Extruderhead

The present invention relates to an extruderhead of divided construction for use on two superposed screw extruders for extruding flat profiles of different mixtures. The extruderhead comprises three parts of which the middle part is fixed to the screw extruders while upper and lower parts are hinged. Channels for the material to be excluded are inclined with respect to a horizontal extruder plane so as to lead upwardly and downwardly from the respective cylinders of the extruder presses to a common extruder nozzle.

German Pat. App. No. P2201631.5 discloses an extruderhead of divided construction for connection to two superposed screw extruders to form shapes of different compounds. The extruderhead is divided into two planes which are inclined upwardly and downwardly from the horizontal extrusion plane to the cylinders of the extruders. The extruderhead is composed of three parts of which the middle part is fast with the screw presses while the other two parts are hinged so that the two outer parts are held together during operation of the extruder by two horizontally slidable clamps which have clamping faces that are slightly inclined to the horizontal and which support opposed clamping faces of the hinged parts. The two outer parts lie against supporting faces of the middle part which are inclined with respect to the horizontal with an inclination opposite the inclination of the parting plane. This extruderhead is characterized by being easy to open and also easy to clean. The flow channels of the extruderhead lie wholly in the parting plane so that material remaining in the channels can be easily removed. In this extruderhead there are no channels in the form of tubing.

An extruderhead of this kind can be designed for a group of products which are of similar form. It can also be designed to produce other groups of products. However, there are disadvantages which become greater with greater differences in the profile cross section. These disadvantages are the following. With small profiles an undesirable pressure builds up in at least one of the extruderhead parts which by reason of the relatively large material guiding faces produces a high load force on the head. It forms unfavorable slow points which can lead to temperature rise and particularly to prevulcanization of the material to be extruded. In some parts of the flow channel material can dwell for a longer time. This results at elevated temperatures which can lead to prevulcanization and heterogeneousness in the mixture. When the portions of material which have been retained at higher temperature in unfavorable locations in the flow path are freed after a period of time and again enter in the stream of material they cause noticable homogenity disturbing characteristics in the product.

These disadvantages in products which on account of their profile cross section cannot satisfactorily be produced with an extruderhead of this kind narrows down the range of products that can be produced with this kind of extrusionhead. For this reason it is necessary to use several extruderheads for one on the same extruder unit in order to produce a wide product line. The initial cost of several extruderheads is considerable. Moreover, production time is lost by reason of the installation time involved in changing the extruderheads.

In the production of particular flat profiles there is also the disadvantage that the screws of the extruders cannot be pulled out through the opened extruderhead because the walls of the flow channels are so formed that they are in the way of pulling out the screws. This greatly increases the difficulty of cleaning or of changing over the extruder apparatus.

It is an object of the present invention not only to provide greater ease of cleaning the apparatus but also to provide an unlimited adaptability to the form and size of the desired product line. This is achieved by forming the flow channels in insert plates which are insertable in receivers provided in the three parts of the extruderhead.

The forming of the flow paths in insert plates has the advantage that in changing from one group of profiles to another group of profiles of quite different profile cross section of the material part of one extruder relative to the material part of the other extruder it is only necessary to change the insert plates in order to obtain optimal matching with respect to amount of flow and flow characteristics. However, if in addition it is desired to change the transport characteristics of one or the other extruder, this can easily be done by also taking out the conveying screw of the extruder when removing the insert plate. There is thus provided an unlimited possibility of matching the form and size of the desired product strands also with respect to the number of strands and strands parts. If for example, it is desired to produce on the extruder installation a side strip composed of two different material parts for automobile tires it is possible through changing of the insert plates, to produce one or two running strips with so called mini-skirts or one or more bead filling cores. Also side strips as well as all similar parts for all other uses with greatly different geometrical form can be produced from two different compositions in optimal manner merely by interchanging the insert plates.

In this manner a better technical and economical utilization of the apparatus can be achieved. It is no longer necessary to accept a compromise solution by being bound to one group of profiles since greatly different groups of profiles can be produced with optimal form design by selection of corresponding insert plates.

It is advantageous if the insert plates have a tapered cross section in the flow direction of the material to be extruded which is preferably wedge shaped. With this construction the insert plates under the pressure of the compressed material are held fast on the mounting surfaces of the parts of the extruderhead. Moreover, this wedge shape has the further advantage that the way is clear to take out the screws of the extruders when the extruderhead is opened and the insert plates are removed.

It is advantageous if the mounting surfaces for the insert plates are flat and are provided with matrix form screw holes and/or centering holes or projections and/or quick release fasteners. This kind of matrix of screw holes and centering recesses or projections accommodates all locations of screw points and centering points for the different inserts and provides the possibility of securing each insert in an optimal manner on the mounting surface.

It is also advantageous if removable bars are mounted in the flow channels of the insert plates by means of screws which extend through to screw holes in the mounting surfaces of the extruderhead parts. Such bars make it possible to optimize the flow of the material to be extruded with regard to the desired profile characteristics.

The nature and advantages of the invention will be more fully understood from the following description in conjunction with the accompanying drawings which illustrate schematically preferred embodiments. In the drawings:

FIG. 1 is a vertical section through an extruder installation with the extruderhead open,

FIG. 2 is a vertical section through the extruder installation with the extruderhead closed,

FIG. 3 is an enlarged schematic section of the extruderhead of FIGS. 1 and 2 shown in closed position,

FIG. 4 is a schematic view showing the mounting faces for receiving the insert plates of the extruderhead,

FIGS. 5A - 5D illustrate insert plates for the production of small side strips for automobile tires,

FIGS. 6A - 6D illustrate insert plates for the production of wide side strips,

FIGS. 7A - 7D illustrate insert plates for the production of high side strips,

FIGS. 8A -8D illustrate insert plates for the production of bead filling cores,

FIGS. 9A - 9D illustrate insert plates for the production of a tread strip with mini-skirts, and

FIGS. 10A - 10D illustrate insert plates for the production of two tread strips with mini-skirts.

