Theoretical and experimental analysis of circular saw tensioning

Summary Tensioning is the saw prestressing procedure most commonly used in the forest products industry to increase the stability of thin circular saws. This procedure stiffens the saw blade by introducing favorable in-plane residual stresses either by local plastic deformation or by local heating. In industry today, rolling is the standard procedure for introducing such stresses.The first part of this paper is concerned with a method of tension evaluation. The method examined consists of measuring saw blade modal stiffness, and it correlates the elastic stiffness of the saw, which approximates the vibration modes, and the natural frequencies associated with these modes. The predictions of the saw frequency shift due to stiffness variations were found to agree closely with experimentally determined frequencies. The method thus offers a practical procedure for tension evaluation and could replace the currently used technique of measuring the light gap under a straightedge placed along the saw diameter.The second part of this paper theoretically analyzes the relationship between the rolling load and the resulting tensioning stresses. The procedure followed in the theoretical model determines the identation load by equating the external power of loading with the power of storing in the elastic zones and of internal dissipation in the plastic zone.The residual stresses obtained by superpositioning the stresses due to unloading were generally in good agreement with the experimentally determined tensioning stresses outside the rolled region. The theory developed can be very useful in predicting tensioning stresses for a given rolling load and roller geometry.List of Symbols a, b Inside and outside saw disc radii - A, B Arbitrary constants - c Saw disc tensioning radius - c_i, c₀ Inside and outside rolling/indentation radii - c_n Neutral radius - d Track width - E Modulus of elasticity or strain energy - E_ext External power of the loading - E_p Power dissipation due to plastic deformation - E_d Power dissipation due to velocity discontinuity - E_e Power stored in elastic zones - f_n Resonant frequency of a saw disc n — nodal diameters - f _n ^TM Measured resonant frequency - f _n ^TC Resonant frequency calculated from the variation in the saw disc stiffness - F Rolling load - H Half saw disc thickness - K_n Modal stiffness, n=number of nodal diameters - K _n ^* Conventional or bending stiffness - K _n ^** Geometric or tensioning stress stiffness - K _n ^T Modal stiffness of a tensioned saw disc - M_n Modal mass, n=number of nodal diameters - M, N Integration constants - P_ave Average indentation pressure - p, p, p' Radial pressures at elastic-plastic boundaries; loading, unloading and residual - p_i, p_O Radial pressures inside and outside the elastic-plastic boundaries The Authors would like to express their gratiude to C. H. Zierdt and J. Rhemrev for assistance in the experimental investigations. The authors are also grateful to Hanchett Co. and California Saw Knife and Grinding, Inc. for supplying stretcher rolls and experimental saw discs, respectively. They are also grateful for the financial support of the project from the U.C. Forest Products Laboratory, California Cedar Products Co., California Saw Knife and Grinding, Inc., Hudson Lumber Co., MacMillan Bloedel Research Ltd., Potlatch Corp., Simpson Timber Co., Sun Studs, Inc. and Weyerhaeuser Co. Finally, the authors thank the National Science Foundation for its generous support of the research     

Origin of idling noise in circular saws and its suppression

Summary This paper concerns the mechanism of noise generation and methods of noise reduction for idling circular saws. Experiments were conducted to examine the sources of saw noise. Saw resonant vibration is proven to be excited aerodynamically rather than by mechanical imbalance. The source of noise generated from a resonating saw and that generated from a nonresonating saw are shown to be identical. A mathematical model is proposed to formulate the dependence of the noise source upon saw kinematic and geometric parameters. Based upon this model and the associated experiments, several potential techniques for noise reduction through design of saw tooth geometry are recommended and discussed.     

数控双圆锯裁边机的研制

我国制材生产中,多采用先将原木锯解成毛边材,然后再用截边锯对毛边材进行加工的工艺。目前国内毛边材的加工设备,普遍存在结构简陋、制造精度低等不足。为提高木材出材率和板材加工精度,在分析国内外同类设备的基础上,研制出实用的数控双圆锯裁边机。     

Wear of tungsten carbide tipped circular saws in cutting particleboard: Effect of carbide grain size on wear characteristics

