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Article

The Role Played by the Rake Angle of a Strander-Canter When Processing Jack Pine Logs

by
Irsan Alipraja
1,2,
Roger E. Hernández
1,* and
Ahmed Koubaa
3
1
Centre de Recherche sur les Matériaux Renouvelables, Département des Sciences du Bois et de la Forêt, Université Laval, Pavillon Gene H.-Kruger, 2425 Rue de la Terrasse, Quebec, QC G1V 0A6, Canada
2
Department of Forest Products, Faculty of Forestry, IPB University, Bogor 16680, Indonesia
3
Institut de Recherche sur les Forêts, Université du Québec en Abitibi-Témiscamingue, 445 Boul. de l’Université, Rouyn-Noranda, QC J9X 5E4, Canada
*
Author to whom correspondence should be addressed.
Forests 2023, 14(11), 2182; https://doi.org/10.3390/f14112182
Submission received: 16 August 2023 / Revised: 16 October 2023 / Accepted: 27 October 2023 / Published: 2 November 2023
(This article belongs to the Special Issue Innovative Use of Timber and Wood-Based Composites: Applications, Design and Sustainability)
Browse Figures
Versions Notes

Abstract

:
The optimization of the machining parameters of strander-canting is the best way to obtain the optimum strand size, a better quality of the cant surface, and lower energy consumption. The effect of the rake angle on the performance of a strander-canter when processing jack pine logs was evaluated. Thirty-nine logs were cut with three rake angles (59°, 64°, and 69°). The counter-knife angle used in this study was 20° for frozen logs and 35° for unfrozen logs. The cutting speed and width were fixed at 25 m/s and 20 mm, respectively. The results showed that the rake angle affected the strand width, strand proportion, and energy requirements to transform the logs under frozen conditions. The rake angle of 64° produced a higher proportion and larger strands with less energy consumption than the rake angle of 59°. However, using a rake angle of 64° produced poorer surface quality. On the other hand, the effect of the rake angle on the processing of unfrozen logs was only noticeable when the rake angle changed to 69°. The proportion of pin chips increased, and the surface quality became poorer as the rake angle changed from 59° to 69°. The rake angle did not affect energy consumption when transforming the logs under unfrozen conditions.

1. Introduction

Strander canting is a relatively recent wood machining process that transforms logs into strands and cant in a single operation. It is an alternative process to chipper canting to diversify the manufacture of by-products by the sawmill industry. This is becoming increasingly important, given the declining demand for chips from the pulp and paper industry. The results of previous studies indicate that the developed cutterhead has good feasibility in strand production [1]. The strands produced have a slight parallelogram shape with a relatively small coefficient of variation in length and thickness. However, the dimension of the resulting width (<20 mm) was still relatively narrower compared to that of commercial strands in general, which is around 25 mm [2,3]. The width of the strand is believed to influence the orientation of the strand when forming the board, which could impact its mechanical properties. A narrow strand has more space to rotate, increasing the degree of disorientation and porosity, while extremely narrow strands are more difficult to orient. On the other hand, very wide strands tend to cross the orienter disk, and while being carried across the top of the orienters, they tend to fall through the orienter over a wider distance [4]. Thus, obtaining the ideal width size is needed to produce good-quality boards.
Optimization of the wood machining parameters is the solution that is commonly used to increase efficiency, productivity, and product quality, which reduces production costs. In the case of the strander-canting process, the optimization must aim to produce a large volume of strands, optimal dimensions, and cants of good surface quality while ensuring low power consumption.
One of the most common optimization processes in wood machining is modifying the cutting angles (sharpness, rake, or clearance angles). The rake angle is the angle between the cutting tool face (rake face) and a line perpendicular to the direction of the cutting-edge movement. This angle is well known to affect several parameters of the machining results, such as chip formation and chip size [5,6,7], surface quality [8,9,10,11], cutting force or energy consumption [8,10,11,12,13], and cutting tool life [14].
For the conventional stranding process, the effect of the rake angle was reported by Stiglbauer et al. [15]. A higher rake angle produced fewer fines when cutting wood above 20 °C. Increasing the rake angle is also used to reduce the bending moment in the cutting mode 0–90° [16]. This angle also affects the formation of lathe checks [17], which could ultimately modify the surface topography of the veneers [18]. A higher rake angle could increase the strand yield and width in the stranding process. On the other hand, there is no agreement on the effect of the rake angle on the surface quality. Hernández et al. [19] reported that the proportion of defect-free boards from the planing process increased as the rake angle decreased from 30° to 15°. Similar results were also reported by other studies with different parameters tested [20,21,22]. On the contrary, Cáceres et al. [23] reported that the roughness obtained from the orthogonal cutting decreased as the rake angle increased from 10° to 40°. Thus, the effect of the rake angle on the surface quality depends on the type of machining applied.
This study evaluated the effect of rake angle on the strand size distribution, the electrical performance, and the surface quality of the cant produced from the strander-canting process. The experiment was conducted in two different temperatures (frozen and unfrozen) to simulate seasonal influences (winter or summer) on the tested parameters.

2. Materials and Methods

2.1. Preparation of Logs

Thirty-nine jack pine logs (Pinus banksiana Lamb) were obtained from Abitibi-Témiscamingue, QC, Canada. The logs were cut into 2.4 m long pieces and freshly hand-debarked. An electric hand drill was used to remove knots with a diameter of more than 10 mm to minimize knife damage during the log processing. A 25 mm thick disk was crosscut from each end of the logs to measure their physical properties.
Two opposite sides of the logs were chosen based on their straightness. The first side was transformed at −14 °C, while the other was cut at 21 °C. The length and diameter of the logs were measured to calculate the cutting volume. The logs were then wrapped with plastic to minimize the moisture content (MC) loss and then stored in a freezer at −19 °C until processing.

