The drive housing of extruders
A double-worm or sheet production extruder has a housing with at least two compartments extending over its length and a drive at an end of the housing for rotating the screws or worms in the same or opposite senses. The screws are rotatable in the respective chambers of the extruder housing and have their flights intercalated so that they subject a synthetic-resin mass to plastification and liquefication. The extruder also pressurizes the thermoplastified mass so as to force the synthetic resin material through an extrusion die or into a mold.
The drive housing has a mechanism for rotating the worms or screws and the principles described are applicable not only to single screw extruder but also extruders having more than two worms. It is common to provide so-called double-worm or double-screw extruders with a drive motor which is coupled to the two worms or screws. For example, the extruder screws can be connected by means of a transmission with the drive motor. depending on the type of drive or transmission used, the double-screw extruder can be relatively bulky. In addition, the transmission or drive may be subject to failure and the maintenance thereof can be comparatively expensive.In one system, each of the screws or worms with a twin screw extruder can be separately driven by a respective drive motor and corresponding transmission. To achieve synchronism between the two extruder screws, the two drives can be coupled with one another. This arrangement also is quite voluminous and there always may be problems with the reliability of the synchronism system. In addition, such double-screw extruders are comparatively expensive.These earlier systems lack a simple, space-saving drive system for a multiscrew extruder with reliable synchronism of the extruder screws.
According to a feature of the invention, the extruder drive comprises a drive housing and at least one drive motor with a stator and rotor. Each of the single screw extruder has a connecting shaft at least partly encompassed within the drive housing. In the drive housing there is at least one cylindrical stator and this stator surrounds a cylindrical rotor. The two extruder worms with their connecting shafts are independently connected with the rotor, but out of direct contact with each other. As has already been indicated in the preferred embodiment, the apparatus is a double-worm extruder.According to a preferred embodiment of the invention a cylindrical stator is mounted in the drive housing and surrounds a single cylindrical rotor that in turn is connected with both of the connecting shafts of the two extruder screws or worms. It is possible in accordance with the invention that the rotor is directly connected to one shaft or at least one shaft, i.e. without the interposition of further elements.
In a highly preferred embodiment, the single rotor is internally toothed and each of the shafts is formed like a gear with external toothing, usually in the form of a pinion. In this embodiment, the outer gear teeth of the rotor, which is thus a ring gear, mesh directly with at least one of the pinions and thus form a direct transmission link therebetween. The pinions of both shafts can mesh directly with the teeth of the ring gear, namely, the rotor. In this manner a synchronous drive of the worms in the same sense is effective.