The importance of good connections

[NeoMoses]

I was needing some new electrode wires and was considering buying another roll of soft 1100 series aluminum wire, which is what I currently use, but I was upset at the high cost every place was charging.

I stumbled across aluminum welding rods, like those used for TIG welding, and liked the price, so I bought 5 pounds of 3/32" diameter x 36" long 5356 aluminum rods for about $30. Not a bad price when compared to the wire, which is usually about $10-$20 per pound.

What did I find when using these? They are extremely stiff when compared to the soft 1100 series wire! It actually made me re-consider some of my attachment methods, and it has saved me a good deal of time. I've now completed 2 completely successful batches, and am thrilled at the abilities of this stiffer welding rod, so I wanted to share this with everyone.

Here's one of the most troublesome shapes I've found for attaching an electrode to: a cylinder with no threaded holes. In addition, no external 'white spots' are an option. I used to hate anodizing parts like this, now they're a breeze. A simple J-bend in the end of the welding rod provides plenty of clamping force to provide a good connection throughout anodizing while leaving tiny electrode connection marks.

[Fibergeek]

A pound of 14 AWG Al wire is 268 ft., that's about 4 cents a foot. Price based on $12.00 / lb. from www.parawire.com

As you surmised, the welding wire is working for you in this case because the hardness and diameter are providing enough spring tension. Since you are using CC you should notice that the peak voltage is higher with this method compared to bolting or threading for the same anodizing conditions. This higher voltage is proportional to the higher connection resistance. The voltage compliance in Neomoses' CC/CV power supply automatically corrected for this. If you weren't using CC and failed to adjust the voltage to compensate, your current density would have gone down.

You're now one step from titanium wire, which would provide more spring tension.

Neomoses has the experience to use this method successfully, beginners should stick with threading or bolting until they understand the whole anodizing process. Spring connections are not as simple as they look.

[M_D]

I used that method with stiff aluminum wire for a while, and also made use of soft aluminum wire. As a note, the titanium wire sold by Caswell is quite soft, and doesn’t have a lot of stiffness. But it will work harden by bending enough, or cold working with a hammer, so it can be made into smaller clips with adequate spring qualities. It doesn’t appear to heat treat well as a hardening option.

I like the titanium racking a lot, the picture below is some I bought from Servisure. While it might seem kind of expensive at a glance, the hassle it removes from the entire anodizing process makes it an excellent value in my opinion.

The four sided finger rack is meant for doing more parts than a hobbyist is likely to need, but the other modular clips and angles to bolt them too are ideal for a few parts at a time, and provide quite a bit of versatility and configuration options. I'm just going by memory, but they are about $2-$3 each, the perforated angle to bolt them to is about a $1 an inch, and then a bolt and nut are less than a buck if I remember correctly.

The titanium clips can be reformed (within reason, of course) to fit the need, so you don't need to worry about the measurements fitting the part exactly; they just need to be within range. On large parts I may use 2-3 clips per part to secure the part and increase the electrical contact areas.

The angle can be configured with one or two risers, and by configuring it with a base to make it freestanding you can move it from tank to tank without the hassle of hanging it. That makes it much easier to handle the parts without touching them accidentally, or dropping them.

[Fibergeek]

M_D, I have a racking question for you:

Since titanium won't anodize under the anodizing conditions for aluminum, it would be reasonable to think that that two things are occurring:

1. When the surface area (SA) of the racking is much larger than the SA of the combined work (like in your picture) the rack will draw the majority of the current and dissipate most of the power.

2. Since the titanium won't anodize here, the electrical bulk resistance of the titanium SA will show a low resistance (lower than the work) and will remain constant.

It seems that because of 1 & 2 there going to be a current density problem with the work, the racking is setting the current density (not the work). Worse still, since the work and the rack are electrically in parallel, the constant resistance shown by the rack will lower the current density of the work as its coating builds up. This can be substantial when the rack is much larger than the work. In effect, this defeats constant current operation as far as the work is concerned (where it counts).

This can be reduced by only operating with lots of work; so that the work SA is much larger than the rack SA, or insulating the non contacting areas of the rack, reducing its SA. Plastic goop or something like that would probably work.

Have you experienced any problems with this?

[M_D]

I'll reply latter with what I know, when I have time to focus a bit.

[M_D]

I have been wondering about this also, and I am not going to be able to fully explain the issue, so will just convey some observations.

It hasn’t seemed to give us any trouble that I know of in results or consistency. We usually don’t anodize part loads this small, and I just “mocked” these up for illustration. However, on the finger rack that has the smaller washers we run parts that aren’t in the picture with theoretical current requirements that range from .0179 - .5664 amps for each part at 8 amps CD. Since the resolution on the power supply is only .1 amps we do try to run total loads of at least 2.5 amps to try and minimize the error some. But even then the surface area of the rack is much larger than the combined parts.

