Speed reducer torque calculation 1

[krsh]

Dear colleagues,
I am a beginer in the field of mechanical engineering and i need to know what kind of gear i need to lift a 10 tons wheight if i use a 22 Kw / 750 rpm 8 pole electric motor.
The application consists in a electrical winch that pulls rail cars to a loading bunker with linear speed of 10 meters/minute.
The designer calculated that to pull a 700 tons wheight on railway we must use a 10 tons lifting capacity winch. The problem now is to find a speed reducer to do this job. Someone told me that i need a 63 ratio speed reducer but i think this is to small for this requirement. I attached the data sheet of the gear(3H-B-645 with the ratio of 63)

 

[zekeman]

Looks approximately OK to me, depending on the efficiencies of the motor and gearbox.

Using 63 as GR the winch rpm is

750/63=12 RPM

With a winch dia of

10m/min/12RPM/Pi=.265m

The power delivered

20000lb*10m/min*3.3/33000=20HP

With an efficiency of 0.6, I get

20Hp/0.6*.746=25KW for the motor.

You will have to got to the mfrs to get the gearbox and motor effiencies.

 

[krsh]

Thank you zekeman for the answer, i was not sure about the speed reducer because i found info on internet that to know the torque of a gear you have to know the torque of the motor and multiply with the ratio of the gear.
So:
The motor has approx 290 Nm
63*290Nm = 18270 Nm
and i know that to lift 1 Kg of weight you need 10 Nm so i thought i need a torque of 100KNm to lift 10 tons but 18270 Nm < 100KNm ...

 

[Occupant]

I think you're mixing potential energy with torque. A body of 1kg weight at 1m height has a potential energy of ~10N*m, but that doesn't mean that's what it takes to lift it.

 

[ScottyUK]

Just a thought: the electrical folks at your customer are going to hate you if you use an 8-pole machine.

Use a 4-pole motor which is smaller, lighter, draws less current, has a better power factor and higher efficiency, and is easily replaceable from stock. 8-pole machines are quite unusual these days even though they are available.


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If we learn from our mistakes I'm getting a great education!

 

[tygerdawg]

A full dynamic analysis may be needed here, else you may undersize your gearmotor. Most of the gearmotor manufacturers have very good sizing & engineering sections in their catalogs: Nord, Falk, Dodge, and probably the most rigorous is the SEW-Eurodrive engineering documents from the German website (at least it was this way some years ago). Some (again, SEW) have very good online sizing programs.

Your motor must be sized for peak torque comprised of the following components:
(1) Torque required to spin up and accelerate the rotational inertias (gears, etc)to steady-state speed.
(2) Torque required to start moving and accelerate the translational inertias (load) to steady-state speed.
(3) Torque required to overcome gravity acting on load.
(4) Torque required to keep it all moving at steady-state speed.

Then you must also account for holding the load, either through brakes or other means.

Once you determine the peak torque, then you can apply efficiencies, safety factors, and "number of starts per hour" de-rating to get your max required torque and the motor frame size to accomodate the thermal requirements. THEN you can go look for a gearbox & motor combination.

And Scotty is correct: an 8-pole motor is a high-torque / low-speed oddball. 4-poles are "common".

If none of this Engineering Mechanics & Dynamics stuff makes any sense to you, then you should contact a gearmotor manufacturer's Applications Engineering Department or hire a consulting engineer to size it properly for you. ESPECIALLY if you are LIFTING a load.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[PeterCharles]

At the size of motor being considered you usually get 200% full load torque at startup when started direct on line. Covers a multitude of starting inefficiencies, especially when used with a fluid coupling between the motor and gearbox.

 

[zekeman]

"and i know that to lift 1 Kg of weight you need 10 Nm so i thought i need a torque of 100KNm to lift 10 tons but 18270 Nm < 100KNm"

No, Kg do not translate to torque, only to a force,Newtons, so
1kg is 9.8 Newtons and the output torque for 1Kg is the radius of the winch times 9.8. I got previously got .265 m for the winch so the 9.8 Newton force yields

9.8*.265/2=1.3 nM, so your calculation of 100Knm is reduced by the ratio
1.3/10
or
100Knm*.13=13Knm

And BTW, you do not start with the motor to get the gearbox, you start with the load and its linear speed and choose a winch diameter to get the output torque and speed of the GB and then work your way to get the motor and then to the gear ratio.

 

[krsh]

The mechanical designer said:
700t (weight to pull)* 0.03(coefficient for advancing the railway line)= 21 tons which you divides by 2 because we use a pulley at the opposite to the winch. The other factors are negligible because the railway line is straight and without inclination.
I chose the 8 pole motor because that is what the gear manufacturer said to use, it is a 22Kw 750 rpm with electromagnetic brake and i will start the motor with a frequency drive to avoid damage to the gear teeth by the starting inertia.
The question is whether this gear is capable to pull the weight if i use a 130 mm diameter drum to roll the cable. I have attached a hand sketch of 2 possible applications of the winch.
Tygerdawn can you help with some links for a online sizing programs.

 

[krsh]

Thank you zekeman, the exact answer i was looking for.