Съдържание


Vol. IX, Issue 1 2020

A METHODOLOGICAL APPROACH FOR NUMERICAL ANALYSIS OF UPHOLSTERED SOFA WITH FINITE ELEMENT METHOD (FEM)

Автори: Tolga Kuşkun, Ali Kasal, Ersan Güray, Recep Birgül, Yusuf Ziya Erdil

Резюме

Engineering design of furniture is an important issue for modern industry and it can be accomplished by means of creating a model structure and analyzing by a convenient software. A fair strength analysis of furniture structure is a computationally complex process since various types of member types, e.g. springs, upholster plates and complicated mechanisms type connections, are included in modelling. Finite element method (FEM) is the most convenient approach to analyze furniture systems because of the member variety and the furniture’s, in general, complex geometry. In this study, an improvable methodological approach was recommended for numerical analyses. Upholstered sofas are tested under backrest frame loads according to the principles of FNAE 80-214 General Services Administration Upholstered Furniture Test Method (GSA), then numerical analysis is carried out to simulate the performance tests on virtual platform. 3D modelling of sofa is made with SpaceClaim 3D solid models software and analyses are performed with a Finite Element Software, Ansys Workbench. Entire system of the sofa, including all members, joints, connections and springs are defined with convenient parameters related to mechanical properties of the material and the resulting deformations of the experiments. In this study, the sofa model is developed in a methodological manner, in three different ways. The model is improved with small details and it is observed that small changes in the model resulted in essential outcomes such that consistent results are decided to be achieved by means of tuning some parameters, e.g. spring constants, upholster thickness and elasticity. According to the results, reasonable estimates are obtained from the numerical analyses by using this methodological approach.

Ключови думи: numerical analysis, upholstered furniture, furniture performance test

EN Version

INFLUENCE OF THE APPLIED PRESSURE ON FINGER JOINED END-TO-END WOOD

Автори: Todor Petkov, Vladimir Mihailov

Резюме

In the production of finger-jointed details, it is most important to provide the required applied pressure to achieve the desired adhesion strength of the joint. The results of the study of beech wood elements (Fagus Sylvatica) are presented, with applied different pressure for the face ends of the details (0,4 and 0,7 N/mm2). The following properties have been determined of the tested samples: bending strength, modulus of elasticity and the density of wood. The pneumatic-piston system also provided for securing the bonding pressure in the longitudinal direction of the wood. In the carried – out experiments, it was used a polyvinyl acetate adhesive with a class of water resistance D3. The mechanical properties of the glued elements depend on their structure, the type of adhesive and the type of wood. The paper presents the values of strength and modulus of elasticity in static bending of elements derived from beech wood.

Ключови думи: beech wood, finger-joint, polyvinyl acetate adhesive, pneumatic-piston system

EN Version

MATHEMATICAL DESCRIPTION OF THE CHANGE IN THE ATMOSPHERIC TEMPERATURE DURING DAYS AND NIGHTS

Автори: Nencho Deliiski, Neno Trichkov, Natalia Tumbarkova

Резюме

A mathematical description of the periodically changing during many days and nights temperature of the atmospheric air as a processing medium has been suggested. It is introduced in the boundary conditions of our own mutually connected 2D non-linear mathematical models of the logs’ freezing and defrosting processes. For the numerical solving of the models a software program has been prepared in the calculation environment of Visual Fortran Professional. Results from a simulative investigation of the 2D non-stationary temperature distribution in beech logs with a diameter of 0.24 m, length of 0.48 m, moisture content of 0.6 kg·kg-1, and initial temperature of 0 oC during their 5 days and nights continuous freezing and defrosting at sinusoidal change of the air temperature with initial values of –5 oC and different amplitudes are presented and analyzed.

