IL43040A - Process and apparatus for injection moulding of plastic pipe fittings - Google Patents

Abstract

1443313 Injection moulds KUNSTOFFWERK Gebr ANGER GmbH & CO 21 Aug 1973 [25 May 1973] 05500/76 Divided out of 1442824 Heading B5A An injection mould core 1 is provided with magnetic holding means 2 ... 5 embedded therein for detachably holding at least one core element 10a ... 10d mounted on the core to define a recess in the moulded article. As shown, a plurality of core elements 10a ... 10d are mounted on the core so as to form a collar which may be used to form an internal annular recess in a moulded pipe or container. The magnetic holding means may comprise at least one electromagnet and/or at least one permanent magnet. The magnets may be received in insulating sleeves 6 ... 9. [GB1443313A]

Description

The present invention relates to a process and apparatus for the injection moulding of articles.

The production of fittings from synthetic materials by an injection moulding process is known as such. Such fittings, for example branch connections, T -pieces or the like are injection moulded in practically any required nominal width for pressureless pipelines of the most varying synthetic materials. Fittings are also produced by a blowing process, such fittings being disclosed for example in United States patent specifications 3 435 and 3 2 1 70. Fittings of such a kind may however be too inexact as regards their dimensions, and may be found to be expensive to produce.

Another method is disclosed in German Utility Model specifications 1 841 681 and 7031 799· Fittings of this kind are however generally only suitable for pressureless pipelines. The production of a simple branch connection or T-piece for pressure pipelines may bring particular problems as regards shrinkage and frozen-in tensions in the production process. The production of such fittings may be found to be expensive and difficult even in the case of pressureless lines. This may be the more so in the case of so called pressure pipe fittings for supply lines, for example for water, which are steadily stressed with a nominal pressure of 10 atmospheres and more.

Pressure pipe fittings of polyvinylchloride (PVC) are known, which are fixed by adhesion to the pipe to be connected. However, such adhesion may,-involve various known difficulties.

U.K. Patent Specification 835 520 and German published specification 1 238 654 disclose an injection moulding process for fittings, which may be regarded as going some way towards solving the problem of the production of tension-free fittings. However, with this process only fittings of small dimensions and very small wall thicknesses may be produced, and then generally only in awkward and inexpedient manner. For pressure pipe fittings of large dimensions, for example 200 millimetres and more, the wall thickness may have to be increased correspondingly. with the increase in the wall thickness problems in connection with the injection moulding process of such fittings may also increase. Apart from the desire for a completely void-free construction, there is also the desire for the fitting to be free from frozen-in tensions. In connection with this, difficulties may arise with the shrink-in^ of the material during the cooling. The subsequent formation of beads or recesses in the region of the sleeves of the fittings may be very difficult in the case of larger wall/thicknesses, for which reason it may be desired to avoid from the beginning reshaping processes taking place subsequently to the injection moulding process. One reason for this is. that before such subsequent processes take place, the material needs to be heated again to the thermo-elustic region. Because of the difficulties and expensive production methods mentioned ubove, in the past it may have been regarded as impossible to produce such fittings satisfactorily by an injection moulding process.

Sittings put together from individual pipe sections, for example by means of adhesion, welding or the like, for example according to German Utility Model specification 70 18 601 , may be regarded as not meeting the requirements as regards strength and as therefore not standing the required test in practice.

From a technical point of view, the previously known thick-walled shaped pieces of the above described kind may show the difficulty, that in the injection moulding machine the synthetic material injected in the plastic condition needs to be cooled off so far that the injection moulding remains firm in its moulded shape. Only when this condition has been reached can the mould lialves be opened and the injection moulding taken out.

This- means that particularly in the case of thick-walled injection mouldings very much time may be required for the necessary cooling. This means urthermore, that the production times may become very long. The long cooling time originates from the fact that the injection moulding is not cooled directly. The cooling takes place in most cases via the injection mould. Since the injection mould is partially heated, for example according o U.K. patent · specification i.05 5^0, the dwell time of the injection mo lding in the mould can be very long. On the other hand, an intense cooling of the injection moulding machine may not generally be employed, since the mould needs to display a particular temperature during the injection of the material. Thus, the injection mould would require again a relatively long heating-up period if cooling of the mould were employed before injection.

The very long cooling times may also involve the difficulty, that the material in the injection cylinder may be exposed for too long a time to high temperatures, which can lead to decomposition or combustion of the material. There jliould be added, that the injection moulding durin the cooling off process in the mould cannot shrink in the longitudinal direction. Thus, the injection moulding is subjected to high tensions within itself, which for example in the case of fittings for water supply linee under pressure or the like can lend to early breakage even in creep strength load tests in a test laboratory.

In order to shorten the production times, multi-station injection * moulding machines have been employed, which however are generally regarded as expensive and require a complete injection device for each mould closure unit.

The production of undercut portions on hollow bodies, which are produced in an injection moulding process, i.e. in the so called master moulding process, may take place either in the master moulding process itself by means of sliders', hinged core elements etc. or in a reshaping process, which takes place subsequently to the injection moulding process. For this purpose, shaped articles after cooling in a cooling device are heated again up to the thormo-elnstic region and reshaped in this condition. Also, cutting operations may talce place on the hollow bodies if desired.

