Лесотехнически Университет

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The report examines a growing phenomenon: (sport) exercising at home. The reasons for the ever-wider spread of this, can be found in the consequences of the Covid pandemic, but also in the changed everyday culture of society (including the digital revolution and the possibilities for remote work).

The purpose of the research is to track the current needs and appropriate solutions in the creation of sports areas in small spaces, or in zones not originally meant for exercising processes. Comparative analysis and survey research are used.

The expected outcomes are in the fields of design theory, contemporary design and architecture.

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The current article represents a newly introduced model in the training practice of the “Design of Environment for Disabled People” study module, which is a part of the “Engineering design” (Interior and design of furniture) masters program in the University of Forestry.

The main focus is on putting the students in a real situation, where they can meet specialists from the practice of the social activities and the final users of their future-to-be products – disadvantaged children or children with different kinds of disabilities. In this way the studying process is formed into something more: through stimulating the engineering projection in 3D, put in real time with added emotions.

This method differs with its way of stimulating the strengths of the ones being trained and the dynamization of their active involvement in the learning process with independent and individual sides.

It also provokes the development of new ideas and shows a new way of learning and supporting the students as it expands their business operations and includes them in working directly with the final users of different statuses and needs.

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The most common failures and reasons for subsequent repair of large-scale sliding bearings are: deviation from the initial geometric shape of the friction surfaces, scratches and cuts occurring on the friction surfaces, tolerances and defects as a result of diameter and length discrepancies – sagging, bending, divergence, axles intersection and boundary wear. Sliding bearings and the bearing journals below them are flaw detected by measuring the bearing surface macrogeometry, followed by a comparison with the standard tolerances and defects at various diameters and lengths, and inspection of the defects. The present study analyses different friction surfaces of large-scale sliding bearings and the results show a correlation between the type of wearing, the relative position of the bearing supports and the deviations from the correct geometric shape of the friction surfaces. A qualitative correlation between the type of wearing and the relative position of the two bearing supports has been investigated and established. Bearing journal wear is out of the scope of the present study.

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An approach for computing the average moisture content of the whole quantity of wood materials in given batch subjected to steaming in an autoclave has been suggested. This value of the wood moisture content is needed for calculation and automatic realization of optimal energy saving regime for autoclave steaming of the materials. The approach is based on two own 2D mathematical models: one of the temperature distribution in non-frozen prismatic wood materials during their steaming and other – of the heat balance of the autoclave. The calculated by the models increase in the steaming medium temperature in the beginning of basic regime is compared with the real increase of that temperature, which is measured with a sensor in the automatic control system. After proper processing of the obtained differences between measured and calculated temperatures with the software package Table Curve, an equation for calculating the average moisture content of the wood materials in the batch loaded in an autoclave is derived. The application of the suggested approach for the cases of autoclave steaming of beech prisms in the production of veneer is presented.

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The paper presents the differences of color changes of unsteamed and steamed beech wood with saturated water steam with temperature t = 135 °C for τ = 7.5 h caused by long-term exposure of sunlight to the surface of wood in interiors for 36 months. Light white-gray color with a yellow tinge of native beech wood with values ​​on the coordinates of the color space CIE L*a*b* (L* = 76.6, a* = 7.8, b* = 19.8) darkened due to sunlight and the wood turned pale-brown color with a touch of yellow (L* = 71.3, a* = 12.2, b* = 26.8). The degree of darkening and browning is quantified by the value of the total color difference ∆E* = 13.0. The deep brown-red color of steamed beech (L* = 55.3, a* = 14.5, b* = 23.5) brightened during exposure due to sunlight and the wood surface took on a pale brown hue (L* = 77.6, a* = 14.1, b* = 27.8). The degree of lightening of the color of steamed beech wood in the color space CIE L*a*b* is quantified by the value of the total color difference ∆E* = 7.1. A comparison of the color changes of native and steamed beech wood through the total color difference ∆E* due to daylight shows that the surface of steamed beech wood shows 52.2% smaller changes than unsteamed beech wood. The lower value of the total color difference of steamed beech wood indicates the fact that changes in beech wood chromophores caused by steaming steam have a positive effect on color aging due to natural aging and partial resistance of steamed beech to the initiation of photochemical reactions caused wavelengths UV+VIS sunlight.

