technical report no. 131

Wood-Based Composites Center

Oregon State University University of British Columbia University of Maine Virginia Tech www.wbc.vt.edu

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This information is confidential and is to be used only by persons for whom it was prepared.

Technical Report No. 131

Waferboard and Oriented Strand Board: the History and Manufacturing Practices

February 2009 (Originally prepared June 2007)

Wood-Based Composites Center 1650 Ramble Road

Blacksburg, VA 24061 Telephone: (540) 231-7092

Fax: (540) 231-8868 Email: [email protected]



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Prepared By

Graeme Dick

Submitted to

Dr. Greg Smith The University of British Columbia

Faculty of Forestry Department of Wood Science

ABSTRACT

Composite wood based products have become a significant component of the North

American forest products sector. This paper describes the historical development, current status, and manufacturing process for two of these products, waferboard and oriented strand board. While waferboard has become virtually obsolete in recent years, oriented strand board (OSB) has flourished in the commodity sheathing market. It will be shown that the capacity for OSB will continue increasing despite weakening demand. Even with the growing competition, there has been little technological advancement in the production process since the commercialization of OSB in the 1980s.



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TABLE OF CONTENTS Page

ABSTRACT ................................................................................................................................. ii

LIST OF FIGURES .................................................................................................................... iv

LIST OF TABLES ........................................................................................................................v

1.0 INTRODUCTION ..................................................................................................................6

2.0 HISTORY ...............................................................................................................................6

3.0 CURRENT INDUSTRY .......................................................................................................12

3.1 NORTH AMERICAN PRODUCERS ..............................................................................13

4.0 PROCESS .............................................................................................................................15

4.1 STRAND/WAFER PREPARATION ...............................................................................17

4.1.1 Log Yard ....................................................................................................................17

4.1.2 Conditioning ..............................................................................................................18

4.1.3 Debarking ...................................................................................................................19

4.1.4 Stranding ....................................................................................................................20

4.1.5 Drying ........................................................................................................................24

4.1.5.1 Rotary Drum Dryers ...........................................................................................24

4.1.5.1.1 Triple pass ....................................................................................................25

4.1.5.1.2 Single pass ...................................................................................................25

4.1.5.2 Conveyor Dryer ..................................................................................................26

4.1.6 Screening....................................................................................................................27

4.1.6.1 Rotary Drum Screens ..........................................................................................27

4.1.6.2 Shaker Screens ....................................................................................................28

4.1.6.3 Pre-screening .......................................................................................................29

4.2 BLENDING ......................................................................................................................29

4.3 FORMING ........................................................................................................................31

4.3.1 Forming Line Conveyor .............................................................................................35

4.4 PRESSING ........................................................................................................................36



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4.5 PRODUCTS LINE............................................................................................................37

5.0 CONCLUSION .....................................................................................................................39

6.0 LITERATURE CITED .........................................................................................................40

LIST OF FIGURES

Page

Figure 1: Patent drawing for original waferizer. ...........................................................................7

Figure 2: OSB annual prices and forecast (US N-Central 7/16" FOB) ......................................14

Figure 3: Schematic of OSB and waferboard manufacturing process. .......................................16

Figure 4: Example of log yard where the stems are cut-to-length in the forest (left)

and left at tree length (right) .......................................................................................17

Figure 5: Peace Valley OSB log yard .........................................................................................18

Figure 6: Ring debarking concept ...............................................................................................19

Figure 7: Photo (left) and schematic (right) of a ring strander. ..................................................20

Figure 8: Schematic of ring strander configuration ....................................................................21

Figure 9: Photo (left) and schematic (right) of a disc strander ...................................................21

Figure 10: Schematic of disc strander configuration ..................................................................22

Figure 11: Schematic of strands produced on a disc strander. ....................................................22

Figure 12: Picture of a knife pack from a ring strander with the scoring knives circled. ...........23

Figure 13: Schematic of a typical knife-pack from a ring strander ............................................23

Figure 14: Picture of a knife projection measurement on a ring strander, with a calibrated

blank knife-pack indicated by the arrow. ...................................................................24

Figure 15: Conventional tripe-pass rotary drum dryer. ..............................................................26

Figure 16: Cross section of tripe-pass rotary drum dryer ...........................................................26

Figure 17: Cross section of typical conveyor dryer ....................................................................27

Figure 18: Schematic of section of screens inside a rotary drum screen. ...................................28

Figure 19: Illustration of a rotary drum screen. ..........................................................................28

Figure 20: Illustration of a disc screen ........................................................................................29

Figure 21: Beattie’s blender design ............................................................................................31



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Figure 22: Patent drawing for original former ............................................................................32

Figure 23: Schematic of machine direction forming system. .....................................................33

Figure 24: Picture of machine direction orientor discs. ..............................................................34

Figure 25: Example of strand orientation coming from core (left) and face (right)

orientors with the machine direction indicated. .........................................................35

Figure 26: Comparison of the vertical density profile created using a conventional and

a steam injection press, showing a significant improvement in the core density

when using the latter system. .....................................................................................37

Figure 27: Example of Louisiana-Pacific’s notched tongue and groove design ........................38

LIST OF TABLES

Page

Table 1: Comparison of plywood and structural particleboard costs for exterior sheathing

grade assuming a plant capacity of 150 to 170 MMsf-3/8 inches annually ....................8

Table 2: Waferboard plant completions during the 1970s. .........................................................10

Table 3: Structural board plant capacity in Canada and the United States in 1980 and the

predicted capacity growth by 1983, represented in MMsf-3/8 inch basis ....................11

Table 4: North American distribution of plant capacity by owner .............................................13

Table 5: North American distribution of plant capacity, and forecasted capacity, by country ..14

Table 6: Edge seal colors used by three major OSB producers. .................................................38



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1.0 INTRODUCTION

Wood has been used as a building material for centuries. Its insulating and strength properties make it an ideal building material for nearly any structure in most climates. Historically, wood was used in its unprocessed form; however, sawn lumber eventually emerged. It wasn’t until the mid-19th century that structural, engineered wood based products were invented.

Plywood was the first product of this engineered product category. It was composed of stacked veneer sheets oriented in a particular direction. Waferboard was invented nearly 100 years later. Instead of using wood veneers, waferboard was manufactured using wood wafers. The advantage of this product over plywood was that it was able to use previously underutilized wood species. Although building code and market acceptance for waferboard was slow, it eventually grew in popularity in Canada in the 1960s and then in the United States in the early 1970s.

At around the same time as the invention of waferboard, research into using oriented wood strands instead of randomly oriented wafers had begun. By the 1980s, processing challenges related to the use of oriented wood strands had been overcome and waferboard facilities were quickly being replaced by oriented strand board (OSB) facilities. Today, oriented strand board has saturated the construction market. It is primarily used in roof, floor, and wall sheathing applications; however, it is increasingly being employed in specialty applications. Some of these applications include stair treads and stringers, rim board, recreational vehicles, and even concrete formwork.

