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The importance of good connections

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  • The importance of good connections

    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.




  • #2
    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.

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    • #3

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      • #4
        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?

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        • #5
          I'll reply latter with what I know, when I have time to focus a bit.

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          • #6

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            • #7
              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.

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              • #8
                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?

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                • #9
                  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.

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                  • #10
                    NeoMoses,
                    We highjacked your thread, my apology.

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                    • #11
                      Originally posted by Fibergeek
                      NeoMoses,
                      We highjacked your thread, my apology.
                      I guess the hijacking was my fault, sorry NeoMoses. Fibergeek, thanks for the information.

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                      • #12
                        Al welding rod

                        Neo

                        Saw this tread a little late but wanted to post to it. We've been using welding rod exclusively for racking and attaching it to an aluminum busbar. A lot of the parts we do suspend very nicely on the J bend or a U bend.
                        I also use it to connect to my cathodes( 6"x12"plates of 6061..3/8" thick). It tends to get brittle in the anodizing bath but since its disposed of any way its no problem

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                        • #13
                          I'm going to say this one more time:

                          If you don't yet have the necessary experience with the anodizing process (LCD or otherwise) so that you can tell when you have a bad connection and not some other problem, stick to tightly bolting or threading the work with soft aluminum wire. We have been through months of problems caused by beginners with lousy electrical connections, let's not go through that again.

                          NeoMoses as moderator, and M_D as an accomplished anodizer, it would be appropriate you to help me amplify this.

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                          • #14
                            Fibergeek is 100% correct. To drive home exactly how tight the connections are between my workpiece and the wire, realize that I need pliers to squeeze the wire together. Depending on the part and the geometry, I'm getting 20-30 pounds of clamping force. There is absolutely no 'wiggle' or 'play' in the connection. Don't just think that you can loop a wire and let a part hang from it in the electrolyte bath, it's much more detailed than that.

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                            • #15
                              racking/hanging

                              well let me clarify since some seem to have the wrong idea. When I said the parts hang fine from a J bend or U bend the bend is in the form of a 'spring' the is wedged into an opening in the part.. the part is NOT just hanging off the welding rod.. Failure rates so far are less than 1 percent.
                              There indeed is no substitute for a good electrical connection.

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