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Ring Debarkers Lift Fiber Recovery, Profits
Ring Debarking: Nicholson Mfg. Co.'s Technology Lifts Fiber Recovery, Profits
By Staff Writer
Date Posted: 7/1/2000
Decades ago, debarkers were not a part of most normal sawmill operations. Bark was simply sawn off of logs, and then the clean cants were sawn into lumber. The slabs, as often as not, either were burned or discarded in some other way.
That situation has changed dramatically as complete fiber recovery has become more and more important to the bottom line of a sawmill. Now, the ability to recover high value fiber from the outside of the log has made the debarker one of the most critical components in the log breakdown system of the modern mill. When value can be recovered from the outermost portion of the log, a mill can improve profitability.
With the emphasis on recovering more value from the outside of the log, however, errors in debarking that once were acceptable no longer are tolerated. Failing to fully remove bark from a log or removing too much fiber from the log in the debarking process can result in significant product devaluation and an accompanying negative impact on profits.
The best of todayís debarkers now are finely-tuned, precision machines designed to work with other mill machinery to improve fiber recovery and profitability. In the modern mill, debarkers are both figuratively and literally "at the head of the line" in terms of importance to the bottom line.
A number of debarker styles are available to the modern mill manager. Drum debarkers consist of large drums that are filled with wood. The drums rotate, and the logs bang against each other; the bark is rubbed off the stems by the combination of friction and the hammering action. Flail debarkers consist of chains or other flexible materials that are whipped against stems, similarly hammering off the bark. Cutter head or Rosser style debarkers consist of a unit in which the log is turned while a moving cutter head is applied to it.
Ring debarkers consist of a ring of cutting heads or knives that are mounted on a series of arms in a circular position; they rotate around the log as it is fed through them. The rings have a variable pressure capacity, so they relax or constrict to accommodate the different contour and diameter of each log.
Ring debarkers are quickly becoming the technology of choice for some mills, particularly those producing high value softwood and hardwood products, according to Ernie Howard, sales manager for Nicholson Manufacturing Companyís forest products division. "Applications where superior fiber protection, very clean debarking, and a steady and reliable supply of logs into the mill are the keys to increased profitability," he said.
Ring debarking technology offers the modern mill manager a powerful tool for improving profits, according to Ernie. He characterized the major benefits of Nicholson ring debarkers as: speed, reduced maintenance, improved bark removal, better chip quality, enhanced processing of crooked wood, and durability.
In terms of speed, ring debarkers usually are installed in-line with the mill, Ernie noted. "In-line processing is faster than off-line methods, such as Rosser heads," he said. "Logs are fed continuously through a ring debarker rather than being loaded into a Rosser, debarked, and unloaded back to the conveying system."
Ring debarking systems offer reduced maintenance because the tool tips on a ring system are replaceable, Ernie pointed out. Tool life varies according to the application; however, they may last weeks to months, whereas the cutter life on a Rosser head is measured in shifts, and it is common for a Rosser head to last only one shift before replacement is required.
Ring debarkers also offer significantly improved bark removal over other methods, according to Ernie. The arm and tool design of Nicholsonís equipment, he said, allows for removal of the bark at the cambium layer without damaging wood fiber; Rosser-style heads, he added, are prone to gouge the log beneath the cambium layer, damaging valuable wood.
Ring debarking technology improves chip quality because ring systems remove more bark from the wood, said Howard. With less bark residue, sawmills get higher prices for their chips and experience a lower level of rejects.
Since the quality of stems delivered to the mill has declined over time, the ability of a ring debarker system to efficiently and completely debark crooked wood has become crucial, according to Howard. "A ring debarker feed and processing system is more tolerant of crooked logs than is a Rosser system, where the log is turned and a moving head is passed along the log."
Howard also noted particular benefits that Nicholsonís ring debarking systems provide. "One of the main reasons," he said, "is that our ring technology is designed to allow arm pressures to match the log diameter." This is an important feature, he pointed out, because many ring systems have a fixed pressure for all log diameters. "Our arms are more responsive and react faster to better accommodate knotty and out-of-round logs."
Nicholson ring debarking systems are fed and perform automatically, Howard also noted, freeing up mill staff for other duties.
Several Nicholson customers were interviewed for this article and discussed the performance of their companiesí ring debarking systems. In each case, they switched from previously utilizing Rosser-style debarking at their mill. The ring debarking systems lived up to the billing from Nicholson representatives, they agreed.
Anderson-Tully Company is a manufacturer of hardwood lumber headquartered in Tennessee. At more than a century old, the company is a pillar in the forest products industry. Anderson-Tully harvests more than 70 million board feet of mixed hardwoods a year from its own lands. It owns timber lands situated along a 700-mile stretch of the Mississippi River corridor, stretching from Cairo, Illinois to Natchez, Mississippi. Anderson-Tully harvests more than 65 species; 28 are used to produce high grade lumber for the U.S. and foreign markets, and the rest go for paper pulp, veneer, and other specialty products. The company harvests its timber and ships it to its mills at Vicksburg, Mississippi on its own barges, towboats, docks, and derricks. Anderson-Tully proudly proclaims that its vast operations at Vicksburg comprise the largest hardwood sawmill complex in the U.S. at one location."