Such processes may be regarded as awkward and costly, above mostly additional work force may be necessary. However, the automation of such a process may only be possible with very great expenditure. The necessity to produce beads or recesses and sleeve sections, above all in articles en masse, such as for example synthetic material fittings, may however be obligatory.

Sliders, core elements which can be taken apart etc. are known for use in injection moulding devices. However, such a construction may be realisable only with very great expenditure and may be subject to trouble. The susceptibility to trouble is brought about on the one hand by the necessary mechanism and on the other hand because during the injection of the synthetic material moulding mass into the mould under high pressure this mass can flow also into the gape between the individual segments of the core element of variable shape. These gaps arise owin to wear between neighbouring metallic surfaces and become steadily larger. As a result, a relatively high servici g expenditure may be necessary. A further proposal relates to the insertion of a ring of gypsum, pnenolic resin or the like into the mould, this ring surrounding the core element. At the place at which the ring was placed, by injection moulding around the core element with the ring fitted thereon the shaped article is produced together with the undercut or projecting bead in the master moulding process. The ring moulded around is finally removed from the mould together with the shaped article, and subsequently destroyed, after which the undercut portion, for example in the case of fittings for the reception of a rubber sealing ring, is finished. A *· possible difficulty with these rings pushed onto the core and to be destroyed is that this process also can become expensive and costly.

According to one aspect of the present invention, there is provided a process for the injection moulding of hollow articles from thermoplastic synthetic materials by injection of a mass of synthetic plastic material into a temperature controlled mould consisting of mould parts and mould cores, subsequent cooling of the cores, removal of the injection moulding on the core from the mould, cooling of the injectio moulding on the core in a cooling means and subsequent complete withdrawal of the core after the injection moulding has reached the required stability of shape, characterized in that for the production of a thick-walled pressure pipe fitting a machine consisting of one mould and two mould cores is used, of which the mould parts and the mould cores are maintained by temperature controlling media at temperatures below the temperature of flowability of the injected mass of synthetic material, that the cores are partially retracted in the closed mould, which is placed in the cooling means, shortly before or after the mould is opened, and that the injection moulding is cooled in the cooling means by a coding medium which is applied to it from the outside after the temperature of the outer surface of the injection moulding has reached by heat conduction a value which is above the temperature of flowabilxty of theainjected mass of synthetic material.

Suitably, three mould core elements are provided to define respective openings in the shaped article. ft < Conveniently, one of the core elements is retracte^ at least partially before termination of said shrinking, the .two other core elements being retracted after termination of said shrinking, and preferably said retraction of said one core element takes place through such a distance that said one core element after that retraction remains in contact with a ring retained by the shaped article to surround that core element and be movable relative thereto, while further preferably said retraction of the two other core elements takes place through such a distance that those core elements are separated from the shaped article or after said retraction the two other core elements are retracted through respectively corresponding distances before termination of said shrinking.

Expediently, the three core elements are letracted simultaneously through said distance before termination of said shrinking, and are separated from the shaped article after termination of said shrinking.

Suitably a stream of a fluid cooling medium is employed to effect said cooling, and preferably the cooling medium comprises a mist.

Advantageously, the or each core element is maintained at a lower temperature than the mould parts.

The process may comprise the steps, prior to said cooling step, of moving the shaped article in a direction away from the mould parts and simultaneously moving at least one further core element in a direction towards the mould parts for the subsequent formation of a further shaped article.

Suitably, the mould parts when in contact with one another define a plane of separation, the or each core element describing after said separation of the mould parts movement in a direction substantially perpendicular to the Expediently, a ferromagnetic core component is applied about an external surface portion of said one core element, the process comprising the steps of magnetically locating the core component on the external surface portion, and after said retraction of said at least one core element removing the core component from a recess provided by the core component from a recess provided by the core component in the shaped article.

Suitably, the core component is located on the external surface portion at least partly by electromagnetic means, the process comprising the step of de-energising the electromagnetic means prior to the removal of the shaped article together with the core component from the moulding means.

Preferably, the core elementis provided with a plurality of magnet polepieces to locate the core component, and further preferably the polepieces are received in insulating sleeves.

Expediently, the core component comprises a plurality of mutually cooperable parts.

Conveniently, the core component is permanently magnetised.

According to a third aspect of the present invention, there is provided a mould for the production of hollow synthetic articles such 'as fittings, containers, pipe sections and the like having one or more undercuts by the method defined aboveΛ comprising several, ferromagnetic mould parts detachable from the core at the plate at which the undercut is to be produced on the injection moulding and a core provided with a number of electro-magnets, permanent magnets or electro and/or permanent magnet groups which correspond to the number 30 0 2 An apparatus for carrying out the method according^ to the invention may comprise automatically operable displacing means to displace the shaped article together with said one core element in a direction away from the mould parts towards the cooling means, which comprise means to direct a coolant towards the shaped article, and preferably the displacing means include means to displace simultaneously at least one further mould core element in a direction towards the mould parts.

