Съдържание


INNO 1/2016 2016

SAWING OF DOUGLAS FIR LOGS WITH NARROW BAND SAW BLADES IN WINTER CONDITIONS

Автори: Zhivko Gochev, Valentin Atanasov

Резюме

The report presents some experimental studies carried out by sawing of logs with narrow band saw blades in winter conditions. The experiments were carried out in manufacturing conditions in February. For the purpose a horizontal band saw "Wirex CZ-1/ZM" was used.

Operating conditions were established and the quality of sawn lumber from semi frozen logs of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) was tested. The quality preparation of the band saw blade with the used horizontal band saw provides good parameters of the sawn lumber: surface roughnessm = 190 μm; variation in the accuracy of the size and shape of 1.5 mm and 1.8 mm at a feed speed of U = 11.5 m.min-1.

Ключови думи: logs, Douglas fir, sawing, narrow band saw blades, winter conditions

EN Version

CORRELATION BETWEEN PHYSICAL AND MECHANICAL PROPERTIES OF THE WOOD

Автори: Todor Petkov, Panayot Panayotov

Резюме

The results of testing for the presence of correlation and how strong it is between some physical – mechanical properties - bending strength, modulus of elasticity in bending and density are established. This analysis compared the coefficients of correlation between one or more pairs of variables in order to determine statistical correlations between them. The results reflect the behavior of the test specimens made from the wood of various tree species common in Bulgaria – white pine, spruce, black pine, beech and oak.

Ключови думи: correlation coefficient, physical - mechanical properties of wood

EN Version

COMPUTATION OF THE AVERAGE WOOD TEMPERATURE AND THE RATE OF ITS CHANGE DURING UNILATERAL HEATING OF FLAT SPRUCE DETAILS BEFORE THEIR BENDING

Автори: Nencho Deliiski, Neno Trichkov, Dimitar Angelski, Ladislav Dzurenda

Резюме

An approach for the computation of the average mass temperature of the wood and the rate of its change during unilateral heating of flat wood details aimed at their plasticizing in the production of curved outside parts for corpses of stringed music instruments, has been suggested. The approach is based on the numerical integration of the solutions of a linear model for the calculation of the non-stationary 1D temperature distribution along the thickness of subjected to unilateral heating flat wood details.

Ключови думи: average mass temperature, rate of change in average temperature, spruce details, unilateral heating, plasticizing

EN Version

THE EMISSIONS EMITTED BY SPRUCE THERMOWOOD WITH AND WITHOUT SURFACE FINISHED

Автори: Daniela Tesařová, Petr Čech

Резюме

This paper investigates the problematic of VOC emissions emitted by the massive spruce wood and by heat treated wood at temperatures 180 °C and 200 °. In this contribution is investigated the influence on the temperature of the spruce wood heat treatment on the quality and quantity content of volatile organic compounds, especially on the amount of emitted Phenol and Furfural. This contribution researches the correlation between the times after the modification of heat-treated wood and amount and contents of VOC emitted by this heat treated spruce wood. This study contains the results of the influence of finished Spruce heat-treated wood by the water born lacquer on emissions of VOC.

Ключови думи: Spruce massive, TVOC, emissions VOC, finished surface of thermal wood, heat-treated wood, finishing by water born lacquers

EN Version

INTEGRATION OF DAMAGE DIFFERENTIALS: APPLICATION FROM THE FOREST INDUSTRY INTO THE CIVIL ENGINEERING

Автори: Stefan Stefanov

Резюме

Integration of Damage Differentials (IDD) method was developed in Faculty of Forest Industry. It is applicable e.g. for fatigue life computation of bandsaw blade. In this regard, stress oscillograms were presented. They vary about a comparatively great mean stress: in the order of the half of the maximum stress. An analogous case in bridge construction is considered in a Ph.D. thesis developed in Sofia University of Architecture, Civil Engineering and Geodesy where IDD was adopted. The great mean stress effect is clarified regarding how IDD takes it into account in contrast to standard methods in the civil engineering.

