When should you buy a complete new commutator?

Most of the time, don't.
A "new" commutator refers to a commutator designed and built from scratch, including all copper, mica and steel components.

The key is steel:
The only time you need a new commutator is when you do not have an existing steel part in good condition to fit the style and size of commutator you need.
• Conversion
• Replacement of damaged parts
• Spare
• Design improvement
Conversion: When an existing unit is molded (i.e. nonrefillable), the commutator needs to be replaced. Either a new molded unit, if available, can be purchased, or a new v-ring or glassband refillable commutator can be manufactured. None of the steel components of molded commutator should be re-used (see Motor Fax Issue 11) due to design limitations and space requirements for maximum stability. Conversions between refillable types also require new steel parts.

Replacement of Damaged Parts: Whether damaged from arcing in operation, galded or warped from removal from the shaft, or cracked due to porous castings, damaged steel parts must be replaced to ensure stability of the commutator in operation.

Spare: With the aim of reducing down time for the future, manufacturing a spare new unit is another circumstance in which new steel is a requirement. Either purchased from the OEM or designed by an aftermarket manufacturer, key dimensions can be obtained from prints or from the existing unit, ideally upon refill. Alternatively, if shaft profile information is available, along with any flange mount details if required, a new unit can usually be designed. As long as accurate and detailed information about the external dimensions of the commutator and its application environment is available, a new commutator can typically be designed to fit.

Design Improvement: In some cases, an existing steel design may cause problems in a specific application. For example, a v-ring commutator with a floating front cap and no spool may prove unstable or particularly susceptible to contamination in the wrong environment.
New steel can be designed to incorporate a front bore fit and spool to address the operational issues. In short, buying a new commutator when a refill is an option is rarely the most cost effective or timely choice. With no sacrifice in quality by re-using good quality steel parts, refilling a commutator typically represents the best option available in motor repair.

Should you or your customer have any questions regarding this issue, contact an ICC representative and we will be happy to assist you in making a decision on your specific
situation.

When should you dip a commutator in varnish?

Never.
There are several good reasons to make sure that you never subject a v-ring commutator to varnish or VPI, all of which are critical to the unit's operation.

Commutators are designed with gaps throughout (see Fig. 1). This allows for differential expansion and contraction of the various materials in operation, and results in successful operation over many years. If varnish is introduced into these gaps, the commutator can no longer perform as designed and the varnish can cause three distinct problems:

Overheating: When dipped with varnish, these gaps are filled, which inhibits cooling and can often result in overheating in specific areas of the commutator.

Imbalance: Uneven distribution of the varnish may result in imbalance of the armature. For example, if the unit is dried horizontally, the varnish will pool to one side, and within the confines of the commutator, it may never entirely cure. This material can then result in the overheating noted above, but also in imbalance in operation.

Shorting: In addition to the problems noted above,exposing the commutator to any impurities in the varnish can also result in failure due to shorting bars. Though most repair facilities keep their varnish as clean as possible, minimal impurities which would not affect coils, will potentially bridge the small spaces between commutator bars.

What should you do if you receive a commutator that has been dipped?
Depending on the severity, the comm may indeed need to be refilled. However, if after having banded the unit and taking it apart, you discover that the varnish deposits are minimal and contained mainly to the dovetail area, you may be able to simply clean the dovetails and replace the v-rings. Sanding or taking a very light skim cut should do this effectively.

For tips on v-ring replacement, see Motor Fax "Replacing V-Rings", or call us for information.

How do you avoid loosening a comm when you take it apart? And why is it important?

It's important because a loose commutator will cause endless amounts of problems in operation. High bars, chipped brushes, and poor commutation make your job of checking for commutator tightness an important part of routine maintenance. 

How is tightness built into a commutator?
In manufacturing, the copper and mica segments are assembled in a circular form. The resulting "segment pack" is checked for skew and angle. A steel ring which has been machined to the rough OD of the commutator, is then compressed over the segment pack in a press. The tonnage used will vary depending on the size of the comm, but can easily range from 10 tons to 90 tons. The resulting compression provides the commutator tightness which all following procedures are designed to maintain. In some instances, the commutator may be banded to obtain additional stability.

What keeps a v-ring commutator tight?
The dovetail angles that are cut into the segment pack are the foundation for keeping the commutator tight. With the compression ring still in place, the segment pack is assembled to the steel caps and hub, and insulated with mica v-rings. The caps seat against the internal angle (typically 30°) and retain the compression after a series of thermal closings under torque and tonnage. When the compression ring is removed, this assembly keeps the commutator tight. In effect, we have created a spring, which is held tight by the pressure exerted internally.

