GB2098918A - An injection assembly for an injection moulding machine - Google Patents

Abstract

The assembly comprises a hydraulic unit 19, a plasticiser unit having a plasticiser cylinder 16 and a worm located therein, an injection unit including an injection cylinder 9 and an injection nozzle 39, a plasticiser drive 36 and a support construction for these components. The support construction includes a base 34 and a support 18 to which the base 34 is detachably secured and which is resistant to bending and torsion. The plasticiser drive 36, which comprises a motor 1, a gearing 2 and a coupling 3 with an intermediate shaft, is rigidly disposed on the base 34. The injection cylinder 9 and the plasticiser cylinder 16 are disposed so as to be axially displaceable on the support 18 and are connected to the plasticiser drive 36 via a shaft-hub connection. <IMAGE>

Description

SPECIFICATION Injection assembly for injection moulding machines This invention relates to the arrangement of the injection assembly, substantially comprising a hydraulic unit, a plasticiser unit having a plasticiser cylinder and a worm, an injection unit including an injection cylinder and an injection nozzle, a plasticiser drive and a support construction for the above-mentioned components.

The invention is preferably for use with large injection moulding machines for the processing of plastics and elastomeric materials.

In order to ensure that the moving components of the injection unit operate with an admissibly low degree of wear and that the forces and torques of reaction, which balance the operating forces and the weight of the components, are transferred, it is necessary to produce an accurately aligned, stable connection between the three components comprising the plasticiser cylinder, the injection cylinder and the plasticiser drive. In order to provide a thermal separation between the hot nozzle of the injection unit and the cooled injection moulding of the machine, it is usual for the injection unit to effect a reciprocating (forward and return) movement with a short stroke.

For the purposes of assembly, it is moreover necessary to return the end of the plasticiser cylinder with the injection nozzle from the fixed mould clamping plate. This requires a reciprocating movement of the plasticiser cylinder with a large stroke.

For this reason it is necessary to construct the injection unit as a unit which is displaceable and as compact as possible.

In the case of some technical arrangements the plasticiser drive is rigidly connected to the piston rod of the injection cylinder, so that the latter is moved both during the displacement of the piston during injection moulding and also during the reciprocating movement of the injection nozzle.

Different embodiments of this arrangement are disclosed in the German Offenlegungsschrift 2 227 133 and 2 353 250 and in the German Utility Model 7 235 519. However, these solutions are disadvantageous in that during each displacement of the feed worm and the injection assembly the plasticiser drive is also displaced.

In the case of other technical solutions the plasticiser drive is rigidly connected to the housing of the injection cylinder and the rotary movement is transmitted to the worm via the piston rod or a particular shaft or hollow shaft by means of an axially displaceable shaft-hub connection. Various embodiments of this solution are disclosed in the German Auslegeschriften 1 812 961 and 1 908 530, and in the German Utility Models 7 135 155, 7 247 800 and 7 343 372. Although in these solutions the displacement of the plasticiser drive is stopped during the displacement of the worm, it is still required for the reciprocating movement.

Moreover, the German Democratic Patent Application WP B29F/223 312 is also known as a prior application. In this it is proposed to fasten the hydraulic drive unit together with the plasticiser unit, the injection cylinder and the worm drive motor on a frame as an integrated unit. This frame is disposed in a displaceable and pivotable manner as a unit with respect to the support by means of a sliding guide. Although essential pressure ducts may advantageously be embodied in a rigid manner in this way, in this solution the plasticiser drive again forms an integral unit with the injection cylinder so that both are displaced together.

This is a substantial drawback in the same way as in the previously mentioned arrangements.

The common drawbacks of all the solutions considered lie in the fact that the necessity for the displacement of the plasticiser drive, in particular in the case of large injection moulding machines, is disadvantageous for the following reasons.

In order to satisfy the above-mentioned requirements with respect to the injection assembly (stable, aligned connections of the components), in the case of the known arrangements all the components moving together must form a compact injection unit. This leads to high costs for materials. The drive must be fitted as an integral component of the injection assembly which requires a special construction which, in particular in the case of large injection moulding machines which are only built in small numbers, is costly with respect to the use of standard gearings and motors.

Exchange or modification of the plasticiser drive using a mechanical assembly principle is complicated and costly. As the injection cylinder is the central component of an integrated assembly it is accessible with difficulty. Conventional spur gearings which often represent a considerable source of noise in units of this type transfer the noise to other components as a result of the compact construction so that secondary measures for decreasing noise levels are difficult. The heavy weight and the large dimensions of the various components require high costs in terms of construction and materials for the construction of the sliding guide.

It is an object of the invention to provide an injection assembly characterised by low material, constructional and manufacturing costs which may be effectively used as a result of its variability and which offers optimum possibilities for secondary control of noise.

