No abstract

One of the possible ways to transfer the tractive power of a drive unit to the traction element is to use fibre friction. When a steel rope is used as the traction element, there is a transfer of tractive power in the groove created on the perimeter of the rim of the driving rope sheave. The transmission capability of the drive is directly proportional to the size of the angle of wrap and the shear friction coefficient of the rope surface when the rope is in contact with the surface of the groove wall. The relationship for calculating the size of friction coefficient in the grooves is given by relevant technical standards. The coefficient of friction determined in this way does not take into account the state of possible operational contamination of the groove or the diameter of the rope used. Using a unique laboratory instrument, tensile forces were measured for both rope sides in the state of a non-rotating sheave or when the sheave started to rotate rope. Experimental measurements were carried out for two different diameters of steel ropes, which were guided by two types of grooves for the rope sheave under two limit operating states of the groove wall surface: clean and dirty with oil. By evaluating the measured tensile forces in the approaching and outrunning rope side girded with the groove of the rope sheave, it was found (using a measuring apparatus) that a rope of a larger diameter acquires a higher value of the friction coefficient for the groove than a rope of a smaller diameter. The coefficient of friction in the groove decreases with the increasing size of the sum of the acting tensile forces on both sides of the rope. Lower values of the coefficient of friction achieve semi-circular grooves, and V-shaped grooves show higher values. Lower values for the coefficient of friction, close to theoretical values which were calculated using the relevant relationships specified in the standards, were found for grooves contaminated with oil as opposed to dry and clean grooves.

In this paper, the authors draw attention to biomechanics connected with the possibilities of treatment of complicated bone fractures. They present information about their own design, laboratory tests and numerical solutions (i.e. strength analyses and reliability assessments) of the various types of external fixators applied in traumatology and orthopaedics (i.e. intended for fractures of limbs and pelvis and its acetabulum). The new design of external fixators is based on the development of Ilizarov and other techniques and satisfies new demands of science.

The presented article investigates the biomechanics of the calcaneal nail C-NAILTM by numerical calculations and, partially, experimentally. This nail is widely used in trauma and orthopaedics. A numerical model of implants directly interacting with the bone tissue model obtained from CT scans was calculated. The material properties of the bone tissue can be described by several models; in this work, a non-homogeneous material model with isotropic elements and prescribed elastic modulus was used to provide a more accurate model of the applied force distribution on the individual parts of the implants. The critical areas of the nail and its fixtures were investigated using finite element strength calculations to verify their strength and reliability, contributing to the safety and faster and easier treatment of patients. These analyses suggest that the strength of the calcaneal nail C-NAIL, as well as the stabilization of bone fragments resulting from its use, are sufficient for clinical practice.

This article is focused on design issues concerning the long spindle used to grind the internal pipe diameters. In the article an example of spindle design for an internal pipe diameter grinder can be found to process 11 m long pipes with external diameters ranging from 270 to 610 mm. Furthermore, this article offers a theoretical proposal for the spindle stroke in connection with its engagement, taking into consideration the internal diameter of the ground pipe and the outside diameter of the grinding wheels. The pipes used in this example are designed for transport in the mining industry, requiring a high quality of inner pipes surface for their long service life.