Largest-known scanning electron microscope proves big asset to Tinker

Published March 30, 2012
By Brandice J. O'Brien
72nd Air Base Wing Public Affairs

TINKER AIR FORCE BASE, Okla. -- Four-and-a-half years ago, the Oklahoma City Air Logistics Center purchased the largest-known scanning electron microscope in the world. It had been estimated the $2.2-million Ellcie, formerly Visitec, Microtechnik GmbH Mira-X large-chamber scanning electron microscope would save the Air Force approximately $1 million per year. To date, it has achieved that and then some.

"The return of investment to the Air Force exceeded expectations because we have been able to salvage components that previously would have been condemned," said Scot Roswurm, 76th Maintenance Support Squadron Metallurgical Analysis Section chief. "Now we're able to return them for use and the value lies not only in the cost of the part, but saving and salvaging strategic alloys and in sparing the supply chain the disruption of having components that are not always readily available returned to service."

Designed by a German company, the microscope stands 9 feet by 10 feet by 12 feet with an operating volume of 5 feet by 5 feet by 5 feet. The actual volume inside is 6 feet by 7 feet by 8 feet.

The chamber's generous size allows technicians to view objects and study them in ways that were previously impossible. Formerly, components were cut to 6 inches or less so they could fit in the chamber.

"What really sets it apart from the three other scanning electron microscopes we have is the size of the chamber and what we can achieve," said Karl Koch, 76 MXSS Metallurgical Analysis Section materials engineer. "In the standard chamber size you'd be lucky to fit an apple in there. Here, we can put in anything from the plane and we have the capability of looking at a large case or a spool or a complete disc from the engine, without having to cut it up and destroy it; that is the key factor."

Technicians using the large scanning-electron microscope can take a whole component, polish it and magnify it up to 100,000 times and rotate its stage 360 degrees. When finished, the component is taken out of the chamber and can be put right back on the aircraft or engine.

"We refer to it as 'inspect and fly,'" Roswurm said. "...I think it will be the future of the Air Force, to do as much as possible non-destructively."

Large-chamber scanning electron microscope operators are performing, pioneering and perfecting several non-destructive techniques. Roswurm said in the cases when an engine shows indications that it has experienced temperatures higher than its limits, technical orders have stated the item should be analyzed or scrapped. Instead of scrapping the items, the lab team can create a non-destructive replica and perform the necessary tests. By sparing the real parts, the team can save the customer thousands of dollars and determine the root of the problem. Previously, the method had only been used with certain components and certain alloy metals.

"What we sought to do is improve the turn time to evaluate these components and minimize the requirements for destructive analysis," Roswurm said. "This resource isn't just languishing on an island. It's in the context of a very well-equipped metallurgical lab with a number of instruments and a lot of educated talent that can stretch its applications even more."

Judith Freer, 76 MXSS Metallurgical Analysis Section senior engineering technician, said the microscope is here for Tinker's benefit and personnel should take advantage of its abilities.

"Tinker needs to think outside of their box and think of what we can do for them with this instrument," she said.

The 76 MXSS Metallurgical Analysis Section has analyzed compressor rotors, damaged fan blades, shafts, spacers and air seals, fan frames, nozzle segments and thermal sprayed parts. While several groups and shops use the microscope's abilities, technicians said the F100 and F101 shops are their biggest customers.

The microscope operates using a vacuum. After a component is cleaned of any excess oils or dirt, it is put in the chamber where a vacuum will pull out any moisture to minimize the interaction with air molecules. Technicians said it takes approximately 30 to 35 minutes to create the vacuum and 20 minutes to break it.

Koch said the vacuum isn't as strong as the infinite vacuum of space, but close to it. In fact, if a marshmallow were placed in the chamber, it could theoretically expand to fill the entire container.

"Air pressure at Tinker is around 14 pounds per square inch, but the air pressure inside the chamber is only 0.0000000065 PSI," Koch said. "I should point out that it really couldn't stretch that far. It's like stretching gum too far; the marshmallow would break before it reached about 2 feet tall."

On average, it takes approximately eight hours to complete a component interrogation, which does not include part cleaning, part set-up, creating or breaking the vacuum, or other preliminary procedures.

Despite its strength, the microscope is a fragile and delicate piece of equipment and must be properly cleaned. Operators must abide by the strictest of protocol procedures because even loose hair, lint or a string off of someone's coat can contaminate the machine and findings.

"We're very conscious of touching it," Freer said. "When we have it open and have a tour in here, that's our biggest fear; everyone wants to touch it. They're like kids in the candy store. It's so pretty and shiny in there and their natural instinct is to touch it, but it is a serious instrument."

Roswurm agreed.

"The instrument is constantly in use and continuously adding value to the Air Force," he said. "It has already proven to be a game changer and we anticipate it will do more as time goes on."