Reduction In Speed

A1) if he pulley system requires to slip if the gearbox gets jammed, it goes on the input shaft.

A2) -

We want pully system should not slip on load & able to take 350hp load for desired output of machine.

A belt drive on the input side will be more economical (cheaper), PROVIDED the gearbox you propose to use is rated for the added torque you will be subjecting it to. Was the original set-up direct drive input and output? What is the rating of the proposed gearbox? That's going to be some drive. Is your motor designed for belt drive loads?

I'm curious if you know why the old gearbox got damaged and did you correct the root cause of this failure?

Quite.

Dear Ashok,

It seems that you have not many options but, to help you improve your chances of success, a bit of information would be great:

1. Which kind of raw mill do you have?

2. Which gearbox?

Regarding the belt driven solution:

3. How this change of ratio affect to the power load in the motor? Can the motor take the change?

4. Are there chances for a "loaded" start-up? If so, belts could slip till burn or snap.

In case of slipping, some good willed guy could try to overtight them, and transfer the problem to to a worse / more expensive place (like shaft or bearings).

Best of lucks,

Abel

As this new gearbox is a lesser reduction than the older one, and therefore the output shaft will rotate roughly 20% faster, and the motor is a slip ring type, have you considered simply using the motor's inherent speed control characteristics to adjust the speed? I don't know what type of starting gear you have, but many have the ability to maintain a 20% lower speed for long periods. Losses may be greater if you don't have slip energy recovery technology, but that may be acceptable until the new gearbox is available.

Torque transmission via the gearbox will be down by around 17% but, depending again on your motor starting gear, you may be able to compensate for that, provided of course the gearbox is sufficiently robust, so that may need to be considered.

You and Energygod state the advantage/drawback of the same attribute of a pulley system transmission. It is up to the OP to decide if belt slip is a protective advantage or an operational drawback.

Thanks to all.

Following are the more details.

1) Original gear box damaged due to misalignment & poor civil foundation, same this time we are doing better.

2) Original gear box input & output is direct coupled with gear coupling to motor & Raw mill gerth gear first pinion.

3) The new gear box rating is higher than original gear box( 500hp).

4) Motor drive is Direct on line starter with ACB.

Kindly advice for following

1) Pully belt system should at input or output of gear box? which is good to take rated load. We wish to put it on output side to sustain misalignment from raw mill side. What care should we take to avoid slip of belt due to load.

2) We want to put two pully c-c distance 1 meter appox. It should be more or less?

I have to wonder if/why you are using a wound rotor motor and starting it DOL.

Apart from a high inrush current, the starting and pull up torques of a 350hp slip ring motor starting DOL would be immense especially if the line voltage is a high value which, while reducing the current would also limit voltage depression and therefore maximise torque, this could be the reason for the demise of your gearbox and the failure of the footings as it may have literally ripped them to pieces.

It's been a fair while since I calculated the starting torque of one of these, and never DOL, so please correct me if my figures are awry, but I'm guessing at a full load torque of around 1700Nm and starting torque of anywhere up to 34,000kg-cm, so that acting on a 10cm diameter shaft could exert something around a 170 tonne kick on the gearbox from rest if the static load is high.

We have several old, turn-of-the-century wound rotor motors at many of our sites that are driving high starting torque loads such as crushers, ball mills, and conveyor belts.

All that I have examined and worked on so far provide the starting torque required via by shorting the rotor windings through a resistor bank during the start cycle then transferring to controlled rotor field excitation once the motor has reached synchronous speed.

I wonder if the OP's application is this type?

Then it's not DOL.

Most, if not all, V-belt manufacturers (I assume you're thinking of using V-belts), have drive design resources available on-line, or could possibly be contacted for drive design. A properly designed drive will address your questions.

I suspect you are in for an eye-opening experience.

Given your ratios: you are changing from 3.95 revs/second to 4.743 revs/second. Given this is a temporary fix for 3 months if it will run at the slighter faster speed why not just run it? If everything goes okay, probably no one will even notice except that maybe you are getting a little more throughput.

I don't believe they got their transmission custom built in the first place, so I agree with you, they could live with that slight ratio change 'till they get the new transmission.

You should always install the belt and pulley on the gearbox INPUT shaft. I don't know of a belt and pulley system that could take the torque from the OUTPUT shaft and not just slip until failure.

This next statement is beside the point but I figure the more info I am able to give the OP the better.

Belts and pulleys are for transmitting HIGHER rotational speeds.

1. Was the original gearbox installed with a solid / rigid coupler?
2. Was the original gearbox installed with a flexible coupler?
3. How was the motor connected to the gearbox?

It will always be easier to get the correct speed ratio when you transmit the higher speeds with a belt and pulley from the motor to the gearbox INPUT than trying to transmit the gearbox OUTPUT torque with a belt and pulley to a connection that was previously directly coupled.

Have an experienced fabricator build a platform for the new gearbox that can be easily removed or modified when you receive the new 350 HP replacement gearbox.