CONFIDENTIAL TO MEMBER COMPANIES University Report PUR 946 March 2008 570 Saint-Jean Blvd., Pointe-Claire, QC, Canada, H9R 3J9 • 514-630-4100 • www.fpinnovations.ca These reports describe research work performed in FPInnovations – Paprican's University Collaborations. Ces rapports décrivent les travaux de recherche effectués dans le cadre des collaborations universitaires de FPInnovations – Paprican. Forces During Bar-Passing Events in Low-Consistency Refining: Distributions and Relationships to Specific Edge Load Brett Prairie 1 , Peter Wild 1 , Peter Byrnes 1,3 , Dustin Olender 1 , Bill Francis 2 , and Daniel Ouellet 2,4 1. Department of Mechanical Engineering, University of Victoria, BC, Canada 2. FPInnovations – Paprican, Vancouver, BC, Canada 3. Current Affiliation: Herzberg Institute of Astrophysics, Victoria, BC, Canada 4. Current Affiliation: BC Hydro, Burnaby, BC, Canada
These reports describe research work performed in FPInnovations – Paprican's University Collaborations. Ces rapports décrivent les travaux de recherche effectués dans le cadre des collaborations universitaires
de FPInnovations – Paprican.
Forces During Bar-Passing Events in Low-Consistency Refining: Distributions and
Relationships to Specific Edge Load
Brett Prairie1, Peter Wild1, Peter Byrnes1,3, Dustin Olender1, Bill Francis2, and Daniel Ouellet2,4
1. Department of Mechanical Engineering, University of Victoria, BC, Canada 2. FPInnovations – Paprican, Vancouver, BC, Canada
3. Current Affiliation: Herzberg Institute of Astrophysics, Victoria, BC, Canada 4. Current Affiliation: BC Hydro, Burnaby, BC, Canada
University Report
PUR 946 MARCH 2008
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FORCES DURING BAR-PASSING EVENTS IN LOW-CONSISTENCY REFINING: DISTRIBUTIONS AND
RELATIONSHIPS TO SPECIFIC EDGE LOAD
Brett Prairie1, Peter Wild1, Peter Byrnes1,3, Dustin Olender1, Bill Francis2, and Daniel Ouellet2,4
1. Department of Mechanical Engineering, University of Victoria, BC, Canada 2. FPInnovations – Paprican, Vancouver, BC, Canada
3. Current Affiliation: Herzberg Institute of Astrophysics, Victoria, BC, Canada 4. Current Affiliation: BC Hydro, Burnaby, BC, Canada
ABSTRACT A piezoceramic sensor was used to measure normal and tangential (shear) forces applied to a bar at one location in the refining zone of a Sunds Defibrator Conflo JC-00 conical refiner over a range of specific edge loads (SEL) from 0.3 to 0.5 J/m. For each bar-passing event, parameters including peak shear force and peak normal force, coefficient of friction, and shear work were determined. Distributions were calculated for each parameter. Weibull distributions were found to provide good fits to the data. Median peak shear and normal forces were shown to increase with increasing SEL. Estimates of shear work during a bar-passing event, based on SEL, are within a factor of two of the shear work measured by the sensor.
RÉSUMÉ Nous avons utilisé un capteur piézocéramique pour mesurer les forces normales et tangentielles (de cisaillement) appliquées à une barre à un endroit dans la zone de raffinage d’un raffineur conique Sunds Defibrator Conflo JC-00 dans une plage de charges spécifiques de bord (SSB) de 0,3 to 0,5 J/m. Pour chaque activité de passage sur les barres, nous avons déterminé certains paramètres dont la force de cisaillement maximale et la force normale maximale, le coefficient de friction et le travail de cisaillement. Nous avons calculé les distributions pour chaque paramètre. Nous avons trouvé que les distributions Weibull concordaient bien avec les données. Nous avons observé que les forces de cisaillement maximales médianes et les forces normales augmentaient à mesure que la SSB augmentait. Des
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prévisions du travail de cisaillement au cours des activités de passage sur les barres, en fonction de la SSB, sont à un facteur de deux près du travail de cisaillement mesuré par le capteur.