How do you take a comm apart without releasing the tightness?
Since the steel caps are keeping the commutator tight, removing the outboard cap will immediately release this pressure, loosening the comm. It is almost impossible to get the compression back in the segment pack once it has been released. Before pulling a commutator cap, always band the brush track, preferably with a resiglass tape, applied hot and cured (see banding material specifications for temperatures). You should be applying the tape at 300-400 psi, covering approximately 3/4 of the brush surface, and building it up to about 1/4" per side. To finish, wrap 8-10 wraps over your tucking loop to ensure that the banding stays in place. Alternatively (though not preferred), a steel ring machined to between 0.010" and 0.020" smaller than the brush diameter (depending on the size of the unit) can be heated and applied over a nomex sleeve covering the brush track. The ring should be first measured cold before installation, and then measured again once cooled after installation to ensure that sufficient fit has been obtained. With banding or a ring in place, the cap can now be safely removed, and the v-rings replaced or other maintenance performed.

Checking for tightness.
During routine maintenance, bolt and nut v-ring commutators can be checked for tightness by applying a specific torque to the bolts, or to the nut with a spanner wrench. Typically, torque values are approximately 50% of the maximum rating for the bolt grade and size. If you have questions regarding a specific unit, call us for a recommendation

How can asking for a change in commutator riser style save you time on your next rewind?

By giving your winder the style that works best for personal preference... and by knowing where you can safely make changes, and where you can't. Inserted risers come in many different styles... from open, to closed, to straight blade, and with a large number of foldover configurations.

Different winders have different preferences, and generally speaking, risers can be designed to meet those preferences; as long as the overall material remains the same for current carrying capacity and stability in operation.

When working with foldover tabs, the biggest challenge can be in placing the coils. Though it may seem that the top coil should fall entirely between the two sides of the riser, in fact, the short side of the riser should come only halfway up the top coil. This original OEM design may cause problems in aftermarket rewinding, since you'll end up working with a very small amount of the long side of the risers which can be difficult to bend.

The solution? Have your commutator manufacturer make an adjustment to the design. Some of the conversions available (shown below), may fit better within your winders' preferred work scope and may save time in the rewind as a result. Also, if you choose to stay with a full foldover, you can always instruct your comm manufacturer to increase the length of the long side of the riser to make it easier to bend.

Should you change riser material thickness?
Not if it means going thinner. By going from 0.060" to 0.040", you reduce the current carrying capacity of the copper, and also reduce the strength of the material. However, the reverse (0.040" to 0.060" is typically possible, and it is also possible to convert from a double inserted riser of 0.040" material to a single inserted riser of 0.093".

Can I do anything to stop inserted risers from cracking in operation?
Riser cracking is typically due to one of two causes. Vibration can be addressed in some cases by adding a row of lashing to help minimize the effect. Hydrogen embrittlement is seen in copper which contains oxygen. Over time, it will react with the hydrogen in the air and cause the copper to become brittle and crack. Using Oxygen-free copper for inserted risers will solve this problem, and should be specified for virtually all inserted riser commutators.

When is reinsulating a comm an option?

Usually if it has inserted risers, is a v-ring style commutator, and uses over 1000 pounds of copper. 

There are, of course exceptions to this. If the commutator doesn't use quite that much copper, but it has a very thick or very wide copper bar, reinsulating may still be a great cost saving alternative.

What is replaced in a reinsulated commutator?
Typically, reinsulation refers to the replacement of segment mica between the bars, and replacement of the mica v-rings and mica tube. It should also include new risers, and any 
peripherals like lashing or wrapped caps.

Why would you want to reinsulate instead of refill?
Cost. Reinsulating a commutator typically doesn't save any labor hours, since each bar has to be cleaned thoroughly before re-use. However, if the comm uses a significant amount of copper, the material savings can quickly amount to several thousand dollars. On a smaller comm, however the material savings would be quickly outweighed by the disadvantages of reinsulating.

When shouldn't you reinsulate a commutator?
When there is limited brush life left, and when the copper is damaged in some way.
If the copper has been overheated and annealed, it will no longer be re-usable. If the dovetails have been bent or cracked, a refill will be necessary. Finally, if there is insufficient flat on the interior of the comm to allow for removal of copper for reassembly, reinsulation would not be
recommended.

How can you tell if reinsulating is possible?
For thorough inspection and final determination, the commutator will have to be entirely disassembled. While an external inspection will show the condition of the bars and the amount of brush life left, inspecting the dovetails and copper hardness requires individual bar inspection.

Can you reinsulate a solid riser comm?
Not typically, and not cost effectively. Solid riser comms are slotted, and the slots would need to be plugged to withstand the new compression for reassembly and subsequent machining. In addition, in reinsulating, in order to maintain brush diameter, mica thickness is increased. On a solid riser comm, this would also increase the riser diameter, and would change the slot depth and position.

