Lumber processing technology has come a long way and requires attention to achieve precision and speed. To stay competitive as lumber demand increases, industry expert Carl Dyke shares guidance on how to keep sawmill hydraulic systems running optimally.
Digital technology paired with powerful hydraulics turns nonuniform logs into precisely sized, quality lumber. Image: Adobe Stock
As part of its Timber Products Output (TPO) mill survey, the U.S. Department of Agriculture’s Forest Service reported that in 2018, approximately 4,624 sawmills across 41 states processed 12,083,025 mcf of roundwood products. Of that data, 13 states with about 1,665 sawmills processed 8,693,063 mcf of roundwood, accounting for nearly 72% of the year’s total. In 2022, numbers for those same 13 states dropped to 1,565 sawmills processing 8,354,893 mcf. Though the number of sawmills decreased, the average processing volume across the mills increased slightly. (At the time of this article, only 13 states reported data for 2022.)
Any market forecast report predicts that lumber demand will increase, further straining the mills and increasing competition within the industry. To meet lumber quality demands economically, many industrial sawmill owners use optimization scanners and software to plan and cut logs to yield as much value lumber as possible. They also turn to advanced hydraulics to increase cutting speed and precision.
“Hydraulics for the sawmill is an interesting topic that I don’t think a lot of people appreciate,” said Carl Dyke, hydraulics expert and founder of CD Industrial Group. “If you go to your local lumberyard and buy two-by-fours, sheets of plywood, or some type of sheathing wood, you might wonder: How did it go from being a tree in the forest to such a precision-sized, quality-controlled item? And the involvement with hydraulics, I don’t think many people know that robotic precision is involved now.”
Dyke grew up in forests and mills and describes those days as slow and rough. At the time, sawmill owners weren’t overly concerned with accuracy or optimal fiber usage. Supply was plentiful, so errors could be corrected with the next log, and waste pieces were piled up for folks to purchase off-grade lumber some other day. Neither processes nor technology needed to be perfect for a sawmill to profit.
“The hydraulics were crude back then,” he said. “Sometimes, the hydraulic valves were directly operated, and we didn’t worry too much about sawdust, dirt, and pine needles in the hydraulic oil because we had the force of our big strong arms to push and pull on the levers and drive the spool through the valve body. We weren’t talking about contamination issues back then. We weren’t looking for that level of precision. It wasn’t available in the hydraulic valves. Internal leakage wasn’t really anything people worried about nor the efficiency of the hydraulic system. Of course, that all changed to a large degree, as it needed to.”
Today’s industrial sawmills use advanced technology, including hydraulic valves and sensors derived from military fighter jet aircraft and helicopter gunships. Sensors inside the valves help equipment move quickly and precisely to ensure optimal lumber quality and maximum value from each log. Setworks systems command equipment into action immediately, requiring hydraulic servovalves to open and send oil to hydraulic cylinders that position cutter heads or feeding devices. Magnetostrictive or Hall effect transducers inside the cylinders ensure precise positioning, and valves must shut quickly to hold the position for a perfectly calculated cut.
“It’s got to happen so fast that it’s dizzying for the casual observer looking down at the production line from the catwalks overhead,” said Dyke.
A magnetostrictive linear displacement sensor inside this hydraulic cylinder ensures precise positioning. Image: CD Industrial Group
It’s clear that modern hydraulics play a critical role in sawmill speed and precision, which directly influences profit. Therefore, owners and workers must prioritize monitoring and maintaining hydraulic components. Dyke shares six things every sawmill should do to optimize production.
1. Keep the equipment clean
Ideally, a hydraulic power unit should be separated from the machine to avoid contamination. However, units are typically placed under the machines and continually collecting sawdust. Dyke admits, it’s easy for operators to forget or not have time to clean the debris covering all the machinery.
“I’ve yet to visit a sawmill where there isn’t sawdust in the hydraulic oil,” he said. “Nobody’s shocked about that because it’s hard to keep it out. The fiber gets in there, so you have to work hard at filtration. Hydraulic systems, especially servovalves, many of which came from the world of aircraft, are only meant to work with a pure liquid, not a slurry. A slurry is a liquid that has a lot of solids in it. And as soon as you depart from a pure liquid, you’ve challenged how well they work.”
Many manufacturers place a straining screen inside the servovalve to catch large contaminants that can seize the valve’s internal elements. However, smaller contaminants are harder to keep out, requiring conscientious maintenance work habits and carefully selected breather filters. As small material accumulates, it degrades the valve’s performance and, consequently, the machine’s performance.
2. Continuously monitor hydraulic fluid
Though advanced sensors and real-time condition-monitoring technology have become more widely available at more reasonable prices, many sawmills still perform minimal maintenance on set schedules.
“I’m always looking to see if somebody has written with a sharpie on the filter when they last changed it,” said Dyke. “It’s still popular in so much heavy industry to only change hydraulic oil filters based on time. They may change it every six months or every year. If they do that with some degree of consistency, then at least they have that, but much better, of course, is to monitor the condition of the hydraulic fluid either by sampling more frequently or by some type of real-time particle contamination monitor.”
Real-time data on hydraulic fluid is invaluable. It’s unlikely that sawmill owners will apply such technology to every hydraulic system, but it should be installed on critical systems for which precision, reliability, and speed are vital. Instead of annual filter changes, continuously measuring and monitoring the quality of hydraulic fluid is the best approach.
