miun.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Gradin, Per
Alternative names
Publications (10 of 70) Show all publications
Nyström, J., Gradin, P. & Thörnberg, B. (2018). An experimental study of the chipping process with focus on energy consumption and chipping angles. Nordic Pulp & Paper Research Journal, 33(3), 460-467
Open this publication in new window or tab >>An experimental study of the chipping process with focus on energy consumption and chipping angles
2018 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 460-467Article in journal (Refereed) Published
Abstract [en]

A series of chipping experiments were performed under both dynamic and quasi-static conditions in a laboratory wood chipper (dynamic) and in a MTS-servohydraulic testing machine (quasi-static). One aim with the experiments was to investigate the rate dependency of the energy consumption during chipping. Another aim was to try to determine the load per unit knife edge length required to initiate cutting. The experiments were carried out using different combinations of spout and edge angles. It was found that for large edge angles (keeping the spout angle constant at 30 °30^\circ ) there was a slight rate dependency such that the energy consumption was larger at higher cutting rates which is quite in opposite of what is expected if wood is assumed to be a viscoelastic material. It was also found that to determine the force at initiation of cutting, is not a trivial task. Both Acoustic Emission monitoring and visual inspection was used to this end. The wood species used in this study was pine (Pinus silvestris). 

Keywords
energy consumption, rate dependency, wood chipping
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-34599 (URN)10.1515/npprj-2018-3055 (DOI)000450923900012 ()2-s2.0-85052632762 (Scopus ID)
Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-12-11Bibliographically approved
Engstrand, P., Gradin, P., Hellström, L., Carlberg, T., Sandström, P., Liden, J., . . . Mats, E. (2016). Improved refining energy efficiency in thermo-mechanical pulping by means of collimated wood chipping – from solid mechanics to full scale evaluation. In: Greg Hay (Ed.), PaperWeek Canada 2016 Conference February 1 to 5, 2016, Montreal: Technical Track Program. Paper presented at PaperWeek Canada 2016 Conference, Montreal, February 1-5, 2016.
Open this publication in new window or tab >>Improved refining energy efficiency in thermo-mechanical pulping by means of collimated wood chipping – from solid mechanics to full scale evaluation
Show others...
2016 (English)In: PaperWeek Canada 2016 Conference February 1 to 5, 2016, Montreal: Technical Track Program / [ed] Greg Hay, 2016Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The wood chipping process was never optimized with regard to high yield pulping processes as thermomechanical pulping (TMP) and chemithermomechanical pulping (CTMP). It is generally believed that wood chips for pulping should be produced in such a way that the degree of damage is minimized and that the chip dimensional distribution should be as narrow as possible. Since the TMP and CTMP processes were developed in the 60-ies and 70-ies, compression screw as well as roll nip equipment have been developed to pretreat wood chips as a way to reduce refining energy consumption to given fiber and pulp properties and also in order to improve impregnation. The general conclusions are that a combination of shear and compression in the tangential or radial direction of the wood initiates cracks that later in the refiner will enhance and optimize fiber separation and also fiber property development. The idea with the collimated chipping technology is to utilize the wood chipper as a tool, combining cutting of wood logs to wood chips with a pretreatment of the chips by creating cracks that would enhance fiber separation, fiber surface development as well as chip-impregnation. In this case the compression is performed in the wood fiber direction, in which direction wood actually is weakest when it comes to compression induced cracking. The maximization of the amount of cracks in wood-chips is performed by optimizing the knife angle (or spout angle) in the chipper, to what we call collimated chipping (according to a patent owned by CCT AB). This presentation describes a theoretical background and two demonstration scale studies performed by SCA Forest Products at their Ortviken mill. One conclusion drawn, based on two-month test period with three weeks of collimated chipping, was that specific refining energy reduction was around 100 kWh/adt of the 1400 kWh/adt used in primary stage double disc refining. Most probably the potential is higher if the whole system is optimized. Tests were performed at constant production rate and energy was reduced by reducing power to constant freeness, leading to similar tensile and light scattering levels. The deliberately increased forces created in the wood chipper by means of an optimized (increased) edge angle caused more problems with knife holder equipment than normally, as well as increased vibrations. These problems will have to be solved for future long-term implementation of the technique.

