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Quick question on "old" ano method......

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  • #16
    M_D- thanks for the input.

    I have been adding 1.5A to the current needed to try to compensate for the Ti racking. I may call the manufacturer tomorrow and see if I can get and exact surface area of the different clips im using. Do you guys think the exact surface area of the rack should be accounted for, or only a percentage of it since the Ti conducts differently?

    I just ran a batch of 6061 and all looks well(with Ti racking). I'll try the 2011 and red, this should be fun!


    • #17
      Nice and definitive, M_D.

      To answer Sid's cathode question:
      The possible cathode issue you raise would be a connection problem, not cathode area actually. If CC isn't being compromised too much by the rack SA, CC will raise the voltage to compensate for what it sees as lower conductivity in the anodizing tank circuit. This is why cathode area isn't critical at all in CC anodizing circuit. Yes it is a circuit and all the physics and electronics math does apply.

      As far as calculating the exact compensation required by the racking it is certainly possible, using Ohm's Law and Kirchoff's Law of DC Circuits. You will need to know the SA of the submerged portion of the rack, the SA of the work, the conductivity of the Ti alloy, the change in bulk resistance of the work as it anodizes, and the conductivity of the electrolyte. To do it accurately the math will be messy, and the applied ASF will have to increase somewhat over the anodization time, not remain at one value. I think a simplification can be made, where only a fixed increase in current density will work well enough. M_D is probably close to that right now, but his increase in ASF would only apply to his setup and his racking. You will need to develop a fudge factor that works in your case.


      • #18
        [quote="Sid03"]M_D- thanks for the input.

        I have been adding 1.5A to the current needed to try to compensate for the Ti racking. I may call the manufacturer tomorrow and see if I can get and exact surface area of the different clips im using. Do you guys think the exact surface area of the rack should be accounted for, or only a percentage of it since the Ti conducts differently? ………….quote]

        I wish I could answer that with certainty, but I can only say that I don’t think you want to compensate for the Ti with the amps per square foot as the aluminum. We have been using the 720 rule for some time now. When I try different current densities, I use this factor to estimate the time needed to comparably match the thickness of parts done at another density. Right now, we are usually going to 600, which seems to be working well (parts are dying nice, and no real problems are evident). So if we are using 10 amps per square foot of parts, we anodize for 60 minutes (60 x 10 = 600). If we use 12, we go for 50 minutes (50 x 12 = 600), and so forth. On the 6061, for red we go a little longer to a full 720, and it seems to give a noticeable difference in the depth of color possible when dying red. It may not be the thickness per se that is helping; it may be the pore structure instead. I don’t know for sure why, it just helps.

        One difference I notice between 6061 and 2011 is this; the 6061 seems to be more tolerant of “over” anodizing than the 2011. One thing that is puzzling though, is that 2011 doesn’t build the thickness as fast as 6xxx series. But if we anodize the 2011 at the same rate and time as 6061, it looks like a good match. There again, it may be the pore structure balances it out, rather than actual thickness. But, if we anodize longer than usual, the 6061 takes longer before it deteriorates than the 2011 does.

        On some of our parts, the racks even exceed the total part area. If the Ti needed as much current as the aluminum, I think that we would be needing to add more current or add more time, if you compare the dying tendencies we see with Ti racking against parts anodized with aluminum hanging wire where the wire area is either insignificant, or calculated in and compensated for.

        At some point, I will carefully do some identical parts with both aluminum and Ti racking, and see what I learn.

        I know this is just general and highly unscientific, but it is working. The unfortunate thing about it is not being able to factor it all like the LCD instructions outline. If one were doing odd batches, where the part surface area to rack surface area varied constantly, then it might be pretty tough to maintain any predictability at all. As it is, we are using either a little different current or time for various parts, to compensate for the area ration between the racks and parts. It has been from trial and error, seeing the tendencies, and adjusting accordingly. That’s why Fibergeek has rightly referred to it as Kentucky windage.


        • #19
          Well, my batch of 2011 turned out ok. I kept in for about the same time as yesterday(50 minutes) but changed the ano bath from 1:1 ratio to 1:2 ratio, and ran a better connection to all the cathode plates. Once again, the voltage decreased while anodizing. It started at 17V and ended at 11V. The bath temp also went up about 3-4 degrees, dont know how much that effected it.

          Do you think the fume control balls actually help maintain bath temp much(I read that they do somewhere)?

          How bad is the hydrogen gas to breathe? Its getting very noticeable again since im not using LCD anymore. If I put a papertowel inside a regualr dust mask I can work fine without noticing it, but without the mask your coughing. Im going to make some sort of fume hood, just wanted to know how dangerous it is until I get that complete.

          Thanks guys


          • #20
            OK. Glad to hear things are improving.

            The voltage drop that you are seeing is characteristic of a 2xxx series anodization curve. 7xxx series does this too, but not as pronounced. 6xxx and 1xxx series have a curve that slopes up, and the coating forms much faster.
            You don't want the bath temp. to get much higher than that, you should be thinking about some sort of temperature control.

            That isn't hydrogen that you are breathing, hydrogen is ordorless, colorless and tasteless. The small amount of hydrogen generated escapes quickly (its the lightest element) and isn't any sort of hazard. You are breathing sulfuric acid fumes, the ventilation where you are anodizing isn't adequate. You will want to fix that fast.