Summary In order to study the wear of tungsten carbide tipped circular saws, three kinds of carbide tips (fine, medium and coarse grained ones) were employed, when sawing particleboards. The saw with coarse grained carbide tips showed the longest working life, while the fine-grained carbide tipped saw retained its usefulness for only a short period of sawing. In an experiment using a saw with all three kinds of carbide tips, it was also confirmed that the fine grained tips wore most and the coarse least. From the observations of the worn tips, it was found that the wear boundary on the clearance face was quite distinct for these tips, although for the fine grained one it was remarkably indented. There were many striations on the wear surface of the fine grained tip, but they scarcely appeared on those of the other two tips. The wear mechanism and the wearing process of the carbide tips are discussed.This paper was presented at the 22nd Annual Meeting of the Japan Wood Research Society at Tokyo, April, 1972The authors wish to express their appreciation to Dr. T. Kawakita, Sumitomo Electric Industries, Ltd., for supplying the carbide tips and to Mr. M. Hiraiwa, Nittokukan Saw Mfg. Co., Ltd., for manufacturing the saws. They are also greatly indebted to Dr. H. Saiki, Wood Structure Laboratory, Kyoto University, for taking scanning electron micrographs and for his valuable advice. This investigation was supported in part by Grants in Aid for Scientific Research in 1972 and 1973 from the Ministry of Education, Japan     

Vibration control of band saws: Theory and experiment

Summary Active vibration control is a key to the improvement of the cutting performance and productivity of band saws. In this paper a new method is presented for active control of band saw vibration. The transfer function of a closed-loop system consisting of the band saw, a feedback control law and the dynamics of the sensing and force actuation devices is derived. Analysis of the root loci of the closed-loop system gives two stability criteria. Stabilizing controller design is carried out for both collocation and dislocation of the sensors and actuators. It is found that vibration in all the modes can be damped through use of only one sensor and one actuator and that the control algorithms presented are realizable in practice. The theory presented is experimentally verified.This work is supported by the National Science Foundation, the University of California Forest Products Laboratory, and the authors' group of industrial sponsors     

圆锯片适张状态检测方法的研究(英文)

文章论述了一种圆锯片适张状态的检测方法及实现的系统 .该方法采用锯片适张前后固有频率的变化幅度 ,锯片单点加载情况下一定半径圆周上的横向变形量和端面圆跳动三个特征参量 ,表述一个锯片的适张程度、适张均匀性和平整性 .应用计算机控制的检测系统 ,经过对大量不同规格木工锯片和大型金刚石锯片的检测 ,结果表明该方法是切实可行的     

Aerodynamic sound and self-excited vibration of circular saw with step thickness I: Comparison of dynamic characteristics between the common circular saw and the circular saw with step thickness

The natural frequencies, aerodynamic noise, whistling noise, and self-excited vibration between the common circular saw with uniform thickness and the circular saw with step thickness (thin on its outer part and thick on its inner part) were researched during idling. The natural frequencies of the circular saw with step thickness increased with an increase in the thickness and in the radius of the thick part. The frequencies of the circular saws with step thickness (thick at the inner part) were higher than that of the thin circular saw with a uniform thickness of 0.5mm. The aerodynamic sound pressure level induced from circular saw teeth increased with an increase in the tooth thickness. The whistling noise and self-excited vibration easily occurred in the thick circular saws (1.5, 2.0, and 2.5mm). The whistling sound pressure level and the vibration amplitude increased with an increase in the thickness of the saw. None of the designed circular saws with step thickness generated whistling noises or self-excited vibration during idling.Part of this report was presented at the 45th annual meeting of the Japan Wood Research Society at Tokyo, April 1995 and the 12th International Wood Machining Seminar at Kyoto, October 1995     

Analysis of roll tensioning and its influence on circular saw stability

Summary In a typical sawmill, about 12% of the wood which is cut is reduced to sawdust. Further material is lost during subsequent planing. A substantial part of this large loss of a costly natural resource can be saved by the use of thin, stable sawblades, but only if proper saw tensioning conditions are developed. The thickness of a stable sawblade can be minimized through optimal tensioning, an increasingly urgent objective because of sharply rising raw material costs. A theoretical model is presented which accurately describes the development of residual stresses in a roll tensioned circular sawblade and the resulting changes in saw critical speed. This model is essential for the reliable prediction of optimal tensioning conditions for any given saw operating state, and for the development of automated control of the tensioning process. An example is presented of an optimally tensioned circular sawblade for which a 40% thickness reduction is achieved compared with an equivalent untensioned sawblade with the same critical speed.Paper awarded First Place Wood Award Price, Forest Products Research Society, June 1981     

The critical rotational speed of circular saw: simple measurement method and its practical implementations

