The present invention relates to a radial extruder for extruding different materials, e.g. plastic, into a desired form, said extruder unit consisting of a disclike rotor and stator plates placed on each side of the rotor, the stator plates having larger dimensions than the rotor and thus constituting an extruder frame which substantially encloses the rotor.

The radial extruder has been known for a long time, but its usability and field of application have been restricted by their large power consumption, large size and considerable need of maintenance.

The known types of radial extruder have a construction based on that of the axial extruder, for which reason there are problems with the loading capacity of the bearings and the supply mechanisms. Conven¬ tional radial extruders have a single input through which the material is supplied separately to each side of the extruder, and they generally use a power transmission device of enormous dimensions and a power capacity of several tens of kW, each extruder requiring one such device. The bulky supply and power transmission equipment, being asymmetrically positioned, involves uneven loading and problems with bearings, and it also makes it impossible to couple several extruders together.

The object of the present invention is to produce a new type of radial extruder in which the problems of supply and power transmis¬ sion are solved in a new way that decisively reduces the space requirement of the extruder and enables several extruder discs to be coupled in series. This in turn opens new perspectives in the application of extrusion techniques. The radial extruder of the invention is characterized in that the extruder unit has a modular construction enabling several extruder units to be coupled together if necessary, and that the extruder frame is provided with one or more radially placed locations through which a pressurized fluid is supplied, and that the rotor rim is correspondingly provided with power transmission means enabling the rotor to be rotated by the pressure of the fluid, and that in the region of the rotor rim there is a circular zone provided with openings through which the material

to be extruded can be supplied into the two extrusion spaces between the rotor and the stator plates by means of a pressurized gas, e.g. air, from one or more points placed radially in the extruder frame.

As the explicit purpose of the invention is to provide a compact extruder unit, the solution consists of a few basic features which have to be combined in the same extruder in order to achieve the desired function. Thus the problems associated with the space requirement, power transmission, bearings, lubrication and cooling of the device are solved, as if automatically, by the construction of the invention. A partial implementation of the extruder would involve at least one of the problems associated with the known types of extruder, so that the device would not function adequately in practice. Therefore, the objects of the invention are only achieved by a combination of the characteristics defined above.

One of the most significant advantages achieved by the invention is that the currently used multiple-stage extrusion press unit con¬ sisting of several extruders in a radial arrangement can be replaced by a few extruder units coupled together, which will only occupy a space about as large as that required by the nozzle part of the multiple-stage unit alone. Furthermore, the invention ensures great versatility because the units are attached with just a few bolts and can thus be easily added or removed.

The characteristics of the other preferred embodiments of the invention are presented in the claims to follow.

In the following, the invention is described with reference to the drawings attached, wherein:

Fig. 1 represents a radial extruder according to a preferred embodiment of the invention, in a partially sectioned end view.

Fig. 2 shows the extruder unit of fig. 1 in transverse section and in a somewhat larger scale.

Fig. 3 shows a combination of three extruder units like that in figs 1 and 2.

Fig. 4 shows a feeding device for the extruder of the invention.

The modular radial extruder unit, shown in fig. 1, for the extrusion of plastic materials as provided by the invention consists of a disclike rotor 1 and stator plates 2, the latter having larger dimensions than the rotor, which is enclosed in a space between the stator plates. The rim of the rotor 1 is provided with a toothing 4 and the rotor is rotated by means of at least three pivoted gears 5 placed radially at equal distances in the extruder frame and actuated by oil pressure. The outer sphere of the rotor is provided with spiral feed grooves 6 cut through the whole thickness of the rotor, the material to be extruded being supplied via these grooves into the extrusion spaces 7 between the rotor and the stator plates on each side of the rotor by means of a pressurized gas, such as air, from at least three locations 8 placed radially at equal distances in the extruder frame.

