[R-390] White lines on knobs and more

[Dan Merz]

Hi,  I think you are chasing the wrong animal trying to get oxide off of aluminum.  Maybe it would be better to say that you would like an even oxide on the knob.  Aluminum has a tremendous affinity for oxygen and will immediately form an oxide skin in air.  So use whatever method to get a clean, smooth surface, e.g. bead blasting, NaOH etch, mechanical sanding, scotch-Brite, etc., and don’t be stuck on the idea that you are going to remove aluminum oxide, which will form right away.  I’m not familiar with all the possible ways aluminum surfaces can be treated, some of which likely produce more complex coatings, and I believe Bonderite  must work pretty well when applied in the manner described as a base for subsequent painting.  I believe it produces a chromate surface coating which aids paint adhesion.  Dan

Sent from my iPad Air2

> On Sep 11, 2019, at 5:55 PM, Larry H <larry41gm at gmail.com> wrote:
> 
> Thank you, John, for the nice explanation.  Your R-390 panels look very
> nice.
> 
> Question - would sanding the knobs remove the oxide well enough?  Is there
> an easy way to tell if the oxide has been removed?
> 
> Regards, Larry
> 
>> On Wed, Sep 11, 2019 at 1:53 PM John Gedde <jgedde at optonline.net> wrote:
>> 
>> The whole idea is to get the surface coating of aluminum oxide off.  For
>> the knobs, I bead blasted them.  For panels and what not, scotch brite
>> followed by a quick dip in diluted metal “prep and etch” available from
>> Home Depot.
>> 
>> 
>> 
>> The coating I speak of is what Collins et al used for a surface treatment
>> on unpainted aluminim like chassis panels, the Utah plate, etc.  So,
>> getting up to speed with Bonderite gives you not only the ability to prime
>> for painting but to restore coated parts in the radio as well.  I have done
>> several unpainted panels and covers on my radios using this method.  I used
>> scotch brite brushed in one direction carefully to clean off the old
>> conversion coating the OEM put on and also to duplicate the brushed finish
>> they had originally.
>> 
>> 
>> 
>> I’ve attached a pic of my R390 inside.  All the covers shown have been
>> restored using this method…
>> 
>> 
>> 
>> John
>> 
>> 
>> 
>> *From:* Larry H <larry41gm at gmail.com>
>> *Sent:* Saturday, September 7, 2019 5:47 PM
>> *To:* John Gedde <jgedde at optonline.net>
>> *Cc:* R-390 Forum <r-390 at mailman.qth.net>
>> *Subject:* Re: [R-390] White lines on knobs and more
>> 
>> 
>> 
>> Thanks John,  Good to know about your new method.  I was wondering, how do
>> you clean and deoxidize the aluminum in prep for the dip?
>> 
>> 
>> 
>> Regards, Larry
>> 
>> 
>> 
>> On Sat, Sep 7, 2019 at 9:52 AM John Gedde <jgedde at optonline.net> wrote:
>> 
>> Hi Larry,
>> 
>> It looks great!  I have moved away from using a spray primer on aluminum
>> prior to paint in favor of a chromate conversion coating.  Loctite
>> Bonderite is what I use.  It's what we use at work for spaceborne
>> mechanisms that get painted or aluminum surfaces that remain bare
>> (non-anodized).  I've never had any issues with adhesion using this stuff.
>> Basically you clean and deoxidize the aluminum, dip it in Bonderite for a
>> minute or so, rinse and let dry.  The aluminum turns a golden color and
>> paint readily adheres to it if you spray within 24 hours.  The coating is
>> also known by other names: ChemFilm, Alodyne, Iridite, etc.
>> 
>> John
>> 
>> 
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