Tinker has largest electroplating shop in DOD
By Mike W. Ray, 72nd Air Base Wing Public Affairs
/ Published July 26, 2013
TINKER AIR FORCE BASE, Okla. -- Almost every part on a U.S. Air Force jet aircraft engine has a thin coat of plating or plasma spray on it, and that process is performed here at what is billed as the largest electroplating shop in the Department of Defense.
According to John Foster, Special Processes Flight Chief in the 548th Propulsion Maintenance Squadron, electroplating -- affixing a thin layer of metal onto a metal object -- is undertaken for three reasons: "dimensional recovery" to restore thickness that has worn away, corrosion prevention, and/or to prepare a metal surface for paint.
An electroplating layer is mere thousandths of an inch thick. For example, a part left in a chrome plating tank will increase in thickness by about one-thousandth of an inch per hour, Foster said.
Hard chrome plating is just one type of electroplating performed at Tinker. Others include soft nickel, hard nickel, electroless nickel, zinc nickel, nickel on titanium, specialized nickel, Borazon, Alodine, black oxide, passivate magnesium chromate, and silver.
"We do a lot of silver plating," Foster said, "mostly for anti-gall purposes" to act as a lubricating surface.
Borazon, an expensive process, is used to prepare a cutting surface on knife-edge seals.
"We do this on rotating air seals on high-pressure turbines," Foster said.
Chrome is used "if we need to restore dimension," while Alodine and zinc nickel are utilized primarily for corrosion prevention or for paint preparation. "Air Force planes fly through sandy and salty atmospheres," Foster noted.
Before a new coating is added, the existing coating -- which could be chrome, nickel, cadmium, plasma spray, etc. -- must first be stripped off. To do that, the part is submerged into an acid or alkaline bath based upon the coating to be stripped and the base metal.
Prior to a part being plated, the area on the part where the electroplating will be applied is masked off with lead or vinyl tape -- a tedious process -- and then the entire part is dipped into a vat filled with liquid beeswax.
Afterward, the tape is removed and the exposed area is electroplated. After plating, the part is dipped into a hotter-wax tank to melt away most of the wax, then dipped in a chemical solution to remove whatever wax remains. Finally, the part is rinsed off and returned to supply chain.
The electroplating shop "turns" approximately 150 parts per workday, Foster said.
Much of the industrial by-product from the electroplating process is recycled.
The shop houses approximately 130 tanks, each capable of holding about 1,000 gallons of liquid solution. The electroplating shop has its own wastewater plant that pre-treats approximately 30,000 gallons of wastewater each day.
"We remove the heavy metals and neutralize the acidity/alkalinity," Foster said, before piping the water to Tinker's Industrial Wastewater Treatment Plant.
Wax recovered from the shop's vats "can last for 8 to 15 years," and some of the beeswax used in the shop is finally being replaced after 25 years of continuous use and reuse, Foster said. "We recycle 90 percent of the wax," he said.
At one time the electroplating shop ran three eight-hour shifts, but now it operates one shift per day of about 30 workers.