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Reasonable Expectation- Black Anodizing 7075

troyk

Aluminum
Joined
Mar 7, 2008
Location
cincinnati
I have a few intricate shoe box sized prismatic parts that have pockets on all six sides. The material is 7075 and bead blasted before black anodizing. I am getting back parts with air pockets in them (light bubble looking features) and a lot of dark gray looking splotches and light spots on surfaces. The splotches look kind of like zebra striping. I've talked to my anodizer and discussed the critical nature of the exterior surfaces of the part needing to be consistent and completely covered. These are extremely high dollar parts for the elite military and well you get the point.

My question is can you share any experience of black anodizing on 7075? Pictures maybe? Are my expectations of complete, consistent, dark black coverage too high here? Just trying to see if I'm out of line.

Thanks,
TK
 
What type of Anodize I , II or III ? Did they know the material Type was 7075 before they started? You may also have caused some issue with the bead blasting I'm sure their was glass partials left in the aluminum.
 
Type II and yes they knew the material before hand.

It seems some of the grayness comes off after washing with a bit of water and elbow grease. Does anyone wash their parts after anodize? If so, in what?
 
Looks like you answered your own question right there. I send relatively high volumes of parts to anodizing, we never blast, just parts washer, thorough dry then straight into shipping box. Parts come back looking beautiful for the most part.
 
Do you need a flat finish. If so the Anodizer can probably etch them longer during the prep process. This will dull down the finish.
I have seen it called out as Matt Black. Mainly for optical parts.
 
I forgot to say. If you are going blast you might be better of using Aluminum Oxide. Again our company would do this when they
were optical parts that they didn't want a possibility of reflection.
 
I've anodized my share of AR receivers from 7075 forgings. My experience is that anodizers are becoming like custom bike painters these days. Sketchers and tweakers. Make sure they know what 7075 is. Make sure they know how to properly clean and rinse. Make sure they know what type and size blast media to use. Make sure they know how to clean it all off afterwards. And make real good and sure they know to not leave the f$^k|ng receiver ( oops... "part" ) in the bath forever so you don't end up with .005" - .007" thick coatings that require re-reaming to assemble. Personally, I always wash things when I get them back. With "these" kinds of "parts" I also give'm a hand rub of oil afterwards, as well.

10th_MTN_1_small.jpg
 
What kind of oil are you using?


I've anodized my share of AR receivers from 7075 forgings. My experience is that anodizers are becoming like custom bike painters these days. Sketchers and tweakers. Make sure they know what 7075 is. Make sure they know how to properly clean and rinse. Make sure they know what type and size blast media to use. Make sure they know how to clean it all off afterwards. And make real good and sure they know to not leave the f$^k|ng receiver ( oops... "part" ) in the bath forever so you don't end up with .005" - .007" thick coatings that require re-reaming to assemble. Personally, I always wash things when I get them back. With "these" kinds of "parts" I also give'm a hand rub of oil afterwards, as well.

View attachment 104436
 
Zahnrad... just out of curiosity, what are you charged to anodize that AR. Looks great.

I wanna say _around_ $35 but I can't recall at the moment, and frankly it doesn't matter because I have not found anyone I like, nearby. That one had to be gone over extensively due to WAYYYYYYYY too much coverage. It really sucked because I thread mill my buffer threads and don't even have that tap, so cleaning them out was a real PITA that I'll not forget ( or forgive ) too soon. It used to be easy to find a good Ano guy. Anymore? Not so much... And if you do find one, then you gotta see if they're "friendly"... Ack. :scratchchin:

What kind of oil are you using?

Hoppe's and CLP. :)
 
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Did you do the machining? If so, I was under the impression that shop build firearms could not be sent off for any work. Don't know where I read that but I have one I build from bar stock I would love to have ano by a pro. :drool5: I tried my self with results similar to the op. I ended up cerakoting it but I also have a 1911 from bar stock almost done and don't really want to try again.
 
I have a Lot of 7075 T7 and 7050 T7 parts type II hardcoated. We've had lots of trouble with our ano guy too, as some of the parts come back extremely Matte finished. They have to sometimes re-etch or over etch the parts I guess. Problem with this is that It takes away too much material and = out of tolerance parts :willy_nilly:

I know a guy that drives three hours away just to get a guy that know his sh!t on anodizing...
 
