GB1561589A - Injection-mouldingapparatus and method - Google Patents

Description

PATENT SPECIFICATION

( 11) Ct E ( 21) Application No 50565/76 ( 22) Filed 3 Dec 1976 X ( 31) Convention Application No.

tn 2554269 ( 32) Filed 3 Dec 1975 in 0 e 33) Fed Rep of Germany (DE) In ( 44) Complete Specification published 27 Feb 1980 ( 51) INT CL 3 B 29 F 1/03 1/08 ( 52) Index at acceptance B 5 A 2 A 4 D 2 Q 1 X 3 D 3 3 D 7 T 14 V ( 54) INJECTION-MOULDING APPARATUS AND METHOD ( 71) We, DEMAG KUNSTSTOFFTECHNIK ZWEIGNIEDERLASSUNG DER DEMAG AKTIENGESELLSCHAFT, a German Body Corporate of, Rennweg 37, D-8500 Nurnberg, West Germany, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:This invention relates to injectionmoulding apparatus An injection-moulding machine having an injection cylinder and a bore leading to the injection nozzle, the bore being narrowed to define a restricted flow channel, at least locally, during the injection process, has been proposed in British Patent Specification No 1514541.

In this proposal, the cross-section of the injection nozzle bore, or at least the rehstricted flow channel therein through which the plastics material is forced during the injection process, is variable in order variably to introduce shear energy and frictional heat into the plastics material.

It is an object of the present invention to provide an injection-moulding machine which can give a more advantageous flow of plastics material both in, and downstream of, the restricted flow channel.

According to the present invention, therefore, there is provided injection moulding apparatus for use with plastics material having a bore leading to an injection nozzle, an obstructing element and means to position the element in the bore to partially obstruct the bore and thereby to define a flow channel for the plastics material with substantially smaller cross section than the bore, the axial extent of the element within the bore being variable thereby to control to a predetermined value the flow impedance to plastics material flowing through the restricted flow channel independently of the channel cross section.

The invention also provides injection moulding apparatus for use with plastics material having a cylindrical bore leading to an injection nozzle, an obstructing element and means to position the element 50 in the bore to partially obstruct the bore and thereby to define a flow channel for the plastics material with substantially smaller cross section than the bore, the axial extent of the element within the bore 55 being variable thereby to control to a predetermined value the impedance to the flow of plastics material flowing through the restricted flow channel.

A further aspect of the invention provides 60 a method of injection moulding comprising conveying plastics material to an injection nozzle along a bore, obstructing the bore to define a flow channel of restricted cross sectional area which imparts flow imped 65 ance on the plastics material flowing therethrough, and adjusting the position of the obstruction in the bore to select an appropriate length for the said flow channel which controls the flow impedance exerted on the 70 plastics material flowing through the channel independently of the cross sectional area of the channel.

As a result, the magnitude of the shear energy introduced into the plastics material 75 can be controlled by a change in the length of the restricted flow channel in the direction of flow of the plastics material Whilst achieving essentially the same effect as before, the flow of the plastics material in 80 and near the restricted flow channel tends to be disturbed less, and dead spaces upstream of the restricted flow channel are either avoided or, at the very least, not increased as a result of varying the channel 85 length.

Preferably, the obstructing element is an elongate member, such as a needle, by which term it will be hereinafter referred to, which is axially movable in the injection 90 1 561 589 1 561 589 nozzle bore By this means it is possible to produce, for example, an annular restricted flow channel the length of which is determined by a greater or lesser penetration of the needle into the bore An advantage of this arrangement is that no sealing problems occur around the obstructing element, i.e the needle, which defines the channel because the needle can be mounted in the nozzle head or within an injection cylinder which is part of, or in use associated with, the apparatus, for example on the feed screw of the cylinder It is also possible to constrict the injection nozzle bore on the orifice side by providing the bore with a portion of reduced cross section adjacent the orifice of the nozzle, there being a step between that portion and the remainder of the bore, in such a way that the reduced cross section portion can be closed by the needle Preferably the step matches the cross-section of the needle With this arrangement the needle has two functions, namely to define the variable-length restricted flow channel during the injection process and to seal the injection nozzle bore after the injection operation A further function may be added if, in addition and as is preferred, the needle can be introduced with a close sliding fit into the reduced portion of the bore, because it is then possible, during the follow-up pressure period after injection, to apply follow-up pressure to the plastics material contained in the mould by using the needle as a piston This also makes it possible to dispense with a backflow valve, because the needle itself serves as such a valve Accordingly, the plastication of material for the next injection operation can be commenced during a follow-up pressure period.

