WO2008026230A1

WO2008026230A1 - Machine for extruding thermoplastic products

Info

Publication number: WO2008026230A1
Application number: PCT/IT2006/000632
Authority: WO
Inventors: Tiziano Spiazzi
Original assignee: Sovema SpA
Current assignee: Sovema SpA
Priority date: 2006-08-29
Filing date: 2006-08-29
Publication date: 2008-03-06
Anticipated expiration: 2009-02-28

Abstract

Machine for extruding thermoplastic products, of the type provided with an externally heated plasticization chamber (5) connected at one end to a unit (70) supplying the material to be plasticized and at the other end to an extrusion unit. The chamber has, arranged inside it, a feeder screw for feeding the material, which is rotationally actuated by a torque motor (17) at the same number of revolutions. A thrust bearing unit (18) is envisaged, which unit is able to oppose the axial thrust imparted by the material to the rotating screw and is fixed to the support structure (2) between the torque motor and the feeder screw and is provided with a transmission shaft connected at one end to the feeder screw and at the other end to the shaft of the torque motor.

Description

MACHINE FOR EXTRUDING THERMOPLASTIC PRODUCTS

DESCRIPTION

Field of application

The present invention concerns a machine for extruding thermoplastic products, in particular sheet- like laminated articles, various profiles, sheets or film.

The machine in question is intended to be advantageously used industrially in Lines for producing thermoplastic products from polymer material such as, for example, polystirol, PET or the like

State of the art

On the market various machines for extruding thermoplastic products are known, these conventionally being composed of a support structure resting on the ground and having, mounted thereon, a plasticization chamber with an elongated form supporting, associated with a first end, a supply unit provided with one or more hoppers for introducing into the chamber the raw materials, master batch and other additives. At the other end the plasticization chamber has, associated with it, an extrusion head which determines the profile of the extrudate and which is usually preceded by a filter, by a gear pump and by a mixer. A feeder screw is housed inside the plasticization chamber and is made to rotate by a motor unit so as to cause feeding of the plastic, confined by the heated walls of the chamber, towards the extrusion head.

In accordance with a constructional solution which is very common on the market, a first type of extrusion machine envisages that the motor unit transmits the power from a motor, typically an asynchronous motor or direct current motor, to the shaft of the feeder screw, by means of a reduction gear. Such a type of machine is shown in Figure A appended to the present patent application in which A denotes the motor, B the reduction gear unit and C the connection of the hopper, D the plasticization chamber, and E the filter unit, gear pump and mixer as a whole intended to be connected to the extrusion head (not shown in the figures) .

This mechanical configuration is particularly noisy owing to the high number of revolutions of the motor, the gears of the reduction gear and the presence of fans for air-cooling the motor.

A further drawback of the abovementioned configuration consists in the low efficiency of the reduction gear which also has the disadvantage of being bulky. The abovementioned configuration is difficult to maintain since, for example, in most cases, extraction of the feeder screw from the plasticization chamber requires disassembly of the extrusion head, or removal of the reduction gear and the motor, or also extraction of the feeder screw through the reduction gear, contaminating the latter with plastic material.

In order to overcome, at least partly, these drawbacks, more recently a machine for extruding thermoplastic products has been proposed on the market, which machine is equipped with a motor directly coupled to the shaft of the feeder screw, the reduction gear being no longer necessary. Such a type of machine is described, for example, in the patent EP 1,182,027.

For some years now this configuration has been widely adopted owing to the appearance on the market of motors of the synchronous type with a large number of poles able to transmit a high power also at a low number of revolutions.

The advantage of these motors is that it allows water cooling of the stator which is much more silent than the conventional air cooling systems and that there is a high performance, no longer requiring reduction gears which, in addition to producing noise owing to the intermeshing of the gearwheels,, resulted in a loss of efficiency during transmission of the power. - A -

The machines for extruding thermoplastic products which have these motors are also more compact and lighter than the previous motors.

On the basis of these machines, particularly compact configurations have been developed, such as, for example, the configuration where the motor is at 90° with respect to the shaft of the feeder screw described in the patent

EP 1,574,315.

These machines, although improving, therefore, the performance of the previous machines, have nevertheless also proved to have certain drawbacks.

The mechanical configuration for transmission of the power of these machines envisages the use of a thrust bearing device mounted on the head of the motor or otherwise at least partly arranged inside the latter, in this case making use of the thrust bearings of the said motor (see patent EP 1,182,027).

The hoppers are usually connected to the front end of the feeder screw so that their weight is transmitted at least partly onto the casing of the motor.