2.2. Physical Properties Measurements

The two disks cut from each log were used for sapwood thickness, moisture content (MC), and specific gravity (SG) measurements. Sapwood thickness was measured at three different points on each cutting area on the disk. A sample of 25 mm (longitudinal direction) by 20 mm (tangential direction) by 20 mm (radial direction) was then cut from each side of the cutting area on the disk for the MC and SG measurements. MC was calculated by the ratio between the weight of water and the oven-dry weight of the sample, while SG was calculated by using the ratio between the oven-dry weight and the green volume of the sample. The log characteristics and physical properties (Table 1) were used to separate the logs into three groups of 13 replicates each.

2.3. Strander-Canting Process

Log transformation was carried out using a prototype of a strander-canter cutterhead manufactured by DK-SPEC (Quebec City, QC, Canada). The cutterhead was fitted with 33 straight knives arranged in a spiral direction. Three different wedge or sharpness angles were used in this study (20°, 25°, and 30°), while the clearance angle was fixed at 1°. Therefore, three rake angles (59°, 64°, and 69°) were studied using 13 logs (replicates) each. The vertical position of the cutterhead was controlled to obtain a 0–90 cutting mode at the middle of the logs (Figure 1).
The logs were placed on the carriage and held by five hydraulic arms. The logs were constantly fed by the small end first. The linear cutting speed used in this study was 25 m/s. Rotation and feed speed were adjusted to obtain a strand length of 102 mm. Log transformation was performed in two sequences to simulate the winter and summer seasons. One side of the log was cut under frozen conditions with the counter-knife angle of 20°, while the other was cut 24 h later, under unfrozen conditions, with the counter-knife angle of 35°. The temperature of the logs for frozen conditions was −14 °C with a standard error (SE) of 0.2, while the temperature for unfrozen logs was 21.1 °C with an SE of 0.7. The cants produced from the cutting process were wrapped with plastic and stored back in the freezer until surface analysis was carried out. The cutting parameters of the strander-canting process are shown in Table 2.

2.4. Strand Size Measurements

All wood fragments were air-dried at ambient temperature until they reached the equilibrium MC of about 10%. The wood fragments were then screened with a LabTech classifier (Tampa, FL, USA) for 15 min to separate the strands and small particles (pin chips and fines). Strands were defined as the wood particles retained in the screens with a hole diameter of 9.5, 15.9, 22.2, 28.6, 45 mm, and 70 mm. Pin chips were the wood chips that passed through a 9.5 mm hole screen but were retained on a 4.8 mm screen, while all the particles that passed the hole screen of 4.8 mm were classified as fines. The proportions of strands, pin chips, and fines were then calculated.
Strand width measurements were performed on 100 strands taken proportionally from each LabTech screen classifier. Thus, the width of 1300 strands from each treatment was measured. The strands were scanned using an Epson Expression 1640XL scanner (Epson, Los Alamitos, CA, USA). The measurement of strand widths was then carried out by using Image-J 1.53e software. The width of each strand was defined as the mean of five measurements perpendicular to the grain.

2.5. Power and Energy Consumption Measurements

The strander-canter was equipped with an encoder that measured the tool head’s rotation speed and torque of the tool during log processing. The encoder was connected to the “DAQLog” data acquisition system, which allows data recording continuously. The scan rate was fixed at 2500 Hz.
The voltage data were used to calculate the total power consumption during log machining. Cutting power consumption was calculated by subtracting the unloaded power from the total power. Energy consumption (EC) was determined by multiplying the power consumption by the cutting time. Specific energy (SCE) was also estimated using the ratio between energy consumption and the volume of wood cut. This volume was calculated according to the method used by Kuljich et al. [24]. All electrical consumption was evaluated from the cutting length of 1.7 m.

2.6. Surface Quality Analysis

Three-dimensional measurements of cant surfaces were obtained using a HandyScan 700TM (Creaform, Lévis, Canada). This portable scanner uses the laser triangulation technique to project 7 red laser crosses onto the surface to be studied. It also has a single laser mode which can capture fine surface detail and deep cavities. Positioning targets were used to create a reference system around the cant. The HandyScan700 is able to automatically position itself according to targets, which ensures high accuracy. The resolution of the scan was set at 0.2 mm with an acquisition rate of 480.000 measurements/s. The images were subsequently treated with VXelement software to remove the noise that appeared during the scanning process. The images were then analyzed using Mountainsmap version 8 software (Digital Surf, Besançon, France).
Form errors of the cant (slope or curves) were first removed by the least square (LS) plan method. The new surface profile obtained by removing the form error was then termed a primary surface profile. This profile consists of a low-frequency component (waviness) and a high-frequency component (roughness). Surface quality was evaluated on ten random cutting traces on the cant surface (Figure 2a). Each cut trace surface was converted into a series of profiles across the grain. The measurement length corresponded to the cutting height of each cut trace. The profiles were filtered using the robust Gaussian regression filter (ISO 16610-31: 2016) with a cut-off length of 8 mm. The surface topography was evaluated with each of the six amplitude parameters of the roughness (R) and waviness (W): arithmetical mean deviation (Ra and Wa), maximum profile peak height (Rp and Wp), maximum profile valley depth (Rv and Wv), maximum height of profile (Rz and Wz), total height of profile (Rt and Wt), and root-mean-square deviation (Rq and Wq). The depth of torn grain (DTG) was measured by detecting the deepest hole on the surface profile (Figure 2b). The HandyScan image was used to check the hole to make sure it was not a resin pocket or a knot. The mean depth of the five deepest torn grains and their volume (VTG) were then evaluated for each primary surface profile of the cant.

