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.