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Epoxy to Aluminum

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Dennis Johnson

Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.

Posted: Sun Apr 27, 2008 9:11 am Post subject: Epoxy to Aluminum

Greetings,

  

 As part of building a composite airplane, I studied everything I could find  about epoxies, materials, and adhesive bonding in general.  I  concluded that I did not have the ability to make an epoxy bond to aluminum that  I could be confident that it wouldn't fail.  

  

 The problem is that aluminum begins oxidizing immediately after  cleaning.  No matter how quick you are, unless you use  extraordinary measures, there will be aluminum oxide on the surface you are  bonding.  Aluminum oxide has relatively low strength.  The epoxy bonds  well to the aluminum oxide, but the aluminum oxide isn't stuck very well to  the underlying aluminum.  After some number of hot/cold and wet/dry  cycles, the bond may weaken enough to fail.

  

 Obviously, Boeing and others solved this problem long ago.  However,  based on the great reference book, "Composite Basics," by Andrew  Marshall, their methods aren't practical for most of us homebuilders.   >From chapter 11, Marshall says, "Unfortunately, both the FPL etch and the  PAA treatments (the ones widely and successfully used in the industry) involve  extensive chemical control and a large investment in equipment."

  

 As an interesting aside, he describes an industry standard "wedge"  test where two .125" thick aluminum pieces are bonded together.   After curing, a wedge is driven into the end of the assembly, between the two  pieces of aluminum, which forces the bond to break at that  point.  A mark is placed at the point where the fracture stops.  The  test piece is then placed into a warm, wet chamber for one hour.  The  assembly is then removed and the additional distance the crack propagated  during the warm/wet test is measured.  If the crack grew less than  three-fourths of an inch, the bond is considered to be good for life.   Marshall says that if the aluminum was cleaned but not chemically treated, the  assembly will likely totally delaminate during the one hour test!  

  

 Since I didn't have the ability to duplicate Boeing's chemical treatment  process, I didn't make any bond to aluminum that would cause anything more than  inconvenience if it failed.  Heat and humidity seem to be the culprits,  which might explain why some people report long lasting bonds and others have  failures.  

  

 Best,

 Dennis  

    [quote][b]

ceengland(at)bellsouth.ne
Guest

Posted: Sun Apr 27, 2008 10:07 am Post subject: Epoxy to Aluminum

Dennis Johnson wrote:

 	  Quote: 	
		   Greetings,

  

 As part of building a composite airplane, I studied everything I could 

 find about epoxies, materials, and adhesive bonding in general.  I 

 concluded that I did not have the ability to make an epoxy bond to 

 aluminum that I could be confident that it wouldn't fail. 

  

 The problem is that aluminum begins oxidizing immediately after 

 cleaning.  No matter how quick you are, unless you use 

 extraordinary measures, there will be aluminum oxide on the surface 

 you are bonding.  Aluminum oxide has relatively low strength.  The 

 epoxy bonds well to the aluminum oxide, but the aluminum oxide isn't 

 stuck very well to the underlying aluminum.  After some number of 

 hot/cold and wet/dry cycles, the bond may weaken enough to fail.

  

 Obviously, Boeing and others solved this problem long ago.  However, 

 based on the great reference book, "/Composite Basics/," by Andrew 

 Marshall, their methods aren't practical for most of us homebuilders.  

 From chapter 11, Marshall says, "Unfortunately, both the FPL etch and 

 the PAA treatments (the ones widely and successfully used in the 

 industry) involve extensive chemical control and a large investment in 

 equipment."

  

 As an interesting aside, he describes an industry standard "wedge" 

 test where two .125" thick aluminum pieces are bonded together.  After 

 curing, a wedge is driven into the end of the assembly, between the 

 two pieces of aluminum, which forces the bond to break at that point.  

 A mark is placed at the point where the fracture stops.  The test 

 piece is then placed into a warm, wet chamber for one hour.  The 

 assembly is then removed and the additional distance the crack 

 propagated during the warm/wet test is measured.  If the crack grew 

 less than three-fourths of an inch, the bond is considered to be good 

 for life.  Marshall says that if the aluminum was cleaned but not 

 chemically treated, the assembly will likely totally delaminate during 

 the one hour test! 

  

 Since I didn't have the ability to duplicate Boeing's chemical 

 treatment process, I didn't make any bond to aluminum that would cause 

 anything more than inconvenience if it failed.  Heat and humidity seem 

 to be the culprits, which might explain why some people report long 

 lasting bonds and others have failures. 

