Thick peeled products (TPPs) — An overview on their production and characterisation

Coniferous roundwood of common qualities is usually industrially processed in chipping-sawing lines which are widely limited to log diameters of < 45 cm. The rising stock of large-diameter softwood in the DACH-region, especially of Norway spruce, necessitates a rethinking of the processing of sawn wood and the subsequent products produced. One possible option for processing such large-diameter roundwood is through rotary-peeling in combination with an extended peeling thickness range to produce a new class of raw materials called ”thick peeled products (TPPs)” (thickness > 6 mm). This paper demonstrates that peeling of softwood up to a thickness of 20 mm is possible but this results in deeper lathe checks (up to 85 % of the TPP thickness). Due to the wide variation in the quality of the peeling logs, a first physical / mechanical characterisation of the base material leaded to a mean static MOE of E t,0,cor,mean = 9 . 3 G P a and a mean tensile strength of f t,0,cor,mean = 19 . 6 M P a . In this study, the peeling process achieved a maximum yield of 92.5 % and revealed no disadvantages in terms of mechanical behaviour for shorter soaking duration, i.e. less process energy. Additional recommendations regarding optimal peeling process parameters are given in this paper. • First known rotary peeling experiments of thick peeled products (TPPs) up to a thickness of 20 mm in an industrial environment. • First physical / mechanical characterisation of these TPPs in terms of density, MOE and tensile strength. • Extensive statistical analyses of the effects of process parameters pre-treatment, peeling thickness, compression ratio and relative roller bar velocity on the aforementioned properties. • Evaluation of the effect of the radial location in the peeling log on the physical / mechanical properties. • Characterisation of the lathe check behaviour and the grain direction deviation around knots. • Evaluation of the yield of thick peeled products and comparison with sawn products.