2.7. Statistical Analysis

Data were analyzed using SAS 9.4 (SAS Institute Inc., Cary, NC, USA). Multivariate analysis of variance (MANOVA) was used to test if the physical properties of the groups of logs used in this study were similar. The variables tested were the diameter, wood taper, sapwood thickness, specific gravity (SG), and moisture content (MC).
A principal component analysis (PCA) test was applied to the roughness and waviness data given the number of parameters studied (12) to regroup them into two common factors. This grouping was done to simplify the analysis while retaining the variation in the dataset as much as possible.
Analyses of covariance (ANCOVAs) and mean comparison tests were performed to assess the effects of rake angle on strand width; the proportions of strands, fines, and pin chips; energy consumption; specific cutting energy; waviness; roughness; and depth and volume of torn grain, for each log temperature separately. SG, MC, and cutting volume were used as covariates. Only significant covariates were kept in the model. Shapiro–Wilk and kurtosis tests were used to verify the normality of data, and graphical analysis of residuals was used to verify the homogeneity of variance.

3. Results and Discussion

Tests using a 69° rake angle in frozen conditions could not be performed adequately due to unwanted vibrations occurring in the machine due to probable uneven pressure from the hydraulic feed carriage, which held the log with five clamps during machining. Results for this cutting condition were thus not available in this study. Moreover, the results showed that all the criteria used to measure the performance of the strander-canter were different when processing frozen logs than when processing unfrozen logs. Thus, frozen logs produced fewer and narrower strands, more fines and pin chips, and required more cutting energy. The results cannot be just attributed to the difference in wood temperature since the counter-knife used varied for the two conditions (20° for frozen logs and 35° for the unfrozen logs). However, the contribution of the counter-knife to the total energy consumption must be minor since the knives performed the cutting action with the same cutting geometry for both wood temperature conditions. According to previous results [1], if the fragmentation had been carried out with the same counter-knife angle, the difference in behavior between the two log temperatures would have been even greater.

3.1. The Proportions of Strands, Pin Chips, and Fines

The ANCOVA showed that the rake angle significantly affected the proportions of strands, pin chips, and fines produced from frozen logs (Table 3). The volume of strands from the frozen logs was higher and that of the pin chips and fines was lower when using the rake angle of 64° instead of 59° (Table 4). This result was as expected since a lower rake angle should have generated higher stresses on the tension area of the strand sheet when it passed the rake face of the knives. Consequently, the crack frequency on this strand sheet was higher, producing fewer strands and more fines and pin chips. However, the effect of rake angle on the strand and fine formation was not observed when transforming unfrozen logs. A difference of even 5° in the rake angle for the frozen logs affected the particle size distribution due to the more brittle behavior of wood at these temperatures [25,26]. The rake angle only affected the proportion of pin chips when cutting unfrozen logs but to a lesser degree. The strand yields obtained from unfrozen logs were statistically similar for all the rake angles tested, around 95.9% (means of three rake angles pooled). This may be because the unfrozen jack pine wood generally has a low modulus of elasticity [27], making the wood more pliable and easily deformed into strand sheets with a lower fracture frequency.
Between the covariates tested, the specific gravity only affected the proportion of strands and fines when transforming the logs under frozen conditions (Table 3). A slight decrease and increase in the volume of strands and fines, respectively, were observed for denser wood. However, the effect of the SG was small, as deduced from the F-values.
On the other hand, Table 3 also showed that for unfrozen logs, the proportions of strands and fines were not affected by SG but rather by the cutting volume. However, this effect was also small, as can be seen from the F-values.

3.2. Strand Width

The rake angle affected the width of the strands when transforming the logs under frozen conditions (Table 3). As the rake angle decreased from 64° to 59°, the mean width of the strands decreased from 32 mm to 25 mm (Table 4). As mentioned earlier, a lower rake angle should generate a higher bending stress on the strand sheets, which decreases the distance between fractures (or increases the fracture frequency) within them (Figure 3a). As a result, narrower strands were produced when cutting the logs with a lower rake angle. In frozen conditions, this effect can become more noticeable as the wood is more brittle as the temperature drops below 0 °C, causing the wood to tend to break at lower bending strains.
For logs processed under unfrozen conditions, a change in rake angle from 59° to 69° did not significantly affect the strand width. In fact, the strand width for these temperature conditions varied between 66 mm and 69 mm (Table 4). As indicated earlier, unfrozen wood was more flexible, making the strand sheet tend to bend rather than break as it passed the rake face of the knife and the counter-knife. Thus, fewer fractures occurred during this process, resulting in wider strands.
The strands obtained from the unfrozen logs were too wide to ensure a good orientation in OSB manufacturing. The mean aspect ratio (ratio between strand length and width) for unfrozen wood strands was 2 (all the rake angles pooled). However, most individual strands measured (>68%) had an aspect ratio below 2. Generally, a strand should have an aspect ratio of at least 2 to produce a good-quality panel [28], although commercial strands typically have an aspect ratio of at least 3 [29]. Apart from causing poor orientations, too large strands could also affect the panel density variation and the mill productivity by increasing the pressing time. Therefore, the machining process for unfrozen logs needs to be improved to obtain narrower strands. These results showed that the counter-knife angle used in the tests (35°, Figure 3b) was too low to cause more frequent fractures of the strand sheet. A greater counter-knife angle and a lower rake angle should produce narrower strands.
The SG, MC, and CV covariates only affected the strand width under unfrozen conditions (Table 3). According to the F-values, the cutting volume had a more significant effect on the strand width than SG and MC. Wider strands were produced as the cutting volume increased. As noted earlier, the frequency of fractures in the unfrozen strand sheets was low. In fact, the mean cutting height of the logs was 119 mm (Figure 2a). This height corresponds to the maximum cutting height, i.e., the chord of an ideal circular segment of the log transformed into strands. The mean strand width for the unfrozen logs was 67 mm (all rake angles pooled). The strand sheet often did not suffer fractures and was obtained entirely in the test (corresponding to the cutting height or full path of each knife in the log). The width of strands was thus affected by the cutting height (or CV), increasing proportionally with it. However, the effect of cutting volume was not observed in frozen logs because the fracture frequency producing strands from the strand sheets was much higher.

