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 Post subject: How does Loctite work?
PostPosted: Tue Mar 02, 2010 6:16 pm 
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Joined: Tue May 17, 2005 11:59 pm
Posts: 129
Location: Las Vegas NV
This is a dumb question. I've used Loctite successfully for years. Mainly #680 for little Gauge 1 live steam applications. I have no idea how it works.

Thanks

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 Post subject:
PostPosted: Tue Mar 02, 2010 6:24 pm 
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Joined: Sat Jan 04, 2003 10:45 am
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Location: Albuquerque NM
It's "anaerobic" (if I spelled that right) it sets up in the absence of air.
It also has some requirement for iron unless an activator is used.
I use to know a lot more about the chemistry but it's been about 15 years
and if you don't use it you loose it. :-)
...lew...


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 Post subject:
PostPosted: Tue Mar 02, 2010 8:40 pm 
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Joined: Sun Nov 18, 2007 12:46 am
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Location: peekskill, ny
At least some of the locktite grades, like the 600 series ones, have
a PMMA chemistry base. Poly Methyl Methacrylate. Basically
un-polymerized plexiglas.

Jim


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 Post subject:
PostPosted: Tue Mar 02, 2010 9:50 pm 
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Location: Vallejo California
Glorified crazy glue?

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Retired journeyman machinist and 3D CAD mechanical designer - hobbyist - grandpa


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 Post subject:
PostPosted: Wed Mar 03, 2010 1:28 pm 
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Joined: Tue May 17, 2005 11:59 pm
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Location: Las Vegas NV
Jose Rivera wrote:
Glorified crazy glue?


Thanks for the answers. I am not a chemist, but understand the general idea.

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Bob Sorenson, Las Vegas, Nevada


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 Post subject: how it works
PostPosted: Wed Mar 03, 2010 5:37 pm 
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Location: Somewhere in the World
It is more than glorified crazy glue. "crazy glue" or its immediate ancestor was created by the Eastman to glue soldiers back together during the Vietnam era - to get them back to a proper hospital. (stuff sticks to skin like nobody's business).

I think that the answer being sought is:

the stuff expands when confined in an area with no air

It doesn't like temperatures greater than 300F (falls apart)
Likes nice CLEAN surfaces to work with - so forget porous castings that have been exposed to dirt / oils unless you have a way of really getting them clean (vapour degreaser is my favorite)
USUALLY likes a 'gap' to fill (how I have always used it), but technically it can be use with press fits to fill 'roughness voids'

There are variants that are intended to be 'taken apart' (thread locker) and others that are NOT intended to be removed without pressing / heating. Be sure you get the correct type for your application.


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 Post subject:
PostPosted: Wed Mar 03, 2010 8:14 pm 
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Joined: Sun Nov 18, 2007 12:46 am
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Location: peekskill, ny
I think it polymerizes, rather than expanding. But the effect
is the same - torch to remove!

Jim


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 Post subject:
PostPosted: Wed Mar 03, 2010 9:40 pm 
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Joined: Mon Jun 18, 2007 10:33 am
Posts: 504
Location: Taylorsville Ky USA
There are many grades and brands of "locktite". Some types will hold temps up to 600 deg F and have high pressure/strength. Do a google and you will find out all you ever wanted or didn't want to know about it. They may even have higher temp types now.

The stuff I use for loose bearings and cylinder liners is good to 600 deg F.

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 Post subject:
PostPosted: Thu Mar 04, 2010 12:27 am 
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Joined: Fri Jul 07, 2006 10:29 pm
Posts: 624
Location: Lebanon MO
The different grades work differently in some respects. Yes, the stuff is anerobic, however you might wonder why it does not harden in the bottles. According to some of what I have read, the bottle material is special in that it "breathes to prevent hardening. When trapped in the threads between a screw and a nut, the reduced access to air brings about the "hardening"

A point about the mechanical functioning of the thread locker is that it fills the space in the threads. As you may know when you want something to slide, it is harder to get it started than to keep it moving. When a threaded fastener is loaded sideways, the nut or head can slip on the surface it contacts and the threads can slip sideways as well because of the slight clearance between the the male and female threads. Once the surface is slipping it is not all that particular about which way it goes (same reason a car sliding on ice goes all over the place). If the thread is slipping, the easiest direction to go is "downhill" which in this case happens to be tangential motion in the threads, or "unscrewing". If the initial lateral slip is stopped then the "downhill" sliding between the theads (unscrewing) does not get a chance to loosen the bolt.

When reviewing the performance specifications, an interesting point to note is that "red" 271 and some of the other High strength versions show a peculiar characteristic. The breakaway torque for the removal strength "blue" 242 loctite is higher than the "prevailing" torque to keep it moving once it breaks away (as you would expect). BUT for some of the high strength loctites the prevailing torque is higher. That is to say soon after it breaks loose and starts moving, it jams up tighter than ever. Apparantly the crumbs roll up in little lumps that jam up the threads even more.

And when you are stocking up on various grades, don't overlook what I like to refer to as "Afterthough Loctite" (#290). It is a penetrating grade that can soak into the assembled threads and lock them. I even tighened up an "ejector pin" on a mechanism that was held by a rivet that had come loose It soaked in and locked up the play in the rivet so that the pin would flip the parts out as they were pulled from the recess I has functioned for years and has not come loose yet. (the rivet was rather inaccessable and would have required some fancy tooling to tighten up by the usual method)
.

There is more information to be had at:
http://www.loctite.com
And some interesting history of the stuff at:
http://en.wikipedia.org/wiki/Loctite


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 Post subject:
PostPosted: Thu Mar 04, 2010 4:30 pm 
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Location: Miami
Learned some fun stuff about Loctite last week.

To break it free, try acetone. If that doesn't work, try heat. Depending on which grade of Loctite you're working on, a hair dryer may do it, or you may need something hotter.

Heating Loctited fasteners in aluminum can ruin the aluminum, even if the temperature isn't very high.

To heat a fastener without heating the material around it much, touch the tip of a soldering iron to the fastener.

If you don't have acetone, loosen Loctite by applying fresh Loctite and waiting ten minutes.

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 Post subject: Regauarding tempature
PostPosted: Thu Mar 04, 2010 10:14 pm 
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Joined: Tue Mar 21, 2006 2:44 pm
Posts: 1227
Location: East Hartford, CT
There are some grades that will take higher temperatures. Go to the Loctite web site and give all the data.

The high temp stuff is nearly impossible to get apart unless its heated up to a softening temperature though. I have used it at 375 degrees F with no problems in an industrial application.

Rob


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 Post subject: Reguarding Loctite
PostPosted: Thu Mar 04, 2010 10:19 pm 
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Joined: Tue Mar 21, 2006 2:44 pm
Posts: 1227
Location: East Hartford, CT
Another tidd bit is never use around Plexiglas (acrylic) or Lexan (Polycarbonate). It will make it stress crack or craze overnight.

Rob


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