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Introduction The authors have developed a sensor to simultaneously measure normal and shear forces on bars in high-consistency refining. Measurements have been made in a laboratory-scale refiner [1], two pilot-scale refiners [2,3], and a mill-scale refiner [4]. In the current research, the sensor design used in these past studies was installed in a low-consistency refiner at FPInnovations – Paprican, in Vancouver, BC. This report is the second in a series on the same installation. The first report described the effects of refiner run-out on bar forces [5]. Low-consistency refiners apply cyclic stresses to mainly chemical pulp fibres, making structural changes to these fibres that are critical for the production of paper. This type of refining involves the same type of machinery as in high-consistency refining, capturing the fibre in the nip of crossing bars, but takes places at much lower temperatures and pressures, and involves a much simpler flow regime of water and pulp. The process is currently modelled using energy-based quantifiers, such as the specific edge load (SEL), which estimates the force per unit bar length imparted to the pulp flow. These quantifiers are estimates of actual forces on the pulp, as they are based on global process variables, such as motor load. Recent research by Kerekes and Senger [6] suggests that a more thorough characterization of pulp properties can be achieved by modelling forces on individual fibres – a technique that would greatly benefit by a more precise estimate of the forces in the refining zone. Previous studies have also theorized about the distribution of these forces [7,8], and linked them to process efficiency. This theory remains unproven, likely because of the limited availability of empirical data. The only available force data from low-consistency refiners was recorded in the 1970s by Goncharov et al. [9], and did not include information on their distributions. The refiner force sensor has been designed specifically to measure normal and shear forces over a short section of refiner bar, proving its capability in the challenging environment of high-consistency refiners. This work presents empirical data on the forces experienced during individual bar-crossings in a low-consistency refiner. Applications of this data include comparison to existing quantifiers such as SEL, use as an empirical input in force models, or use in validating existing theory on force distributions. Experimental Methods The Sensor A photograph of the sensor is shown in Figure 1a. The principal component of the sensor is the probe, which is designed to protrude into the refining zone of the refiner, replacing a short section (5 mm) of bar. The sensor was installed in a Sunds Defibrator Conflo JC-00 conical refiner at the Vancouver Laboratory of FPInnovations – Paprican. The capacity of this refiner is 5-50 tonnes/day, operating at between 40 to 110 kW. Its major diameter is approximately 0.4 m. To accommodate the sensor, a hole was bored in the stator of this refiner. This hole was centred at the mid-span point of a refiner bar. A photograph of the sensor installed in the stator is shown in Figure 1b.
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Figure 1a: The force sensor.
Figure 1b: The force sensor installed in a Conflo® JC-00 LC refiner.
Sealed within the sensor are two piezoelectric elements, which are pre-loaded between the base of the probe and the interior of the housing. When a normal force is applied to the probe, the two piezoelectric elements share the applied load equally. When a shear force is applied to the probe, one element is subjected to increased compression and the other to decreased compression. The voltages generated in response to these load changes are processed such that shear and normal forces are independently determined.
