Allodining and priming empennage parts
10 hours of toxic fun
Our Dear Reader:
Many years ago, chemistry sets were real chemistry sets. They had really cool chemicals, the kind that would melt metal, fizz, or explode. Just think of it: Strontium Chloride, Sodium Cyanide, Ammonium Nitrate, Potassium Nitrate, Sulfur, powder charcoal, and for the budding nuclear weapons enthusiast, a nice little chunk of Jenny-wine Uranium.
The Good Old Days
Plenty of ingredients for some good ol’ fashioned adolescent mayhem. All gone now. Thanks to draconian regulations, unrestrained feral lawyers, and overzealous neurotic parents, the wonderful fun, art, and science of real chemistry sets of decades ago have been barbarously usurped by cartoon boxes of pretty fluids and things that make goop. It makes the well-known observation “Science is doing stuff in a lab that would be a felony to do in a garage!” sadly true.
What a sad and tragic state of affairs.
But all is not lost, we slingers can do our own chemistry fun, in our garage, in defiance of the nanny state.
What we used:
Supplies:
All Purpose Mixing Tub, 11 gal. / 1.5 cu. ft. – Tractor Supply
2 Gallons Bonderite M-CR 1201 AERO – Aircraft Spruce and Specialty
2 Gallons Bonderite C-IC 33 AERO – Aircraft Spruce and Specialty
AKZO NOBEL EPOXY PRIMER 2GAL – Aircraft Spruce and Specialty
6” PVC Pipe – Granite Supply (Groton CT)
6” PVC End Cap – Granite Supply
6″ x 6″ DWV PVC Female Adapter w/ raised plug- FW Webb (Waterford CT)
½” PVC Male MPT x S Adapter – Cash True Value Hardware (Mystic CT)
½” PVC Elbow – Cash True Value Hardware (Mystic, CT)
½” PVC Ball Valve – Cash Hardware
Tools
Rubber boots (Walmart, We had that kind of money)
¾” drill bit (Montville Hardware, Montville CT)
¾” NPT hole Tap (Montville Hardware)
Brushes
Rubber Gloves (Home depot)
Polyethylene Plastic (Cash’s true value, Mystic CT)
And now for a chemistry lesson from our Ministry of Truth and Information. Read this next bit at night, while in bed…just before you shut out the light and go to sleep.
Aluminum Sling parts had a thin itty bitty teeny microscopic layer of Aluminum Oxide. In other words, it had been corroding, even after Mike Blyth touched it. (Mon Dieu!) To get rid of it, we have to clean and etch the part. This is a bug zapper watching fun time. When the Sling Part is lovingly placed in the dilute Bonderite C-CI 33 solution, it fizzes. What fun. The phosphoric and hydrofluoric acids eat away at the aluminum oxide, Behind the scenes we have this:
Al2O3 + 2H3PO4 -> 2AlPO4 + 3H2O
And some of this:
Al2O3 + 6HF -> 2AlF3 + 3H2O
And bubbles. Lots and lots of bubbles. The kind Lt. Don Ho (C-97 pilot, USAF ret.) sang about when he wasn’t flying C-97’s. Sorta. Only our bubbles are steam not CO2 like his.
While all that is going on, the 2-Butoxyethanol is dissolving residual oil and gunk on the aluminum left after we cleaned the Sling part with the Simple Green, that isn’t really green.
After all that, the Aluminum Oxide turns into bare aluminum, and the oil is gone leaving the Sling Part plain old aluminum clean and ready for the next treatment.
Next comes the allodining. When an Aluminum Sling part is gently and reverently placed in the chromic acid bath at a pH of 2, an oxidation and reduction reaction occurs between the hexavalent chromium, which is missing 6 electrons, and the 6061 aluminum Sling part. The aluminum in the Sling part gives out 3 electrons to every chromium atom, which makes the chromium tri valent and the aluminum the same:
Cr6++ Al0 → Cr3++ Al3+
Because it happens in water, the chromium and aluminum react with hydroxide ions in the water to form hydroxides.
Cr3++ 3 HO−→ Cr(OH)3Al3++ 3 HO−→ Al(OH)3
Meanwhile, Ferric cyanide accelerates the reaction, making the aluminum and chromium react faster and faster, like throwing gas on a fire. Next, the aluminum and chromium hydroxides mix up in the water and the whole magic sauce turns into a gel that coats the whole sling part, every nook and cranny. After a few hours drying, it is tough, and corrosion resistant, just like a Jello Knox blox that sat on a saucer under your bed for a week when you were a kid.
WAKE UP!!!!!!!
Jeezum Crow! that was dull. Blah Blah Blah. Dry Rag in a desert wind dull. Boring, and a drab expanse of dribble supplanting wisdom and enlightenment. Mike Ojo would be rolling his eyes and shaking his head were he to read this.
Its just this simple:
Dunk the Sling part in the first tub. 2 to 3 minutes of fizzing later, it goes from shiny to dull aluminum. Dunk in the rinse tub. Finally, dunk in the M-CR 1201 AERO, and 2 minutes later, the piece has a gorgeous mesmerizing gold color. Don’t pawn it. It’s not worth it. Trust us.
