Cylinder and VTM

Enhancing Sawmill Performance with “Ideally” Cushioned Aluminum Cylinders

Air cylinders with ideal cushioning reduce or eliminate the heavy shock, noise, and reduced service life associated with high cycle rates without sacrificing productivity.

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Pneumatics technology continues to be a valuable player in many types of industrial automation applications. When OEMs need reliable components, a compact design, and low-maintenance technology to actuate machinery, pneumatics can be trusted to deliver steadfast and long-lasting operation even in very difficult and dirty environments.

Modern sawmills are perfect examples for this type of application. Mill operators seek the highest throughput rates possible, with machine downtimes kept to a minimum—and that requires heavy-duty machines with components engineered for durable, repeatable performance.

Baxley Equipment Co. is a leading supplier of sawmill technology to the North American lumber industry, providing a broad range of products and complete systems such trimmers, sorters, stackers, feeders, and edgers. Weve used Aventics aluminum cylinders with ideal cushioning technology in our trimmers and sorters for several years, and we’ve found them to be superior to other cylinders on the market.

Ideal cushioning, combined with the lighter weight and relatively lower cost of aluminum pneumatic cylinders (compared to steel construction), allows Baxley Equipment to supply highly competitive trimmers that accelerate lumber processing while reducing excess piston movement and bounce.

Reliability in Demanding Sawmill Environments

“The sawmill environment can be brutal on machinery: Wide temperature fluctuations are common, dust from the manufacturing process damages equipment, and vibrations stress and grate machinery,” says Jim Apel, Aventics district sales manager. “In the past, heavy-duty steel pneumatic cylinders were preferred for lumber production machinery. Many mill operators felt that the speed of equipment like planar mill trimmers and sawmill trimmers, combined with harsh conditions, required steel cylinders.” More recently, that preference has changed.

“Sawmills are always striving to produce more lugs per minute. Working with companies like Baxley, we’ve shown that our medium-duty TRB ISO 15552 aluminum cylinders with ideal cushioning technology do just that,” Apel adds. “In fact, our cylinders allow the trimmers to actuate faster than they did with steel cylinders, and they last longer.”

We use Aventics TRB ISO 15552 cylinders with ideal cushioning on two key types of equipment: high-speed sawmill trimmers, and sorter systems, which separate and stack finished lumber according to length. Both systems operate at very high throughput rates, and the cylinders actuate key movements on both systems.

The Aventics velocity time meter (VTM), allows precise monitoring of the piston speed and cycle times, eliminating any guesswork used to set the cushioning.

In the sawmill trimmer, we use cylinders with 100 mm and 125 mm bores with various strokes. The cylinders actuate the saws that trim boards in lugs to the desired length. Standard trimmers have between nine and 11 saws, controlled by a PLC.

The saws are spaced approximately 2 ft apart; two saws drop down in tandem between boards in lugs. One cuts the forward, or zero end, and the other cuts the board to the desired length, ranging from 6 to 24 ft.

Throughput ranges from 120 to 200 lugs per minute, and we have engineered our latest-generation trimmers to operate with very tight intervals between each board—26 in. from the trailing edge of one board to the next. This means the cycle time for the saws to drop, cut, and retract is ultra-tight—120 msec or less is the usual cycle time. Each cylinder is paired with an Aventics Series 581 ISO directional control valve with integral flow control. The 581 ISO valve is one of Aventics’ fastest valves, with PTFE-encapsulated O-rings with low friction so they can keep up with the trimmer’s high cycle rates.

At the speeds we run now, other cylinder designs can’t go that fast and wouldn’t hold up. With the Aventics cylinders and Ideal Cushioning we can do that, and with almost no downtime related to cylinder failure.

Ideal Cushioning adjustments are made with a standard screwdriver (as shown on this PRA-type pneumatic cylinder) so that the piston stops right at the end cap with zero speed.