What about glassbound commutators?
Glassbound comms are a totally different design. Since the copper shrinks to a mica wrapped hub, any additional removal of material would adversely affect the fit. In addition, once grooved for banding, the copper material remaining under the band is very thin, and unlikely to withstand compression.

Options for repairing broken commutator risers

If the risers are broken at the brush track or only slightly beyond, your options are severely limited.

 

Inserting new risers is not a viable option, since the heat required to braze the new riser in place would quickly burn and destroy the segment mica between the bars. Soldering is also not recommended, due to the likelihood of contamination of the segment insulation. In addition, solder will rarely withstand the operating temperature requirements of the unit.

T.I.G. welding extensions is not an option due to the small amount of riser material remaining attached to the comm. In this situation, there are typically two possible options remaining for repairing the problem:

Refilling the commutator - involves reusing the steel core, but manufacturing new copper, risers, and insulation. Reinsulating the commutator - involves reusing the steel core, and the copper bars (on large units), replacing the risers and insulation. Note: reinsulation is not typically an option for glassband commutators, which we will address in a future issue of Motor Fax.

If the break is further along the riser, the repair is much less complicated.

T.I.G. welding extensions is a good solution to this problem, assuming that the commutator is otherwise in good condition and that there is still substantial brush life left on the unit. To effectively perform this repair, the risers need to be thoroughly cleaned, removing all carbon contamination.

New risers should be fabricated from the same material used in the original unit. This is typically half hard, oxygen-free copper, in thicknesses ranging from 0.020" to 0.125". Riser extensions should be bent prior to installation, allowing 0.002" in width and 0.312" in depth greater than coil sizes for easy coil installation.

For recurring problems with cracked risers due to vibration, you may want to consider adding a row of lashing to help minimize this effect.

Shown below are some of the more common riser styles, to help in your identification.


Having trouble with banded commutators?

Glassband commutators were first designed by General Electric in 1960 for their redesigned line of 580 and 8000 frame machines, and later for their MD800 Armored Motors. Although performance of these commutators is good, end users and motor repair shops sometimes give them less than favorable reviews because of the difficulty in field repair of the units. With v-ring commutators, bolts can be tightened and vrings replaced, but glassbound commutators are designed to be virtually maintenance-free. In addition, the glassband comms are significantly lighter in weight than their v-ring equivalents, and under normal duty requirements, routinely out-last v-ring units by 50%.

However, how many motors do you see operating under anything but "normal duty requirements?" The problem arises when end-users in high contamination environments end up having to replace bands on a far too regular basis.

The only restraining force on glassband comms are the res-iglass bands. This material is made from high tensile glass yarns laid parallel and bonded with fully catalyzed thermosetting resins. The glassband commutator is set with an interference fit of approximately 0.030" to a mica wrapped and cured steel hub. The retained interference fit, measured by the growth of the segment pack, should be, at minimum, 0.015". The inside of the segment pack is bored smooth, specific to the cured mica-wrapped hub. Glassband grooves are cut after the segment pack is assembled to the core. Finally, the commutator is banded to an OEM specified number of wraps at 500 lbs PSI. It is then baked for several hours at approximately 300 degrees. The bands are applied multi-stage to ensure maximum strength.

Most repair shops will apply a coating of Viton® to the bands prior to the commutator going into operation; this step should not be omitted. If the bands have not been coated, carbon can creep behind the band, causing burning from the inside out. Though this might not be seen in a visual inspection, it can easily result in the failure of the unit.

What you should consider before converting from a glassband to V-ring comm:

Converting a glassband comm to a v-ring is an alternative to dealing with ongoing problems. But there are several things to consider when presenting this as an option to your customer:

Weight
A v-ring style commutator will be significantly heavier than the glassband it replaces. The v-ring design requires not only the addition of a hefty steel part including a spool and two caps, but also a substantially wider (and therefore heavier) copper bar.

Performance
As a result, performance may be affected and the weight gain should be measured against the motor as a whole and the application for which it has been designed.

Maintenance
V-ring comms are more familiar, but they do require ongoing maintenance such as checking for  tightness. However, if your glassband is being rebanded once a year, v-ring tightening is going to be a welcome change.

Cost
Converting to a v-ring will mean a substantial cost outlay (typically 3x) compared to the cost of a refill. However, when weighing the cost of contant band replacement, the capital expenditure associated with the conversion will often make sense.

Experience
Conversion to a v-ring is a major redesign and requires both engineering and production experience from your commutator manufacturer. Ensure that you are being asked to approve conversion drawings, and ask for references.

Your commutator supplier should be able to help you explain this alternative by providing you with support materials and technical references. If this is a topic which applies to one of your customers, let us know, we'll be glad to help.​

How much damage can flux contamination cause?

Enough to kill a commutator.