Ключови думи: mathematical description, atmospheric air, temperature, 2D models, beech logs, freezing, defrosting

EN Version

COMPUTATION OF THE AVERAGE MASS THERMAL CONDUCTIVITY OF OAK FURNITURE ELEMENTS SUBJECTED TO CONVECTIVE HEATING BEFORE LACQUERING

Автори: Nencho Deliiski, Neno Trichkov, Dimitar Angelski, Ladislav Dzurenda, Zhivko Gochev, Natalia Tumbarkova

Резюме

A methodology for the computation and research of the following two mutually connected problems has been suggested: 1D non-stationary temperature distribution in subjected to unilateral convective heating process of flat wooden furniture elements before lacquering and change in their average mass thermal conductivity. For the realization of the methodology, created earlier by the authors 1-dimensional nonlinear mathematical model has been solved for the transient heat conduction in the furniture elements during their unilateral convective heating. The model contains a mathematical description of the average mass thermal conductivity of the elements and their surface layer, which is intended for lacquering. For the numerical solution of the model with the aim of applying the methodology a software program has been prepared and input in the calculation environment of Visual FORTRAN Professional. Using the program, computations have been carried out for determination of the 1-dimensional non-stationary temperature distribution along the elements’ thickness and of the average mass thermal conductivity for flat oak furniture elements with an initial temperature of 20 oC, moisture content of 8 %, thickness of 16 mm, width of 0.6 m, and length of 1.2 m during their 10 min unilateral convective heating at temperature of the processing air medium of 100 oC, which circulates above the elements with a velocity of 2 m·s-1, 5 m·s-1, and 8 m·s-1 aimed at improvement of the conditions for the subsequent lacquering. During the computations a temperature of 20 oC for the surrounding air near the non-heated surface of the carrying rubber band has been used. The change in the average mass thermal conductivity of the studied furniture oak elements and also of their heated surface layers during the heating is graphically presented and analyzed.

Because of the wide range of applications, the need for paulownia is constantly increasing.

Ключови думи: oak furniture elements, one sided convective heating, lacquering, thermal conductivity

EN Version

INFLUENCE OF UV RADIATION ON COLOR STABILITY OF NATURAL AND THERMALLY TREATED MAPLE WOOD WITH SATURATED WATER STEAM

Автори: Ladislav Dzurenda, Michal Dudiak, Adrián Banski

Резюме

The aim of this paper is to present the results of color change on the surface of natural maple wood and thermally treated maple wood with saturated water steam after UV irradiation in Xenotest 450 – simulation of natural wood aging process. Thermally untreated maple wood is white to light white-gray-yellow in color with coordinates L* = 86.6 ± 2.5; a* = 5.3 ± 1.7; b* = 19.3 ± 2.3 in CIE L*a*b* color space. The thermally treated maple wood is brown-red in color with coordinates L* = 65.3 ± 1.4; a* = 10.8 ± 1.3; b* = 19.3 ± 1.3. The surface of samples maple wood with moisture content w = 12% was irradiated in Xenotest 450 with a xenon lamp with UV radiation of 340 nm. Irradiation of the wood surface took place in the exposure cycle A1 for 7 days. While the irradiated surface of the thermally untreated maple wood darkened and acquired a brownish-yellow hue, the brownish-red hue of the thermally treated maple wood turned paled slightly. The total color difference ∆E* caused by UV radiation of thermally untreated maple wood is ∆E* = 15.2 and thermally treated maple wood is ∆E* = 10.8. A comparison of the simulated aging of thermally treated and thermally untreated maple wood in Xenotest 450 suggests that the overall color change of thermally treated wood is 28.9 % less.

Ключови думи: mountain maple, CIE L* a* b* color space, UV radiation, wood color aging simulation

EN Version

PHYSICAL AND MECHANICAL PROPERTIES OF COMBINED WOOD-BASED PANELS WITH PARTICIPATION OF PARTICLES FROM VINE STICKS IN CORE LAYER

Автори: Rosen Grigorov, Julia Mihajlova, Viktor Savov

Резюме

The growing needs for wood and the impact of forest ecosystems on the climate of the planet require the rational use of wood raw material. One possible way to "save" forests is to increase the use of agricultural lignocellulosic residues. The research efforts of scientists around the world are aimed at improving the properties of wood-based panels and to increase the share of agricultural residues in that production.

