Why add a capacitor to the Anodizer?

August 6, 2008

I received the following question:

I have a variac and full wave rectifier but no cap.
What is the reason behind adding a capasitor to the anodizer? I know it will reduce electrical ripple but what will it mean to the anodize process or final results?

In principle, the smoother, ripple-reduced output allows more even anodizing starting at the initial surge. Whether this is truly useful, I don’t really know. My experience is almost exclusively with a smoothed DC supply. But I have a switch on my main anodizer to disconnect the capacitor for those occasions when I feel like it.

RMS vs Peak Voltage The voltage will read wrong with ripple. The anodized color depends on the peak voltage. But a rippled current shows on a meter as the rms voltage, that is somewhat lower. So the color is less predictable, and the time spent at that voltage is more critical to watch.

Also, once you reach your final voltage (or at least asymptotically close enough), the smooth DC current is stopped. But a rippling supply still produces a trickle of  current as the piece you are anodizing acts as a capacitor. If you wait long enough, you can see the color continues to rise at a fixed ripply voltage.

This latter point is more important if you mask and do a succession of lower voltages for multiple colors. With ripple, the higher voltage colors will creep as you anodize the lower voltage areas.

Another note is that AC is more dangerous than DC. Edison (General Electric) made sure that the first electric chair used the AC current promoted by his rival Tesla (Westinghouse), to popularize that point. (source) But I doubt it makes much difference in any practical sense of anodizer safety.

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How can I get consistent colors?

March 26, 2008

This frustrated email arrived today:

I live in Belgium (Europe) and have been making titanium jewellery for 4 or 5 years now. Sometimes I colour the pieces. I have a machine from Wieland, a German company. All this time I did not have any problems because the pieces I made had always the same size. Now lately we are doing titanium leaves in various sizes; Grade 2 thickness 0.5 mm. The problem with coloring these pieces is that I do not seem to have any control over the colours due to the variable sizes of the pieces. Is there a way to make a formula that gives me control (more or less) by taking the weight of the piece? Because of the irregular shape it is impossible to know the amount of surface I am working with.

At the moment I am really taking what comes out of the machine. I did make several colour charts using various shapes but with pieces 6 to7 times as big as my trials I have no control .

I would be very grateful if you have some advise on this, or maybe even a solution.

Thanks in advance.

Peter

My reply: I can’t know exactly what the problem is, for I encounter the same difficulties.
The color you end up with is a function of the electrical current density, the total time, the surface finish, and the grade/alloy (which also affects finish and current flow).

The weight is not as good an indicator as the surface area. If all the pieces are always the same thickness, then the two are functionally interchangeable. But the risk is that if you calibrate on weight, and then start working with other thicknesses, the calibration will not stand.

I passed the question on to Bill Seeley.


How can I build an anodizer for UK Current?

March 22, 2008

Another reader question:

I am thinking of making an anodizer based on your anodizer digram. I live in the UK but was thinking that the volts for your electricity is different from the UK’s 240 volts?
If so do you know any diagrams that can help me with this, what I need to change?
My first thought is: In the UK, you can use the same Variac circuit. I wouldn’t trust the dimmer circuit because of the instability at lower voltages.
The U.S. uses 110 vac (150 volt peak), so we use about 3/4 of the range of the variable transformer (less if it is wired to provide over-voltage).
In the U.K, you would just just use 3/8 or even half of the available range.

If you really want to use the inferior dimmer-switch design, you can probably find a simple step-down transformer to cut your voltage in half upstream of the rest of the circuit.

Then came a follow-up:

Thank you for your reply; it was a big help. I am going to be doing the variable transformer one. I have been looking for stuff, but wow its hard to find anything that is needed.

I didn’t like the idea of using light bulbs, so I wanted to get Power resistor 200w 100 ohm but no one sells them, any idea of other Power resistors that I could use?

Try eBay.

I found several by a simple search for 200 watt resistors on eBay. You could vary the search for whatever power and resistance values you want, or use a search to find a good seller, and then ask them if they have what you need.

There are also a wide variety of variable transformers on eBay. But these heavy items cost more to ship, especially internationally.

