Maximizing lumber use: the effect of manufacturing defects on yield, a case study.
This study analyzed the effect of lumber manufacturing defects on part yield for different lumber grades, lumber lengths, and cutting orders in the furniture industry. The defects investigated were spike marks, conveyer marks, pressure roller stain, drying checks, machine gouge, and machine burn in terms of their occurrence, size, and impact on yield. A database of 5,574 board feet of random width and length white birch boards and two cutting orders were used to conduct rip-first simulation. Boards came from two sawmills, one processing conventional-length logs and the other processing short-length logs. Drying checks had the largest impact on yield, reducing yield by 5.9 percent for one cutting order and 6.4 percent for the second cutting order. The average yield reduction for No. 2A Common lumber was 9.6 percent, vs. 6.6 percent for No. 1 Common and 3.2 percent for Selects lumber. No. 2A Common lumber yields were most affected due to inherent physiological properties that are more common in this grade of lumber, i.e., presence of heartwood and juvenile wood, which make drying more difficult. Spike marks lower yield by about 3 percent for both cutting orders, but they occur only in lumber manufactured at mills using ring debarkers, and mostly on high-grade external boards. Pressure roller stain affected yield by less than 2 percent, and affected smaller sized boards because the defect location offers less flexibility to cut the defect out in the rough mill. Machine burn reduced yield by about 0.6 percent for each of the cutting orders, and it appears to affect conventional-length lumber more due to the dynamics of handling longer boards. Conveyer marks reduced yield by about 0.7 percent. Machine gouge affected yield by 0.5 percent, and most strongly affected yields from short-length lumber.
When processing wood using heavy equipment, the wood is often damaged. This paper presents an exploratory case study of the occurrence and potential impact of such mechanical defects on yield when processing northeastern white birch (Betula papyrifera, Marsh.). From the moment the trees are felled, care must be taken with handling, loading, and unloading the logs and lumber. Even when operators follow appropriate procedures, mechanical damage caused by mishandling and mismanufacturing can happen. The objective of this study was to assess the importance of various manufacturing defects--spike marks, conveyer marks, pressure roller stain, drying checks, machine gouge, and machine burn--that are introduced after trees are felled and during processing into dry lumber. The impact these defects have on yield when boards are processed in a rip-first rough mill will be analyzed.
The boards selected for this study were required to show a range of qualities typical of what is currently available in northern Quebec. Two sawmills were chosen to typify two sawing techniques. The first sawmill processes conventional logs into National Hardwood Lumber Association (NHLA) grade lumber, whereas the second processes short-length logs into the same product. Petro and Calvert (1990) described conventional sawlogs as logs of sufficient size and quality to be sawn into NHLA lumber. A large number of clear cuttings in lengths of 8 feet or more can typically be obtained from these boards. On the other hand, short-length logs are logs that do not conform to the criteria defined by Petro and Calvert (1990) because they are too short, too crooked, too small in diameter, or present a combination of these characteristics. These logs often have a length between 4 and 8 feet and are generally classified as pulpwood. However, they are increasingly considered fit for sawing.
A large volume of random width and random length hardwood factory lumber produced in Quebec is used in furniture, cabinetry, and flooring industries. Both the conventional- and short-length green lumber used in this study were graded using the National Hardwood Lumber Association (1998) lumber-grading rules. Following these rules, the lumber was graded according to the potential recovery of clear cuttings that can be obtained by combinations of ripping and crosscutting. The number of cuts that can be made is determined through surface measure for each board. In order to determine the lumber grade, areas of placements of potential clear cuttings are determined considering the location of natural defects such as knots, wane, and checks. Manufacturing defects were tallied as natural defect equivalents.
Table 1 shows the number of boards analyzed per grade for each of the two sawmills included in the study. One sawmill, located at Senneterre, Quebec, provided 659 boards (2,942 board feet [BF]) of conventional-length white birch lumber. The other, located at Ste-Monique, Quebec, provided 954 boards (2,632 BF) of short-length white birch lumber. The sample consisted of 1,613 random width and length boards (5,574 BF). All boards were dried in a commercial kiln using high-temperature drying schedule No. 23 (Cech and Pfaff 1980) and surfaced on both faces at Forintek Canada Corp., Eastern Laboratory to allow easier defect identification during the digitizing process.
