Cylinder Rod End Condition

[elphou]

I am designing a cylinder rod to be used in transmitting fluid at pressure. I've attached a picture that described what we have.

We are column loading a cylinder rod and I wanted to seek advice on the "K" value end condition constant.

The cylinder piston is fixed on either end but when extended by about 25" looks pretty slender. An O-Ring retains the pressure and a short rod bearing is used to somewhat keep it straight.

On the column loading of the rod, does anyone think I can use K=1 for the end condtion. Does the rod bearing provide enough support to justify K=1.

The cylinder rod is basically a hollow tube within a tube.

 

[GregLocock]

Can't you work out the likely deflected shape of the ram, taking into account the clearance in the sleeve bearing, and then calculate buckling for an eccentrically loaded column using the secant formula? Alternatively I would have thought inspection of hydraulic ram catalogues would give some idea of what they regard as practical limits.




Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dvd]

When I assumed a 10 lb load on the rod it looked pretty good; when I assumed a 1000 kip load on the rod it looked like I ought to know what the rod diameter was.

It doesn't seem very prudent to put a sketch that doesn't give enought information for someone to make an engineering judgement on an internet website and solicit opinions from strangers. Give a better description of the guiding for the load and cylinder. Explain your forces, etc. by doing this you might even answer your own question.

I think your seals may fail due to rod deflection at the rod seals before the column will have problems. Can you design for a longer length of rod to remain inside the cylinder to act as a stop-tube?

 

[MikeHalloran]

Given normal bearing clearances and normal o-ring gland gaps, you can't assume any part of the cylinder is fixed in the usual sense.

I'd be inclined to fix one end of one of the tubes, e.g. by screwing it against a shoulder, or bolting an integral flange to a face.



Mike Halloran
Pembroke Pines, FL, USA