New Day - new problems :(

[kickn]

okay - Yet again I'm having more problems.

After running a couple scrap pcs though without a hitch (and a surprisingly good finish despite the lack of prep) I thought I would start for real. This involes of course lots of prep. I'll run what I did.

1. deburr
2. bead blast with glass bead
3. deoxidise
4. desmut
5. anodise
6. dye
7. seal

okay - all within normal recommendations with a rinse with demineralised water in between. What I ended up with was a patchy dye finish.

A couple more tries and I noticed that the unprepped surface came out great but the bead blasted surface didn't.

Could the bead blasting be forcing the oxidised layer deeper into the metal?

I thought that could be the case so I'm just now trying to give it a very hard sand. A very long soak in lye and a rinse, dry, bead blast, and so on.

I'm still getting some mixed results and have been getting slightly more aggresive with things but I was just curious to see if anyone has had this before?

The other thing I noticed was that when the parts are anodising that I sometimes get darker grey areas while in the sulphuric acid.

Could there be a contaminate somewhere? Could the glass bead be embedding itself in the metal?

Everything is clean and fresh. All solutions are new and made with demineralised water. The glass bead is fresh. I can't think of anything else.

I need a good solid black finish! So come on fibregeek - HELP ME!

On a side note I've figured out how to rack screws if anyone is interested. At least with a 90/95% success rate.

[Fibergeek]

I've had something like occur before.
It turned out to be a tiny amount of compressor oil was geting blown along with the glass beads, a better oil trap solved it.

You don't mention a degreasing step before beadblasting. If you have traces of cutting oil on the work before blasting, its possible that the blasting could be driving the same into the surface, making it much harder to get off..

The only difference between the prep for scrap and work is the beadblasting, right? Trouble shooting is best done by elliminating one variable at a time. The "shotgun" approach usually winds up taking more time.

There could very well be some other contamination somewhere.

[kickn]

Hmmm..... It might be compressor oil - although I have a not bad trap there already. I'll double check that.

I am trying to 'rifle strategy' it down to whatever is causing it and I think I'm getting there.

I guess the bead that I've loaded would be kaput so I'll go get some more tomorrow and change that as well as add another trap.

But it sounds like contaimination though right? I was thinking it was oil or something but just couldn't see where it was coming from. Thanks though - i'll see what happens with this batch

[Fibergeek]

The oil trap that came with my compressor was a POS, I had to get a better one.

Do you degrease before beadblasting?

[kickn]

Ya I did.

Right now the test I'm running is:

1. degrease
2. debur/sand
3. deoxi
4. beadblast
5. degrease
6. deoxi (for a good while to keep the texture I'm looking for and make sure there is no leftover rubbish)
7. anodise

I've also got a test thats without beadblasting but exactly the same as above.

I'll run out tomorrow and see if I can get a new oil trap. THe only thing I have hooked up right now is the combination reg/trap which is probably rubbish.

[acidrain]

I had similar blotchy dye results on beadblasted finishes too. I found that a light blast worked much better that a prolonged one. I discovered that while concentrating on small blemishes with the blast, it created a blotch that was dark and did not dye well.
The following try, I cleaned, etched, de-smutted first, then bead blasted with some distance between the nozzle and the work with just a quick back and forth motion. That worked well.
I've since made it my rutine to prepare the surface to a uniform appearance before beadblasting so that the matte finish is completely even.

[kickn]

I'll give that a try but I wanted a very heavy bead blasted finish.

I've got a good oil filter for the compressor coming tomorrow so we'll see how that does.

Cheers for all your help

[kickn]

okay - a couple more questions here as I start to get some pretty good results.

One thing I've noticed is that on some of the parts the that are dyed black either come out a bit streaky or with water-like splotches.

I'm sure its something simple and I'm thinking either its the dye (strength or ph?) or its the rinse before and after the dye.

The other thing is that sometimes it comes out a bit light or bluish. I know that this is probably a blue-based black so its the depth of the layer or the dye.

I don't think its the depth/etc of the anodising layer but I could be wrong.

I have a new oil filter (filtering up to 0.01 micron!) coming tomorrow so I'll let you know how that works. It would isolate the problem exactly as I will still bead blast like I was before and try that.

Also - I'm been anodising the screws with pretty good success - I would have to take a video of how I've been using 'half-hitch' style knots to fix them. If you want I'll do the video but only if someone wants it.

Cheers and thanks again.

[acidrain]

I would love to see any tips you may have. I "tie" my wires on too (too poor for a sput welder). Thanks.

[M_D]

On the bluish look with the black dye, a thin anodize layer or short dye time are probable causes. You could try a longer time in the dye first, then if that doesn't do the trick a little longer anodize time and/ or more amps might be what you need. Heating the dye to 120-140º may help, if you aren't already. Most any dyes are supposed to be heated anyway.

On the streaks or spots, it is hard to say what they are from. It could be from numerous things, such as incomplete rinsing, or common sealer smut.

I haven't heard or read any "official" specifications for black dye ph, although we have found the black dye from Caswell's to do considerably better with a ph of about 6-7, which reduces smut compared to a low dye ph. For us, it is normally about 3 when freshly mixed. Also, too strong of a concentration ( with black at least) will produce a smut layer.