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The transition to a circular bio-oriented industry requires the search for alternative raw materials, sources and binders in producing materials for the furniture industry.

Lignosulfonates (sulphite lignins) are by-products, residues, of cellulose production, and they are bio-based materials with adhesive properties.

This work presents a study evaluating lignosulfonates as binders in the veneering of Medium Density Fibreboards (MDF). An adhesive composition of urea-formaldehyde (UF) resin and ammonium lignosulfonate was used in the veneering. Preliminary experiments have been carried out that show a significant reduction in the adhesion strength when the lignosulfonate content in the adhesive system passes 60%. Therefore, the study used the substitution of UF resin with lignosulfonate from 0 to 60%, with a step of variation from 10%. It is carried out at the gelling time of the various adhesive systems.

An analysis of the adhesive strength in veneering at adhesive systems with different lignosulfonate content was performed. Based on this, conclusions and recommendations were derived.

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Volarization of agro-industrial residues into value-added materials such as particleboards will increase the utilisation of natural bio-resources and support the transition to a circular economy.

In the first part of the publication, research was presented regarding the effect of the content of vine, hemp and wood particles in the core layer of three-layered particleboards on the properties of these panels. It was established that the variation in the content of vine and hemp particles does not affect the waterproof properties.

The present part represents the results of the optimisation of the core layer of the panels, given their mechanical properties. Data are delivered with accompanying analysis regarding the screw withdrawal resistance of particleboards. This property is of primary importance in using particleboards as a structural element in furniture production.

As a result of the conducted research, it was established that the panels fabricated with a core layer entirely of hemp particles have the best exploitation properties. It was also found that when using vine particles for the core layer of particleboards, their content is not recommended to be over 30%.

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This paper presents the results of a study that was conducted to establish the basic performance characteristics of a specialized forestry tractor for skidding of a whole tree stems and long timber sections in mountainous conditions. The tractor travel speed at different gradients as well as the hourly productivity for a tree-length harvesting system in the Western Balkan Mountains region were determined. The regression analysis method was used to conduct the study and to determine the influence of various factors on the hourly productivity of the tractor, at a constant trip load volume. For this purpose, a planned two-factor experiment with three levels of variation of input factors was conducted. The time for tractor’s moving in different gradients was determined by timing. Running speeds were found at range from 3,23 to 4,82 km/h, hourly productivity from 5,36 to 10,98 m³/h with trip loads ranging from 6,9 to 8,5 m³. Regression equations were derived and by their use could be determined the productivity for different gradients and different lengths of skidding distances.

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A technological study on the operation of a pneumatic separator on a BCC Cleaner&Seed Sizer (mini) machine for extraction of Scots pine (Pinus sylvestris L.) seeds has been carried out. It is part of the new technological equipment for greenhouse production of container seedlings in the Lokorsko forest nursery. Compared to the traditional production of saplings in Bulgaria for afforestation, the new production requires the extracted seeds to have higher quality indicators. In order to establish the optimal operating modes of the pneumoseparator for high quality seed production, with minimal seed losses in the waste in the aspiration system, a multifactor active experiment and optimization in the treatment of Scots pine seeds was conducted. The obtained results were used to establishment of a regression models to predict the technological parameters and the quality of the obtained seeds depending on the operating modes of the machine. The optimal parameters for setting the pneumatic separator have been established and functional modes for Scots pine seeds extraction have been determined.

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Forestry milling machines for soil preparation of afforestation are featured by higher technological and ecological properties, but also with higher energy costs, compared to the traditional machines used in our country. This paper presents the results of the conducted experimental studies to establish the main operational properties of forestry milling machines for complete soil preparation for afforestation in the lower forest vegetation zone in Bulgaria. The study were carried out with FAE SSH/HP 250 forest tiller in experimental sites located in open forest areas, forest fellings and field protection forest belts on the territory of the Shumen Forest North-East State Enterprise. The fuel consumption and productivity for complete soil preparation of open forest areas and clearings with stumps of hardwood species, with an average stumps diameter from 10 cm to 38 cm and stumps density from 220 pcs/ha to 1310 pcs/ha, at tilling depth up to 40 cm, at different rotation speed of the tiller were determined. Based on the obtained results, regression models were developed to determine the main operational indicators of the forest cutters and the optimal operating modes of the machines under certain working conditions were established.