Bridge Crane build

[rabler]

I decided to go down the route of running a shaft from one truck to the other on the one getting built up here. That shaft needs to be supported at several points, or be a pretty stout shaft. However, rather than drive the wheel directly the shaft drives a sprocket on each end, with roller chain run down each rail. It was the cheapest way I could come up with to drive/clock the trucks. $80 for chain, CNC milled sprockets, etc. Adding a motor later would be easy.

The big advantage was being able to use off the shelf rollers. As you're finding out bearings for that sort of load aren't easy/cheap to find. What ended up in the one here are 12,000 lb rated, but are smaller in diameter than what would have preferred. But at $80 ea, they didn't break the bank.

More complex, but the chain clocking should allow the lift hook to get within about 16"-18" of the wall.

IPlanning here on pre-drilling my bridge for two mounting points (basically 8' spacing) for such a shaft. Again not sure I'll use them. But having them and not needing them beats needing and not having. Anything drilled into the bridge would be on/near the neutral axis of the web and relatively small holes. The chain/sprocket approach had occurred to me but I'm really only at the point of facilitating motor/shaft as a potential rather than a requirement.

I'm thinking I'll want the guide bearings (track rollers) on the trucks regardless. With a free-standing frame I want to ability to accomodate flex/motion in the frame so the bearings keep things from binding. I may well be overthinking it, which isn't a bad thing in this case.

 

[motormech1]

As I was reading your last post I looked out the office window and thought "Well hell, maybe a pic of an industrial unit might give him some ideas/inspiration." Hope it helps. Been following this.



P.S. I can get take as many detailed pics as you want of the various setups we have around the facility. There are probably 100 bridges. Some are not motorized with small hoists too that we pull where we need them.

 

[rabler]

Hope it helps

The interesting thing for me in these huge bridge cranes is the building tie-in. From what little I can tell from these pictures, it looks like the crane is suspended from the ceiling structure. If that is true then I'm guessing the crane was part of the building design specs. A few pictures of how all of that works would be interesting to me. Uniform beam load or point beam loads are not too hard to calculate, but when you start building structures incorporating these things is where it gets complex and fascinating.

The above pics do highlight how cabling management gets to be tricky. Another reason, where you're trying to preserve ceiling/lift height, that motorized adds more challenges.

 

[motormech1]

I'm off now for the weekend but when I get back Monday I can get some detail pics of different features I think might be useful to you if you'd like. The place was originally built to manufacture gas turbine power generation units or "Power Systems" as the company calls it. Over the years it was occupied by a couple other divisions until the early 90's when they outfitted it for jet engine production. I'll get pics of it later but above all the lower steel that our current hoist systems hang from is a massive probably 8-10ft tall rail that a 250 ton diesel crane ran the full building length which is about 300 yds. It's so big that when they decommisioned it they could only park it on one end and abandon it. 20+ yrs. ago, me and a friend used to go up there late on 2nd shift and start it and move it back and forth a few feet. Lol. Now, it's no longer maintained and won't start. Anyway, I'll report back when I go back to work.

 

[dkemppai]

I'm thinking I'll want the guide bearings (track rollers) on the trucks regardless. With a free-standing frame I want to ability to accomodate flex/motion in the frame so the bearings keep things from binding. I may well be overthinking it, which isn't a bad thing in this case.

Sound like a reasonable plan.

Planning on guide rollers also. Basically the chain keeps the gantry square, over running truck with simple rollers support it, guide rollers keep it centered. (Like yours, welded steel plates will keep it captive on the rails, in the even something unforeseen happens!) For now the guide rollers are just bearings ($2 ea), but the mount was machined to use guide rollers (~$40 ea) if those fail.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

The design (which is currently unproven!) uses rollers fit into heavy wall rectangular tube. Tight tolerance pockets were machined into the tube to fit the rollers and shims. To facilitate removal (if necessary) a weld nut was welded onto the tube, and a grade 8 bolt spans the tube to the weldnut. (Longer bolt shortened so that the threads on the bolt exist within the weldnut and one shim).

Bolt failure means the roller goes into the tube, and the truck drops ~1/4" to the rail (inherently safe). Even without the bolt being torqued, it has something like 25x the strength needed. Rollers and bolt were overkill, but still the cheapest option found, so...

 

[rabler]

Planning on guide rollers also. Basically the chain keeps the gantry square, over running truck with simple rollers support it, guide rollers keep it centered. (Like yours, welded steel plates will keep it captive on the rails, in the even something unforeseen happens!) For now the guide rollers are just bearings ($2 ea), but the mount was machined to use guide rollers (~$40 ea) if those fail.

