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Design and comparison of a suitable dust separation technique during the machining process in a CNC machining center
Design and comparison of a suitable separation technique during the machining process in a CNC machining center. The paper deals with the issue of chip extraction from the milling process in a CNC machining center. The paper aimed to compare the particle size distribution of dust generated in the milling process of natural wood (beech, oak, and spruce) and MDF on a 5-axis CNC machining center. The particle size distribution was evaluated using sieve analysis of samples from the total weight of the captured dust. The results showed that the processing of natural wood is mainly characterized by the formation of coarse dust fractions (2 mm - 1 mm sieves), while the processing of MDF was associated with the formation of fine dust fractions with a size below 100 μm. Another of the objectives was to compare the separation values on the fractional separation curves of selected mechanical separators and filters with the size distribution of dust particles and to propose a suitable separation technique that meets the criteria of "best available technique" (BAT) in the processing of natural wood and MDF, as well as to point out the creation of and the production of harmful dust fractions, which arise mainly during the processing of MDF. We intended to assess whether the introduction of the given technology with the given material mix will also require modifications on the side of the extraction device.
Effect of Low-Thermal Treatment on the Particle Size Distribution in Wood Dust after Milling
The thermal treatment of wood can improve the appearance of the wood product’s surface, its dimensional stability, and resistance to fungal attacks. However, the heat treatment changes the technological properties of wood, making it a new engineering material. This work investigates the effect of the low-thermal treatment of birch wood (Betula pendula Roth.), European beech wood (Fagus sylvatica L.), and alder wood (Alnus glutinosa L.) on the fine dust particles creation during woodworking. The samples of thermally treated wood with temperatures commonly used for the change of wood colour (105, 125, and 135 °C) were compared with reference samples made of natural wood. All 12 variants of the tested woods were milled using the 5-axis CNC machining center (20 mm diamond cutter, rotational speed 18,000 rev·min−1, the depth of cut 3 mm, feed rates of 2, 4 and 6 m∙min−1). A sieving analysis method allowed measuring the dust particle size distributions in all dust samples. The experiment’s result analysis points out that wood type, thermal treatment, and feed rate meaningfully affect the size distribution of dust particles. Compared to birch wood and beech wood, the milling of alder wood samples created a much higher content of the finest dust particles, with particle sizes smaller than 0.032 mm. Increased temperatures in thermal treatment increase the share of fine dust particles with sizes smaller than 0.125 mm, compared to wood in its natural state. Milling with a lower feed rate (2 m·min−1) creates finer dust than processing with higher feed rates (4 and 6 m·min−1). Generally, the milling of alder in a natural or thermally treated state is a source of fine dust particles, particularly at low feed speed-rate milling, compared to birch and beech wood. In general, these results indicate that the low temperature thermal treatment parameters attribute new technological properties to all thermally modified types of wood tested.
Fine dust after sanding untreated and thermally modified spruce, oak, and meranti wood
AbstractAirborne wood dust poses health and safety risks in the construction and furniture industry. The study verified whether the thermal modification affects the share of fine wood dust particles (< 10 μm) generated during spruce, oak, and meranti wood sanding. The experimental research involved nine material variants, including three wood species in three states: untreated, thermally modified at 160 °C, and thermally modified at 220 °C). To collect at least 200 g of each dust sample, a belt sander with P80 sandpaper and a belt speed of 10 m/s was used, along with a dust collector. The collected dust was then separated into fractions using a set of sieves with aperture sizes of 2000, 1000, 500, 250, and 125 μm. A laser particle sizer was employed to measure the sizes of dust particles in the under-sieve fraction (dust with particle sizes smaller than 125 μm). The under-sieve fraction was decomposed into three subfractions, with particle sizes: <2.5, 2.5-4.0, and 4.0–10 μm. Surprisingly the results indicate that sanding dust from thermally modified wood generates a lower average mass share of potentially harmful fine particle fractions than dust from untreated wood. Oak dust contained a higher mass share of fine particles compared to the spruce and meranti dust samples. Dust from thermally modified oak and meranti wood had a lower content of harmful particle fractions than dust from untreated wood. The average mass shares of these dust fractions for modified wood at 160 and 220 °C showed no statictically significant differences (p < 0.05). Conversely, spruce dust had a low content of fine fractions because spruce particles exhibit a more irregular elongated shape. The study considered the extreme temperatures of 160 and 220 °C used in the thermal modification of wood. Therefore, the above statements are assumed to be valid for all intermediate thermo-modification temperatures.
