Ametek® maintainance

[hayfarmer]

 Hi , changed the blades recently from 3 galvanized to 6 composite fiber due to wind damage in a high wind site and now have a new problem,the set screws wont keep the hub on blades from turning

on the Ametek® motor shaft and wore the shaft down so it wobbles. Can you replace the shaft? and where can you find a replacement? also as long I have it apart may as well do the bearings,any thing else

I should look for?  thanks


 hayfarmer

[zvizdic]

Take it to machine shop they can weld shaft and machine to original size.
Since you are repairing a shaft ask to turn it smaller and then weld stainless on top.

[snake21]

hi friend,i couldnt understand your question.is the screw in the hub which holds it to the shaft causing problem or the screws of the blades?

[fabricator]

I would start by taking the motor apart to see how the shaft is attached to the rotor inside.

[hayfarmer]

what happend was the 2 set screws that hold the hub onto the shaft were spinning/grinding around the shaft and wore a lot of metal off shaft and it wobbles badly.I

will take it apart and see what I can do to fix it. I think the cause was the extra 3 blades.

 hayfarmer

[snake21]

something like this happened to me,then i drilled a small hole in the shaft so that the screw for the hub can go inside the shaft some 2 or 3mm avoiding the problem.after that,i got another problem,the screws were loosening,then i make a slot on the head of the screm,then i pass a wire through the slot round the hub to prevent it from unscrewing

hope it helps

[ghurd]

I would suggest NOT letting the core be out too long without a 'magnet keeper'.

Long story.
A guy reported to me his experience of sending his Ametek to a machine shop to have one of the magnets re-glued in place.
Much later, when he got it back, the Voc/RPM was FAR lower.
I know they did not rewind it (though they charged him almost enough to do a rewind).
The only thing I can figure is the magnets became weaker after some extended time without a 'magnet keeper'.

When I have a 'keeper' out of a motor, single layers of microwave transforer laminations are bent/bent to fit against at least 2 magnets, and many layers are placed over those layers.
Better safe than sorry.
2 cents.
G-

[Flux]

The loss of magnetism when you break the magnetic circuit is instantaneous. Unless you can insert a keeper as you slide the rotor out there will be a loss of flux that can only be regained by magnetising.

As well as the instantaneous loss, old magnet steels also suffered progressive loss from vibration and heat changes without a keeper, ferrite does not suffer from this.

All these type machines are magnetised after assembly. At that point you have maximum flux. When you load it the flux drops to a lower value and will drop to a new stable level during a short circuit run.  If you pull the rotor out it will drop to the air stabilised value. If the makers air stabilised it you will see no loss from removing the rotor and replacing it but nearly all servo motors run with higher flux than the air stabilised value so expect loss if you dismantle it.

I can't imagine how people expect to keep hubs on with set screws, you need a taperlock coupling or one of the clamp type hubs.

Flux

[Scott]

I've been running Ametek motor mills for almost 10 years and have had many apart.  If the motors fine don't bother taking it apart, you cannot change the shaft without changing the whole armature. There's 4 brushes too that can frustrate you if you don't know how to wire them back for re-installation.  The bearings last a long time btw.  I've got one 99v ametek mill that's been in the air for 8 years and the bearings are still good. 

Best thing to do is weld the hub to the shaft.  I do this on all of mine.  I weld it on the end so I can grind it off if I need to get at the top bearing.  It will have to be centered so there's no wobble though, that will be the tricky part.  If there's still some good shaft left maybe you could slide it down farther.

[Ungrounded Lightning Rod]

All these type machines are magnetised after assembly.

I presume this is done with a high-current pulse through one of the coils, right?

Seems to me you might be able to remagnitize one by the following procedure:

 - Hook a bunch of batteries in series to come up with a "hard" high-voltage DC source.

 - Hook this to one coil of the Amtek through a big resistor to provide a trickle current.  The armature will turn to a position where the energized coil is lined up with the still moderately-magnetized permanent magnets, with the current in the energized coil producing a field in the correct direction to remagnitize the magnets (though far to small to do so).

 - Short the resistor with a fuse, or a piece of wire significantly thinner than the wire in the coil.  A burst of very high current will flow and then the fuse will blow.  (Beware of bouncing drops of molten metal, which could start a fire.  So do this somewhere in a shop with no flammable material nearby.)  The burst of current will remagnize the magnets while the fuse SHOULD blow before it fries the coil.

Chancy and may fry the motor.  But if it's already trashed by loss of magnetization why not give it a shot?

(Note that I didn't suggest a charged capacitor because it may "ring", reverse charging the cap (which could damage an electrolytic) and/or produce an oscillating field with decay, which could DEmagnetize the magnets even further.