4,855 research outputs found
Kinematics and Geometry of Helical Chipping with Cylindrical Helical Blades
No full textThe chipping of wood with helical chippers can be done with either a conical or a cylindrical helical blade. These methods vary not only according to the shape of the blade and rotor but, importantly, also with respect to the direction of the material infeed. The infeed is parallel to the axis of the rotor with a conical chipper; in contrast, with a cylindrical chipper; the infeed occurs at a specific infeed angle, which is apparently determined by the chipper's blade angle. Machines are available on the market with either of these chipping concepts. Because of this, the question arises as to how these two concepts can be compared with each other and whether there are any differences between them. In this article, the geometry and kinematics of a cylindrical helical chipper are discussed theoretically and compared with the geometry and kinematics of a conical helical chipper The results show that both concepts function in generally the same manner The main difference is that all the tool parameters under consideration and the angular relationships of the blade of the cylindrical rotor are constant, whereas with a conical rotor they are not. In addition, the slice/push ratio of a cylindrical rotor occurs due to the tool and work piece interaction and not the blade's radial feed motion, as with a conical rotor Furthermore, the comparison of the two concepts confirmed the assumption that the work piece is set vertically to the cutting face and that the wedge angle determines the direction of the rate of feed
Wood chipping with helical chippers: Observations based on the construction and use of different prototypes
No full textThe aim of this investigation was to gain empirical knowledge from the practical usage of three different helical chipper prototypes and to determine which construction parameters influence the performance of a helical chipper the stability of its components and the quality of the wood chips. Initially, a qualitative classification of eight tool, three machine, and two feedstock parameters with respect to their impact on these three target variables was undertaken. Further two-work piece parameters were also included in the classification. These parameters were then described more specifically and justified theoretically The results of the investigation showed that the interaction of these 15 individual parameters is very complex and it was found that a purely empirical consideration which has been commonly used for helical chippers does not provide an adequate basis for the optimization of their construction. For this reason, the development of theoretical fundamentals for helical chippers is deemed vital, so that the understanding of the principals of this cutting method can be developed further. This can be done by amalgamating the available knowledge about screw theory with that related to chipping processes which have characteristics similar to helical chipping
Wood chipping with conical helical blades - Theoretical deliberations and practical experiments concerning the adjustment of chip length with a set pitch of the blade
No full textChipping wood with helical chippers has the disadvantage that the geometry of the chipper's rotor determines the length of the chips. A variation in size through the use of different infeed speeds is not possible due to the self-feeding mechanism of their construction. Until now, a variation in chip length could only be achieved by exchanging the chipper's rotor with one having another pitch. Theoretical deliberations show, that a variation in chip length is possible using different infeed angles. In the present investigation, this hypothesis was tested using practical experiments. Standardised preformed test rods were chipped with a small scale helical chipper at seven different infeed angles. The experimentation was done using poplar wood with a moisture content of 10% and 60% (wet basis). The results showed that the length of chips produced by helical chippers with a set pitch could also be changed in practice using this method. As assumed the length of the produced chips are decreasing with increasing infeed angles. Furthermore, it could be observed that the use of poplar wood with a higher moisture content leads to larger chip length in average. In addition, the infeed angle was found to have a significant influence on chip quality. Moreover, the chips formed during these experiments using an infeed parallel to the rotor's axis showed an exceptionally high degree of fraying and a lack of clean division between individual wood chips which had not been seen in the chips produced by other helical chippers so far. (C) 2014 Elsevier Ltd. All rights reserved
Kinematics and geometry of helical chipping with conical helical blades
No full textThe technique of helical chipping has not been well established on the market despite being able to produce large wood chips with a narrow variation in size. One reason for this is that the basic knowledge required for the optimization of such machines (e.g., how the individual tool parameters affect target variables such as power requirement, stability of the components under load, and quality of the wood chips) is still largely unknown. In this study, the tool geometry of helical chippers and their kinematics are explained by extrapolating from known relationships for standard machining technology and the mechanics of threaded connections. With this approach, the tool geometry of a conical helical chipper could be effectively characterized and shown to be influenced by many different parameters, which vary along the length of the blade and are dependent on its radius. In addition, the results show that important characteristics of the tool with respect to the kinematics of this method are determined by a helical chipper's construction (i.e., cone angle, flank lead, and pitch). Other factors also play a role in the chipping process of a helical chipper, such as the feed motion per blade, which depends on the material characteristics of the workpiece and influences the interplay between the workpiece and the blade. This study is a first attempt to develop a better theoretical understanding of helical chipping. Based on the presented findings, the interaction between the tool and workpiece needs to be investigated next
Wood chipping with helical chippers: Observations based on the construction and use of different prototypes
No full textThe aim of this investigation was to gain empirical knowledge from the practical usage of three different helical chipper prototypes and to determine which construction parameters influence the performance of a helical chipper the stability of its components and the quality of the wood chips. Initially, a qualitative classification of eight tool, three machine, and two feedstock parameters with respect to their impact on these three target variables was undertaken. Further two-work piece parameters were also included in the classification. These parameters were then described more specifically and justified theoretically The results of the investigation showed that the interaction of these 15 individual parameters is very complex and it was found that a purely empirical consideration which has been commonly used for helical chippers does not provide an adequate basis for the optimization of their construction. For this reason, the development of theoretical fundamentals for helical chippers is deemed vital, so that the understanding of the principals of this cutting method can be developed further. This can be done by amalgamating the available knowledge about screw theory with that related to chipping processes which have characteristics similar to helical chipping
Kinematics and geometry of helical chipping with conical helical blades