In laboratory conditions were produced three-layer combined wood-based panels with a face layer of wood fibers and a core layer of wood and vine sticks particles. The participation of vine stick particles in the core layer was: 0; 15; 30 and 45%. As binder was used urea-formaldehyde resin. The content of resin in core layer was 8; 10; and 12%. The properties of the panels with and without participation of vine particles were compared. The final data for physical and mechanical properties of the panels, with participation of vine particles, were processed by the methods of regression analyze.

In the result of conducted study was established and analyzed the influence of the participation of particles from vine stick and resin content on the physical and mechanical properties of combined wood-based panels.

Ключови думи: combined tree-layered wood-based panes, wood fibres, vine sticks particles, physical and mechanical properties

EN Version

ENGINEERING OF SELECTED PROPERTIES OF LIGHT MEDIUM DENSITY FIBREBOARDS PRODUCED FROM HARDWOOD TREE SPECIES

Автори: Viktor Savov

Резюме

In this paper are presented results from study for the influence of hot-pressing temperature and press factor on some properties of light Medium Density Fibreboards (MDF) from hardwood tree species. MDF were produced from under laboratory conditions with phenol-formaldehyde resin as binder. The press factor varied from 45 to 90 s.mm-1 and the hot-pressing temperature was from 150° to 190 °C.

For the engineering of selected properties of the boards were applied the methods of regression analyze. Experimentally-statistical models that describe the studied relations and the optimal values of the factors were deduced. It has been established that by adjustment of the studied factors the properties of MDF from hardwood tree species can be significantly improved. It was also found that in the studied range, the temperature of hot pressing has a significantly greater influence on properties of MDF than the press factor.

Ключови думи: light MDF, hardwood tree species, phenol formaldehyde resin, temperature of hot-pressing, press factor

EN Version

EVALUATION OF VARIOUS LIGHTWEIGHT ARMCHAIRS IN TERMS OF ERGONOMICS

Автори: Mehmet Yuksel, Yusuf Ziya Erdil, Ali Kasal, Mehmet Acar

Резюме

This study aimed to evaluate comfort level of the lightweight armchairs based on user’s feedback. For this purpose, 5 different lightweight armchairs were selected and a total of 30 healthy adult volunteers (15 males and 15 female) joined to the study. A survey composed of 10 questions based on three times interval that consist of 5, 15, and 30 minutes was applied to the volunteers. The survey concentrated to obtain subject’s feedbacks related to their body reactions while they are sitting on the armchairs by five point Likert Scale. Results were analysed statistically and according to the results, some of design criteria such as backrest form, armrest height, sitting depth, and sitting height significantly affected the comfort feeling while sitting on sample armchairs. As a conclusion, it can be said that comfort in use can be increased by consideration of ergonomic criteria in design process.

Ключови думи: Armchair, furniture ergonomics, furniture design, comfort

EN Version

AUTOMATION OF TECHNOLOGICAL OPERATIONS IN THE MANUFACTURE OF WOODEN TOYS

Автори: Izabela Radkova, Zornica Petrova

Резюме

Traditional universal and specialized woodworking machines perform the industrial production of details for toys made of solid wood. The automation of such discrete technological processes and operations can be accomplished by designing and implementing automated complexes that provide high performance. The report presents three effective solutions for automated complexes for the automation of technological operations in the production of rotary details for toys of solid wood. These are key factors for automating discrete processes and specific prospects for the development and automation of the production of wooden toys.

Specific solutions are shown to automate the flow of details when processing the rotary parts. A theoretical analysis was carried out and cyclograms of the work of the specific automated complexes were presented.

Ключови думи: wooden toys, rotary parts, automated complex

EN Version