Brake Pad options
Ned Simmons
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.
--
Ned Simmons
Pete C.
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.
Tim Wescott
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?
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Ned Simmons
wrote:
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.
--
Ned Simmons
Ned Simmons
wrote:
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.
--
Ned Simmons
Ned Simmons
wrote:
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.
http://www.suscom-maine.net/~nsimmons/news/VerticalCar100315a.jpg
--
Ned Simmons
Pete C.
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.
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.
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.
Ned Simmons
wrote:
>
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:
http://www.google.com/patents/about?id=HaEvAAAAEBAJ&dq=4331219
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.
--
Ned Simmons
co_f...@yahoo.com
> On Mon, 15 Mar 2010 10:05:04 -0600, "Pete C." <aux3.DO...@snet.net>
> wrote:
>
>
>
>
>
> >"Pete C." wrote:
>
> >> Ned Simmons wrote:
>
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
Tim Wescott
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.
Pete C.
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.
Ned Simmons
wrote:
>
>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.
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.
--
Ned Simmons
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.
>
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.
--
Ned Simmons
Paul Hovnanian P.E.
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.
--
Paul Hovnanian pa...@hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
Ned Simmons
<pa...@hovnanian.com> wrote:
>>>Ned Simmons wrote:
>>>>
>>>> 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.
>
>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.
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.
--
Ned Simmons
co_f...@yahoo.com
> ----------------------------------------------------------------------
> Have gnu, will travel.
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
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.
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.
--
Ned Simmons
Ned Simmons
wrote:
>
>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.
The fastest lifts I saw were too slow by a factor of 5. I only showed
one column, but there are two.
--
Ned Simmons
Brian Lawson
wrote:
>On Mon, 15 Mar 2010 12:09:45 -0700, "Paul Hovnanian P.E."
Hey all,
Not sure where this thread emanated, and normally I don't get into
discussions about elevators, but elevators have "safety devices", not
safety "brakes" as I read here. Elisha Otis developed the "broken
rope safety" in the late 1800's, and the principal is still used to
this day on certain parts and on slow speed elevators of <101 FPM.
This type safety, designated "Type A", is a toothed cam held clear by
the weight of the load on the cable or chain, and which rolls freely
into engagement immediately that the load is removed by any means.
This action is by gravity or heavy springs starting the engagement.
Stopping distance is typically from essentially "zero" to 6 inches.
The only way to release after application is re-establishing lift on
the cable (or chain).
Higher speed elevators use a centrifugal trip governor to activate a
gradual wedge clamp, so the stop is not "instantaneous", which would
cause structural damage. These are designated as "Type B". Stopping
distances for "Type B" may be from as rapidly as 1 foot and upwards of
13 feet depending on method, speed, and weight. Both types of safety
action is reactive against the guide rails. In Mr. Otis' case, the
guide rails of the day were wooden, whereas for many many years now
the guide rails are a solid steel, shaped as a vertical "T" section.
Geared and gearless elevators do have brakes at the machine of course,
but these operate in a control means rather than as "safeties",
although a power loss would cause full application of those brakes but
not initiate "the safeties". Since my retirement 10 years ago,
there has also been an industry effort to provide "cable grippers" to
prevent or stop "uncommanded motion", but while presently workable
these are still in a development stage, and further design/engineering
is necessary to assure that these don't cause undue damage to the
cables when applied.
The majority of today's hydraulic elevators have neither "safety
devices" nor brakes per se, although there is some ongoing work to
provide some form of overspeed safety device in the event of a
catastrophic failure, either by grabbing the plunger or even the rails
(as with the geared above) as long as the elevator has solid steel
rails. Many hydraulics use rails formed from sheet into what is
called an "Omega" section, and therefore not suitable to the crushing
action of the type A & B .
There is a further "Type C" for elevators over 500 FPM and with
reduced overtravels, but nothing to do with this thread any=way.
Take care.
Brian Lawson,
Bothwell, Ontario.
Bruce L. Bergman
wrote:
A few thoughts - If this is done like the drawing involving load
rollers and chains against that column, there's going to be greases
and oils about... Running any sort of a friction brake acting on that
steel tubing column directly is simply not going to happen.
You could use a vertical toothed gear rack and a triggered pawl,
just like the original Elisha Grey Otis "Safety Elevator" patent - but
that was meant for slow freight elevators...
You'll have to design in some sort of a buffer to absorb the energy
of hauling your lift to a stop when the pawl is engaged. Or it'll
just strip all the teeth off the stop pawl and Pshhooom! down it goes.
If you can come up with a place or way to mount it that is
relatively shielded from grease (Good Luck...) you could use a
vertical brake fin on the device, and a clamp-style brake mounted on
the structure, like on roller coasters. (Intamin design on California
Screamin' at DCA would work great for this.)