This paper presents the current status of OSB production in North America, the development of waferboard and OSB, as well the production process for OSB. While most of the information related to the current status and history of OSB and waferboard was found in literature, most of the processing information was obtained through experiences of the author.

2.0 HISTORY

Waferboard was first introduced in the 1950s; at the time however, it was referred to as structural particleboard. By 1961 waferboard had become widely accepted by the Canadian building codes. It took nearly an additional 10 years for it to become accepted into the United States (US) building codes and practices (Meakes, 1972). Today, waferboard has evolved into oriented strand board (OSB) and has saturated the residential home construction market.

Clark and Mottet received the first patent for structural particleboard that used a special class of wood particle known as a wafer in 1954. This patent was part of a series of patents that described the manufacturing process for structural particleboard and the process of producing these wafers. The wafer was unique from the wood elements used in conventional particleboard as it was produced by predominately cutting along the grain of the wood to create an element approximately 0.030-inches thick and 1.50-inches long


and wide. This was achieved using a waferizer equipped with a series of knives mounted on the perimeter of a drum, similar to a planer head. The wood was fed into this cutting head parallel to the wood grain. Originally, these devices were intended to waferize sawmill waste. One of Clark’s and Mottet’s patent drawings for this process is shown in Figure 1, where square lumber is being fed into the waferizer. The overall objective in producing these wafers was to minimize the breakage along the wood fibers (Gunn, 1972).

Figure 1: Patent drawing for original waferizer.

The first attempt at commercially producing structural particleboard was by the Pack

River Lumber Company in 1955 in Sandpoint, Idaho based on Clark’s and Mottet’s work (Gunn, 1972). The intent of this project was to produce a product with good machinability, strength properties, and dimensional stability, while requiring less resin compared with conventional particleboard and dry processed hardboard. The product could be used for exterior applications; however, this was not the primary intent (Gunn, 1972). This first attempt failed in the US markets. This was largely because there was little or no cost advantage compared with conventional plywood (Table 1). In addition, at the time there was still an adequate supply of quality peeler logs for plywood manufacturing (Vajda, 1974). The typical costs for a plywood and structural particleboard operation with the same production capacity are listed in Table 1. The principal cost differences between the two products are caused by labor, chemicals and wood.


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Table 1: Comparison of plywood and structural particleboard costs for exterior sheathing grade assuming a plant capacity of 150 to 170 MMsf-3/8 inches annually (Vajda, 1974).

Plywood Structural particleboard

Press size (feet) 4 x 8 4 x 24

Capital cost of plant (million) $13.0 -- $15.0 $11.5 -- $13.5

Unit costs

Labor $16.00 -- $19.00 $7.00 -- $9.00

Chemicals $3.50 -- $6.50 $12.00 -- $15.00

Power and fuel $2.00 -- $3.00 $2.00 -- $4.00

Operating and maintenance

supplies

$2.00 -- $3.50 $3.00 -- $3.50

Administration and office

overhead

$1.50 -- $3.00 $2.00 -- $3.00

Insurance and taxes $1.00 -- $1.50 $1.00 -- $1.50

Depreciation (15 years) $5.00 -- $7.00 $4.50 -- $6.00

Total conversion costs $31.00 -- $42.00 $32.00 -- $42.00

Wood costs $25.00 -- $33.00 $15.00 -- $23.00

Total costs $56.00 -- $75.00 $47.00 -- $65.00

The second attempt at commercially producing structural particleboard was in Saskatchewan, Canada. Beginning in the mid-1950s the Saskatchewan Government’s Industrial Development office explored options for economically utilizing the northern forest reserves. These resources were comprised predominately of aspen and poplar, species often referred to as a weed because of their rapid growth and perceived uselessness. It was found that while these species were not acceptable for the manufacture of dimensional lumber products they could be used in the manufacture of structural particleboard. Wizewood Limited, a private company, was assembled by a group of Prince Albert businessmen, whom after further research began construction of a structural particleboard plant in Hudson Bay, Sk. The facility was completed in 1961 and by December of the same year was producing product (Meakes, 1972). In the spring of 1962 Wizewood began marketing its product under the trademark name Aspenite.



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Aspenite was marketed as a “revolutionary new building board for interior and exterior use” (Gunn, 1972). It was said to be economical, weatherproof, warp resistant, and will not crack, check or splinter. Because of this, it was ideal for sheathing, sub-flooring, cabinetry, and panelling. Interestingly, these claims were all made without a proven track record. Fortunately, ten years later all of these claims had been validated (Gunn, 1972).

This operation was different from the Sandpoint, ID facility in several important aspects. First, the Hudson Bay plant used phenolic-resins, which are waterproof, instead of urea-resins. Urea resins have relatively poor durability and creep over time. Second, the Hudson Bay plant used roundwood rather than residual wastes.

In 1965, following several years without significant success, Wizewood was purchased by MacMillan Bloedel. Under MacMillan Bloedel the production was increased to three shifts a day and a plant capacity of 75 million square feet, ¾ -inch basis annually (150 million square feet, 3/8-inch basis). As a comparison, in October, 2000 Footner Forest Products began operation in High Level, Alberta with a designed annual capacity of 860 million square feet, 3/8-inch basis. This is currently the world’s largest designed capacity OSB plant (Ainsworth Engineered, 2007). MacMillan Bloedel quickly turned this product into a success in Canada and was the sole producer of waferboard for a little under a decade (Gunn, 1972; Meakes, 1972).

There were three driving forces that facilitated the success of Aspenite. Some of the first panels produced at the facility were installed on barns and fences throughout the three prairies provinces. Over time it was shown that the panels performed very well given the harsh winters and extreme summers. Also, unlike the US, Aspenite had a cost advantage over Canadian plywood. Because plywood typically had to be shipped from British Columbia, Aspenite was cheaper overall. Further, Aspenite eventually qualified as a structural board according to the Canadian Standards Association (CSA) and was included in the Canadian Building Code of 1970 under the generic name waferboard. The code provided prescriptive requirements for three major markets: residential, farm buildings, and industrial buildings. A fourth market was the over the counter, do-it-yourself market (Meakes, 1972). By 1974 it was estimated that 20 percent of the Canadian sheathing market was supplied by waferboard instead of plywood. Prior to becoming certified by the CSA, Aspenite was used primarily in low risk construction, such outbuildings (Maloney, 1975).

Construction of the second waferboard plant began in 1969 in Timmins, Ontario for the Malette family. This company was later named the Waferboard Corporation of Canada and was the first operation to produce waferboard using three layers of distinctly different sized wafers.