The effect of average chip thickness on the potentially respirable dust from CNC finish milling of wood-based materials
Milling wood-based materials on CNC devices causes the creation of chips in small sizes that may escape the chip extraction zone to the surrounding environment and pollute the air. The article studied the effect of the feed rate (vf) and the width of cut (ae), transformed into kinematic average chip thickness, on the amounts of chips in respirable sizes <10.0μm created in the cutting zone from particleboards (PB) and medium-density fibreboards (MDF). The amounts of dust-sized chips are discussed and were determined by the sieving analysis. The sizes of potentially respirable chips were estimated by weighting with the laser diffraction method. The highest amounts of chips from PB were of 0.250-0.500 mm (38-41%w), but in MDF, amounts varied depending on cutting conditions. With (ae) 1 mm were in the size range of 0.125-0.250 mm (35-54%w), for (ae) 2 mm (33-35%w), and (ae) 3 mm (36-40%w) with combinations of (vf) 6-8 m·min-1. With a combination of (vf) 10 and 12 m·min-1 distribution moved to a higher size range. Chips in sizes 10.0-4.0 μm were estimated by <1%, for 4.0-2.5 μm <0.5%, in 2.5-0.1 μm <0.3%, and <0.1 μm by <0.05%. Statistically was proven (p<0.05) only in PB, with adjusted (ae) by 1 mm, increasing the value of (vf) from 6 to 12 m·min-1 and also with (vf) at 6 m·min-1, between values of (ae) 1 and 2 mm (hm of 0.025-0.035 mm), will significantly (p<0.05) lower the percentual amounts of chips in sizes 10.0-4.0 and 4.0-2.5 μm.
The effect of the feed rate and revolutions of the cutting tool on the amounts of created chips in dust and respirable sizes from milling particleboards, and medium-density fibreboards
The CNC finish milling of wood-based materials creates chips in a wide size range, where considerable amounts were found even below <10.0μm. The presented article studied the effect of technological variables on determined amounts of chips in dust sizes and respirable range from medium-density fibreboards (MDF) and particleboards (PTCB). The materials were milled at a constant width of cut (ae) by 1mm, with the feed speed (vf) in the range of 6, 8, 10, and 12m·min-1, and with revolutions of the cutting tool (n) in the range of 16,000; 18,000; and 20,000revs·min-1. In dust size, we cover chips in the size range below <0.125mm, and respirable size below <10.0μm. The dust sizes from collected chip samples were determined by sieve analysis with pre-defined mesh sizes by weighting the retained mass on specific sieves and with the laser analysis we estimated the amounts of chips in sizes <10.0μm. The number of chips in the dust size ranged for MDF by 34.7-40.8w% and in PTCB by 38.1-54.7w%. Amount of chips in respirable size for MDF by 0.01-18% and for PTCB by 0.01-4.5% of the total mass volume. Increasing the (vf) from 6 to 12m/min significantly lowered amounts of Fine and chips in respirable size (p<0.05) in PTCB, no matter on adjusted cutting tool (n). In MDF such effect was observed only with (n) 20000revs/min for respirable sizes.
Long-term operation of pulse-jet filters for wood dust
Long-term operation of pulse-jet filters for wood dust. The study specifies the value of flow resistance and separation efficiency of filter material during long-term use in pulse-jet filters for wood dust. The experiments were carried out for one type of material working in two different filtration installations in one furniture factory. The bags were obtained from the installations after working for 67, 133 and 272 days, respectively. All tests were performed on the pilot-scale test stand under identical filtration conditions. Studies have shown that long-term filter material use increases airflow resistance and improves filtration efficiency. The range of these changes depends on the operating conditions of the pulse-jet filters. The obtained results made it possible to determine the properties of the long-term use of filter materials in various filtration conditions.
The effect of operational parameters on the size of chips in the finishing wood-based materials by milling
The effect of operational parameters on the creation of chip particles in the CNC finishing processingof wood-based materials. The object of this study was a comparison of created chips from the process of milling two wood-based materials: medium-density fiberboard, and particleboard, using a modern CNC 5-axis milling center. The materials in the form of blocks were milled at constant revolutions of the cutting tool (18,000 rev/min), with changeable variables of feed rates (8, 10, and 12 m/min), and width of cut (1, 2, and 3 mm). The size of created chips was measured by gravimetric weighing from sieving analysis of the retained volume of chips on sieves with pre-defined mesh sizes. The main emphasis was aimed at studying particles of chipsobtained in the finishing process of the milling below <0.125mm. However, the others are mentioned and discussed. Gravimetric differences of the retained volume of chip mass show that created MDF chips are mostly in the size range of <0.250 to 0.125 mm, and particleboard in the size range of <0.500 to 0.250 mm. Distribution of average values in dependence on different conditions shows a decreasing effect with increasing feed rate on the amount of very small chip particles in the volume of both materials. Increasing the feed rate can decrease the amount of very particles in the range below <0.125 mm in the volume of chip mass.