Am just wondering what is the best way to mount a 30 tonne hydraulic ram onto the top cross member of a hydraulic press? It needs to be moved from side to side (as you'd expect) and the ram is double acting. All the ideas I've thought of do not allow for both movement and a decent lock to prevent any slippage when the ram is in action. Any comments on this would be much appreciated!
Hydraulic cylinders and presses come in many shapes and sizes. With out some details of the configuration of both, I don't know how anyone will be able to help you. A few drawings would be a great start.
"BLOliver" wrote in news:1125520675.600214.243700 @g14g2000cwa.googlegroups.com:
Well, actually I wouldn't expect the ram on a hydraulic press to move from side to side. I've never encountered one that did. I expect that this indicates that you mean something other than my reading of your post. It is difficult to convey in a few words particular design constraints and requirements. If you could throw a drawing up on the web and post a pointer, we would be more likely to be able to help.
When you say double acting, does that mean that the ram retracts via hydraulic pressure or that it is actually taking a load during retraction? Is it single or double ended?
Assuming you keep the ram's "column stability" under control (not too long a ram) , then if you keep the ram's "force-axis- to- mount" angle under 3 degrees from the axis of force, and you don't use a trunion mount, it self-locks.
You might consider using a heavy T-slot bar on the cross-head, and support the ram from a plate with the machinists T-bolts up into the T-slots (T-bolts for dogging down after horizontal movement),
if location directly under the ram is not always the reaction pad, you can move the reaction pad by using threaded rods in the ram mount plate and same-pitch threaded rod on the reaction pad below - you connect the two (four, actually) rods via chain and chain sprockets - the upper ram moves with the lower reaction pad, inch per inch.
The first link is a company that makes a press similar to what you're asking about. You can even download the manual for the press, and see how the parts go together. The second is a picture of the
15,000 lb. version that press in my shop. They make it up to 60,000 lbs.
The ram on this machine hangs between rails which make up the top of the frame. It has four rollers that ride on top of the rails, and which allow the ram to move left and right by means of an acme screw and crank handle. The lower end of the ram casting has heavy ribs on it, fore and aft, which hook under the rails. The distance between the rollers and the ribs is about .015 more than the depth of the rails. When the ram is extended, and pressed downward against the work, the body of the ram is lifted against the ribs, and force is transfered to the rails, and thereby into the whole frame.
I've had this press for about 10 years, and it's always worked well and easily. Your double acting ram might be a problem, though. Does it actually work in both directions, or is the powered upstroke just a way to retract the ram without using springs. My press uses springs; but I'm quite happy with it that way.
Hope this helps!
KG __ I'm sick of spam. The 2 in my adress doesn't belong there.
The first website you gave me was perfect for what I wanted... really helped me with the visual side of my design.. it is very similar to what I was thinking...
Just a couple of queries tho...
1) The manual from the first website did not allow for the ram to move from side to side though right? Or am I reading the plans wrong?
2) It is a little off topic but I didnt want to spam new threads :P If a ram has an "effective area" of X. and a hand pump has "Oil volume per stroke" of Y. Does that mean that per stroke the ram will move Y/X per stroke? (Assume all are in correct dimensions ofc). I ask this because I wanted to make my press portable and use a hand pump but it seems for me to extend the ram by 300mm i almost need 100 strokes! Is 100 strokes deemed as acceptable by hand or am I doing something wrong?
Look at the manual, and at the picture on my site, more carefully. There's a horizontal screw, with a crank at it's right end. That's attached to the ram via a small bracket. When the ram is retracted (sitting on its rollers, and not squeezed upward against the frame, the screw will move the ram easily to the left or right. That's one of the features that I liked when I bought the press.
And yes, you've got the stroke count right; but 300mm is pretty long for a portable hand pump, so 100 strokes is going to be a lot of pumping. Look again at the press manual. The ram has a big screw at the business end, which is used for fast, rough positioning. If the ram (fully retracted), is 100 mm from the work, but I only need, say, 25mm of actual high force pressing, I can extend the screw at the end of the ram to get close to the work before I start pumping. That saves a lot of time and effort.
Of course, if the ram on your system will be loaded for all of 300mm of travel, then this won't help you any. Consider a bigger pump, or a smaller ram and higher pressures (probably from a longer handle) if long strokes are going to be common. I suspect that there are two stage hand pumps out there someplace, so you could get fast action when the load is light, and high pressure when it's needed.
Now that I think about it, the manual that I pointed you to might be for a model that doesn't have the left and right motion feature. Take a look at the other models in that family. Or, look again at the picture on my site. This is a relatively simple thing, once you see it.
Hydraulic hand pumps sometimes use a dual piston system, a large volume low pressure cylinder closes the press until it 'bites', and the low pressure piston can no longer close the press, the high pressure, low volume piston then finishes the job.
I have engineered air-over-oil presses, that used air pressure (via the oil) to extend the ram to contact the workpiece.
Additionally, there are circuits that will divert the rod-end flow to the non-rod-end. This will give you a faster advance (but lower applied force), until you switch over. Usually a sequencing valve is used to switch over.