Mirrored Finish/Chromed Aluminum

 I would like to have a mirrored finsish on many of the parts attatched to my
handlebars.  I have replaced the satin finished aluminum brake and clutch
levers with a mirrored finished aluminum set.  My bike is a '95 Honda Shadow
ACE1100.  Many of these parts are unavailable in a mirrored finish such as
the clutch perch and front brake master cylinder.  My question is what would
be involved in getting these parts to have a mirrored finish and what would
the results be.  I would assume I would have to get a special polishing
wheel for my bench grinder along with compounds and various grades of fine
abrasive paper.  I have a sandblaster available if this would help.  I know
that there are five commonly used aluminum alloys in use and wonder as how
the actual alloy the part is made of will affect my result.

As I possibly dumb question side note, I assume that manufacturers who
describe their offerings as "chromed aluminum" are using a misnomer as the
part actually just has a mirrored finish from a polishing process that
results in a part that has a finish similar to a chromed steel part and that
there is no acutal electroplating involved.  I know that this once could be
true for plastic parts until a chroming process was developed for plastic
(ABS?).

Thanks for your answers and comments in advance.

Tom Haughton

 

No, some manufacturers do chrome-plate aluminium, but for some reason it
doesn't adhere as well as it does to steel. Someone who knows about
metallurgy will tell you why.

I find that polishing is best for alloy, anyway.

I remember chromed plastic components from model kits in the 1960s.




--
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 The Older Gentleman schreef:


Mine were from the 1950s. Those day the 'chrome' was in
fact aluminum, vaporized onto the plastic. It was
extremely thin, very susceptible to fingerprints and easily
wiped off.

Later Revell switched to for those parts to some other
plastic (I think ABS) that was electrically conductive, so
that they could electroplate that plastic with real chrome.
I even think they used an intermediate layer of copper.

My mam used to dust my models, so that each week
parts disappeared. Not to mention my pride; a big P51 with
electrically retractable undercarriage and bombs that you
could drop.
She placed that above the stove, so one morning
I found that Mustang with two drop down wings.

I lost all my models.

Rob.

 The Older Gentleman wrote:

I remember them from Honda Runes.

 Tom Haughton schreef:

There is no such thing as 'a dumb question' Tom,
there maybe a dumb answer. Like this one.

Like The Older Gentleman, I think that polishing
is the way to go.
Sandblasting may be fine to begin with when the
part needs to be cleaned before polishing, but be
aware that sandblasting leaves a matte finish, which I
do like, but you don't.


And now from memory, dating some 40 years ago.

Alu itself is very soft, and unsuitable for
parts that can handle any stress. So what you
and I call Aluminum usually is Alu plus one
ore even more other metals.
What other metals are used depends on
a couple of things, such as the way the part
is produced.
If it is produced by drop forging, like my brake
lever seems to be, the alloy can be pretty stiff
and copper may be used in the alloy.
When the part is produced by the injection-molding
process, then in liquid form the alloy must flow
easy (like water) and thus something else
than copper  (I can't remember it's name) will be
used for the alloy.
Injection-molded parts usually have a grayish
look, and the thinner the alloy had to be in the
production process, the more grayish it looks,
and the easier it breaks too.

Every pro has it's con.

Alu and copper are on the other end of
the range of 'noble' materials. If you take
a sheet of alu, cover it with some water,
and then lay on top of that a sheet of copper,
then you have created what is known as
a battery. If there is an electrical conductive
path (the places where alu and copper
are in metallic contact!) then a current will flow,
and the alu (being the less noble material) will
dissolve. Just as the zinc of the old fashioned
zinc-carbon dry battery 'eats away'.

On airplanes they used to clad stiff
alu-copper alloy sheets with pure alu (it was
named alclad). The thin pure alu surface
oxidizes very fast, like alu does) but the
oxide layer prevents deeper oxidizing because
it is not permeable. Apart from that, the
oxide is hard, and wear resistant, and
--if memory serves me right--
the oxide is also known as carborundum
and used as abrasive material for sandpaper.

Specifically the press-molded alloys had
a tendency to act as battery. I remember
many neighbors cleaning their car wheels weekly
and muttering about 'pitting'. The eaten away
alu (or maybe the other metal) created
pits, and it never stopped, because the
oxide was like dust and did not protect
the underlying material from further oxidizing.
Nowadays I don't hear so many neighbors muttering,
so I suppose either the injection-molding process has
improved and other materials are being used
for the alloy, or the wheels are cladded with
something. I definitely see some plastic-like
finish on many aged alu car wheels. At first the
wheels have a nice shine, but it gets kind
of yellowish when it ages. And seems to flake
off too.
 (That is all I know about cars, I never
 owned one).


One remark: Never polish alu with steel wool.
Tiny steel particles will embed in the alu and
you create a 'perfect' battery. Steel is more
noble than alu, and the alu around the tiny
steel particles will oxidize. The effect is that you
created an alu part that 'rusts' and keeps on
'rusting'. And you will keep on polishing.

A second remark: When two different materials
meet, try to avoid electrical contact and/or
moist entering in between them. E.g. If
possible use nylon washers under steel bolts
screwed into an alu casing. It really helps.
The thread is in contact, but no moist can get
in between, so you don't have a 'battery' there.
Apart from preventing oxidation of the alu
around the edge of the bolt head, the bolt will
later be easier to unscrew too.

Back to chrome.
Chrome does not really stick to steel. Chrome
sticks well to copper, and copper sticks well
to steel, so a chromed steel part is usually
comes as steel-copper-chrome
I recall a bike with stanchions that had no copper
in between chrome and steel, and within a year I
could peel off the chrome. Literally. It came off
in flakes of a couple of square inches a time.

You might now say: "You write about
steel-copper-chrome. What about your
battery story?"
Well, chrome is nobler than steel (and maybe
nobler than copper too, I forgot) so this is a
hefty battery, and the steel will dissolve.
Yes, it would, if it wasn't a fact that
the chrome layer is a material without pores.
And as long as there is no pore, no moist
can reach the point where steel and copper meet.
And without moist there is no battery.
Unfortunately (every pro has it's con) when
the chrome layer ages it will get pores and
moist will creep in. And the 'battery' starts working.
You will see brown rusty (steel rust!) spots appearing
on your nice chrome finish. You then polish
your chrome and the brown spots will go away,
only to reappear pretty soon thereafter because
the pore is still there.

And now for chrome on aluminum:
I don't know anything about that really. Never seen
it. But in view of my chrome_on_steel story (alu is
even less noble than steel) I *think* that
chroming alu is not a good idea.
Cladding alu with Zinc would be good. But
that is definitely not what you want your bike
to look like.

FWIW
Rob