Now for the real details. We had three ways to deal with all the parts, based on how big they were. For the small parts we used mixing tubs. We followed the instructionson the jugs and mixed the C-IC 33 AERO with 3 jugs of water in a tub, and the M-CR 1201 AERO with 2 jugs of water.
as you guessed, we put water in the third tub.
We found timing the soak in each tub was important. Too short a time, and it wouldn’t get enough treatment, too long, and it would get too much and waste the chemicals. We soaked for 2 minutes in each tub, going a little longer at 2½ minutes with the last several pieces. The parts in the C-IC 33 Aero fizzed away in a stately frothy bubbling, less fun than coke and mentos, but the parts came out nicely etched into dull shine-less bland new style chemistry set gray.
Once rinsed in the water tub, the parts went into the M-CR 1201 AERO and came out beautifully golden, like the fields of waving rapeseed splashing across the Aroostook river valley.
Alodinin’ and Lovin’ it!
With the small parts through the Midas slog, our attention turned to the spars.
The spar pieces were too long to fit in the tub, and trying to find a larger tub was both expensive in tub and in alodine solution. So, we came up with a wonderful clever Third World scheme of using tanks made from 6=inch PVC pipe. We saw a version on one of the blogs (May have been for an RV-12). That version had the pipe sawn in half lengthwise and capped at both ends to make open troughs. The downside was the floor space it took and handling the solutions when done could get even more toxically messy.
Fortunately, the CT Slingers Headquarters has high ceilings, so we would go vertical to create new system, the Vertical PVC Pipe Sling Parts Allodining System (in keeping of our pledge to use acronyms, VPPSPAS). Featuring three vertical tubes with drains in the bottom and removable caps which could seal and store the nasty solutions safe and sound.
After a fevered scurry down to Granite Plumbing Supply in Groton, and some tedious redneck engineering, we had our VPPSPAS. As you can see from the photo, we made three tanks out of 6” PVC pipe, with drains at the bottom and caps at the top to make handling of the cancer agents easier. Each drain was made from ½ inch PVC tubing and valves connected to the bottom of the tanks using threaded fittings. We are pleased to say we had no leaks, hopefully we’ll have the same success when we assemble the fuel tanks.
To save space, we to set these up vertically by mounting them to the side of the Sling Parts Drying Rack with a holder we made out of 2x 6’s and plywood braces. You can see in the photo how we put it together.
To keep the whole thing from toppling over from the Howard Taft weight of the fully filled VPPSPAS, we installed an aesthetically pleasing tub of rocks in the bottom of the SPDR. The whole setup looked elegant, real Ghetto Industrial, especially with the brawny red strap accessory holding it all together.
We should get a patent.
We filled the tubes to about 5 and a half feet high with our solutions, and then proudly started the treatment. We stood on a ladder while lowering each piece into the VPPSPAS with safety wire looped through rivet holes. Sounds really clever except we had to hold them with gorilla hands fattened with the hazmat handling gloves. The wires would sometimes slip out of our sausage fingered grasp, and down it would go. It would take a herculean effort involving a Mutter museum variety of tongs, pliers, and hooks to fish them from the deep cancerous murk.
In the end, we got the spars through to process without getting cancer or our hair falling out. (as of yet), so we can declare a qualified victory, even with doing the circus act on the ladder with all the toxic nasties dripping all over the tubes.
And then the skins. How do we do the skins. We didn’t have a big enough vat to immerse them in. The only solution was to do the brush on technique the way they say in the directions, with the adamant demand to not let the M-CR 1201 AERO dry out during treatment. Right. Don’t let it dry out. Of course, the directions didn’t say why we needed to keep it wet. Whatever the reason, it must be too catastrophic to reveal. all the more reason to keep it wet. Our zeal with the whole “Don’t Let It Dry Out!!!!!” thing led us to believe we needed to keep brushing for 2 minutes, the nominal time for treatment. This rigid interpretation and implementation of the rules yielded less than desirable results.
It all started out innocently enough. Instead of using the diluted solution, we used it straight up, pouring a half gallon into the mixing tub. We stood the skin up on the edged of the tub, and since the skins are designed to fold over the whole frame of the empennage component, we had to spread them apart to deal with the interior and went to work with some cheap brushes that we had on hand. Good thing none of this would hang in the Louvre.
We dipped the brushes in the Fizzy C-IC 33 AERO acid prep and started in with the brushing. it was brush, brush, brush, keep it wet for 2 minutes, brush, brush, brush, brush in earnest, ye lowly swab! Got to keep it wet! Then rinsed and started in with the M-CR 1201 AERO for 2 minutes, keep brushing, keep it wet! the admonishment burned into our brains. And therein was what caused the problem.
All the brushing was preventing the allodine from reacting with the aluminum. The result was an inelegant streaking all over the surface. Similar in appearance to tiger stripes, not on the tiger, but those left on the idiot who found out whether it hurt to pet a kitty the wrong way. We eventually learned that by backing off on the frenzied brushing, and just brushing the solutions on and waited, there was a huge reduction in streaking. We decided to live with all the streaked pieces, perfection is the enemy progress.
Next: Prime Time