A digitized database of 5,574 BF random width and length boards containing information on all grade defects was developed by Clement et al. (2005). Table 1 describes the database characteristics, i.e., the number and volume of boards that were digitized along with the average width and length for each grade and lumber length. For this study, 1,156 BF of Selects, 912 BF No. 1 Common (1C), 874 BF No. 2A Common (2AC) NHLA-graded lumber and 960 BF Selects, 970 BF No. 1C, and 702 BF No. 2AC custom-graded short-length lumber were used.
Two cutting orders, Furniture and Panel, were used in this study. The Furniture and Panel cutting orders were obtained from Canadian furniture manufacturers that use white birch lumber in their operations. The Furniture cutting order (Table 2) was obtained from a rough mill that produces precut components and panel parts for several furniture plants. This cutting order has an average length of 803 mm and an average width of 36.2 mm. The specified cutting order is representative of the production of buffet and hutch types of dining room furniture.
The Panel cutting order is from a plant that produces solid wood panels of specific lengths. This cutting order calls for parts of random width between 25 mm and 114 mm in a set of specified lengths. Due to software restrictions when processing only panel parts, the 25-mm to 114-mm width interval was divided into 14 discrete widths in 6.3-mm (1/4-in) increments. This resulted in an order that consists of all combinations of 25, 32, 38, 44, 51, 57, 64, 70, 76, 83, 89, 95, 102, and 114 mm widths and 445, 546, 749, 940, 991, 1041, 1092, 1143, 1245, 1372, 1549 mm lengths (445, 546, and 749 mm are salvage-specific lengths). An infinite part quantity for each part size was specified.
Rough mill processing simulation
For the purposes of this study, ROMI-RIP, a rip-first rough mill processing simulation program (Thomas 1999) was used to estimate the yield loss. First, the processing was simulated using boards without any manufacturing defects present. Then, simulation was repeated while adding each of six manufacturing defects to the existing database individually. Finally, the simulation was performed with all manufacturing defects present. Based on standard deviation estimates of initial yield, simulations were replicated 20 times in order to verify significance as described by Clement et al. (2004, 2005).
ROMI-RIP simulation parameters:
Arbor type: All-blades movable arbor with 6 spacings:
Kerf: 4 mm;
Prioritization strategy: complex dynamic exponent (CDE);
Part prioritization: updated constantly for all cutting orders except for Panel cutting order, which was never updated;
Salvage cuts: made to primary part dimensions, except in Panel cutting order, where three lengths were salvage specific.
The incidence of defects was analyzed by calculating average defect frequency (number of defects per [m.sup.2]) and average defect size (area of each defect type [cm.sup.2]/[m.sup.2]). Mechanical defects included in this analysis were spike marks, conveyer marks, pressure roller stain, drying checks, machine gouge, and machine burn. Defects are listed in the order in which they occur during processing. Table 3 shows average defect frequencies and their differences by grade and sawmill type. Pressure roller stain and drying checks are not listed here because their occurrence was sometimes so frequent that they were digitized as groups. Table 4 shows average defect areas for all six defect types.
Yield loss caused by defects, whether natural or manufacturing, will manifest itself during board processing in the rough mill. Table 5 (Furniture cutting order) and Table 6 (Panel cutting order) show 1) yield for lumber without any manufacturing defects; 2) yield decrease for each defect individually; 3) yield decrease for all defects combined; and 4) statistical differences in yield change for Selects, No. 1C, and No. 2AC lumber from conventional- and short-length sawmills.
Spike marks (Fig. 1) are defined as small (<3 mm), discolored spots caused by excess pressure on the feed system at the debarker. This defect occurs when using ring debarkers. While feeding logs into the debarker, the endwise conveyer cylinders must exert sufficient pressure and grip to move frozen, wet, slippery, muddy, and misshaped logs forward. In order to prevent slippage, operators sometimes set pressure on conveyer cylinders too high, especially in winter, when processing frozen logs.
Lumber from both conventional-length and short-length logs in this study came from sawmills using a ring debarker. The spike marks only occurred in lumber from the short-length sawmill. Their occurrence (Table 3 and 4) was likely caused by debarker conveyer cylinder pressure set too high in this sawmill because short-length logs are more difficult to handle. Additionally, in small logs, more lumber comes from the zone close to the bark when compared to proportions of such lumber from larger logs. Incidence of spike marks was higher in Selects grade (3.7 spike marks per [m.sup.2]) than in No. 1C (2.0) or No. 2AC (0.9) grades. This can be explained by the location of Selects grade lumber on the outside perimeter of the log, where fewer naturally occurring defects are found, but also where the pressure cylinders from the ring debarker make contact.
