subject: Twin Screw Extruder [print this page] Each screw shaft of a twin screw extruder with power branching gearing is driven by a gear train comprising a driven pinion, a first pair of intermediate gears meshing with the driven pinion from opposite sides, a second pair of intermediate gears each meshed with a respective one of the first pair of intermediate gears and a drive pinion meshed on its opposite sides with the second pair of intermediate gears and coupled to a power shaft. The first and second pairs of intermediate gears are capable only of rotation in a gear casing in which they are mounted but the drive pinion and the driven pinion are capable of radial movement in the casing. As shown the driven pinion has an axial extension with curved teeth engaged in one end of a coupling sleeve with internal curved teeth and a portion of the shaft has curved teeth engaged with the curved teeth in the other end of the sleeve, the shaft being mounted in bearings.
he distance between the axes of the screw shafts of a twin screw extruder limits the diameters of driven pinions on the shafts and forming part of gearing for driving the screws. These driven pinions cannot be just any amount larger than the screw shafts themselves. Even if the driven pinions of the two drive shafts for the screws are staggered axially with respect to one another, with the high torques required nowadays it is no simple matter to obtain a long enough life for the gearing and small loads on radial bearings of the drive shafts for the screws. Many different proposals have already been made regarding torque transmitting arrangements and gear constructions to avoid the difficulty.
The principle of branching the power for driving the driven pinion of the screw drive shafts has found the greatest acceptance. In twin screw extruder gearings it has been proposed to divide the driving torque by means of an appropriate gearing construction, on account of the limited space for driving a screw shaft. The component torques are transmitted from two opposed sides to the driven shaft of the bearing, which is also the screw drive shaft, at the same time taking the load off the radial bearings of the screw drive shaft.
With this power branching then, preferably two engagements between teeth on each driven pinion are used for transmitting torque. It has been found, however, that the two engagements at the pinion in question cannot be uniform, since the distances between the axes of the intermediate gears and driven pinions and the shapes of the teeth on the gears vary due to manufacturing tolerances. Proposals have therefore already been made with a view to transmitting the torque components uniformly to the driven pinion. Such proposals comprise providing for self adjustment in the gearing; this is said to allow for uniform clearance between engaging teeth and thus to compensate for inaccuracies in manufacture.