It is in principle known that vibrational impulses applied to plasticised material facilitate moulding and make it possible to' influence the degree of orientation of the plastics and hence the properties of the product, but hitherto this principle has hardly ever been utilised for technical reasons For instance if a pressure pulsation is applied hydraulically or mechanically via an injection cylinder, as has been proposed, the pulsation action at the desired point, namely in the mould, is only slight, because of pressure losses The alternative of inducing the pulsation directly at the mould entails considerable expense and technical difficulty.

The apparatus of the present invention is well suited to avoid this problem because the length of the restricted flow channel can be periodically variable and means may be provided for this purpose, for instance by axially vibrating the needle The needle can thus be moved periodically in the direction of flow and counter to the direction of flow, during the injection process land/or the follow-up pressure period particularly if the needle is a sliding fit in the reduced portion,l, so that the gap is periodically lengthened and shortened and pressure 70 vibrations are produced in the material in the direction of flow, and these propagate into the mould This allows application of pulsations in the nozzle region, which is the most effective area for the purpose and 75 results in the same rheological advantage as those which have been explained above in conjunction with the non-periodic variation of the gap length.

Control means may be provided to vary 80 the length of the restricted flow channel as a function of injection moulding parameters, for example the screw stroke, the pressure and the temperature of the plastics material in the mould If pulsations are to be intro 85 duced into the plastics, it is possible to control the frequency and/or the amplitude of the periodic variations in length of the restricted flow channel as a function of these or other injection parameters For 90 this purpose the needle can be coupled, directly or indirectly, with a vibration generator in order to generate axial variations of the needle, the generator being controlled in accordance with signals dependent 95 upon the parameters mentioned However, the vibration generator can also operate independently of any parameters of the injection process.

In order that the invention may be more 100 clearly understood, the following description is given, merely by way of example, with reference to' the accompanying drawings, in which:Figure 1 shows a schematic longitudinal 105 section through the nozzle region of an injection cylinder, with a device for adjusting a needle located in the injection nozzle bore, the section only being continued partially above the centre line in the 110 regidn of the adjustment device, and Figure 2 shows a section, analogous to Figure 1, through a modified embodiment.

As shown in Figure 1, the front end of an injection cylinder 1, only partially shown, 115 of an injection-moulding machine carries an insert 2 for holding and guiding a nozzle needle 3 A nozzle head 4 is screwed to the insert 2 and has within it a nozzle bore 5 and an accumulation chamber 6 At 7, near 120 the orifice of the nozzle, there is a step to the left of which the nozzle bore 5 has a smaller diameter The step 7 defines a conical seat for the nozzle needle 3, the tip 8 of which is of a corresponding shape At 125 the orifice of the nozzle bore 5, the nozzle head 4 can be pressed against a mould 9, which is only shown schematically.

Between the accumulation chamber 6 and the conical step 7 the nozzle bore 5 is recti 130 1 561 589 linear The nozzle needle 3 has a smaller diameter than bore 5 and projects into it to form therewith an axially extending annular flow restricting channel 10, the length of which can be altered by moving the nozzle needle 3, by means of an adjustment device indicated in general at 11, so that it extends to different extents into the nozzle bore 5 In this way, the length of the annular gap may be varied between, for instance 1 and 5 mm.

