DETERMINING THE COEFFICIENT OF FRICTION OF WOOD-BASED MATERALS FOR FURNITURE PANELS IN THE ASPECT OF MODELLING THEIR SHREDDING PROCESS

In order to improve the power selection of the drive unit for the shredding machines,theauthors determine the values of friction coefficients used in the cutting force models. These values consider the friction between steel and such wood-based materials as chipboard, MDF and OSB. The tests concern laminated and non-laminated external surfaces and surfaces subjected to cutting processes. The value of the coefficient of friction for the tested materials is in the range: for the static coefficient of friction 0.77-0.33, and for the kinetic coefficient of friction 0.68-0.25. The highest values of the static and kinematic coefficient of friction were recorded for MDF (non-laminated external surface) and they were equal respectively: 0.77 and 0.68. In turn, thesmallest values of the discussed coefficients were recorded for chipboard (laminated external wood-base surface), which were at the level of 0.33 and 0.25, resp.

Investigating the Effect of Preimpact Energy Dissipation on Coefficient of Restitution regarding the Slope-Boulder Interaction

Coefficient of restitution is regarded as a dominating parameter in rockfall research. Generally, small-scale experiments were developed without considering interactions between boulder and slope. However, preimpact moving statuses are essential to evaluate rockfall behaviors. To reveal the effect of preimpact interactions on coefficient of restitution, energy dissipation considering initial velocity, surface type, and slope angle is executed based on medium-scale tests. The results show that (1) as the inclination of initial velocity, higher rebound height, and the declining normal coefficient of restitution occur, a determinable linear function could demonstrate relationships among energy dissipation and all coefficient of restitution; when initial velocity exceeds 5 m/s, the recovery ability shows and produces an increasing trend with respect to the variation of kinematic coefficient of restitution and kinetic energy coefficient of restitution. (2) As the surface material varies, slope hardness and rebound ability influence normal coefficient of restitution, and the surface roughness and rotation feature dominate tangential coefficient of restitution; considering preimpact slope and boulder interactions, four types of coefficient of restitution follow declining trend with different material sequence. (3) Slope angle affects normal coefficient of restitution, and tangential coefficient of restitution relatively descends 18% and inclines 10% when the angle ranges from 30° to 75°; regarding preimpact moving status, it differs from bounce times. The correlation between preimpact energy dissipation and four coefficients of restitution can be represented by the same decreasing linear function, when increasing the slope angle.

THE AIR VISCOSITY COEFFICIENT AND OTHER RELATED VALUES

Experimental measurements of the dynamic coefficient of air viscosity were done. Numerous other related values such as the kinematic coefficient of air viscosity, the mean free path and the mean thermal square velocity of air molecules were determined. The dependence of the air dynamic viscosity coefficient on temperature was also obtained. It allowed us to determine the Sutherland’s corrections and to estimate the dimension of air molecules and the temperature gradients of the dynamic and kinematic coefficients of the air viscosity. The determined values were compared to the similar theoretical and experimental data obtained by other authors.

Determination of the kinematic coefficient of uneven rotation of the gear-belt transmission with a compound pulley

Known drive gears are analyzed. A gear-belt transmission with a composite roll pulley, including an elastic rubber sleeve, is proposed. Analytical expressions are obtained for determining the coefficient of kinematic non-uniformity of rotation of the driven pulley, its speeds and angular displacement as a result of deformation of the sleeve. Keywords gear-belt transmission, pulley, speed, coefficient of kinematic non-uniformity of rotation, moment, elastic modulus, stiffness, load. [email protected]

MATHEMATICAL MODEL OF INTERACTION OF MILLING KNIVES WITH SOIL

As working units of tillage mills, both curved (L-shaped) blade knives and straight blade knives are used. The soil reactions to these working units depend on soil properties, geometric parameters of the working parts, parameters determining the modes of their operation and the angle of rotation of the working units. When constructing a mathematical model for the interaction of working parts with soil, all these factors must be taken into account, while striving to simplify the proposed model. Accounting for the dependence of force characteristics of the working units on the angle of their rotation is not an easy task, and in most cases it is solved with the help of specially set experiments. A mathematical model is proposed for the interaction of a direct lamellar milling knife with soil, which makes it possible to determine the components of the resulting soil reactions to such a knife, the total moment of these reactions, and the power consumed for cutting the soil, depending on the knife rotation angle. This model takes into account the geometry of the working unit through the radii of the hub and cutters, the angle of installation of the milling knife and its length. The operating mode of the knife is set by the kinematic coefficient, equal to the ratio of the circumferential velocity of the knife end to the speed of the translational motion of a mill, and the maximum relative depth of the milling knife in the soil. The constructed model makes it possible to determine the dependence of the maximum values of the considered power characteristics of the knife on the indicated geometric parameters and the parameters of the knife operating mode, which makes it possible to simplify experiments to determine the power characteristics of the cutter and significantly reduce its volume. This model can be used to select the optimal knife parameters. In addition, the proposed model can be used to calculate the power characteristics of the rack of a curved blade knife, which consumes a significant amount of energy during milling.

