Experiencing Excessive Brush Wear: How to Extend Brush Life?

Not being able to inspect the motor myself. First I would inspect the commutator. ls it all carbon up. Are there grooves in it. Hot spots evident by the discoloration of the copper contacts. Look for raised contacts evident by arcing before and after a contact.

The US navy did a extensive research into DC brush wear in the 70's & 80's. They found the most common problem to be volatile organic compounds (VOC's) in the air contaminating the interface between the graphite and the copper. The interface is a highly conductive semi-fluid layer of graphite and copper carbide formed when electrical current flows through the contact point. The interface layer reduces the contact resistance which prevents excessive heating of the brush. The layer also reduces the mechanical friction between the brush and commutator, minimizing wear. The most frequent VOC sources were epoxy paint outgassing as it cured, and lubricating oil while the turbine or other lubricated machine was in operation.

The color of the commutator should be a rich chocolate brown while running (once the commutator warms to normal operating temperature). If the commutator is very dark or streaky, I would suspect some the oil in the chocolate may become airborne and contaminate the brushes. If this is the case, you need to remove the brushes, then remove the top layer of the commutator film until you reach virgin copper. This is normally done with an abrasive stone fitted to a jig. The stone is gently pressed against the commutator while the shaft is spinning at normal speed (somewhat like a lathe). Once the commutator is clean, install new brushes and set up some type of clean air source for the brush area of the motor, or seal it in an enclosure to prevent contamination.

I know nothing about these things so please ignore me if I'm talking rubbish.

Why are you using three items: controller, motor and fan when lots of companies sell "off the shelf" solutions? :-

http://process-equipment.globalspec.com/SpecSearch/Suppliers/Processing_Equipment/Heat_Transfer_Equipment/Industrial_Fans_Blowers?SrchItem=1&frmqry=DC%20squirrel%20cage%20Blower

How important is the speed control in this application?

If there is feedback in the system: is the loop "hunting"?

11000 rpm seems very fast for a fan: are there any gears? Could there be any backlash causing vibration in the motor.

While you're cleaning the commutator, get a dial gauge and check it for run-out. An out of round commutator could contribute to excessive brush wear. Ditto for the motor bearings.

A rough commutator or out-of-round condition is one problem. The other might be porus / poor quality brushes. Are you running the OEM Bodine brushes? Have you asked Bodine what the normal brush life is?

Have you considered going another direction? Like one of Exair's Air knives. It would run off of your plant air (assuming you have such), controlled by a regulator and virtually maintenance free.

I assume that you are running a small operation whithout compressed air installed if not then consider using this. If you have had this problem for a while then I would suspect that at sometime the motor will have overheated it which case scrap it and replace it with another unit. It can be the same motor as I am sure there is no fundamental problem with your set up. However small DC high speed motors cannot stand to run hot if the feild coils are at all darkened then you are going to have brush problems and they will never stop arcing and wearing out. If as guest two mentioned there are VOCs present after fitting the new motor replace the brushes as part of your monthly routine maintenance. Problem she go away

Just a few suggestions: I belive the conditions you are running the motor is probably dry and in that case you will need a brush which can handle low humidity/ dry conditions. I do not know what kind of brushes you are using currently.

To take care of commutating difficluties you can try what are called bonded brushes which help in reducing circulating currents and hence arcing . This will prolong the brush life.