Using hydraulic cylinders for cannon barrels

[jeeper1]

I know there have been postsin the past about them but I don't remember the outcome.
This thursday 8-11 there will be a "cummins industrial tools" truckload tool sale blow into town. I know most of what they sell is just so much junk. One thing did catch my eye, it's described as "tie rod hydraulic cylinder, 4' diameter, 1 3/4" shaft, 24" stroke, 2,500 psi. $69.99
Does that mean  the bore is 4 inches and just the shaft is 1.75 inches or does that mean the OD is 4 inches and the bore is 1.75 inches?
 And would 2,500 psi be enough for either?
Or would a high pressure plug be needed?
Would $70 be too much if it is OK to use for either a cannon or mortar?
 I know, lots of questions.

[Terry C.]

Hydraulic cylinders are generally classified by bore diameter, so a 4" cylinder would have a 4" bore. For a 2500 psi cylinder, wall thickness would probably be ¼" giving it an OD of 4½".

The shaft is 1¾" diameter. That's about average for a cylinder this size. Retractable (two-way) cylinders have a shaft that is smaller in diameter than the piston. FYI: These cylinders are able to exert more force in one direction (extending) than the opposite direction (retracting) because the surface area of the piston is reduced on the side where it mates to the shaft. This is a trade-off. The shaft must be of sufficient diameter that it will not flex under load, but the effective surface area of the piston is reduced by an amount equal to the cross-section of the shaft.

(probably way more info than you wanted)

But since this is a sale, there's no guarantee that the person doing the listing knows squat about cylinders. It could very well be a 3½" cylinder with a 4" OD.

As for the suitability for a cannon project, I will have to leave that to our more experienced members. Personally, I would be reluctant to use a tube with a bore that big with a wall thickness that thin.

[GGaskill]

I would say that the OD is 4" and the bore is 1.75" and the 2500 psi is the maximum pressure the seals will resist.  Sounds something like this:
http://www.harborfreight.com/cpi/photos/36400-36499/36468.gif">
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=36468" target="_blank">Harbor Freight long stroke jack
 
Although the 2500 psi is not the strength of the steel, that is a quite low number even for black powder pressures.  Since you don't know what the material is, I would be real leary of trying to make a cannon from one of these.  It's way too long for a mortar unless you cut it off.

[Terry C.]

I just re-read your post and noticed that this is a "tie-rod" cylinder (missed that the first time).

That means that the butt and head will be held in place with threaded rods. When the rods are removed, the butt and head will separate from the tube.

[jeeper1]

I was hoping it was a 1.75inch bore so I could have a golfball launcher. My 37mm launchers are fun but getting the 35mm filmcans is getting harder especially when I launch 100 plus of them in under an hour like I did yesterday.

[Cat Whisperer]

The pressures generated with golf balls is minimal.  Not so for denser projectiles as zinc or iron (about the same).


Hydraulic cylinders take tremendous pressure.  BUT they also take a fair amount of wear.  That says to me that the steel is most likely heat treated to gain strength and hardness (for abrasion resistance).  With hardness you lessen ductility - which when you loose it you've got a brittle material.  So for light loads they're most likely ok, but for heavy loads and for many many rounds I'd pick something else.

JMHBAO

[GGaskill]

Without knowing the details of the cylinders in question, I expect they are case hardened for wear resistance but not through hardened.

But keep that first phrase in mind.

[jeeper1]

I guess I'll pass on the idea. Thanks for the help.

[Cat Whisperer]

Agreed on both counts.

Case hardening gives the depth of hardness needed (minimal) with the strength/ductility needed right behind it.  Consistant with theory and the (few) cylinders that I've encountered.

There's a company here in town (Xaloy) that makes bimetalic tubes for extrusion.  (Food and plastics industries.)  They use 4140 with a propriatary mix of alloy that is melted onto the inside then honed.  Cores of 4140 are found from time to time on the second hand market and end pieces of the cored tubes have made there way into mortars by several local folks.

[Cannonmaker]

The hydraulic cylinders may make good liners for a cast tube, although I personally would not use as the tube itself.
  With the tie rod rams I have had them swell up at the ends and start to leek, so even at 2500 psi they can deform.