Although the first attempt to produce waferboard for the US markets failed, the US Federal Housing Administration (FHA) eventually accepted Canadian waferboard as an acceptable product for exterior structural wall and roof sheathing (Meakes, 1972). However, unlike Canada where the acceptance of a product into the national building



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code results in the general acceptance across the country, the US is composed of multiple building codes and agencies that must approve a product before it is widely accepted. As reported by Maloney (1975), this is potentially a very long and expensive process. Nonetheless, the acceptance by the FHA resulted in the construction of a new waferboard facility in Grand Rapids, Minnesota in the early 1970s for the Blandin Wood Products Company. During the 1970s at least seven waferboard facilities began operation (Table 2) (Moeltner, 1980).

Table 2: Waferboard plant completions during the 1970s.

Year Company Location

1973 Blandin Wood Products Grand Rapids, Minnesota

1975 MacMillan Bloedel Thunderbay, Ontario

1975 Weldwood Longlac, Ontario

1975 Great Lakes Paper Thunderbay, Ontario

1976 Alberta Aspen Lesser Slave Lake, Alberta

1979 Northwood Bemidji, Minnesota

1979 Louisiana-Pacific Hayward, Wisconsin

In addition to the acceptance by US authorities, the market conditions in the US also facilitated the success of the second launch of waferboard. In 1978 the US Department of Agriculture (USDA) assembled a symposium on structural flakeboard. During this symposium the USDA predicted that the US housing market would remain strong until the mid 1980s, when it would likely slow down for a few years before continuing a strong growth rate. In addition, the cost of Douglas-fir plywood was rapidly increasing (Dickerhoof & Marcin, 1978; Spelter et al., 2006; Vajda, 1980). Together, the prediction of a strong housing market and the increasing cost of plywood created favourable conditions for structural particleboard. In 1979 another twelve structural particleboard operations were announced to be constructed in Canada and the US during the early 1980s (Moeltner, 1980). Interestingly, nearly half of all new growth in the structural particleboard industry was in oriented strand board; a technology that had been virtually ignored until this time (Table 3).



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Table 3: Structural board plant capacity in Canada and the United States in 1980 and the predicted capacity growth by 1983, represented in MMsf-3/8 inch basis (Vajda, 1980).

Waferboard OSB Total USA

1980 210 210 1982/83 500 640 1,140

Total 710 640 1,350 Canada

1980 820 820 1982/83 170 170

Total 990 990 North America

1980 1,030 1,030 Total 1,700 640 2,340

Oriented strand board was by no means a recent invention in the 1980s. During the development of waferboard it was widely known that wood is an orthotropic material. Orienting the wood strands with the grain in a specified direction therefore allowed for the strength and stiffness of the board to be optimized. The easiest way to ensure that the grains were all aligned in the same direction was to create strands where the grain always ran along the length of the strands. The elongation of the wafers, or strands, facilitated the alignment of the grain during manufacturing. Early on it was this process of creating strands with a specific length and width that proved to be one of the major stumbling blocks for applying this technology on a production scale (Vajda, 1980).

Armin Elmendorf first referred to the use of wood strands in 1949; however, at the time he was proposing the manufacturing of these strands as a means of utilizing veneer wastes. In the late 1950s, from his research laboratory in California, US, Elmendorf researched the use of oriented wood strands in structural particleboard. Concurrently, similar research was being undertaken in Germany and Czechoslovakia. In 1965 Elmendorf received a US patent for Oriented Strand Board (OSB). Elmendorf’s OSB was composed of wood strands oriented ±20 degrees from parallel to the long edge of the board, often referred to as the machine direction. These strands had a length to width ratio of at least 3:1, but ideally greater than 10:1 (Elmendorf, 1949; Elmendorf, 1965).

Building upon Elmendorf’s research, Talbott (1972; 1974) completed extensive work investigating the relationship between the mechanical properties of panels and the strand orientation. He also investigated several means of achieving uniform strand alignment. During his work he found that the stiffness and strength of structural particleboard could be increased as much as twofold by orienting the surface strands parallel to the machine direction and the core strands perpendicular. Two approaches at obtaining the desired strand alignment were researched, mechanical alignment and



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electrical alignment. The former method will be discussed in further detail later in this report.

Despite extensive research outlining the benefits of using oriented strands or wafers there was minimal industrial interest in this technology. It was not until the 1970s when Potlatch began researching an oriented strand type product, known as Stranwood, that any commercial application was even on the horizon (Brown & Bean, 1974; Snodgrass, Saunders & Syska, 1973).

Stranwood was the first OSB product to be manufactured in North America with the intent of producing it commercially. It employed a similar manufacturing process as waferboard; however, with several important differences. Stranwood was produced using strands of wood rather than wafers. These strands had a significantly higher slenderness ratio compared with wafers that were virtually square. As an example, the strands used in Stranwood were approximately 0.015 –inches thick, 0.25 -inches wide, and 1.50 -inches long. The second difference with Stranwood was the use of strand orientation to improve the mechanical and dimensional stability properties of the board. Where this product differed from Elmendorf’s original patent for OSB was its three-layer design. The strands on both surfaces were aligned parallel to the machine direction and the strands in the core layer were aligned perpendicular to the machine direction. Stranwood was first produced at a pilot plant in Lewiston, ID. It was not until the 1980s that commercial production of oriented strand board began in North America. The Bison company in Germany was first to produce OSB during the late 1970s.

Most of the structural particleboard plants in Canada and the US were producing oriented strand board by the end of the 1980s. The production of waferboard in the US ceased by the 1990s, being completely replaced by OSB. While the lifespan of waferboard was relatively short, there is no denying the fact that it paved the way for future wood strand based products, including oriented strand board (OSB), oriented strand lumber (OSL), and laminated strand lumber (LSL).

3.0 CURRENT INDUSTRY

OSB and waferboard production is largely limited to North America, where the capacity was 28.3 billion square feet in 2005, compared to 3.6 billion square feet in Europe and even less in South America. China produces a small amount of waferboard; however, there have not been any investments into OSB. Unlike North America where OSB has matured since its advent in the early 1970s, OSB in Europe is still at its infancy (International Wood Markets Group, 2006). As European building codes continue to adapt to allow for OSB in structural applications, OSB production and consumption is expected to grow. Being the second largest consuming region of forest products, Europe is a major potential market for OSB (World Forest Institute).



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3.1 NORTH AMERICAN PRODUCERS OSB facilities require significant investment. Because of the financial resources

required only a few companies operate a large percentage of the production capacity (Table 4) (Spelter et al., 2006). In 2005, the largest North American producer was Louisiana Pacific, which represented 23% of the total production. This was followed by Weyerhaeuser and Georgia Pacific with 15% and 13% respectively. Despite significant growth in the capacity of new facilities from 100 million square feet in the late 1970s to nearly 900 million square feet in 2005, the average number of employees per facility has only increased marginally from 125 to 136. As a result, the average capacity per employee has tripled during this period. This represents an output per employee of nearly 3 million square feet (International Wood Markets Group, 2006; Spelter et al., 2006)

Table 4: North American distribution of plant capacity by owner (Spelter et al., 2006).

