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.
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Abbreviations
- a, b:
-
Inside and outside saw disc radii
- A, B:
-
Arbitrary constants
- c:
-
Saw disc tensioning radius
- ci, c0 :
-
Inside and outside rolling/indentation radii
- cn :
-
Neutral radius
- d:
-
Track width
- E:
-
Modulus of elasticity or strain energy
- Eext :
-
External power of the loading
- Ep :
-
Power dissipation due to plastic deformation
- Ed :
-
Power dissipation due to velocity discontinuity
- Ee :
-
Power stored in elastic zones
- fn :
-
Resonant frequency of a saw disc n — nodal diameters
- f TMn :
-
Measured resonant frequency
- f TCn :
-
Resonant frequency calculated from the variation in the saw disc stiffness
- F:
-
Rolling load
- H:
-
Half saw disc thickness
- Kn :
-
Modal stiffness, n=number of nodal diameters
- K *n :
-
Conventional or bending stiffness
- K **n :
-
Geometric or tensioning stress stiffness
- K Tn :
-
Modal stiffness of a tensioned saw disc
- Mn :
-
Modal mass, n=number of nodal diameters
- M, N:
-
Integration constants
- Pave :
-
Average indentation pressure
- p, p′, p′':
-
Radial pressures at elastic-plastic boundaries; loading, unloading and residual
- pi, pO :
-
Radial pressures inside and outside the elastic-plastic boundaries
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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
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Szymani, R., Mote, C.D. Theoretical and experimental analysis of circular saw tensioning. Wood Sci. Technol. 13, 211–237 (1979). https://doi.org/10.1007/BF00350225
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DOI: https://doi.org/10.1007/BF00350225