The brake is a Linear 'Disc Brake' with two pads clamping together
onto the fin mounted on the car, activated using standard Class 8
Truck spring brake air chambers.
How about a huge Acme screw and half-nuts setup? Or steal one from
a Saginaw Gear steering box, a big ballscrew and a recirculating-ball
nut on the lift arm? Like a worm-gear drive, you stop the motor
spinning the screw shaft with a small motor clutch-brake and your load
isn't moving anywhere barring mechanical failure. And it gets rid of
the chain or cables, except perhaps to a counterweight...
--<< Bruce >>--
Richard J Kinch
> "uncommanded motion"
That's a term I'll have to remember.
"The expensive bit was broken by uncommanded motion into the workholding
vise."
Steve Lusardi
You should consider existing brakes first. Reinventing the wheel rarely makes economic sense. Check out Kobelt
Manufacturing...they are excellent.
Steve
"Ned Simmons" <ne...@nedsim.com> wrote in message news:fbgsp5pb6e3fsnfk2...@4ax.com...
Steve W.
How about a safety latch system. Real simple design.
First weld a stop rack to the column. Only needs to be 1/2" thick or so.
Then for the stop a simple rocker that is spring loaded.
On the rocker you place two sprockets that will engage the chain. The
chain running between the two sprockets holds the latch off the track.
If the weight drops on the chain the weight of the latch drops it into
place.
I
OI
I
IO
I
I is your chain, The Os are the sprockets. With weight on the chain the
sprockets stay in this position.
I
O/
/
/O
I
Chain fails and the sprocket and mount rock down and the latch drops
into the track.
Wouldn't need to use sprockets if the space is tight. Simple nylon or
UHMW plastic could be used as rubbing blocks.
Simple, Safe and easy.
--
Steve W.
Stephen B.
Great description of those safeties. I think the cable grippers you
are referring to are these:
http://www.hollisterwhitney.com/products/gripper.html
Which are now regularly installed both in the Canada (where code
required it first) the US and world-wide to prevent "unintended
motion". I think these can accurately be described as "Safety brakes"
because they actually use brake pads to slow the car to a stop over a
controlled distance, as opposed to as fast as possible.
Interesting how terminology changes, I never heard of "uncommanded
motion". I like the term "uncommanded motion".
--
Stephen B.
Remove the first Spam only to e-mail directly
Steve W.
Simple, higher pump output.
--
Steve W.
Pete C.
Exactly, in the new application you'd replace the basic hydraulic power
pack normally mounted on the column, with a "real" industrial hydraulic
power unit with a large tank and probably 10HP+ motor rated for
continuous duty.
Ned Simmons
wrote:
>I'm working on a fail safe brake...
Thanks to everyone who responded. I still have to do some tweaking and
check proportions and strengths of the various components, but this
should be pretty close.
If the chain goes slack: the stack of Belleville washers (magenta)
pulls the chain rod (gray) down; as the collar on the rod (gray) falls
the arm (green) rotates CW; allowing the torsion spring to rotate the
collar (gray) CCW; the pawl (green) rotates along with the collar and
engages the slotted track (orange).
http://www.suscom-maine.net/~nsimmons/news/SafetyStopIso_100316a.jpg
http://www.suscom-maine.net/~nsimmons/news/SafetyStopBack_100316a.jpg
--
Ned Simmons
Ned Simmons
wrote:
>
>How about a safety latch system. Real simple design.
>First weld a stop rack to the column. Only needs to be 1/2" thick or so.
>Then for the stop a simple rocker that is spring loaded.
>On the rocker you place two sprockets that will engage the chain. The
>chain running between the two sprockets holds the latch off the track.
>If the weight drops on the chain the weight of the latch drops it into
>place.
>
> I
> OI
> I
> IO
> I
>
>I is your chain, The Os are the sprockets. With weight on the chain the
>sprockets stay in this position.
>
> I
> O/
> /
> /O
> I
>
>Chain fails and the sprocket and mount rock down and the latch drops
>into the track.
>
>Wouldn't need to use sprockets if the space is tight. Simple nylon or
>UHMW plastic could be used as rubbing blocks.
>
>Simple, Safe and easy.
There was something very similar in one of the patents I looked at.
Unfortunately, I have about .050" between the attachment points for
the chain and the column.
--
Ned Simmons
Ned Simmons
wrote:
>Ned Simmons wrote:
I'd be surpised if it was that simple. At 1+ ft/sec an appropriately
sized cylinder would be borderline for oil velocity with standard
ports and full-size plumbing to match. Considering that the lift
business is very competive, I doubt that the mfrs run 3/4" lines if
3/8" will do. On top of that, there's some sort of flow divider to
keep the two columns in sync, which I'm sure is also sized for the
actual flow, not 5x as big as required.
