| 1. |
- Bellani, Gabriele, et al.
(författare)
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Experimental study of the forming process : Fluid velocity and fluid-fiber interaction measurements
- 2008
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Ingår i: Paper Conference and Trade Show, PaperCon '08. - : TAPPI Press. - 9781605605104 ; , s. 1145-1176
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Konferensbidrag (refereegranskat)abstract
- A study of the flow in the direct vicinity of a forming wire and a fiber network during forming is reported. The measurements are performed with Particle Image Velocimetry in a scaled system. Index-of-refraction matching is used to gain optical access to the flow. Time resolved measurements of the flow velocity in the vertical and horizontal direction is obtained in a plane with a size of 60 × 40 fiber diameters. The spatial resolution is 2 fiber diameters. Data is obtained for three drainage velocities and two different lengths of the fibers. The relative level of the velocity fluctuations are found to decrease with drainage velocity and is higher in the flow above a network mat of shorter fibers compared to the network made of longer fibers. The size of the flow structures is obtained by spectral analysis and compared for the six cases.
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| 2. |
- Carlsson, Allan, et al.
(författare)
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Fibre orientation in the boundary layers of a planar converging channel
- 2008
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Ingår i: TAPPI Press - Paper Conference and Trade Show, PaperCon '08. - : TAPPI Press. - 9781605605104 ; , s. 384-408, s. 384-408
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Konferensbidrag (refereegranskat)abstract
- Experimental results on the fibre orientation in a laboratory scale headbox are reported. A steerable filter was used to determine the orientation of bleached and unbeaten birch fibres at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only low concentrations were studied. It is shown that the orientation varies with the distance from the wall. For most studied cases a more anisotropic profile was found closer to the wall.
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| 3. |
- Lindberg, Siv M, et al.
(författare)
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Making subjective assessments objective : A mottle ruler for calibration of panel assessments of perceived print mottle
- 2008
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Ingår i: Paper Conference and Trade Show, PaperCon '08. - 9781605605104 ; , s. 2086-2124
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Konferensbidrag (refereegranskat)abstract
- The objective was to establish principles and procedures for: a) digital simulation and output of reference samples for perceived print mottle assessment, b) calibration of subjective assessments to a common unit of measurement. We decided to calibrate our scales using the just-noticeable difference (jnd) as the unit of subjective measurement and adapt a ruler system for the assessment of perceived print mottle as suggested by Keelan [1]. Jnd used in this context means the smallest difference in mottle required for 50 % of a test panel to genuinely detect a difference. Reference samples were designed in Matlab by adding a stochastic noise to a homogeneous gray (33 % reflectance) and a cyan image, that, when printed would have the resemblance of print mottle typically seen in offset printing. Digital images were converted to CMYK images, rasterized using a Best Color Rip, and printed on Epson Archival Matte paper on an Epson Stylus Photo 2100 ink-jet printer. The resulting prints were evaluated for the magnitudes of perceived visual mottle as well as for the just-noticeable differences, jnds, using panels of assessors. The prints were also evaluated for instrumental mottle using STFI-Packforsk’s image analysis based STFI-mottle software. Two mottle rulers were assembled. A mottle ruler is a set of 5 cm ×—5 cm reference samples, varying widely in magnitudes of reflectance variation resembling real print mottle. Rulers were constructed for simulated K40 % (gray) and cyan 100 % (cyan) samples. The rulers are arranged with approximate twelve reference samples separated by intervals of three jnds each. A Round Robin evaluation of visually perceived print mottle was performed. Two rulers, cyan and gray, together with test samples to be evaluated against the rulers, were sent out to four participating companies. The test sets consisted of eight commercially produced samples (printed paper and board) and twelve simulated samples varying not only in the magnitude of mottle but also in character (e.g. coarseness and the orientation of the simulated noise). The purpose of using test samples with appearances that differed from the reference samples was to test the performance of the approach. The mottle rulers were also applied at Iggesund Paperboard during a test period of eight months in which more than 300 printed samples were assessed against the rulers. Round robin results showed good agreement between participating paper companies. The average standard deviations of the ratings against the rulers were ˜2.5 jnd units for the gray samples and ˜3.5 jnd units for the cyan samples. Some difficulties with the assessment technique were observed for the simulated samples, due to some samples having a very different visual character in terms of uncovered areas or noise that had a distinct orientation e.g. banding. Results from the testing period at Iggesund show less variability; average standard deviation for cyan 1.61 jnd and for gray 2.3 jnd. Overall, the calibration approach developed works very well, with the results showing a low variability of the ratings and a very good agreement between the different test panels, as well as a reasonably good correspondence between ratings of commercially produced samples and mottle measurements.
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| 4. |
- Söderberg, Daniel
(författare)
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A new technique for stratified forming
- 2008
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Ingår i: TAPPI Press - Paper Conference and Trade Show, PaperCon '08. - : TAPPI Press. - 9781605605104 ; , s. 3529-3563, s. 3529-3563
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Konferensbidrag (refereegranskat)abstract
- A new technique for stratified forming has been developed where a thin passive liquid layer (a liquid vane or "Aq-vane") is injected in the between neighbouring pulp streams through a narrow hollow channel, thereby preventing mixing between the layers. The Aq-vanes have been implemented in extensive pilot scale trials where the technical solution has been tested and evaluated. In addition, the impact of this new technique and sheet stratification on product properties has been evaluated.
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| 5. |
- Söderberg, Daniel, et al.
(författare)
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The fundamental mechanism behind headbox jet break-up
- 2008
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Ingår i: TAPPI Press - Paper Conference and Trade Show, PaperCon '08. - 9781605605104 ; , s. 3564-3596, s. 3564-3596
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Konferensbidrag (refereegranskat)abstract
- It has previously been shown that MD streaks are created in the headbox jet, which is closely connected to the appearance of waves on the jet surface. The fundamental mechanism behind this break-up is presented. This has been achieved by implementing state-of-the-art methods for determining the characteristics and evolution of hydrody-namic instabilities. The methodology also allows the headbox slice to be designed in order to minimise jet break-up. This possibility has been evaluated in pilot-scale.
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