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Debarkers and Fiber Loss

In the veneer and plywood industries, there’s an understandable emphasis on reducing fiber waste. Millimeters matter to veneer manufacturers. Less waste means more veneer. But while the need to conserve “good fiber” (i.e., sapwood and heartwood) is less pressing in industries like lumber, chip producers, and pellet manufacturers, the need nonetheless exists. The need is evident especially when one considers that the same machinery that eats into usable fiber can at the same time do a poor job at removing “bad fiber” (i.e., the bark, outer cambium, and root flares).

Why Fiber Loss Matters

​​​​​​​In the veneer and plywood industries, every millimeter of good fiber is precious. Many veneers are less than 1mm thick, with 0.6mm and 0.5mm thicknesses being typical. Millimeters are even more critical in markets like Japan, where veneers as thin as 0.2mm are common. Thin product is why some veneer manufacturers invest so heavily in updates to software and machinery—improvements in yield measuring fractions of an inch are meaningful.

While not to the same extent, reducing wasted fiber is meaningful in other wood-processing industries as well. Among chip and pulp manufacturers, wasted fiber also means less product. While that product has less value than veneer, profit from the fiber is nonetheless lost. Over time, that lost profit becomes significant. The same is true for pellet manufacturers. More waste means less of the log fiber is going into their product. Again, this loss can be significant at scale.

Among lumber manufacturers, waste can be an issue where mills use poorly designed debarkers. We’ve witnessed such debarkers take as much as an inch of fiber out of logs. Where inches matter, waste can mean the differences between selling a 2×4 and a 1×4.

Waste also matters to lumber manufacturers in what byproducts they produce. Generally speaking, the more good fiber they conserve, the higher value byproduct they can sell. Depending on the species, mills can sell their wood chips for smoking. They can also use the chips to make pellets or fuel briquettes. They can sell at volume to particleboard manufacturers or pulp mills, too.

As bad as removing good fiber from a log can be, leaving bad fiber on the log can be just as problematic. For example, pulp mills must remove as much bad fiber as possible from their logs, as the bark negatively affects their product. MDF, particleboard, OSB, and pellet companies likewise want bark removed for the same reason. Bad fiber uses up time at the lathe for veneer and plywood makers. And lumber manufacturers may not want it mixed with their wood chips, which they make from scrap woodcuts.

Choosing a Debarker

Manufacturers across the board benefit from solutions that remove less good fiber and remove more bad fiber. In accomplishing this, they must confine themselves to three styles of debarkers: roller, rosserhead, and ring.

Roller debarkers (aka rotary debarkers) are en-masse-style debarkers that use several rotating drums to debark logs mechanically and frictionally. Compared with drum debarkers, they pose many advantages, the primary of which is that they do a better job debarking logs, including logs with stringy or frozen bark. They’re also less likely to break small stems. Tests conducted by pulp manufacturers have proven their superior performance over drum debarkers in that they remove less good fiber and more bad fiber.

Rosserhead debarkers have far a lower throughput rate than roller debarkers but cost less and can produce better finishes, which is why mills that process hardwood logs typically use them. While there are plenty of poorly constructed rosserheads in the North American market, high-precision, European-grade models are available that remove minimal amounts of good fiber. Such a rosserhead is available from Veneer Services®.

Ring debarkers provide a higher throughput rate than rosserhead debarkers, but they cannot provide as good a finish as high-end rosserheads. While some hardwood mills use ring debarkers for their logs, these debarkers typically appear at softwood mills, which process longer and more uniform logs. As with rosserheads, the model and manufacturer largely determine the quality of the finish.

In determining which debarker is suitable for your operation, you must consider the throughput rate you require and the required percentage of bad fiber you need to remove. Beyond that, your choice is among manufacturers, the quality of their equipment, and the technical advantages of their controls.

Are you researching debarkers for your mill? Veneer Services® offers highly accurate rosserhead debarkers for use in hardwood and veneer applications. For high-volume applications, our sister company, Biomass Engineering & Equipment, offers modular roller debarkers. Visit the respective machine pages to learn more!

 

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