Currently battling the same problem.

Troyk: glass beads can fracture and embed and cause finish probs. We tumble in a big tumbler, then rinse and send to ano.

good anodizers are hard to find, totally agree. Type 3 hard is all we get done, and since moving to colorado, cannnot find anyone worthwhile.

First guy made a batch tungsten-grey for us. Even with a sample of deep matte black. "Oh, I didn't know you wanted it black-black." Morons, you suck. $100 / batch

Second shop didn't etch long enough to dull down the finish, and the coating was too so thin you could see changes in the black level. Even with a sample to match to. Morons! you suck too. $120 / batch

We're on our third shop now, they just let us know the batch was ready, but we didn't bother to set up an open account with them yet, because they haven't proven to us they don't suck. Now they are telling my guys they don't take credit cards, and if we send them a check for this test batch they want to hold it to clear. WTF?? Really? Morons! Put down the crack pipe and run a damn business. $125 / batch

I'm really getting frustrated with anodizers, wish we could powder coat or alodyne parts instead because I'd be first in line to tell them all to take a flying leap into the abyss. :mad5:
 
Glass beads, low pressure. Although we are in Colorado, we send our parts to Ohio, because nobody here can get it right the first time. $250 lot charge, but I don't worry about them ruining thousands of dollars worth of parts. Priceless.
 
What problems can arise from using glass bead as a blasting media?

I'm no expert in anodizing, but apparently nobody else in America is either, so I decided to do it myself on my own product line. Take the following advice at your own risk, it's just what I have observed during a long and frustrating saga.

Any kind of blasting will embed particles of the blasting material in the soft aluminum surface. As MachEng said, if you feel you have to blast, aluminum oxide is your best bet. This is because part of the prep in the anodizing line is etching; a dip in sodium hydroxide (lye) which removes the outer layer of aluminum oxide that is formed on the surface of all aluminum alloys seconds to minutes after it is cut, ground, sanded, etc.

If the blasting grit that is left behind is aluminum oxide, it has the best chance of also being removed during the etching process, but I've found it to still be hit or miss. The surface can be very splotchy and unpredictable, and the larger the area, (such as your shoebox size part) the more pronounced it can be. Extending the etching time may help this, but it does remove material, so you have to control this as well.

I gave up on blasting, and now only tumble my parts in plastic media with water running through it. The problem with your parts is the size and shape is not going to be very conducive to that, and if the have sharp corners, you're probably going to have to do them one at a time.

Since they are high dollar items, I would probably experiment a few different ways (on scrap of course). If they are flat-sided, I would try wet/dry paper spray stuck to a surface plate and lightly lap (600 grit) to remove milling marks. Then I would etch them myself to a consistent looking finish before sending off to the anodizer. You can control the temp and time in the lye to get what you want visually, plus the added benefit of being able to measure between "dunks" to see if you're going to far. If the lapping is not practical, blasting with aluminum oxide on a low pressure setting would be the next process to try.

If the grayness is coming off with elbow grease, your anodizer's sealant tank is probably getting long in the tooth. What happens is after repeated heating cycles, the desmut chemicals come out of solution, and residue is left on the parts. The good news is that it still seals fine, it just looks like crap and you do have to remove it manually. I just bought new sealer yesterday because of this. I was using food grade mineral oil on mine, but still didn't look quite right. Tell your anodizer to call U.S. Specialty Corporation (704-292-1476) and order a gallon of Specialty Ni Additive for $50.00. This way he won't have to put down his crack pipe and drain his tank, he can just dump this right in (16 oz./100 gallons I believe).

Yesterday I got a wild hair while waiting for the new sealer and used Meguire's heavy cut #4 automobile buffing compound (water based) to remove the smut, and it worked like a champ. The surface is very smooth to the touch, not polished, but with a sheen to it. This may be too much reflection for your application, but it sure does look nice.

If you do pre-etch, try and keep from handling it too much afterwards, use rubber gloves to keep fingerprints/oil off it, just in case the guy's not cleaning it too well. Clean with a non-lye based product (purple degreaser a big no-no) such as Simple Green or Dawn dishwashing liquid (or both in that order). Rinse with de-ionized or distilled or reverse osmosis water and dry before sitting it down somewhere. Setting it down wet even on a non-metal table can caused discoloration where it's been sitting a even a slight bit of water.

Hope this helps, but if this is a product you're going to be producing long-term, the best solution is to either set up your own anodizing line, or find a competent anodizer. Both are going to be a lot of work, but the last might just prove impossible.

Good Luck,

Burt
 
I'm not familiar with different types of bead blast media, but we do a lot of this where I work, where we bead blast to create a matte finish. We've always had good results. For what it's worth, our typical drawing note is:
BEAD BLAST #5 GRIT 4050 TO A UNIFORM FINISH.
 
Glass beads, low pressure. Although we are in Colorado, we send our parts to Ohio, because nobody here can get it right the first time. $250 lot charge, but I don't worry about them ruining thousands of dollars worth of parts. Priceless.

Where in Ohio?
 
I'm no expert in anodizing, but apparently nobody else in America is either, so I decided to do it myself on my own product line. Take the following advice at your own risk, it's just what I have observed during a long and frustrating saga.

Any kind of blasting will embed particles of the blasting material in the soft aluminum surface. As MachEng said, if you feel you have to blast, aluminum oxide is your best bet. This is because part of the prep in the anodizing line is etching; a dip in sodium hydroxide (lye) which removes the outer layer of aluminum oxide that is formed on the surface of all aluminum alloys seconds to minutes after it is cut, ground, sanded, etc.

If the blasting grit that is left behind is aluminum oxide, it has the best chance of also being removed during the etching process, but I've found it to still be hit or miss. The surface can be very splotchy and unpredictable, and the larger the area, (such as your shoebox size part) the more pronounced it can be. Extending the etching time may help this, but it does remove material, so you have to control this as well.

I gave up on blasting, and now only tumble my parts in plastic media with water running through it. The problem with your parts is the size and shape is not going to be very conducive to that, and if the have sharp corners, you're probably going to have to do them one at a time.

Since they are high dollar items, I would probably experiment a few different ways (on scrap of course). If they are flat-sided, I would try wet/dry paper spray stuck to a surface plate and lightly lap (600 grit) to remove milling marks. Then I would etch them myself to a consistent looking finish before sending off to the anodizer. You can control the temp and time in the lye to get what you want visually, plus the added benefit of being able to measure between "dunks" to see if you're going to far. If the lapping is not practical, blasting with aluminum oxide on a low pressure setting would be the next process to try.

If the grayness is coming off with elbow grease, your anodizer's sealant tank is probably getting long in the tooth. What happens is after repeated heating cycles, the desmut chemicals come out of solution, and residue is left on the parts. The good news is that it still seals fine, it just looks like crap and you do have to remove it manually. I just bought new sealer yesterday because of this. I was using food grade mineral oil on mine, but still didn't look quite right. Tell your anodizer to call U.S. Specialty Corporation (704-292-1476) and order a gallon of Specialty Ni Additive for $50.00. This way he won't have to put down his crack pipe and drain his tank, he can just dump this right in (16 oz./100 gallons I believe).

Yesterday I got a wild hair while waiting for the new sealer and used Meguire's heavy cut #4 automobile buffing compound (water based) to remove the smut, and it worked like a champ. The surface is very smooth to the touch, not polished, but with a sheen to it. This may be too much reflection for your application, but it sure does look nice.

If you do pre-etch, try and keep from handling it too much afterwards, use rubber gloves to keep fingerprints/oil off it, just in case the guy's not cleaning it too well. Clean with a non-lye based product (purple degreaser a big no-no) such as Simple Green or Dawn dishwashing liquid (or both in that order). Rinse with de-ionized or distilled or reverse osmosis water and dry before sitting it down somewhere. Setting it down wet even on a non-metal table can caused discoloration where it's been sitting a even a slight bit of water.

Hope this helps, but if this is a product you're going to be producing long-term, the best solution is to either set up your own anodizing line, or find a competent anodizer. Both are going to be a lot of work, but the last might just prove impossible.

Good Luck,

Burt

Thanks for the info! Years of priceless knowledge.
 








 
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