Before the internet, I always shopped an electronics salvage store in my county. Many cities have at least one of those. Some junk yards and metal salvage yards also have a room full of gizmos that seem too nice to melt down. Call around.

Note: If you are not comfortable rewiring a lamp or replacing an electrical outlet, then you are probably not qualified to build your own anodizer. Buy a read-made regulated 0-150 vdc power supply.


Uneven results from dimmer switch anodizer

March 18, 2008

Here’s another question I frequently get:

I followed your instructions on building an anodizer and I would like to say that you have made a great job illustrating it. My anodizer is the dimmer and light bulb type it delivers a maximum of 160 Volts.I prepared a solution of TSP in distilled water placed the cathode (aluminum foil) and the Ti at the anode ran the circuit. The voltage keeps rising slowly and I get shades instead of definite colors (mostly violet, golden and pale blue). I can’t hold the voltage at a definite value. What should I do to get smooth colors? I tried adjusting the voltage first then immersing the piece but the voltage after immersing is lower than what I’ve just set it to. Please help me out here and thanks in advance.
David S.

First of all, the dimmer based voltage control is going to be a bit temperamental and unstable. But I used one myself for years before replacing the dimmer with a Variac.

Aluminum should work for a cathode, but should be lightly sanded to remove the invisible insulating oxide layer that spontaneously forms. I usually use titanium, but have been told by many that stainless steel works well.

When you have a large capacitor smoothing a the choppy dimmer voltage, the top end will be a bit mushy. The lower voltages are the worst for this effect. The tan, violet and blues are at the low end of the voltage scale.

Another issue in getting smooth colors is getting the voltage everywhere simultaneously. You should have the piece to be anodized immersed in the solution before completing the circuit to the leads. That is, you need a switch to turn the leads on and off, while the anodizer is running at the voltage you want.

Cleaning and chemically etching the metal before anodizing also helps assure a uniform color, and is generally considered necessary for getting the higher voltage colors.

The voltage measured on the leads or capacitor will drop when you start anodizing, and should rise back to your preset voltage in a minute or so. The time depends on how big a piece you are anodizing, how big your cathode is, and on the efficiency of your electrolyte.

Another possible problem might be the material of your attachment to the anode piece. Only titanium or niobium should touch the electrolyte at the positive side. Never use copper wire or regular (galvanized or tinned) alligator clips to immerse your piece. The current will just go though that, and little will be applied to your piece.


Getting started in anodizing: Mesh?

March 18, 2008

Here is a typical question that I get asked:

I would like your advice: Besides the plastic container, what else do I need to anodize titanium grade 23 or grade 5. I called Reactive Metals to buy the machine for $206 , they told me to buy a mesh but I do not know what or where to buy it. I am a little scared of getting hurt if I do not know how it really works.

Any help will be really appreciated.

Peter

The question seems to be, what is needed to get started. Peter has already bought an anodizer, a 0-150vdc voltage supply.

The “mesh” might be one of three things.

  • A large-area cathode (negative pole immersed contact) could be a mesh of titanium or even stainless steel. I use a coil of wire for this, but a plate of metal does fine. Ideally, you want to have a non-conductive porous material ( maybe a plastic mesh) between the cathode and the work piece, in case of contact. Rubber non-skid shelf liner mesh/screen is cheap and good for this.
  • A mesh basket made of niobium wire makes a good anode connection for loose parts. A titanium wire basket will work, too. Just not quite as reliable at higher voltages.
    Note: I haven’t tried this myself. I use a homemade titanium clip and the niobium clips that ReactiveMetals sells.
  • A plastic mesh basket such as a salvaged automotive windshield washer fluid filter can also be used on the anode side by running a niobium or titanium wire into the basket full of little parts.
    Note: I haven’t tried this myself, but have heard of it being used by others.

One can easily weave your own basket from titanium or niobium wire.

One important final note: If you are afraid of getting hurt, please do some more reading about electricity and safety precautions. Wear rubber gloves, and always double check where all the live contacts are when you are working. Read my old anodizing page over until you understand everything in it. It may not be complete, so do ask questions to help me fill it out.