I need use something that has an adjustment on it of 0" to 2" and the ability hold 500 tons and prevent it from moving the adjustment more than .020". It needs to be able to relatively quickly adjusted back and forth without adding shims, etc. Preferably it can be adjusted with some sort of chain drive and electric motor.
I don't need to *lift" 500 tons, I just need to be able to hold it fairly precisely. So whatever is used for the adjustment needs to be pretty rigid and not able to be back-driven.
I'm thinking of maybe a large Acme threaded rod and nut. How big would I have to go and where would a cheap source for one of these be?
At that sort of weight, I would consider hydraulics. A suitable ram with PO check valve on the load port should hold within your limit. If you really want to go the screw jack route, Google "screw jack" and there are a number of suppliers like this
Cheap idea: Build a couple of wedges and use a come-along and some pulleys to drive them together. Or a bottle jack. Since you'll be making the adjustments unloaded, don't lube anything, so you have more friction to hold it in place when loaded.
500 TONS is a steam locomotove, 1,000,000 Lbs. At 1000 PSI, that requires a piston with 1000 square inches. Let's see A= pi r squared. 1000 = pi (17.8) ^ 2 Whew, an 18" diameter piston.
House movers do this with giant Acme screws that are DRIVER by hydraulic motors. I believe this is still the current technology. No check valves, and even a burst hose will just require you to stop and replace the hose.
These things should be commercially available, but I'd guess pretty expensive. What the HELL are you moving that weighs as much as main-line steam loco?
The forces required to press these wedges together, even if lubricated, is going to be enormous! The two wedges need to slide on TWO load-bearing surfaces. Even if the wedges are made with an angle of just a couple of degrees to reduce the vector force pushing them apart, the friction is going to be staggering. Neglecting the force to spread the wedges, you think you can slide a 1,000,000 Lb. object with a come-along? ONE MILLION POUNDS?
He said pretty clearly that he's not going to lift with it, just hold position. Even if you skipped his part of the message, I said "Since you'll be making the adjustments unloaded...." INGLESH!
The OP specified that the adjustment won't be made under load. Wedges may be the best approach. The leveling feet used for large machinery come to mind. The levelers on this page get in the neighborhood (~
250,000 lbs), though I think they're able to adjust that much weight, so can probably support much more.
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My SWAG is a screw around 8-10" in diameter would be required to support
10^6 pounds, depending on material, length of the nut, etc. Oh, and whether anyone may stick their head under the load .
How are you dropping the load on to your support/adjuster?
We have power presses in the 800 ton capacity (and much larger). They will easily drive 4 6" diameter hardened cylinders a couple of millimeters into a 2" thick mild steel plates under less than their maximum capacity.
While your load may be 500 tons, the capacity of your support should be much greater, depending on how the load will be lowered onto it.
If your support fails when the load is dropped, it will likely come out sideways (going *through* any fleshy bodys in the way. Seriously).
Hmm, this sort of thing was right up my alley......600 ton CANDU reactor assembly alignment.
What is "fairly precisely"? .001", .010", 1/2", it matters, because at
500 tons the floor will deflect a certain amount which you would also have to adjust for.
As a minimum your load needs to be supported on three "legs". If you arrange for 6 hard points on your load you can support it on three hydraulic cylinders temporarily, and three structural "stools".
Check the levelness of your set-up, make notes of what height adjustment is required at each of the support stools, jack up the load with hydraulics, and place shims between the load and the stools. Repeat until load is "level" for your purposes.
There are a number of variants available on this scheme. You can get hydraulic cylinders with follower nuts to provide hard stops for the rams, if you cannot have 6 hard points on your load.
In practical terms you can get away with one hydraulic jack and three "stools". You would have to move the jack to adjust the elevation of the load at each stool location. This could get tedious if your levelling requirements are very tight, because you will have to "go around" several times until things remain level. You may also have to make "in-process" adjustments as the floor settles, unless you happen to be on bedrock.
You might be able to rent the jacking equipment from a large millwrighting/construction company if your requirement is of a temporary nature.
Further, I seem to recall that cylinders up to 18" dia. are standard items, although probably not "off-the-shelf".
Good advice from all (well, not the guy thinking I was pulling your legs).
I think the simplest method is a pattern of really big bolts. I only need to maintain a height of .020 so it's not super critical to have really tight tolerances. They just can't backdrive. Do normal bolts backdrive? I'm pretty sure acme threads don't.
If I use four bolts (four fits my applicaiton better than three) then they each would only have to hold 125 tons. How big of bolt to hold this much tonnage? Any idea where I can find these used and cheap? I don't want to have to machine these myself.
What hardness do these big bolts typically come in? I'm guessing anything that uses something this big won't be made from mild steel.
I don't know what the typical strengths of these bolts are but if I assume a compressive bearing strength of 120ksi then you're talking about four bolts that are 2 1/2" in diameter (with a safety factor of two). If I want to try to do this with one bolt then I'm looking at about a 5" diameter.
The problem I have is I'm just not use to dealing with this much power so I don't know what's commonly available and probably just sitting in a yard somewhere gathering rust (that I might be able to purchase by the pound). A crane or large power equipment guy would know right off the bat. I don't even know where to find these yards. Yellow pages?
Does anybody else find this thread scary? The OP is on unfamiliar ground (Duh - he wouldn't be asking here otherwise), many of the responses are not from experience and we're talking about 500 TONS! Things don't have to go very wrong for it to be very bad! I like a challenge and often do things that many others consider crazy, but this would not be one of them. This is a job for someone who has a lot of experience with these things. A *professional*.
Stan, what is your actual application. As for large bolts, I would suggest calling around for large hydraulics shops. You may get lucky and find some bored engineer who would help you gratis with strength calculations and may find some junk bolts that they would give you (if the lawyers are not watching). Not knowing your application, I am a little scared as safety involes a lot of issues such as strength of foundation and soil, which you have not discussed.
Loads which are not correctly leveled will not exert equal force amongst four contact points. In the case of having four points in a square or rectangular configuration with the force centered, only two of the contact points (kitty-corner) will be acted upon until the object is "leveled" amongst all four contact points.
Now, it sounds that you may be leveling your load first, and then applying the full force. In that case, it's not such an issue. If you're leveling your block under full load, each support must safely support 250 tons.
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