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Experiments Softwood chemi-thermomechanical pulp (250 mL initial CSF) was refined during a single pass through a Sunds Defibrator Conflo JC-00 refiner. The refiner fillings (SM) had a bar width of 2.54 mm and a groove width and depth of 3.09 mm and 9.02 mm, respectively. The average bar angle on the rotor was approximately 29º. Experiments were conducted with the following operating conditions: 3.15% consistency; 200 to 400 L/min flow rate; 60°C temperature; 900 rpm refiner speed; and 0.33 to 0.5 J/m target specific edge loads (SEL). SEL was calculated from the net refining power (refining power less no-load power), rotor speed and plate factor (i.e. 5.2 km/rev). SEL was varied by varying the motor load. Twenty-seven data intervals with relatively constant motor load were identified and extracted for analysis. The mean and range of specific edge load for these data samples are given in Appendix I. Data Processing Physically, a bar-passing event is defined to begin when the leading edge of a bar on the rotor just overlaps a bar on the stator and ends when the leading edge of that bar on the rotor just overlaps the next bar on the stator. Custom software was used to search the force sensor data to identify blocks of data containing distinct peaks in the normal forces that are consistent with this definition. Various parameters that describe the forces that occur during each identified bar-passing event, such as peak normal and shear forces, peak coefficient of friction, and shear work were then extracted for analysis. The process by which bar-passing events are identified and then extracted from sensor data consisted of a number of operations. First, the acquired normal force data were subjected to a Butterworth notch filter with corner frequencies of 6 and 20 kHz to remove frequency components associated with sensor resonance. The first natural frequency of the sensor occurs at 15 kHz. This smoothed the data, allowing the events to be more easily identified. Second, any peak in the data contained between two local minima, with each minimum value having a magnitude less than 5% of the peak value, was considered a potential event. From these potential events, any peak that had a duration greater than 17% of the bar-passing period (i.e. the duration of a bar passing event, as defined above) and not within one bar-passing period of another event was considered an actual event. Once an event was identified and indexed by time of occurrence, the data for the unfiltered event were then extracted for analysis, based on this index. This method ensured that event parameters such as peak shear and normal force were based on unfiltered and, therefore, unattenuated data. Event Parameters The piezoelectric elements in combination with the charge amplifier act as a high-pass filter and, therefore, the DC component of the signal and the absolute reference to zero force are lost. In this analysis, it is assumed that the forces return to zero between bar-passing events and, therefore, the magnitude of a force is calculated relative to the valley that precedes the event. Peak coefficient of friction for the event is calculated as the quotient of the peak shear force and peak normal force. Peak phase difference for the event is calculated as the delay between the occurrence of the peak shear force and the peak normal force divided by the bar-passing period, as defined above. Finally, the shear work for each
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bar-passing event is obtained by integrating the shear force profile, with respect to travel of the crossing bar, over the duration of the event. Results and Discussion Force Profiles
Typical unfiltered normal and shear force profiles are shown in Figure 2. The normal and shear forces have similar profiles, but the shear force peak values are approximately one order of magnitude lower than their normal counterparts. Both shear and normal forces increase at what is thought to be the onset of a bar-passing event and then decrease dramatically, creating a spike-shaped profile. The spike-shaped force profile typically occurs over less than half of the entire length of a bar-passing event.
(b)Figure 2: Typical unfiltered normal and shear force profiles (SEL=0.47 J/m).
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0%
1%
2%
3%
4%
5%
6%
7%
8%
0.00
2.00
4.00
6.00
8.00
10.0
0
12.0
0
14.0
0
16.0
0
18.0
0
20.0
0
Normal Force Peak [N]
Freq
uenc
y
FrequencyWeibull
Total Number of Events: 15706
β = 2.292
η = 5.547
R2 = 0.978
γ = 0.000
Event Parameter Distributions
Each bar-passing event is unique and, at 900 rpm, these events occur at 2.0 kHz. A convenient way of summarizing the large volumes of data that were accumulated is with distributions of key event parameters. Figures 3 through 7 show typical event parameter distributions for data samples taken at 900 rpm with an SEL of 0.47 J/m. The data from these plots were taken over a span of 8 s, in which 15,706 events were recorded. Figures 3 and 4 show typical distributions of the peak normal and shear forces. These distributions are normal in shape with a slight skew toward smaller peak values. A Weibull distribution, shown in Equation 1, has been fit to the data.
β
ηγβ
ηγ
ηβ
−−
−
⋅
−=
x
exxf1
)( (1)
In this three-parameter Weibull distribution, β is a shape parameter; η is a scale parameter; and γ controls the location of the distribution along the x-axis [10]. For reference, a perfect normal distribution has a β value of 3.
Figure 3: Normalized distribution of normal force peaks [N] (SEL=0.47 J/m).
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0%
1%
2%
3%
4%
5%
6%
7%
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
Shear Force Peak [N]
Freq
uenc
y
FrequencyWeibull
Total Number of Events: 15706
β = 2.845
η = 0.760
R2 = 0.978
γ = 0.000
Figure 4: Normalized distribution of shear force peaks [N] (SEL=0.47 J/m).
