Brake Pad options

I'm working on a fail safe brake along the lines of an elevator safety brake -- it will prevent a heavy load from falling if the supporting roller chain breaks. I need brake pads that can be attached to the device that will bear on a large rectangular tube column when activated, 4 pads near the corners of the column. I found some rough dimensions online of performance auto disc brake pads that are about

2" square, which seems appropriate. The four pads will be required to support about 3000 pounds total.

Potential problems with automotive pads? Any suggestions other than auto pads? McMaster has lining material, but I'd rather not design and fabricate something that can be more easily purchased.

Reply to
Ned Simmons
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Most every vertical column safety I've seen has been a ratchet track type of configuration that will positively lock the load from dropping more than the inch or so ratchet spacing in the event of the lift system failing. That would seem to be the best way to go unless your application is significantly outside the norms.

Reply to
Pete C.

One concern that I can think of is that automotive brake pads are made to be used regularly -- how are they going to work on that one application after years of neither being used or tested? For that matter, after years of building up dust and grease?

Reply to
Tim Wescott

I would prefer that, and it would work if there was room for the track, but unfortunately I haven't found a practical way to mount one large enough to support the load. If I can generate some understandable images of the device I'll post them.

Reply to
Ned Simmons

There's also the question of break-in of the pads, though some of the pad materials claim no break-in is required.

The environment is dusty, but not greasy. In any case, periodic testing and inspection of the braking device as part of the lifting mechanism, is certainly a requirement.

Reply to
Ned Simmons

A picture of the device. The purple plates are 15x22x3/4 and there's

5/8" clearance between the plates and the gray column. No clearance between the column and the yellow chain brackets.
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Reply to
Ned Simmons

Most I've seen were something like a strip of 1/2" plate cut with the ratchet pattern on one side and welded in place on the column. That would only add 1/2" to the column thickness. The safety latches on auto lifts work like this and are rated to hold a 10,000# vehicle over people with just one of these ratchets in each column. You could of course use thicker plate, cut the ratchet pattern on both sides, and have the ratchet pawl engage more than one tooth as appropriate to handle the load.

Reply to
Pete C.

The ratchet plate I mentioned in my other post could readily fit in that

5/8" clearance you have. Indeed, you could do one on either side, double ratcheted, providing four ratchet surfaces and you could make the pawl plates engage several teeth, so you should be able to handle any possible load.
Reply to
Pete C.

Looking further at your drawing, I'd take a close look at the two column auto lifts and see if one of those might provide a good starting point to modify for your application and save some work. These lifts are remarkably inexpensive these days, ~$3k for a basic one.

Reply to
Pete C.

Thanks, Pete. I knew I had seen those ratcheting safeties, but couldn't remember where. I started looking at patents for auto lift safeties and see that some use a slotted bar, which hadn't occurred to me and looks promising.

For example:

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Re the auto lift as a whole, the most restrictive factor in the design of this device was the available space. It also travels at a much higher speed than an auto lift and supports very asymmetrical overhung loads in some orientatiions. It was supposed to be a quick and dirty prototype, but is morphing into a permanent solution, if all the safety issues can be addressed. I wish I could say more -- the manufacturing operation is pretty wild and metal related.

Reply to
Ned Simmons

Ned, can we explore this a little further. Will the safety be such that once activated, it will never be released? Or will the safety be required to operate on a regular basis? The answer will point you in the direction of the simplest device to solve the problem.

Paul

Reply to
co_farmer

Knowing whether a failed safety will result in loss of life & limb or just a bunch of product to be scrapped may help guide your thinking, as well.

Any time I start thinking "life safety" I start getting suspicious of hypothetical future maintenance folks, and the managers who approve their time.

Reply to
Tim Wescott

One column of a two column auto lift will travel at twice the speed, since you will have half the cylinder displacement to fill. A 10,000# rated two column lift carries 5,000# hanging several feet off the column, and with safety margins for overhead lifting (5:1?). Using half an auto lift also provides a complete set of spare parts.

Reply to
Pete C.

It shouldn't be a life safety issue in a direct sense. But if the lift were to fail under certain circumstances lots of excitement would ensue and there may be a temptation for folks to take heroic and foolish actions. The overall process is dangerous enough that safety is taken very seriously by my customer -- hopefully that will continue into the future.

Reply to
Ned Simmons

Hopefully the safety will never operate except when testing it. In use the lifting device reciprocates up and down at relatively high speed and short intervals. I suppose it would be nice if the safety could be manually engaged when the machine is idle, or while being worked on, but not at the expense of reliability. The columns are drilled for pins that serve that function now.

Reply to
Ned Simmons

Could this safety engage while the load is moving? Or just lock it once it has stopped? That's going to make a big difference in the design, particularly if it is moving at a pretty good rate.

Reply to
Paul Hovnanian P.E.

It will only engage if some part of the lifting gear fails (a chain was the example I gave in the original post), or when performing periodic testing.

Reply to
Ned Simmons

I think we are getting closer to design parameters that will work for you.

Will the safety device need to operate immediately in case of power failure, or hydraulic or air pressure? Or just if the chain fails?

If all three, then somewhere there needs to be enough energy stored, compressed springs, weights, etc. to deploy the safety. If just the chain failure, then we need to discover how the device will recognize a chain failure and not a power fail or just turning the machine off at the end of a shift.

Paul

Reply to
co_farmer

Only in case of a failure or a test. I think a simple linkage tied to the rod that connects to the end of the chain will do it. The plan is to spring load the rod so that it retracts when there's less than a couple hundred pouns of tension in the chain. I'm working on it now and will post a pic when it looks practical.

Reply to
Ned Simmons

The fastest lifts I saw were too slow by a factor of 5. I only showed one column, but there are two.

Reply to
Ned Simmons

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