3.3. Energy Consumption

The energy required to transform jack pine logs varied between 3.9 KWh and 16.5 KWh (Table 4). There was a clear difference in the energy required to cut the logs between frozen and unfrozen conditions. When the temperature decreased from 21 °C to −14 °C, energy consumption increased significantly, regardless of the rake angle applied. Thus, the energy consumption increased 3 to 4 times when cutting frozen logs compared to unfrozen ones. It is known that when the wood is exposed to temperatures below 0 °C, especially with a moisture content above the fiber saturation point, the free water in the cell cavities freezes, reinforcing the cell wall and making it stiffer [26]. These conditions then increase the mechanical properties of wood [30]. Consequently, the cutting force also increases, resulting in higher electrical consumption. As previously stated, a greater difference in cutting energy could have been obtained if the test had been carried out with the same counter-knife angle for the two temperature conditions.
The rake angle affected energy consumption when processing frozen logs (Table 3). The energy consumption increased by 35% as the rake angle decreased from 64° to 59° (Table 4). This increase in energy consumption is explained by the increase in cutting forces as the rake angle decreases in the 0–90 cutting direction [8,31]. Therefore, the knife edge could penetrate the wood more easily. However, when the volume of wood cut was taken into account in the energy calculation (SCE), the difference between the two rake angles fell to 27% and became statistically insignificant (Table 4). Thus, in values, the SCE for the rake angle of 59° (6483 kWh/m3) was greater than that for the rake angle of 64° (5094 kWh/m3). A larger number of repetitions or a smaller variation in the volume of wood cut would have been necessary to increase the discriminating power of the test for comparing means.
On the other hand, the effect of the rake angle was not observed when cutting the logs at room temperature (Table 3). The energy consumption and SCE were statistically similar for all rake angles tested, varying between 3.9 kWh and 4.2 kWh and between 1489 kWh/m3 and 1586 kWh/m3, respectively (Table 4). This outcome can be caused by the fact that the cut logs were in a green state (saturated moisture content), which could decrease the friction between the knife and the fibers. This also indicated that the effect of the rake angle (between 59° and 69°) on the electrical consumption depended on the wood temperature conditions, which are correlated to the mechanical properties of wood. In other words, as mechanical properties decreased, the effect of the rake angle became less important.
SG and MC significantly affected the variations in energy consumption (Table 3). The SG, for instance, affected the EC and SCE for both temperature conditions, while the MC affected the electrical performance of the motor when cutting frozen logs. The effects of those wood properties were even greater than the effect of the rake angle, as shown by the F-values (Table 3). EC and SCE increased as the SG increased. Higher SG means more wood material to cut, which increases the cutting forces and therefore the electrical consumption. As the wood is processed under sub-zero temperatures, moisture content becomes very important since it affects the wood’s mechanical properties [32]. A higher MC increases the strength of wood [26,30], which also increases the cutting resistance. The volume of fragmented wood was also observed to affect the energy consumption when transforming the logs under unfrozen conditions. As the volume of fragmented wood increased, the energy consumption also increased.

3.4. Surface Quality Analysis

The PCA showed that 91% and 97% of the variation in surface quality for frozen and unfrozen wood was explained by two factors, i.e., roughness (Factor 1) and waviness (Factor 2). Under frozen conditions, roughness explained 46% of the variance, with high factor loadings for Ra (0.97), Rp (0.95), Rv (0.97), Rz (0.98), Rt (0.79), and Rq (0.97). Waviness accounted for 45% of the total variance, also with high factor loadings for Wa (0.91), Wp (0.95), Wv (0.94), Wz (0.95), Wt (0.89), and Wq (0.92). Under unfrozen conditions, roughness and waviness explained 51% and 46% of the total variance, respectively. Both roughness and waviness parameters in this temperature condition also had high factor loadings: 0.89 for Wa and Wq, 0.88 for Rz and Rv, 0.87 for Rq, 0.86 for Ra and Rp, 0.85 for Wt, 0.84 for Rt, 0.78 for Wv, 0.77 for Wz, and 0.76 for Wp.
The ANOVA showed that the rake angle affected the roughness when transforming the logs under unfrozen conditions (Table 5). The rake angle of 69° generated a rougher surface (Ra = 47 µm) compared to that of 59° (Ra = 23 µm) and 64° (Ra = 26 µm), as can be seen in Figure 4a. According to Pinkowski et al. [33], a knife with a low sharpness angle (high rake angle) is effective in fiber cutting but becomes less stiff and could cause vibrations. This vibration may be the reason for the higher roughness of the unfrozen cant generated when cutting with a rake angle of 69°. Figure 4a also shows that the wood temperature has less impact on the roughness. This can be seen in the log transformation using rake angles of 59° and 64°, where the Ra values obtained for frozen and unfrozen cant surfaces were relatively similar (23 µm to 26 µm).
On the other hand, the effect of wood temperature was more pronounced on the waviness (Figure 4b). Log processing under unfrozen conditions generated lower Wa than log processing under frozen conditions. Wa of the unfrozen cants varied between 38 µm and 62 µm. When the logs were cut below 0 °C, Wa increased significantly to 94 µm and 123 µm for the rake angles of 59° and 64°, respectively. As mentioned above, under sub-zero temperatures, since the mechanical properties of wood increase [26], the cutting edge requires higher cutting forces to penetrate the log. Therefore, vibration during the cutting process also increases, resulting in higher waviness [34]. This vibration appeared more significant with the increase in the rake angle to 64°, probably because of the insufficient stiffness of a knife with a sharpness angle of 25° (Figure 4b).
The ANOVA showed that the rake angle affected the waviness (factor 2) in both temperature conditions. The Wa of the frozen cant surface, for instance, increased by 30% as the rake angle increased from 59° to 64°. However, the same rake angle change did not affect Wa when the logs were cut under unfrozen conditions, where this parameter was relatively similar (around 38 µm). Wa then increased to 62 µm when the rake angle increased to 69°. These results indicate that the effect of the rake angle on the waviness depended on the wood temperature. As the temperature decreased, the influence of the rake angle became more noticeable, as can be seen when cutting the logs using the rake angles of 59° and 64° (Figure 4b).
Furthermore, the visual inspection showed that the lower part of the unfrozen cant was rougher than the upper part (Figure 5). Cutting the wood with a larger rake angle (69°) amplifies the roughness, in good agreement with a previous study on a conventional chipper-canter [8,34]. According to these authors, the difference in roughness between the upper and lower parts of the cant is caused by differences in cutting direction along the cutting path. At the entry point, the knife tends to cut nearly across the grain, and the angle between the cutting edge and the grain becomes more oblique as the knife exits the log. Surface roughness then increases as the angle between the cutting edge and the grain becomes more oblique [35,36].

