The aim of this research was to investigate the effects of various temperatures of thermal treatment of red meranti (Shorea accuminata) wood on mass concentration and size distribution of wood dust produced by a hand-held belt sander. The experiment was conducted during the sanding of the meranti wood in the natural state and using specimens that were heat-treated via the ThermoWood® technology at the temperatures of 160 °C, 180 °C, 200 °C, and 220 °C. An analysis of variance was used to measure the significance of the effects. Average values of the inhalable and respirable fractions of wood dust mass concentration determined via the optical and gravimetric method was highest at the treatment temperature of 160 °C. The results showed that mass concentration was not significantly influenced by thermal treatment.
Thermal Treatment’s Effect on Dust Emission During Sanding of Meranti Wood
Lucia Mikušová,a,* Alena Očkajová,b Miroslav Dado,a Marián Kučera,c and Zuzana Danihelová d
The aim of this research was to investigate the effects of various temperatures of thermal treatment of red meranti (Shorea accuminata) wood on mass concentration and size distribution of wood dust produced by a hand-held belt sander. The experiment was conducted during the sanding of the meranti wood in the natural state and using specimens that were heat-treated viathe ThermoWood® technology at the temperatures of 160 °C, 180 °C, 200 °C, and 220 °C. An analysis of variance was used to measure the significance of the effects. Average values of the inhalable and respirable fractions of wood dust mass concentration determined via the optical and gravimetric method was highest at the treatment temperature of 160 °C. The results showed that mass concentration was not significantly influenced by thermal treatment.
Keywords: Thermowood; Meranti; Sanding; Wood dust; Mass concentration
Contact information: a: Department of Manufacturing Technologies and Quality Management, Faculty of Environmental and Manufacturing Technology, Technical University in Zvolen, Studentska 26, 96053 Zvolen, Slovakia; b: Department of Technology, Faculty of Natural Sciences, Matej Bel University, Tajovského 40, 97401 Banská Bystrica, Slovakia; c: Department of Mechanics, Mechanical Engineering and Design, Faculty of Environmental and Manufacturing Technology, Technical University in Zvolen, Studentska 26, 96053 Zvolen, Slovakia; d:Institute of Foreign Languages, Technical University in Zvolen, T.G. Masaryka 24, Zvolen, 96053, Slovakia; *Corresponding author: firstname.lastname@example.org
Various types of sanders (belt sander, disc sander, and special sander) used for refining the surface of individual parts before the surface finish treatment are some of the most important devices in both furniture manufacturing and joinery. However, their operation is associated with dust production, which is seen as a negative effect. Although every sander is equipped with suction, most hand-held band sanders do not have the whole part of the sanding belt covered. Thus, fine dust (dust particles ˂ 100 µm) is released into the working environment and poses a risk to safety as well as to human health.
High concentration and long-term exposure to any type of dust in the air causes deposition of dust particles in the eyes, nose, and mouth, and on the skin; it stresses the lungs’ self-cleaning system and decreases overall human immunity, which can eventually lead to chronic bronchitis (Schwarz et al. 2009). The highest risk to the human respiration system is posed by the respirable fraction with particle sizes lower than 10 μm. Following several research studies (Marková et al. 2016; Mračková et al. 2016; Očkajová et al. 2016) of several dust types, including wood dust, it is important to consider also other fractions, mainly the fine dust that is hardly deposited in the working environment with a particle size ˂ 100 µm. These fractions are harmful for humans, and the wood dust of some hardwoods (beech, oak) and their inhaled particles cause mostly paranasal sinus cancer (WHO 1999). From the viewpoint of evaluating the potential health risks according to the Slovak legislation (Regulation of the Government of the SR No. 471/2011 Coll.), meranti wood dust is classified as a solid aerosol of a mostly irritating character. The permissible exposure limit (PEL) for solid aerosols (dust) is determined as the time-weighted average of exposure of the overall (inhalable) concentration of the solid aerosol (TWE), and its value for exotic wood species is 1 mg.m3. The PEL for solid aerosols does not consider the possible allergic effects or presence of microorganisms in the dust.