Ключови думи: fatigue life, integration of damage differentials (IDD), bandsaw blade, bridge, mean stress effect

EN Version

STUDY MODULE „PROJECT WEEK“: THROUGH THE EYES OF STUDENTS

Автори: Regina Raycheva, Vassil Jivkov, Desislava Angelova, Pavlina Vodenova

Резюме

Competition in the educational field today brought awareness of the need of change in the manner of teaching and knowledge acquisition. It is clear that the university, as an educational and scientific institution, should follow and answer the demands of society for highly qualified and self-confident young professionals. The University of Forestry in Sofia introduced a new study module, called Project Week, in the regular curriculum for Engineering Design Bachelor Program. The module aims at increasing the skills and competence of students and preparing them for their future professional career. The paper presents the results of our experience from the past two years from the students’ point of view. Inquiries were held with the participants, students of 3rd year of study. The authors of this paper put the accent on the expectations and results of this new form of teaching.

The final results are an indicator of work done and give us the guidelines for future development towards improving the manner and conditions of work.

Ключови думи: study module, new form of teaching, intensive training, team work

EN Version

INFLUENCE OF DRYING ON DOUGLAS-FIR HEARTWOOD IMPREGNABILITY TO WATER

Автори: Mohamed Tahar Elaieb, Anélie Pétrissans, Ali Elkhorchani, Rémy Marchal, Mathieu Pétrissans

Резюме

Within the next ten years, the Douglas-fir will be the main softwood resource harvested in France, largely due to the growing market for wood frame construction in Europe. A large part of this supply will be devoted to EWP production, particularly plywood and LVL. To process these products, bolts must be peeled and therefore require a heat treatment of around 50 °C. Usually, bolts are soaked in hot water for12 to 72 hours, depending on the wood species and bolt diameter. However, Douglas-fir green wood shows two particularities that complicate boiling efficiency: (i) the heartwood has a MC near FSP (30 to 40 %) i.e. there is nearly no free water in the tracheid; and (ii) it is impossible to impregnate this heartwood at atmospheric pressure with water. As a result, wood material being a very efficient insulator, boiling Douglas-fir prior to peeling for veneer production will take a very long time, since free water is the main medium allowing heat transfer into green wood.

This paper includes a review of the anatomical, chemical and physical factors responsible for the very low impregnability of Douglas-fir heartwood. In this analysis, a first set of preliminary tests was performed in order to improve impregnation. It consisted of (i) soaking small samples (20 × 20 × 120 mm3 in RTL basis) in hot water at atmospheric pressure at different temperatures (every 10°C between 50 and 90 °C for different treatment durations (5 to 22 hours)); (ii) putting a tensoactive product into water; and (iii) applying ultrasonic waves (200 kHz / 400 W) in order to provoke micro-cavitation and then rupture the bordered pit torus. The results proved the inefficiency of such treatments on Douglas-fir impregnability, even on small samples. A second set of tests was conducted to quantify the influence of extractives and of drying (heating, vacuum) under the FSP on heartwood permeability. If extractives do not appear to have a real impact, then drying treatment will also not greatly improve permeability. One of the hypotheses is that the drying process may have caused micro cracking in the cell walls.

Other tests are in progress to quantify the speed of absorption of liquid in both longitudinal and transverse directions.

Ключови думи: Douglas-fir, permeability, boiling, ultrasonic treatment, drying

EN Version

ADDITIONAL LOAD FROM RADIAL MISALIGNMENT OF SHAFTS AT THEIR COUPLING

Автори: Slavcho Sokolovski, Nelly Staneva

Резюме

A methodology for determining of additional load of shafts from deformation due to radial misalignment at their coupling is proposed. Shafts connected with rigid compensating coupling with cross coulisse (Oldham coupling) and with sleeve coupling are considered. The shafts displacement due to the additional load is determined for two cases: when supports are considered as perfect solid and when supports are considered as flexible with a radial clearance in the bearing. The elastic deformation of coupling sleeve is determined.

Ключови думи: misaligned shafts, coupling, rolling bearing, displacement, strain

EN Version

POSSIBILITIES FOR OPTIMIZATION OF DISTRIBUTIVE INDICES FOR AVERAGE COSTS CALCULATION IN JOB ORDER AND SMALL SCALE SERIAL PRODUCTION

Автори: Nikolay Neykov, Anna Dobritchova, Mariela Cvetkova

Резюме

Calculation of total costs is often associated with distribution of costs like overhead which cannot be placed to one or another product costs at the end of planning period or just period of time. Furniture in Bulgaria consists mostly of small enterprises which produce individual customized products. In these cases, exist wide variety of approaches that could be implemented. In this paper is made an attempt to find an optimal solution of cost distribution mechanisms, suitable to furniture.