Firm Capacity (x 1000 m3) 1995 2000 2005

Louisiana Pacific 3 9151 6 4401 6 5051 Weyerhaeuser 1 5032 3 5532 4 1302 Georgia Pacific 1 1963 1 8453 2 6955 Potlatch 1 0824 1 115 - Norbord 8155 1 5904 3 7433 Huber 7216 1 2505 2 1206 Grant 570 1 2206 1 280 International Paper 545 955 - MacMillian Bloedel 370 - - Ainsworth 350 935 2 9253 Forex 305 - - Martco 260 300 453 Langboard 215 211 450 Malette 200 - - Longlac 160 - - Tolko - 545 1 520 Slocan - 470 - Canfor - - 635 Peace Valley - - 620 Voyageur - 400 - Williamette - 350 - Tembec - 200 - Kruger - 160 170 Footner - 30 810 Jolina Capital - - 270 Total 12 367 21 569 28 276 Top 6 Share 75% 74% 78%


In 2005 there were 60 OSB facilities in North America. High margins in OSB over the last few years has led to another 12+ OSB projects being either confirmed or proposed for start-up before 2010. During times of exceptionally high OSB prices (1995/1996, 1998 to 2000, and 2004/2005) the payback period for an OSB facility could be as little as three years. If all of the planned projects go ahead, North American capacity could balloon to 37 billion square feet by 2010, with most of this capacity located in the US (Table 5). Increasing supply has resulted in a surplus of OSB beginning in mid-2006, as slumping housing starts and rising interest rates eroded the demand. This trend is expected to increase as more projects are completed (International Wood Markets Group, 2006; Spelter et al., 2006). One outcome of this increasing competition is diversification amongst producers away from commodity sheathing products and towards specialty products, such as oriented strand lumber.

Table 5: North American distribution of plant capacity, and forecasted capacity, by country (International Wood Markets Group, 2006). 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

US 12.53 13.52 13.62 14.27 14.99 15.29 15.87 17.30 18.23 19.24

Canada 9.00 9.27 10.04 11.10 11.17 11.42 11.07 11.85 12.43 13.01

For those companies that continue to manufacture commodity sheathing products, it is expected that commodity OSB prices will remain relatively low until 2009/2010 in light of increasing supply and decreasing demand (Figure 2). By 2010 it is projected that supply and demand will balance and the market price will improve (International Wood Markets Group, 2006).

0

50

100

150

200

250

300

350

400

1995 1997 1999 2001 2003 2005 2007 2009

US$

/Msf

Year

Projected

Figure 2: OSB annual prices and forecast (US N-Central 7/16" FOB)

(International Wood Markets Group, 2006).


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4.0 PROCESS

The manufacturing process for waferboard and OSB has remained relatively unchanged since the commercialization of waferboard in the 1960s. Unlike plywood, waferboard and OSB production is highly automated. Modern facilities operate under a crew of skilled individuals working from within the confines of control rooms. In fact, Ainsworth Engineered’s OSB facility in Grande Prairie, Alberta can operate with only 25 employees per shift; an impressive feat for an operation with a designed capacity of 665 million square feet, 3/8" basis (Kryzanowski, 1996). Because of the extent of automation, millwrights and electricians have become invaluable in ensuring the process operates smoothly.

The entire process may be divided into five distinct phases: strand/wafer preparation, resin and wax addition, mat formation, mat consolidation, and the products line where final panel alterations are completed prior to shipping (Figure 3). The entire process from the time the logs arrive at the facility to the time the product is shipped will be described in this section.


Log Yard

Conditioning

Debarking


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Figure 3: Schematic of OSB and waferboard manufacturing process.

Blending

Stranding

Drying

Screening

Forming

Pressing

Tongue & Groove

Edge Sealing

Packaging

Sanding

Shipping

Strand/wafer preparation

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4.1 STRAND/WAFER PREPARATION

Strand/wafer preparation is the initial phase in the production process. It includes all aspects of the overall process related to converting the raw material into a useable form. 4.1.1 Log Yard

The production of OSB and waferboard begins in the log yard. Stems are shipped to the facility either cut-to-length, where the log is cut in the forest to the correct length for the mill, or left at tree length (Figure 4). Mills are designed to accept one or the other. In either case, the small end diameter of the log is typically no smaller than 4-inches.

Figure 4: Example of log yard where the stems are cut-to-length in the forest (left) and left at tree length (right) (Cloutier, 1998).

When the logs arrive they are weighed, and/or scaled and then unloaded from the truck or rail car and sorted by species and arrival date. The goal is to utilize the logs on a first come basis and to feed the mill with a specific species mix. Some facilities may also grade-out certain logs that can be re-sold at a higher value. For instance, high quality, large diameter logs may be sold as peeler-logs for plywood manufacturing. The log yard is the most noticeable aspect of most operations because of its overall size. This size will depend on the capacity and location of the mill. As an example, the log yard for the Peace Valley OSB plant in Fort St. John, British Columbia is 2 500 feet long (Figure 5). This operation requires 1.1 million cubic meters annually to meet its designed capacity of 820 million square feet (Peace Valley OSB).


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Figure 5: Peace Valley OSB log yard (Peace Valley OSB).

While waferboard and OSB were originally manufactured using aspen and poplar, today OSB is produced using nearly any local species; however, depending on the species mix, processing parameters need to be adjusted to ensure that the mechanical properties of the product are not compromised. These products are most commonly produced using small diameter softwood and underutilized hardwood logs. Some common species used in North America include: lodgepole pine, southern pine, douglas-fir, sweet gum, maple, and birch. In Canada, aspen and poplar remain the dominant species because of their fast growth rates and limited use (O'Halloran, Kuchar & Adair, 1996). Recently in British Columbia there has been an increased use of mountain pine beetle (MPB) killed lodgepole pine as a result of the current MPB infestation. Using this material has required considerable alterations to the process to achieve quality strands and to avoid processing issues from occurring, such as dryer fires.

From the log yard the logs are transported and fed into the facility using a crane or loader. Tree-length logs can be trimmed to size at this point on a slasher-deck.

4.1.2 Conditioning

Before the logs are processed they are usually conditioned. Conditioning serves two purposes. First, it will thaw the logs during the winter months in cold climates. In order for optimal processing, the logs should be approximately 20oC through the diameter. Second, during warmer weather conditioning will soften the wood fibers, facilitating the stranding process. Of the two purposes, thawing the logs during the winter is most critical. Because of this, not all processes condition the logs, particularly in parts of the southern United States.


