 |
 |
 |
 |
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
 |
|
Chapter 6. Nonveneer
Panel Products: Particleboard, Hardboard, Medium Density Fiberboard,
OSB/Waferboard, and Insulation Board
ClassificationMeasurementStandard Reporting BasisVolume of Nonveneer Panels•Converting surface measure of any thickness to the standard thickness basis Wood RequirementsProcess RecoveryFormula for Estimating Wood RequirementsWeight of Nonveneer PanelsDerivation of Formulas for Green Wood Requirement
Unlike plywood, which is made from veneer, these panel or "board" products are made from chips, wafers, strands, flakes, and particles of wood or from wood fiber after pulping or refining. Collectively, they are often called composition, reconstituted or nonveneer panels, or boards. Another widely used term for this collection of panel products is composites. Adhesives and other substances are often mixed with the furnish to create desired properties. Depending on species, particle type, and orientation, the type and amount of adhesives and additives used, and thickness and density to which the board is pressed, a very wide spectrum of these products is possible. Agencies reporting statistics often combine them into other groups. For example, OSB/waferboard is often combined with softwood plywood into a grouping called structural panels. Table 6-1 presents a simple classification based on panel density. The reader should consult the Wood Handbook (USFS 1987), Maloney (1977), and Suchsland and Woodson (1990) for further details on specifications, uses, and processes for these products. The references also include the U.S. Department of Commerce standards for these products.
Square Foot Basis (SF). Like plywood statistics, nonveneer panel statistics are generally reported in North America in square feet of a standard thick-ness basis. This represents a piece one foot square and 1/8, 3/8, 1/2, or 3/4 inch thick depending on the product. Respectively, these represent 1/96, 1/32, 1/24, and 1/16 of a cubic foot. Table 6-1 presents the standard thickness basis for each of these products and the metric equivalents. Square Meter, 1 mm Basis. The standard basis for reporting these products in countries using the metric system is the square meter, 1 mm basis. This represents a piece 1 m square and 1 mm thick or 1/1,000 of a cubic meter. Table 6-1. Basic measurements of nonveneer panels.
The methods for converting surface measures and calculating volume of these products are similar to those used for plywood. Converting Surface Measure of Any Thickness to the Standard Thickness Basis. Like the method for plywood, to convert surface measure from any thickness (SMt) to the standard basis for the product, divide the actual thickness (t) in inches by the standard thickness in inches and multiply by the surface measure. The last column of Table 6-1 shows the equation for each product. Table 5-1 summarizes conversion of actual panel thickness to each of the four thickness standards. See also Example 1. Note that any one of the formulas can be used to standardize all panel products to the same thickness basis. In its assessment of the U.S. timber situation, the USFS expresses all of these panel products on the 3/8 inch basis (Appendix 2). Cubic Foot Calculation. The general formula developed for plywood (Chapter 5, p. 70) can be used: ft3 = SMt* t / 12 = 0.08333 * t * SMt. Therefore, Table 5-4 can be used to convert a quantity of panels of a given thickness to cubic feet or cubic meters. See also Example 2. Metric Calculation. Outside North America, nonveneer panels are produced in metric sizes; width (W) and length (L) are in meters, and thickness (t) in millimeters. Statistics are generally reported in square meters surface measure (on a 1 mm basis) or cubic meters. Formulas are SMt = L *
W = surface measure, m2, of SM1 = SMt *t = surface measure, m2,1 mm basis. m3 = SMt* t / 1,000 = SM1 / 1,000. Example 1 Convert 2,500 ft2 of 3/4 inch insulation board to the 1/2 inch standard basis, using the formula in Table 6-1. SF1/2 = SMt* t / 0.5 = 2,500 * 0.75 / 0.5 = 3,750 or multiply 2,500 ft2 by the factor 1.5000 in column 5 of Table 5-1. Convert 1,500 ft2 of 7/16 inch particleboard to the 3/4 inch standard basis, using the formula in Table 6-1. SF3/4 = SMt * t / 0.75 = 1,500 * (7/16) / 0.75 = 875 or multiply 1,500 ft2 by the factor 0.5833 in column 6 of Table 5-1. Example 2 Convert 1,500 ft2 of 7/16 inch particleboard to cubic feet: ft3 = 0.08333 * (1,500 * 7/16) = 54.7 or multiply 1,500 ft2by the factor 0.03646 in column 3 of Table 5-4.