In lumber from short-length logs, spike marks lowered yield by 3.4 percent for the Furniture cutting order (Table 5) and 3.0 percent for the Panel cutting order (Table 6). No occurrence of this defect was found in the lumber from conventional-length logs. Spike marks are of concern for two reasons. The first is that they are barely visible in rough lumber, but they become obvious when the finishing coat is applied to the final product. The second is that they occur mostly in Selects lumber, where an average 5.4 percent yield decrease was observed for the two cutting orders. This compares to 2.2 percent for No. 1C and 1.9 percent for No. 2AC (Tables 5 and 6). This affects lumber desirability from such a mill and makes it necessary to be extremely vigilant during processing, so that quality issues do not arise for the customer.
Spike marks can be controlled, to an extent, by use of sharp spikes and appropriate cylinder pressure. Cylinder pressure on newer systems can be adjusted on a per-log basis. This procedure along with appropriate maintenance can considerably decrease spike mark occurrence. In a follow-up study at this short-length sawmill, it was found that spike marks were likely caused by inadequate pressure at the debarker feed system. After customers expressed their concern, the appropriate automated pressure adjustment and maintenance procedures were applied, which largely solved the problem.
Conveyer marks (Fig. 2) occur when wood is torn away by a chain dog. They typically were about 6 mm (1/4 in) in width. For all lumber grades, conveyer marks were more frequent in lumber from short-length logs (Table 3). A short-log sawmill, to be economical, has to process the lumber more quickly, which may lead to more handling defects. Also, short-length lumber, being of lesser size (Table 1) and weight, seems to be more difficult to convey correctly using standard chain dogs, hence leading to more conveyer marks.
Conveyer mark incidence had in general more impact on yield in lumber from short-length logs than in lumber from conventional-length logs. The presence of conveyer marks affected yield by 1.1 percent for the Furniture cutting order (Table 5) and 0.5 percent for the Panel cutting order (Table 6). Conveyer marks reduced yield in lumber from short-length logs most, which was to be expected due to their large area of 8.8 [cm.sup.2]/[m.sup.2], vs. 2.0 [cm.sup.2]/[m.sup.2] in lumber from conventional-length logs (Table 4).
Pressure roller stain
Pressure roller stain, a brownish stain less than 5 cm (2 in) wide across the width of the board, is believed to be a chemical discoloration of wood that sometimes occurs during air-drying or kiln-drying, and apparently is caused by the application of excessive mechanical pressure on wood (Chauret and Giroux 1999). As opposed to spike marks, in pressure roller stain, the wood fibers are not mechanically altered but rather chemically altered. This defect type is closely related to spike marks, but it occurs a little deeper in the wood. The same methods applied to decrease the occurrence of spike marks should also help reduce pressure roller stain.
Most pressure roller stains occurred in Selects grade lumber from short-length logs (33.6 [cm.sup.2] per [m.sup.2]) and No. 1C (4.3) and No. 2AC (6.5) from conventional-length logs. The order of magnitude difference in Selects grade lumber from short-length logs points to excessive debarker conveyer cylinder pressure in this sawmill. The significantly lower occurrence of pressure roller stains in lower grades of lumber from short-length logs and in all grades of lumber from conventional-length logs is attributed to other machine feed systems imposing excessive mechanical strain on the board surface during sawmill processing.
The effect of pressure roller stain on yield corresponds to the average size of the stain in each lumber set. For the two lumber sets combined, pressure roller stain affected yield by 2.3 percent in the Furniture cutting order (Table 5), and by 1.8 percent in the Panel cutting order (Table 6). Pressure roller stain affected lumber from short-length logs more when using Selects grade lumber--by 2.4 percent and 2.7 percent for the Furniture and Panel cutting orders, respectively--but reduced the yield in lumber from conventional-length logs more for No. 1C and No. 2AC grades. With the Furniture cutting order, the yield difference was 2.2 percent for No. 1C lumber, and 5.9 percent for No. 2AC lumber, while the Panel cutting order provided differences of 2.2 and 1.0 percent for No. 1C and No. 2AC lumber, respectively.