Here's my latest CAD ideas for the end truck. The yellow "plane" is the reference for the top of beam.

You can see the slots and bolt holes at the ends for mounting a shaft and roller bearings. You can also see that my bearing caps interfere with that so obviously this is a work-in-progress.

Structurally, I'm aware the notch for the beam in the center is the weak point of the truck. I can make the side plate wider (lower) to provide more support if needed, or put in a doubler plate in that area, or just use heavier side plates, those are all TBD.

This is based around tapered roller bearings, which means the bearing plates would need to be shimmed to pre-load/fit, which is less than ideal. Could look at needle bearings instead. Hard to find straight roller bearings with high enough static load.

 

[dkemppai]

Here's my latest CAD ideas for the end truck. The yellow "plane" is the reference for the top of beam.

Got it!

Structurally, I'm aware the notch for the beam in the center is the weak point of the truck. I can make the side plate wider (lower) to provide more support if needed, or put in a doubler plate in that area, or just use heavier side plates, those are all TBD.

That is the area of peak bending moment alright. IIRC, this is 'only' a 2T crane, correct? My guess is it won't take much to support the worst case ~2T plus beam weight over that span. Plus, that failure isn't catastrophic in this design.

This is based around tapered roller bearings, which means the bearing plates would need to be shimmed to pre-load/fit, which is less than ideal. Could look at needle bearings instead. Hard to find straight roller bearings with high enough static load.

Tapered rollers are probably a good compromise. Could you fix one end to the plate, and have a slip fit bushing in the other? That way one plate centers the bearing/wheel/hub assembly, and the other supplies vertical support only (and allows for slight axial misalignment and preload adjustment with the axle). Probably just drill bore 1-1/2 hole and turn a few thou under shaft for it, if that makes sense...

 

[rabler]

Got it!


That is the area of peak bending moment alright. IIRC, this is 'only' a 2T crane, correct? My guess is it won't take much to support the worst case ~2T plus beam weight over that span. Plus, that failure isn't catastrophic in this design.


Tapered rollers are probably a good compromise. Could you fix one end to the plate, and have a slip fit bushing in the other? That way one plate centers the bearing/wheel/hub assembly, and the other supplies vertical support only (and allows for slight axial misalignment and preload adjustment with the axle). Probably just drill bore 1-1/2 hole and turn a few thou under shaft for it, if that makes sense...

Correct, 2 ton, so 2 ton plus half the bridge weight. The side plates will default to being cut from 3/8" thick HRS so pretty substantial. But I haven't done the numbers yet.
I'm trying to keep the side plates symmetric so that getting a run of 4 from a laser/waterjet is straighforward, and that got me to thinking symmetric on the whole thing. But I could work the asymmetry into the bearing blocks easily enough. Thanks for the idea!

 

[dkemppai]

View attachment 441318

Look at the beam profile of the accrual gantry. It's a special I beam shape. Narrower bottom, wider top. Relatively thin web. Certainly not wide flange iron.

Don't know for sure, but guessing that's to counter buckling of the top flange when loaded. The bottom flange you want narrow to prevent the 'ears' from folding down under load, and under tension it isn't going anywhere. The top flange you're worried about it squirting left or right with the high compressive load. I shaped beams are weak in this regard. That's one advantage of the under hung design.

Some of this was actually things thought about when looking for steel for my build. A W beam profile without too wide a flange, but still wide enough to prevent it from buckling under load. Some of the cheaper cranes I've seem pics of have supports coming from the top flange to the truck. I assumed that was to help reduce that issue.

 

[rabler]

Look at the beam profile of the accrual gantry. It's a special I beam shape. Narrower bottom, wider top. Relatively thin web. Certainly not wide flange iron.

Don't know for sure, but guessing that's to counter buckling of the top flange when loaded. The bottom flange you want narrow to prevent the 'ears' from folding down under load, and under tension it isn't going anywhere. The top flange you're worried about it squirting left or right with the high compressive load. I shaped beams are weak in this regard. That's one advantage of the under hung design.

Some of this was actually things thought about when looking for steel for my build. A W beam profile without too wide a flange, but still wide enough to prevent it from buckling under load. Some of the cheaper cranes I've seem pics of have supports coming from the top flange to the truck. I assumed that was to help reduce that issue.

Good catch, hadn't noticed that. I'd bet you're right about the buckling issue. Does an excellent job of highlighting how complex these type of design get.