A decreasing exponential distribution of the forces in low-consistency refining was first suggested by Giertz [7], and later theorized by Mayade [8]. Recent experiments were performed by Senger et al. [2] in a high-consistency pilot-scale refiner, using an earlier prototype of the sensor used in the current study. Senger found the distribution of forces to be decreasing by exponential. Aside from the effects of rotor tram [5], the findings of the current study reveal bar-passing impacts to be regular, occurring with each bar-crossing, and to be similar in shape and magnitude. As discussed above, the distribution of these forces, over a wide range of operating conditions, is skewed normal or Weibull. A hypothesis that provides an explanation for the distributions found in this study and that of Senger et al. [2], considers the composition of the mixture in the refiner. Low-consistency pulp consists of relatively uniform fibre bundles in a relatively homogeneous suspension. This provides a relatively uniform flow of flexible material into the nip of crossing bars. By comparison, a more irregular mixture of coarse wood fibre, water, and steam exists in a primary-stage, high-consistency refiner, which would explain the dominance of small or missing impacts recorded by Senger et al. This hypothesis does not, however, resolve the lack of agreement of the data from the current study with earlier theory [7,8]. The distribution of the peak coefficient of friction (COF) is shown in Figure 5. The median peak COF for the sample taken in Figure 5 is approximately 0.14. This value is close to the coefficient of friction of 0.11 observed in experiments performed by Goncharov [9] using a strain gauge based sensor which, similar to the current sensor, replaced a short segment of a bar in a low-consistency refiner.
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0%
2%
4%
6%
8%
10%
12%
0.00
0.03
0.05
0.08
0.10
0.13
0.15
0.18
0.20
0.23
0.25
Peak Coefficient of Friction
Freq
uenc
y
FrequencyWeibull
Total Number of Events: 15706
β = 2.210
η = 0.050
R2 = 0.980
γ = 0.100
0%
1%
2%
3%
4%
5%
6%
0.00
0.20
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1.00
1.20
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1.80
2.00
Shear Work
Freq
uenc
y
FrequencyWeibull
Total Number of Events: 15706
β = 2.30045η = 0.830
R2 = 0.985
γ = 0.000
Figure 5: Normalized distribution of the peak coefficient of friction (SEL=0.47 J/m).
Figure 6 shows the distribution of the shear work measured by the sensor during bar-passing events. The profile of the shear work distribution has a similar shape to the peak force distributions shown in Figures 3 and 4.
Figure 6: Normalized distribution of shear work [mJ] (SEL=0.47 J/m).
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The distribution of peak phase difference is shown in Figure 7. The peak phase difference for each event has been expressed as a percentage of the bar-passing period. At a refiner speed of 900 rpm, the bar-passing period is calculated to be 0.5 ms. Over the vast majority of events measured, normal and shear peaks occur almost simultaneously (i.e peak phase difference is close to zero). This is consistent with the force profiles observed by Goncharov in an LC refiner [9]. In a small percentage of events, there are a non-zero peak phase differences. A positive peak phase difference can be explained by a build-up of fibre material on an advancing rotor bar. This material would impart a shear force to the probe prior to the overlap of the rotor bar on the probe. Clear interpretations of negative values of peak phase difference are less apparent. However, these values may be associated with a “rolling” motion of material between passing bars, leading to high normal forces prior to the onset of high shear forces.
Figure 7: Normalized distribution of peak phase difference [ms] (SEL=0.47 J/m).
Event Parameters and Specific Edge Load The relationship between the median value of each event parameter and specific edge load was investigated. Figure 8 shows an increase in median peak normal force as a function of increasing SEL. This result is not unexpected, as SEL is a measure of the shear work per unit bar length, and is therefore a function of shear force. Due to the relatively constant peak coefficient of friction found throughout these experiments, the peak normal force is proportional to the peak shear force and should therefore also increase with increasing SEL.