The invention aims at minimizing the displaceable components within the injection assembly and therefore at enabling the use of the mechanical assembly principle, so that an exchange of modification of the plasticiser drive by the use of standard gearings and motors is possible at any time and so that the units of the injection assembly are readily accessible for assembly and repair purposes and for secondary noise control.

Accordingly, the present invention consists in an injection assembly for an injection moulding machine, comprising a hydraulic unit, a plasticiser unit having a plasticiser cylinder and a worm, an injection unit including an injection cylinder and an injection nozzle, a plasticiser drive and a support construction for the above-mentioned components, wherein the support construction comprises a base and a support to which said base is detachably secured and which is resistant to bending and torsion, the plasticiser drive comprises a motor, a gearing and a coupling with an intermediate shaft and is rigidly disposed on said base, whilst the injection cylinder and the plasticiser cylinder are disposed so as to be axially displaceable over the length of a maximum stroke hdon the support and are connected via a shafthub connection to the plasticiser drive.

Advantageously, the stroke of the shaft-hub connection corresponds to the maximum possible reciprocating movement of the plasticiser cylinder and the injection cylinder, which are disposed displaceably on the support by means of travelling cylinders, and is greater than the maximum injection stroke of the worm in the plasticiser cylinder.

Preferably, the worm is connected to the injection cylinder via a further coupling and a sleeve projects through the injection cylinder, said sleeve has one end secured to the coupling of the worm and the other end connected to the hub of the shaft-hub connection and is displaceably disposed with respect to the intermediate shaft by the stroke (hd).

Conveniently, said support is box-shaped or tubular and the displaceable injection cylinder, the displaceable plasticiser cylinder and a stationary bearing for the intermediate shaft are supported on said support, and wherein the interior of the box-shaped or tubular support is completely or partly used as an oil container.

Preferably, the injection cylinder has two end covers and the plasticiser cylinder has a holder and a support, the support surfaces of said cylinder covers of the holder and the support of the plasticiser cylinder are aligned horizontally in a plane and form a sliding guide which comprises two guide rails respectively having two sliding surfaces disposed in the shape of a V, one of which surfaces is disposed horizontally.

So that a play-free construction is possible, one of the sliding surfaces is preferably pre-stressed by means of a plate spring or the like.

The guide rails preferably form a unit together with a plate and are constructed as a detachable cover for the oil container.

Advantageously, in order to supply the two pressure chambers of the injection cylinder with hydraulic fluid two telescopic tubes having respective connection blocks are disposed parallel to the axis of the injection nozzle and the respective blocks are directly flanged to the respective cylinder covers of the injection cylinder, a further stationary connection block being rigidly connected to the support.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which:~ Fig. 1 is a side view of the injection unit; Fig. 2 is a top view of the injection unit; Fig. 3 is a cross-section on the line A-A of Fig. and Fig. 4 is a cross-section on the line B-B of Fig. 2.

Figs. 1 to 4 show a possible embodiment of the injection unit of the invention, the plasticiser drive 36 of which comprises, for example, a variable speed motor 1 and a commercially available spur gearing 2 with base fastening.

In accordance with the invention the plasticiser drive 36 is arranged at the end of the injection assembly on a separate support 34 in order to enable simple exchange of the drive. The plasticiser cylinder 16 and the injection cylinder 9 are mounted on a box-shaped or tubular support 18. The support 18 is fixed to the machine base 20. The cross-section of the support 1 8 is dimensioned in such a way that it is capable of receiving the forces and torques of reaction of the operating forces and the mass forces of the components disposed thereon and is deformed to such a slight extent that the requirement of exact alignment of the components of the injection assembly is ensured. With respect to the transfer of the torque of reaction of the torque of the plasticiser drive 36 from the support 18 to the foundation 34, the latter is secured in a detachable manner to the support 18.As a result of this arrangement of the supporting components the injection assembly, substantially comprising the plasticiser cylinder 1 6, the injection cylinder 9 and the plasticiser drive 36, may be embodied using an open method of construction which is economic in terms of materials and readily accessible during assembly work. Only the force of reaction of the injection force is transmitted directly to the injection cylinder 9 from the cylinder holder 1 5 of the plasticiser cylinder 16 vis tie rods 42. The support 18 is embodied in the shape of a box up to the zone in which the cylinder holder 15 is located. As the support 18 must have a large cross-section to provide the necessary rigidity, the hollow chamber provided in this way may be used as an oil tank 26. The zone of the support up to the cylinder support 17 is formed with an open U-shaped profile which tapers towards the end.

Between the fixed plasticiser drive 36 and the displaceable injection cylinder 9 there is disposed an axially displaceable shaft-hub connection 37 (Fig. 4) for transmitting the rotary movement of the plasticiser drive 36 to the worm 21 during simultaneous axial displacement of the worm with respect to the drive 36 on one hand as a result of the reciprocating movement (forward and return) of the plasticiser and injection cylinders 1 6 and 9 and, on the other hand, as a result of the displacement of the worm 21 in the plasticiser cylinder 16. The axially displaceable shaft-hub connection 37 comprises a profiled intermediate shaft 25, for example with involute teeth and a matching hub 24.Within the injection cylinder 9 there is disposed a sleeve 22 one of whose ends ius fastened to the clutch 14 of the worm 21, and whose other end is fastened to the hub 24, 24' of the displaceable shaft-hub connection 37. The sleeve 22 projects through the cylinder cover 11 of the injection cylinder 9 adjacent the coupling 14 and is mounted in said cover so as to be rotatable and axially displaceable and outwardly sealed. The sleeve 22 receives the annular piston 23 rotating therewith which is held by a tubular piston rod 13.

It is necessary to produce the internal profile of the hub 24, 24' with accuracy and subsequently to connect the hub 24 with the sleeve 22 without distortion and in exact axial alignment. An adhesive or solder connection or a press fit is therefore preferably provided for the connection of the sleeve 22 and the hub 24, 24'. The connection of the sleeve 22 to the coupling 14 of the worm 21 is effected in a similar manner.

The intermediate shaft 25 of the axially displaceable shaft-hub connection 37 is supported at the end facing the drive by a support bearing 4 which also prevents axial displacement of the intermediate shaft 25. The bearing 4 is rigidly connected to the support 18 and is constructed in such a way that operation of the shaft-hub connection 37 with an admissibly low degree of wear is ensured. The intermediate shaft 25 is connected to the plasticiser drive 36 by means of a conventional, if possible standardised, readily detachable coupling 3. The coupling 3 should, moreover, enable a certain axial displacement. As a result of the provision of the support bearing 4 and the coupling 3, the plasticiser drive 36 may be readily detached, has no particular requirements in terms of accuracy during assembly and may be constructed in accordance with various embodiments.

The particular advantage of the abovedescribed arrangement of the displaceable shafthub connection 37 lies in the fact that its stroke is dimensioned to be as large as the greater of the two strokes, either the stroke of the reciprocating movement of the injection nozzle 39 or the stroke of the worm 21 in the plasticiser cylinder 1 6, the first mentioned stroke generally being the greater.

In this way it is possible to embody both stroke movements in accordance with technical requirements relating to processing and assembly on the machine without additional component lengths.

The plasticiser cylinder 16 and the injection cylinder 9 are connected to the support 18 via a sliding guide in order to ensure the reciprocating movement. This sliding guide is subject to high accuracy requirements, as the exact alignment of the moving components of the injection assembly and therefore its reliable operation are dependent on these requirements. For this reason this connection is embodied as a clamped and thus play-free sliding guide. This guide preferably comprises two guide rails 30 each having two sliding surfaces 29a and 29b arranged in the shape of a V, and of which the surface 29a is disposed horizontally. A support therefore comprises four sliding surfaces, three of which are arranged in a rigid manner and one is arranged in a resiliently pre-stressed manner, so that spacing changes resulting from expansion due to temperature are compensated.The pre-stressing is provided by a plate spring 27.

The displacement of the entire injection unit on the sliding guide with respect to the support 18 in order to ensure the reciprocating movement of the injection nozzle 39 required during operation of the moulding machine and for assembly purposes is provided in a known manner using conventional travelling cylinders 40.

If the support 1 8 is provided as an oil container 26 it must be provided with a large aperture. For this purpose the plate 28 with the two guide rails 30 is provided as a cover which may be unscrewed. In this respect it is necessary for the sealing surface 41 of the oil container 26 to be produced so as to be as regular as required for the accuracy of the sliding guide.

Moreover, the accuracy of the spacing between the horizontal sliding surfaces 29a and the sealing surface 41 of the cover 28 must also correspond to the accuracy of the guide.

In order to achieve accurate alignment of the components during assembly, adjustment devices are provided on the individual sliding surfaces 29a and 29b.

The simplest possibility of orientating the dlsplaceable components with respect to one another lies in interposing compensating plates between the support elements, for example the cylinder holder 15 (Fig.3) and the sliding surfaces 29e, 29b fastened thereon.

The alignment of the entire injection assembly with respect to the mould closure unit (not shown) is effected via mutually displaceable wedges 31, 32 under the feet of the support 1 8.

