Commutator of D.C.Motors

The wear is load dependent, with some manufacturers specifying brush wear according to load. Therefore, it would seem that the wear is caused by arc erosion, more than by simple mechanical abrasion. I don't clean commutators enough to have a favorite brand of cleaner. CRC is a widely used brand.

Others will probably have more info, but I am not aware of any way to prevent this wear, other than the obvious ones of keeping dirt away, and periodically checking spring tension.

As u mentioned spring tension is not affected,and the brushes are from the motor manufacturer. Still we observe this wear.

But in some D.C. tachogenerators of make Hubner,RadioEnergie etc.there is absolutely no wear even after working for years.

Is it necessary to inform the motor manufacturer about our normal running load to supply a suitable grade for our load?

Also please let me know what is meant by "CRC"

And where can I buy this.

In general tachogenerators have very low load, so the brushes should last a long time.

Yes, I think it would be worth giving the manufacturer a call. Perhaps there is a softer brush, that might not last as long, but which would reduce commutator wear.

CRC is one manufacturer of contact cleaner, and other solvents. They have manufacturing and distribution facilities in many countries.

I have browsed this website.

Thank you.

Oh this brings back memories...

As an apprentice back in the early seventies, at the plant where I did my time, we had wound rotor AC drives, this was in the day before frequency drives, whose slip rings had to be cleaned, for the same reasons you bring up, on a regular basis. Many an hour was spent with a flexible abrasive cleaning stick, made by Ideal, in my hand cleaning the slip rings on these motors. Worked quite well. We also used them on large 250+ HP DC motors as well.

badly made commutators can do this. The gap between the segments must be filled with an insulator and it must be non abrasive and flush to the copper or it can cause wear.

The arc does cause wear. You can get harder graphite, but if you go too far that way you wear out the copper and brushes are cheaper to replace than commutators

There is no arc while running.Still this wear is there.

I have seen the arc in commutating devices while running. There is no way to avoid it completely. slip rings can be arc free

Some DC machines has ability to compensate mech/arc malicious effects by adjusting angle of brush holders. Read the manual or ask manufacturer. Excessive wears could be an effect of misalignment too.

"1) What are the reasons for inwardly formed step --in carbon brush location equal
to the width of brushes throughout the circumference-- on commutators of D.C.
motors? I mean a strip / band of width nearly equal to width of carbon brushes is formed on surface of commutator and sparking increases and finally we have to remove the motor for commutator undercutting. Is there any way of avoiding/reducing this wear? Is this wear load dependent?"

Replace the coils with appropriate permanent magnets. Eliminates brushes, exciter, commutators etc.

"2) Also what are best and safe methods of cleaning of commutators of D.C.motors?
Please suggest any liquid claeaning agent which will evaporate fast or any other
idea."

Use automotive brake cleaner.

"Please reply my all questions." Did. Done.

There are some variables here. Try the GE site and the National Carbon Brush / Morgan Crucible site. If the brush position is not correctly set this can be a cause. For reversing motors the brushes need to be at the electric neutral position. A slight lead is often used on unidirectional drives.

When the commutators are turned and undercut are the comm bars bevelled and the slots raked clean. Dirty slots will cause something like described. Brush grade can also be a problem especially in low humidity locations.

Is the field strength from your field exciter strong enough?

We normally set neutral axis properly and also field supply is equal to rated on motor name plate.

On one of our New machine's motor, after 6 months of using we observed this groove along commutator circumference.

Please suggest.

"Use automotive brake cleaner."???!!!

Will it not affect the insulation?

Will it evaporate fast?

Pls reply.

you should remove the brushes and remove any metal/graphite grit with a small brush/vacuum cleaner

Then with non flammable brake cleaner (hopefully will not dissolve anything). But do not flood the area. Just moisten a cloth and hand rotate the armature in contact with the pad .