Machinist fabricates parts for gate repair
A machinist at the Tennessee Valley Authority’s Power Service Shops in Muscle Shoals is fabricating parts needed to repair gates on the downstream side of Wilson Lock.
Barge tows have been backed up since September, waiting to pass through the twotier auxiliary lock at the dam since the U.S. Army Corps of Engineers closed the larger main lock due to damage to a hinge at the bottom of the lock gate.
Members of the U.S. Corps of Engineers assessed the situation and dewatered the lock to be able to make the necessary repairs.
The main Wilson Lock, which was completed in 1959, is 110 feet by 600 feet with a 115-foot-tall gate, making it one of the largest lift locks in the country, according to TVA.
In September, operators with the U.S. Army Corps of Engineers reported hearing noises and vibrations, then reached out to the Power Services Shops, according to an article in TVA. com.
TVA said inspections revealed gate damage that included a hinge at the bottom of the gate. In addition to carrying most of the weight, the bottom hinge also acts as a seal, preventing the lock from emptying while in use, the article stated.
Apparently, decades of wear and tear rendered the hinge inoperable, so the Power Service Shops team began drafting a plan.
Instead of going back to the drawing board, Machine Tool Specialist Joseph Hardwick said they would use the same specifications and tolerances as the original design fabricated in the 1950s. They even have the original handwritten blueprints.
“The first thing we did was create a 3D model of the components,” Hardwick said.
Utilizing a 3D printer, Hardwick and his team were able to create a scaled-down model of each component for visual reference.
Then they were able to begin generating a toolpath, a set of programming instructions for the fabrication process.
The pintle casting was fabricated from a rectangular block of steel, according to the article.
The pintle bushing, installed and nested into the casting, was made from leaded bronze, a material that exhibits qualities of lubricity when paired with a hardened steel. Lubricity means the quality of being smooth or slippery, or the ability to reduce friction.
The pintle ball, the hardened steel counterpart, rests inside the bushing like a ballpoint pen.
TVA said this heattreated steel provides a better wear surface and is more resistant to movement fatigue. And finally, there’s the pintle base, a steel piece on which the ball will glide.
Up next is machining, a process in which these blocks of steel will be shaped into components with tolerances measured in microns, thinner than a strand of hair.
The components will also undergo nondestructive examination testing to verify that the material is not defective. Using ultrasonic sound waves, this testing detects any flaws that are imperceptible to the human eye.
The main chamber of the lock remains inoperable due to the repairs. The Corps of Engineers estimates the repairs will be completed in June.
TVA said more than 3,700 vessels pass through Wilson Lock each year, carrying freight along the Tennessee River.
