Epoxy Bonding to Aluminum and Magnesium

Why no washers? The little bit of radius at the root of the shank of
the bolt needs somewhere to go, yes? And may I assume you're putting
these bolts in a reamed hole?

You'll find the bolt will bury itself into the aluminum or magnesium and
that little radius will tend to
squeeze the metal onto the shaft. Try it on a sample and have a look, the
bolt will be hard to get back out of the hole also.
A radius on the nut can do the same.

Cheers Cam

Ps. maybe not "aeronautically correct," but it works.

Vernon Klukas wrote:
5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need something
to separate the two or the magnesium is going to get gobbled up !!

Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
cars, with WATER running through their engines, have cast iron blocks
and aluminum heads. In this situation, there is no ready source of
electrolyte. I don't see this as a huge concern. I'm more bothered
by oil leaks.


Auto engines have head gaskets between the electro different metals,
plus if you don't run an inhibitor is a mutli-metal water cooled engine
you will corrode the aluminum away, period.

Yours
Vern

Rotary engines don't. Some people are running straight H20. Never
heard of that particular problem...period.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

(Ryan Young) wrote in message . com...
I'm working on a Hummel Aviation Ultracruiser Plus. The way the
engine mounts is quite different from the mounts on most VW powered
homebuilts.

Snipped to save bandwidth

To see what this installation looks like:

FOR A 1/2 VW -- I've figured out since then that the full meal deal
needs 4 bolts, longer angles, and a new bolt pattern

http://flyhummel.com/forums/album_pic.php?pic_id=170

I've posted a page of drawings, photos, and my usual snide remarks:
http://users.lmi.net/~ryoung/Sonerai/UCPlusEngMnts.html

Thanks for all who have contributed to this discussion!

I have never seen an epoxy that will work to 500 deg F ... the limit from
what I have seen is approx 450 deg F and even that is pushing it. However
whilst some epoxies are claimed to be able to have Tg's of 350-450 F it is
not quite that simple. I know because I am working with these adhesives on a
current project ... in fact I have just had a series of Tg tests run non 4
different epoxies and the results were surprising. The issue is that you can
only achieve the high Tg numbers quoted by a very careful and usually very
complex post cure heating cycle. A homebuilder would never achieve this.
With a simple post cure (i.e. ramp up, hold, ramp down) some of the resins
with more modest Tg values will perform a lot better ... actually the Tg
numbers you will get from these resins will surpass those for the the resins
which claim higher Tg values.


"Ryan Young" wrote in message
om...
(Ryan Young) wrote in message
. com...

These angles are bolted and epoxied to the side of the magnesium case.
My point: what good is the epoxy?

I had further conversation with Scott Casler.
================================================== ===
Hi

I use a epoxy that is similar to JB Weld.

Scott ( Hummel Engines)
----- Original Message -----
From: ryoung@
To: humeng@
Sent: Monday, September 13, 2004 3:24 PM
Subject: What Epoxy do you use?


To bond the aluminum angles to the side of the magnesium case?

Thanx for your previous reply to my inquiries.

Ryan Young
Ultracruiser Plus Builder

================================================== ==

From the JB Weld web site:

Properties (lbs/psi)
Tensile Strength: 3960
Adhesion: 1800
Flex Strength: 7320
Tensile Lap Shear: 1040
Shrinkage: 0.0%
Resistant to 500º F

I'm not sure what "Resistant" means in this context. JB Weld is a
steel-filled epoxy adhesive. Belzona is much the same stuff, and I'm
intimately familar with both of them. Devcon is another brand, and
they have both the widest variety and the best technical information:

http://www.devcon.com/techinfo/107.pdf Aluminum filled epoxy.
Temperature Resistance Wet: 120°F; Dry: 250°F
Adhesive Tensile Shear 2,600 psi
Compressive Strength 8,420 psi
Modulus of Elasticity 8.0 psi x 10(5) in.
Flexural Strength 6,760 psi
Coefficient of Thermal Expansion 29 [(in.)/(in). x °F)] x 10(-6)

Wowee Kazowee, look how much it expands! Twice as much as aluminum or
magnesium!

http://www.devcon.com/techinfo/101.pdf Steel filled epoxy putty, more
like JB Weld
Adhesive Tensile Shear 2800 psi
Compressive Strength 8260 psi
Modulus of Elasticity 8.5 x 10(5) psi
Flexural Strength 5600 psi
Coefficient of Thermal Expansion 48 [(in)/(in) x °F)] x 10(-6)
Even more expansive, and not much stronger.

Application instructions which cut pretty close to Hummel's plans:
1. Thoroughly clean the surface with Devcon® Cleaner Blend 300 to
remove all oil, grease, and dirt. This is probably a detergent - RRY
2. Grit blast surface area with 8-40 mesh grit, or grind with a coarse
wheel or abrasive disc pad, to create increased surface area for
better adhesion
3. Clean surface again with Cleaner Blend 300 to remove all traces of
oil, grease, dust, or other foreign substances from the grit blasting.
4. Repair surface as soon as possible to eliminate any changes or
surface contaminants.

(Ryan Young) wrote That got me to thinking. Taper
pins.

http://assist.daps.dla.mil/docimages...3/28/54217.PD4

Threads on the outside. I'll have to run the reamer in from the sump
side, through the aluminum angle and control the depth pretty
carefully.

Another dabbler chimed in:

Hi Ryan,
I am not keen on using taper pins in this application. You will be relying on
the magnesium to hold the pins and I think it is a little soft for that task.
It seems like the sandwich idea with the through bolts will keep the mount from
moving around better.

CW

AS21 and AS41 have compressive yields up around 20ksi, comparable to
2024 - in the Annealed state! In the tempers we usually use for things
like wing spars, the yield is about 62K.

Plus, it looks like there is no way to get a reamer in from the case
side anyway. See the web page I built last night,
http://users.lmi.net/~ryoung/sonerai...sEngineMnt.jpg

Scratch that idea. Back to AN3 bolts in reamed holes, hold the epoxy
;-)

(Ryan Young) wrote in message om...
(Ryan Young) wrote in message . com...


I've posted a page of drawings, photos, and my usual snide remarks:
http://users.lmi.net/~ryoung/Sonerai/UCPlusEngMnts.html

Re the question on your site about removing the oil pick up:

Remove the 10mm bolt/nut, heat around the front with a propane torch
and wiggle. The tube should come out fairly easly. Older cases are
more work. Reverse the procedure to install. If your lucky all will
be well. A bit of "bearing n stud mount" helps seal. If your really
picky check to see that it holds a vacuum. Some stock tubes get
cracked so this may not be a bad idea anyway................

Some really old cases don't have the hold down 10mm nut. A 17mm nut
(old case nut)welded/brazed to the top of the tube (under the cam
bore) keeps the tube from rotating up and out of the oil.
==============
Leon McAtee
Still looking for Aeronca C-2/3 factory drawings

And maybe a Franklin 2A-120