Keeping up with production demands is a continuous challenge in the lumber industry. To remain competitive, operations demand higher performance and lower cost of ownership for automated equipment. OEMs and timber processing end-users want solutions to the problems encountered in the harsh environment of the mills where temperatures fluctuate, dust produced from the manufacturing process damages equipment, and vibrations stress and grate machinery.

Traditionally, heavy-duty steel pneumatic cylinders were the only long-lasting hardware used in lumber production machinery. However, in the past few years, pneumatic solutions combined with lighter weight and less expensive aluminum have gained popularity and are proving to be extremely valuable for improving outputs and production, particularly in sawmills.Bosch

Mills had resisted using aluminum in the past because failure of aluminum pneumatic cylinders was common on equipment such as high-speed trim saws. This was due in part because trim saw applications involved such speed and shock load that they stressed the aluminum units to the maximum. As a result, even though aluminum cylinders were less than a quarter of the price of steel, the cost of downtime from inevitable failure made sawmill operators question their use.

This reasoning has changed recently, however, because of a process that reduces wear and tear on pneumatic cylinders. A unique combination of pneumatics, aluminum, and the concept of ideal cushioning increases cylinder longevity and performance and provides sawmills with greater savings, faster productivity and more profit.

Ideal cushioning for trim saws
Ideal cushioning is a specialized pneumatic solution developed by Bosch Rexroth Corp., Pneumatics Technology group, Lexington, Ky. Cushioning is particularly important for the fast process cycles and high kinetic-energy levels that often occur in sawmills, especially in trim saws where pneumatic cylinders are constantly driving saw blades up and down. Ideal cushioning helps accelerate lumber cutting by using a combination of lighter cylinders, elimination of excess piston movement and bounce, and quicker cycle times. In addition, less wear on the cylinders reduces the amount of maintenance and cost needed for replacement parts.

Ideal cushioning is a method of decelerating a pneumatic piston as it reaches the end of its stroke inside the cylinder. Essentially, there is no end-of-stroke bounce or end cap slamming, which is a main culprit of cylinder wear, speed, and noise. The piston velocity is at its maximum speed throughout the entire stroke sequence. Its velocity is exactly zero by the time it reaches the end cap. By reducing the piston velocity to zero speed at the end of travel, the cylinder incurs less stress. Vibration in the host structure is reduced and the total cycle time is improved, sometimes boosting machine speed by as much as 30%. In addition, the loud noise from the piston striking the cylinder’s end cap is negligible.

Calculating the amount of cushioning needed is easy to accomplish. An electronic meter, such as the Bosch Rexroth velocity time meter (VTM), allows monitoring of the piston speed and cycle times. In the past, the velocity of the piston was difficult to detect and was done by guesswork or “eyeballing.” This electronic aid, which is attached to the outside of the cylinder tube, enables the true velocity of the piston to be determined quickly and easily.

Ideal cushioning adjustment is done with a simple screwdriver and allows a free outlet flow adjusted so the piston stops right at the end cap with zero speed. Pistons are then adjusted one at a time with the first one used as a standard to conform to a maximum speed for a given pressure and cylinder load.

The end result: By knowing how to control a high-speed mass moving at a consistent speed and reducing the non-cushioned lag and bounce, the machine’s controls can be adjusted to reduce the usual program lags and thereby tighten the entire operation to increase board count. Bosch

Rexroth aluminum cylinders with ideal cushioning substantially increase speed, lower component costs, decrease downtime, reduce noise, and increase overall lumber production.