            Mist suppressant and balls will certainly help, but you do need good ventilation.


            • #21
              So, how do you detect PAR with 2000series? Will the voltage stop dropping? As for temp. control......I got a larger container to sit the ano tank in. Going to add water and some ice.....just have to play around and get a feel for how much ice to add right before starting to anodize I guess.

              As for ventilation.....any tricks of the trade for that? I do have a wall mounted ventilation fan but it isnt keeping up. I was thinking of having a fan near the ano tank to suck fumes into a dryer hose and run that hose up to the wall vent. Think that would be enough? How lethal are sulfuric acid fumes?

              Also, I do alot of 2 color parts. While doing the second color on a part I can see the already colored side starting to dry. Is it bad to let it dry? I try to keep it wet by spray with water every once in awhile......does it matter?



              • #22
                I doubt that you will be able to detect PAR if you are using racking, the rack's resistance will hide it from you, I would expect this racking any alloy. Use the 720 rule.

                In my setup; I use a 1/4 HP modified aquarium chiller in series with a 420 GPH pump, this combines the cooling system with the agitation system, it works very well. My tank uses 5 gal. of electrolyte, the chiller can maintain a 32 deg. bath temp, with 300W of electrical power being dissipated in it (hardcoat experiments).
                Agitation (recirculating the electrolyte very fast) has an advantage over aeration (air bubbles) in that it generates little to no acid mist. This will greatly reduce the ventilation issue all by itself.

                Sulfuric acid fumes are both toxic and corrosive, and not only to you. It will rust anything ferrous in the same room in time.

                You will want to keep your anodized parts wet until they are sealed, it does matter. A spray with water periodically should do it.


                • #23
                  Hey guys, we put together quite a thread here today.


                  • #24
                    Originally posted by Fibergeek
                    Hey guys, we put together quite a thread here today.

                    Well, I seem to be making headway over here. So, you dont think there would be a difference from using one 8X8 cathode to using 4 of them since im using CC anodizing? Keep in mind im doing about 150sq. in. batches at this time.

                    Also, I would love more info on your chiller setup if you wouldnt mind. I like the circulation pump idea, other then the fact that I could picture a hose breaking somewhere and shooting acid all over my workshop. I remember some people having problems with the pumps burning up in the sulfuric acid and grease from the pump making its way into the ano bath. I would consider a system like yours, if it doesnt break the bank TOO bad


                    • #25
                      Cathode Area:
                      An easy way to check this to get your setup working with your usual 4 plates, and wait 10-15 minutes until some anodize has formed and the voltage starts to settle down. Note the voltage and current. Then remove or disconnect one plate. You should see the voltage go up a bit, but the current stays the same. Then do the same with another plate. If the current does change, it indicates that CC control has been compromised. The difference in voltage is proportional to the increase in power dissipation caused by the reduction in cathode area in the anodizing circuit.

                      Power (Watts) = Volts (V) x Current (A)

                      I should have thought of this earlier, this will tell you about how much the racking is compromising CC control. If you see little or no change in current with less cathode, the only electrical downside to racking is the added power dissipation. If you see a substantial change, you probably have a problem. M_D should try this too, its quick, easy, and will disrupt your operation for only a few minutes.

                      I'll describe the pump and chiller I'm using later.


                      • #26
                        Would you see any current change since your using a CC supply? Only the voltage will change to compensate for the current change....right?


                        • #27
                          CC means Constant Current, the PS is holding the current constant and varying the voltage as the load changes. CV (Constant Voltage) does the opposite.

                          This simple test will indicate how much the racking is interfering with CC operation. The Ti racking will have some adverse effect on CC operation, because it doesn't anodize with the aluminum. This test should give an indication if its actually bad enough to be a problem. You should do this with a typical batch size, since this counts too.

                          Do the test, and post your voltage and current readings (before removing a plate and after) and I'll walk you through the math.


                          • #28
                            I may be able to try that today. My cathode area is pretty large (at about 7 square feet) each compared to the batch size.

                            The 2011 voltage curve falls off a lot more in our setup when compared to 6011.

                            One thing I have done to expedite calculating "optimum" anodize times is to load up a rack of parts, and pull one off every 5 minutes or so (and adjust the current accordingly). Then they can be layed out and compared after they are dyed and sealed. It graphically illustrates the difference, the first ones take longer to dye and don't reach the color depth, then they dye progressively faster and deeper, and one anodized beyond that for long enough you can see the effects of too much anodize time.


                            • #29
                              Even with cathode area that much larger than the work you should still see a change in voltage when you disconnect 1 plate, probably not as much as Sid. Ideally the voltage should go up, and the indicated current should remain the same. Kindly post your results also.

                              Your 5 minute staggered testing would be cheating in true Kentucky Windage anodizing, good idea.


                              • #30
                                I didn't have time to experiment today. I did read somewhere that the distance between the work and cathodes would change the required voltage. So this past weekend I was moving the racks closer to one side, about 6-7" off center from the vertical cathode sheets, and the voltage would go up 2 or 3 tenths (was running in the 17 V range). So I imagine taking one out would change it allright. I may have time to disconnect one cathode tomorrow.