The adjustment device 11 is of generally known type, being similar to devices for the hydraulic actuation of the needles of needle-seal nozzles One difference, however, is the possibility, provided in the present case, of controlling the stroke of the nozzle needle 3 not only between a closed position and an open position but also as desired, between these two terminal positions An infinitely variable adjustment is preferred To move the nozzle needle 3, a slide ring 21, movable on the outer surface of the injection cylinder 1, is provided, which acts, via a yoke 22, on the nozzle needle 3 which is firmly coupled to the yoke 22 or merely rests against the yoke.

The yoke 22 can be moved within a radial bore of the insert 2, in the axial direction of the injection cylinder The nozzle needle 3 can slide, in a leakproof manner, in a bore 23 of the insert 2 The insert 2 contains axial passages 24 for plastics material, which in use is transported by a screw, or a piston (not shown) A forked lever 25 is connected at one end to the slide ring 21 and is pivotally mounted on the injection cylinder 1 and can be actuated by a hydraulic cylinder 26 acting as its other end.

A piston 27 which is slidable in the cylinder 26 can be subjected to a pressure medium, on either side, from a pump P The stroke of piston 27 can be limited by a stop 28, which is adjustable relative to the hydraulic cylinder 26, in the axial direction.

This stroke defines the maximum length of the annular gap 10 The position of the stop 28 can be adjusted as a function of the parameters relating to the injection sequence, for example the pressure and/or the temperature of the plastics material in the accumulation chamber 6 or in the mould 9, and also as a function of the stroke of the screw or piston An appropriate hydraulic regulating device is described, for example, in Figure 2 of the initially mentined British Patent Specification No.

1514541 An actuating device, which is not shown in the drawing can be provided for appropriate adjustment of the stop 28.

The pressure medium, which is applied to the piston 27, can be subjected to pulses, either directly by means of the pump P or by an impulse generator which generates pressure vibrations in the hydraulic cylinder 26.

Figure 2 shows a somewhat modified embodiment of apparatus of the invention in which the nozzle bore is different Like reference numerals are used to indicate like 70 parts compared to Figure 1 In Figure 2, the nozzle bore, starting from the accumulation chamber 6 is initially rectilinear and has a constant cross-section for a first portion 5 ' terminating at a conical shoulder 15, after 75 which there is a second rectilinear portion " of smaller diameter At the end of this second portion 5 " a shoulder 7 as in Figure 1, which acts as a seal seat for the nozzle needle 3 is provided The first portion 5 ' 80 of the nozzle bore 5 is of such diameter that, as in the embodiment according to Figure 1, an annular restricted flow channel is formed between the nozzle needle 3 which extends into the nozzle bore, and the 85 wall of the portion 5 ' The section portion " however is of the same diameter as the nozzle needle 3, so that the needle can be introduced into the portion 5 " in the manner of a piston to seal the portion in a slidable 90 leakproof manner.

In this embodiment, the length of the annular restricted flow channel 10 can be adjusted in the same manner as has been explained in connection with Figure 1 95 Furthermore, as indicated by the doubleheaded arrow in the nozzle needle 3, a pulsating axial movement of the nozzle needle 3 can be employed In addition, it is possible with this embodiment, at the end of 100 the injection sequence to exert a follow-up pressure, which may also be pulsating, on the plastics material contained in the mould 9, by means of the nozzle needle being introduced into the section 5 " of the nozzle 105 bore This follow-up pressure can be regulated as a function of the injection parameters, for example of the internal pressure in the mould When the nozzle needle 3, as a result of penetrating into the portion 5 " 110 of the nozzle bore, seals the bore from the space behind it, the plasticisation of further plastics material can be carried out in the injectiion cylinder 1, since the nozzle needle 3 serves as a non-return valve 115 Obviously the length of the channel 10 is in each case decided by the nature and viscosity of the plastics material and by its throughput If the gap length is regulated according to the pressure and/or the tem 120 perature of the material in the mould, these parameters must accordingly be predetermined It is possible for instance to set the gap to width of from 0 1 to 5 mm and lengths of from 1 to 50 mm Despite the 125 Figures hereto, it is in no way essential to maintain a constant gap cross-section over the length of the gap The cross-sectional shape is also optional and can be varied, for instance by rotating a needle which is 130 1 561 589 not circular in cross section For example, by appropriately designing the nozzle bore and the nozzle needle, a gap of rectangular cross-section can be produced, and would be suitable.