3.5. Torn Grain Analysis

The mean of the maximum depth of torn grain (TG) varied between 0.4 and 0.8 mm, depending on the log temperature and rake angle applied. Unfrozen cant surfaces had deeper and slightly bigger torn grains than the frozen cant surfaces. As mentioned earlier, frozen wood is more brittle than unfrozen wood, making the fiber break rather than pull out during the cutting process [37]. As a result, less torn grain occurred on the frozen cant surface. Conversely, under unfrozen conditions, the vibrations that occur during the cutting process can more easily degrade the surface quality since the wood fibers are more easily lifted.
The ANOVA showed that the rake angle affected torn grain defect (depth and volume) when transforming the log under unfrozen conditions (Table 3). The TG depth was 33% greater for the rake angle of 69° than for the rake angles of 59° and 64° (Figure 6a). A significant increase was also found in the TG volume, where the rake angle of 69° generated 385% and 480% bigger TG volume than the rake angles of 64° and 59°, respectively (Figure 6b).
Previous works have reported that rake angle is the variable that most affects normal force (FN) and roughness [8,31]. Additionally, FN is also correlated with the occurrence of torn grain [7]. Therefore, a change in the rake angle may indirectly affect torn grain formation. Previous works have shown that FN is negative when machining with high rake angles, as used in the present work [28], indicating that wood material is subject to a pulling action. Increasing the rake angle from 59° to 69° should increase the FN, producing a higher pulling action in the workpiece, causing deeper and coarser torn grains.
On the other hand, the depth of torn grain obtained in this study was at least 2 times lower than that obtained using a conventional chipper-canter [35]. This result can be an advantage for the sawmill industry since this directly increases the yield and economic value of the resulting lumber.
From a practical point of view, using a lower rake angle (59°) is more suitable for the strander-canting process for several reasons. First, the average width of the strands obtained from the frozen logs was similar to that of the commercial strands [2,3]. The fine proportion was 2% higher than that for the rake angle of 64°; however, it was still within the limit of the volume of fines allowed on an OSB board, which is around 10% [38]. Second, in terms of surface quality, the 59° rake angle produced the lowest Wa when transforming the frozen and unfrozen logs. Similarly, the depth and volume of torn grain were also relatively small. Third, since the rake angle did not affect most aspects of strand size distribution and energy consumption when cutting unfrozen logs, using a lower rake angle is preferable because it will give a longer cutting tool life. A tool with a higher knife sharpening angle is generally stiffer and more resistant to wear. In fact, some knives were replaced during the test when using the rake angle of 64° and 69° due to small fractures produced when traversing knots. However, the drawback when using a lower rake angle was the higher energy consumption when transforming frozen logs. Thus, a study aimed at reducing energy consumption under these temperature conditions should be encouraged to increase the performance of the strander-canting process.

4. Conclusions

A difference of 5° in the rake angle, between 59° and 64°, was sufficient to detect the effect of this angle on the properties of the proportions of strands, pin chips, and fines; strand width; energy consumption; and waviness when transforming jack pine logs under frozen conditions. The strand width and strand proportion increased while pin chips, fines, energy consumption, and surface quality decreased as the rake angle increased.
Under unfrozen log conditions, the rake angle significantly affected the yield of pin chips, waviness, roughness, and torn grain defect (depth and volume). Processing logs using a rake angle of 69° produced a higher volume of pin chips, while the rake angles of 59° and 64° produced similar proportions of these particles. In addition, the rake angles of 59° and 64° generated better surface quality in all tested parameters (waviness, roughness, depth, and volume of torn grain).
Visual inspection showed that the upper part of the cant had a better surface quality than the lower part of the cant. This was more pronounced when cutting the wood with a larger rake angle (69°).
The use of a rake angle of 59° was more suitable for the strander-canting process. It gave an optimum strand width with a low volume of fines and produced the best surface quality among the tested rake angles. However, this rake angle required higher cutting energy to transform the logs under frozen conditions.

Author Contributions

Conceptualization, I.A., R.E.H. and A.K.; methodology, I.A. and R.E.H.; software, I.A.; validation, I.A. and R.E.H.; formal analysis, I.A.; investigation, I.A.; resources, R.E.H. and A.K.; data curation, I.A.; writing—original draft preparation, I.A.; writing—review and editing, I.A., R.E.H. and A.K.; visualization, I.A., R.E.H. and A.K.; supervision, R.E.H. and A.K.; project administration, R.E.H. and A.K.; funding acquisition, R.E.H. and A.K. All authors have read and agreed to the published version of the manuscript.

