Is JB Weld is the only thing available for preventing magnet shift?

SonicCraft

Late to the conversation, but the JB cold weld will work well. No need for the fast set because the magnet will suck the JB in. Yes, JB is magnetic. With no surface prep, it is as good as any epoxy out there.

Mystery

SonicCraft wrote: »

Late to the conversation, but the JB cold weld will work well. No need for the fast set because the magnet will suck the JB in. Yes, JB is magnetic. With no surface prep, it is as good as any epoxy out there.

Cold weld is not in this test but original JB Weld did great while extreme heat did really bad job when gluing metal to metal.
https://www.youtube.com/watch?v=XObmZIbHOzY

F1nut

Which epoxy is the best? It sure as hell isn't JB Weld, not even close. West Systems and 3M make the best with 3M offering a multitude of options depending upon the application.

Mystery

F1nut wrote: »

Which epoxy is the best? It sure as hell isn't JB Weld, not even close. West Systems and 3M make the best with 3M offering a multitude of options depending upon the application.

10 year old but it was a world record by Loctite super glue.

Impressive video footage demonstrating Loctite® Cyanoacrylate Adhesive breaking the Guinness World Record after lifting a car weighing more than five tons with just nine drops of adhesive.

https://www.youtube.com/watch?v=2tfo98Ansxo

F1nut

That's impressive, but super glue and epoxy are very different.

Mystery

F1nut wrote: »

That's impressive, but super glue and epoxy are very different.

Yes but will that work on Polk magnets?
20 gram tube is around $6.
With that much strength, few drops around should be enough for a lots of drivers.

F1nut

If you could get the super glue to wick into the area between the plate and magnet it sure wouldn't hurt, but you have consider there is adhesive in there already, which would likely inhibit the adhesion of the super glue and there's no practical way to know if that's the case or not. IMO, one is much better off applying an adhesive such as epoxy around the edges.

pitdogg2

SonicCraft wrote: »

Late to the conversation, but the JB cold weld will work well. No need for the fast set because the magnet will suck the JB in. Yes, JB is magnetic. With no surface prep, it is as good as any epoxy out there.

Is this Jeff?

motorcityguy

I've had good success (over 20 drivers to date) with the method described in this thread:

https://forum.polkaudio.com/discussion/184463/a-different-twist-on-the-magnet-gluing-process

I know many well-respected members swear by the water-based Power Grab, but the manufacturer's own recommendations say at least one of the materials being bonded needs to be porous. That's not the case with the magnet and pole piece. Not saying it won't work--in fact many report it works well. Just saying I was more confident using an adhesive designed for bonding two non-porous surfaces.

audioluvr

motorcityguy wrote: »

I was more confident using an adhesive designed for bonding two non-porous surfaces.

Like Powergrab Ultimate? Just saying...

Gardenstater

I'm feeling like one of us needs to do a construction adhesive comparison test like was done with the bolts and angle iron youtube video and to compare also to the two epoxy winners in that video. Only in our case maybe it should be done with something closer to ferrite, like etched glass and the steel bolt as a combination, and maybe even unetched glass with unground bolt for a worse case scenario. Also, I didn't notice whether he oriented the hex head bolts the same in each case, which needs to be done.

However, my thinking is that epoxy would be very hard to beat for impact (g-force) protection, due to the rigidity and hardness of the cured end result. So, I mean, it's not just the bond strength that is an issue here, to protect from damaging the voice coil, and it isn't *just* an issue of whether the bond actually fails or not. Short term impact resistance is pretty hard to evaluate, but should be directly related to the hardness of the cured adhesive.

delkal

Gardenstater wrote: »

However, my thinking is that epoxy would be very hard to beat for impact (g-force) protection, due to the rigidity and hardness of the cured end result.

This is what I am thinking too. If you take 2 metal blocks with a perfectly flat surface and glue them with a couple drops of cyanoacrylate glue the bond will hold a thousand pounds. Maybe even more than epoxy. But if the surfaces are slightly rough cyanoacrylate glue will lose much of its strength and you need something like epoxy to fill in the gaps. On a speaker you are gluing it from the side and glue penetration between the surfaces is negligible. For those applications cyanoacrylate is worthless. Take those 2 blocks and put a drop of cyanoacrylate glue on the side and you will easily be able to break them apart. There is not enough mass and just a microscopic coat of glue with no bending strength. With epoxy the thickness and hardness of the glue when cured will hold the pieces together from the side and with an 1/8-1/4 inch and it would be difficult to break the bond apart. You can try this for yourself. Pour 1/8 inch of epoxy on some aluminum foil. Then try and break it.