0%
10%
20%
30%
40%
50%
60%
-20% -10% 0% 10% 20%
Peak Phase Difference (percentage of bar-crossing)
Freq.
Total Number of Events: 15706
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y = 12.702x - 1.178R2 = 0.817
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
0.30 0.35 0.40 0.45 0.50 0.55 0.60
Specific Edge Load [J/m]
Peak
Nor
mal
For
ce [N
]
y = -0.082x + 0.180R2 = 0.793
0.130
0.135
0.140
0.145
0.150
0.155
0.160
0.30 0.35 0.40 0.45 0.50 0.55 0.60
Specific Edge Load [J/m]
Peak
Coe
ffici
ent o
f Fric
tion
Figure 8: Comparison of median normal forces at various SEL.
Figure 9 shows the effect of SEL on the peak coefficient of friction. As the specific edge load is increased, the peak COF slightly decreases. The average peak COF over all tested SEL is approximately 0.145. As noted earlier, this is close to the value of 0.11 observed in experiments performed by Goncharov [9].
Figure 9: Comparison of the median coefficient of friction at various SEL.
A comparison between the peak phase difference of each bar-passing event and specific edge load showed that varying the SEL had no effect on the time lag between normal and shear peaks.
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0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.30 0.35 0.40 0.45 0.50 0.55 0.60
Specific Edge Load [J/m]
Bet
a
As noted earlier, Weibull parameters describe the scale and shape of a distribution. Figure 8 shows that SEL has an effect on the force magnitudes of the bar-passing events, which means that the scale of the force distributions is dependent on the specific edge load. A comparison between the shape of each distribution and SEL is shown in Figure 10. All distributions are close to normal with a slight skew toward smaller forces, regardless of the SEL, indicating that SEL has no effect on the shape of the force distributions, over the range of operating parameters in these tests.
Figure 10: Comparison of the normal force distribution shape, β at various SEL.
Segment and Bar Variations The preceding plots show trends in the normal force data based on all of the recored bar-passing events. Rotor misalignment caused variations in the plate gap of 0.06 mm (approximately 40% of typical plate gap) and thus variations in the normal force data over the seven rotor plate segments. The gap is smallest at segment #4 and is largest at segments #1 and #7. The normal force increased from segment #1 to segment #4 and then decreased to segment #7 in response to the changes in plate gap [5]. Data processing methods were developed which identified each bar-passing event with a specific bar on the rotor [11]. Median force values for bar #4 on segment #4 on the rotor are shown in Figure 11. The regression parameters for bars #4, #8 and #12 are shown in Table 1. These bars are located 25%, 50%, and 75% across segment #4, respectively. Also shown in Table 1 are the regression values for the events associated with all bars on segment #4 and for events recorded over the entire rotor. If variations in forces at a given bar were due solely to variations in rotor and stator bar geometry, then the average coefficient of determination for an individual bar would be significantly higher than for all of the bars on the rotor. However, the coefficients of determination for the individual bars are lower than the coefficient of determination for all of the bars on the rotor. These results suggest that the variations in forces at bar-crossing events are due principally to local variations in the properties of the pulp suspension
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y = 23.294x - 4.116R2 = 0.565
0.0
2.0
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10.0
12.0
0.30 0.35 0.40 0.45 0.50 0.55 0.60
Specific Edge Load [J/m]
Peak
Nor
mal
For
ce [N
]
such as floc size, structure and distribution as well as the effects of plate gap. These results also highlight the general lack of clear correlation between a macroscopic parameter such as SEL and the actual forces at the point of application to the pulp.
Figure 11: Comparison of median normal forces for bar #4 on segment #4 at various SEL.
Table I. Linear regression values for various bars on segment #4.