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Conditioning takes place in large ponds, where the logs are submerged for six to

eight hours. Log ponds are sometimes a bottleneck for the process, as a result it is not always possible to submerge the logs long enough to achieve 20 oC in the core (Industry Canada, 2007). The temperature of the ponds varies by geographic region and wood supply characteristics; however, 30oC in the winter is common. The ponds do not need to be heated during the summer.

4.1.3 Debarking

Bark is low in density and strength and often contains dirt and other foreign matters; therefore, it is removed using a debarker prior to further processing. Some operations remove the bark before conditioning to facilitate the heat transfer through the log; however, this requires a special debarking system for removing potentially frozen material (Industry Canada, 2007).

The most common debarker used in industry is the ring debarker (Figure 6). This is because of the relatively high throughput rate and ability to accept variable length logs. These debarkers are capable of processing up to 550 feet of log per minute (Nicholson Industries Inc, 2007). One of the difficulties with debarking logs used in the production of waferboard and OSB is the tendency for excessive crook in the logs, causing plugging and splintering. From the debarker the logs are fed into the strander.

Front Back

Figure 6: Ring debarking concept (Nicholson Industries Inc, 2007).


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4.1.4 Stranding

The logs are converted into strands ranging from 3 1/2" to 6" (90 to 150 mm) long by approximately 1" (25 mm) wide and 0.027" to 0.035" (0.69 to 0.89 mm) thick using one of four strander designs (Structural Board Association, 2006). These strander designs include: the ring strander, the disc strander, the drum strander, and the high-speed knife ring flaker. Of these, ring and disc stranders are the most common. Carmanah, formerly CAE, followed by Pallmann are the two major suppliers of these stranders in North America (Spelter et al., 2006).

As the name suggests, ring stranders are shaped in a ring, with knives mounted on the inside diameter. Inside this ring is known as the cutting chamber. A batch of logs enters the chamber and is clamped in place. The strander ring then slides along the carriage and across the cutting chamber, stranding the region of the logs that are within it. The strander ring then returns to its original position and the batch of logs is jogged forward and re-clamped before the stranding process repeats (Figure 7 and Figure 8).

Knife-pack

Strand flow

Figure 7: Photo (left) and schematic (right) of a ring strander (Pallmann Pulverizers Company Inc).


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Figure 8: Schematic of ring strander configuration (Carmanah Design and Manufacturing

Inc).

Rather than a ring of knives, the disc strander is a large flat disc with knives running along its radius (Figure 9 and Figure 10). Similar to a ring strander, a batch of logs is fed into a cutting chamber, in this case directly in front of the disc. The disc slides along a carriage and across the cutting chamber, stranding the region of the logs that are in front of it. The strander ring then returns to its original position and the batch of logs is jogged forward and re-clamped before the stranding process repeats. While ring stranders only produce rectangular shaped strands, disc stranders produce either rectangular strands or strands shaped similar to a parallelogram (Figure 11). Ultimately, the shape depends on the location of the log relative to the center of the disc.

Figure 9: Photo (left) and schematic (right) of a disc strander

(Carmanah Design and Manufacturing Inc).


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Figure 10: Schematic of disc strander configuration (Carmanah Design and

Manufacturing Inc).

Strand cut on lower half of disc

Strand cut at center of disc

Strand cut on upper half of disc

Figure 11: Schematic of strands produced on a disc strander.

With both strander designs the length, width, and thickness of the strands are controlled in a similar manner. Of the three dimensions, the length is the easiest to control. This is accomplished using scoring knives on the face of the knife pack (Figure 12 and Figure 13). The thickness of the strands is slightly more difficult to control. It is determined by the projection of the knife from the face of the disc or ring. Routine measurements must be taken to ensure that this projection remains within specifications (Figure 14). As the ring and disc will wear over time, this will require that adjustments be made to the knife pack. The projection of randomly selected knives should be measured every time the knives are changed. The width of the strands is the most difficult to control. Rather than cutting the strands to the appropriate width, the strands


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collide with a steel plate on the backside of the knife (Figure 13) as they pass through the ring or disc, causing the strands to split to the appropriate width.

Figure 12: Picture of a knife pack from a ring strander with the scoring knives circled.

Knife

Slitter bar

Scoring knife

Knife holder

Figure 13: Schematic of a typical knife-pack from a ring strander. The strand is split to width when it collides with the splitter bar.


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Figure 14: Picture of a knife projection measurement on a ring strander,

with a calibrated blank knife-pack indicated by the arrow.

After stranding, the strands can either proceed directly to a wet strand storage bin or the short strands and particles may be screened out and sent to the burner. Wet strand screening is uncommon in industry as the wet material tends to agglomerate as a sheet, making it difficult to effectively screen out the smaller material. The wet strand storage bin, and the dry strand storage bin as will be discussed later, is critical in ensuring that the facility is capable of accommodating interruptions in the process. As previously mentioned, it is common for the debarker to become plugged, shutting down the supply of wood to the strander. If there were no storage bins this would halt the overall production. Instead, the facility will continue to feed from these storage bins.

4.1.5 Drying

From the wet strand storage bins the strands are sent to a dryer. The dryer reduces the moisture content of the strands to between 2 and 5%. There are two general classes of dryers, rotary drum and conveyor. Rotary drum dryers have been used since the advent of waferboard, being adopted from the particleboard industry. Conveyor dryers for OSB however, were only first introduced in 1992 (Teal, 1995).

4.1.5.1 Rotary Drum Dryers

As explained by Teal (1995), rotary drum dryers may be “characterized by high-temperature air drying, aggressive handling of strands, and short product-retention times.” There are three designs for the rotary drum dryer: triple-pass, double-pass, and single-pass. The triple-pass and single-pass designs are common in today’s OSB industry; however, the later design is becoming increasingly dominant.


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4.1.5.1.1 Single pass

Single pass dryers have been gaining popularity in today’s industry. This is largely because of the increased use of longer strands. In a triple pass dryer these longer strands undergo a higher rate of attrition as they move between concentric cylinders. The single pass design is a more gentle drying process; however, higher outlet temperatures are often required because of the reduced drying space, increasing the need for automatic moisture controls to avoid fires. Despite the higher outlet temperature, without the structural support found in triple-pass dryers, single-pass dryers cannot exceed 900oF because of thermal stresses and expansion that will occur. Single pass dryers are assembled on site and can be as long as 96 feet with a diameter of 20 feet and a capacity of 100 000 OD lbs/hr. The principal drawback of single pass dryers is the increased footprint (Kaff, 2007; Maloney, 1993).

