October 08, 2012
Jerome Greer Chandler Anniston, Ala.
Sometimes, repurposing proven technology can provide big payoffs. That's precisely what happened when Air France Industries KLM Engineering and Maintenance brought electron beam welding to bear on repairing a critical engine part for General Electric's CF6-80C2. The powerplant propels Boeing 747s, 767s and MD-11s.
The part in question is the fan mid-shaft tang, which comes with a list price of around $400,000, says Rene Scholten, the MRO's program manager for repair and industrialization. Contrast that with the price of an electron beam repair. That can cost $30,000-35,000 says Miranda Oele, AFI KLM E&M's program manager for aeroderivatives.
The tangs are situated on each end of the powerplant's fan mid-shaft, locking the coupling nuts on the low-pressure turbine rotor side and on the low-pressure compressor rotor side. Those tangs can crack, such as from “light impact during transportation,” says Scholten. Then, because the nut is secured with a locking ring, “We [also] suspect damage occurs during the removal of this ring. It's very tight. You have to be very cautious.”
Scholten says most of the time “the entire tang is gone.” It chips off. The maintenance manual says a maximum of two tangs can be cracked—as long as they are not located next to one another. After that, the shaft has to be scrapped—assuming there is no repair option available.
Now there is. AFI KLM E&M began fan mid-shaft tang replacement repairs employing Sciaky-built electron beam gear this past spring. The MRO did so in an application Scholten calls unique to the industry, with machines that cost roughly $2 million each.
“It's an expensive technology to establish in your repair process,” says Oele. Since spring, AFI KLM E&M has performed “something like 15 tang replacements,” she adds.