Steel/epoxy adhesion

Obviously oxidisation occurs when the steel comes into contact with oxygen, so storing the mandrels in some kind of helium chamber would prevent it (Helium being an inert gas). Failing this there are a number of things which accelerate oxidisation, namely

Heat

Water

Salt

Storing the mandrels in a cool, dry, ventilated (maybe dehumidified) area will substantially reduce any oxidisation.

Al

"Pardons"... but, simply in the context of "Let us NOT lead others astray"...

In corrosion terminology, "oxidation" is the giving-up of an electron. "Reduction" is the picking-up or gaining of an electron (thus "REDOX" reactions, reduction and oxidation are involved in corrosion of metals).

Except for the fact that oxygen is frequently involved in corrosion reactions (at the CATHODE, as the reduction of oxygen is one of the more common cathodic reactions) corrosion does NOT "Depend-Upon" the presence of O₂. Corrosion can, and does happen quite often in total absence of oxygen. Just because both words begin with 'ox" means nothing. "Oxidation", in corrosion techno-speak (and with the exception of the above statement) has nothing to do with "oxygen".

That having been said, for clarification ~~~ "True" to each of the posts here ascribing to the concept that 'atmospheric corrosion' of the mandrel(s) will be eliminated by storing in some manner which excludes both humidity and O₂ from the component. Lots of ways to achieve that end.

Electroplating or cathodic protection over night? Acid wash? If it's a short time maybe paint the mandrel with unactivated resin. When you subsequently apply activated resin I bet the curing reaction will spread right through? I suppose this might require excluding oxygen while it's waiting.

For this reason, I wet sand pieces like this using mixed epoxy as the "water". Personally, I would not use unmixed resin, because the cure is not certain to spread , and you could significantly change the properties of the epoxy due to the hardener-lean area. (A hardener is not simply a catalyst, and small differences in ratio affect properties in significant ways.)

I bow to those with proper knowledge/experience.

What about standing the sandblasted parts in a bucket of alcohol or a volatile liquid, like carbon tet? Something that will keep air and water away, but will evaporate quickly when the part is removed.

Of course, I'm suggesting you do this in a responsible manner.

Come on Vermin you realy do not want to use that nasty old carbon tet, definatly on the dangerous chemicals list.

I reckon the best procedure is to coat the items with unactivated resin then when ready to use them give them a stiff brushing of activated resin from my experience with epoxies this will give a 100% cure so long as there are no deep pockets on the mandrels.

There was a time when we basically swam in carbon tet, tri chloral ethane, and MEK. And we like it! We loved it!

...Actually we worried our asses off, but that was what the company wanted.

You ask about protecting the surface so I will answer that first:

Vapor phase inhibitor:

http://www.cortecvci.com/Publications/Papers/VCIProducts/CTP-10.pdf

Vapor Corrosion Inhibitor:

http://www.vapor-tek.co.uk/html/vaporol.htm

Zerust:

http://www.zerust.com/

I have a couple of these capsules in my lockers and travel cases holding my shootin' irons.

They work best in enclosed packaging. Some of these sites sell a paper that is treated with these inhibitors. Wrap your parts and they should be fine when you unwrap them. Perhaps you could just wrap the parts with an ordinary capsule of dessicant like silica gel ( http://www.gracedavison.com/products/adsrbnts/descpkg/overview.htm ) if you are worried about the VPI/VCI interfering with your epoxy.

Real Question unasked but implied in yours: why are you batch processing mandrels 48 hours early? 48 hours of waiting is a lot of waste. Failure to use Just in time will cost you whatever the cost of the materials, labor and additional processing steps of this remediation is...

milo

Spray or dip in WD-40 or the like and then just before epoxying wipe them with acetone.

...or Methylated Spirits.

What the heck are Methylated Spirits?! Are we talking menthol cigarettes here?!

Vermin

FYI

http://en.wikipedia.org/wiki/Methylated_spirit

Al

Perfect explanation, many thanks for the link.

Methyl Alcohol for the non UK speakers, sorry......forgot myself!!

It turns you blind if you drink it!!!

Now where is my white stick and the Blind Dog?

Several good, logical replies here...(e.g, Milo). Options certainly exist, but of course the values of one over another hinge on a couple critical parameters not yet mentioned. The question, in "NACE" terminology is: "How do you hold the blast?"

What SIZE (LxD) mandrel are we discussing...? 3 inches... 3 feet...? (And, solid or hollow?) Just one ... or, is it an occasionally repeated effort? (Worthy of constructing a dehumidified storage box?)

Two other questions come to mind: 1) If the bond is 'oh-so-critical', have you collaborated with (inquired-of) the epoxy mfr to determine the optimal surface (blast) profile in mils? And, are you using the optimal blast media? ... Pre-cleaning the surface BEFORE blasting, so as not to drive any existing contaminants INTO the profile...? Testing the surface for presence of (invisible) contaminants / FE++ ions prior to the winding... etc, etc? and:

2) Curiosity compels the question; what is function of the mandrel? Is the filament winding truly necessary / justified...? Is there any possibility that there exists a more appropriate "finish" ... which might render your current conundrum meaningless?

Regardless... Best of luck with the endeavor.