Segment # Bar # m [Nm/J] b [N] r2 4 4 23.294 -4.116 0.565 4 8 28.337 -4.543 0.659 4 12 26.337 -2.980 0.550 4 All 23.799 -2.632 0.620
All All 12.702 -1.178 0.817 Comparison of Measured Shear Work and Theoretical Shear Work SEL is a measure of the energy expended on the pulp over one bar-passing event, per unit length of bar. Equation 2, derived by Kerekes and Senger [6], relates SEL to: the average shear force per unit bar length during a bar-passing event, FS ; the sliding distance over which the force is applied, s; and, the bar angle, φ. The bar angle is measured in the plane tangent to the surface of the cone of the rotor, between the projection of the axis of the cone onto this tangent plane and the bar itself.
φcos⋅=⋅ SELsFS (2)
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The left-hand side of equation 2 is equal to the average shear work done in a bar-passing event per unit
length of bar, SW , and, thus,
φcosˆ ⋅= SELWS . (3)
Given a sensor with a probe of length, l , in the direction of the bar, the average work done on the sensor probe in a bar passing event, SW , is as shown in Equation 4. This assumes that the average work done per unit length of probe is equal to the average work done per unit length of bar for the rotor as a whole.
lSELWS ⋅⋅= φcos (4) The average shear work done on the sensor in a bar-passing event was calculated for each test condition using Equation 4. The average measured shear work for each test condition was also calculated, based on sensor data. Figure 12 compares these two measures of shear work. The idealized case, where the sensor measurements equal the values based on SEL, is indicated by the line with a slope of one. The slope of the least-squares linear fit to the sensor data is 0.513.
Figure 12: Comparison of measured shear work on the sensor and shear work on the sensor based on SEL. (Shear Work (SEL) is based on the average bar angle, φ=29°). As noted above, the shear work measured by the sensor is for one sensor location only, mid-span on a stator bar. The distributions of shear work along this bar and all other stator bars are unknown. Therefore, the shear work at this location is unlikely to be equal to the average shear work for the entire stator. The sensor measurements of shear work and the values based on SEL, shown in Figure 12, are in reasonably good agreement, given the potential error that may be introduced by this assumption that average shear work on the sensor is representative of the entire refiner.
y = 0.513x - 0.28
R2
=0.835
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.5 1.0 1.5 2.0 2.5
Shear Work (Sensor) [mJ]
Shear Work (SEL) [mJ]
Work(Sensor) = Work (SEL)
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Forces with Water-Only Feed Experiments with water only were carried out at the same operating conditions as the pulp experiments described in Table 1 in Appendix I. Water was fed through the refining zone while the sensor acquired data. Figure 13 shows the forces measured with the sensor for a plate gap of 0.05 mm (similar to plate gap during pulp refining). Plate gap is adjusted manually by turning a ball screw on the refiner. The plate gap was measured through the sensor’s mounting hole in the stator, and various turns of the ball screw were measured with a base reference taken during plate touch. The motor load in Figure 13 was 16.2 kW and the flow rate was 400 L/min. The results shown in Figure 13 are typical of the forces measured under all other conditions with water only as the fluid medium. The peak forces with water only were at least one order of magnitude less than the peak forces measured in the pulp experiments. These results are consistent with the work of Nordman [12] and Caucal [13], who found that refining was primarily the result of fibre-fibre and fibre-bar contact, with hydraulic forces playing an insignificant role.
(a)
(b) Figure 13: Forces measured in the refiner without pulp present (0.05 mm gap).
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Conclusions A piezoelectric force sensor was used to measure normal and shear forces in a low-consistency refiner. Bar-passing event parameters such as peak shear force, peak normal force, shear work, peak coefficient of friction, and peak phase difference were determined for each event. Distributions of these event parameters were generated and a three-parameter Weibull curve was fit to the distributions. Both peak normal and shear force distributions were essentially normal in shape with a slight skew toward smaller force values. Comparisons between the median values of each parameter were made with respect to changes in specific edge load from 0.3 to 0.5 J/m. Peak normal and shear forces along with shear work increased with increasing SEL. The peak coefficient of friction (COF) decreased slightly with increasing SEL. The average peak COF was approximately 0.14. Specific edge load appears to have no effect on the shape of the peak normal and shear force distributions. Mean peak forces associated with individual bars on the rotor show poorer correlation with SEL than peak forces averaged over an entire segment or over the entire rotor. This emphasizes heterogeneity in the pulp, over imperfections in bar and gap geometry, as a major source of variability in the forces generated during bar-passing impacts. Finally, measured shear work during bar-passing events was compared with a theoretical calculation of shear work at measured SEL. Measured values of shear work were within a factor of two of theoretically calculated values. These findings have potential applications in assessing theoretical models of refiner operation. Acknowledgments The authors gratefully acknowledge funding provided by the Natural Sciences and Engineering Research Council, Andritz Ltd. and FPInnovations – Paprican, access to experimental facilities provided by FPInnovations – Paprican, and the contributions provided by Dr. Richard Kerekes of the Pulp and Paper Centre, University of British Columbia.