Sawdust constantly accumulates on hydraulics components, making fluid cleanliness an ongoing challenge. Image: CD Industrial Group
3. Monitor the filter pressure differential
Standard pop-up differential pressure indicators and switches visually indicate when a hydraulic filter is plugged with contaminants and needs to be replaced. But by the time the indicator pops out and someone notices, it could be too late.
“That requires somebody constantly paying attention. Whereas, for not too much more money, you can have a filter housing with a sensor that lets you keep track of just how plugged up that filter is getting,” said Dyke. “And the same programmable controller that optimizes positions for lumber cutting can be on a side channel at a lower priority level. That same controller can sample once every five minutes, look at that filter, and update the data on how plugged up it is.”
With more filter monitoring options than ever and sensor prices much lower than 20 years ago, keeping a close watch is increasingly easier. There’s abundant modern technology to help sawmill operators keep track and avoid unplanned downtime.
4. Install test points
Numerous issues can result when hydraulic pressure valves don’t react quickly or aren’t adjusted correctly, even if they’re designed for high shock loads. For example, machine welds can break, electrical connections can loosen off sensors, and seals on the rod end of a cylinder or the shaft end of a hydraulic motor can leak.
“It’s a rugged environment,” said Dyke. “I’ve yet to be in a sawmill that isn’t absolutely shaking, everywhere you go. The entire frame of the main production line is always vibrating and shaking. There are a lot of shock loads involved because trees and logs are not uniform, and they exert their own push-back forces as you cut them. They spring on their own as the fiber is cut and you push them around. There are a lot of shock forces at work.”
The last thing anyone wants is breakdowns and unplanned events. Operators can lower such risks by keeping track of the hydraulics and machinery’s runtime conditions, including pressure and temperature. However, monitoring equipment, such as pressure gauges, also runs the risk of damage from projectile lumber.
“I don’t really recommend that you keep installing the standard $30, two-and-a-half-inch pressure gauge. In a sawmill, every time you install a gauge like that, lumber finds a new way to fall off the line and smash that gauge out of existence,” said Dyke. “But installing test points that are so popular — the global standard M16x2 test point connection — allows the maintenance worker to walk up to that test point with a well-adjusted digital pressure gauge, connect to it, take a reading, and write down that value.”
5. Monitor cylinder cycle times
To reiterate, sawmills aim for speed and precision to produce as much high-value lumber as possible.
“To be that fast, hydraulic fluid flow rates must be high speed — how many gallons per minute or liters per minute can be moved,” said Dyke. “Then you must provide the forces, so you need a large piston in the cylinder, and the pressure oil is working against a large surface area, but you must move a high volume and get the speed as well. So, there’s demand for a lot of power from the prime mover.”
Cutter head and saw positioning hydraulic cylinders require high-speed and high-volume fluid flow rates. Image: CD Industrial Group
Dyke joked about maintenance technicians in white lab coats walking up to equipment with charts like doctors recording patient vitals during office visits. No one in a sawmill would ever wear a white lab coat, but there is value in regular “checkups” and writing down data.
“I was with a sawmill crew recently, and we talked about how important it is to watch the cycle time of cylinders. You can get out your stopwatch — your $1,200 stopwatch that we all have on our belts — and time the cylinder cycle time. Keep track of how long it takes at its highest speed to extend to the end of stroke and come back, at least on a weekly basis.”
Overall, Dyke said mills monitoring temperatures, pressures, cylinder cycle times, and the hydraulic fluid condition have a big head start.
6. Watch the electrical current
Sawmills often monitor the electrical current to the cutter head motors as an indicator of the saw blades’ sharpness. If the electrical current increases, the blades could be dulling, and maintenance may need to replace them with a sharp set.
Hydraulic components such as pumps, valves, and cylinders must withstand heavy shock loads as logs and lumber pieces exert forces during cutting and trimming.
“Applying those same current monitoring transformers to the electric motors that run the hydraulics system also pays off,” said Dyke. “It lets you know that something is changing. If the current is going up, you might think, ‘That’s odd. Did somebody increase the pressure setting? We don’t usually achieve that level of electrical current turning the pump. What’s changed there?’ Whereas if the current is going down, hydraulic oil is hot, and the viscosity of it is lower. So, some things can be easily learned with sensors that aid the maintenance department and help ward off surprises and breakdowns.”
Additionally, with all the shock loading, electrical current can help workers identify weak points where heavier-duty hydraulic cylinders may be needed.
“If you were cutting thin and light logs one year, and a couple years later, you’re cutting much heavier material, maybe you didn’t design the mill for all those contingencies. So, sometimes an upgrade is called for,” said Dyke.
Dyke also noted that electrical work and all the digital technology that ensures nonuniform logs get cut with precision is mostly invisible, but essential to modern sawmills.
“Open the electrical cabinets, and the amount of LED lights blinking will enlighten you as to how many motion controllers, PLCs, and other electronics are at work in the background to process a nonuniform log, size it up quickly, and saw it for maximum value lumber products as quickly as possible,” he said. “It’s a whole ballet of automation.”
CD Industrial Group
cdiginc.com
Filed Under: Filtration/Contamination Control, News, Sensors & Gauges, servohydraulics, Valves & Manifolds