Keywords
chipping, mechanical pulping, energy reduction
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-29474 (URN)
Conference
PaperWeek Canada 2016 Conference, Montreal, February 1-5, 2016
Projects
e2mp forskningsprofil
Funder
Knowledge Foundation, 2010/0178VINNOVA, 2012-00786
Available from: 2016-12-07 Created: 2016-12-07 Last updated: 2017-02-07Bibliographically approved
Gradin, P., Berg, J.-E. & Nyström, S. (2016). Measuring Tangential Forces in a Pulp Refiner: A Novel Approach. Experimental techniques (Westport, Conn.), 40(2), 789-793
Open this publication in new window or tab >>Measuring Tangential Forces in a Pulp Refiner: A Novel Approach
2016 (English)In: Experimental techniques (Westport, Conn.), ISSN 0732-8818, E-ISSN 1747-1567, Vol. 40, no 2, p. 789-793Article in journal (Refereed) Published
Abstract [en]

To get some insight into the processes that are active during the refining of wood, the tangential force distribution in the plate gap is of interest. Over the years several designs of force sensors have been developed for this purpose. One drawback with these designs is that each sensormeasures forces over quite a small area such that in order to cover the whole disc with a reasonably good resolution, many sensors have to be used. Also, there are problems to protect the active parts of the sensors from the harsh environment in the plate gap. In this paper a different concept is presented, in that the sensor is continuous and consists of a hollow radial bar equipped with strain gages on the inside. The force sensor was calibrated before mounting by loading it with a known load in the tangential direction and in different positions while measuring the strains in the points where the gages are located. This makes it possible to determine the so-called influence (or Green) functions. Knowing these it is possible to determine the tangential force distribution from strain values measured during operation of the refiner. Guidelines for doing this are presented together with a detailed description of the load sensor and some experimental results.

Keywords
Pulp Refining, Plate Gap, Force Sensor, Refiner Disc, Strain Gages
National Category
Applied Mechanics
Identifiers
urn:nbn:se:miun:diva-23849 (URN)10.1007/s40799-016-0079-8 (DOI)000384752900031 ()2-s2.0-84969722092 (Scopus ID)
Projects
Filling the gap
Funder
Swedish Energy AgencyVINNOVA
Available from: 2014-12-17 Created: 2014-12-17 Last updated: 2017-12-05Bibliographically approved
Hellström, L. M., Biller, S.-O., Edvardsson, S. & Gradin, P. A. (2014). A theoretical and experimental study of the circular sawing process. Holzforschung, 68(3), 307-312
Open this publication in new window or tab >>A theoretical and experimental study of the circular sawing process
2014 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, no 3, p. 307-312Article in journal (Refereed) Published
Abstract [en]

To gain further insight into the energy dissipation during the wood sawing process, a theoretical model has been developed. The model is based on the assumption that there are two basic causes for energy dissipation during sawing: the creation of a new surface and the compression of material below a saw tooth. It is assumed that both contributions can be dependent on the cutting angle (the angle between the fiber direction and the tangent to the path followed by a saw tooth) because a saw tooth changes its angle of attack during its way through a log. To determine this dependence of the dissipation on the cutting angle, a series of experiments with pine plank sawing were performed by means of different feeding rates and cutting angles while the electrical power supplied to the saw was measured. The parameters in the theoretical model were derived from the experimental findings. Finally, two tests were carried out under different conditions with respect to thickness and cutting angles and the validity of the model was confirmed concerning the prediction of the electrical power consumption.

Keywords
chipper canter, energy consumption, modeling, sawing, sawmill, surface energy
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-22593 (URN)10.1515/hf-2013-0066 (DOI)000333798400007 ()2-s2.0-84903118796 (Scopus ID)
Available from: 2014-08-19 Created: 2014-08-19 Last updated: 2017-12-05Bibliographically approved
Isaksson, P., Gradin, P. A. & Hellström, L. M. (2013). A numerical and experimental study regarding the influence of some process parameters on the damage state in wood chips. Holzforschung, 67(6), 691-696
Open this publication in new window or tab >>A numerical and experimental study regarding the influence of some process parameters on the damage state in wood chips
2013 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 6, p. 691-696Article in journal (Refereed) Published
Abstract [en]

The specific energy consumption during mechanical refining operation can be reduced by choosing the optimal process parameters in the wood chipping process such that a beneficial pretreatment is obtained. In the case of the utilization of a larger knife-edge angle, which is one such process parameter, the energy reduction is presumably due to the increased compressive loading parallel to the wood fibers. In the present article, a chip damage parameter D of spruce is in focus, which is relevant for cracking parallel to the fibers. D is defined and its dependence on the chip length and edge angle of the chipping knife is analyzed numerically by means of finite element analyses (FEA). The cutting force was measured in a pilot wood chipper for a number of knife-edge angles. There is a good correlation between the experimental results and those of FEA.

