Capping the loop end of an electric motor!

[[email protected]]

Okay, here's a good one... I work with a group of "engineers" from
the Czech Republic that manufacture DC electric motors (~180 HP).
We've been having a problem where the loops of the armature are
destroying the resin wrapping that is supposed to hold them down. The
centrifugal force of the loops is just tearing this wrapping apart
after the motor has been in service for awhile. Usually the loops
flare out enough that they contact the field windings and then the
motor is toast.

We've determined that the wrapping process is a very low quality. It
is almost the consistency of cardboard rather than a very hard
material like it should be. The proper fix for these motors should be
to rewrap both ends in the proper manner and then the centrifugal
force won't tear it apart.

The manufacturer wants to install a CAP over and around the entire
looped end of the armature! I've been able to determine so far that
this cap will probably seriously restrict air flow and cooling. I
also believe that the cap is just going to tear itself apart
eventually.

My question to the group is what other reasons is this a bad idea?
Also, have any of you seen this capping method used elsewhere? I
can't find anyone I know that's ever heard of such a thing. The funny
thing is that this method is coming from a fairly well known company
in CZ... You can probably think of it.. Thanks.

 

[Rheilly Phoull]

Okay, here's a good one... I work with a group of "engineers" from
the Czech Republic that manufacture DC electric motors (~180 HP).
We've been having a problem where the loops of the armature are
destroying the resin wrapping that is supposed to hold them down. The
centrifugal force of the loops is just tearing this wrapping apart
after the motor has been in service for awhile. Usually the loops
flare out enough that they contact the field windings and then the
motor is toast.

We've determined that the wrapping process is a very low quality. It
is almost the consistency of cardboard rather than a very hard
material like it should be. The proper fix for these motors should be
to rewrap both ends in the proper manner and then the centrifugal
force won't tear it apart.

The manufacturer wants to install a CAP over and around the entire
looped end of the armature! I've been able to determine so far that
this cap will probably seriously restrict air flow and cooling. I
also believe that the cap is just going to tear itself apart
eventually.

My question to the group is what other reasons is this a bad idea?
Also, have any of you seen this capping method used elsewhere? I
can't find anyone I know that's ever heard of such a thing. The funny
thing is that this method is coming from a fairly well known company
in CZ... You can probably think of it.. Thanks.

Whats wrong with the normal steel wire binding just behind the commutator ??

 

[Degaully]

what are the specs on the motor ?

 

[Ian Stirling]

Okay, here's a good one... I work with a group of "engineers" from
the Czech Republic that manufacture DC electric motors (~180 HP).
We've been having a problem where the loops of the armature are
destroying the resin wrapping that is supposed to hold them down. The
centrifugal force of the loops is just tearing this wrapping apart
after the motor has been in service for awhile. Usually the loops
flare out enough that they contact the field windings and then the
motor is toast.

What is the specified wrapping.
Is it in fact being installed, or are they using strips of old
T-shirts with flour and water paste?

 

[[email protected]]

That's part of the problem. I don't actually know the specs on the
wrapping, however it is very clear that this wrapping is soft compared
to every other wrapping I've seen. Most wrappings are almost like
steel when you tap on them, this one sounds hollow and soft like
cardboard. It appears to be the reason it can't hold the lops down.
Typical speed of the motor is 4400 RPM.

 

[Ian Stirling]

That's part of the problem. I don't actually know the specs on the
wrapping, however it is very clear that this wrapping is soft compared
to every other wrapping I've seen. Most wrappings are almost like
steel when you tap on them, this one sounds hollow and soft like
cardboard. It appears to be the reason it can't hold the lops down.
Typical speed of the motor is 4400 RPM.

Have you suggested that the manufacturer check that the workers are
actually installing it properly, and that it is the proper stuff?
It might be worth getting someone with a microscope, and some test tubes
to have a look at it to find out what it is.

 

[[email protected]]

Well you hit the nail on the head there, because this is exactly what
happens when you buy from a place where English isn't the primary
language. In addition we are totally separated by a cultural gap in
terms of manufacturing and quality assurance practices, warranty,
failure analysis, etc...

 

[Ian Stirling]

Well you hit the nail on the head there, because this is exactly what
happens when you buy from a place where English isn't the primary
language. In addition we are totally separated by a cultural gap in
terms of manufacturing and quality assurance practices, warranty,
failure analysis, etc...

Nope.
It's what happens when you buy from a place where the foreman does not
understand the design, or does not enforce it, or where management
substitutes cotton for glass fiber.

A german factory is quite unlikely to have the same problem.

 

[Big John]

See my comments in the text.

Okay, here's a good one... I work with a group of "engineers" from
the Czech Republic that manufacture DC electric motors (~180 HP).
We've been having a problem where the loops of the armature are
destroying the resin wrapping that is supposed to hold them down. The
centrifugal force of the loops is just tearing this wrapping apart
after the motor has been in service for awhile. Usually the loops
flare out enough that they contact the field windings and then the
motor is toast.

We've determined that the wrapping process is a very low quality. It
is almost the consistency of cardboard rather than a very hard
material like it should be. The proper fix for these motors should be
to rewrap both ends in the proper manner and then the centrifugal
force won't tear it apart.

I agree.

The manufacturer wants to install a CAP over and around the entire
looped end of the armature! I've been able to determine so far that
this cap will probably seriously restrict air flow and cooling. I
also believe that the cap is just going to tear itself apart
eventually.

I also agree - not good for cooling. Cheap, quick fixes usually don't work.

My question to the group is what other reasons is this a bad idea?

Yes, if the cap is metal. You will have some flux from the main field in
this area (especially near the core). When the metal cap spins through this
field you will get an induction braking effect. This will add heat and
lower the motor's efficiency.

Also, have any of you seen this capping method used elsewhere?

No, and I worked for a motor manufacturer for 16 years. You should also
check to make sure they are using an armature design with closed slots.
This is necessary for a larger motor running at 4400 RPM. A cheap company
might want to use open slots to make armature winding easier, but
centrifugal forces will tend to throw the windings out of the armature slots
at speeds this high.
I

 

[BFoelsch]

It almost sounds like the coils are too long, leaving excess loop length.

What speed are these units?

 

[[email protected]]

4400 RPM is about normal. The loops extend about a few inches out.

 

[Don Lancaster]

Nope.
It's what happens when you buy from a place where the foreman does not
understand the design, or does not enforce it, or where management
substitutes cotton for glass fiber.

A german factory is quite unlikely to have the same problem.

Americans announce technology for the finest drawn wire.
Japenese drill a hole in it.
Germans tap it.

--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Tim Auton]

Americans announce technology for the finest drawn wire.
Japenese drill a hole in it.
Germans tap it.

Then the English claim they invented it all 100 years ago


Tim, an Englishman.

 

[Keith R. Williams]

Americans announce technology for the finest drawn wire.
Japenese drill a hole in it.
Germans tap it.

Good grief, I heard that yarn 40 years ago, though it was French,
Germans, Americans. ...the Japaneese drill bit broke. ;-)