Operation safety during sawing operations as well as dimensional accuracy and surface roughness depend on circular saw dynamic features among other factors such as circular saw blade accuracy and static/dynamic properties of the machine tool. Manufacturers of saw blades have an obligation to mark tools with a value stating the maximum allowed rotational speed for each saw. However, in some cases the value indicated on the saw corresponds to the critical rotational speed or is dangerously close to this critical value. Saw operation at the critical rotational speed is inadvisable and may result in serious injury or depreciation of product quality. This report outlines a simple methodology for evaluation of circular saw critical rotational speed. The assessment was conducted with a camera vision technique on the basis of an impulse test. Results are compared with theoretically calculated critical rotational speeds and the marks on saw blades.     

Friction coefficient as a guide to optimum rake angle in wood machining

Summary In spite of the obviously important role of friction in the wood cutting process, there has been little application in wood machining practice of true friction coefficients obtained from rubbing tests. Friction coefficients were measured during slow rubbing of incense-cedar blocks at two moisture contents on surfaces of saw steel, high speed steel and tungsten carbide. The coefficients were used in an orthogonal model of cutting to estimate the optimum rake angle for the planing of incense-cedar, and some evaluation of the estimate was made using data from cutting experiments reported elsewhere.The author wishes to thank Charles Berolzheimer, Director, The California Cedar Products Company Research Department, for his support of this work, and Richard Lemaster, University of California Forest Products Laboratory, for provision of facilities and assistance in that laboratory     

无料圆锯片的初步研究

分析了无料圆锯片的发热因素，说明了无料圆锯片的应用可能性，并提出了具体的技术条件。     

Development of kiln drying schedule severity indices for degrade control

Summary Severity of kiln schedules used to dry wood has traditionally been determined after the fact. As an alternative, analytical indices using integral calculus have been developed to rate kiln schedule severity. Theoretical justification is presented for the general form of an index as well as for several specific cases. Possible uses of this type of index are also indicated. The indices take into account the dry and wet bulb temperatures used throughout a schedule as well as the duration of application and points of application of each combination of temperature and humidity used.The assistance of the California Cedar Products Company, Stockton, California, and, in particular, Charles Berolzheimer and John Rhemrev, is gratefully acknowledgedThe authors are, respectively, Research Associate and Project Leader, Forest Products Laboratory, University of California, Richmond     

Development of kiln drying schedule severity indices for degrade control

Summary A previous article presented the theoretical development of analytical indices to rate the severity of kiln schedules used to dry wood. These indices take into account the dry and wet bulb temperatures used during a kiln schedule together with the points of application and duration of application of each combination of temperature and humidity used. Experimental data for several such indices are presented for collapse development during the kiln drying of incense cedar pencil slats. While promising, the results were inconclusive as to the use of a severity integral for prediction of the effect of different schedules or schedule changes on drying degrade. A lack of homogeneity in the test material confounded the results.The assistance of the California Cedar Products Company, Stockton, California and, in particular, Charles Berolzheimer and John Rhemrev, is gratefully acknowledgedThe authors are, respectively, Research Associate and Project Leader, Forest Products Laboratory, University of California, Richmond     

Research on the effect of yield strength of circular saw blade on roll tensioning process

In this paper, a 2-D and 3-D finite element model of roll tensioning process of circular saw blade were established by Static/General module of ABAQUS software based on finite element method. The rolling force and tensioning stress distribution of circular saw blade were calculated by these two models which were proved to be true and reliable. The effects of yield strength of circular saw blade on tensioning stress distribution and rolling force were studied. The research achievements showed that a circular saw blade made with high yield strength obtained a higher tangential compressive stress and radial compressive stress in the rolled region during roll tensioning process, which has both advantages and disadvantages for the stability of the saw blade. Besides, a circular saw blade made with high yield strength also put forward higher requirements for roll tensioning equipment because of the large rolling force during roll tensioning process.     

径向槽对硬质合金圆锯片"啸声"影响的研究

"啸声"是木工硬质合金圆锯片空转的主要噪声源,是一种自激振动噪声.本文主要研究径向槽对硬质合金圆锯片噪声的影响.研究结果表明,采用金属铜填塞径向槽底部圆孔技术,可以消除硬质合金圆锯片在整个测试转速范围的"啸声".而其他两种普通径向槽的圆锯片只能在较高转速下消除"啸声".此外,径向槽底部塞有金属铜圆锯片的空气动力性噪声比未塞有金属铜的圆锯片略低2～3 dB(A).     

