Making Every Cut Count : NDE Helps Optimize Forest Usage

Buildings, furniture, bridges, and musical instruments — all of these wood products start with the the same fundamental building block — the log. The quality of the log can make or break the final product, and this begs the question: are all logs created equal?

The Forest Products Laboratory (FPL) and the Northern Research Station (NRS) don’t think so. In one of FPL newest publications, Nondestructive Evaluation of Wood: Second Edition, researchers document different nondestructive evaluation (NDE) methods, including x-rays and ultrasounds, to assess and report on the condition and integrity of wood. These techniques help industry professionals make informed decisions about a wooden material without destroying it or compromising its structural integrity.

Laser scanning systems consist of two primary components — a laser generator, and a camera.

One of these NDE methods used for logs is laser scanning. Although there are many variations on this technology, each laser scanning system has two main components: a laser line generator (which projects a laser line onto an object), and a camera. The camera and the laser are separated by a measured distance, and the camera is aimed toward the projected laser line at a specific angle. Using the camera angle, the distance between the camera and the laser, and triangulation, the distance of the points along the laser line projected onto an object can be determined.

When scanning logs, a series of laser lines are projected around the surface of the log along its length — and the more lines, the better. By increasing the lines and decreasing the distance between them, the resolution of the scan is increased, and operators can get a more detailed scan of the log. A laser scanning system typically has lasers spaced 6 to 24 inches apart, but the Forest Service has developed an experimental, high-resolution, scanner with lasers placed 0.0625 inches apart. At this resolution, any defects on the log’s surface become obvious.

A high-resolution scan of a hardwood log. Laser scanning technology helps industry professionals better utilize our forest resources.

“Laser scanning is normally done just before processing,” writes Edward Thomas, NRS Research Scientist and contributor to FPL’s NDE book. “To effectively convert logs into lumber, their attributes (diameter, shape, length, sweep and taper) must be accurately measured.”

If the width of the first board cut from the log is too narrow, the grade and the value of the board is decreased. If it’s too wide, then too much wood will be wasted. In addition, by knowing a hardwood log’s taper and sweep, it can be positioned so that there is minimum volume loss from the “jacket boards,” the most valuable boards cut from a hardwood log.

The use of laser scanning technology has become an accepted and economical means of determining the size, shape, and features of logs and lumber. Newer systems can determine grade, yield, and value of a log, even before sawing. The FPL, NRS, and the Forest Service will continue to work with industry partners to develop new technologies to help maximize yield, decrease waste, and maintain the health and integrity of our forests. In this pursuit, every cut counts.

An Evolutionary History of Oriented Strandboard

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New house construction with OSB underlayment.

A new FPL report, by retired Wood Technologist John I. Zerbe, Supervisory Research Materials Engineer Zhiyong Cai, and retired Economist George B. Harpole gives us the story behind a product that we all use and take for granted every day.

An Evolutionary History of Oriented Strandboard (OSB) tells us that historically, logging and wood processing residues offered a utilization challenge for those who harvested and manufactured wood products. Logging operations typically left stumps, tapered log butts, tree tops, and limbs for forest fires to remove or to compost into bed­ding for destructive forest insects.

Even after the delivery of logs to a sawmill or plywood plant, residue materials have represented up to 60% of the log volumes delivered. Thus, commercial efforts have attempted to utilize as much of these residue volumes as possible with production of char­coal, poultry bedding, and heating fuels. Forest fires, tepee burners, and burn piles, however, have often provided a quick answer for getting rid of the surplus accumulations of forest and processing residues. Today, with the increased use of logging residues and wood chips for production of OSB panels, about 80% of the wood volume removed from the forest is now processed into marketable products and tepee burners no longer exist for getting rid of processing residues.

The pathway to OSB production appears to have started in the 1920s with production of hardboards from pulp mats that were produced from wood chips. This was the begin­ning for producing composite panel products from wood residue types of materials. Following hardboard production and skipping the pulping step for producing hardboards, the utilization of waste materials was increased in the United States in the 1940s by the production of nonstructural and appearance grades of particleboards. Even as a nonstructural product, the particleboard made in the United States was new compared with plywood.

Manufacturing OSB.

Manufacturing OSB.

But with the decline in the availability of timber suitable for plywood production in the 1970s, the development of technologies for production of structural types of particleboards quickly became a top priority for wood products research. As technology advance­d various products were produced along the way until researchers developed the oriented strandboard or OSB panels we speak of today.

Ideas for particleboard originated in Germany in the 1930s, and the prod­uct yield from harvested trees was only about 40%. Today, with increased use of wood chips and sawdust, logging residues have been reduced to less than 10%, with little to no processing residues to dispose of. OSB is ubiquitous because OSB panels have been essentially a problem-free new commodity wood product. Perhaps no other new wood product has ever been so problem free as OSB com­posite panels.