Equally, the frequency and amplitude of any induced pulsations can be decided depending on the particular plastics material used The frequency is advantageously between 1 and 50 cycles/ second Periodic changes in length of the gap can be brought about, as desired by movement of either one or both of the walls which define the gap; and mechanical, hydraulic, pneumatic or electromechanical devices may be employed for this purpose.

Claims (17)

WHAT WE CLAIM IS:-

1 Injection-moulding apparatus for use with plastics material having a bore leading to an injection nozzle, an obstructing element and means to position the element in the bore to partially obstruct the bore and thereby to define a flow channel for the plastics material with substantially smaller cross section than the bore, the axial extent of the element within the bore being variable thereby to control to a predetermined value the flow impedance to plastics material flowing through the restricted flow channel independently of the channel cross section.

2 Injection-moulding apparatus for use with plastics material having a cylindrical bore leading to an injection nozzle, an obstructing element and means to position the element in the bore to partially obstruct the bore and thereby to define a flow channel for the plastics material with substantially smaller cross section than the bore, the axial extent of the element within the bore being variable thereby to control to a predetermined value the impedance to the flow of plastics material flowing through the restricted flow channel.

3 Injection-moulding apparatus according to claim 1 or 2, wherein said flow channel is annular.

4 Injection-moulding apparatus according to claim 1, 2 or 3, wherein said obstructing element includes an elongate member which is axially movable in the bore.

Injection-moulding apparatus according to claim 4, wherein the bore has a portion of reduced cross section adjacent the orifice of the nozzle, the reduced crosssection portion being such that it can be closed by the elongate member.

6 Injection-moulding apparatus according to claim 5, wherein the elongate member is insertable into the reduced cross section portion, and is a close sliding fit therein.

7 Injection-moulding apparatus according to any one of claims 1 to 6, including means for periodically varying the length of said flow channel 65

8 Injection-moulding apparatus according to claim 7 when appendant to any one of claims 4 to 6, wherein the elongate member is coupled to a vibration generator for generating axial vibrations of the mem 70 ber.

9 Injection-moulding apparatus according to one of claims 1 to 8, including means to control the length of said flow channel as a function of injection moulding para 75 meters obtaining.

Injection-moulding apparatus according to, claim 7 or 8 including control means whereby the frequency and/or amplitude of the periodic variations in length of said 80 flow channel can be controlled as a function of the injection parameters.

11 Injection-moulding apparatus according to one of claims 1 to 10, wherein the cross section of the flow channel varies along 85 the length of the channel.

12 Injection-moulding apparatus according to one of claims 1 to 11, including means for varying the shape of the cross section of the said flow channel 90

13 Apparatus according to any preceding claim, wherein said obstructing element is mounted in an injection cylinder which forms part of the apparatus.

14 Apparatus according to claim 13, 95 wherein the obstructing element is connected to a movable yoke.

Injection-moulding apparatus constructed and arranged substantially as hereinbefore described with reference to and as 100 illustrated in Figure 1 of the accompanying drawings.

16 Injection-moulding apparatus according to claim 15 modified substantially as hereinbefore described with reference to and 105 as illustrated in Figure 2 of the accompanying drawings.

17 A method of injection-moulding comprising conveying plastics material to an injection nozzle along a bore, obstructing 110 the bore to define a flow channel of restricted cross sectional area which imparts flow impedance on the plastics material flowing therethrough, and adjusting the position of the obstruction in the bore to 115 select an appropriate length for the said flow channel which controls the flow impedance exerted on the plastics material flowing through the channel independently of the cross sectional area of the channel 120 18 A method according to claim 17, and substantially as hereinbefore described.

J A KEMP & CO, Chartered Patent Agents, 14 South Square, Gray's Inn, London WC 1 R 5 EU.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd, Berwick-upon-Tweed, 1980 Published at the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained