Noise from Crompton Parkinson 3 phase 1/2 HP motor

This Crompton Parkinson motor came from a Myford ML7 and was stored in poor damp conditions. I have taken it apart and cleaned everything up, reassembled it after converting windings to Delta.

The motor was then left for a week in an electric oven at 70 centigrade, to make sure the windings were dry. Lubrication was dealt with and it rotated smoothly.On turning it on, I was rewarded with a very quiet motor. I then reversed it and there was a high speed knocking. which disappeared when .forward was selected.

The bearings are simple sleeve bearings and although not immaculate they should be good. I have seen and used sleeve bearing motors whose sleeves were more worn than this specimen and they were pretty silent. The rotor shafts were in reasonable condition, some light scoring but otherwise good.

What can cause such a difference between forward and reverse rotation? I am at a loss for an explanation. The motor would have been used exclusively in the forward direction if this is significant.

I have never changed sleeve bearings in these old motors. I assume that it would not be difficult to change them. The major problem might be in getting them! Maybe a make it yourself job.

Andrew.

Edited By Andrew Tinsley on 01/04/2021 19:08:37

Rotor clouting the field coils

Hello Dave,

I did think that the rotor could be making the noise as you suggest. However the play of the shaft in the bearings is minimal. I stripped the motor down and there are no marks on either the stator or field coils, so I don't think that is the answer.

As an afterthought let us assume your answer to be correct, surely one would get the knocking sound in both forward and reverse rotation? Or am I missing something?

Andrew.

Have you tried it at varying rpm?

Are your sleeve bearings white metal and are slighly dammaged so causeing a problem in one direction worth checking. good luck

Regards Bee.m

Andrew,

Can you feel anything if you turn the rotor by hand while applying pressure the same way as the belt does. If it makes a sound you much be able to feel it. Or it might be the layshaft.

That said I just noticed the temperature you cooked it at - most old motors are only good for 60C unless the motor plate says different.

I have only tried the motor off load, that is without the belt fitted. I will check the motor again for any signs of contact between rotor and field windings. It does sound as if the rotor is clouting something, but I could see no marking on the rotor I will measure up the bearings and shaft while I am at it to see what the wear is.

After a close inspection tomorrow morning I will reassemble the motor and see if I can detect any contact as the shaft is rotated.

It is quite safe to oven any motor at 70 centigrade. Remember this is without the motor coils energised! Rule of thumb is that all motors can run to a temperature of 100 degrees Centigrade under load. more modern motors can be run at 120 Centigrade and very recent motors designed for high temperature running are good for 150 Centigrade.

The bearings are of Vandervell white metal construction. Standard Doncaster build for around the 1970s. A bit of a problem, as there have been no replacement parts available for many years. If it is a bearing problem, it sounds as if it is coming from the rear bearing, which is most odd If that is so, then a ball race can be fitted (have done this on another motor). Usually it is the front bearing which wears first due to over tightening of the drive belt.

I still can't figure out why the noise is only heard in reverse. As the motor is to be used only in a forward direction, I am almost tempted to leave well alone. However that really isn't the way to go, something is wrong and should be corrected.

I will update my findings after tomorrows session.

Thanks everyone for your input.

Andrew.

OK, I have stripped the motor down again and checked with a magnifying glass to see if there is contact between rotor and stator. There is no sign of any rubbing whatsoever.

Checked the sleeve bearings and shaft and they are fine, with 3 thou clearance both ends The shaft and bearings were much better than they looked. There is one score mark on the rear end of the shaft, there were no rough patches on either bearing surface. Minimal end float and the two PTFE washers were fine.

I reassembled the motor and carefully rotated the shaft by hand in both directions no sign of anything rubbing or catching.

So I give up! I shall only be using the motor in the forward direction, so it will be quiet. If I have missed anything then it may show up with more run time.

Thanks everyone.

Andrew.

Just a thought- could it be something to do with the direction the fan is rotating. Rotating in different directions might shift the direction of load and if there is significant end float it could affect things.

Sandy

Regardless of fan direction the axial load will always be in direction away from motor, ie the fan impeller is trying to pull itself off the shaft (not that an impeller of that size will have much thrust anyway)

If blades are radial, (omni-directional) which they probably are on a small motor, flow will be much the same, if blades are sloping (uni-directional) flow will differ but again with such a small fan I wouldn't expect variation in thrust to be of any significance.

I am talking about centrifugal impellers here which in my experience is the norm for motor cooling fans, an axial impeller is different, flow direction will depend on rotation, flows in each direction dependent on blade angle. Thrust in the case of an axial flow will vary according to direction of rotation.

Bill D.