  

 Best,

 Dennis

When was the book written? There are some pretty impressive bonding 
	


agents available now (not all are 'epoxy').



Even if you limit the discussion to epoxies, consider JB Weld. There are 

*lots* of aluminum things flying around on homebuilts that were repaired 

(or assembled) using JB Weld, including engine components.



The BD-4's original assembly method for the wing was to bond the 

fiberglass wing ribs to the aluminum tube spar. Just about every one of 

them leaked fuel through the poor quality 'glass rib/skin assemblies, 

but I've never heard of  a debonding event at the rib/spar joints. Note 

that this joint was glued with what amounts to fuel sealant (commonly 

called 'pro-seal'), not a true epoxy adhesive. It wasn't even designed 

to be a structural adhesive.



FWIW,



Charlie

raymondj(at)frontiernet.n
Guest

Posted: Sun Apr 27, 2008 12:02 pm Post subject: Epoxy to Aluminum

Greetings,



The following is intended for hardware mounting on boats.



    After proper dry preparation per the manual, West System epoxy technical 

manual ( catalogue number 002-950, 1994) on page 9, item 5, in bonding 

hardware ( continued from page  says: "Coat the bottom contact surface of 

the hardware with unthickened epoxy.Wire brush or sand the wet epoxy into 

the surface with 50 grit sandpaper. Sanding the base with, coated with 

epoxy, will expose the epoxy directly to fresh metal with no chance for the 

metal to oxidize."



Raymond Julian

Kettle River, MN



"Hope for the best,

but prepare for the worst."



---

bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Mon Apr 28, 2008 3:28 am Post subject: Epoxy to Aluminum

4/28/2008



Hello Dennis, Thanks for your interesting input.



One technique that may be used, if appropriate to the situation, to improve 

joint holding, is to make holes in the aluminum. This permits the epoxy to 

ooze through and form sort of a rivet effect for the glue line.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



-----------------------------------------------------------



Time: 10:11:16 AM PST US

From: "Dennis Johnson" <pinetownd(at)volcano.net>

Subject: Epoxy to Aluminum



Greetings,



As part of building a composite airplane, I studied everything I could

find about epoxies, materials, and adhesive bonding in general.  I

concluded that I did not have the ability to make an epoxy bond to

aluminum that I could be confident that it wouldn't fail.



The problem is that aluminum begins oxidizing immediately after

cleaning.  No matter how quick you are, unless you use extraordinary

measures, there will be aluminum oxide on the surface you are bonding.

Aluminum oxide has relatively low strength.  The epoxy bonds well to the

aluminum oxide, but the aluminum oxide isn't stuck very well to the

underlying aluminum.  After some number of hot/cold and wet/dry cycles,

the bond may weaken enough to fail.



Obviously, Boeing and others solved this problem long ago.  However,

based on the great reference book, "Composite Basics," by Andrew

Marshall, their methods aren't practical for most of us homebuilders.

 	  Quote: 	
		  From chapter 11, Marshall says, "Unfortunately, both the FPL etch and

the PAA treatments (the ones widely and successfully used in the
	


industry) involve extensive chemical control and a large investment in

equipment."



As an interesting aside, he describes an industry standard "wedge" test

where two .125" thick aluminum pieces are bonded together.  After

curing, a wedge is driven into the end of the assembly, between the two

pieces of aluminum, which forces the bond to break at that point.  A

mark is placed at the point where the fracture stops.  The test piece is

then placed into a warm, wet chamber for one hour.  The assembly is then

removed and the additional distance the crack propagated during the

warm/wet test is measured.  If the crack grew less than three-fourths of

an inch, the bond is considered to be good for life.  Marshall says that

if the aluminum was cleaned but not chemically treated, the assembly

will likely totally delaminate during the one hour test!



Since I didn't have the ability to duplicate Boeing's chemical treatment

process, I didn't make any bond to aluminum that would cause anything

more than inconvenience if it failed.  Heat and humidity seem to be the

culprits, which might explain why some people report long lasting bonds

and others have failures.



Best,

Dennis

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Apr 28, 2008 7:32 am Post subject: Re: Epoxy to Aluminum

 	  Quote: 	
		  Greetings, 



After proper dry preparation per the manual, West System epoxy technical manual (catalogue number 002-950, 1994) on page 9, item 5, in bonding hardware ( continued from page  says: "Coat the bottom contact surface of the hardware with unthickened epoxy. Wire brush or sand the wet epoxy into the surface with 50 grit sandpaper. Sanding the base with, coated with epoxy, will expose the epoxy directly to fresh metal with no chance for the metal to oxidize." 

