I agree. I once interviewed for a design engineer position at motorguide, where they make PM motor trolling motors. They use the same method in their production environment.
They place the magnets in a holding fixture, solvent clean, and then a tool dispenses epoxy evenly onto the back. the magnets are then glued into position on a backing plate. After initial cure, it's time to magnetize the magnets! Yes, they magnetize their own magnets! In this case, the heat generated by the magnetizing machine performs the post cure, since it gets hot in there when they run huge currents through it.
They then assemble the magnets plus backing plates into the cases. Having the backing plates makes assembly and keeping the magnets in the right position easier, though having the backing plates discontinuous cuts motor efficiency somewhat.
--- On Thu, 9/30/10, steven1955 comcast net <steven1955 comcast net> wrote:
From: steven1955 comcast net <steven1955 comcast net>
Subject: (ET) ET motor magnet re-glueing
To: elec-trak cosmos phy tufts edu
Date: Thursday, September 30, 2010, 9:02 AM
To all with unglued magnets, I don't know why so many of us think an unglued magnet means you should scrap the motor shell. If you check the archives you'll find a posting I made describing how I have successfully re-glued magnets on two different permag motors, admittedly not Elec-Trak motors. Maybe I should start a business doing this, but then again, I suspect the success rate would be on the order of 70 to 90%. I'm pretty sure I wouldn't want to deal with the unhappy owners of the 10 to 30% of failed re-gluing attempts. You've got nothing to lose, so why not try it. Below I've copied the text from my old 2004 posting describing my method. Steve Naugler I have had that (magnets coming unglued) happen on two DC motors in the past, although neither were
for the Elec-Trak. One had a broken magnet which I fixed by gluing the magnet pieces as close together as possible. (The other
had an unbroken but loose magnet.)
I was able to repair both of those motors with epoxy. I used the normal
cure high strength like you can find in Home Depot, but do not use the 5
minute stuff. It cures faster at the expense of lower strength.
I VERY, VERY thoroughly cleaned the motor shell and the magnet with
solvent, smeared the epoxy on, and placed the magnet back in its original postion.
This may take some doing because sometimes the magnets will fight you. You
need enough epoxy to leave no gaps between the magnet and the shell, but as
little as possible so that the magnet is as close to the shell as possible.
You will want to clamp the magnets in position for a two reasons.
1. The first is that once glued you can't get the magnet off. You need to
get the right position the first time.
2. The second is that you actually want extra epoxy to be squeezed out.
It is important that the magnets are as close to the shell as possible. Use a spring clamp so that clamping force is maintained as the magnets move
closer to the shell.
Now wait for the epoxy to cure hard, at least overnight. The clamps can
come off and they stay off.
Think you're done? Nope. This epoxy will be highly stressed, so I
recommend a post cure. What I did was place the shell on one of those
electric oil filled radiators set on low, covered the shell with a box
making a mini oven, and let it stay there for 24 hours. The shell reached
about 150 to 160 degrees and stayed there for the entire time.
You can also use a kitchen oven if your spouse or significant other will let
you. (Mine didn't, hence the radiator style heater.) Use two cookie
trays, one on the lower rack, and one on the upper rack, Place the motor shell on
the upper tray. The lower tray protects the motor shell from radiant heat
which could get the shell too hot. Set the oven to warm, and "bake" for
12-24 hours.
Bill Gunn had bad luck with fixing magnets, so he wouldn't do it at all
after a few failed attempts. But in Bill's case a 25% failure rate would
have been intolerable. In our cases, if the option is trashing the motor
shell, I'd go for it.
Steve Naugler
-----Inline Attachment Follows-----
|