Some possibilities for reducing circular saw idling noise

The sound pressure level of differently designed circular saw blades were investigated during idling. Nine blade samples were used: three differently designed blade bodies (without slots, with four radial slots, and with four slots with copper cork), each with three diameters (260,280, and 300 mm). The sound pressure level was measured at different rotational frequencies ranging from 25 to 65 rps in increments of 1 rps. Rubber damping rings 80mm in diameter and 0.3 mm thick were placed between the saw blade and the collars, and the emitted noise was measured. Because of the whistling sound the blades without slots emitted high sound pressure levels. There were no significant changes when rubber damping rings were used. The use of rubber damping rings on the samples with radial slots eliminates the whistling noise. The saws with copper corks did not emit a whistling noise at all, and their aerodynamic noise was 2–3 dB (A) lower than the aerodynamic noise of the saws with radial slots. The relation between sound pressure emitted by the damped idling saw and peripheral velocity can be described by the power function with the exponent value between 4.8 and 5.2.Part of this report was presented at the 14th International Wood Machining Seminar, Epinal, France, September 1999     

铜对圆锯片热应力的影响与研究

通过锯切木材试验,分别对锯身槽上嵌铜和不嵌铜设计的同条件下木工圆锯片,进行定点温度、横向摆动量和噪声参数的测量;并结合有限元热应力场分布与计算,以及铜材理化试验分析等手段,得出其嵌铜锯片消除热应力性能好,振声性能较高,锯片使用寿命延长等结论,并提出减振降噪的措施与建议,为优化圆锯片的设计工作提供参考依据。     

Development of a monitoring system for guided circular saws: an experimental investigation

ABSTRACT

Lack of a monitoring system for guided circular saws marks one of the most critical machines in sawmills as a production bottleneck. Monitoring systems are being researched and developed for machine tools, especially for the metal cutting industry; but there are limited studies on the development of monitoring systems for circular saws in wood manufacturing process. In this study, sensors with the possibility to indicate sawing deviation were chosen that could be mounted in or on the saw guides. The sensors were: a microphone, an accelerometer, temperature sensor, an acoustic emission (AE) sensor, and a newly developed displacement sensor. A load cell was used to measure the lateral force on the guides. The outputs from these sensors were compared to the standard deviation of the board surface measured at the top of the cut. The signals from the displacement sensor, microphone, accelerometer, guide force sensor, and AE senor had no correlation to changes in the sawing deviation as measured by the standard deviation at the top of the board. Under laboratory conditions, the sound level and the AE signal did indicate the beginning and end of the cut. It was found that blade temperature is a good indicator of saw cutting performance. A newly developed temperature sensor can provide accurate temperature of the saw during cutting. The sensor can be used for measuring the rate of heating to cooling over time which can be used as a monitoring system to detect if there is any issue in the system.     

圆锯片淬火残余应力的实验研究

就65Mn钢圆锯片基片淬火过程中残余应力的分布特点进行了实验研究,结果表明:经淬火后基片径/切向残余应力主要呈拉应力状态,其中水淬造成较大的残余拉应力,切向拉应力过大是造成基片开裂、变形的主要原因.油淬的残余拉应力较小,生产中若采用油或类似的冷速进行淬火,就能较好的控制淬火质量,为回火和平整等后续工艺奠定基础.     

Microstructure of wood char

Summary Past research on the combustion and pyrolysis of wood have often indicated a link between wood microstructure and its observed properties in fire exposure. The present research, after utilizing an instrumented fire exposure shown to simulate actual fire conditions, examines the microstructure of fire damaged wood and considers the implications of microstructural changes seen on the burning process.Differences in microstructural detail between wood and char, as well as fissure geometry, were shown to be consistent. The demarcation between damaged and undamaged wood was shown to be extremely small (several cell layers in thickness). The resulting microstructural observations are considered in light of published kinetic data on wood combustion and current theories and data on thermal degradation of wood.The authors wish to acknowledge the general support of the University of California Forest Products Laboratory as well as grant support to the University of California Berkeley Fire Research Group (NSF-Rann-S-22053, NFPCA-S-22584), University of California Berkeley Electron Microscopy Lab. (NSF-GB-38359) and the University of California, Davis Department of Botany (NSF-GB-29653). In addition we would also like to thank Dr. Arno P. Schniewind, University of California Forest Products Laboratory and Dr. R. Falk, University of California, Davis, Department of Botany