The material, in this example a plastic material, is supplied by means of pressurized air into the extruder unit via three channels 8. The plastic material is fed from the side (see fig. 2) into the feed grooves 6, in which the material is forced by the rotating movement towards the extrusion spaces 7 in the central part of the rotor. The extruded molten plastic exits via a ring nozzle (not shown in the figure) constituting the centre of the rotor. The feed air, which is supplied into the extruder unit via the supply channels 8 along with the plastic material, is exhausted through separate channels 16.

The hydraulic oil is also supplied via three channels 17 into the gear spaces 13 and, as shown in this example, causes the gears 5 to rotate. The oil flows along the path indicated by arrows and is finally exhausted through the channels 18. The oil is then passed to the container supplying the oil pump and, as provided by a preferred embodiment of the invention, re-circulated via an attempering system. This also allows effective regulation of the operating temperature, which is very important for a smooth and undisturbed operation of the radial extruder. This type of temperature regulators are well known in the art, for which reason they are not shown in the drawings and will not be described in this context.

The power transmission means provided at the rim of the rotor may also consist of the vanes of a vaned or laminated rotor which rotate the extruder rotor by means of pressurized oil supplied from at least

three locations placed radially at equal distances in the extruder frame. Regarding the construction in fig. 1, the main effect would be that no toothed gears 5 would be needed. These solutions are in accordance with the generally known operating principles of hydraulic motors and will not be described in greater detail in this context.

Fig. 2 shows a transverse section through a radial extruder unit 10 of an extrusion press. The illustration is provided with reference numbers corresponding to those in fig. 1. The figure also shows one of the three gears 5. Since the gear transmission space is filled with pressurized hydraulic oil, it is necessary to seal the space against oil leakage into the space reserved for the extrusion material. In an embodiment of the invention, this is effected by providing an air channel 14 in the region between the rotor tooth rim space 13 and the material feed grooves 6 and supplying this channel 14 with pressurized air to force out most of the oil that may leak from the space 13. This air is exhausted through another channel 15. In addition, the gas used to create a pressure in the supply of extrusion material may be passed from the Teed grooves 6 through a narrow slit 12 into the space below the rotor tooth rim space 13, so that any oil that may have leaked through the sealing referred to will meet a counter pressure on its way toward the material space and be removed via the exhaust channels 9 (marked with boken lines) provided for the supply air.

Thus, employing a sealing technique that requires very little or no space, the invention provides a simple and effective solution to the generally difficult sealing problems. Especially, the air used for pressurizing the supply material is heated as it passes through the extruder unit, so that the heat energy carried by the exhaust air can be utilized as explained later.

The design of the geometrical forms of the extrusion spaces 7, into which the extrusion material is fed via the spiral feed grooves 6, may vary e.g. according to the production objectives or the material used, in a manner similar to the design of the screw patterns employed in the extrusion zones of axial extruders. The form of the extrusion spaces 7 is therefore not covered by the invention and will not be described here. Similarly, the heating jackets II and their control are implemented using known techniques.

Fig. 3 shows how three extruder units 10 are connected in parallel. The units are connected simply by setting them side by side and locking them in place by means of securing bolts 20 inserted through the holes 21 (fig. 1) provided in the extruder units. The material supply channels 8 are formed between adjacent units thus coupled. The plastic masses emerging from the extrusion spaces 7 are combined into a multilayer structure in the output channels 22, from where the masses are passed into a ring nozzle 23 or some other type of nozzle (not shown).

Fig. 4 illustrates a feeding funnel 24 used for the supply of the granulated plastic material. At the upper end of the funnel there is a fan 25 which generates a pressure in the supply material. The plastic material 26 is supplied into the funnel via the opening 27. At least part of the air required is obtained from the extruder, because the air which has passed through the extruder and recovered e.g. from the channels 16 carries heat which can be used to preheat the plastic material. The granular plastic delivered from the bottom of the funnel 24 can be fed directly into the supply channels ^~ 8 of the extruder.

It is obvious to a person skilled in the art that the embodiments of the invention are not restricted to the examples discussed above, but that they may instead be varied in the scope of the following claims.