Integrované mechanické přečištění se šnekovým dopravníkem

Abstract

This bachelor’s thesis focuses on the calculation and design of a screw conveyor that is part of an integrated mechanical pre-treatment system designed to transport separated sand at a wastewater treatment plant. The aim of the thesis is to find a technical solution for the screw and its bottom mounting, including the design of a suitable drive unit. The first part of the thesis is a review of screw conveyors and a short description of the existing technically unsuitable equipment. Based on the specified parameters, a calculation was performed. First, the operating speed and pitch of the screw were determined. The pitch was selected as half the pitch over the entire working length due to higher efficiency in inclined transport, and this pitch also stabilizes the conveyor’s operation. A circular shape for the conveyor trough was chosen to increase transport efficiency. The worm conveyor operates at an elevation angle of 40°. The worm conveyor is connected directly to the hopper without a shut-off valve. The conveyor is flooded over two-thirds of its conveying length. The final section of the conveyor’s conveying length serves for the gravitational dewatering of the conveyed sediment. The screw conveyor operates in so-called screw feeder mode. Based on the calculated theoretical conveying capacity, the required torque, gearbox power, and electric motor power were determined. From these values, a flat helical electric gearbox with an electric brake was designed. The drive was positioned on the discharge side due to the overall layout of the machine and to minimize potential shaft deflection. This ensured lower wear on the screw. The strength of the screw shaft was verified by a strength calculation. The shaft should also be able to bear the impact loads that can be expected in this equipment. The design of the lower screw bearing took into account the demanding operating conditions and the abrasive environment. A sliding bearing made of ZX-100K material was designed for the mounting. To prevent possible bearing sticking and the subsequent degradation of the material, automatic lubrication via an automatic lubricator was also designed. Protection of the bearing housing was ensured by a shaft seal. The sliding bearing in the lower bearing was checked for wear and compared with tabulated values. The calculated value was much lower than the tabulated values. The bearing will therefore withstand the load to which it is exposed. Strength calculations were also used to verify the strength of the flange joint bolts. The analysis confirmed that the proposed bolt size, in the specified quantity, is able to transfer the calculated load. A double-row spherical roller bearing was designed for the upper bearing. This bearing handles combined loads well. It withstands impacts well and, thanks to its inclination, allows for compensation of shaft deflection. The bearing’s service life was verified by calculation. The work was complemented by drawing documentation in accordance with the scope of the assignment.