Consequently, with these machines also, the maintenance of the feeder screw is particularly complicated and requires, in the event of having to extract the screw from the front of the machine, removal of the extrusion head, the filter, the gear pump and the mixer. These operations involve a not insignificant amount of time and complexity, which increases in the case where there are several extruders.

Alternatively, extraction of the feeder screw from the rear of the machine requires disconnection and temporary supporting of the hoppers and separation of the motor with the thrust bearing device.

Moreover, maintenance of the motor also requires disconnection of the hoppers which bear with their weight at least partially on top of it and are very heavy since they normally mix several materials including virgin material, reject material and the master batch.

It must also be considered that the abovementioned synchronous motors, below identified by the expression commonly used in the sector "torque motor", have somewhat high costs. Therefore, a requirement which exists in the sector for the production of these machines is the possibility of choosing from among several motors of supplier companies, namely offering customers this possibility if it is required to replace a damaged motor with a new one.

At present, the machines present on the market do not offer these possibility and are substantially intrinsically bound by the use of a single motor since the thrust bearing unit is formed integrally with the - ς -

motor or incorporated inside it, such as to inevitably require replacement thereof together with the motor.

Disclosure of the invention

In this situation, the main object of the present invention is therefore that of eliminating the drawbacks of the solutions of the known type mentioned above, by providing a machine for extruding thermoplastic products allowing easy and practical maintenance and therefore ultimately resulting in reduced management costs. Another object of the present invention is to provide a machine for extruding thermoplastic products in which the feeder screw can be easily accessed not only from the front but also from the rear of the machine in order to perform maintenance. Another object of the present invention is to provide a machine for extruding thermoplastic products in which maintenance of the feeder screw and the motor do not require displacement or supporting of the hoppers.

A further object of the present invention is to provide a machine for extruding thermoplastic products which is not obliged to use the motor produced by a single manufacturer.

A further object of the present invention is to provide a machine for extruding thermoplastic products which is simple to produce and operationally entirely reliable .

Brief description of the drawings

The technical features of the invention in accordance with the abovementioned objects may be clearly determined from the contents of the claims reproduced below and the advantages thereof will emerge more clearly in the detailed description which follows, provided with reference to the accompanying drawings which show a purely exemplary and non-limiting embodiment in which: FIG. 1 shows a first overall perspective view of a machine for extruding thermoplastic products according to the present invention;

FIG. 2 shows a second perspective view of the machine according to Figure 1; FIG. 3 shows a perspective view of an enlarged detail of the machine according to Figure 1, relating to a thrust bearing unit;

FIG. 4 shows the detail of Figure 3 with further parts removed so that others may be seen more clearly; ' FIG. 5 shows the detail of Figure 4 with some parts removed so that other parts may be seen more clearly;

FIGS. 6, 7 show two different perspective views of the details according to Figures 4 and 5, respectively;

FIGS. 8, 9 show two further perspective views, split cross-sectionally, of the thrust bearing unit of the machine according to the invention;

FIG. 10 shows a split cross-sectional view of the thrust bearing unit in an enlarged view which includes a portion of a motor and a portion of a plasticization chamber;

FIG. 11 shows a perspective view of the extrusion machine after removal of the thrust bearing unit;

FIG. 12 shows a detail of the thrust bearing unit, relating to an adjustable support for a receiving tank. Detailed description of a preferred example of embodiment With reference to the accompanying drawings 1 denotes overall the machine for extruding thermoplastic products, according to the present invention.

It comprises a support structure 2 for resting on the ground, to which it is rigidly fastened by means of brackets 3 using fixing bolts which can be clearly seen in the first two accompanying figures.

The support structure 2, which is usually made of steel, may be provided with legs 4 or other support means varyingly distributed along the length of the machine 1 in order to take account of the weight of the specific units which form it.

The support structure 2. is provided on top with a plasticization chamber 5 which has an elongated shape and which extends in a longitudinal direction X, also over various metres depending on the type of machine and the injection force which is to be obtained.

The plasticization chamber 5 essentially consists of a hollow steel tube externally supporting heating means covered by an insulated casing 6 and not described in detail in that known per se.

The plasticization chamber 5 has a first end 7 in communication with a tank 70 for receiving the material to be extruded and a second end .8 in communication with an extrusion unit 9 with an associated extrusion head which determines the profile of the extrudate and in particular allows the production of laminated articles, sheets, films, profiles or similar products.