4.1.5.1.2 Triple pass

Triple-pass dryers are designed with three concentric cylinders (Figure 15 and Figure 16). The overall dimensions of the dryer may be as large as 72 feet in length and 14 feet in diameter with a capacity of 40 000 OD lbs/hr. The strands enter through the center of the dryer and migrate to the outer cylinder before being discharged. This is accomplished using a fan at the outfeed, which draws the material through. The dryers are direct fired, using hot air as the drying medium. The triple-pass design relies on the changing drum diameter to facilitate the drying process. As the diameter decreases towards the inlet, the velocity of the strands increases. Coupled with a relatively high temperature, this causes the surface moisture to evaporate quickly. During the second and third pass the strands are warmed through their thickness under a reduced velocity and temperature. It is important that the severity of the drying conditions be reduced at this point as the strands may otherwise be prone to fires. Typical inlet temperatures may range from 1200 to 14000F (649 to 7600C) with a velocity of around 1600 fpm. The inlet velocity at the second and third cylinder may be around 640 and 320 fpm respectively. Triple-pass dryers rely on a heavy, structural support system to maintain the shape of the cylinders under the extreme temperatures. Because of the skill and equipment involved in constructing this support system, triple-pass dryers are assembled off-site (Kaff, 2007; Maloney, 1993).


Figure 15: Conventional tripe-pass rotary drum dryer (T. M. Maloney, 1993).

Figure 16: Cross section of tripe-pass rotary drum dryer (Maloney, 1993).

4.1.5.2 Conveyor Dryer

As previously mentioned, conveyor drying of strands is relatively new to the waferboard and OSB industry. As with rotary dryers, heated air is the drying medium. There are five primary components of a conveyor dryer: the conveyor assembly (typically constructed of perforated plates), a means of heating the air (for example, oil or steam), several fans to move the air, an enclosure, and the system controls (Figure 17). These dryers may be configured as a single stage dryer or, to conserve space or increase capacity, may be configured as a multi-stage dryer. The strands are carried along the perforated conveyor through the assembly. As the hot air passes over the strands the air picks-up the moisture and cools. This cool air is then removed. As reported by Teal (1995), the strands remain in the dryer for about 15 minutes at a temperature of less than 4000F. Because the strands do not tumble through the dryer, as with rotary drum dryers, there is minimal strand attrition during this process. Other benefits include: reduced emissions of pollutants, lower likelihood of fire, lower volume of exhaust air (thermal oil), and greater process control. Based on some early estimates, the capacity of


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conveyor dryers may be slightly less than triple-pass rotary drum dryers at 35 000 OD lbs/hr (Industry Canada, 2007; Teal, 1995).

Figure 17: Cross section of typical conveyor dryer (Teal, 1995).

4.1.6 Screening

After drying the strands are screened to separate the small strands, or fines, from the furnish. Fines are not desirable as they contribute very little to the overall bending strength of the final product and they consume a large proportion of the resin while in the blender. Rotary drum screens have historically been the popular choice for removing fines; however, shaker screens are increasing in popularity. The main advantage of shaker screens is its gentler strand handling and subsequently reduced strand breakage. In addition to shaker screens, pre-screening has also been gaining in popularity.

4.1.6.1 Rotary Drum Screens

Rotary drum screens employ a series of cylindrically shaped screens with different sized openings (Figure 18 and Figure 19). These screens are aligned adjacent to each other in order of increasing screen size, as measured by the size of screen opening. Strands enter the process from the end with the smallest screen and migrate through to the end with the largest screen. As the strands pass through the screens those strands that are small enough will fall through a particular screen section. The strands are classified depending upon the respective screen size that they pass through. In order to transfer the strands along the screens, the screens revolve and its axis is tilted slightly to the horizontal. This revolution, causing the strands to tumble along the screens, is what results in the strand breakage that occurs during this process.


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Strands Enter

Strands Exit

ω

Smallest Screen

Largest Screen

Figure 18: Schematic of section of screens inside a rotary drum screen.

Figure 19: Illustration of a rotary drum screen.

4.1.6.2 Shaker Screens

Shaker screens use a series of stacked screens with different sized openings, decreasing in size. This is different from rotary drum screening where the screen size increased through the process. These screens vibrate as the strands are fed onto the top screen. The strands migrate through the series of screens until they can no longer pass through the specific screen. The strands are sorted based upon the first screen that they were unable to pass through. Because there is no tumbling of the strands, this process results in less strand breakage compared with rotary drum screening, a significant advantage for producers wanting to increase their target strand length (Industry Canada, 2007).


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In both screening options, those strands considered to be too small for the process are rejected and used as fuel for the plant. Alternatively, a specific amount of these fines could be used for the core layer of the final product, where bending strength is not critical.

4.1.6.3 Pre-screening

Pre-screening has been gaining in popularity. Pre-screening allows for the rapid removal of large strands, reducing the load on subsequent screening operations. The most common pre-screening design is called a disc screen and uses a series of rotating discs spaced a specific distance apart (Figure 20). The spacing between discs will determine the size of strand that will be able to pass through. Those strands that are carried the entire length of the discs without passing through will bypass the next screening operation (Acrowood, 2007).

Figure 20: Illustration of a disc screen (Acrowood, 2007).

After screening the strands are sent to storage bins. There are at least two storage

bins, one for the face layers and one for the core. As previously mentioned, fines may be re-introduced into the core layer. As a result, the core and surface furnish may be different, with the surface furnish containing a greater proportion of large strands. 4.2 BLENDING

Blending had evolved significantly between the advent of waferboard in the 1950s and the advent of oriented strand board in the early 1980s. Since the mid-eighties however, blending has remained virtually unchanged. The most significant advancement was perhaps the shift from powdered to liquid phenolic resins; however, advancement also took place in the blender design and resin feeding system.

Powdered resins had several advantages that resulted in its widespread use during the development of waferboard. These advantages were (Chiu & Scott, 1981):

• Ease of mixing with the wafers, • Ability to achieve a uniform resin distribution over the wafer surfaces, and • Resistance to pre-curing during pressing.


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However, there were also several significant disadvantages that led to the ultimate shift towards liquid resins by the end of the 1970s. Perhaps the largest driving force was the relative cost of powdered resins. Powdered resins cost nearly twice as much as liquid resins. Also, in order for the powdered resins to adhere to the wafers it was necessary to use a large quantity of wax, roughly 1 to 2 percent. This limited the amount of resin that could be applied; restricting the ability to achieve increased product durability and strength. Some powdered resins also presented caul-sticking problems while pressing and the use of powdered resins typically resulted in a fine dusting of resin throughout the facility, posing many health and environmental concerns (Chiu & Scott, 1981). Finally, powdered phenolic resins had a tendency to migrate to the bottom of the mat while on the forming line. By the beginning of the 1980s, application methods and formulations for liquid resins had been created that met all of the advantages of powdered resins, while also overcoming the disadvantages. Powdered phenolic resins remained the standard for waferboard production; however, liquid phenolic resins were used in the production of oriented strand board from the onset.