--
Ned Simmons
Ned Simmons
<steve...@lusardi.de> wrote:
>Ned,
>You should consider existing brakes first. Reinventing the wheel rarely makes economic sense. Check out Kobelt
>Manufacturing...they are excellent.
>Steve
Thanks, Steve, I looked and didn't see anything I could use now. Quite
likely there's something there that would have worked if the safety
was designed in from the start, but as I mentioned elsewhere, this was
a supposed to be a prototype and only to be run to prove out a
concept. Not so anymore.
--
Ned Simmons
Pete C.
Take a look at an actual lift. There is no flow divider, there is a "T"
connecting the two cylinders. Synchronization is provided by steel
cables and pulleys much like on a drafting table.
Pete C.
Looks good. Not sure where the chains are attaching, but you may want to
look at the lower spring loaded one and see if it should be a rigid
mount, i.e. not spring loaded with different types of springs at each
connection point.
co_f...@yahoo.com
> On Mon, 15 Mar 2010 09:34:07 -0500, Ned Simmons <n...@nedsim.com>
> wrote:
>
> >I'm working on a fail safe brake...
>
> Thanks to everyone who responded. I still have to do some tweaking and
> check proportions and strengths of the various components, but this
> should be pretty close.
>
> If the chain goes slack: the stack of Belleville washers (magenta)
> pulls the chain rod (gray) down; as the collar on the rod (gray) falls
> the arm (green) rotates CW; allowing the torsion spring to rotate the
> collar (gray) CCW; the pawl (green) rotates along with the collar and
> engages the slotted track (orange).
>
>
> --
> Ned Simmons
Looks like a good solution. You might think of making the lower
portion of the threaded rod as smooth as it can be. If the chain
breaks it is likely to fly away and pull the threaded rod into a bind.
A smooth, lubricated rod would probably not bind if pulled sideways.
Paul
Paul Hovnanian P.E.
>
> On Mon, 15 Mar 2010 12:09:45 -0700, "Paul Hovnanian P.E."
> <pa...@hovnanian.com> wrote:
>
> >>>Ned Simmons wrote:
> >>>>
> >>>> 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.
> >
> >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.
>
> It will only engage if some part of the lifting gear fails
There's a considerable amount of difference between locking the load in
place once it has come to a stop and having the lifting gear fail (cable
or chain break) if this load is already descending at a pretty good
clip.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
First they ignore you, then they ridicule you, then they fight you,
then you win. -Gandhi
Ned Simmons
wrote:
>
The chain runs in a loop, with the drive sprocket overhead and an
idler at the bottom. The bottom spring protects the drive if the car
overtravels in the down direction as a result of operator error or a
control malfunction. The normal down position is about 1/2" over the
floor. The spring allows the chain drive a couple extra inches of
travel before the frame starts to lift if the car bottoms out on the
floor.
And thanks for aiming me at the garage lifts.
--
Ned Simmons
Ned Simmons
That one of the required tweaks -- the originals are made from alloy
threaded rod, and I just lengthened one for the layout. The new ones
will need to have only enough thread on the lower end to adjust the
chains.
--
Ned Simmons
Wes
>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.
Tim, having spent a lot of time living in or around the maintenance world, I'd say your
suspicion is very well founded. The quality of maint techs and the safety ethos of
management varies widely.
Wes
Wes
Does the number of belleville washers provide the travel you need? I'm used to seeing a
large number of those things in drawbars to provide a small amount of travel.
Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller
Ned Simmons
>Ned Simmons <ne...@nedsim.com> wrote:
>
>>On Mon, 15 Mar 2010 09:34:07 -0500, Ned Simmons <ne...@nedsim.com>
>>wrote:
>>
>>>I'm working on a fail safe brake...
>>
>>Thanks to everyone who responded. I still have to do some tweaking and
>>check proportions and strengths of the various components, but this
>>should be pretty close.
>>
>>If the chain goes slack: the stack of Belleville washers (magenta)
>>pulls the chain rod (gray) down; as the collar on the rod (gray) falls
>>the arm (green) rotates CW; allowing the torsion spring to rotate the
>>collar (gray) CCW; the pawl (green) rotates along with the collar and
>>engages the slotted track (orange).
>>
>>http://www.suscom-maine.net/~nsimmons/news/SafetyStopIso_100316a.jpg
>>http://www.suscom-maine.net/~nsimmons/news/SafetyStopBack_100316a.jpg
>
>Does the number of belleville washers provide the travel you need? I'm used to seeing a
>large number of those things in drawbars to provide a small amount of travel.
There are exactly enough Bellevilles in the model to convince my
customer it'll work. If they decide to go ahead I'll figure out many
are really needed, along with a few other things.
--
Ned Simmons