Funding

This project was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and by DK-SPEC Inc., Quebec City, QC, Canada.

Data Availability Statement

The datasets generated and analyzed during the current study are not publicly available but are available from the first and corresponding author upon reasonable request.

Acknowledgments

The authors are grateful for the support of Rentry Augusti Nurbaity, Philippe Riel, Samuel Perkins, and Adrien Gobeil during the laboratory experiments. The authors also thank Marius Sirbu, Daniel Bourgault, Félix Pedneault, Paul Desaulniers, Luc Germain, and Jean Ouellet for their technical assistance.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Alipraja, I.; Hernández, R.E.; Cáceres, C.B.; Koubaa, A. Towards strand production in primary log breakdown: Effects of the counter-knife and temperature on size distribution of jack pine strands. BioResources 2022, 17, 2632–2651. [Google Scholar] [CrossRef]
  2. [SBA] Structural Board Association. OSB Performance by Design: Oriented Strand Board in Wood Frame Construction; Structural Board Association: Markham, ON, Canada, 2005; p. 2. [Google Scholar]
  3. Dai, C.; Yu, C.; Jin, J. Theoretical modeling of bonding characteristics and performance of wood composites. Part IV. Internal bond strength. Wood Fiber Sci. 2008, 40, 146–160. [Google Scholar]
  4. Chen, S.; Du, C.; Wellwood, R. Analysis of strand characteristics and alignment of commercial OSB panels. For. Prod. J. 2008, 58, 94–98. [Google Scholar]
  5. McKenzie, W.M. Friction coefficient as a guide to optimum rake angle in wood machining. Wood Sci. Technol. 1991, 25, 397–401. [Google Scholar] [CrossRef]
  6. Ekevad, M.; Marklund, B.; Gren, P. Wood-chip formation in circular saw blades studied by high-speed photography. Wood Mater. Sci. Eng. 2012, 7, 115–119. [Google Scholar] [CrossRef]
  7. Iskra, P.; Hernández, R.E. Analysis cutting forces in straight-knife peripheral cutting of wood. Wood Fiber Sci. 2012, 44, 134–144. [Google Scholar]
  8. Kuljich, S.; Hernández, R.E.; Llavé, A.M. Effects of cutting direction, rake angle, and depth of cut on cutting force and surface quality during machining of balsam fir. Wood Fiber Sci. 2013, 45, 195–205. [Google Scholar]
  9. Bakar, E.S.; Chong, Y.W.; Anokye, R.; Ashaari, Z. Effect of different diameters and rake angles of Forstner bit on the quality of drilling on treated oil palm wood. Eur. J. Wood Prod. 2018, 76, 369–374. [Google Scholar] [CrossRef]
  10. Rajko, L.; Koleda, P.; Barcík, S.; Koleda, P. Technical and technological factors’ effects on quality of the machined surface and energetic efficiency when planar milling heat-treated meranti wood. BioResources 2021, 16, 7884–7900. [Google Scholar] [CrossRef]
  11. Jiang, S.; Buck, D.; Tang, Q.; Guan, J.; Wu, Z.; Guo, X.; Zhu, Z.; Wang, X. Cutting force and surface roughness during straight-tooth milling of walnut wood. Forests 2022, 13, 2126. [Google Scholar] [CrossRef]
  12. Barcík, Š.; Kminiak, R.; Řehák, T.; Kvietková, M. The influence of selected factors on energy requirements for plain milling of beech wood. J. For. Sci. 2010, 56, 243–250. [Google Scholar] [CrossRef]
  13. Yu, Y.; Buck, D.; Yang, H.; Du, X.; Song, M.; Wang, J.; Zhu, Z. Cutting power, temperature, and surface roughness: A multiple target assessment of beech during diamond milling. Forests 2023, 14, 1163. [Google Scholar] [CrossRef]
  14. Astakhov, V.P.; Davim, J.P. Tools (geometry and material) and tool wear. In Machining: Fundamentals and Recent Advances; Davim, J.P., Ed.; Springer: London, UK, 2008; pp. 29–57. [Google Scholar] [CrossRef]
  15. Stiglbauer, P.; Conners, T.; Banerjee, S. Influence of knife angle and ambient temperature on fines generation from flakers. For. Prod. J. 2006, 56, 86–89. [Google Scholar]
  16. Benbrahim, Z.; Benotmane, B.; Zerizer, A.; Denaud, L.; Marchal, R. Experimental study of the effect of soaking temperature on the peeling parameters of two oak species (Quercus canariensis Willd. and Quercus afares Pomel). Wood Mater. Sci. Eng. 2020, 15, 241–249. [Google Scholar] [CrossRef]
  17. Denaud, L.; Marcon, B.; Rohumaa, A.; Purba, C.; Viguier, J.; Letourneau, R.; Marchal, R. Influence of peeling process parameters on veneer lathe check properties. In Proceedings of the 24th International Wood Machining Seminar, Corvallis, OR, USA, 25–30 August 2019; pp. 227–236. [Google Scholar]
  18. Daoui, A.; Descamp, C.; Marchal, R.; Zerizer, A. Influence of veneer quality on beech LVL mechanical properties. Maderas Cienc. Technol. 2011, 13, 69–83. [Google Scholar] [CrossRef]
  19. Hernández, R.E.; Bustos, C.; Fortin, Y.; Beaulieu, J. Wood machining properties of white spruce from plantation forests. For. Prod. J. 2001, 51, 82–88. [Google Scholar]
  20. Malkoçoğlu, A.; Özdemir, T. The machining properties of some hardwoods and softwoods naturally grown in eastern black sea region of Turkey. J. Mater. Process. Technol. 2006, 173, 315–320. [Google Scholar] [CrossRef]