Kinematic coefficient ratios, anisotropy parameters, and polarization degrees of L3 X-ray transitions of Bi, Pb, Ta, Lu, and Yb

The anisotropy parameter values β of the L shell fluorescent X-rays (Lι (L3-M1), Lβ6 (L3-N1), Lα1,2 (L3-M5,4) and Lβ2,15 (L3-N5,4) of Bi, Pb, Ta, Lu, and Yb excited by 22.6 keV photons were measured. These values were used to determine the kinematic coefficient ratios α(Lι/Lα1,2), α(Lι/Lβ6), and α(Lα1,2/Lβ2,15). The Lι and Lβ6 X-rays were found to be anisotropically emitted whereas Lα1,2 and Lβ2,15 X-rays showed less anisotropic spatial distributions. Also, the polarization degrees of Lι and Lα X-rays were measured for the present elements and observed that the Lι lines were found to be strongly polarized whereas the Lα lines showed less polarization.

Analysis of components effecting free convection intensity in steel rectangular sections

Free convection is one of the heat transfer modes which occurs within the heat-treated bundles of steel rectangular section. A comprehensive study of this phenomenon is necessary for optimizing the heating process of this type of charge. The free convection intensity is represented by the Rayleigh number Ra. The value of this criterion depends on the following parameters: the mean section temperature, temperature difference within the section, kinematic coefficient of viscosity, volume expansion coefficient and the Prandtl number. The paper presents the analysis of the impact of these factors on free convection in steel rectangular sections. The starting point for this analysis were the results of experimental examinations. It was found that the highest intensity of this process occurs for the temperature of 100 °C. This is mainly caused by changes in the temperature difference observed in the area of sections and changes in kinematic coefficient of viscosity of air. The increase in the value of the Rayleigh number criterion at the initial stage is attributable to changes in the parameter of temperature difference within the section. After exceeding 100 °C, the main effect on convection is from changes in air viscosity. Thus, with further increase in temperature, the Rayleigh number starts to decline rapidly despite further rise in the difference in temperature.

Rockfalls: influence of rock hardness on the trajectory of falling rock blocks.

Rockfalls pose significant hazard on human activities and infrastructure. The assessment of rockfall risk along roads and on other human activities is of great importance. Geological assessment can predict the outbreak of such events; explain the mechanism of occurrence and assist in the effective design of protection measures. The trajectory of a falling block is significantly affected by its response to the impact with the slope, since block kinematics properties mainly depend on the coefficient of restitution values. In this research a laboratory procedure based on the free fall of small blocks of different rock types and artificial materials was implemented in order to address the effect of their mechanical properties on the coefficient of restitution values. From the evaluation of testing results a correlation between kinematic coefficient of restitution and Schmidt rock hardness is proposed.

Kinematic Analysis and Synthesis of Geneva Mechanism Combined with Elliptic Gear

When the slot number of geneva is fixed, the kinematic coefficient of common geneva mechanism is a fixed value, too. Using the elliptic gear mechanism as the drive crank of the Geneva, the variable transmission ratio of the elliptic gear mechanism is utilized, which makes the kinematic characteristic of the geneva mechanism changed. A synthesis method of combined geneva mechanism is put forward according to the kinematic coefficients in this paper. The calculation methods of the maximum and minimum kinematic coefficient are proposed. The parameters of the combined geneva mechanism are presented, which the middle position of the kinematic range of the geneva has approximate constant velocity characteristics.

Dynamics of Mechanisms With Slider Joints and Clearance

In this study a planar mechanism with a rotating sliding joint is investigated. Periodic behavior is observed for zero clearance of the sliding joint. The sliding joint with clearance is modeled using a kinematic coefficient of restitution and a coefficient of friction. Nonlinear dynamics tools are applied to analyze the simulated data captured from the connecting rod of the mechanism. The stability of the motion is studied using the Lyapunov exponents. The largest Lyapunov exponents will be considered as a stability index for the chaotic behavior of the system with slider clearance. The chaotic behavior is studied for different clearances of the sliding joint and different angular velocities of the crank.