Raymond Julian 

Kettle River, MN 	




The West System method seems brilliant to me. It seems to use the approach often used in soldering aluminum where a stainless-wire brush removes the oxide while being protected from re-oxidation by the solder (and flux). Nice.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

Speedy11(at)aol.com
Guest

Posted: Mon Apr 28, 2008 6:50 pm Post subject: Epoxy to Aluminum

Dennis,

 Very interesting information.  Thanks for sharing it.

 I had never thought about it, but your explanation makes sense.  It  also may explain why I had such poor results with the Click-Bond nutplate  adhesion.  Perhaps the Click-Bond products are most ideal for composite  airplanes and regular nutplates are better for aluminum airplanes.

 Thanks again,

 Stan Sutterfield

 Do not archive

  

  	  Quote: 	
		  Greetings,



As part of building a composite airplane, I studied    everything I could 

find about epoxies, materials, and adhesive bonding in    general.  I 

concluded that I did not have the ability to make an    epoxy bond to 

aluminum that I could be confident that it wouldn't    fail.  



The problem is that aluminum begins oxidizing immediately    after 

cleaning.  No matter how quick you are, unless you use    extraordinary 

measures, there will be aluminum oxide on the surface you    are bonding.  

Aluminum oxide has relatively low strength.  The    epoxy bonds well to the 

aluminum oxide, but the aluminum oxide isn't stuck    very well to the 

underlying aluminum.  After some number of hot/cold    and wet/dry cycles, 

the bond may weaken enough to fail.



Obviously,    Boeing and others solved this problem long ago.  However, 

based on    the great reference book, "Composite Basics," by Andrew 

Marshall, their    methods aren't practical for most of us homebuilders.  

 	  Quote: 	
		  From    chapter 11, Marshall says, "Unfortunately, both the FPL etch and 

the PAA    treatments (the ones widely and successfully used in the 
	


industry) involve    extensive chemical control and a large investment in 

equipment."



As    an interesting aside, he describes an industry standard "wedge" test 

where    two .125" thick aluminum pieces are bonded together.  After 

curing, a    wedge is driven into the end of the assembly, between the two 

pieces of    aluminum, which forces the bond to break at that point.  A 

mark is    placed at the point where the fracture stops.  The test piece is 

then    placed into a warm, wet chamber for one hour.  The assembly is then    

removed and the additional distance the crack propagated during the    

warm/wet test is measured.  If the crack grew less than three-fourths    of 

an inch, the bond is considered to be good for life.  Marshall    says that 

if the aluminum was cleaned but not chemically treated, the    assembly 

will likely totally delaminate during the one hour test!     



Since I didn't have the ability to duplicate Boeing's chemical    treatment 

process, I didn't make any bond to aluminum that would cause    anything 

more than inconvenience if it failed.  Heat and humidity    seem to be the 

culprits, which might explain why some people report long    lasting bonds 

and others have failures.     



Best,

Dennis 	


 

  



Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos.

  [quote][b]

rshannon

Joined: 05 Sep 2007
Posts: 62

Posted: Tue Apr 29, 2008 11:56 am Post subject: Epoxy to Aluminum

 	  Quote: 	
		       ...  Perhaps the Click-Bond products are most ideal for composite  airplanes and regular nutplates are better for aluminum airplanes.

	
 

FWIW, all my 200+ Click Bond fasteners are on aluminum. Surface prep is essential, but easy. Just a scuff with the provided Scotch Brite pad, a swipe with the provided solvent/cleaner, thoroughly mix the two part epoxy from the pre-measured packet... and on they go. Wait 24 hrs. to cure and bolts torque down fine.

 

Ron



  [quote][b]

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Apr 30, 2008 5:42 am Post subject: Re: Epoxy to Aluminum

After following this thread it occurred to me that I had to learn ONE very important thing when using epoxy particularly--there must be epoxy in the bonded interface...Duh....It is easy to prepare the surfaces, put epoxy on one or both parts and press or clamp the parts together squeezing out virtually ALL the epoxy. Thus no bonded joint, or the bond has inadequate flexibility and fails.



Pay attention to the minimum bond-line specification, or failing that, if the joint is between two very flat surfaces, assure that a few thousandths bond-line remains.