I have not used powergrab but if it loses most of its mass when cured and leaves only a thin layer behind it should behave closer to a cyanoacrylate glue. If someone has any do the same aluminum foil test. It will be interesting to see how much glue mass you end up with and how rigid it is when bent.

bigmontana

motorcityguy wrote: »

...the manufacturer's own recommendations say at least one of the materials being bonded needs to be porous. That's not the case with the magnet and pole piece.

I see this concern mentioned often. I'm certain the context of this warning is when applying Powergrab between two flat surfaces of non-porous material. In that case, only the outer edges would be exposed to the atmosphere and cure properly. The interior would be completely sealed off and would not be able to cure. When applied around the perimeter of a magnet, the bead of adhesive is exposed to the air and it won't matter if the magnet underneath it is porous or not. There are a few reasons why you might choose one adhesive over another for gluing magnets, but I wouldn't let porosity be one of them.

Gardenstater

One consideration is coefficients of thermal expansion. Is the Polk adhesive losing its adhesion after many hot and cold cycles over the years because of different expansion rates of the magnet vs the steel?

I looked up the coefficients:
https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

Barium Ferrite: 10
Steel: 10.8 to 12.5
Cast Epoxy Resins: 45 to 65

Will peripherally applied epoxy eventually lose its bond, especially to smooth surfaces like in this case, due to a combination of it being hard and somewhat brittle and repeated heat-cold cycles?

SonicCraft

Maybe I should clarify... I said JB Cold..., but I meant the original JB. When I need a good epoxy, I've never used JB. I suppose it depends on the application, and then I'd use an application specific epoxy. As far as a general epoxy, I like Bob Smith Industries. But when bonding a magnet to anything, JB has some nice characteristics. JB is more than sufficient for this half a$$ magnet repair. Cheap, easy to find, and easy to use. Once liberally applied, that magnet ain't going anywhere.

xschop

Gardenstater wrote: »

One consideration is coefficients of thermal expansion. Is the Polk adhesive losing its adhesion after many hot and cold cycles over the years because of different expansion rates of the magnet vs the steel?

I looked up the coefficients:
https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

Barium Ferrite: 10
Steel: 10.8 to 12.5
Cast Epoxy Resins: 45 to 65

Will peripherally applied epoxy eventually lose its bond, especially to smooth surfaces like in this case, due to a combination of it being hard and somewhat brittle and repeated heat-cold cycles?

I do believe this is an issue with the old Polk midwoofers. I like using the blue Loctite when magnet and pole piece have been separated and recentered, because it will expand and contract more due to it's slightly higher elasticity than the Red when cured.
New Peerless midwoofers are using blue as well I have found.

For a non-slipped magnet, a thin layer of Power Grab is sufficient, but I'm sure an epoxy is much stronger and can take a much larger impact.

Gardenstater

xschop wrote: »

Gardenstater wrote: »

One consideration is coefficients of thermal expansion. Is the Polk adhesive losing its adhesion after many hot and cold cycles over the years because of different expansion rates of the magnet vs the steel?

I looked up the coefficients:
https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

Barium Ferrite: 10
Steel: 10.8 to 12.5
Cast Epoxy Resins: 45 to 65

Will peripherally applied epoxy eventually lose its bond, especially to smooth surfaces like in this case, due to a combination of it being hard and somewhat brittle and repeated heat-cold cycles?

I do believe this is an issue with the old Polk midwoofers. I like using the blue Loctite when magnet and pole piece have been separated and recentered, because it will expand and contract more due to it's slightly higher elasticity than the Red when cured.
New Peerless midwoofers are using blue as well I have found.

For a non-slipped magnet, a thin layer of Power Grab is sufficient, but I'm sure an epoxy is much stronger and can take a much larger impact.