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The manufacturing defects that occupied the most board surface area were drying checks (Table 4). Drying checks are a lengthwise separation of the wood that usually extends across the rings of annual growth. They occur during drying when the moisture gradient is too high, especially at the beginning of the drying schedule. This defect was more frequent in No. 1C and No. 2AC lumber from short-length logs. A higher proportion of lower grade boards generally come from a log center, thus they have a larger proportion of juvenile wood and heartwood, and are more prone to checking. Also, there were significant differences in check occurrence between lumber from short-length and conventional-length logs for all grades (Table 4). These may have come from the higher proportion of juvenile wood in the short logs.
Drying checks were the defect with the greatest yield-decreasing impact, reducing average yield by 6.2 percent for the Furniture cutting order (Table 5) and 6.7 percent for the Panel cutting order (Table 6). No. 2AC lumber was the most affected grade. Checks had the greatest effect on the yield of lumber from short-length logs. The yield difference when drying checks were included was 2.5 percent for Selects lumber and 3.3 percent for No. 1C when using the Furniture cutting order, and 2.2, 2.9, and 8.7 percent for Selects, No. 1C, and No. 2AC, respectively, with the Panel cutting order. These differences indicate that the drying of lumber sawn from lesser quality logs requires greater care. In lower grade lumber, sawn from the part of the log closer to the pith, the proportion of juvenile wood and heartwood is, on average, higher, which appears to lead to checks having a greater negative impact.
Machine gouge (snipe) is a depression across the width of a board due to the machine cutting below the desired line of cut. This defect arises at the planer when boards are not properly held in position by pressure rollers. In the Selects grade, the frequency (Table 3) and average area (Table 4) of machine gouge was higher in lumber from short-length logs. For other grades, the differences in occurrence of machine gouge were not significant. However, these differences cannot be attributed to the lumber length. The machine gouge is caused by incorrectly set pressure on infeed and outfeed rollers of a planer. Since the two lumber samples were processed using different machines, we only compared differences within each lumber length.
On average, for both lumber samples, machine gouge reduced yield by 0.5 percent for the Furniture (Table 5) and by 0.4 percent for the Panel (Table 6) cutting orders. The No. 2AC lumber from short-length logs was more affected by this defect, when processing the Panel cutting order. This indicates that the longer lumber was easier to hold firmly by planer pressure rollers, reducing the occurrence of this type of defect. This defect had more negative impact on yield for Selects lumber from short-length logs than on the corresponding lumber from conventional-length logs. It lowered yield by 0.6 and 0.9 percent when processing lumber from short-length logs with the Furniture and Panel cutting orders, respectively. This defect did not have a significant influence on yield for lumber from conventional-length logs.
Machine burn is a darkening, or charring, of the wood due to overheating by the machining knives when a piece is stopped in a machine. This defect also occurs mostly at the planer. Caused by a pause in the feed, the knives either rub on the wood or, if dull, are forced into the workpiece, increasing temperature in one spot and burning the wood, Machine burn was well controlled at the sawmill processing conventional-length logs (Tables 3 and 4). Lumber from short-length logs had more machine burn area in Selects and No. 1C lumber (Table 4) than the lumber from conventional-length logs. This could be related to the average size (length and width) of the lumber (Table 1) or to the differences in machine set-up.
Machine burn lowered yield by 0.6 percent for the Furniture cutting order (Table 5) and 0.6 percent for the Panel cutting order (Table 6). The effect of this defect on yield was low and not statistically significant when No. 2AC lumber was processed using the two cutting orders. At the same time, the lower grades have shorter average lengths (Table 1). The impact of machine burn was statistically significant for No. 1C when processing the Panel but not the Furniture cutting order. There was a yield difference of 1.1 percent when processing Selects lumber with the Panel cutting order but that difference was only 0.1 percent when using the Furniture cutting order.
All defects combined
When all six defects were included in the simulation, a sizable yield reduction occurred. Yield for lumber from conventional-length logs was reduced by about 7 percent and for lumber from short-length logs by 14 percent. The smallest yield reduction of 2.6 percent was for Selects lumber from conventional-length logs when processing the Furniture cutting order. The largest yield reduction of 17.2 percent was for No. 2AC lumber from short-length logs when processing the Panel cutting order. This indicates a sizable potential for yield increase by focusing on process improvement.
