What copper alloy are slip rings made from?

I have an old rotating spindle for a sinker EDM that needs repair and two of the things that need replacement in it are a copper slip ring (~3.5" OD, ~.125" thick, ~.5" ring width) and the copper brushes (three of them) which are about .5" x .25" They "look" like copper. The slip ring rides on springs and does not rotate and the brushes are fixed in a rotating steel disk. Anyone know what a conventional copper alloy might be for these items. The spindle is a Rotobore unit that has been well used. Would it be ordinary 110 copper? I need to fab and replace these items and I wonder about the wear aspects of the copper, galling, etc.


Cheers,
Rich

Most likely 95-5 gilding metal

For brushes you might try to find some really big starter brushes. I use brushes out of the ill fated GM diesels. Too small for you perhaps. They are made from sintered brass with carbon.

John

Thanks, guys. I looked up the 95-5 gilding metal (C21000) listed under brass or copper depending on the seller or manufacturer but I could not find a source for a small amount such as what I need. Also seems that depending on the vintage of my unit, the brushes were either some sort of soft copper (as in what I have) or a brittle sintered material (as what amoretti is suggesting) or a sandwich of the two where the copper base is pressed into a hole and the sandwiched carbon/graphite does the brushing. The latter would be easy to make and install but would require some kind of conductive glue (silver epoxy). A solid sintered material might be installed in the mounting holes with the same kind of glue. Solid copper (say, the C21000) would also be easy to install.

Cheers,
Rich

Bill,
Thanks for that input. I'll look for some conductive thermoset glue as I know it exists. The stuff I had anticipated in using is epo-tek h20e which is a two part silver epoxy that has a continuous operating temp spec of 200ºC. The unit I'm repairing is a low speed spindle and the slip ring/brush assembly is not for running a motor. It's only for keeping the spindle housing and the spindle itself electrically continuous. Low temp operation, to be sure. Maybe you know all this already but the spindle for the Rotobore is driven externally through a cable.

I'll be making the brush sandwich from old automotive brushes.

Cheers,
Rich

Any help ? Brushes Main Page

FWIW 40 + years back, I used to make slip rings from a high copper content bronze, can't remember the grade -they were big - for something to do with newspaper printing.

thermite said:

Idea was, AFAICS, that any one wire were to 'bounce' the others would remain in contact - they did not sit on quite the same radial.

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Similar logic to rotary relays, used in USN nuclear sub relay logic back in the day. Actuation is not bending, it's twisting. And hard shocks might lift the contact on one side, but they'd force the contact on the other side to mash even harder against the mating contact.

I've been using Aero-Motive sliprings and brushes for wind turbines for 30 years or so. The manufacturer says only that "brushes are copper-graphite with braided-copper shunts and copper-alloy rings." Some mfgers use graphite brushes so it seems that could work, too.

I have quite a few brushes and rings rated at 30 amps and 200amps. Dunno what your size requirements are, but I can measure 'em up if you like. Both rings and brushes are readily disassembled and machinable, so approximate might be close enuf.

Neil

thermite said:

Doubt that silver-bearing epoxy would stand a chance. We used it for hearing aids, and DIS-assembly was a mere touch of a soldering iron. IOW- it melts.

Brushes - per a Reliance 'white paper' - are meant to live on a commutator at just above the boiling point of water for most durable compromise of 'slippery' copper-oxide formation/re-formation, eg: "sustenance", and slip rings should not be all that different as to the temp of their operating zone. For durability, one would want a thermo-SETTING binder, not a thermo-PLASTIC one. Anyhoo .. brush conductivity and other characteristics are an Engineered - even 'black art' area for longest service life. They are not all the same.

What about robbing the more well-regarded of legacy automotive / truck / marine alternators - if not for parts, at least for pre-engineered examples of what to copy that is know to work well and last a reasonably long time?

Bill

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Minor bone-picking: All epoxy systems are basically thermo-set chemistry, which indicates that the catalysis and cross-linking are essentially one-way reactions. Thermoplastic materials will recover their properties when brought back below the plastic transition temp, but heat applied to thermoset materials will just destroy the bonds. It's not melting in the strict technical sense, but more in the Wicked Witch of the West sense.

neilho said:

I've been using Aero-Motive sliprings and brushes for wind turbines for 30 years or so. The manufacturer says only that "brushes are copper-graphite with braided-copper shunts and copper-alloy rings." Some mfgers use graphite brushes so it seems that could work, too.

I have quite a few brushes and rings rated at 30 amps and 200amps. Dunno what your size requirements are, but I can measure 'em up if you like. Both rings and brushes are readily disassembled and machinable, so approximate might be close enuf.

Neil

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WOW! They are pretty proud of some of those
Aero-MotiveDirect.com: Home

Rich L said:

... copper slip ring (~3.5" OD, ~.125" thick, ~.5" ring width) and the copper brushes (three of them) which are about .5" x .25" ...
Rich

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Limy Sami said:

Any help ? Brushes Main Page

...

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Thanks for that link!

neilho said:

I've been using Aero-Motive sliprings and brushes for wind turbines for 30 years or so. The manufacturer says only that "brushes are copper-graphite with braided-copper shunts and copper-alloy rings." Some mfgers use graphite brushes so it seems that could work, too.

I have quite a few brushes and rings rated at 30 amps and 200amps. Dunno what your size requirements are, but I can measure 'em up if you like. Both rings and brushes are readily disassembled and machinable, so approximate might be close enuf.

Neil

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Brushes: contact surface is .500 x .312 x .100 but the kicker is the mounting "stud" which is centered and is .125 long and .130 Ø (peened from the back to stay in)(the half that gets mounted is copper) (hence my glue problem)

Ring: 3.43 OD x 2.68 ID x .125 thick

30 amp material would be sufficient as the machine can only produce that much presuming that's a peak current and not an RMS. Anyway, I never get anywhere near that capacity.