In order to supply the displaceable injection cylinder 9 with hydraulic fluid, two telescopic tubes 7, 8 are disposed parallel to the injection axis adjacent to the injection cylinder 9 on the side on which the hydraulic unit 19 is located. In this respect movable connection blocks 5 and 10 are directly flanged on the respective covers 6 and 11 of the injection cylinder 9. The stationary connection block 12 to the hydraulic unit 19 is rigidly connected to the stationary support 18 via a carrier 38. This results in an arrangement which is economic in terms of space with short ducts.

The mode of operation of the arrangement of the invention is described briefly as follows: In the operating condition the plasticiser cylinder 1 6 together with the injection cylinder 9 is displaced (to the right as viewed in Figs. 1 and 2) by the travelling cylinders 40 in the direction of the mould closure unit (not shown). They only effect a slight displacement during the forward and return movement of the injection nozzle 39 for the thermal separation of the plasticiser cylinder 16 from the injection mould. In this condition the stroke hd (Fig. 4) of the displaceable shaft-hub connection 37 enables the displacement of the worm 21 during plasticising and injection.If the plasticiser cylinder 16 6 and the injection cylinder 9 are to be completely removed from the mould closure unit for purposes of assembly, the worm 21 is in the first instance brought into the forward position in the plasticiser cylinder 16.

Consequently the stroke hd of the displaceable shaft-hub connection 37 is completely available for the return of the plasticiser cylinder 1 6 and the injection cylinder 9. In the completely returned position there is no longer any possibility of displacement of the worm 21 in this plasticiser cylinder 16 which is also unnecessary. In the partially returned position the displaceability of the worm 21 in the plasticiser cylinder 16 is completely maintained as long as: h=hd-hs where: h = the return path already travelled hd = the stroke of the displaceable shaft-hub connection 37 hs = the maximum stroke of the worm 21 in the plasticiser cylinder 16.

Consequently the further the plasticiser cylinder 1 6 is then returned, the greater the restriction of the displaceability of the worm 21. According to the position of the plasticiser cylinder 1 6 in the returned condition, the injection assembly is therefore completely or partially operational for testing.

Claims (9)

1. An injection assembly for an injection moulding machine, comprising a hydraulic unit, a plasticiser unit having a plasticiser cylinder and a worm, an injection unit including an injection cylinder and an injection nozzle, a plasticiser drive and a support construction for the above mentioned components, wherein the support construction comprises a base and a support to which said base is detachably secured and which is resistant to bending and torsion, the plasticiser drive comprises a motor, a gearing and a coupling with an intermediate shaft and is rigidly disposed on said base, whilst the injection cylinder and the plasticiser cylinder are disposed so as to be axially displaceable over the length of a maximum stroke hdon the support and are connected via a shafthub connection to the plasticiser drive.

2. An assembly as claimed in claim 1, wherein the stroke hdof the shaft-hub connection corresponds to the maximum possible reciprocating movement of the plasticiser cylinder and the injection cylinder, which are disposed displaceably on the support by means of travelling cylinders, and is greater than the maximum injection stroke hs of the worm in the plasticiser cylinder.

3. An assembly as claimed in claim 1, wherein the worm is connected to the injection cylinder via a further coupling and a sleeve projects through the injection cylinder, said sleeve has one end secured to the coupling of the worm and the other end connected to the hub of the shaft-hub connection and is displaceably disposed with respect to the intermediate shaft by the stroke (hd).

4. An assembly as claimed in claim 1, wherein said support is box-shaped or tubular and the displaceable injection cylinder, the displaceable plasticiser cylinder and a stationary bearing for the intermediate shaft are supported on said support, and wherein the interior of the box-shaped or tubular support is completely or partly used as an oil container.

5. An assembly as claimed in claim 1, wherein the injection cylinder has two end covers and the plasticiser cylinder has a holder and a support, the support surfaces of said cylinder covers of the holder and the support of the plasticiser cylinder are aligned horizontally in a plane and form a sliding guide which comprises two guide rails respectively having two sliding surfaces disposed in the shape of a V. one of which surfaces is disposed horizontally.

6. An assembly as claimed in claim 5, wherein one of the two sliding surfaces is pre-stressed by means of plate springs.

7. An assembly as claimed in claim 5 or 6, wherein said guide rails are connected to a plate which together with the guide rails is constructed as a cover for the oil container and which is unscrewable.

8. An assembly as claimed in any of claims 5 to 7, wherein in order to supply the two pressure chambers of the injection cylinder with hydraulic fluid two telescopic tubes having respective connection blocks are disposed parallel to the axis of the injection nozzle and wherein the respective connection blocks are directly flanged to the respective cylinder covers of the injection cylinder, a further stationary connection block being rigidly connected to the support.

9. An injection assembly for an injection machine, substantially as herein described with reference to and as shown in the accompanying drawings.