In addition to the increased use of liquid resins, the blender design had also adapted. The first waferboard plant in Sandpoint, ID used a small diameter drum blender measuring 3 feet in diameter by 25 to 30 feet long (Vajda, 1981). A similar design was used in the Hudson Bay, SK plant. In the late-sixties the blender design was changed to include two blenders in series. The first blender was 4 feet in diameter and was for wax application. The second blender was 5 feet in diameter and is where the powdered phenolic resin was added. The powdered resin adhered to the wax droplets (Coil, 2002). Both blender designs relied on the application of molten wax using low-pressure steam-atomization and powdered phenolic resins using a 4 inch conveyor at the wafer infeed chute (Watkins, 1981).

As previously mentioned, since the commercialization of oriented strand board in the early-eighties, liquid phenolic resins has been used nearly exclusively. This required a new approach for dispersing the resin onto the strands. Originally, air-assisted or airless spray nozzles were used. Unfortunately, spray nozzles capable of producing a fine resin mist were prone to plugging (Coil, 2002; Nyberg & Beattie, 1981). Spinning disc atomizers, which rely on centrifugal force to disperse resin, were the solution. The first systems were powered by air motors, followed by hydraulic motors, and finally electric motors (Coil, 2002). In addition to the research surrounding the use of spinning disc atomizers, Nyberg and Beattie (1981) also completed extensive research to determine the optimal blender design (Figure 21), their findings were:

• The blender should be 8 to 10 feet in diameter and equipped with flights, • The drum should be filled between 1 and 2 inches deep with wafers or strands, • The drum should revolve at an rpm sufficient to carry the wafers or strands nearly

to the top of the drum before they break free of the drum or flight, • Spinning disc atomization should be used to ensure superior resin coverage, and • The atomizers should be located in one of two ways:


o Using a rotating line shaft with spinning disc atomizers appropriately

positioned, or o Using a cantilever beam from either end of the drum with a spinning disc

atomizer located at the end positioned to 45-degrees.

Today, rotary drum blenders are typically 8 feet in diameter and are equipped with flights to help carry the strands to the top of the blender drum before they begin a free-fall decent. Spinning disc atomizers are attached to a shaft located along the length of the blender drum; however, the shaft does not spin. Instead, the atomizers spin independently, dispersing resin radially (in a horizontal direction) and wax is generally applied using nozzles on the infeed face of the blender drum. Also, rather than filling the drum between 1 and 2 inches with strands, blenders are typically filled to a third of their respective volume.

Figure 21: Beattie’s blender design (Nyberg & Beattie, 1981).

4.3 FORMING

Once the resin and wax has been added to the strands, they are ready to be formed into a mat. Since the creation of structural particleboard in the 1950s, the forming process has been completely revamped, mostly because of the commercialization of OSB. Wafers and strands tend to agglomerate, creating challenges for transporting and distributing the strands evenly. One of the first formers designed relied on a revolving distributor head, which directed the material into a series of pipes or tubes that formed a circle (Figure 22). The tubes extended to a moving conveyor below, where the tubes were aligned across its entire width. As the material fell through the tubes this arrangement created a continuous mat of material, and because the tubes were adjustable, alterations could be made to fine-tune the material distribution (Gunn, 1972).


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Side view

Top view

Figure 22: Patent drawing for original former (Gunn, 1972).

With the creation of oriented waferboard and oriented strand board it was necessary to refine the forming process to facilitate material alignment. Today, the forming process for oriented strand board includes a series of formers, or orientors. Each former system includes a forming bin, forming bin conveyor, doffing rolls, distributor rolls, and a series of orientors (Figure 23). Generally, there are two types of formers, those equipped with machine-direction orientors and those equipped with cross-orientors.


Forming bin

Forming conveyor

Infeed

Distribution rolls

Orientors

Doffing rolls

Forming line Figure 23: Schematic of machine direction forming system.

The forming bin is a cueing region for resinated strands. This helps to ensure that there is an even flow of material fed to the forming line, regardless of any disruptions that may occur in the process previous to the forming line. Within the forming bin, the forming bin conveyor jogs the pile of strands into the doffing rolls that are located at the front of the forming bin. The doffing rolls are series of spinning picks that draw strands from the forming bin and into the distributor rolls, which disperse the strands evenly across the orientors.

Machine-direction orientors align the strands parallel to the machine-direction of the final product. This is in the same direction as the motion of the conveyor line. These orientors are used for the surface layers of the product. Originally, orientors contained a series of baffles that directed the strands as they passed through. Today, revolving disc orientors have become the norm. In this design, discs are mounted onto a series of revolving shafts at a particular spacing. Each successive row of discs overlap (Figure 24), ensuring that there are no gaps for the strands to potentially pass through without being oriented. As the strands are dispersed over the discs from the distributor rolls located above, the strands migrate between the discs, causing them to become aligned. As a result, the spacing of the discs is critical. If the spacing is too large the strands will pass through without becoming aligned; however, if the discs are spaced too close the strands may not pass through fast enough or become lodged between the discs, in either case creating plugs and resulting in production downtime. Once the strands pass through the discs they are deposited on either the empty conveyor line, if it is the former for the bottom of the panel, or another layer of strands, if it is the former for the top of the panel.


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Figure 24: Picture of machine direction orientor discs.

Cross-orientors are used for the core layers and align the strands perpendicular to the machine-direction of the final product. There has been very little advancement in the design of these systems since Potlatch designed their first one in the 1970s (Brown & Bean, 1974; Snodgrass et al., 1973). It includes a rotating shaft with baffles extending from the surface. Because of its shape, these orientors are sometimes known as fin formers. The baffles collect strands, which then migrate towards the inner shaft where they are aligned using the V-shape that the baffle and shaft form at the connection. As the shaft rotates, strands slough off of the baffle and onto the moving mat beneath. As with machine-direction orientors, there are a series of cross-orientors; however, they do not overlap.

With both classes of orientors, the distance they are placed above the surface below impacts the final alignment. Ideally, the orientors are placed within an inch above the surface. This reduces the opportunity for the strands to lose their alignment before being deposited. In reality, the orientors should be placed as close as possible without causing orientor plugs. Photographs of the mat of strands exiting both classes of orientors is shown below (Figure 25).


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Figure 25: Example of strand orientation coming from core (left) and face (right)

orientors with the machine direction indicated.

Between the formers it is common to have large magnets to collect debris that could damage subsequent equipment. It is also common to have mat height detectors, pre-press rolls, and scales. Mat height detectors and scales are used as a process control tool to ensure proper operation and to adjust the orientor heights accordingly.

Pre-press rolls help remove air from the mat before pressing and create a smooth surface for subsequent layers of strands to be deposited. Garlick (1984) reports that “experience has shown that the orientation of the strands can be disturbed by the discharge of air when closing the press.” Garlick (1984) also mentions that a pre-pressed mat requires less daylight space in the press, reducing the press closing time and ultimately reducing costs (Garlick & Young, 1984). These rolls can be placed either between formers or after the entire may has been formed.