No full textThe technique of helical chipping has not been well established on the market despite being able to produce large wood chips with a narrow variation in size. One reason for this is that the basic knowledge required for the optimization of such machines (e.g., how the individual tool parameters affect target variables such as power requirement, stability of the components under load, and quality of the wood chips) is still largely unknown. In this study, the tool geometry of helical chippers and their kinematics are explained by extrapolating from known relationships for standard machining technology and the mechanics of threaded connections. With this approach, the tool geometry of a conical helical chipper could be effectively characterized and shown to be influenced by many different parameters, which vary along the length of the blade and are dependent on its radius. In addition, the results show that important characteristics of the tool with respect to the kinematics of this method are determined by a helical chipper's construction (i.e., cone angle, flank lead, and pitch). Other factors also play a role in the chipping process of a helical chipper, such as the feed motion per blade, which depends on the material characteristics of the workpiece and influences the interplay between the workpiece and the blade. This study is a first attempt to develop a better theoretical understanding of helical chipping. Based on the presented findings, the interaction between the tool and workpiece needs to be investigated next
Kinematics and Geometry of Helical Chipping with Cylindrical Helical Blades
No full textThe chipping of wood with helical chippers can be done with either a conical or a cylindrical helical blade. These methods vary not only according to the shape of the blade and rotor but, importantly, also with respect to the direction of the material infeed. The infeed is parallel to the axis of the rotor with a conical chipper; in contrast, with a cylindrical chipper; the infeed occurs at a specific infeed angle, which is apparently determined by the chipper's blade angle. Machines are available on the market with either of these chipping concepts. Because of this, the question arises as to how these two concepts can be compared with each other and whether there are any differences between them. In this article, the geometry and kinematics of a cylindrical helical chipper are discussed theoretically and compared with the geometry and kinematics of a conical helical chipper The results show that both concepts function in generally the same manner The main difference is that all the tool parameters under consideration and the angular relationships of the blade of the cylindrical rotor are constant, whereas with a conical rotor they are not. In addition, the slice/push ratio of a cylindrical rotor occurs due to the tool and work piece interaction and not the blade's radial feed motion, as with a conical rotor Furthermore, the comparison of the two concepts confirmed the assumption that the work piece is set vertically to the cutting face and that the wedge angle determines the direction of the rate of feed
Wood chipping with helical chippers ¨C A theory about the process of wood chip formation dependent on the tool geometry
No full textIn experiments with conical helical chippers, it was found that the wood chips produced were always shorter than the chipper's pitch. Until now, no explanation of this phenomenon has been given in the literature. This article considers theoretically the process of wood chip formation in a helical chipper with respect to its geometry and the length, thickness, and width of the resulting chips. Additionally, an approximation formula for the chip length has been derived using geometrical relationships. According to this approximation formula, the chip length is predominantly influenced by the cone angle of the rotor and the wedge angle of the blade. A comparison of the results of this approximation formula with wood chips made from three different types of wood produced with an experimental helical chipper showed that the calculated chip length correlated relatively well with the average length of the chips produced during the experiments. In addition, however, the experimental results revealed that the characteristics of the material also influenced the chip length and especially its thickness. The latter dimension appears to be negatively correlated with the material's shear strength
Wood chipping with helical chippers ¨C A theory about the process of wood chip formation dependent on the tool geometry
No full textIn experiments with conical helical chippers, it was found that the wood chips produced were always shorter than the chipper's pitch. Until now, no explanation of this phenomenon has been given in the literature. This article considers theoretically the process of wood chip formation in a helical chipper with respect to its geometry and the length, thickness, and width of the resulting chips. Additionally, an approximation formula for the chip length has been derived using geometrical relationships. According to this approximation formula, the chip length is predominantly influenced by the cone angle of the rotor and the wedge angle of the blade. A comparison of the results of this approximation formula with wood chips made from three different types of wood produced with an experimental helical chipper showed that the calculated chip length correlated relatively well with the average length of the chips produced during the experiments. In addition, however, the experimental results revealed that the characteristics of the material also influenced the chip length and especially its thickness. The latter dimension appears to be negatively correlated with the material's shear strength
Biogeochemical processes and microbial diversity of the Gullfaks and Tommeliten methane seeps (Northern North Sea).
No full textFluid flow related seafloor structures and gas seeps were detected in the North Sea in the 1970s and 1980s by acoustic sub-bottom profiling and oil rig surveys. A variety of features like pockmarks, gas vents and authigenic carbonate cements were found to be associated with sites of oil and gas exploration, indicating a link between these surface structures and the underlying, deep hydrocarbon reservoirs. In this study we performed acoustic surveys and videographic observation at Gullfaks, Holene Trench, Tommeliten, Witch's Hole and the giant pockmarks of the UK Block 15/25, to investigate the occurrence and distribution of cold seep ecosystems in the Northern North Sea. The most active gas seep sites, i.e. Gullfaks and Tommeliten, were investigated in detail. At both sites, gas bubbles escaped continuously from small holes in the seabed to the water column, reaching the upper mixed surface layer. At Gullfaks a gas emitting, flat area of 0.1 km(2) of sandy seabed covered by filamentous sulfur-oxidizing bacteria was detected. At Tommeliten, we found a patchy distribution of small bacterial mats indicating sites of gas seepage. Below the patches the seafloor consisted of sand from which gas emissions were observed. At both sites, the anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) was the major source of sulfide. Molecular analyses targeting specific lipid biomarkers and 16S rRNA gene sequences identified an active microbial community dominated by sulfur-oxidizing and sulfate-reducing bacteria (SRB) as well as methanotrophic bacteria and archaea. Stable carbon isotope values of specific, microbial fatty acids and alcohols from both sites were highly depleted in the heavy isotope C-13, indicating that the microbial community incorporates methane or its metabolites. The microbial community composition of both shallow seeps shows high similarities to the deep water seeps associated with gas hydrates such as Hydrate Ridge or the Eel River ba
- …