  21. Malkoçoğlu, A. Machining properties and surface roughness of various wood species planed in different conditions. Build. Environ. 2007, 42, 2562–2567. [Google Scholar] [CrossRef]
  22. Razaei, F.; Gaff, M.; Sethy, A.K.; Niemz, P.; Kamboj, G.; Ditommaso, G.; Corleto, R.; Das, S.; Gašparík, M. Surface quality measurement by contact and laser methods on thermally modified spruce wood after plain milling. Int. J. Adv. Manuf. Technol. 2020, 110, 1653–1663. [Google Scholar] [CrossRef]
  23. Cáceres, C.B.; Uliana, L.; Hernández, R.E. Orthogonal cutting study of wood and knots of white spruce. Wood Fiber Sci. 2018, 50, 55–65. [Google Scholar] [CrossRef]
  24. Kuljich, S.; Hernández, R.E.; Blais, C. Effects of cutterhead diameter and log infeed position on energy requirements of a chipper-canter. Wood Fiber Sci. 2015, 47, 399–409. [Google Scholar]
  25. Gaete-Martinez, V.; Shaler, S.M.; Edgar, R.; Hill, J. Effect of strand geometrical distribution (SGD) in oriented strand composite (OSC) formation quality. In Proceedings of the 51st International Convention of Society of Wood Science and Technology, Concepción, Chile, 10–12 November 2008; pp. 1–10. [Google Scholar]
  26. Hernández, R.E.; Passarini, L.; Koubaa, A. Effects of temperature and moisture content on selected wood mechanical properties involved in the chipping process. Wood Sci. Technol. 2014, 48, 1281–1301. [Google Scholar] [CrossRef]
  27. Green, D.W.; Evans, J.W. The immediate effect of temperature on the modulus of elasticity of green and dry lumber. Wood Fiber Sci. 2008, 40, 374–383. [Google Scholar]
  28. Kuklewski, K.M.; Blankenhorn, P.R.; Rishel, L.E. Comparison of selected physical and mechanical properties of red maple (Acer rubrum L.) and aspen (Populus grandidentata Michx.) flakeboard. Wood Fiber Sci. 1985, 17, 11–21. [Google Scholar]
  29. Stark, N.M.; Cai, Z. Wood-based composite materials: Panel products, glued laminated timber, structural composite lumber, and wood-nonwood composites. In Wood Handbook: Wood as Engineering Material. General Technical Report FPL-GTR-282; USDA: Madison, WI, USA, 2021; pp. 11.1–11.29. [Google Scholar]
  30. Özkan, O.E. Effects of cryogenic temperature on some mechanical properties of beech (Fagus orientalis Lipsky) wood. Eur. J. Wood Prod. 2021, 79, 417–421. [Google Scholar] [CrossRef]
  31. Hernández, R.E.; Llavé, A.M.; Koubaa, A. Effects of cutting parameters on cutting forces and surface quality of black spruce cants. Eur. J. Wood Wood Prod. 2014, 72, 107–116. [Google Scholar] [CrossRef]
  32. Gerhards, C.C. Effect of the moisture content and temperature on the mechanical properties of wood: An analysis of immediate effects. Wood Fiber 1982, 14, 4–36. [Google Scholar]
  33. Pinkowski, G.; Szymański, W.; Krauss, A.; Stefanowski, S. Effect of sharpness angle and feeding speed on the surface roughness during milling of various wood species. BioResources 2018, 13, 6952–6962. [Google Scholar] [CrossRef]
  34. Hernández, R.E.; Kuljich, S.; Koubaa, A. Effect of cutting width and cutting height on the surface quality of black spruce cants produced by a chipper-canter. Wood Fiber Sci. 2010, 42, 273–284. [Google Scholar]
  35. Elloumi, I.; Hernández, R.E.; Cáceres, C.B.; Blais, C.B. Effects of log temperature, cutting width, and knots on the surface quality of the cants produced by a chipper-canter. Wood Mater. Sci. Eng. 2023, submitted.
  36. Kuljich, S.; Hernández, R.E.; Blais, C. Effects of the cutterhead diameter and log infeed position on surface quality of black spruce cants produced by a chipper-canter. Wood Fiber Sci. 2017, 49, 235–248. [Google Scholar]
  37. Meulenberg, V.; Ekevad, M.; Svensson, M. Thin kerf cutting forces of frozen and non-frozen Norway spruce and Scots pine wood. Wood Mater. Sci. Eng 2021, 16, 414–420. [Google Scholar] [CrossRef]
  38. Barnes, D. An integrated model of the effect of processing parameters on the strength properties of oriented strand wood products. For. Prod. J. 2000, 50, 33–42. [Google Scholar]
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Figure 1. Cutting scheme on the strander-canter (adapted from Alipraja et al. [1]).
Figure 1. Cutting scheme on the strander-canter (adapted from Alipraja et al. [1]).
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Figure 2. (a) Cut mark on cant surface and (b) depth of torn grain measurements (adapted from MountainsMap® 8 software).
Figure 2. (a) Cut mark on cant surface and (b) depth of torn grain measurements (adapted from MountainsMap® 8 software).
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Figure 3. (a) Illustration showing the knife and counter-knife actions and (b) cutting geometry.
Figure 3. (a) Illustration showing the knife and counter-knife actions and (b) cutting geometry.
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Figure 4. The effect of rake angle and temperature on the Ra (a) and Wa (b) values of the cant surface.