I agree, but I would use one of the newer clear construction adhesives like Power Grab Ultimate or Gorilla Max Strength that specifically say they are good for the materials in question......ok they don't actually mention ferrite, but glass and ceramic should cover that. These ones are quite a bit stronger than basic Power Grab and the slight resilency may protect a bit more from losing its bond with repeated heat and cold cycles and *may* be rigid enough, especially if you build up the fillet a couple times, to withstand your speakers being knocked off their stands by children or dogs, or hand to hand combat with a burglar/home invader (lol), etc..

Having said all that, if you are sure that you will never store the speakers in a non climate controlled space, then I'd go with epoxy if you want the maximum impact resistance.

Gardenstater

The differences in thermal expansion coefficients between Sintered Ferrite (Ceramic) and low carbon steel used in pole pieces (1006 and 1008) is even worse than I thought.

Sintered Ferrite (perp. to direction of magnetism) = 8
1006 and 1008 low carbon steel = 12.6

https://www.allianceorg.com/pdfs/PhysicalPropertiesofMagnets.pdf



https://www.azom.com/article.aspx?ArticleID=6537
https://www.azom.com/article.aspx?ArticleID=6538



Edit to add: If Polk had used Samarium Cobalt magnets instead, would the slipped magnet issue have never come to pass?

Mystery

To test the two part epoxy, I glued two pieces of metal together and left it for over 3 days.
I tried to pull it and it didn't even take any force.
The glue was stuck on both side but the brass looking side just peeled off along with a layer of epoxy.
I don't think this particular epoxy does anything to magnet except probably blocking shift by obstructing the movement, not even sure of that now.

Gardenstater

Yep. Epoxy can definitely have adhesion issues to metal, no doubt! Companies like West Systems that put out how to guides will definitely always stress surface preparation such as: cleaning/degreasing and sanding/etching/grinding/sandblasting to provide something for the adhesive to key into and get a grip. With autobody work they even recommend wire brushing or sanding a thin application of wet epoxy into the steel and then building it up from there. The only thing that is practical for us with the speaker drivers is cleaning.

You don't mention what epoxy your experiment was with and what metals were used. Plated, unroughed up metal would probably be one of the worst possible case scenarios.

Here's a couple West Systems Guides. Probably if I were to pick which of their products I would try it would be the G/Flex with one of the fillers like colloidal silica, or even better, High Density #404.

https://www.westsystem.com/wp-content/uploads/User-Manual-2015.pdf

https://www.westsystem.com/wp-content/uploads/OtherUses.pdf

And another one:

https://epoxycraft.com/trade-secrets/we-asked-hamish-can-you-use-epoxy-with-metals/

PS: For impact resistance with the drivers, adhesion to the ferrite magnets is probably the most important factor, rather than to the steel, to prevent shifting.

TennMan

To test the two part epoxy, I glued two pieces of metal together and left it for over 3 days.
I tried to pull it and it didn't even take any force.

Then that brings us back to JB Weld or Devcon. They were made to use on metal.

joebass3

Loctite Go2 Glue was mentioned in a thread a couple of years ago. It looks very promising. Is Powergrab Ultimate still considered the gold standard when it comes to preventing magnet shift?

https://forum.polkaudio.com/discussion/184312/magnet-shift-preventing-adhesive-take-a-look

pitdogg2

joebass3 wrote: »

Loctite Go2 Glue was mentioned in a thread a couple of years ago. It looks very promising. Is Powergrab Ultimate still considered the gold standard when it comes to preventing magnet shift?

https://forum.polkaudio.com/discussion/184312/magnet-shift-preventing-adhesive-take-a-look

DO NOT USE IT!! I tried it and several months later I could peel it off.

JB weld or Powergrab

Rob2069

One of the big problems with super glue is filling gaps and a good way to mitigate that is to combine it with baking soda but unlike epoxy you don't have time to work with it you have to do it on location so to speak right where you're gluing add the glue like normally would and then the baking soda and the exothermic reaction is normal it just happens a lot faster than it would normally do without the sodium bicarbonate and it will definitely fill a gap or crack and not shrink as it cures bike super glue typically does and in addition to that it can be sanded grounded filed painted or whatever you want to do in the way of making it prettier for the ladies to appreciate

F1nut

Oki doki

VR3

Did he forget the link?