"A witty saying proves nothing." 

    --Voltaire

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

JohnInReno

Joined: 08 Sep 2007
Posts: 150

Posted: Sun May 04, 2008 6:19 am Post subject: Epoxy to Aluminum

Has anyone tried re-using the click-bond "worms" with standard K1000 

plate nuts? It seems to me that the rivet holes would aid in bonding and 

the rubber "worm" provides alignment, compression, and protects the 

threads from the adhesive.



john



bakerocb(at)cox.net wrote:

 	  Quote: 	
		   



 4/28/2008



 Hello Dennis, Thanks for your interesting input.



 One technique that may be used, if appropriate to the situation, to 

 improve joint holding, is to make holes in the aluminum. This permits 

 the epoxy to ooze through and form sort of a rivet effect for the glue 

 line.



 'OC' Says: "The best investment we can make is the effort to gather 

 and understand knowledge."



 -----------------------------------------------------------



 Time: 10:11:16 AM PST US

 From: "Dennis Johnson" <pinetownd(at)volcano.net>

 Subject: Epoxy to Aluminum



 Greetings,



 As part of building a composite airplane, I studied everything I could

 find about epoxies, materials, and adhesive bonding in general.  I

 concluded that I did not have the ability to make an epoxy bond to

 aluminum that I could be confident that it wouldn't fail.



 The problem is that aluminum begins oxidizing immediately after

 cleaning.  No matter how quick you are, unless you use extraordinary

 measures, there will be aluminum oxide on the surface you are bonding.

 Aluminum oxide has relatively low strength.  The epoxy bonds well to the

 aluminum oxide, but the aluminum oxide isn't stuck very well to the

 underlying aluminum.  After some number of hot/cold and wet/dry cycles,

 the bond may weaken enough to fail.



 Obviously, Boeing and others solved this problem long ago.  However,

 based on the great reference book, "Composite Basics," by Andrew

 Marshall, their methods aren't practical for most of us homebuilders.

> From chapter 11, Marshall says, "Unfortunately, both the FPL etch and

 the PAA treatments (the ones widely and successfully used in the

 industry) involve extensive chemical control and a large investment in

 equipment."



 As an interesting aside, he describes an industry standard "wedge" test

 where two .125" thick aluminum pieces are bonded together.  After

 curing, a wedge is driven into the end of the assembly, between the two

 pieces of aluminum, which forces the bond to break at that point.  A

 mark is placed at the point where the fracture stops.  The test piece is

 then placed into a warm, wet chamber for one hour.  The assembly is then

 removed and the additional distance the crack propagated during the

 warm/wet test is measured.  If the crack grew less than three-fourths of

 an inch, the bond is considered to be good for life.  Marshall says that

 if the aluminum was cleaned but not chemically treated, the assembly

 will likely totally delaminate during the one hour test!



 Since I didn't have the ability to duplicate Boeing's chemical treatment

 process, I didn't make any bond to aluminum that would cause anything

 more than inconvenience if it failed.  Heat and humidity seem to be the

 culprits, which might explain why some people report long lasting bonds

 and others have failures.



 Best,

 Dennis

_________________
John Morgensen
RV-9A - Born on July 3, 2013
RV4 - for sale

Frank Davis

Joined: 05 Dec 2007
Posts: 3
Location: Minden, NV

Posted: Mon May 05, 2008 7:55 am Post subject: Epoxy to Aluminum

Yes, I have re-used the "worms" with K1000 nutplates and J-B Weld.  

Worked well.  However if the plate is in a critical non-accesable 

location, I spring for the more expensive Click-Bond adhesive (paranoia).



As an aside, Click-Bond is located at the Carson City Airport, NV,  

where my EAA Chapter is.  We have toured the factory several time.  One 

of the things discussed was the strength of the adhesive bond.  They 

said that while it doesn't have great peel strength, it has good shear 

strength, which is required to counteract the torque of inserting the 

fastener. 



Frank

*Time: * 	*/07:20:00 AM PST US/*



*From: * 	*/John Morgensen <john(at)morgensen.com 

<mailto:john(at)morgensen.com>>/*



*Subject: * 	/*_Re: Epoxy to Aluminum_*/



* Has anyone tried re-using the click-bond "worms" with standard K1000 

plate nuts? It seems to me that the rivet holes would aid in bonding and 

the rubber "worm" provides alignment, compression, and protects the 

threads from the adhesive. john*

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