So your saying the worm gear will hold the car? Please explain.....Go prove it take the brake off a geared car around the 2nd landing and see if it works 😉
Oh we do know why mate think about it. If you disconnected the worm gear from the brake drum, with the car still attached via the ropes, unless the car/cwt are balanced perfectly in the shaft the car will roll up because the cwt is generally 40 to 50% heavier by design. if the ropes were removed from the traction sheave then there is no load and therefore the no movement on the sheave/crownwheel/worm gear.
Hope this clears it up for you.
THIS is how we know your theory doesn't work.
Who is RCD?
Maybe an apprentice or someone who works or studies near elevators.
Some people have suggested you try disconecting brake.
My advise don't do it.
RCD do you think anybody would waste money on anything that isn't absolutely necessary?
RCD if you are in the lift industry eventually you will see a lift car belonging to a geared traction machine crashed up into top of shaft or fully loaded crashed in pit that the holding brake failed and the penny will drop.
Good luck and stay safe lifts are killers hope you make it to retirement age alive there is a reason why 7% of a lifties pay is danger money.
All theoretical analyses of self-locking worm gears deal with static conditions. In such an analysis, the load on the worm gear can�t drive the worm if the coefficient of friction between worm gear and worm is larger than the tangent of the worm�s lead angle. In other words, the friction angle must be larger than the lead angle to prevent backdriving.
Within the last 3 years, our failure analysis engineers investigated two accidents involving worm gears where the user was injured. In each case, a designer selected a worm gear speed reducer from a catalog and incorporated it into a lift device intended to raise and lower people. In both cases, the designer was under the impression that the load (person plus platform) could not self-lower. They both relied on self-locking worm gears to hold the cargo in a desired position and genuinely believed that no brake was necessary to supplement the worm gear in such a critical application.
So it is a matter of friction. There is your answer!
Theory and reality are two different things. You can't tell untill you try it.
There are safety codes written because theory doesn't equal safety.
Firstly I would assume that when it states its 'self locking' (depending on any 'locking feature' on the worm gear ie caravan winders that have that clicking sound which is a reverse lock), I would imagine it has a load maximum and that it depends on runaway characteristics as well ie if the load is down hill. So if the winch is over loaded then it can runaway. Remember to that a dumbwaiter is also an 'old style' hoist ie a drum drive system which also has a braking system either a drum brake on the old units or a disc brake on the new units like a overhead crane motor.