slow speed Induction motor

You have a valid concern. It is preferable to use an inverter-duty rated motor. Among other modifications, inverter duty motors have cooling fins built into the housing to prevent overheating.

A question for you. What is an 'inverter-duty' motor? I saw your comment but I have no idea what you're on about.

It's a real problem. You have to use an external fan for forced cooling.

You should use a primary gear box to drop down from 1750rpm[US] to 100rpm

running even an inverter duty motor @ 100rpm will be a bad idea, if its even possible.

Please don't worry about it. Worry about your torque of motor in 100 rpm or less.

Because you have to choose correctly the power of motor and inverter unit.

Or can you use the V belt tranmission between gear and motor to increase the torque, or use motor with 6 or 8 poles.

Please tell us what the power of worm gear box or required power of motor is? And what speed rate of gear box is?

May i suggest you rechoose gearbox that, input is 500 rpm or 300 rpm instead of 100 rpm with output is the same your design.

First - What is Inverter-duty rated motor?

Second - I can't change the gearbox or the required RPM. Actually the required RPM is still low, around 40 RPM. Now, the required torque is 60 N.m, if we take a higher value of say 100N.m then for 40 RPM the power comes out to be around 0.4 kW, let's take 0.5kW considering motor efficiency of 80%.

Is there any special kind of motor, which can run at 40 RPM with o/p torque of 100N.m & still have a long life. Actually the motor will not run continuously but will run for say 60 times a shift (7 hours) with cycle time of 30sec.

Or do I have to go for VFD with external cooling fan only?

Or will it really require cooling considering the usage?

Don't change the gearbox

Add another one in series!

or maybe some thing like this

http://web5.automationdirect.com/adc/Overview/Catalog/Motion_Control/Servo_Systems

How about looking at a stepper motor. They have full torque at zero speed. The duty cycle you are discussing sounds like it may fit a stepper motor's capabilities very nicely. I have never installed any, so I don't have anything more to share, but suspect that lots of information is available from motor manufacturers or the web. It is quite possible that a stepper motor will not even need the gear box.

Regards--JMM

If you don't care about cost please use torque motor or servo motor.

I think that, your drive system was exist, not be new designed?

The power of gear box is 0.4 kw and ratio 100/40=2.5/1, the economic way is change new gear box with ratio 20/1 or 10/1, this mean input speed is 40*20=800 rpm or 400 rpm. From this you don't worry about your motor fan.

Or can't change the gear box, you can choose a motor and VFD with 0.75 KW power. And this motor will not be hot when running at 100 rpm speed.

Just like DC motor, now AC motor driven by VFD also desgined with separation of cooling system supply, so no matter the motor's rpm is, cooling fan motor are turning constantly.

"Inverter duty motor" is defined in NEMA MG-1

"Inverter duty" is somewhat stronger than "Standard duty" in dealling with the stresses cause by the inverter for reduced fan speed, clipped current, non-sin wave current, etc. As I understand, it has more copper and a heavier housing with more fin area. (simplified description from a mechanical engineer that doesn't know all the details)

what if you use a hydrolic coolant that surrounds the whole assembly. Because your motor runs at low rpm it will not matter the friction in the fluid. The motor fan can be replaced with a small impellor that will circulate the fluid. The outside of the housing can still have fins to transfer the heat to the air outside.

Howzit,

You can always use another fan cover that comes with its own fan mounted on it. there is quite a few. You can use a 230vac fan with a capacitor, you can wire an external supply to the fan cover.