The objective of this study was to analyze the effect of manufacturing defects on lumber yield. We used lumber from two sawmills, one that processed conventional-length logs and another that processed short-length logs. While we found significant differences in occurrence of manufacturing defects between the two, it was not our objective to analyze the effect of lumber length on yield reduction. This is due to the fact that the manufacturing defects are caused by the equipment used to process the logs into lumber, and each sawmill used its own equipment. Therefore, we cannot be certain whether the differences in defect occurrence between the two lumber sets were due to equipment set-up or lumber characteristics. We have simply stated what the effect on yield was for each case.
With this in mind, manufacturing defects definitely have a quantifiable influence on rough mill yield. On average, they reduced yield by about 10 percent. Therefore, an investment made to reduce the occurrence of certain defect types would be worthwhile. Manufacturing defects such as machine burn, conveyer marks, and machine gouge can be related back to drying defects, such as checks and warp that may cause board handling problems, mostly at the planer mill.
For lumber from conventional-length logs and two cutting orders combined, the average yield was reduced by 7.25 percent (3% for Selects, 8% for No. 1C, and 11% for No. 2AC) when all manufacturing defects were included. On average, about 5 percent (2% for Selects, 5% for No. 1C, and 7.7% for No. 2AC) of this yield reduction can be attributed to drying checks.
For lumber from short-length logs and two cutting orders combined, the average yield was reduced by 14 percent (13.7% for Selects, 13.8% for No. 1C, and 14.6% for No. 2AC) when all manufacturing defects were included. On average, about 8 percent (4.4% for Selects, 8.1% for No. 1C, and 11.6% for No. 2AC) of this yield reduction can be attributed to drying checks.
The remainder of the yield reduction, 2.25 percent for lumber from conventional-length logs and 6 percent for lumber from short-length logs, can be attributed to all other manufacturing defects. Results from this study show that close attention to mechanical handling of the wood during both primary and secondary processing steps can lead to significant yield improvements and that improvement of dry-kiln operation will bring the highest benefit.
Cech, M.Y. and F. Pfaff. 1980. Kiln Operator's Manual for Eastern Canada. Special Publication SP504ER. Forintek Canada Corp., Eastern Lab., Ste-Foy, QC, Canada. 185 pp.
Chauret, G. and Y. Giroux. 1999. Erable a sucre tache, essais preliminaires (Stained sugar maple, preliminary trials). Project report 1122. Forintek Canada Corp., Eastern Division, Quebec, QC. Canada. 14 pp. (in French).
Clement, C., R. Beauregard, R. Gazo, and T. Lihra. 2004. Correspondence analysis as a tool towards optimizing the use of white birch in the panel industry. Wood and Fiber Sci. 36(4):598-610.
_______, R. Gazo, R. Beauregard, and T. Lihra. 2005. Comparison of rough mill yield for white birch lumber between a conventional and a short-log sawmill. Forest Prod. J. 55(3):71-80.
National Hardwood Lumber Association (NHLA). 1998. Rules for the measurement and inspection of hardwood and cypress. NHLA, Memphis, TN. 19 pp.
Petro, F.J. and W.W. Calvert. 1990. How to grade hardwood logs for factory lumber. Forintek Canada Corp., Eastern Lab., Ottawa, ON, Canada. 64 pp.
Thomas, R.E. 1999. ROMI RIP 2.0 user's guide: ROugh MIII RIP-first simulator. Gen. Tech. Rept. NE-259. USDA Forest Serv., Northeastern Forest Expt. Sta., Radnor, PA.
The authors are, respectively, Wood Technologist, Texas Forest Serv., Lufkin, TX (firstname.lastname@example.org); Group Leader, Development of Value-Added Wood Products, Forintek Canada Corp., Eastern Lab., Ste-Foy, QC, Canada (email@example.com); Associate Professor, Purdue Univ., West Lafayette, IN (firstname.lastname@example.org); and Associate Professor, CIBISA, Universite Laval, Pavillon Abitibi-Price, Ste-Foy, QC, Canada (Robert.Beauregard@sbf.ulaval.ca). This paper was received for publication in March 2003. Article No. 9643.
*Forest Products Society Member.