The extrusion unit 9, which does not form the subject of a specific claim, may be preceded in an entirely conventional manner by a filtration unit 10 and by a mixing unit 11 for homogenizing the material, which unit 11 has a gear pump moved via a Cardan shaft 2 by a reduction gear 13 connected to a motor 14. The receiving tray 70 is connected via a mouth 15 to a supply unit generally provided, in a manner known per se, with one or more hoppers with mixing and metering units for one or more plastic materials.

The hopper, which normally mixes several materials such as the virgin material and the reject material or also the master batch, is very heavy and bears with its weight on top of the receiving tank 70.

The plasticization chamber 2 has, coaxially mounted inside it, a feeder screw 16, the peripheral profile of which co-operates with the heated internal surface of the cylindrical chamber 2 so as to feed the material from the receiving tray 70 to the extrusion unit 9.

Usually, the gear pump 11 acts as a pilot for adjusting the revolutions required of the feeder screw 16.

The feeder screw 16 is made to rotate by a torque motor 17 directly at a same number of revolutions.

As mentioned above, the term "torque motor" must be understood as meaning a permanently excited, three-phase current, synchronous motor with a large number of poles, in particular 24-40 poles, which produces a high torque, typically in the range of 50p-14,000 N/m, also with a not particularly high number of revolutions, typically between 100 and 500 revolutions, and is provided with a hollow shaft rotor and is intended to be directly incorporated in the machine structure.

The choice of motor 16 will be dictated by the constructional requirements of the machine 1 and the performance features required for it. The term "torque motor" therefore defines in the sector a precise type of synchronous motor with the performance features of the type described above.

The forces transmitted axially to the feeder screw 16, which are produced as a reaction of the thrust feeding the material, are absorbed by a thrust bearing unit 18.

According to the idea forming the basis of the present invention, the thrust bearing unit 18 is fixed to the support structure 2 between the torque motor 17 and the feeder screw 16 and is provided with a hollow transmission shaft 19 (or sleeve) connected on the one hand to the feeder screw 16 and on the other hand to the shaft 22 of the abovementioηed torque motor 17. As can be seen in Figure 10, the feeder screw 16 is provided with a shaped cylindrical portion 90 which is inserted inside the transmission shaft 19 being coupled thereto by means of key 91.

In greater detail, with particular reference to Figure 9, the annular flange 92 of the shaft of the feeder screw 16 comes into abutment against the end 20 of the transmission shaft 19 of the thrust bearing unit 18.

It is important to note that, in accordance with the present invention, the thrust bearing unit 18 of the shaft of the feeder screw 16 is provided with its own transmission shaft 19 which can be coupled mechanically, and removably if required, to the shaft 22 of the torque motor 17.

Advantageously, therefore, the torque motor 17 may be separated from the rest of the machine 1 for ordinary maintenance, without the need to disconnect the thrust bearing unit 18 and without the need to support temporarily the supply unit with the heavy hoppers.

In addition to maintenance, the torque motor 17 may be replaced with a new one without the need to modify or replace at the same time the thrust bearing unit 18 as well.

The replacement of the torque motor 17 will require simply the provision of a new torque motor with a connection bush 23 precisely calibrated for coupling with the end 21 of the transmission shaft 19 of the thrust bearing unit 18.

This connection bush 23 is fixed to the transmission shaft 19 by means of a key- 93 and to the shaft of the motor 22 for example by means of a plurality of screws (see Figures 10 and 11) .

In greater detail, the thrust bearing unit 18 mentioned above comprises a steel box-shaped body 24 fixed with feet 25 bolted to a support surface 26 of the support structure 2. A thrust bearing 26 is housed inside the box-shaped body 24 and is able to oppose the axial forces transmitted to the transmission shaft 19 by the feeder screw 16 and due to the reaction force exerted by the material on the screw of the feeder screw 16, and one or two centring bearings 27 which are able to support in a centred position the transmission shaft 19 and one of which, for this purpose, is positioned on the motor side and the other one on the plasticization chamber side.

The bearings 26 and 27 are immersed in the oil of a lubrication circuit 29 which extends inside first grooves formed in the box-shaped body 24 which can be seen in Figures 8 and 9 together with the return connection 30, the delivery connection being situated underneath the said box-shaped body 24. Advantageously a cooling circuit 31 may be further envisaged, said circuit extending inside second grooves formed in the support body 24 and visible in Figures 8 and 9 together with the return connection 31, the delivery connection being situated underneath the said box-shaped body 24.

In accordance with a further characteristic feature of the present invention, the machine 1 comprises a support bracket 33 advantageously consisting of a support which can be adjusted by means of a screw 80 and is formed by two rods provided, at one end, with eyelets for adjustable fixing using bolts to the rim 35 and fixed at the other end to the support surface 26 of the support structure 2 by means of a common base-piece 34.

