Gearbox Backlash 4

[Gustavo Silvano]

Hello there!

I'm an electrical Engineer working as Industrial Engineer here in Brazil. I'm working on a steelmill industry, and I've being making some improvements on the process. The newest one was the implementation of a safer device to reduce the diameter of a bundle of bended wire. To do that, I've assembled the machine that is represented on the attached picture.
So I use this device to reduce the diameter of the bundle, to do that I'm using steel cords to embrace the bundle, and them the gearmotor will start to run, choking the bundle until it stays with a lesser diamenter.
The problem is, when the motor stops to run, the steel cord will get a little loosen. I think that this problem is happening due to the chain that I'm using to transfer the power from the gearbox to the shaft.
I'm thinking that this problem can be solved by using a coupling to couple the gearbox directly on the shaft (as shown on the image attached).
Do you guys think that with this action, the problem of the bundle getting loosen by the stop of the gearbox will be solved?

Best regards!

 

[BrianE22]

I doubt if it is backlash - unless the load is reversing somehow. What kind of gears in the gearbox? Self locking worm gearing is what you'd want.

 

[John2025]

Seems like the motor must be spinning backwards when you remove the power. You can't have backlash without motor reversal. A brakemotor seems like the easiest solution. Or maybe a clutch so you could secure the bundle before turning off the motor. Either way I'd be worried about safety with this set-up. Is someone going to get caught up in it?

 

[Gustavo Silvano]

BrianE22, it's helicoidal gear.
John2025, the motor is without brake indeed, but want to solve the problem without having to buy a new one. The bundle, when compressed by the gearbox, have a kind of spring effect that makes it expand, and that's what makes the gearbox rotate a little.

 

[waross]

You need some type of brake.
The tension is causing the gearbox and motor to rotate backwards.
This is not back-lash, this is back-spin. Changing from a chain drive to a direct drive will just waste time and money and will not change anything. You will still have the same gearbox and the same tension driving the gearbox and motor backwards.
Some gear-motor manufacturers offer double "C" flange brakes that may be a bolt in mount between the existing motor and gearbox.
A GOOD picture of the motor and gearbox nameplates will help us to help you find a suitable brake.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Gustavo Silvano]

it's the motor with a picture of the plate attached.

 

[waross]

Take a look here:
Link
Contact your local Euro-Drive customer support. You may have to replace the motor rotor to facilitate the installation of the brake.
Replacing a 1:1 chain drive ratio with a direct drive will not change any of the forces involved and will not change the operation at all. You need a brake.
The other option may be to add a VFD with the ability to hold a motor in position. That is not guaranteed.
If you are running the motor to stall or close to stall, you may be generating breakdown torque or close to breakdown torque. To hold against the backspin torque reacting from the higher than rated running torque, you may need a larger than normal brake to hold against the higher back-spin force.
You may want to consider removing the shipping plastic so that the motor may properly cool itself.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Compositepro]

An alternative to a brake would be a ratcheting mechanism anywhere in the drive line, or at the loop that tightens around the bundle. Like a nylon wire tie works.

 

[waross]

Another possible cheap and dirty solution:
Try two turns of cable around the bundle rather than the one turn that you are presently using.
That will reduce the back-spin force to about one half of what it is now for the same compression of the bundle.
You may even try three turns.
Start looking for a small pulley or snatch block to replace the hook that you are presently using on the end of the cable.
The reason for this will become apparent with the passage of time.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Gustavo Silvano]

The problem is that the chain that I was using broken during the operation. It lasted about a month, but just recently broken. That's why I want to copule the gearbox direcly to the shaft.

The chain that I was using is a 10B-1, where the force of rupture is about 2,240 kg.

 

[waross]

The motor is rated at 1710 RPM. That is a fairly high slip.
A characteristic of high slip motors is high locked rotor torque, possibly over 250% of rated running torque.
Are you running this motor to stall?
You may want to find some way to avoid running to stall.
If you have designed your gear train based on rated torque you may be low by 250% or 300%.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[CouplingGuru]

That is an interesting set up. With only a 1.5 KW motor you must have a really high reduction ratio on that gear box in order to rupture a 2,240kg chain. I guess the gear box could be slipping back causing reversal, but that just seems like it would be a lot of REVs in reverse on the motor, probably quite noticeable. I think directly coupling your gear box inline is good practice, but you may want to focus on why that chain was breaking. Reversing torque applications significantly de-rate power transmission components, over-sizing the chain or directly coupling your gearbox to the drive line might just move the problem to another component.
Plus keep in mind, when pulling long cables they tend to store a lot of energy. Could be other factors at play from the cables themselves as well.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[Gustavo Silvano]

CouplingGuru, my idea is to couple it directly to the shaft in order to avoid the use of the chain. The rotation force will be delivered directly by the gearbox so, with I'm running below the nominal current, the gearbox will not break their mechanism, because they are rated to work with this magnitude of load. Am I wrong? I mean, the operator just press the button to run the gearbox. If he push to much the motor, it will trip the protection.

 

[CouplingGuru]

Well sounds like the chain was the weakest link in the system, (no pun intended). And the operator pressed it too much and snapped the chain. What is the reduction ratio of the gearbox and the output shaft diameter of the gearbox? Direct coupling it will definitely solve the chain issue, but maybe your motor overload protection isn't an adequate safety mechanism, plus I am sure the motor guys out here would say that shouldn't be your primary safety.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[waross]

I agree.
It will not be good practice to depend on either the operator or the normal motor protection to stop the motor.
My first choice would be to add a magnetic coupling between the motor and the gearbox so that when the gearbox stalls the motor may continue to turn without overloading.
But I was solving this sort of problem long before VFDs became readily available.
A VFD with a torque limit enabled may be the modern solution.
If you properly limit the torque the chain may work as intended.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Gustavo Silvano]

CouplingGuru The ratio of reduction is 1:56,89 and the gearbox shaft diameter is 25mm.

 

[chief]

A ratchet and pawl assembly would maintain the tension and prevent slipping of the motor.It would not be difficult to retro fit. This is similar to the freewheel arrangement on a bicycle wheel rear hub or an anchor winch brake.

Offshore Engineering&Design

 

[CouplingGuru]

Gustavo,

Seems like based on your numbers if you have less than a 3" pitch diameter sprocket coming off that gearbox you would be pushing that chain very hard, especially in a reversing torque application. I would recommend at least a 3" diameter, maybe even a 4" because of its reversing nature. A Larger sprocket will change your speed though. Or just direct couple it, 25mm shaft is very common and wouldn't be that expensive.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[Gustavo Silvano]

CouplingGuru: indeed if I'll change the diameter of the chain, I'll have to buy a new gear, that will cost around R$400,00. But the couple will cost me around R$ 200,00.

To prevent the gearbox to turn to the otherside, as said before, I'm thinking to use a fall arrester attached to the steel cable, so with that the bundle will not get loosen when the motor stops.
An example of the fall arrester is attached.