the grooves, or chamfer the inside edges of the wear bands.
If your piston is steel, the od should have more that .015" clearance which means using a piston seal with some sort of anti extrusion device.
T seals arn't my favorite, but they will do the job.

Keyur, I got your drawing. I've got the following suggestions for your cylinder:

Attached is a drawing of a gland cartridge. There is a lot of guess work with everything in reference to the outside diameter of the cartridge, which is unknown to me.
The changes I have made were to eliminate one wearband. It’s a poor design to have a wearband located between the rod seal and wiper as it will not get any lubrication. The rod wiper style has changed to a single lip design to reduce friction, the rod seal has been changed to a single lip design to reduce friction and to maintain a very small amount of film lubrication for the wiper. It also has a smaller cross section, to provide a little more strength to the structure of the cartridge. Also the oring groove in the od has been moved closer to the piston end to provide more material in between the oring grove and the rod seal groove.
It’s just a rough drawing with no chamfering or radiuses.

Use Bussak/Trelleborg rod seal RU0300180
Bussak/Trelleborg Rod wiper WAP000180
Parker glass filled nylon wearband G022018048GB/N (2mm cross section, 4.8mm height)


I don’t have the clearances on your current piston arrangement, just check the radius in the corners of the wear band grooves, and I would change the wearbands and seal to the following:

Use Bronze filled Teflon piston seal Parker# P032024032P2B Check groove diameter – 24.5mm, height 3.2mm
Use 2 glass filled nylon wear bands Parker # G032028048GB/N Check groove dimensions, groove diameter 28mm height 5mm
Make sure the wearbands have a large endgap or groove across them to help trapped air get out from between the wearbands and the piston seal.

The glass filled nylong wearbands may need to be trimmed down from larger wear bands, but your seal supplier should be able to do this. If you want I could put seal kits together for you, but I’m sure your current supplier can figure it out.

The other problem I noticed is the oring/back up rings used. For the tube seals, if the groove diameter is 41mm and the tube diameter is 37mm, you would want to use a 2.5mm cross section oring with an od of 41mm = 36mmx2.5mm oring and a 2mm cross section back up that had an id of 37mm = 37mmx2mm backup ring.

Hope this helps.

gland.pdf (19 KB, 23 downloads)

quote:

cylinder vibrations

What vibration are you trying to reduce? presumably the prop doesn't care, and the engine is OK. Have you considered cutting the entire nose of the plane off and mounting it very softly back to the rest of the plane?


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