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Traditionally, equipment in rugged sawmill environments used pneumatic cylinders made of steel for their assumed ability to tolerate the debris, temperature fluctuations, vibration, and shock generated in tough applications, such as a lumber trim saw.
Today, however, aluminum pneumatic cylinders coupled with ideal cushioning provide multiple cost and performance advantages. These aluminum cylinders offer faster cycle rates at a lower overall component cost. Aluminum’s lighter weight, compared to steel — combined with the ideal cushioning’s elimination of the end-of-stroke bounce — are making aluminum cylinders increasingly competitive.
Ideal cushioning means there is no end-of-stroke bounce of the piston in the cylinder. The piston’s direction of travel is the same throughout the entire cushioning sequence, and its velocity is exactly zero when it reaches the end of its travel. This lowers the stresses on the cylinder while reducing vibration in the overall structure.
The need for speed
To meet higher production demands from its customers, sawmill equipment manufacturer USNR needed saw actuation cylinders capable of extending 90 mm in 50 milliseconds and retracting in 80 milliseconds on its Accu-Trim Trimmer highspeed trim saws. The goal was a machine capable of cutting 200 boards/min — a considerable production increase.
The company’s trim saw processes 4- to 6-in. wide boards with thicknesses from 2 to 4 in., and lengths from 6 to 10 ft. Boards pass laterally via chain conveyor through the machine for cutting. Saw blades are actuated independently in a quick down-and-up motion to trim the boards.
Aluminum cylinders offer ideal fit
After evaluating several cylinder suppliers, USNR chose Bosch Rexroth ISO/ VDMA 523 aluminum cylinders and used the cylinder’s ideal cushioning concepts. According to Tommy Green, USNR’s chief engineer for lumber handling equipment, the company initially had doubts about the durability and performance of aluminum cylinders within such a harsh, demanding environment.
“We were concerned whether the cylinders would withstand a bad cut, which can send a chunk of wood spinning out of control and really batter the trimmer,” said Green. “We were also skeptical whether or not the aluminum cylinders could perform at high speeds without wearing out from the impact shock in each cylinder.”
Green said USNR tested components from several different pneumatic suppliers to see what type of cylinder was best suited to meet the Accu-Trim’s speed and durability requirements.
“We chose this aluminum cylinder because it proved to be the best performer,” he explained. “The heavy-duty aluminum, wall thickness, and forged housing of the cylinder held up impressively well during testing. The ideal cushioning successfully dampened the shock and prevented the cylinder rod ends from breaking. All of these benefits, including an overall weight reduction from the aluminum, were remarkable given the unprecedented speed we demanded of the cylinder.”
For more information, email John Bridges at john.bridges@boschrexroth-us.com.