Table 1. -- Database characteristics. No. of Width Length Grade Volume boards avg. avg. ([m.sup.3]) (BF) (m) Conventional-length Selects 2.73 1,156 183 0.165 3,560 No. 1C 2.15 912 241 0.141 2,475 No. 2AC 2.06 874 235 0.140 2,456 Short-length Selects 2.27 960 312 0.134 2,120 No. 1C 2.29 970 292 0.152 2,030 No. 2AC 1.66 702 350 0.124 1,490 Table 2. -- Number of parts required of each specified length and width in Furniture cutting order. Width Length 25-mm 32-mm 38-mm 44-mm 51-mm 57-mm 64-mm 70-mm 76-mm (mm) 362 -- -- -- -- 5 -- -- 7 -- 387 36 8 3 2 1 1 1 5 -- 451 42 10 4 2 1 1 1 -- -- 514 57 13 5 3 2 1 1 10 -- 584 9 2 1 1 -- -- -- 20 -- 768 29 7 3 2 1 1 -- -- -- 914 49 11 5 3 2 1 1 5 -- 1073 51 12 5 3 2 1 1 8 35 1175 8 4 1 -- -- -- -- -- -- 1245 24 6 2 1 1 1 -- 4 -- 1295 13 3 1 1 -- -- -- -- -- 1346 19 4 2 1 1 -- -- -- -- Table 3. -- Average frequency of mechanical defects. (a) Machine Machine Grade Lumber length Spike mark Conveyer mark gouge burn (no./[m.sup.2]) Selects Conventional 0.0 (0.0) 0.2 (0.7) 0.1 (0.4) 0.1 (0.6) Short 3.7 (9.2) 3.1 (6.7) 0.2 (1.0) 0.3 (1.4) p-value 0.00** 0.00** 0.00** 0.07 No. 1C Conventional 0.0 (0.0) 0.7 (2.4) 0.1 (1.0) 0.1 (0.7) Short 2.0 (6.5) 2.6 (6.3) 0.3 (1.9) 0.3 (1.2) p-value 0.00** 0.00** 0.06 0.01** No. 2AC Conventional 0.0 (0.0) 0.8 (2.7) 0.1 (0.8) 0.2 (1.0) Short 0.9 (4.3) 3.1 (7.5) 0.3 (1.9) 0.2 (1.1) p-value 0.00** 0.00** 0.04* 0.45 (a) Values in parentheses are standard deviations. * = significant difference between conventional and short lumber ([alpha] < 0.05); ** = highly significant difference between conventional and short lumber ([alpha] < 0.01). Table 4. -- Average area of mechanical defects. (a) Lumber Spike Conveyer Pressure Grade length mark mark roller stain (cm./[m.sup.2]) Selects Conventional 0.0 (0.0) 2.0 (9.1) 0.5 (3.8) Short 6.2 (43.2) 8.8 (29.2) 33.6 (217.8) p-value 0.01** 0.00** 0.00** No. 1C Conventional 0.0 (0.0) 4.1 (17.2) 4.3 (20.3) Short 1.0 (4.5) 5.9 (17.5) 0.1 (1.9) p-value 0.00** 0.13 0.00** No. 2AC Conventional 0.0 (0.0) 4.3 (22.9) 6.5 (25.9) Short 0.2 (1.2) 6.4 (29.4) 2.3 (25.7) p-value 0.00** 0.17 0.03* Lumber Drying Machine Machine Grade length check gouge burn (cm./[m.sup.2]) Selects Conventional 25.0 (56.2) 0.1 (0.9) 1.5 (9.1) Short 41.4 (155.3) 8.1 (59.8) 8.4 (70.6) p-value 0.05* 0.01** 0.04* No. 1C Conventional 71.2 (255.0) 0.8 (5.6) 1.6 (13.8) Short 123.9 (429.2) 3.1 (29.5) 8.4 (44.1) p-value 0.04* 0.13 0.01** No. 2AC Conventional 87.0 (278.0) 4.4 (31.9) 1.4 (10.1) Short 213.9 (669.3) 6.1 (52.7) 1.7 (13.0) p-value 0.00* 0.31 0.39 (a) Values in parentheses are standard deviations. * = significant difference between conventional and short lumber ([alpha] < 0.05); ** = highly significant difference between conventional and short lumber ([alpha] < 0.01). Table 5. -- Yield by grade and lumber length for different types of mechanical defects for Furniture cutting order. (a) Selects No. 1C Conventional Short Conventional (%) Base 69.7 (0.5) 64.6 (0.9) 63.3 (1.0) Spike mark 69.7 (0.5) 60.7 (1.9) 63.3 (1.0) p-value 0.500 0.000** 0.500 Conveyer