In the manufacturing of extrusion products composed of several material layers, e.g. cables, bottles, pipes or blown films, it is necessary that the various layers have uniform thickness and that t additives contained in the plastic mass be evenly distributed in th product. The additives, which are either premixed in the moulding compounds or introduced during the extrusion phase by pumping, have tendency - due to differences in pressure, speed and temperature gradients - to be separated from the mass and deposited on the surfaces of the mass flow channels. When the manufacturing process uses an extruder head that combines different mass flow components, the product shows stripes or seams along the lines where the components were merged. In current practice, the additives are usua pumped into mixer units incorporated in the extruder machine, the f components being passed from the mixer units into the mass distributors.

The method of the invention employs ring-shaped rotors sandwiched b ween plates placed on top of each other, the mass being introduced at the rotor periphery and spread on both sides of the rotor toward the circular inner edge of the rotor, from where it proceeds in a tubular formation into the extruder nozzles. The rotors are rotated either by the kinetic energy of the moving mass or by an external force. The various components of the mass are mixed in the narrow spaces between the rotors and the plates, the mixed mass being thus directly output as a tubular flow, obviating the need for merging separate flow components. Therefore, the product is free of seams stripes and has uniform thickness as well as a centric structure.

Figure 1 represents a cross-section of a three-layer embodiment of the extruder head of the invention.

Figure 2 represents the extruder head of figure 1 in lateral view.

Figure 3 represents a rotor as used in the extruder head.

Figure ft represents a supply channel arrangement that may be used instead of that in figure 2.

Figure 5 represents another embodiment of the extruder head of the invention in lateral view.

In figure 1, the masses are supplied via the channels 8 provided between the plates la-Id to the peripheries of the rotors 2a-2c. T plastic mass may be fed in by means of the presses used for meltin and pressurizing the plastic materials; the other substances may b supplied e.g. by means of geared pumps. From the channel 8, the ma proceed into the input slit 9 and further into the bearing groove 10, from where they are introduced into the narrow spaces between rotors and the plates, where the various mass components are mixed passed further towards the central openings of the rotors. As the masses flowing from each side of the rotor are merged at the edge the opening, they form a two-layer tubular flow, which is directed into the nozzles 3. using e.g. a device consisting of four plates la-Id and three rotors 2a-2c. With such a device it is possible to produce tubular structures consisting of as many as six layers, depending on the materials pumped into the supply channels. Channe is used for the input of liquids and gases.

Figure 2 shows a lateral view of an extruder head as provided by t invention, comprising the plates 1, provided with vanes 6 (corresp ding to the guide vanes of a radial turbine) attached to the rotor chamber surfaces, the rotors 2, provided with vanes 7 (correspondi to the runner vanes of a radial turbine) arranged in a converse an the channel system 4 for the supply of plastic mass and a channel for the supply of additives. The rotors shown in the figure rotate freely with the flow of the plastic mass at a speed corresponding the speed of the mass flow. The vanes 6,7 attached to the plates 1 the rotors 2 effectively mix the masses supplied into the rotor sp and cause them to move toward the central openings of the rotors.

The drawings do not show the auxiliary devices needed for purposes like heating, mounting etc., which are irrelevant to the principle the invention.

Figure 3 shows the structure of the rotor 2 in greater detail. The groove 11 at the rotor periphery is for the bearing balls supportin the rotor.

Figure H shows an alternative supply channel arrangement, in which supply channel 12 forks into two branches directly communicating wi the input slit 9 so that the supply pressure is evenly distributed over the whole periphery of the rotor. Thus, in principle, there ar an infinite number of points from which the masses are introduced i the rotor space.

Figure 5 shows an embodiment of the invention in which the rotors a driven by means of gears 14, which are attached to the shafts 13. I this case the rotor periphery must be provided with a gear track instead of the groove shown in figure 3.

This solution may be applied in cases when for some reason the mass flow does not impart a sufficiently high or low speed to the rotor achieve the desired result. This applies to cases when e.g. the tem perature or the degree of treatment or mixing of the plastic mass i to be changed by changing the speed of rotation of the rotors.

The method of the invention can be used in a wide variety of applic tions in the plastic industry and the manufacture of extrusion products in general, to mix together different materials, whether liquid, melted, pastelike, gaseous etc. , in order to produce rotati nally symmetric structures consisting of several layers, the number which may vary.

It is also possible to pump in the same material via all the suppl channels. In this case, the desired additives may be supplied to t desired rotors or just one side of the rotor to produce different layer structures. Further, the number of plates 1 and rotors 2 can easily be increased, since this does not involve increased require ments regarding resistance to pressure and since all the rotors ca be driven by the same power transmission shafts.

The geared pumps used for supplying additives can also be integrat between the plates 1, and so can the screw extrusion devices used supplying plastic materials. The latter devices may be very small rotate at high speeds, since the final plasticity of the mass is achieved by means of the rotors 2 and since the supply channels ca also be utilized to raise the mass temperature to the desired leve By adjusting the rotational speed of the rotors, the frictional he can be controlled to regulate the final temperature of the mass. I this way, a system is provided in which the thermal time constants very short and the mass is of uniform quality in the thermal respe as well.