This section presents a method for estimating the quantity of solid wood equivalent needed to produce a unit quantity of a nonveneer panel product. Since these products are produced from small wood elements, the raw material need not be in the form of roundwood logs. The USFS timber assessment provides national averages for wood required (cubic feet roundwood equivalent) to produce one MSF 3/8 inch basis or one cubic foot of these products (Appendix 2). Manufacturing processes for nonveneer panels are often referred to as "wet" or "dry." In a dry process, the conveying medium for the wood particles or fibers is air; in a wet process it is water. Particleboard and waferboard processes are dry, and insulation board processes are wet. Hardboard and medium density fiberboard (MDF) may be manufactured either way, although the dry process predominates in the manufacture of MDF. Conversion efficiency of nonveneer panels is most meaningfully expressed as a percentage by weight of the original wood input. Conversion efficiency of these products depends on the type of raw material (logs or mill residues), species mix, process used, and board density and thickness (Tables 6-2, 6-3). OSB/waferboard typically uses roundwood logs that are not suited for lumber or plywood. These are processed by machines to create flakes or strands with a particular geometry. A major source of loss is flakes that are rejected because of small size. Particleboard, which often uses mill residues such as sawdust, planer shavings, and so forth, mills these to a small size such that much less loss occurs due to rejects. Insulation board, hardboard, and MDF may use either roundwood logs or mill residues which are converted to fiber feedstock by thermomechanical pulping processes that generally have a yield in excess of 90%. The major source of wood fiber loss in the manufacture of wet-process panels is from wood fiber that is partly solubilized and lost through the screen during the mat forming process. These residues are usually converted to other salable products. Dry-process nonveneer panels are often sanded after pressing. The percentage of volume lost to sanding depends on board thickness, since the thickness removed by the sander is usually constant (about 0.060 inch). In the case of OSB, relatively little production is sanded. Depending on the type of product and process, some or all of the sander dust may be recycled.
Table 6-2. Nonveneer panel process conversion efficiencies(percentage of acceptable furnish).
Source: Adapted from Nielson et al. (1985). aThe trim loss percentage varies with the size of the panel as pressed. The common 4' x 8' panel is often made in an 8' x 16' or 8' x 24' press. Note: These
values should be regarded as general guidelines. Actual values
vary among manufacturers due to differences in raw material, technology,
 Formula for Estimating Wood Requirements Calculation of green solid wood equivalent required to produce a nonveneer panel product depends on many factors. An approximation can be obtained by combining process recovery, board density, species density, adhesive/additive weight, and moisture content/shrinkage data. Table 6-3 provides rough estimates of these variables; a particular manufacturer's recipe may deviate substantially from values in the table. Note that the sander and trim loss fractions are gross losses that should be reduced depending on the degree of recycling of these residues back into the process. (See Example 3.) The volume of green wood required to produce 1,000 ft2 or 1,000 m2 is: Imperial GWRI
= [1,000 * t * d *
(1 - MCw/100 - Metric GWRM
= [t * d * (1
- MCw/100 - a/100)] / where GWRI = green solid wood requirement,
cubic GWRM = green solid wood requirement,
cubic f = wood raw material
loss, percent of wood SGg = wood specific gravity of species
used, a = percent of
product weight due to MCw = moisture content of finished
panel on S = percent loss during sanding T = percent loss in trimming panel to size t = panel thickness,
in inches or Derivation of these formulas is detailed in the box on page 82. Densities of these panels vary depending
on the manufacturer and species. Table 6-1 presents the typical
range of specific gravity and density for these products. Actual
board densities are often indicated by the manufacturer and are
based on the moisture content as shipped, usually 6 to 8% MCod. If the density is known, it is easy to
calculate weight. (See Example 4.) In the absence of manufacturer's
label information, an average density must be assumed, and various
statistical agencies have their own assumptions. For example,
FAO assumes the following: Specific Density gravity (lb/ft3) Particleboard 0.65 40 Fiberboard: Compressed 0.95 60 Noncompressed 0.25 15 In the absence of such assumptions, the midrange of the densities given in Table 6-1 can be used.
