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Rectifiers


#1

Hi all, I want to build a rectifier to anodise Aluminium and Titanium.
Does anyone have experience of these things or have plans to build
one?

Richard


#2

Rick, I wouldn’t build one by the time you by the parts and put it
together it will cost you more than buying a new one.Like I said in a
recent post I have three that I bought used and have never paid more
than $75 for one,If you are in a remote local you can find them on
e-bay occasionally or in the newspaper. Best J Morley Coyote Ridge Studio


#3

Richard, To anodize Aluminum, your rectifier can be a Battery Charger
that you can purchase at Sears for $30. Anodizing Titanium is a whole
other matter. The voltages used in anodizing Titanium can be VERY high
and VERY dangerous. You could easily build a Ti anodizer yourself, but
I dont recommend it. Reactive Metals Inc. are specialists in this area
and they sell a small unit for jewelers. You can see it on their
website at: http://www.reactivemetals.com/rmsmini.htm
Regards…Bob Williams


#4

Richard, You will need two different rectifiers. Aluminum anodizing
is a low voltage high current process typically 12 VDC . Titanium
anodizing is a high voltage low current process in the 80-180 VDC
range. I built my Titanium rectifier many years ago I will look for
the plans and see if I can find them. Please be aware that you will
be mixing electricity and water and be very careful in the design and
construction of these tools and make sure that the house current
socket that you plug into is protected with a Ground Fault
Interrupter (GFI) for your safety. –

James Binnion Metal Arts


@James_Binnion
Member of the Better Business Bureau


#5
    Hi all, I want to build a rectifier to anodise Aluminium and
Titanium. Does anyone have experience of these things or have plans
to build one? 

The aluminium anodiser and the niobium and titanium anodiser are
different, so you’ll need to make two machines. While both types have
DC output, aluminium uses a current-regulated power supply and Ti
and Nb uses a voltage-regulated supply (zero to mains variable
transformer). I can supply a wiring diagram for the latter. I built
one and use it all the time. Or buy the machine from Reactive Metals
<www.reactivemetals.com> and get their brush attachment and paint your
anodised designs.

I use it with a Ground Fault Interrupter. Here they’re called Residual
Current Device. This is a device that can come in the form of a
replacement line receptacle or circuit breaker that trips on imbalance
of hot and neutral current. This translates into a trip anytime
someone/something makes a connection between a hot terminal and earth
ground - the usual scenario for electrocution.

Brian
B r i a n � A d a m
w o r k s h o p s 2 0 0 1
www.adam.co.nz/workshops summer in Canada/USA


#6
    Hi all, I want to build a rectifier to anodise Aluminium and
Titanium. Does anyone have experience of these things or have plans
to build one? 

G’day; this is another of the ‘hardy annuals’ - have a look at the
archives under ‘plating’ ‘stripping’, 'anodizers etc. Meanwhile, don’t
bother to build one - it won’t work out much cheaper than a decent 6
or 12 volt battery charger, which is the same thing as what you need.
Control the output by means of a light dimmer on the input side.
Cheers, –

John Burgess; @John_Burgess2 of Mapua Nelson NZ


#7

A nice inexpensive small plating rectifier for small scale plating
and aluminum type anodizing can be found ready made as a “bench power
supply” used by electronics enthusiasts . See:

http://www.web-tronics.com/30serdigrobe.html

This is a very nice o-30 volt 0-3 amp voltage or current regulated
supply at $99.00 US. 3 amps fits a lot of small scale work and is
easily built with low cost integrated control circuit hense the low
price. Similar units at 0-12 amps are about $500. If you homebuilt
one of the 3amp ones you may spend about the same $100 for parts for
something the same but not as attractive a package. If you want a
bigger amprerage supply there are electronic surplus power supplies
available at low cost. You want a linear supply not a switching power
supply if you go this route. These will not have the metering and
conbtrol function but if you understand the electrical concepts or
have a friend who does these can be quite usefull. The titanium
anodizer is a higher and variable voltage unit and is probably best
bought from Reactive Metals Lab. unless you understand the required
safety considerations. If you do you probably won’t be reading this.
Jesse


#8

Anodizing in its simplest form is the application of direct current
through an electrically conductive solution to force a controllable
oxidation on the metal. For it to work you need a source of direct
current, a way to control the force and amount (Voltage and amperage)
of the electricity, and incidentally, a way to avoid anodizing
yourself (shock or electrocution).

