Extrusion-Shaping of Curved Hose Reinforced with Short Cellulose Fibers

Abstract

Abstract A new development in hose technology, the direct shaping of curved hose reinforced with short fibers at the extrusion die, is described. By moving the inner and outer portions of the tube die out of concentricity in a programmed sequence, the extrusion direction can be made to deviate from the machine axis and thus to produce bends in the hose. This process has been demonstrated on planar S-bends of a 38 mm hose. Bend radii as tight as 13 mm to the inside of the bend are feasible. Such a hose might find various industrial applications. Performance characteristics are similar to cord reinforced coolant hoses. The reproducibility of the die motions and timing sequences to produce the hose shapes are maintained by a digitally controlled hydraulic cylinder that is driven through a stepper motor. The driver for the stepper motor could involve hard-wired or microprocessor circuitry. All of the components for this system are commercially available with the exception of a customized extrusion head to accomodate the mounting and connection of the hydraulic cylinder. This unique process for producing curved hose is contingent upon the use of short fiber reinforcement for several reasons: (a) The reinforcement must be present in the stock before it is extruded. (b) The dispersed short fibers give the hot extruded hose structural integrity to minimize shape distortion before cure. (c) The hoop-wise fiber orientation pattern produced in the novel conically expanding die is augmented by additional reinforcement in the thinner hose wall that occurs on the inside of the bend. An important consequence of the third item above is that the curved hose sections display practically the same burst strength as a straight section, despite the wall thinning that occurs as a result of offsetting the die and pin. The production and performance of these short-fiber reinforced curved hoses can be rationalized in terms of the fluid and mechanical behavior of short fiber composites.