4.3.1 Forming Line Conveyor

The mat of strands is formed onto a smooth forming line conveyor or onto caul screens. Caul screens are heavy, wire screens that are used for transporting the mat along the forming line and into the press. During pressing the heat and steam must be able to pass through the screen and into or out of the panel. Because the screen has a rough surface it leaves an impression on the final product. Although it can be sanded off in an additional stage, the rough surface is often desirable as it creates a skid resistant surface. This is particularly useful for roof sheathing applications.

Alternatively, a smooth forming line conveyor may be used. With this system the length of the mat is not restricted to the caul screen length, so it can be cut to different lengths. In addition, a screen may or may not be used during pressing. Typically, continuous presses do not use a screen while batch presses do.


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4.4 PRESSING

Formed mats are consolidated under heat and pressure in a continuous or batch press. Batch presses have historically been the industry standard; however, continuous presses are gaining popularity particularly with processes that solely produce commodity sheathing products.

Batch presses can be single- or multi-opening and can be as large as 8 feet by 64 feet. For mult-opening presses the largest is 12 feet by 34 feet with 12 openings and was produced by Siempelkamp (Siempelkamp). Continuous presses are considerably larger. For example, the Conti-Roll press by Siempelkamp is as large as 12 feet by 230 feet and has a throughput speed as high as 2 000 mm/second, or 6.6 ft/second (Siempelkamp). The disadvantage of continuous presses is the complexity and difficulty in adjusting for different products.

As Geimer and Robert (1982) report, mats are consolidated and cured in the press using successive steam fronts. Initially, moisture in the surface layer is converted into steam and migrates into the board until it condenses. The condensation is converted again into steam and migrates further into the board. This continues until the heat reaches the centre of the board, causing the core temperature to plateau and any remaining moisture to escape from the board edges. The time it takes for this cycle to complete depends on many factors, including: strand size, board thickness, moisture content, mat density, platen temperature, and press closing speed. It is necessary to find a balance between these factors to reduce the overall press-cycle time, while achieving suitable panel properties. Steam injection pressing has shown considerable promise in reducing the overall press-cycle time while not jeopardizing the panel properties (Geimer, 1982).

Steam injection pressing has been around since the 1950s; however, it has just recently started to become adopted by OSB operations. This has largely been driven by the shift towards manufacturing thicker products and a need to reduce the associated press-cycle time. Until recently, presses were typically not the bottle-neck for an operation; therefore, shorter press-cycle times were not necessary to improve production capacity. In addition to reduced press-cycle times, steam injection pressing also improves the vertical density gradient (Figure 26) (Geimer, 1982).


Figure 26: Comparison of the vertical density profile created using a conventional and a steam injection press, showing a significant improvement in the core density

when using the latter system (Geimer, 1982).

4.5 PRODUCTS LINE

From the press the panels are cut to the final product width and length, which is typically 4 feet by 8 feet; however, there are some exceptions. For instance, panels bound for Japan are cut to 3 feet by 6 feet if intended for post and beam construction. The panels are then stamped with the appropriate grade and mill reference number.

Depending on the final product’s use there are several additional stages that may occur before the panels are packaged, strapped, and shipped. These include sanding, application of a tongue and groove, and edge-sealing.

Sanding is performed when the final application requires a smooth finish, such as flooring or stair treads. Because OSB is produced using wood strands of varying dimensions, the surface quality is relatively poor when compared with similar grades of plywood. As a result, sanding is required to obtain a uniform, smooth surface.

A tongue and groove profile is often applied to OSB sold as suflooring. This profile facilitates the consolidation of the floor system, reducing the occurrence of noise caused by the movement of individual panels. It also improves the transfer of forces between panels. This is particularly important when the floor overlay is a brittle material as cracks may occur if the panels move independently. As an alternative to tongue and groove panels, solid blocking could also be used at each of the panel joints (Structural Board Association, 2006).

Oregon State University University of British Columbia University of Maine Virginia Tech

www.wbc.vt.edu

Confidential This information is confidential and is to be used only by persons for whom it was prepared.


There is no standard tongue and groove profile used throughout the industry. In fact, even between mills operated by the same company there has been variability in the profile. Some companies, such as Louisiana-Pacific market their product based on the benefits of their particular profile. Louisiana-Pacific’s notched profile is intended to allow any water that accumulates on the floor during construction to pass through (Figure 27). Fortunately, all of the different profiles tend to fit together.

Figure 27: Example of Louisiana-Pacific’s notched tongue and groove design

(Louisiana-Pacific Corporation, 2007).

Edge-sealing is performed on nearly every panel and occurs after the panels have been stacked into bundles. Because of OSB’s relatively low density and inherent voids caused by the use of wood strands, OSB is susceptible to significant water absorption and swelling along its edges if exposed to water or high humidity conditions, such as during the construction phase of a building. The most significant affects of this exposure have occurred with OSB subflooring. When exposed to water the edges may swell, resulting in an uneven floor. Depending on the overlay, these edges may need to be sanded smooth, adding considerable work. The tongue and groove profile used on flooring increases the impact of water absorption as the shape of the profile dramatically increases the surface area of the edge. As mentioned, some companies have designed their tongue and groove profile to reduce the affect; however, edge-sealing is the most widespread approach. Edge seal is a waterborne latex/wax emulsion that is sprayed onto the edges of the panels (Technical Industrial Sales - Oregon). It is available in a variety of colors, which companies use as a form of marketing (Table 6). Once the panels have been edge-sealed they are packaged and strapped in preparation for shipping.

Table 6: Edge seal colors used by three major OSB producers.

Company Colors

Louisiana-Pacific Orange, grey, black

Weyerhaeuser Gold, green

Ainsworth Purple, turquoise


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5.0 CONCLUSION

Composite wood based products capable of meeting structural requirements have increasingly become a major component of the North American forest products industry. While plywood was the first product of this category, it was not until the 1960s that this category of products began to flourish with the acceptance of waferboard. Today, waferboard has become virtually obsolete; however, it was the first of a growing list of products produced using wood strands/wafers. Oriented strand board succeeded waferboard and has saturated the North American construction sector. Since the early 1980s OSB has captured markets that were historically met using plywood. The production process for OSB has undergone only minor changes in recent years. Having stemmed from the waferboard process, most of the process evolution took place during the waferboard era. That said, in light of the recent explosion in OSB capacity with a corresponding weak demand, it will be necessary for operations to compete on one of two fronts. First, operations can compete on cost and/or quality. This requires that operations dedicate resources to improving the process. The second option is to compete on the end use of the product. This has become a popular choice as evident by the increasing number of companies manufacturing OSB for special applications and producing a new product known as oriented strand lumber. Again, this option requires resources to improve the process, but also requires significant resources for research and development efforts. In order for the OSB industry to remain competitive it must look at options for extending its life cycle beyond its current maturity.



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6.0 LITERATURE CITED

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