Thermally treated wood is currently being researched in many studies. The primary aim of thermally treated wood is to prepare a material that brings the following benefits: a lower hygroscopicity, higher dimensional stability, higher resistance to wood-decaying and discolouring fungi, moulds, and ligniperdous insects, maintaining or improving the aesthetics (colour, minimal cracks, gloss, texture, etc.), and preservation or improvement of the mechanical properties (strength hardness, stiffness, etc.) (Požgaj et al. 1997; Bengtsoon et al. 2003; Niemz et al. 2010; Barcík and Gašparík 2014). Thermally treated wood is designed for various applications both in exterior and in extremely humid indoor environments because it has a reduced moisture absorption capacity, with decreases in the range 30 to 50% (e.g. terrace and pool tiles, garden furniture production, sauna furniture production etc.). The thermal process results in an equilibrium moisture content of 5 to 7%, although it is found in a significantly higher humidity environment. Another benefit of this material is the fact that it is treated using heat, steam, and water without the use of any chemicals. Thermally treated wood has been studied regarding various aspects: physical and mechanical properties (Gunduz et al. 2009; Dzurenda and Orlowski 2011), chemical properties (Kačíková and Kačík 2011; Čabalová et al. 2016; Miklečić and Jirouš-Rajković 2016), quality of the modified surface (Budacki et al. 2013; Kvietková et al. 2015; Pinkowski et al. 2016; Vančo et al. 2017; Korčok et al. 2018), wood color and machinability (Sandak et al. 2017; Hrčková et al. 2018), the energy consumption in the milling process (Kubš et al. 2016), stability against weather conditions (Panayot 2008; Yildiz et al. 2011), the granulometry of the created chips (Barcík and Gašparík 2014; Očkajová et al. 2014), and the granulometry of the sawdust (Dzurenda et al. 2010).
In general, thermally treated wood has increased fragility and brittleness, which results in the production of smaller dust particles than unmodified wood (Očkajová et al. 2016). There is minimal quantitative data describing the mass concentration and particle size of airborne wood dust produced when sanding thermally treated wood. The majority of previous studies (Rogoziński et al. 2015; Kučerka and Očkajová 2018; Očkajová et al. 2018) analyzed dust that was captured by exhaust piping/dust extraction systems attached to the sander. However, there are no known studies analyzing airborne thermally treated wood dust during sanding that was not captured by exhaust systems, as described in this paper.
The aim of this study is to investigate the effects of various temperatures of red meranti wood heat treatment on the mass concentration and size distribution of wood dust produced by a hand-held belt sander.
All experimental wood pieces were in the form of planks with dimensions of 20 × 100 × 700 mm. Specimens were obtained from a commercial supplier (Wood Store, Prague, Czech Republic). The specimens were subsequently dried to the residual moisture content of 8%. The entire process was completed in the Development Workshops and Laboratories of the Technical University in Zvolen (Slovakia).
The test specimens were heat-treated in the Arboretum of the Faculty of Forestry and Wood Sciences (Czech University of Life Sciences, Prague, Czech Republic) in Kostelec nad Černými lesy. The S400/03 chamber (LAC Ltd., Rajhrad, Czech Republic), designed for thermal wood treatment using the technology ThermoWood®, was used for the heat treatment of the specimens. Four specimens were prepared for each variant of the heat treatment (160 °C, 180 °C, 200 °C, and 220 °C). The process of the heat treatment is described in detail in the study by Očkajová et al. (2018).
The experimental measurements were taken in a room according to requirements of the standard STN EN 50632-1 (2016). The temperature and humidity in the room during the experiment reached a relatively constant level of values in the range of 20 to 21 °C and 36 to 37%, respectively. The average speed of air circulation in the place of dust sampling was determined using a Thermo-Anemometer Testo 480 (Testo Ltd., Alton, United Kingdom) and ranged from 0.21 m.s-1 to 0.28 m.s-1.
The meranti wood moisture was evaluated by the gravimetric method and reached 8% at sanding time. Sanding was performed using a commercial hand-held belt sander PBS 75A (Robert Bosch Power Tools GmbH, Stuttgart, Germany) without a microfilter system. The belt sander was adjusted to the maximum speed (350 m.min-1). The abrasive belt LS309XH (Klingspor Schleifsysteme GmbH & Co. KG, Haiger, Germany) with dimensions 75 mm × 533 mm was used for sanding, and it was replaced after each test cycle. The grain size of the sanding papers was p80. The mobile workbench PWB 600 (Robert Bosch Power Tools GmbH, Stuttgart, Germany) was used for clamping the samples. The experimental set-up is illustrated in Fig. 1.