As I understand it, Aluminum does not need a broad range of voltages,
but Titanium, Niobium and Tantalum do require various voltages for
various colors. With Aluminum, one creates a layer of Aluminum
Oxide on the surface. This oxide is hard but porous. Dyes are
introduced to this porous layer, the object is then heated to close
the porosity and “fix” the dye. With Ti, Nb, and Ta (reactive
metals), a surface oxidation takes place, which directly controls the
color. This color is the result of the thickness of the film reacting
with the wave form of the light, much like the colors of a soap
bubble, oil slick on water, or a butterfly’s wing. The thickness of
the film is directly controlled by the voltage applied. With Ti, at
around 2-4 volts you have a film that is so thin that you do not see
any effects. As you increase the voltage the colors change, from tan,
through brown, purple, blue, blue-green to clear again (around 30-40
volts) then on to second order colors starting again with yellows etc.
The same is true of Nb with even more brilliant colors. Ti is at an
additional disadvantage over Nb, it is so reactive that it forms an
oxide all by itself (TiO2) that interferes with great color formation.
This oxide is tough and very stable. The best way to remove it is
with HF, hydrofluoric acid - a very nasty acid!

So, what equipment do you need? A source of electricity - one could
use battery power, but controlling it for reactive metals means a
range of 0-100 or so volts. While it is possible through the use of
addition / subtraction of batteries or the use of voltage dividers /
resistors, it is not easy to achieve good smooth control. The best
way is with a variable transformer, often called a powerstat or
autotransformer (the cost, perhaps US $50 on eBay used), and rectify
the output with a full wave bridge rectifier (cost a few US$). The
major drawback to these is the fact that the output is connected
directly to the mains or house power. Touch one side and any ground
and YOU get anodized. This is solved with the use of an isolation
transformer before the variable transformer (again around US $50 on
eBay).

Once you have the source of electricity, the rest is easy (well
-except for the ART thing). Simply connect one side of the DC power
to the Ti or Nb and the other to a piece of Ti or stainless, immerse
in an electrically conductive bath (TSP - trisodium phosphate, pickle,
or many others) and slowly crank up the voltage and watch the colors
change. You can mask of areas and apply higher voltages to areas
which previously received a lower voltage.

This is a very simplistic view. The best thing to do is forget all
this, go to the Reactive Metals Studio homepage
http://www.reactivemetals.com/ and learn from the very best in the
reactive metals jewelry business. They offer metals, “safe” power
supplies, a safer version of the HF etch for Ti and most important, a
vast amount of practical knowledge. I took a workshop from Bill
Seeley, owner of Reactive Metals Studio and cannot stress enough how
impressed I was - this guy is GOOD.


#9
 [snip] The best way is with a variable transformer [snip] The major
drawback to these is the fact that the output is connected directly
to the mains or house power.  Touch one side and any ground and YOU
get anodized.  This is solved with the use of an isolation
transformer before the variable transformer (again around US $50 on
eBay). 

You are better off grounding all exposed metal surfaces that are not
hot, and installing a GFI (Ground Fault Interrupter) in your primary
circuit. You can also install interlock switches that kill the high
voltage when something is opened that shouldn’t be - like the lid of
the electrolyte container. This would be much more sensible.

According to my sources, the isolation transformer just floats the
mains voltage away from ground. This means there is no longer a
connection - as there is with the line fed voltage. This does nothing
to protect you from getting zapped by mains voltage (up to 240VAC in
some countries). You have plenty of mass-produced appliances that are
perfectly safe because all expose metal surfaces are at GND. This
protects you; it is impossible for these surfaces to rise above GND
potential without blowing the fuse/ breaker.

However a GFI (here they’re called a Residual Current Device) trips on
imbalance of hot and neutral current. Trips anytime someone/something
makes a connection between a live terminal and earth ground - the
usual scenario for electrocution.

Brian
B r i a n � A d a m
w o r k s h o p s 2 0 0 1
www.adam.co.nz/workshops summer in Canada/USA