When you are using heated solutions, try to remove the parts and submerge them in a rinse tank as fast as possible to reduce the amount of solution that dries on the part. Using only as much temperature as required for the various solutions can help avoid excess dried on solution.

Also, some water will leave spots, so if you rinse with tap water that could cause water spots. There may be other causes also that are causing your streak. Do the spots wipe off? If so if it is easy or hard, and what does the color uniformity look like after wiping?

Incomplete native oxide removal will tend to leave a streaked or splotchy appearance. The places where there was more oxide will not look as good as where the oxide was more completely removed.

[kickn]

After some carefull testing and trials I think it was down to the anodising layer.

Which brings a question. I'm experiencing very high voltages - any ideas on what that could be? I'm using the 720 rule strictly by the book and when I start out I get a voltage that about 15 or so. My surface area calculations are exact as I'm using a cad program to model the parts first and pull the values from there.

Another thing I'm a bit perplexed byis that when I initially power the tank up (gradually increasing the current) it seems to hold at a very low value (say .5A or somethign) and then jumps up - is this due to capacitance of the parts?

I also have to find more power since I can't anodise a complete set of parts at once which I would like to do to keep the finish as close as possible. Is it possible to add power supplies in series or anything? I have a good 10A one here but need more. My parts are about 5sq ft (4.96 to be exact) so I'm estimateing that I'll need 15A @ ASF3 or which I would prefer - 22A @ ASF4.5. Any ideas bar a single BIG psu?

Proper rinsing has also helped with the streaks and water marks. I think the water here is pretty heavy.



(I'll try to do the video later to day and put it up somewhere)

[Fibergeek]

Another thing I'm a bit perplexed byis that when I initially power the tank up (gradually increasing the current) it seems to hold at a very low value (say .5A or somethign) and then jumps up - is this due to capacitance of the parts?

That's not right; in CC mode the voltage starts at a very low value and increases after some minutes to something close to the peak voltage, the current stays the same (at the value you set it for) throught the entire anodization, regardless of the voltage. If this isn't happening you aren't running in CC mode.

In CC mode there is no point in increasing the current slowly; that isn't doing anything, good or bad.

Causes of this in no particular order:

1. Your PS isn't setup correctly, or something is broken.
2. Marginal cathode connection; this connection doesn't anodize like the anode connection, but since its close the acid it does corrode quickly. This is the most likely based on your symptoms.
3. Marginal anode connection; since I think you are welding this connection, if this is what's happening you are the very first to experience it (AFIK) the cause would be a lousy weld.

The dielectric constant of the electrolyte is very low (its a conductor not an insulator) the resulting capacitance would be a few pF at most, totally irrelevant.

Large power supplies often have the capability to be paralleled for more power directly; one acts as the master and it controls the others as slaves. If your's can do this it will say so in their manuals. This isn't common in small power supplies (10A is small).
The other way is to connect them in parallel through isolation diodes, one per supply. The diodes are wired to the PS + terminal with the cathode facing the work. The diodes must be sized to handle the current and power dissipation they will experience. Both PS must be capable of CC operation, and each has it's current set for the portion of the load current it has to handle, easier to do if the two PS are identical units. If you don't follow this explanation don't try it. One big PS is obviously the best way.

Since we have capable assistance from other members in this thread now, I will restrict my input to electrical issues.

[kickn]

I think its either the power supply or the cathode. The connection to the cathode is outside the acid and its bolted tightly on multiple plates. I have about 8 cathodes around the tank.

When I said that I turned the current up slowly I wasn't very clear. I turn the dials slowly but only take say 15 secs. to get up to where I want it. I just do it fairly slowly so that I compensate for the initial fluxuations. The delay that is sometimes there with the amp/voltage only generally lasts for say 30 seconds or so and then it clicks in and not all the time. My guess is the PSU but I didn't know if I was experiencing anything else.

I'll keep a look out for a 20A psu with current control.

Thanks again

[Fibergeek]

and then it clicks in and not all the time

A ha, a voltage compliance issue.
This means that your PS is having difficulty sourcing current when the required voltage is real low, not uncommon with cheaper power supplies.

You should be able to fix this by putting a power resistor in series with the + terminal, anything between 1 and 4 Ohms and rated for at least 15 Watts should do. This will drop some voltage and allow the PS to turn on normally. After maybe 5 minutes you can short out the resistor as it isn't doing anything useful anymore, but it won't hurt anything if you leave it in.

Tightly bolting the cathode leads doesn't guarantee the connection won't corrode.

[Sid03]

kickn- I have noticed the same PS issue you stated with my 20A CC PS. Although I dont doubt at all what Fibergeek says.....im not 100% sure as I sometimes have the same issue when the required voltage is rather high and my gains are up fairly high.

I think I was having luck by making sure I turn the current dials completely back to zero when starting up the PS, then turning the fine dial up halfway then adjusting the main dial. I cant remember offhand, but thats just something that you may want to play around with. I know exactly what your talking about......thought my PS was broken when I first got it......esp when it makes the strange sound when it actually starts outputting the current.

Just curious....where did ya get your .01 micron filter and hows that working for you?