[SEL] Cracked Head/Epoxy information

[Jim Hardman]

Jerry, specify a "high peel strength" epoxy for brass.  It doesn't cure as 
hard as most epoxies, you can dent the stuff with your fingernail.  But it 
sticks like grim death.

The secret with brass is surface preparation (as rough as possible and as 
clean as possible) and thick sections of brass to prevent "stretching" off 
the bond when stressed.

Epoxies bond well due to their ability to wet the surface;  these chemicals 
have the ability to gain really close molecular contact.  But mechanical 
roughness (rough grinding) truly helps mechanical purchase.

With all epoxies, wash up well with plenty of soap and hot water after use. 
There are no "safety cures" that really avoid possible skin rash.  Everyone 
has a natural threshold resistance to dermatitis (a rash like poison ivy), 
but once the threshold is reached, the user becomes sensitized and has to 
avoid epoxies in the future.  It's like rolling in poison ivy as a kid.  The 
first or second time you got away with it, but after that, just get near the 
ivy patch and you had the rash.  Just be clean... most of our shop mates 
formulated epoxies for years with no ill effects.

Jim in Vermont

----- Original Message ----- 
From: "Jerry Evans" <jerrye at databak.co.za>
To: <sel at lists.stationary-engine.com>
Sent: Saturday, January 24, 2009 1:48 PM
Subject: Re: [SEL] Cracked Head/Epoxy information


> At 07:00 PM 24/01/2009, you wrote:
>>From: "Jim Hardman" <Jim at hardmanfamily.net>
>>Subject: Re: [SEL] Cracked Head
>>
>>Hi all...
>>
>>I spent my working life in the epoxy business and agree that the 5-minute
>>formulations are not the best for water resistance.  The slower setting
>>varieties will perform a lot better, especially when driven to a more
>>complete cure under heat.  Yes, warming the head at the time of 
>>application
>>will thin the mix and promote pentration.
>>
>>I used a 5-minute epoxy to make a repair inside a boat house and a year
>>later it had reverted to a cheezy mass, about like chewing gum except 
>>easily
>>flaked.  Slower varieties will do a lot better inside shower stalls, boat
>>houses or engine water jackets.
>>
>>My father-in-law repaired his broken boat throttle with our 5-minute epoxy
>>and it scared the lights out of me when he'd come charging in to the dock 
>>at
>>a full plane and then haul back on the throttle at the last second.  The
>>good Lord was watching over him. Repairing a broken throttle arm with a
>>butt-joint repair with 5-minute stuff ain't smart.
>>
>>If I can offer a suggestion to anyone using epoxies, mix them twice as 
>>long
>>as you think you have to.  The extra mixing time allows greater 
>>association
>>between the resin and the curing agent and results in a much stronger 
>>cure.
>>And avoid adding solvents to either thin the mix or extend potlife.
>>Reaction rate doubles with an increase of about 18 degrees fahrenheit (10
>>degs. C.) which also benefits the final cure.
>>
>>Maximum temperature allowed varies with the recipe, but anything over the
>>boiling point of water should be suspect.  Use silicones to repair 
>>anything
>>exposed to higher temperatures.  JB Weld should do fine for a crack in an
>>engine head as long as there's enough cast iron to take the stresses of
>>compression and ignition.
>>
>>As for surface prep, grind down into fresh metal and wash down the 
>>surfaces
>>with  a fast solvent like toluene to get rid of any oil residue.  Avoid
>>mineral spirits (paint thinner), it takes too long to evaporate.  Wipe up
>>the solvent with a clean rag, that's the only way to reduce oil film.
>>Evaporation just leaves the oil behind.
>>But I'll bet you already know all this.
>>Jim in frozen Vermont
>
> Jim,
>         Thanks for the post - very interesting and a few things to 
> remember.
>
>         Now, is there an epoxy that will successfully bond to "brass to
> brass" ? I mean really bond it - not just stick it together.
>
>
> Keep the revs up (or down)
> Jerry Evans
> Near Johannesburg in Sunny South Africa.