Ключови думи: calculation, costs, optimization

EN Version

INFLUENCE OF THE TYPE OF UPHOLSTERY MATERIALS ON THE SOFTNESS OF UPHOLSTERY WITH INNER SPRING UNITS

Автори: Yancho Genchev, Teodor Lulchev, Desislava Hristodorova

Резюме

The upholstery with inner spring units, is composed of materials, which have various stress-strain behavior under load. In the work is studied softness and behavior of structures composed of different combinations of upholstery materials. The type of the innerspring unit, materials and thickness of the upper layers are changed. As criteria for evaluation of the specimens are used coefficients of softness and requirements for general deformation of the structure of the upholstery for seat and back elements. Conclusions are made and recommendations for their application in the structure of upholstered furniture.

Ключови думи: upholstery materials, innerspring units, Bonnell spring unit, Pocket spring unit, structure of upholstery

EN Version

ANALYSIS OF THE DEWINGING PROCESS ON SCOTS PINE SEEDS WITH SMALL-SIZED DEWINGER

Автори: Konstantin Marinov

Резюме

In recent years, in Bulgaria there is a tendency to reduce the yield of seeds of conifers. This implies a more efficient use of machines with less power and performance. The forest seed producing stations in the country are equipped with small-sized dewingers "Unitech", but at this stage we still lack research and data to work with seeds of Scots pine. In the present work, a study has been conducted and an analysis has been made on the dewinging process of the Scots pine seeds (Pinus silvestris L.) with a small-sized paddle dewinger "Unitech". As a result, functional dependencies have been identified, which express the relationship of the rotation speed of the working bodies and the duration of the process on the quality of the harvested seeds and the operating performance of the machine. On this basis, the optimal process parameters have been established and specific modes of dewinging of Scots pine seeds have been proposed. The obtained results have an applied science nature in the field of forest seed production and the design of machines for dewinging of seeds.

Ключови думи: forest seed production, small-sized dewinger, technological parameters, Scots pine

EN Version

QUANTITATIVE YIELDSFROM THE CUTTING OF THE STEMS OF WHITE PINE (PINUS SYLVESTRIS L.), DEPENDING ON THE THICKNESS AND LENGTH OF THE DETAILS AND THEDEFCTS OF THE WOOD

Автори: Daniel Koynov

Резюме

In the current work are presented the results from an experimental procedure for the establishment of quantitative yields and their variation depending on the thickness and length of details, the defects of the wood and the location of the logs in the stems of Scots pine (Pinus sylvestris L.). The experimental procedure was performed according to standardized methodology with selected model stems. It has been established the presence, size and number of defects of treated wood by using EN 1927-2 standard. In the normal technological sequence the stems were cut of sections with lengths 1, 2 and 4 m, and from the obtained sections (logs for sawing) according to acute sawing method the boards were cut of details with a thickness of 3, 6 and 9 cm. The obtained results allow drawing analysis and conclusions in relation to quantitative yields and their change depending on the thickness and length of the details. On the basis of these results an analysis can be drawn in relation to the impact of disadvantages of the wood and the importance of the place for harvesting of the logs from the tree stems. The resulting information allows more accurate and objective assessment of the technology and the machines in terms of more efficient wood processing and manufacturing of materials from solid wood.

Ключови думи: Scots pine (Pinus sylvestris L.), stems, size-qualitative characteristics, materials from solid wood

EN Version

CHARACTERISTICS OF THE TRUNKS OF SCOTS PINE (PINUS SYLVESTRIS) FOR PRODUCTION OF SOLID WOOD MATERIALS

Автори: Neno Trichkov, Daniel Koynov

Резюме

The results from the studies on the dimensional and qualitative characteristics of model trunks of Scots pine have been presented in this report. The following dimensional characteristics: diameter, length and taper have been determined. The presence, type and dimensions of knots on the outer surface of the tree trunks and inside the wood have been determined. The presence of decay, spiral grain and other defects of wood and trunk shape have been established. The results have been analysed and relations to the existing standards, possible application of wood and requirements to the solid wood materials have been made. Relevant methods and techniques for efficient processing have been suggested.

Ключови думи: Scots pine (Pinus sylvestris), trunks, dimensional and qualitative characteristics, solid wood materials

EN Version