Multiple extruder configuration

The invention concerns a multiple-extruder configuration in which two co-rotating twin-screw extruders and a counter-rotating twin screw extruder are connected to each other with respect to the flow of material.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of application under 35 U.S.C. §371 of international stage application No. PCT/DE02/04503, filed on Dec. 5, 2002. Priority is claimed under 35 U.S.C. §119(a) and under 35 U.S.C. §365(b) from German Patent Application No. 101 62 076.4, which was filed on Dec. 7, 2001, and from which priority was properly claimed in the aforementioned international stage application.

FIELD OF INVENTION

The invention concerns a multiple-extruder configuration with the use of twin-screw extruders.

BACKGROUND OF THE INVENTION

There are many processes used in compounding, which are limited either by torque or residence time.

Example of a Process Limited by Torque: continuous mixing of rubber compounds. In this case, the speeds of the twin-screw extruder must be kept as low as possible, since otherwise the very high viscosity of the mixture leads to temperature problems due to mechanical dissipation in the mixture. Of course, at these low speeds and at an acceptable throughput, the screw shaft torques are very high. The speed is then usually raised at constant throughput until the torque is slightly below the maximum allowable torque. However, this causes the temperature of the compound to rise again.

Example of a Process Limited by Residence Time: continuous silylation of a rubber mixture that contains silicic acid or dynamic vulcanization of fully crosslinked vulcanized thermoplastic elastomers (TPE-V).

In both processes, a chemical reaction occurs during the extrusion with the twin-screw extruder, which requires a certain residence time (depending on the allowable average temperature of the compound). The machine length with twin-screw extruders is limited by the absolute torsion of the shafts, which increases with increasing length and is about 60 D. Greater lengths would mean increasing wear.

Increasingly, the industry is demanding that the finished compounded mixture be formed through a die in the same operation and/or be pressed through a screen pack to screen out larger particles. Both are associated with a relatively large pressure buildup. Although the co-rotating twin-screw extruder is very well suited for mixing tasks, it is very poorly suited for building up high pressures due to its low pumping efficiency. In the case of highly viscous mixtures, very large amounts of heat are then produced by dissipation.

SUMMARY OF THE INVENTION

The invention may create a multiple-extruder configuration which, on the one hand, allows a high mean residence time for processes that are limited by residence time and, on the other hand, allows a high torque relative to the screw length for processes limited by torque. The new configuration should exploit the good mixing characteristics of a co-rotating twin-screw extruder and the excellent pressure buildup capacity of a counter-rotating twin-screw extruder.

In accordance with the invention, this may be achieved by connecting, with respect to the flow of the compound, two co-rotating twin-screw extruders and a counter-rotating twin-screw extruder.

In accordance with a first embodiment of the invention, the two co-rotating twin-screw extruders and the counter-rotating twin-screw extruder are connected in series. In this way, the torque per screw length and the residence time can be doubled. The counter-rotating twin-screw extruder, which follows the two co-rotating twin-screw extruders, then serves to build up the pressure.

In accordance with a second embodiment, the two co-rotating twin-screw extruders are arranged parallel to each other, where the rotational direction of the one pair of screws can be the same as or different from that of the other pair. The two co-rotating twin-screw extruders are followed by a counter-rotating twin-screw extruder that serves to build up the pressure.

If the two pairs of screws have different directions of rotation, one of the screw shafts in each pair can be lengthened and connected to a screw shaft of the twin-screw extruder that follows it, so that its screw shafts then counter-rotate.

This multiple-extruder configuration can have a drive with four output shafts, which are connected to the screw shafts of the co-rotating twin-screw extruders.

However, it is also possible to use a drive with six output shafts, so that each screw shaft is driven separately.

Finally, however, in a multiple-extruder configuration of this type, it is also possible to provide gears at the end of each screw shaft, which intermesh in such a way that the screw shafts of the co-rotating twin-screw extruders drive the screw shafts of the counter-rotating twin-screw extruder.

In this regard, it is advantageous to mount a total of six gears in such a way that the two gears of each twin-screw extruder mesh with the gear on one of the screw shafts of the counter-rotating twin-screw extruder and the gears of the counter-rotating extruder engage with each other.

The invention is explained below with reference to specific embodiments.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1shows a multiple-extruder configuration, in which the two co-rotating twin-screw extruders1,2are arranged parallel to, and one above, the other. The material to be extruded is fed into the upper extruder1at first feeder3a. After it has been pushed Through the first extruder1, it is fed into the second extruder2via second feeder3band finally reaches the counter-rotating twin-screw extruder4via a third feeder3c, which is designed as an expeller. InFIGS. 2 and 3, the material flows in the same direction as in the design shown inFIG. 1. They merely show different types of drives. InFIG. 2, the screw shafts of the co-rotating extruders2and3are driven by four drive shafts10of a drive12. Gears5, which are mounted at the end of each of the screw shafts, drive two additional gears6, which are mounted on screw shafts7of the following counter-rotating twin-screw extruder4.

In the design shown inFIG. 3, the drive12includes six drive shafts10such that each of the gears5,6is driven with a separate drive shaft10. Alternatively, the drive12may include only four drive shafts10which act on the gears5. In this alternative embodiment, the gears5then drive the screw shafts of the following twin-screw extruder4via the gears6. Unlike the design inFIG. 2, the drive shafts of the counter-rotating twin-screw extruder are parallel to the pairs of screws of the co-rotating twin-screw extruders. The gears6may or may not mesh with each other in this case.

As a further alternative, the drive12in the embodiment shown inFIG. 3may act only on the gears6, which in this case drive the screw shafts of the twin-screw extruders2,3via the gears5. In this case, the drive power is transmitted via two drive shafts10.