Eliminating the Waste in Wood Processing|
Let's take the United States annual cut of timber for lumber products as an example - It is equivalent to approximately 240 million trees. However, if the sawmills operated at a 70% recovery efficiency, the same annual harvest of
lumber could be derived from 171 million trees. The saving would be the equivalent of 69 million trees annully if recovery effiency improved from 50% to 70% in the primary processing industry. In addition, these same 69 million trees, if permitted to grow in the forest, would continue to absorb about 900,000 tons of carbon dioxide and produce about 650,000 tons of oxygen each year.
"Thin Kerf" Sawing - A Case Study in Improving Efficiency
Today, a typical circular sawmill converts 50% of the log into primary product with band mill conversion at about 57%. Saw Kerf averages 21% for the circular sawmill and as low as 12% for high production band mills. Obviously, saw mill efficiencies have increased since the 1920s but there is still much room for improvement. In addition, trends such as environmental constraints on timber harvesting, smaller logs from the forest, and an incresed demand for wood products makes it imperative that we improve sawmill efficiencies.
The good news is that technologies currently exist that can enable 70% or more conversion efficiencies at sawmills. However, the adoption of new technologies such as "thin kerf" sawing have not yet become state-of-the-art in many mills.
What is "Thin Kerf" Sawing?
Simply put, saw kerf is the width of the path cut by the sawteeth as the saw blade moves
through the log. "Thin Kerf" is a relative term, however, because it only has meaning when compared to something else. If circular saws are compared to band saws, then band saws would be considered "thin kerf" since they are generally 50% thinner than circular saws. If today's saw kerfs are compared with those of the past, we can generally say that today we have "thinner kerfs".
The saw kerf has a significant impact on conversion effiency, often referred to as lumber recovery. A crude but effective way of calculating the amount of sawdust that develops during sawing is to determine the total wood usage per "pass", the action of logs moving or "passing" back and forth through the saw blade. Wood usage per pass includes the average thickness of the piece being sawn plus the saw kerf. For example, in cutting a board that is 1.125 inches thick with a saw kerf of 0.300, the total wood usage per pass is 1.425 inches. Calculating the saw kerf as a percentage of the total wood usage per pass results in 21% of the wood removed as sawdust or about one-fifth of the log resource. A band saw with a kerf of 0.140 inch would result in an increase in lumber recovery of about 10%.
Does it Work?
A recent study by the US Forest Service, State & Private Forestry (S&PF), demonstrated the potential of thin kerf sawing when used in combination with other lumber recovery practices. Twenty red oak logs in lengths of 4-6 feet and diameters between 12 and 20 inches were sawn with a saw kerf band saw (0.062 in saw kerf). Boards sawn were one inch thick and ranged in lengths from 2-6 feet. Lumber recovery or conversion efficiency for the 20 log sample averaged 82% which is 30% greater than the typical circular sawmill!
A similar study of small diameter (4-8 inches) red and white pine logs was conducted by S&PF. Using the same thin kerf band saw as noted above the lumber recovery for the 47-log sample was 67%. Sawdust averaged 12% for the study.
A third study conducted at a Missouri pallet mill in 1993, produced results very similar to the pine study. The Missouri mill reduced "short" hardwood logs (45 inches in length) to 5/8 inch thick pallet parts. The bandsaws utilized in the pallet operation had saw kerfs of 0.050 inch. The average conversion effiency at this mill was calculated at 69% which is remarkable considering 5/8 inch thick lumber, rather than one inch lumber, was produced. "Thin" lumber such as 5/8 inch means more cuts and, consequently, more kerf removed, resulting in a reduced conversion efficiency. However, 69% is still very impressive!
As well as the obvious benefits described above, on a more local level, thin kerf sawing will enable the use of lower quality and/or smaller diameter logs which otherwise may have little or no economic value. Consequently forest management could be stimulated to improve and expand the resource base and lead to more successful rural development efforts in retaining, expanding, and attracting wood-using industries.
In increasing lumber recovery and simultaneously reduces waste, thin kerf sawing has the added potential benefit of keeping some sawmills profitable and in-business. In effect, the adoption of thin kerf technologies can save jobs by enabling mills to continue to operate.
Less Waste to the Landfill
Thin kerf sawing is only one process which eliminates waste; there are many others. Improved harvesting methods, which include on-site processing and full tree chipping leave the wood residue in the forest for natural breakdown or can be spread as mulch in the cutover.
Many primary manufacturing facilities are using waste wood as an energy source - in some cases, to generate electricity or for heating.
A whole array of new procucts and manufacturing methods have been developed from the need to conserve and to be environmentally responsible. One is hard-pressed to find large-sized dimensional lumber in modern home construction. Today's engineered structural systems - beams and trusses - are a combination of smaller-sized dimensional lumber and manufactured wood paneling products, which are a by-product of wood waste.
Here are some other manufactured construction wood products which use wood materials that would have been discarded in the past:
- Finger joined studs
- Oriented strandboard (OSB)
- Medium Density Fibreboard (MDF)
- Laminated veneer lumber (LVL)
- Pellet fuels
In practically every arena of wood processing, wasteful old methods have been replaced by innovative production techniques which make use of the whole tree while leaving a smaller mark on the environment.
Northwest Ontario Forest Industries examines:
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