Failure analysis and design improvement considerations of wood screw conveyors

摘要

Screw conveyors are a well know and well recognized means of moving material from one point to another. The wood products industry uses screw conveyors in the transportation of their raw materials throughout the mills. These screw conveyors are typically categorized by the common name of "wood screws". Failures of wood screws are usually related to the imposed operating loads. Many wood screws are subjected to abonormally high loads that are sometimes not anticipated in the original design. Wood screws are also subjected to the effects of fatignue due to rotation. An unconventional new wood screw design was used at one location to address a condition of reoccurring failures and increase the reliability of the mill's feeder system. This new design deviated from the popular method of fabricating the screw from one continuous piece of seamless piple. Instead the new screw was fabricated by welding together pipe of two different wall thicknesses. The new screw design used one piece of thicker wall thickness pipe in the center one-third section and used two pieces of the original wall thickness pipe at each end. This design modification increased the section modulus and decreased the deflection of the screw at the center, but did not alter the existing drive and support arrangement of the screw. The welds between the different wall thickness sections of pipe were located at the quarter points which are away from the highly stressed areas of the center section of the screw.