Keywords
chipping process, finite element analysis (FEA), knife angle, numerical analyses, pretreatment of chips, wood chips
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-20648 (URN)10.1515/hf-2012-0142 (DOI)000324719100010 ()2-s2.0-84906960697 (Scopus ID)
Available from: 2013-12-11 Created: 2013-12-11 Last updated: 2017-12-06Bibliographically approved
Lusth, H., Gradin, P. A. & Hellström, L. M. (2013). A theoretical model for the prediction of energy consumption during the chipper canter process. Nordic Pulp & Paper Research Journal, 28(2), 211-215
Open this publication in new window or tab >>A theoretical model for the prediction of energy consumption during the chipper canter process
2013 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 2, p. 211-215Article in journal (Refereed) Published
Abstract [en]

In modern sawmills, chipper canters are used to transform the approximately circular cross section of logs into a rectangular shape before the log is sawn into planks and boards. The chipper canter is in essence a conical disc equipped with knives on its periphery and a circular saw blade at its base. Thorough the action of the chipper canter, the outer parts of a log is removed and transformed into sawdust and chips. In some situations it might be important to be able to predict the energy consumption during canting, for example when one wants to know whether a particular canting strategy can be used considering that there is a limit to the electrical power supply. The aim of this paper was therefore to develop a theoretical model that can perform such a prediction. The canting process can be divided into two parts; the chipping performed by knifes and the sawing performed by the saw blade on the chipper head. The sawing part is performed in order to get a smooth enough surface of the reduced portion of the log. In this paper, emphasis is put on the chipping part of the process and the contribution from sawing is treated only in principal. The results from the theoretical model were compared to results from a field trial and it was concluded that the model gave a fair prediction of the power needed.

Keywords
Canter chipper, Energy consumption, Specific cutting energy
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-19930 (URN)000321291900006 ()2-s2.0-84883004296 (Scopus ID)
Available from: 2013-10-08 Created: 2013-09-25 Last updated: 2017-12-06Bibliographically approved
Edvardsson, S., Gradin, P., Isaksson, P. & Gulliksson, M. (2012). A Note on Wet Paper Web Adhesion Strength. Journal of Testing and Evaluation, 40(4), 682-686
Open this publication in new window or tab >>A Note on Wet Paper Web Adhesion Strength
2012 (English)In: Journal of Testing and Evaluation, ISSN 0090-3973, E-ISSN 1945-7553, Vol. 40, no 4, p. 682-686Article in journal (Refereed) Published
Abstract [en]

This work is concerned with the determination of the adhesion strength between a paper web and an adhesive surface. Edvardsson et al. [Edvardsson, S., Gradin, P., and Isaksson, P., "On Dissipative Effects of Paper Web Adhesion Strength," Int. J. Solids Struct., Vol. 48(1), 2011, pp. 24-30] suggested recently a model that takes into account the energy dissipation caused by elastic plastic deformation in the bent structure of a paper specimen. This model is further developed and investigated in the present work. A linear relation in plastic dissipation is discovered facilitating a novel analysis of the peeling tension and a more convenient determination of the proper adhesion strength. Industrial relevant examples are made with wet newsprint and kraft stock. A straightforward experimental procedure for determining the consistent adhesion strength is suggested. It is found that the agreement between the model and the experimental observations is good.

Keywords
adhesion strength, paper web, peeling test
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-17064 (URN)10.1520/JTE103851 (DOI)000307424100020 ()2-s2.0-84864119770 (Scopus ID)
Available from: 2012-10-01 Created: 2012-09-26 Last updated: 2017-12-07Bibliographically approved
Hellström, L., Carlberg, T., Engstrand, P., Gradin, P. & Gregersen, Ø. (2012). Evaluation Of Collimated Chipping Technology For Reducing Energy Consumption In Mechanical Pulping. Journal of Science & Technology for Forest Products and Processes, 2(3), 6-9
Open this publication in new window or tab >>Evaluation Of Collimated Chipping Technology For Reducing Energy Consumption In Mechanical Pulping
Show others...
2012 (English)In: Journal of Science & Technology for Forest Products and Processes, ISSN 1927-6311, E-ISSN 1927-632X, Vol. 2, no 3, p. 6-9Article in journal (Refereed) Published
Abstract [en]

