We are building an AK-47, and we have already bent the receiver and milled its top rails. Meanwhile, we have also restored the wood stock. Now it's time to apply a protective phosphate treatment to all the metal parts. This is called parkerizing, and it provides much better protection than the original bluing or even simple paint applied to the cheaply manufactured Kalashnikov guns.
Another page has more details on the parkerizing process, but here is an overview of the process and its application to the AK-47 project.
Parkerizing is an electrochemical process that creates an iron-phosphate layer on the outer surface of the steel, producing a grey matte finish that helps to protect from corrosion and increases wear resistance. Electrochemical does not mean that batteries and wires are involved! It refers to chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution.
Before the parkerizing chemical bath, however, the steel is bead blasted. This produces a surface that is irregular at a fine scale, better holding protective lubricant.MIL-HDBK-205A
Phosphate and Black Oxide
Coating of Ferrous Metals
The parkerizing process generally involves a phosphoric acid (H3PO4) solution with key ingredients of zinc or manganese, with varying amounts of nitrates, chlorates, and copper, the solution being heated to 88-99°C, close to the boiling point. Different metal salts in the solution produce different colors of non-reflective finish:
|Zinc||Light to medium grey|
|Manganese||Light to dark grey, or black|
|Iron||Dark grey to black|
Here we see a collection of Kalashnikov parts on a table with a variety of chemicals used in the process. The brown jug with the yellow label holds new Brownell's managanese based parkerizing solution, the white jug to its left holds used solution.
The red and white cans are spray brake cleaner, a witches' brew of light hydrocarbon solvents.
The blue and white cans with red spray caps at right are WD-40, a spray lubricant and, critical to this operation, water dispersant.
The parts have been bead blasted, yielding a nearly white matte surface due to the fine scale texture.
Notice the dark circles around the rivets on the receiver at center, the one on which the trigger guard has been riveted into place.
Those dark areas are caused by oil seeping from underneath the rivet heads. This piece needs further cleaning with brake cleaner, which will dissolve and float off all the hydrocarbon based lubricants as well as skin oil.
Wear latex gloves for all handling of the parts once you get to this stage in the process.
The red material is high-temperature RTV sealant protecting the surfaces we don't want to parkerize: the chamber and the barrel interior.
Appropriate sized cartridge cases have been used to plug the chamber and gas port, and high-temperature RTV spread around them. A cork is in the muzzle now, a soft rubber plug will be used when it is immersed in the parkerizing solution.
The RTV material is quite easy to clean off the steel when we have finished.
Here is the pan used for the barrels and receivers. It is the result of cutting the ends off two stainless pans and welding them together.
A large plank forms the base.
Steel brackets hold up burners made from black pipe, end caps, and a tee.
Small cinder blocks hold the tank above the burners.
A standard propane valve for a grill controls the gas supply to the burners.
Restaurant supply firms can be a source of the pan or pans. We couldn't find one steam table pan long enough, so this was fabricated from two medium pans.
The burner was custom made from black iron pipe, with lines of small holes drilled on a drill press.
We have filled the pan and started to heat it. We are aiming for 180°F or 82°C.
Meanwhile, a large stainless steel stock pot is used for treating the smaller parts.
A stainless steel ladle is used to lower and hold the smallest pieces in the parkerizing solution. We had drilled three 1/8" holes near its center. The end of the ladle handle can be hooked on the edge of the pot so you do not need to hold it.
Every minute or two, we raised the ladle out of the solution and swirled the liquid around within the ladle's bowl. This rearranged the small parts so that all surfaces were exposed at times.
This video shows that ladle lowering the collection of small parts into the parkerizing solution. The solution started fizzing almost as soon as the parts are submerged, as you can clearly see in the video.
The solution in the long pan has reached the target temperature. A Kalashnikov barrel is ready to be submerged. We have replaced the cork with the orange rubber stopper.
The barrel has been placed into the pan. A receiver at its upper left has been in the solution for a little longer, and it is already bubbling.
Another receiver is about to be turned over with stainless steel hemostats. We turned the parts frequently, so no surfaces rested against the bottom of the pan the entire time.
All parts were left in the solution until they stopped bubbling. Small parts were dumped into a bucket of water.
We manually rinsed large parts with a hose and sprayer.
After tap water has thoroughly flushed the parkerizing solution from the parts, they must be shaken, patted with paper towels to remove most of the water, and then sprayed thoroughly with WD-40.
WD-40 is a water-displacing lubricant spray. Its name indicates that it was the inventor's 40th attempt at devising a water displacement mixture. It's a non-volatile viscous oil diluted with a volatile hydrocarbon. The volatile solvent evaporates, leaving the oil behind on the surface.
Here is the collection of parkerized parts. Top to bottom, at left, in the first picture: the receiver cover, bolt and bolt carrier, receiver, and the butt plate, safety lever, and the long bolt mounting the pistol grip.
To the right you see the gas cylinder above the barrel, and below that are screws, pins, and a sling loop.
We did not disassemble the bolt. Were we to repeat this, we would have.
The bolt is standing on its rear end in the second picture, showing its front face and the extractor and firing pin.
Some of the glass beads remained within the bolt. The bolt would be very dangerous to use in this condition, as the firing pin could become jammed in the forward position. That would lead to a slam-fire — pull the trigger and it will fire all the rounds in the magazine as fast as it can load, fire, and cycle the bolt.
Disassemble and thoroughly clean the firing pin and interior of the bolt before continuing.
Here are the two ends of the barrel. The muzzle end of the barrel includes the front sight and gas port.
The firing chamber is in a thickened section at the rear of the barrel. This larger cylinder fits tightly into the front trunnion, and then a cross pin is pressed in to hold them together. We covered the exterior surface of this cylinder and the interior of the front trunnion using RTV.
The "G" indicating the Garda version of the Romanian PM md. 63 is still visible. This was done for the rifles of the Romanian Patriotic Guards. I will have to get some orange paint or fingernail polish...
To the last step — Final Assembly!