GB1504277A - Extruders - Google Patents

Abstract

1504277 Extrusion-calendering apparatus FARREL BRIDGE Ltd 5 March 1975 [7 Dec 1973] 56814/73 Heading B5A Rubber or plastics material is delivered to the nip of opposed sheeting rolls 14 from the screw 20 of an extruder, via a connecting portion which includes a channel defined in part by an upper plate 34 which, when the pressure of material in the channel exceeds a selected value, is upwardly pivotably displaced by the pressure against resilient means, to permit escape of material from the channel and a reduction in the pressure. The displacement and return of the plate 34 may also act to maintain the valence of material in the connecting portion within predetermined limits, by actuation of a pair of spaced microswitches 62 to alter either the screw speed at a constant roll speed, or the roll speed at a constant screw speed. The channel is also defined by side plates 32, and a bottom plate 36 which may be downwardly displaceable similarly to, but at a higher pressure than the plate 34, the plates 34 and 36 being mounted to a plate 22 having a rectangular opening 24 through which material is delivered by the screw, and which is of a vertical dimension slightly less than that of the extruder bore, and of a horizontal dimension which diverges from a width equal to that of the bore. A nose piece 26 of the screw projects into the opening 24 with a slight upper and lower clearance to thereby divide the material from the screw 20 into two streams from which the rotative effect of the screw is eliminated, with the end of the screw flight also shearing the material against the upstream face of the plate 22. The lower plates 34, 36, may be movable towards a vertical position to permit access for cleaning and the resilient means which bias the plate 34 to a horizontal position may comprise a spring of adjustable tension, with the bottom plate 36 being fixed by removable screws, with the access being obtained by removing the spring and screws and bolting the plates in the vertical position. Alternatively, as in the described embodiment, the plates 34, 36, are maintained in the horizontal position by resilient means comprising pneumatic cylinders 42, 70, pivotally mounted to the plate 22, and to the plates 34, 36, which are pivotable at 40. 38, between the horizontal and vertical position. The pressure in the cylinder 70 is set for displacement of the plate 36 by the material, at a pressure higher than that at which the plate 34 is displaceable. Access for cleaning is obtained by releasing air from the cylinder 70, and respectively releasing air from and admitting air to the upper and underside of the piston in cylinder 42, with the plate 34 being maintained in the vertical position by a wing nut 51, on an upper extension 50 of the piston-rod of the cylinder 42, abutting a frame 49 carried by the cylinder 42. The frame 49 carries the pair of microswitches 62 which are operated by cams 54 on the extension 50 to control the speed of the screw or rolls. In operation, pressure of the material in the channel displaces the plate 34 upwardly so that a cam 54 operates the lower one of the microswitches 62 to rotate the rolls at a slowly accelerating speed. As the plate 34 is returning towards the horizontal upon the consequential drop in pressure in the channel, the lower switch 62 is disengaged to cause the rolls to rotate at a constant speed, and a continuing drop in pressure and consequent returning movement of the plate 34 then operates the upper microswitch 62 to cause a gradual reduction in the speed of rolls 14. The consequent increase in pressure in the channel then causes upward displacement of the plate 34 until the upper switch 62 disengages and the rolls rotate at constant speed, until increasing pressure again actuates the lower microswitch to increase the speed of the rolls. and thereby repeat the actuating sequence of the switches to maintain the volume of material in the connecting portion between the predetermined limits. The plates 22, 34, and 36 may be provided with passages for cooling or heating fluid circulation, and side guide members 60 are provided exteriorly of the plates 22, and which are of an adjustable spacing apart and extend into the nip as a close fit. The members 60, together with the rolls 14, are carried by frame members (58), Fig. 3 (not shown), which are mounted on vibration insulators permitting displacement of the rolls from the extruder under excess pressure of material therebetween, e.g. upon failure of the motor rotating the rolls, the displacement acting to operate a microswitch to half rotation of the screw 20.