When soldering coils into the risers of a commutator, the worst potential consequence is flux contamination, especially in solid riser comms. The same flux that cleans the copper to permit the solder to adhere uniformly to the risers creates a potential for contamination that can destroy a commutator. Flux contamination can occur during the soldering process when flux and/or excess solder seeps away from the riser slots and finds its way to the underside of the commutator. Because the flux and solder are conductive, they render the mica insulation useless. When the insulation can no longer prevent electricity from jumping from bar to bar, the commutator shorts out. Once the mica insulation is contaminated, almost nothing can be done to restore its insulating properties. When the commutator shorts out due to flux contamination, there are usually only two options: Reinsulate (replacing all mica insulation throughout the commutator) or rebuild.

When inspecting a commutator for flux contamination, look for discoloration of the copper bars. The discoloration may take several forms. Streaks of solder and flux are silver in color; carbon residue where arcing has occurred is black; contaminated copper bars can take on a darker, mottled and greenish coppery hue, or the contaminated area may just appear lighter than others. Compare the rear dovetail to the front, since the front will be free of contamination. As always, when taking a comm apart, be sure to band it tightly and bake it before attempting to remove the v-rings.

There are several ways to reduce the risk of flux contamination during the soldering process:

  • While soldering, angle the comm so that flux and solder run away from, and not toward, the bottom of the comm.
  • Use flux and solder sparingly.
  • Flux and solder small sections of the comm at a time.
  • Use a rosin-core solder to reduce the need for flux, or a flux- based solder so the solder contains the flux.

If the commutator is contaminated, some solvents will clear minor contamination, but call your ICC representative at any time for advice on how to proceed.

If you have any technical questions don't hesitate to call, we can talk you though the troubleshooting process. 865-983-7444

Our sincere gratitude.

We would like to thank our customers for their support, concern and flexibility during last week’s unfortunate train derailment and subsequent evacuation of our facility. There were no ICC employees injured and we are back in full production. Customers can expect updates on their jobs and if there was any impact to their specific job production or shipping.

A special thank you goes out to the Maryville, Blount and Alcoa first responders, volunteers, the local Red Cross and CSX emergency team for their swift reaction and tireless efforts to keep our community informed and safe. Your selfless acts have not gone unnoticed.  ICC had the privilege of working with CSX to set up a command post during the early hours of the incident and we were quite impressed by their policies and procedures for cleanup and their immediate attention to how this impacts local business and workers.

The Maryville community pulled their strengths and without hesitation helped their fellow community members, ICC is proud to call Maryville their home.     

Seamless Extension Banding Can Save a Commutator

When you band commutator extensions with skill and a few tricks of the trade, all seams are sealed and carbon won't infiltrate.  Preventing carbon from entering behind the copper bars, or between the mica v-ring and the steel can prevent problems with arcing bar-to-bar, as well as bar-to-ground.  The pressure used, technique applied, and finishing touches make a big difference.  A feeler gauge should not be able to enter a seam. If it can, your comm is at risk.  Contact us if we can help walk you through it the next time you have to replace a band. 

Nail down a procedure for replacing V-rings in house.

Replacing v-rings can be the answer to giving your customer's commutator new life, without having to resort to a refill. By firming up a procedure, you take the guesswork out of the process, and end up saving time and money on the repair. 

Following these steps will help you provide a tight comm, fully cured and ready for operation. 

"Gotcha's"

Overtightening: While the values provided may seem low, please use caution. If you have any questions, call ICC and we'll be happy to discuss your commutator specifically. Overtightening can bend the dovetails, resulting in bar movement, broken brushes, seized motors and overheated copper segment packs requiring re-manufacturing or replacement.

Insufficient Closings: The guidelines for thermal cycles are provided to ensure a tight, solid commutator. These closings allow for proper seating of the copper and mica segment pack to the steel, in addition to curing the mica v-rings.

Contamination: It will never be easy to get a good test on a unit that has been in operation, but a thorough cleaning is imperative to ensure proper operation once the commutator is reassembled.

Easy steps for flawless v-ring installation

  1. Heat the commutator to 300°F, band it tightly using res-i-glas banding tape and cure.
  2. Remove the caps.
  3. Clean and sand the internal dovetail angles until the comm is free of all contamination.
  4. Test bar to bar.
  5. Carefully install new mica v-rings and assemble the unit to the steel.
  6. Hand tighten all bolts or nut.
  7. Heat commutator in oven to 375°F.
  8. Remove from oven and torque hot to specifications in the chart shown in a star pattern.
  9. Watch for even cap movement.
  10. Cool to ambient temperature and torque again to specs.
  11. Repeat heating and cooling cycle through two more cycles, torquing at each stage.
  12. Test bar to bar and bar to ground.

*Disclaimer: ICC provides the above information in good faith but due to the wide range of quality of product and levels of experience, ICC is not responsible for the failure to achieve successful v-ring replacement through following the above instructions.