Ideal Cushioning Improves Cylinder Efficiency

“Aventics developed ideal cushioning to significantly improve the efficiency of pneumatic cylinders and lengthen their operating life,” says Apel. “It’s a method of decelerating the 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—a main source of cylinder wear, slowness, and noise. To achieve ideal cushioning, the cylinders must physically have superior cushioning capability.

“With ideal cushioning, the piston velocity is at its maximum speed throughout the entire stroke sequence,” he continues. “Its velocity is exactly zero by the time it reaches the end cap. By reducing the piston velocity to zero 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%.”

Ideal Cushioning, combined with the lighter weight and relatively lower cost of aluminum cylinders (compared to steel construction), lets us supply our customers highly competitive trimmers that accelerate lumber processing while reducing excess piston movement and bounce. In addition, less wear on the cylinders reduces the amount of maintenance and cost needed for replacement parts.

The Aventics medium-duty TRB aluminum cylinders with Ideal Cushioning technology allow the trimmers to actuate faster than they did with steel cylinders, plus they last longer.

Sorter Systems Help Maximize Productivity

We provide similar operational advantages in our sorter systems, which also use Aventics cylinders and valves. These high-speed, large-scale systems automatically sort thousands of finished boards into stacks or packages for warehousing and shipping. One of our sorters can have from 15 to as many as 100 bays. Conveyor chains push finished, trimmed boards through the sorter. When a specific size board reaches the corresponding bay in the sorter, a tipple, actuated by an Aventics TRB cylinder, opens the space to drop the board onto the bay. It then closes, allowing the next board in line to pass through the sorter to reach the correct bay.

Actuation time is even more critical and faster on the sorter. We typically need to open and close the tipple in about 90 msec. Each bay in the sorter has one pneumatic cylinder, so our largest machines can have up to 100 pneumatic cylinders. On the sorters, each cylinder is paired with an Aventics Series 740 directional control valve with integrated flow control. These lightweight valves can be installed close to the cylinder, rather than on it, eliminating the need to add flow control to the cylinder and keeping weight to a minimum.

We use Aventics cylinders on the sorter for the same reason we use them on the trimmers: reliability and speed. We’ve had a really good experience with them, and I know of Baxley machines that have been running in mills for several years without cylinder failure.

The trimmer uses Aventics Series 581 ISO directional control valves with integral flow control. This valve uses PTFE-encapsulated O-rings to reduce friction compared to standard O-rings.

User-Friendly Cylinder Set-up Tools

Apel explains that Aventics provides a range of tools to help companies like Baxley select the right cylinder for a given application, and then easily set the cycle time and cushioning to achieve an “ideal” state: “Calculating the amount of cushioning needed is a straightforward process. The Aventics velocity time meter (VTM), allows precise monitoring of the piston speed and cycle times, eliminating any guesswork used to set the cushioning.

“The VTM is attached to the outside of the cylinder tube and enables the true velocity of the piston to be determined quickly and easily,” he continues. “Adjustments are made with a standard screwdriver to stop the piston right at the end cap with zero speed.”

The sorter machine uses Aventics Series 740 directional control valves with integrated flow control. These lightweight valves can be installed close to the cylinder, rather than on it, eliminating the need to add flow control to the cylinder and keeping weight to a minimum.

We typically set the trimmer cushioning using these tools before the trimmer is shipped to the customer’s mill. Because the sorters are assembled on-site, we provide a start-up service to configure the cylinders and ensure the cushioning is set correctly.

Both the speed and reliability of the Aventics products give us a competitive edge with mill operators who need maximum throughput and minimum downtime. We’re using cylinders and valves that can operate faster than other brands we've tried, which allows us to design faster systems. If we didn’t have the technology and components to run that fast, it would be more challenging to build systems that fully satisfy our customer’s requirements.

Tommy Green is chief engineer at Baxley Equipment Co., a division of Timber Automation LLC, Hot Springs, Ark. For more information on Aventics products and services, click here.

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