Check the stator is not loose in the casing, check that the cent sw wires are out of the way and not touching anything moving. Make sure the rotor is not loose on the shaft, If the motor does not make a noise when rotated by hand in either direction we have to consider that the noise is caused by something to do with either the magnetic flux, or the increased internal airflow due to higher speeds. Is there a fan or vanes on the rotor? are there cooling holes in the rotor? are they clean? You describe the noise as a knocking, can you feel it in the motor casing? Place the handle of a long screwdriver to your ear and put the blade on different parts of the motor to see if you can locate the source or area the noise is coming from. Are the sleeve bearings lubed properly Are the cent switch (if fitted) bobweights held in properly, and are the springs in good condition and holding the bobweights tightly in place? If it makes a noise, something is wrong!

Phil

Hello all.

It is a 3 phase motor, so no centrifugal switches. The rotor is firm on the shaft. As far as the "fan" is concerned this is just some ears on one end of the stator. They don't appear to have any pitch (angle) to them. I suppose they deflect air to the holes cut in the casing. So there is no axial force on the stator due to the "fan" blades

I have used a stethoscope on the motor and for what its worth, the noise seems to be coming from the rear bearing area. The sleeve bearing at both front and rear are well lubricated The knocking sound is at motor frequency by the sound of it. If I hadn't stripped the motor down a couple of times to check. I would say the stator was just touching something. But it isn't and why the sound only in the reverse direction?

I may well install an oilite bush in the rear bearing set up, or simply replace it with a ball bearing. The only clue I have is that it seems to be coming from the rear of the motor. Either retrofit is a quick job, so I may well do it out of curiosity.

Andrew.

Edited By Andrew Tinsley on 05/04/2021 15:33:43

You could try covering the rotor with engineer blue or a marker pen then run the motor in the direction that gives the noise. After it has run for a time you could examine the rotor to see if any of the marker has been rubbed off.
Depending on the design of the motor you could try rotating the end plates or swapping the rotor and end plates end to end. (If you try this make sure that the rotor would still be lined up axially with the stator.

Les.

Long shot from a non electrician.

Reversing a three phase motor only requires changing over two of the phase feeds, but could it be something odd in the way that the switch is configured so that one phase is missing or mis fed in the reverse position?

One brush not making continuous contact with the slip ring when running in reverse? Sticky?

Howard

Ah, I was assuming this was an external fan, usually mounted on a non drive end shaft extension the impeller being enclosed with a cowl that has apertures in the end, the centrifugal impeller draws air in axially through the apertures and discharged radially from the cowl circumference, guided over the motor. This is the method used on standard industrial totally enclosed squirrel cage motors. Yours maybe a non ventilated type or maybe the impeller is missing?

Bill D.

Although Howard's comment about slip rings is wrong (As it will not have slip rings) It made me wonder if it's 3 phase supply was derived from a static converter rather than being a true 3 phase supply. If it was then that MAY have some influence on the problem.

Les.

Edited By Les Jones 1 on 05/04/2021 17:39:39

The motor is a standard Crompton Parkinson made in the now defunct Doncaster factory. I would reckon in the late 70s or early 80s. No external fan, simply the paddles which blow the air out of a ring of holes in the casing, thus drawing air through each end plate ventilation holes.

The surface of the rotor is cast aluminium at each end and blued steel in between, anything catching on either surface would show up like a sore thumb, just as good as engineering blue and not so messy!

Changing end plates from front to rear is a problem, because there is nowhere to mount the inner terminal plate for the electrical connections

The motor is powered from an inverter, so no chance of getting a phase backward. I am going to put in an oilite bearing in the rear bearing position tomorrow. at least that will eliminate that bearing. The oilite bearing is a simple drop in replacement for the Vandervell white metal bearing, except that it is 16 mm ID rather than the 17 mm ID of the white metal bearing. So just a skim off the rear of the main shaft to make everything fit.

I will report back tomorrow evening, after I have done the modification.Thanks again for all the ideas and interest.

Andrew.

Sounds like what is called an open protected frame, or drip proof, probably IP22 or 23 rating.

Bill D.

Hello again,

I replaced the rear bearing with an oilite bush. Result no noise in reverse.

The only thing noted on the rear part of the shaft was a deep score. with no corresponding damage to the bearing. I suspect this means that the rear bearing had been replaced. The rear shaft was turned down from 17 mm to 16 mm to fit the new bush, hence the score was removed.

The play of the shaft in the new bush was about 3 thou, the same as before. So the noise has gone and nothing much else has changed! I really am at a loss to explain the phenomena.

Still I have a good result which is what was required, but why?

Regards,

Andrew.

Glad that the problem is solved. Possibly, the replacement bearing was Imperial and ona Metric shaft giving excess clearance.. Academic now since all is now well.

So now you can sleep at night!

Howard