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Online exclusive: Pneumatic cylinders are ideal for the sawmill industry

Nov. 17, 2008
The ASM Series 140 Trimmer uses pneumatic cylinders with ideal cushioning from Bosch Rexroth to help increase cutting speed and reduce maintenance. Keeping up with production demands is a continuous challenge in the lumber industry. To ...

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.

The ASM Series 140 Trimmer uses pneumatic cylinders with ideal cushioning from Bosch Rexroth to help increase cutting speed and reduce maintenance.

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.

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.

North Florida Lumber runs the ASM Series 140 Trimmer at 140 lugs-per-minute.

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.

Opening new markets

Advanced Sawmill Machinery Equipment Inc. (ASM), Holt, Fla., worked with

Bosch Rexroth to incorporate aluminum cylinders with ideal cushioning in its series 140 trimmer. The machine builder wanted to offer faster cycle rates and more durability. “These Bosch Rexroth cylinders helped us to become very competitive with our high-speed trimmer,” explained ASM president David Seffens. “They’ve played a big role in opening up the 140 to 200 lugs/min market for us.”

The velocity time meter (VTM) enables the true velocity of the piston to be determined quickly and easily.

Seffens said that all the saw ladder surfaces on the series 140 trimmers are machined and keyed and require no alignment by the customer. The saw ladders do not pivot on the line shaft, which results in fewer bearings and longer service life. With the Bosch Rexroth cylinders, each machine leaving the shop is customized for speed at the request of the end user. “If they ask for a certain lug rate per minute we can set it up that way. Using the Bosch Rexroth cylinders and VTM measuring device we can be extremely precise so the trimmer is adjusted before going out the door,” he said. “And, there’s no alignment or adjustment needed for the saw ladder at installation, which means it can be installed quicker.”

Increasing speed
North Florida Lumber, Bristol, Fla., is one example where ASM and Bosch Rexroth improved a customer’s trim saw performance. Arthur Wilson, the company’s general manager, says the need for lighter equipment, reduced

Bosch Rexroth ISO/VDMA series cylinders with patented ideal cushioning.

downtime, and more speed played a big factor in their choice of trimmers when they were seeking to replace old equipment. The company purchased three trimmers from ASM for their saw and planer mills.

“We needed cylinders that could run fast enough,” explained Wilson, who said they were previously running 120 lugs/min. With the new trimmer he has seen substantial speed improvements, especially in the planer mill where they’re now running 140 lugs/min. “Those cylinders are fast and operate very smoothly,” he said.

Wilson said the new trimmers are expected to cut down on maintenance, too. “With our older equipment we had multiple electric motors with a lot of mass moving up and down all the time so the wear-and-tear was incredible. We constantly had to replace parts,” said Wilson. “With the new trimmers, we’ve eliminated a lot of the weight so electrical and mechanical downtime should be drastically reduced. And with the cushioned aluminum cylinders, we feel like we won’t need to replace the cylinders as much, so we don’t have to stock as many parts.”

With lighter equipment, Wilson said the company can begin using smaller blades, too. In addition, the cylinders help lower the noise of the machine. “That’s one of the things people notice is how much quieter the trimmer is,” he said.

Increasing productivity
The Valley Timbers sawmill in Antlers, OK needed improvements on an existing trimmer used for green lumber so ASM incorporated the Rexroth cylinders to help increase productivity.

“We developed a mechanical design for their trim saw so it could operate faster with lower maintenance,” explained Seffens. “They wanted to increase speed because the older design couldn’t cycle fast enough to meet the production required in today’s market.”

ASM had designed and built the original mechanical design. Seffens said Bosch Rexroth offered to put a test cylinder on the machine. The lightweight aluminum cylinders helped reduce the total swinging mass of each saw ladder, which improved ladder response.

“After running the machine through extensive testing in our shop, we found that it was better than the original design. The new cylinders allowed us to increase the trimmer speed from 120 lugs/min up to a maximum of 200 lugs/min,” said Seffens. In addition, he said the new cylinders should lower the maintenance downtime from having to replace worn out, un-cushioned cylinders.

Bill Bowlin, an industry consultant who has worked with Valley Timber making recommendations for machine design and equipment purchases, said the ASM trimmer offers several benefits. “Downtime in a mill is about

$1000 an hour,” said Bowlin. “So if a trimmer stops for some reason, the whole mill stops because all the boards have to pass through the trimmer to get out of the mill. This machine cuts the downtime and saves money. Having the ability to run faster and be more efficient is the most important aspect of being able to stay competitive in our market,” he said.

For more information, contact Bosch Rexroth Pneumatics at (859) 254-8031 or visit www.boschrexroth-us.com.

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