In FIGS. 5A - 5D to 10A - 10D:

A is a view of an insert plate of the upper extruder,

B is a cross section through the product strip or strips to be produced,

C is a view of an insert plate of the lower extruder, and

D is a schematic illustration of the flow paths to the plane of division of the extruderhead.

The extruder installation shown by way of example in the drawings comprises a horizontally arranged screw extruder 2 and a second screw extruder 3 which is arranged above the horizontal screw extruder 2 and is sloped downwardly so that both screw extruders 2 and 3 feed to the same extruderhead 4 which is in position to extrude composite flat profiles formed of different kinds of rubber material fed respectively by the two screw extruders. The extruderhead 4 is divided into three parts namely a middle part 4A which is fixed on the forward ends of the extruders, an upper part 4B which is hinged by a shaft 9B so as to swing upwardly from closed position, as illustrated in FIG. 2, to open position, as illustrated in FIG. 1, and a lower part 4C which is hinged by means of a shaft 9C so as to swing downwardly from closed position to open position. The extruderhead 4 further comprises insert plates 5A, 5B, 5C and 5D which are mounted on the opposite faces of the middle part 4A of the extruderhead and on the inner faces of the hinged upper and lower parts 4B and 4C. These insert plates 5A, 5B, 5C and 5D lie in the planes of division 6 and 7 between the middle part 4A of the extruderhead and the upper and lower parts 4B and 4C. The insert plates 5A, 5B, 5C and 5D are provided on inner faces with flow paths 1 which are formed by channels which are open when the extruderhead is open, as shown in FIG. 1, and closed channels when the extruderhead is closed. The flow channels 1 in the insert plates 5A, 5B, 5C and 5D are arranged to conduct the rubber material fed by the respective screw extruders to the extruder opening or openings formed by the discharge ends of the upper and lower extruderhead members so as to form a composite strip or strips having selected portions formed of the respective rubber compositions.

The hinged upper and lower extruderhead portions 4B and 4C are moved between open and closed positions by means of hydraulic cylinder and piston units 8B and 8C which are arranged to swing the parts 4B and 4C about the pivot shafts 9B and 9C respectively. When in closed position, the extruderhead parts 4B and 4C are held together by clamps (not shown) which are arranged at the sides of the extruderhead. These clamps are operated by draw bars 16 which are connected to a common cross tie girder 17 secured to the piston rod 19 of a hydraulic cylinder and piston unit 18. The clamps are thus operable hydraulically by means of the cylinder piston unit 18.

A vertical section of the extruderhead in closed position is shown on a larger scale in FIG. 3. The insert plates 5A, 5B, 5C and 5D are secured on mounting faces 14 of the middle part 4A and the upper and lower parts 4B and 4C of the extruderhead. In the flow direction of the material to be extruded, the insert plates are tapered so as to be wedge shape. Thus as seen in FIG. 3, the insert plates are thicker at their inner ends. By reason of this wedge shape, the pressure of the material being extruded presses the insert plates against the supporting surfaces of the mold parts with a component of force opposite to the direction in which the material is extruded so as to counteract any drag exerted by the material being extruded on the insert plates. Moreover, with this construction the way is clear for removal of the screws of the extruders when the extruderhead is open and the insert plates are removed.

The insert plates 5A, 5B, 5C and 5D are positioned on the mounting surfaces of the extruderhead parts by means of centering holes or projections and are secured in place by screws screwed into tapped holes in the respective mounting faces of the extruderhead parts. Two of the mounting faces 14A and 14C are shown by way of example in FIG. 4 together with intermediate parts 10A and 10C between the mounting faces 14A and 14C of the extruder. Each of the mounting faces 14A, 14C is provided with a plurality of tapped holes 11 to receive screws for securing the insert plates to the extruderhead parts. The tapped holes 11 are arranged in a matrix patter so as to provide holes in all of the positions required for securing different insert plates to the mounting face of the extruderhead part. With this arrangement of holes all of the different insert plates can be accommodated. The mounting faces are further provided with centering holes 12 which are positioned to receive projections or pins on the insert plates so as to position the insert plates properly on the mounting surfaces. Instead of centering holes, the mounting surfaces of the extruderhead parts can be provided with pins or projections adapted to be received in corresponding recesses in the insert plates.

In FIGS. 5A - 5D to 10A - 10D different insert plates are illustrated by way of example. On the inner faces of the insert plates there are provided bars 20, 21, 22, 23, 24, 25, 26, 27, 28, and 29 which define flow channels 1 of the material to be extruded. Certain of the strips, for example strips 22 and 23 in FIG. 8A, and strips 33 in FIG. 10C are removable and are secured by screws which extend through the insert plate and are screwed into tapped holes in the supporting surface. At opposite sides of each insert plate there are provided bars 15 which support the two plates of a pair of plates. Hollow spaces 30 can be left between the bars. In FIGS. 5B to 10B there are illustrated by way of example composite strips formed with the respective insert plates. Each of the strips is composed of parts 31A and 31B of different material fed respectively by the two screw extruders 2 and 3. It will be understood that still other cross sectional shapes can be obtained by appropriate design of the insert plates. For example, strips can be formed with two cross sectional parts of the same material separated by an intervening part of the other material. The possibilities of the strips that can be produced is virtually unlimited.