Example 3 Estimate the cubic foot volume of lodgepole pine roundwood required to produce 1,000 ft2of 3/4 inch OSB having a panel density of 40 lb/ft3. Specific gravity SGg = 0.38 (Table 1-1) Panel density d = 40 lb/ft3 Panel moisture Furnish rejects f = 20% (Table 6-3) Adhesive/additive a = 4% (Table 6-3) Sanding loss S = 0% (Table 6-3) Panel trim T = 5% (Table 6-3)
GRWI =
[1,000 (0.75) 40 (1 - [12 (1 - 128 ft3 roundwood to yield 1,000 ft2 3/4 inch OSB. If this is converted to 1,000 ft2 on 3/8 inch basis, the need is 63.8 ft3. The USFS timber assessment (Appendix 2) estimates 62.3 ft3 / MSF 3/8 inch basis as a weighted national average for all species and processes making OSB. Example 4 Surface measure of the panels = 100 * 5' * 10' = 5,000 ft2. Table 5-4, column 3, indicates that one square foot of 15/16 inch panel has a cubic volume of 0.07812 ft3. Therefore, the total cubic foot volume is5,000 ft2 * 0.07812 ft3/ft2 = 390.6 ft3. Multiplying by the density gives 390.6 ft3 * 40 lb/ft3 = 15,624 lb.
Derivation of Formulas for Green
Wood Requirement
The amount of solid green wood required to produce 1,000
square feet (1,000 square meters) of a nonveneer panel and screening and the specific gravity of the species used. 1. Imperial:
UWODI =
GWRI * (1 - UWODI = oven-dry weight of usable furnish, in pounds GWRI = volume of solid green wood, in cubic feet f = percent wood loss due to screening, rejects SGg = specific gravity of species used (see Chapter 1) 2.
Metric:
UWODM =
GWRM
* (1 - UWODM = oven-dry weight of usable furnish, in kilograms GWRM = volume of solid green wood, in cubic meters Part B. Amount of wood furnish (WF) required to make finished panels: 1. Calculate panel volume and multiply by panel density to estimate panel weight. a. Imperial: Convert 1,000 square feet of panel to weight in pounds. Let WFI = finished panel weight (lb) d = panel density (lb/ft3) t = panel thickness (inches) WFI = 1,000 * t / 12 * d. b. Metric: Convert 1,000 square meters of panel to weight in kilograms. Let WFM = finished panel weight (kg) d = panel density (kg/m3) t = panel thickness (mm) WFM = 1,000 * t / 1,000 d = t * d. 2. Calculate the amount of oven-dry wood in the panel by subtracting panel moisture content and additive materials (adhesives, etc.). Let MCW = panel moisture content percent, total weight basis (see Chapter 1) a = percent additives in panel by weight. a. Imperial: WODI = oven-dry weight of wood furnish in finished panel (lb). WODI = WFI * [1 - ( b. Metric: WODM = oven-dry weight of wood furnish in finished panel (kg).
WODM = WFM * [1
-
( 3. Increase the wood in the finished panel to account for sanding and trimming losses. Let S = percent sander loss T = percent trimmer loss a. Imperial: UWODI = WODI / [1 - ( b. Metric: UWODM = WODM/ [1 - ( Part
C. The equations from parts A and B are
equivalent expressions for the oven-dry weight of furnish
used to 1. Imperial: Combine equations A.1 and B.3a: GRWI, ft3 =
[1,000 t*
d * (1 -
2. Metric: Combine equations A.2 and B.3b:
GRWM, m3 =
[t*
d * (1 -
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
)] /
)(0.38) (62.4)] = 
) * SG
).
) 
) 
) 
) 
