Commutator

THE NAKED TRUTH... Paint can cover up a lot.

ICC International Glassband Commutator

ICC commutators are stripped down to show we have nothing to hide. You get perfect banding and beautifully sealed edges. Commutators that can stand before you ... naked, in fact. Your coatings will adhere better, and you never have to wonder about what you can't see. With ICC commutators, beauty isn't only skin-deep, but it's a good place to start.

ICC industrial commutators are crafted in small volume by experts using the highest quality raw materials available. Contact your ICC representative today.

ICC International Banding Commutator

Note: If you do need a commutator painted for a specific application, let us know and we'll take care of it.

Can you convert your commutator from inserted to solid risers?

Possibly.

A solid riser commutator is one in which the riser, into which the coils are inserted, is made of the same piece of copper as the rest of the bar. In a solid riser v-ring commutator, a rectangular shaped bar of copper has the three sections machined away - at each end for the dovetail,
and along the brush track, leaving the riser.

If a riser is very long, a tremendous amount of copper would be wasted to leave the riser. Instead, an inserted riser design was developed.

Winders, however, often prefer to work with solid riser designs, so how can you tell if your commutator is a candidate for conversion?

Alloy 116 (silver bearing commutator copper) is typically readily available in sizes up to 4, or even 5, inches in width. If your commutator from the inside diameter of the copper to the outside diameter of the risers fits within this, conversion may be a viable option.

What if the bar needs to be wider than available copper sizes?
An alternative to a solid riser is a lap joint design. A separate riser is brazed to the copper bar, but shaped to match the trapezoid of the bar itself. Though typically more expensive than an inserted riser unit, a lap joint riser will provide all the benefits of a solid riser commutator, i.e. carbon contamination prevention behind the risers.

What should you consider in a conversion?
If the risers in question are quite long, you will be adding weight to the unit, potentially
affecting performance. In addition, if cooling and airflow are considerations for your
application, note that the solid risers or lap joint will cut off this air flow versus the inserted riser design.
Call your ICC sales representative to discuss the possibility of conversion of any
commutator you have in house.

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.

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.


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.