| Abstrakt: |
In core areas of the construction industry, such as e.g., the areas of housing, power engineering and transport, a significant amount of construction minerals is consumed. In the Czech Republic, there are approximately 20·109 tons of verified reserves of construction minerals and about 55·106÷60·106 tons of them are extracted annually. Mined minerals must be first treated (crushed, sorted, etc.) before being used in the production of concretes, mortars and blocks, which places high demands on handling and transporting them. For the vertical technological transport of large quantities of materials in mining, preparation and processing plants, quite often, with very constricted working surfaces, a special belt conveyor design known as 'HAC System' or 'Sandwich belt conveyor' can be used. This paper presents the structural design of a spring mechanism, the purpose of which is to create a compressing force acting on the top belt of a vertical belt conveyor. The individual grains of transported material, supported by the bottom belt and covered by the top one, are subjected to normal forces induced by compression force. Friction forces are then generated between the contact surfaces of the material grains and both conveyor belts. For the safe operation and trouble-free transport of granular materials, the conveyor idler rollers, attached to the frames of the segment, must be pressed against the surface of the conveyor belt by a force the size of which does not fall below the limit value. The minimum volume of the contact force must ensure that the grains of the material located in the space between the top and bottom belts, travelling in the vertical section of the belt conveyor, do not move backwards from the movement of the conveyor belts due to their own weight. A laboratory testing device to test top belt compression uses two types of compression coil springs, each one with different values of spring stiffness. The theoretically calculated results and laboratory-obtained values of the compressive force for the two types of redesigned coil springs are listed in Table 1 and Table 2. The obtained results of the experimentally measured compression forces for the given type of spring, generated by vertical movement of the vertically sliding segment called the 'Testing equipment of the compression mechanism for the top belt', which is proportional to the height of the cross-section of the belt filling, are presented in Table 3 and Table 4. [ABSTRACT FROM AUTHOR] |