mark 69.7 (0.7) 64.2 (1.0) 62.9 (1.0) p-value 0.500 0.076 0.091 Pressure roller stain 69.3 (0.6) 62.7 (1.1) 61.8 (1.2) p-value 0.021* 0.000** 0.000** Drying check 68.7 (0.9) 62.1 (1.0) 60.3 (1.1) p-value 0.000** 0.000** 0.000** Machine gouge 69.4 (0.9) 63.9 (1.0) 62.9 (1.0) p-value 0.071 0.016* 0.087 Machine burn 69.3 (0.8) 64.2 (1.1) 63.0 (1.0) p-value 0.020* 0.107 0.191 All 67.9 (0.6) 55.1 (2.4) 58.7 (1.2) p-value 0.000* 0.000** 0.000** No. 1C No. 2AC Short Conventional Short (%) Base 63.9 (1.5) 57.8 (1.5) 47.4 (0.8) Spike mark 62.1 (1.6) 57.8 (1.5) 46.8 (0.7) p-value 0.001** 0.500 0.009** Conveyer mark 62.8 (1.3) 56.2 (2.0) 47.1 (0.9) p-value 0.012 0.006 0.104 Pressure roller stain 63.7 (1.5) 53.8 (2.9) 47.0 (0.8) p-value 0.385 0.000** 0.043* Drying check 58.7 (0.8) 52.1 (2.0) 43.1 (0.8) p-value 0.000** 0.000** 0.000** Machine gouge 63.8 (1.1) 57.7 (1.7) 47.2 (0.7) p-value 0.403 0.420 0.214 Machine burn 63.6 (1.1) 57.3 (2.1) 47.1 (1.0) p-value 0.256 0.220 0.137 All 54.0 (2.3) 50.4 (1.7) 41.8 (1.0) p-value 0.000** 0.000** 0.000** (a) Values in parentheses are standard deviations. ** = highly significant difference ([alpha] < 0.01); * = significant difference ([alpha] < 0.05); z-test p-value for comparison between base case and treatment. Table 6. -- Yield by grade and lumber length for different types of mechanical defects for Panel cutting order. (a) Selects No. 1C Conventional Short Conventional (%) Base 71.2 (0.3) 63.5 (0.5) 62.1 (0.4) Spike mark 71.2 (0.3) 60.5 (0.7) 62.1 (0.4) p-value 0.500 0.000** 0.500 Conveyer mark 71.1 (0.2) 62.7 (0.5) 61.6 (0.3) p-value 0.283 0.000** 0.000** Pressure roller stain 70.9 (0.1) 61.5 (0.7) 60.6 (0.5) p-value 0.000** 0.000** 0.000** Drying check 69.3 (0.3) 60.4 (0.6) 58.8 (0.4) p-value 0.000** 0.000** 0.000** Machine gouge 71.2 (0.3) 62.9 (0.6) 62.0 (0.5) p-value 0.349 0.002** 0.123 Machine burn 71.1 (0.2) 62.7 (0.4) 61.6 (0.4) p-value 0.270 0.000** 0.000** All 68.9 (0.3) 55.5 (0.8) 56.7 (0.4) p-value 0.000** 0.000** 0.000** No. 1C No. 2AC Short Conventional Short (%) Base 62.2 (0.5) 57.6 (0.7) 50.2 (0.7) Spike mark 61.1 (0.6) 57.6 (0.7) 49.0 (1.1) p-value 0.000** 0.500 0.000** Conveyer mark 62.0 (0.6) 57.5 (0.4) 50.0 (0.9) p-value 0.133 0.230 0.197 Pressure roller stain 62.1 (0.6) 56.0 (0.5) 49.3 (0.8) p-value 0.178 0.000** 0.000** Drying check 57.1 (0.6) 54.4 (0.5) 43.1 (0.8) p-value 0.000** 0.000** 0.000** Machine gouge 62.2 (0.5) 57.5 (0.4) 49.6 (0.8) p-value 0.320 0.330 0.004** Machine burn 61.9 (0.4) 57.4 (0.4) 50.0 (0.6) p-value 0.027* 0.098 0.126 All 54.7 (0.6) 52.5 (0.4) 41.6 (0.9) p-value 0.000** 0.000** 0.000** (a) Values in parentheses are standard deviations. ** = highly significant difference ([alpha] < 0.01); * = significant difference ([alpha] < 0.05); z-test p-value for comparison between base case and treatment.
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|Author:||Clement, Charles; Lihra, Torsten; Gazo, Rado; Beauregard, Robert|
|Publication:||Forest Products Journal|
|Date:||Jan 1, 2006|
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