[volt-nuts] Oil and molded components

[J. Forster]

In a number of precision decade boxes I have, the resistors are wound on
Mica cards and painted with red varnish. I'm pretty well certain this is
the red Glyptal which has been around for ages (since WW II for sure). The
Glyptal company is very much in business.

A caution about painting and varnishing things: When they dry, they
shrink. I saw somebody paint the heat shield shroud of a spacecraft launch
vehicle. The paint shrank and the shroud did not separate. $54 M went into
the Pacific.

-John

===========


> Ed Palmer wrote:
>
>> snip
>> >
>> Earlier in this thread there was mention of resistors that were coated
>> with shellac or lacquer.  Would it be possible to coat a molded resistor
>> to seal it from air, moisture, or oil?  Perhaps one of the high-voltage
>> varnishes like this:
>> http://www.action-electronics.com/msds/GC10-9002%20Spec%20Sheet.pdf
>>
>> Ed
>
> Hi Ed,
>
> Let me forewarn everyone that starting research in WIKI over such subjects
> will
> get you buried into hours and hours of torture from which your brain will
> eventually emerged with a headache.  While WIKI is quite good for a
> general brush
> of knowledge, it is by no means a complete treatise of any subject.
>
> Interestingly WIKI (information) groups shellac and varnish as kissing
> cousins.
> What surprised me is shellac, made from an insect {uck} is used to coat
> candy.
> So watch out for those M&M’s !
>
> The varnish page was less disturbing.  However, both do not really answer
> the
> questions we have for our applications.  So what is needed is to approach
> or
> search companies that provide shellac/varnish materials for the electrical
> industries and see if there are any “WHITE” papers describing the details
> of such
> magic.
>
> It seems that there are many variations of shellac/varnish {all considered
> resins} with varying properties and clearly shows the need for a chemist.
> I know
> one real chemist.  I met him at a favorite little local restaurant dive
> where he
> hangs out.  However, when you ask him questions you mainly get incomplete
> phrases
> {forget sentences}, so I think he has sniffed a few to many formulas.  In
> all
> fairness, he really is a nice person.
>
> So the upshot is some research is needed to get a better grip on the
> subject.  I
> think not one formula fits all.  GC electronics has a number of “coatings”
> for
> different purposes but seemingly all similar, at least their writeups look
> that
> way.
>
> That is why I hate painting.  Just too many choices !  AND never, ever
> take a
> female with you to a paint store.  Unless Fluke, Genrad and others would
> talked
> about why they use such-and-such for their products, we are left up to our
> own
> devices.
>
> Well worth the read is the WIKI for shellac:
>
> http://en.wikipedia.org/wiki/Shellac
>
> And for varnish:
>
> http://en.wikipedia.org/wiki/Varnish
>
> For mineral oil:
>
> http://en.wikipedia.org/wiki/Mineral_oil
>
>
> Bill....WB6BNQ
>
>
>
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