They still seem to anodize consistently though with larger parts and loads using upwards of 20 amps. I can’t explain why the rack surface area doesn’t seem to show up as a problem. Perhaps there is room for improvement though, by learning more about it and maybe factoring the relationship of part area versus rack area into some kind of current adjusting formula.

I do know that the titanium racks make the actual voltage inconsistent with your numbers. For example, when the total part load is small due to small parts, the voltage will be lower than expected, I suppose due to the fact the resistance of the rack is fairly low. If the parts are larger, it draws more voltage at the same CD. I have varied the depth that the racks are submerged and watched the voltage go up and down. PAR is shown, just not necessarily at the voltage expected. That is probably why, (if you remember sometime back) that some voltage peaks we see were low indicating low ohms.

I really don’t have any conclusive answers, although I would like to understand it better myself. Since you appear to enjoy experimenting and understand the electrical aspects, I was wondering if I sent you some titanium racking if you would be interested in playing around with it and perhaps come to some conclusions? If you are interested let me know, and I will some to you.

[Fibergeek]

M_D,
Since you don't run the racks with only a few parts, you are probably minimizing the problems mentioned above.

What I didn't consider was that the conductivity of Ti is about 16X less than Al. This is good because it will reduce the current draw of its large surface area. This is not so good because this increases the voltage drop in the anode connections, meaning you need more voltage for a given current density, thus you dissipate more power in the electrolyte. If the racking was aluminum, and it wasn't masked off to minimize its exposed surface area, this would be a serious problem.

What you are seeing is consistent with what would be expected:

1. Small loads show a lower than normal resistance, because the much larger SA of the rack (compared to the load) is dominating the total resistance. CC is almost useless in this case.

2. Large loads show a higher than normal resistance, because of two reasons;
A. More load SA, so the rack SA may not dominate. i.e: The effect of the parallel resistance of the rack itself is reduced.
B. The lower conductivity (higher resistance) of the titanium is dropping more voltage through the rack and via the contact points to the load. The higher the current, the more voltage dropped (V = I x R).

The lower conductivity means that the actual contact resistance with the work can never be as low as methods not using titanium. This is why Ti racking makes thermal problems (electrolyte temp. rise and contact burning) when used for Type III anodizing. Its not reasonable to expect numbers like mine when using racking, too many variables.

As always, there's never a free lunch.

I may take you up later on the loan of some Ti racking for experimentation.

[M_D]

When I said the Ti had lower resistance, I really should have said it differently. What I meant was in relation to the anodized parts it adds a lot of surface area that I thought should lower the voltage over hanging wires or aluminum racks when the racking surface area is accounted for.

With small loads in the 3 amp range, the peak voltage in our setup may be only be in the 11-13V area @ 8amps CD (rack not factored in). With loads in the ~15 amp range (again @ 8 amps CD), I see it reach 15V to high as 17V.

It just seems like there would be some way to factor the rack in, like adding a consistent amount for a certain rack SA to compensate. I don't know how to factor or calculate that though, and since there hasn't been any known end problems and I don't have much free time there hasn't been much incentive to experiment and learn more about it. I have thought about doing some very small loads to try and compare, but since my power supply resolution is not that small there would probably be a lot of built in error which would make tests inconclusive.

Do you think that calculating an empty racks surface area, and applying a given current that the voltage it takes would provide any usefulness in how much current is "wasted"? Or are saying that it would depend on the work versus rack area?

[Fibergeek]

You might gain some insight by just measuring the resistance of the rack in the electrolyte (empty rack, no work). You can do this by immersing the rack and applying power, note the voltage and the current. The resistance is then R = V / I. Since it won't anodize, this resistance should remain constant if your electrolyte temp. is reasonably constant. It should not be important what current you make the measurement at.

Servisure should be able to provide you with the SA for the rack components, but it will probably be easier to come up with a rack resistance for each rack configuration that you use.

For a given rack, the rack resistance will appear as a resistance that is in parallel with the work, as though it was a seperate resistor across the power supply. The power it is dissapating in the electrolyte would be:

P = V x I, or P = I squared x R, or P = V squared / R, all work equally well.

This will tell you how much power you have to allow just for the rack.

It will be more complicated to account for the series resistance of the rack and the contact points to the work. Maybe you could dispense with this by calculating the resistance again, this time the rack and some typical amount of work (R = V / I) when you think the work is sufficiently anodized. If you subtract the rack resistance from this total resistance, you will have the anodic resistance, plus the rack series resistance, plus the contact resistance.

If the difference between these two calculated resistances is small; you are going to have issues with knowing what current density you are anodizing at, and keeping it constant throughout the anodizing process.

Sorry M_D; I know you didn't want to hear this, but you might need to get good at "Kentucky Windage" anodizing. Its a PITA, but others do it successfully.

Let me think about this a while longer.

[Fibergeek]

NeoMoses,
We highjacked your thread, my apology.