If you've got something that might fit with some alterations we can PM and I can buy some pieces from you.

So I'm hearing that slip rings are some alloy with either tin (bronze) or zinc (brass) and not pure copper. Wear characteristics as the reason?

Cheers,
Rich

Most of the slip rings i encounter appear to be just common brass. Though these are just electric clutches. Normally though its some kinda graphite brush.

Unlike comutators, because slip rings are in constant contact with the right brush material they will have a real long life, theres just no cause for arcing if there running true.

All i have ever really grasped about brushes is its all a bit secret squirrel - black art's magic. The right grade offers good conductivity and is soft enought to be what is worn down. Equally though it has to be abrasive enough that it cleans the oxide of the ring. Get it right and they have silly long life spans, use the wrong brushes and i have seen them eat rings in weeks. The right grade ran for 3 years before needing changeing, its just one of thoes weird things that has to be right and if it is right they just go and go, wrong grade on the wrong grade of slip ring and its game over pretty quick. Helps to have good holders and enough spring pressure to remain firmly in contact. Nothing stuffs commutators and slip rings faster than arcing caused by seized brushes.

Brush material changes depending on sliding speed. High speed brushes are carbon like. Low speed brushes for larger currents have the copper look. Starter motor brushes may well work for you.

Standard Motor Products FX66 Starter Brush or Brushes | eBay

Rich L said:

Thanks for that link!



Brushes: contact surface is .500 x .312 x .100 but the kicker is the mounting "stud" which is centered and is .125 long and .130 Ø (peened from the back to stay in)(the half that gets mounted is copper) (hence my glue problem)

Ring: 3.43 OD x 2.68 ID x .125 thick

30 amp material would be sufficient as the machine can only produce that much presuming that's a peak current and not an RMS. Anyway, I never get anywhere near that capacity.

If you've got something that might fit with some alterations we can PM and I can buy some pieces from you.

So I'm hearing that slip rings are some alloy with either tin (bronze) or zinc (brass) and not pure copper. Wear characteristics as the reason?

Cheers,
Rich

Click to expand...

I may not be understanding your assembly correctly, but it seems that it's rings on a flat disc, while the Aeromotive is stacked cylindrical rings. In any case the 30Amp version has a ring 3" OD, 2.75" ID,.280" high. The brushes have a concave contact end that rides on the circumference. They're .250 thick, and 1.340 long. I think they're able to claim a 30A (continuous) rating because there are two brushes per ring. Have a bunch of these (brushes and rings) I'll never use because they don't often fail, free to you for shipping if you want 'em.


The higher current version has brushes 3/8" wide x 1.340 long. There's also a part # (SMC G60) on them which I believe is from St Mary's Carbon. Catalog here http://www.stmaryscarbon.com/~stmarysc/wp-content/uploads/2013/09/SMC-AutoAftmrktBrushes10.12.pdf . G60 isn't a current (ha!) pt #, but there is a dimensional catalog with application names that look useful.

Can't lay my hands on the big rings, but IIRC they're just 3/8"+ tall, same diameters as the 30A.

And back to your original question of collector ring material. There's a table here for preferred alloys that include commutator segment alloys-maybe not the same as for collector rings, but I'm getting the impression from the reading that for slow speed applications the brush alloy is more important.

Preferred Alloys::Electric Materials Co.

Hope there's something useful in here. If not, it was fun research.

manualmachinist said:

WOW! They are pretty proud of some of those
Aero-MotiveDirect.com: Home

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Jesus, my jaw dropped, too. Thanks for that link- I hadn't seen any retail prices in 25 years. They're so easily disassembled, reconfigured, remachined and reassembled and last so long that almost all crashed, trashed machines have usable slip ring parts. The worst thing that happens to them is when the spring that maintains brush contact breaks and arcing happens, esp on startup at 60 amps or so. Then that particular ring and maybe an adjacent insulator turns to garbage, but it's all fixable.

My slip ring repair rates just went up.

Neil

neilho said:

I may not be understanding your assembly correctly, but it seems that it's rings on a flat disc, while the Aeromotive is stacked cylindrical rings. In any case the 30Amp version has a ring 3" OD, 2.75" ID,.280" high. The brushes have a concave contact end that rides on the circumference. They're .250 thick, and 1.340 long. I think they're able to claim a 30A (continuous) rating because there are two brushes per ring. Have a bunch of these (brushes and rings) I'll never use because they don't often fail, free to you for shipping if you want 'em.


The higher current version has brushes 3/8" wide x 1.340 long. There's also a part # (SMC G60) on them which I believe is from St Mary's Carbon. Catalog here http://www.stmaryscarbon.com/~stmarysc/wp-content/uploads/2013/09/SMC-AutoAftmrktBrushes10.12.pdf . G60 isn't a current (ha!) pt #, but there is a dimensional catalog with application names that look useful.

Can't lay my hands on the big rings, but IIRC they're just 3/8"+ tall, same diameters as the 30A.

And back to your original question of collector ring material. There's a table here for preferred alloys that include commutator segment alloys-maybe not the same as for collector rings, but I'm getting the impression from the reading that for slow speed applications the brush alloy is more important.

Preferred Alloys::Electric Materials Co.

Hope there's something useful in here. If not, it was fun research.

...

Neil

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Thanks for the links - great info.

As to my assembly: it's essentially a flat disk with three brushes embedded near the periphery on the flat side. This flat side contacts the flat side of the slip ring. Nothing touches the edge.

email sent.

Thanks,
Rich