It has recently been shown that the energy efficiency during first-stage TMP (thermo-mechanical pulp) refining can be improved using amodified chipping method (collimated chipping), where the angle between the fibre direction of the wood specimen and the cutting plane is increased. This paper reports the differences in properties of TMP refined from wood chips produced at two different spout angles, 30° and 50°, with and without the addition of sodium bisulphite (NaHSO3) to the dilution water. It was found that the specific energy input for a certain CSF (Canadian Standard Freeness) value was lower for chips produced at spout 50°, but that the addition of chemicals to the dilution water had no influence on the specific energy value for a given CSF value. However, the tensile index and specific light-scattering coefficient were substantially higher for handsheets made from the pulp refined from chips produced at spout angle 50° and with NaHSO3 added compared to handsheets from pulp made from 30° and 50° chips without chemicals added.

Keywords
Collimated chipping, mechanical pulping
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-17789 (URN)000313365400002 ()2-s2.0-84877633077 (Scopus ID)
Note

Same creative work as:

Hellstrom, L.M., Carlberg, T., Engstrand, P., Gradin, P.A., Gregersen, O.W.Evaluation of collimated chipping technology for reducing energy consumption in mechanical pulping(2013) Pulp and Paper Canada, 114 (6), pp. 27-30. 

ISI: 000328436100008

ScopusID: 8489183501

Available from: 2012-12-17 Created: 2012-12-17 Last updated: 2017-12-06Bibliographically approved
Lusth, H., Gradin, P. A. & Hellström, L. M. (2012). The dependency of energy consumption on cutting angles in the canter chipping process. Nordic Pulp & Paper Research Journal, 27(5), 886-889
Open this publication in new window or tab >>The dependency of energy consumption on cutting angles in the canter chipping process
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 5, p. 886-889Article in journal (Refereed) Published
Abstract [en]

Canter chippers are used in sawmills to reduce the circular cross section of logs to a rectangular shape before sawing. The canter chipper is a conical disc equipped with knives on its periphery. When rotated at high velocity it transforms the outer parts of a log into sawdust and chips. It is important to be able to predict the energy consumption during canting since it is useful to know whether a particular canting strategy can be employed in situations where there is a limit on the power supply. A theoretical model in which energy consumption can be calculated is necessary for such a prediction. Data concerning the specific cutting energy is needed to develop the model for the canting operation. In this paper the energy consumption during chipping of spruce is determined by using a pilot wood chipper at two different cutting rates and for several cutting angles. The results indicate that the specific energy to cut wood chips increases as the angle between the fibre direction and the cutting plane increases.

Keywords
Canter chipper, Energy consumption, Saw mill chips, Specific cutting energy
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-17995 (URN)10.3183/NPPRJ-2012-27-05-p886-889 (DOI)000313375400007 ()2-s2.0-84871776583 (Scopus ID)
Available from: 2013-04-04 Created: 2012-12-19 Last updated: 2017-12-06Bibliographically approved
Hellström, L., Gradin, P., Gulliksson, M. & Carlberg, T. (2011). A laboratory wood chipper for chipping under realistic conditions. Experimental mechanics, 51(8), 1309-1316
Open this publication in new window or tab >>A laboratory wood chipper for chipping under realistic conditions
2011 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 51, no 8, p. 1309-1316Article in journal (Refereed) Published
Abstract [en]

In order to be able to study the damage mechanisms and in general the mechanisms active when a wood chip is created during the wood chipping process, it is crucial to have access to an experimental equipment in which chips can be produced under realistic conditions. In this paper is presented a laboratory chipper, which has been developed to admit chipping at rates that can be varied in a large interval i.e. at rates ranging from zero to 50 m/s. The knife used to cut the chips is mounted in a knife holder, which is instrumented in such a way that forces in three orthogonal directions can be measured. Since the actual force and the measured force differs due to inertia effects, a simple mathematical model is developed and used to evaluate the force acting on the knife. Some results are shown from the force measurements and it is concluded that the laboratory chipper is a versatile tool in the process of increasing the understanding of the chipping process.

Keywords
Wood chipping, laboratory chipper, force measurement, vibration synthesis
National Category
Materials Engineering
Identifiers
urn:nbn:se:miun:diva-11915 (URN)10.1007/s11340-010-9452-1 (DOI)000294801600007 ()2-s2.0-80052444327 (Scopus ID)
Available from: 2010-08-16 Created: 2010-08-16 Last updated: 2017-12-12Bibliographically approved
Organisations

Search in DiVA

Show all publications