WOOD RESEARCH Volume 61, Number 6, 2016
Martin Boldiš, Miroslav Gašparík, Milan Gaff, and Daniel Ruman

Compression set of PU foam mattresses with self-clamping joints and sandwich structure

This paper deals with research on the impact of composition on compression set of the PU foam mattresses. Three type of mattress composition, with sandwich structure and self-clamping joints, were used for research. The fourth type, which contained traditional glued joint, served as a reference. During static compression of mattresses, the properties of the individual layers have been recorded or calculated, such as Young’s modulus, shear modulus and coefficient of shear friction, which were necessary for the SolidWorks simulation of the permanent deformation. The results, as well as simulations of mattress compositions, have proven that the compression set is strictly dependent on the loading time. The highest permanent deformation was recorded for mattress type A and the lowest ones for mattress type B, which had permanent deformation almost identical to that of the composition with glued joints. The last two mattress types had permanent deformation 35 % greater. It is clear from the results that the properties of selfclamping joints in upholstery can equal those of conventional glued joints. Using self-clamping joints is more advantageous in that they exclude the negative effects of glues as well as the gluing process itself.

WOOD RESEARCH Volume 61, Number 5, 2016
Josef Cafourek, Milan Gaff, Miroslav Gašparík, Martin Slávik, and Jan Macků

Properties and use of biomass from reclaimed land in the North Bohemian Basin

Spoil heaps are negative urban landscape features resulting from intense human activities to acquire mineral resources. One very positive method for reclaiming spoil heaps is afforestation. This paper analyzes the quality of Black locust wood acquired from the reclaimed area of Varvažov, North Bohemian Basin, Czech Republic. The following characteristics were used as indicators of the quality of wood obtained from the given area: chip dimensions; ash content; bulk density; bark content; contents of C, H, N, and O; and contents of S, P, Ca, Mg, K, Fe, Zn, and Mn. Black locust biomass is suitable for energy purpose, although it contains an increased proportion of inorganic elements. The other properties, such content of C, H, N, and O, ash content as well as heating value, are in compliance with the standardized values. The Black locust chips can be categorized as Coarse-grained energetic wood chips with minimal dust particle content according to particle-size distribution analysis.

WOOD RESEARCH Volume 61, Number 1, 2016
Milan Gaff, Monika Sarvašová Kvietková, Miroslav Gašparík, and Martin Slávik

Dependence of roughness change and crack formation on parameters of wood surface embossing

This paper deals with roughness change and crack formation after surface embossing of aspen wood. Embossing was carried out with three various shapes of embossing wedges (convex, concave and with 45° angle). The embossing was realized with two temperatures, 20 and 160°C. The surface roughness before and after embossing was evaluated on the basis of the arithmetical mean deviation of the roughness profile, Ra. Surface quality measurements were carried out in perpendicular (transversal) and parallel (longitudinal) direction in relation to wood fibers. Embossment area quality was evaluated by the mean of portion of cracks in embossment. This evaluation was based on digital image of embossed area and subsequently calculation of portion of cracks area in relation to total evaluated area. Elevated temperature has a positive effect on the quality of the surface, because of roughness decrease. However, the increase in temperature causes a growth in the proportion of cracks on the embossed surface.

WOOD RESEARCH Volume 62, Number 5, 2017
Milan Gaff, Miroslav Gašparík, and Monika Sarvašová Kvietková

Evaluation of the wood surface quality depending on the parameters of embossing

This paper deals with changes in roughness and crack formation after surface embossing of aspen wood. Embossing was based on pushing a wedge with 45° angle into three embossing depths, i.e. 2, 4 and 6 mm. The surface roughness before and after embossing was evaluated on the basis of the arithmetical mean deviation of the roughness profile, Ra. Surface quality measurements were carried out in perpendicular (transversal), parallel (parallel) and perpendicular/parallel to the wood grain. (Embossment area quality was evaluated by the mean of portion of cracks in embossment). This evaluation was based on a digital image of the embossed area and a subsequent calculation of the portion of the cracked area in relation to the total evaluated area. Increasing the embossing depth has a positive impact on the quality of the embossed surface, i.e. the highest quality was generally achieved with an embossing depth of 6 mm. The worst surface quality was achieved with the perpendicular orientation of the wedge regardless of the direction of the roughness measurement.

WOOD RESEARCH Volume 62, Number 4, 2017
Miroslav Gašparík, Milan Gaff, and Babiak Marian

Tension stress simulations of layered wood using a finite element method

This article investigates the material thickness of the individual layer composition influence on the stresses under tension loading. The SolidWorks application was used for tension stress simulations. This simulated course of tensions was carried out for soft and hard materials as a function of their thicknesses. Hard material was represented by beech wood and soft material by aspen wood. Subsequently, the tensile stress and deformation of various two- and three-layered compositions of these materials were analyzed. Based on our results, the soft material was the weakest link; therefore, the ultimate tensile strength of the entire layered material is directly dependent on it. Hard material can withstand greater tensile stress and deformation without breaking, as soft material does.

WOOD RESEARCH Volume 62, Number 4, 2017
Anton Osvald and Milan Gaff

Effect of thermal modification on flameless combustion of spruce wood

The paper deals with the effect of heat treatment of spruce wood (Picea abies (L) Karst.) at the temperatures of 160°C, 180°C and 210°C – on the change of properties that characterize its relation to fire and burning,in particular in the phase called flameless combustion. A test method, which is sufficiently sensitive to monitor these changes, has been used for the evaluation of these changes. The results show that thermally modified spruce wood has positive assessment even in this regard.

WOOD RESEARCH Volume 64, Number 1, 2019
Patrícia Kadlicová, Linda Makovická Osvaldová, Juraj Jancík, and Milan Gaff

Effect of thermal and retarding treatment on flammability rate of tropical tree species

Wood is integral to the construction industry despite the fact that it is a highly flammable material. Due to thermal stress, it is subject to the process of pyrolysis. However, not every type of wood burns the same. This dissimilarity is caused by the changes in its internal structure. Flammability rate of tree species can be modified by means of thermal modification, i.e. change in its internal structure or by using coating compositions which form a fire-protecting layer on its surface. The paper comprises a testing and an evaluation of iroko wood which is predominantly used as floor covering and cladding material for building structures. The authors focus on determining the connection between the structure of this exotic tree type and the eventual thermal degradation (burning course, significant changes, amount of material burnt, etc.) of the samples. Small size samples were used during laboratory measurements. Their width and thickness were approximately the same as for commonly used cladding boards. The data obtained in the laboratory have been processed, transformed into evaluation criteria and connected with theoretical knowledge, creating an overview of its eventual flammability. Laboratory test results prove low flammability rate of test samples. Mass loss was an important criterion. Thermal treatment, which changes the internal structure and thus improves its properties (T group; test samples), had no significant effect on the eventual flammability. On the other hand, the flammability rate of samples was better when using a fire retardant (R and TR group; test samples), because the retardant lowers the flammability by more than half.