Parker Hall, the plant engineer at Anderson-Tullyís Vicksburg complex, said that maximum utilization of fiber is critical to the companyís operations. One of the principal benefits of the Nicholson debarking system at Anderson-Tullyís Vicksburg mill is that it has enabled the company to handle a large volume of mixed species logs more efficiently, according to Parker. Logs can be debarked in one pass at speeds of about 65 feet per minute, he said; the companyís previous Rosser-style heads processed logs at the rate of about 15 to 20 feet per minute, he said.
The Nicholson system also will completely debark even crooked stems in one pass, Parker added. "The rings do a better job and get the bark completely off the stem." When stems have to be run through a debarking system twice, he noted, production speed is reduced by half.
The Martco Partnership in Lemoyen, Louisiana is another respected forest product company. It produces more than 52 million board feet of lumber, pallet cants and ties, primarily from nine species of hardwoods that include red oak, ash and cypress.
The company decided on a Nicholson Manufacturing Company debarker "specifically to give us better scanning in our mill," said plant manager Keith Snider.
The debarker that Martco installed in its mill is a dual-ring machine. The mill handles a large quantity of cypress and elm, said Keith, so a specialized ring "slits" the stringy bark before it is stripped from the stem. The system produces smaller pieces of bark and makes for easier handling downstream. Stems come out of the machine fully cleaned and ready to go through the scanning system.
The previous system was not effective, according to Keith. Applying sufficient pressure to remove bark completely damaged the outer layers of wood, and the volume and value of lumber that could be produced were reduced. Reduced pressure meant incomplete debarking.
In a modern mill, scanning is crucial to maximizing value. Any bark left on the stem throws off the scanner, ruining potentially valuable lumber. This is a major reason that debarking has become so vital to a millís processing capacity.
According to Keith, the Nicholson ring system gives him a more than a 10-fold improvement in debarking as measured by his companyís chips. "Our bark content in chips produced from fiber debarked with the Rosser was two and a half percent," he said. "Now itís at .195 percent." Cleaner stems mean a truer picture is possible with the sensitive scanning technology, increasing production and value.
Although the improvements in quality and quantity are difficult to measure, they are definitely there, Keith said. An unexpected benefit was the improvement in production from hackberry logs. "We improved on hackberry by eight percent," he said. "Thatís a very significant amount to realize."
When asked what advice he would give someone looking at a new debarking system, Keith replied, "I would definitely tell them to buy a ring debarker. A high lift machine is best so if you have a crooked stem or an over-size log you can still handle it. Lastly, in wood like that we handle at least, use a tandem ring system. It will help you from choking up your bark handling system with over-size material."
In Danbury, North Carolina, a family owned operation, the Bill Hanks Mill, produces 25 to 30 million feet of lumber and timbers per year with about 85% of its production coming from mixed hardwoods. The remaining 15% is primarily Southern Yellow Pine, according to Jeff Hanks, a partner in the mill.
Jeff summed up the primary reason his company went to the Nicholson ring debarking system: "Less damage and better debarking." An earlier Rosser system caused significant damage to the wood, according to Jeff. "Iíve seen 10 to 15 growth rings damaged with a Rosser head," he commented. "Iíve never seen that with a ring."
Another important factor was the high reliability of bark removal with the Nicholson system. Three different machine centers are optimized, noted Jeff, and proper debarking is critical because a scanner cannot distinguish between bark and usable wood fiber. "If the bark isnít off the stem," he said, "you wonít get a good scan, so at a high level of optimization the effectiveness of the debarking machinery is very important. With the Nicholson there is definitely increased yield and value as a result of less fiber damage and better efficiency."
Jeff pointed to another advantage of the Nicholson system that was not a critical factor in his companyís decision to change to ring debarking technology but nevertheless was important: speed. Bill Hanks Mill invested in one of Nicholsonís slower systems, he said, but it is very fast compared to the millís old technology, more efficient, and reduces fiber loss.
In addition to recommending ring debarking equipment, Jeff suggested a mill not cut corners on infeed and down-feed systems; they must be up to the speed of the debarker if a mill wants to maximize production, he pointed out.
In the modern optimized mill, debarking has become one of the most important parts of the wood processing chain. In todayís world, optimization depends upon a quality debarking job. Poor debarking hinders the ability of scanning technology and software to perform their functions accurately, while damage to usable wood reduces both the quality and the quantity of the products produced in the mill.
As the new century dawns, debarking technology, which once was considered an after-thought, if at all, has moved to the head of the line and determines the quality of everything that happens afterward.
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