Increasing the wear resistance and service life of screw presses for dewatering synthetic rubbers

Abstract

In the synthetic rubber production lines for curing and isolation, in order to dewater the moist crumb rubber at a temperature of 140-200~ squeezing and drying screw presses are used which have a single spindle shaft of diameter 250-300 mm [1]. Test operation has shown that the service life of such presses is limited by the intense and nonuniform wear of the crests of the worm spirals, the filter plates (rods) of the filter body of squeezing presses, and the cylinder bushing of drying presses. Wear on the working parts of screw presses reduces the output and quality of the rubber as a result of metal particles entering it. Furthermore, in operation at the eontaetpoints between screw and cylinder there arise considerable loads (up to 6000 kgf and above), leading to fracture of the filter body rods and emergency shutdown of the presses. Analysis of wear on the worm shafts and body components of a type OM-1K-300 squeezing screw press when dewatering type SKS-30 rubber and of a type SM-1K-250 drying screw press when drying type SKD rubber showed that maximum wear at the crests of the worm spirals, filter body rods, and cylinder bushings occurs at the discharge attachment end because the worm shafts are cantilever mounted {Fig. 1). Moreover, the greatest wear is observed in the initial operation period (up to 500 h), and is related to running in rubbing surfaces under different operating conditions. The cause of rod fracture is wear and corrosion cracking accompanied by the development of fatigue microcracks in contact points with the screw. Accordingly, in order to increase the wear resistance and service life of screw presses it is most appropriate to strengthen the crests of the worm spirals, rods, and cylinder bushings on the discharge side and also to select the appropriate materials for all components.To strengthen the worm shafts, the spiral peaks have a welded-on deposit of stellite based on cobalt, while the bushes and rods are made from sand-cast or centrifugally east steilite. Alloys based on cobalt are widely used for this purpose [2, 3], but they are in short supply and costly, while weld overlaying large components is quite complex due to the need for heating up to a temperature of at least 600~ before and during the operation.