Figure 4. The effect of rake angle and temperature on the Ra (a) and Wa (b) values of the cant surface.
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Figure 5. Typical views of cant surfaces (above) and their roughness profiles (below) for unfrozen cants obtained with the rake angle of (a) 69°, (b) 64°, and (c) 59°.
Figure 5. Typical views of cant surfaces (above) and their roughness profiles (below) for unfrozen cants obtained with the rake angle of (a) 69°, (b) 64°, and (c) 59°.
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Figure 6. Depth (a) and volume (b) of torn grain produced on cant surfaces of jack pine.
Figure 6. Depth (a) and volume (b) of torn grain produced on cant surfaces of jack pine.
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Table 1. Characteristics of the jack pine logs.
Table 1. Characteristics of the jack pine logs.
Diameter (mm)205.6 (10.7) a
Length (mm)2326 (0.4)
Taper (mm/m)10.8 (56)
Sapwood thickness (mm)32.7 (32)
Moisture content (%)110.8 (25)
Specific gravity0.461 (8)
a The number in parentheses is the coefficient of variation.
Table 2. Cutting parameters of the strander-canting process.
Table 2. Cutting parameters of the strander-canting process.
Sharpness angle20°, 25°, 30°
Clearance angle1°
Counter-knife angle (frozen condition)20°
Counter-knife angle (unfrozen condition)35°
Edge distance 16 mm
Cutting speed25 m/s
Mean cutting width20 ± 0.5 mm
1 Distance between the knife edge and the counter-knife edge.
Table 3. F-values obtained from the ANCOVA for the strand, pin chip, and fine proportions; strand width; energy consumption; specific cutting energy; and depth and volume of torn grain.
Table 3. F-values obtained from the ANCOVA for the strand, pin chip, and fine proportions; strand width; energy consumption; specific cutting energy; and depth and volume of torn grain.
Source of VariationF-Value
Strands Pin ChipsFinesStrand WidthEnergy Consumption (EC)Specific Cutting Energy (SCE)Depth of Torn Grain (DTG) Volume of Torn Grain (VTG)
Frozen logs
SG4.9 *n.i.4.4 *n.i.6.6 *8.2 **n.i.n.i.
MCn.i.n.i.n.i.n.i.11.4 **21.0 ***n.i.n.i.
CVn.i.n.i.n.i.n.i.n.i.n.i.6.7 *n.i.
Rake angle11.0 **8.7 **10.8 **4.6 *5.2 *2.4 ns0.6 ns1.14 ns
Unfrozen logs
SGn.i.n.i.n.i.6.0 *10.5 **11.0**n.i.n.i.
MCn.i.n.i.n.i.4.4 *n.i.n.i.n.i.9.2 **
CV4.1 *n.i.5.3 *22.0 ***12.3 **n.i.n.i.n.i.
Rake angle1.6 ns3.8 *0.8 ns1.7 ns3.0 ns2.9 ns11.6 ***35.0 ***
*** statistically significant at 0.001 probability level; ** statistically significant at 0.01 probability level; * statistically significant at 0.05 probability level; ns: not statistically significant; n.i.: not included in the model.
Table 4. Means of strand, pin chip, and fine proportions; strand width; energy consumption; and specific cutting energy by rake angle for each log temperature.
Table 4. Means of strand, pin chip, and fine proportions; strand width; energy consumption; and specific cutting energy by rake angle for each log temperature.
Rake AngleStrand Proportion (%)Pin Chip Proportion (%)Fine Proportion (%)Strand Width (mm)Energy Consumption (kWh)SCE (kWh/m3)
Frozen logs
59 86.9 (1.0) B6.5 (0.6) B6.6 (0.5) B25 (1) A16.5 (1.1) B6483 (442) A
64 91.4 (0.8) A4.2 (0.5) A4.4 (0.4) A32 (3) B12.2 (1.2) A5094 (582) A
69 n.an.an.an.an.an.a
Unfrozen logs
59 96.2 (0.4) a1.3 (0.2) a2.4 (0.2) a66 (1) a4.2 (0.1) a1586 (43) a
6496.0 (0.4) a1.6 (0.2) ab2.4 (0.2) a69 (2) a3.9 (0.1) a1489 (42) a
69 95.3 (0.3) a1.9 (0.1) b2.8 (0.2) a66 (2) a3.9 (0.2) a1534 (56) a
Means within a column followed by the same letter are not significantly different at the 5% probability level for frozen and unfrozen logs, separately. Standard errors of means are in parentheses. n.a: data not available.
Table 5. F-values of the roughness (Factor 1) and waviness (Factor 2).
Table 5. F-values of the roughness (Factor 1) and waviness (Factor 2).
Source of VariationFrozen ConditionUnfrozen Condition
Factor 1 (Roughness)Factor 2 (Waviness)Factor 1Factor 2
Rake angle0.5 ns4.9 *104.4 ***74.7 ***
*** statistically significant at 0.001 probability level; * statistically significant at 0.05 probability level; ns: not statistically significant.
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Alipraja, I.; Hernández, R.E.; Koubaa, A. The Role Played by the Rake Angle of a Strander-Canter When Processing Jack Pine Logs. Forests 2023, 14, 2182. https://doi.org/10.3390/f14112182

AMA Style

Alipraja I, Hernández RE, Koubaa A. The Role Played by the Rake Angle of a Strander-Canter When Processing Jack Pine Logs. Forests. 2023; 14(11):2182. https://doi.org/10.3390/f14112182

Chicago/Turabian Style

Alipraja, Irsan, Roger E. Hernández, and Ahmed Koubaa. 2023. "The Role Played by the Rake Angle of a Strander-Canter When Processing Jack Pine Logs" Forests 14, no. 11: 2182. https://doi.org/10.3390/f14112182

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