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References [1] SIADAT, A., A. BANKES, P.M. WILD, J. SENGER, and D. OUELLET, “Development of a
Piezoelectric Force Sensor for a Chip Refiner,” Institution of Mechanical Engineers, Part E, Journal of Process Mechanical Engineering, Vol. 217, 133-140, (2003).
[2] SENGER, J., M. OLMSTEAD, D. OUELLET, and P.M.WILD, “Measurement of Shear and Normal Forces in the Refining Zone of a TMP Refiner,” Journal of Pulp and Paper Science, Vol. 30 No. 9, 247-251, (2004).
[3] SENGER, J., D. OUELLET, P.M. WILD, P. BYRNES, and M. SABOURIN, “A Technique to Measure Mean Residence Time in TMP Refiners Based on Inherent Process Fluctuations,” Journal of Pulp and Paper Science, Vol. 32, No. 2, 83-89 (2006).
[4] OLENDER, D., WILD, P., BYRNES, P., OUELLET, D., and M. SABOURIN, “Forces on Bars in High-Consistency Mill-Scale Refiners: Trends in Primary and Rejects Stage Refiners,” Journal of Pulp and Paper Science, Vol. 33, No. 3, 163-171, (2007).
[5] PRAIRIE, B., P. WILD, P. BYRNES, D. OLENDER, D.W. FRANCIS, and D. OUELLET, “Forces During Bar-Passing Events in Low Consistency Refining: Effect of Refiner Tram,” Pulp Paper Canada, Vol. 108, No. 9, T153-156 (2008).
[6] KEREKES, R.J. and J. SENGER, “Characterizing Refining Action in Low Consistency Refiners by Forces on Fibres” Journal of Pulp and Paper Science, Vol. 32, No. 1, pp 1-8, (2006).
[7] GIERTZ, H.W., “A New Way to Look at the Beating Process,” Norsk Skogindustri Vol.18, No. 7, 239 (1964).
[8] MAYADE, T.L., “Statistical Theory of Chemical Pulp Refining – An Innovative Combined Approach.”, Appita J., 50(3):237-244 (1997).
[9] GONCHAROV, V.N., “Force Factors in a Disk Refiner and their Effect on the Beating Process”, Bumazh. Promst.12(5):12-14, English Trans., (1971).
[10] PRABHAKAR MURTHY, D.N., M. XIE, and R. JIANG, “Weibull Models,” Wiley-Interscience (2003).
[11] PRAIRIE, B., “Development of a Low Consistency Mechanical Force Sensor”. M.A.Sc. Thesis, University of Victoria, Victoria, BC. (2005).
[12] NORDMAN, L., J. LEVLIN, T. MAKKONEN, and H. JOKISALO, “Conditions in an LC-Refiner as Observed by Physical Measurements” Paperi ja Puu, No. 4, pp. 169-180 (1981).
[13] CAUCAL, G., D. CHAUSSY, and M. RENAUD, “Etude Physique et Hydraulique du Raffinage”, Revue ATIP, Vol. 45 No.5, p. 187-199 (1991).
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CONFIDENTIAL TO FPINNOVATIONS MEMBER COMPANIES PUR 946 • MARCH 2008
APPENDIX I
Table A1. Average Specific Energy [kwh/t] and Specific Edge Loads at 900 rpm, [J/m]