The receiving tank 70 has an annular connecting portion 36 from which there extends a rear rim 35 provided with suitable through-holes for frontal fixing by means of bolting to the thrust bearing unit 18. The rim 35 has a central opening 37 for engagement of the transmission shaft 17 and connection of the second end of the latter to the feeder scf_vew 16.

The abovementioned bracket 33 is able to support, together with the plasticization chamber 5, the supply unit on the support structure 2.

In greater detail, the rim 35 and the annular portion 36 form one piece with the tank 70 for receiving the material from the feeder unit (in the drawings the fixtures and the adjustable support situated underneath can be clearly seen) , which tank 70 also has, fixed thereon, a front rim 38 with through-holes for fixing by means of bolting with an opposite rim 39 integral with the plasticization chamber 5.

The advantages which can achieved by the invention are many and in particular relate to the easy access in order to perform the maintenance of the individual units of the machine 1. 006/000632

- 15 -

As already mentioned above, it is possible to gain access to the torque motor 17 for maintenance or replacement thereof without the need to support the supply unit, as is usually performed with a crane according to the art known hitherto.

Moreover, once the tbrque motor 17 has been separated and displaced, it will be easy to extract the feeder screw 16 from the rear, while keeping mounted the bracket 33 for supporting the supply unit. In this way, it is possible to avoid the complex operations of disassembling the extrusion unit, which are required in most of the machines present nowadays on the market where the feeder screw is extracted from the front of the machine . Moreover, the fact that the thrust bearing unit 18 has been separated from the_, torque motor 17 means that the machine 1 according to the present invention can be associated in a versatile manner with all the torque motors present on the market, it being possible to replace in fact the torque motor 17 while maintaining the thrust bearing unit 18, with considerable savings in cost. Moreover, since the motor is a body separate from the thrust bearing unit, it is no longer subject to any axial thrust of the feeder screw, it being easier to design the size of its bearings and being less subject to wear or breakage.

Owing to the presence of the bracket 33 the plasticization chamber and the supply unit may be supported also with the torque motor 17 separated so as to allow maintenance of the feeder screw.

The invention therefore achieves the predefined objects.

Obviously it may assume, in its practical embodiment, also forms and configurations different from that illustrated above, without thereby departing from the present scope of protection.

Moreover, all the details may be replaced by technically equivalent parts and the sizes, forms and the materials used may be of any nature according to requirements.

Claims

1. Machine for extruding thermoplastic products comprising:

- a support structure resting on the ground; - a plasticization chamber with an elongated form mounted on said support structure;

- a supply unit provided with at least one hopper associated with a first end of said plasticization chamber so as to introduce the material to be plasticized inside it;

- an extrusion unit wiirh an associated extrusion head for the production of products, associated with the second end of said plasticization chamber;

- a feeder screw able to cause feeding of said material inside said plasticization chamber from said hopper to said extrusion head;

- a torque motor connected to the shaft of said feeder screw so as to force it to rotate at the same number of revolutions as the torque motor; - a thrust bearing unit able to oppose the axial thrust imparted by the rotation of the feeder screw to the motor; characterized in that said thrust bearing unit is fixed to said support structure, is mechanically arranged between said torque motor and said feeder screw and is provided with a transmission shaft connected on the one hand to said feeder screw and on the other hand to the shaft of said torque motor. t

2. Machine for extruding thermoplastic products according to Claim 1, characterized in that said thrust bearing unit comprises a box-shaped body able to support said transmission shaft by means of at least one thrust bearing and provided with at least one first foot for fixing to said support structure.

3. Machine for extruding thermoplastic products according to Claim 2, characterized in that said thrust bearing unit comprises at least one further bearing for centring and supporting said transmission shaft.

4. Machine for extruding thermoplastic products according to Claim 2, characterized in that said thrust bearing unit comprises at least one circuit for lubricating said thrust bearing.

5. Machine for extruding thermoplastic products according to Claim 2, characterized in that said thrust bearing unit comprises at least one cooling circuit.

6. Machine for extruding thermoplastic products according to Claim 2, characterized in that it comprises a support bracket fixed to the support structure and to a tray for receiving the material from said supply unit so as to support at least partially said supply unit on said support structure.

7. Machine for extruding thermoplastic products according to Claim 6, characterized in that said receiving tray has, fixed thereon, a rear rim provided with through-holes for fixing by means of bolting to said thrust bearing unit and a front rim provided with through-holes for fixing by means of bolting to said plasticization chamber.