On wear of wood-cutting tools : Tool materials, wear mechanisms and modelling

University dissertation from Karlstad : Karlstad University Studies

Abstract: Bandsaw blades are commonly used in the sawmill industry for timber cutting. The saw teeth are gradually worn during cutting and will finally cause unacceptable surface roughness and dimensional deviations on the sawn wood product. Maintenance by re-sharpening of the saw teeth is therefore necessary after a certain time of sawing. The blade replacement is time-consuming and causes decreased operational times, hence improved saw tooth wear resistance directly increases the profitability by better productivity.

An experimental method has successfully been developed, in which wear on timber cutting saw teeth can be simulated. A test time of 30 minutes in the laboratory is comparative to 8 hours cutting in a sawmill.

A fundamental understanding of the saw tooth damage mechanisms occurring during cutting of timber has been established. During the initially high wear rate stage microfractures and chipping damages dominate, while in the succeeding low wear rate stage abrasive and tribochemical wear dominate. For swaged saw teeth of saw steel, high cutting speeds decrease the wear rate causing more abrasive wear. Tribochemical mechanisms are controlling at low cutting speeds causing higher wear rate. A study focused on the abrasive scratch on the tooth caused by the wood material, and displaying the cut wood surface structure, further promotes the fundamental understanding of the abrasive wear mechanism on the saw tooth.

The balance between hardness and ductility of martensitic saw steels controls their wear resistance in different wear regimes during the use of swaged saw teeth. An optimal mixture of carbide size, carbide amount and binder composition is important for wear resistance of Co-based tooth tippings used in timber cutting applications. Similarly, high speed steels and hard metals have been evaluated regarding tipping material for wood cutting.

Finally, a model has been derived to describe wear in wood cutting processes using swaged saw steel teeth. It is based on the experimental wear test results and includes wear damage by fatigue microfracture, and abrasive and tribochemical wear.

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