Tinker bearing shop supports wide range of weapons systems

  • Published
  • By Mike W. Ray
  • Staff Writer
Aeronautical antifriction bearings, as well as aircraft engine, gearbox and instrument bearings, are critical to the operation of jet aircraft and are pricey. Consequently, the Air Force has implemented an initiative to get as much use as possible from each bearing it has.

Accordingly, the 76th Commodities Maintenance Group's bearing shop in Bldg. 3001 supports a wide range of weapons systems, said Warren "Todd" Taylor, acting supervisor of the shop. The Bearing Shop handles in excess of 150 stock numbers, he said.

Shop personnel clean, inspect, measure, preserve and package a variety of aircraft bearings, including gearbox bearings, F118 main bearings, TF33 turbofan engine main bearings, F108 main bearings, three sizes of KC-135 aerial refueling boom bearings, F101 main bearings, C-5 thrust bearings, F107 missile bearings, F110 main bearings, and bearings from the F118 engine, a derivative of the F110.

The Bearing Shop also handles wheel bearings from three types of aircraft: E-3 AWACS planes, KC-135 tankers, and Navy E-6 Mercurys. The shop receives 100 to 150 AWACS wheel bearings "every month or so," on average, because of the constant use of the aircraft, Mr. Taylor said. A set of wheel bearings from E-6s comes into the shop every couple of weeks. KC-135 wheel bearings arrive in "constant rotation."

F107 missile bearings are "some of the smallest bearings we service," Mr. Taylor said; they're slightly larger than a nickel. At the other extreme are F108 main bearings. "The #1 bearing from the F108 turbofan engine is the biggest and heaviest we service: 11½ inches in diameter and weighing approximately 25 pounds."

Bearings receiving attention from the 76th CMXG Bearing Shop range in price from $100 apiece to as high as $50,000. One set of eight bearings from a B-52 engine gearbox costs $12,600. Most of the bearings processed by Tinker's Bearing Shop cost about $2,000 each, on average, according to Nick Willis, management specialist in the Partnership Office of the Oklahoma City Air Logistics Complex Business Office.

Most of the bearings routed to the shop are removed from aircraft that are admitted to the OC-ALC for scheduled depot maintenance. However, Mr. Taylor said, about 20 percent of the bearings they receive and inspect are new.

The shop processed approximately 13,000 bearings in Fiscal Year 2012, Mr. Taylor said, and, "We expect to do approximately 15,000 by the end of this fiscal year" on Sept. 30. Moreover, he added, "This is being done while our people have been training" on several pieces of sophisticated new equipment, including a bearing analyzer.

Whether new or used, bearings sent to the shop are subjected to a five-step process. First they are received from the customer, then they go through:

· Identification. Upon arrival at the shop, the bearings and the work control documents that accompany them are screened "to ensure that we have the right paperwork for each particular bearing," Mr. Taylor said.

· Cleaning. Bearings received from Tinker's engine rebuild shops are subjected to a wash in 170- degree sodium hydroxide, which eats away carbon that accumulates on used bearings. The bearings are then cold-water rinsed in sodium nitrate, which neutralizes the sodium hydroxide, followed by a three-stage solvent rinse. Shop personnel also use a 140- degree high-pressure wash system on aircraft wheel bearings to remove grease; the process includes a 160- degree rinse cycle that employs a rust inhibitor.

Tai Le, Bearing Shop engineer, said all of the shop's tanks are tested and certified weekly. Their chemical properties are analyzed and their particle counts are measured; excess particles are filtered to avoid contaminating any bearings.
· Inspection and measurement.

Next the bearings are sent to a Class 100,000 "clean room" that encompasses approximately 8,000 square feet of space in Bldg. 3001.

After a bearing is cleaned but before it's examined, it spends a couple of hours sitting in the clean room so it can thermally stabilize to the environment, which is held at 72 degrees (+/- 5 degrees) and 30-50 percent humidity. Temperature affects the expansion or contraction of a bearing, while the humidity has a direct effect on the static electricity within the room.

The clean room is access-, climate- and pressure-controlled. "We don't want thermal expansion or contraction to affect the measurements and risk introducing foreign particles and foreign object debris that could lead to premature failure of the bearing," explained Mr. Le. Anyone entering the room is required to don a hair net, paper booties, a paper mask and a lab coat. The cleanroom is tested and certified by the lab monthly for particulate count and to ensure compliance with requirements.

The shop's six technicians use 10X magnifying lenses to inspect the bearings. A thorough inspection takes about an hour and a half to perform, Mr. Taylor said, "because we have to inspect all the active and inactive surfaces of each bearing."

Besides being inspected, each bearing is subjected to various measurements, such as its inside and outside diameters. Some also receive an additional internal radial clearance measurement that calculates the wear patterns of the rolling element.

Bearings are demagnetized at multiple points during the cleaning and measurement process. A bearing is demagnetized prior to cleaning, for example, to ensure that small particles will not cling to the unit while it's being cleaned. Handling, moving and spinning a bearing "will introduce a slight magnetic field," onto a bearing, Mr. Le said. Even the act of rubbing a bearing will create a static charge field, he said.
· Preservation and packaging.

After being cleaned, inspected and measured, the bearings are sent through a preservation process that consists of a fingerprint removal tank and a dry-cleaning solvent rinse, and then the bearing is oven-dried. Afterward, a preservation oil is applied to each bearing to prevent any corrosion before the part reaches the customer. "Our technicians wear protective gloves to mitigate the chance of transferring body oil to a bearing," which can cause corrosion," Mr. Le noted. Any acidic residue can adversely affect a bearing, Mr. Taylor said.

In the final step, each bearing is inserted into a special anti-static, plastic, zip-lock bag, then placed in a foil package that's vacuum-packed and sealed to remove excess air and any contaminants. After an identifying label is affixed, the packaged bearing is then shipped back to the customer.

The typical turnaround time for the Bearing Shop is eight to 10 days, Mr. Taylor said.