The apparatus may comprise cooling means to cooperate individually with each respective said one core element.

Conveniently, the displacing means are attached to the moulding means.

Suitably, the mould parts when in contact with one another define a plane of separation, the displacing means being arranged after said separation of the mould parts to displace the or each core element in a direction substantially perpendicular to the plane of separation and then in a direction substantially parallel to the plane of separation.

The apparatus may comprise support means arranged guidingly to support the or each core element by means of at least one elongate aperture provided in the support means.

The apparatus may comprise a ferromagnetic core component to be applied about an external surface portion of said one core element, and magnetic locating means to locate the core component on the external surface portion during the injection of the moulding mass.

Thus an apparatus for carrying out the method defined above may comprise injection moulding means including a mould core element, the apparatus may further comprise a 43040/2 surface portion of the core element, injecting means to inje *ct· a moulding mass into the moulding means to form a shaped article having a recess formed therei by the core component, and magnetic locating means to locate the core component on the external surface portion during said injection.

Suitably, the location means comprise electromagnetic means de-energisable to facilitate removal of the shaped article together with the core component from the moulding means .

Expediently, the locating means comprise a plurality of magnet polepxeces carrxed by the core element, and preferably the polepxeces are received ¾n insulating sleeves.

Conveniently, the core component comprises a plurality of mutually cooperable parts; expediently the core component is permanently magnetised.

Embodiments of the present invention will now be more particularly described with reference to the accompanying drawings, in which Fig. 1 shows a plan view of an embodiment of injection moulding device in schematic representation; Figss^ to 6 show different positions of the device shown in Fig. 1; Fig. 7 shows an injectio moulded shaped article with the mould cores in section; Fig. 8 shows a section through the core of a modified embodiment; and Fig. 9 shows a section on. the line A - B in Fig. 8. Λη injection moulding machine 1 with an inlet hopper 2 and a cylinder 3 , which is situated in Fig. 1 in the injection position, and a mould closure unit is shown schematically. The mould halves of the injection moulding machine are designated by reference numerals 5 and 6 respectively. These mould halves define when in coitVict with one another a single plane of separation. On each side of the injection moulding machine 1 there is .situated a respective frame 7 The operation of the above described embodiment is as follows. As shown in Figs. 1 and 2, the cylinder 3 is situated in its working position. A heated thermoplastic synthetic material moulding mass is injected into the mould 5 and 6 , moulding then taking place around the core unit 13 to produce the shaped article 23. This takes the form of a T-piece branch pipe connection. Simultaneously, a previously produced shaped article 2h is cooled by the spray cooling means 22. A short time after the ending of the process of injecting the moulding mass into the mould, the mould halves 5 and 6 are moved apart by the closure unit ¾. At this point in time, the shaped article, a pressure pipe fitting, possesses a sufficient stability of shape of the outer wall zones, while the interior of the walls is still in tho plastic condition. The core unit 13 a now moved from the position A (Fig. l) into the position B (Fig. 3) guided by the slotted apertures 15 and 16 in the carrier 11. In this position, the cylinder 3 is situated again in its initial position. Thereupon, the carriers 11 and 12 with the core fittings 13 iiad 1 are moved into the position shown in Fig. . There, the spray cooling means 21 conies into action and cools the shaped article intensively.

Simultaneously with the moving out of the core unit 13 » the core unit 1Ί is moved into the mould 5 and 6. The core unit is thus moved from the position B into the position Λ (Fig. 5), and the cylinder 3 is brought into the injecting position, to produce a new shaped article (Fig. 6) . Thereafter, the process begins again from the beginning.

During the cooling-off process, the shaped article 23 or 2k can shrink without hindrance in the longitudinal direction on the core unit 13 or 1Ί . The shrinking in the longitudinal direction may be improved if the shaped article possesses a sufficient shape stability, the core 13 or 14c is wholly or partially drawn out or retracted, and the core parts 13a and 13_b or I'm and l'ib are not retracted out of or separated from the shaped article until, later.

According to the section of the shaped article 25 shown in Fig. 7» on the cores, the core 26c , which is situated at the point of branching of the shaped article 25 » is the first to be retracted, shortly after the removal of the shaped article from the mould, as a maximum by an amount m, i.e. the length of the upper sleeve part of the shaped article, up to the bead 25c. By this procedure, the core 26c drawn partially back supports the forward part of the sleeve with the bead 25 » while the section of length m can shrink freely. Thus the diameter of the core section 2o corresponds to the diameter of the shaped article at the upper part thereof. In place of only tho core element ^, also the core elumonte 26a_ and 26b can be retracted by this amount together with the. ,c^r^,ele.§ont'.26o or after a certain time t from the retraction of the core element 26jj . Thereby, the shrinking proc m is furthermore favoured and parts of the shaped article 25 » namely the sleeve .'.sections with their beads 2[5a and 25J , are supported in such a manner during ; cooling process, that their functional dimensions are maintained exactly.

The above described process and apparatus are suitable for complete automation, and may be programmed for any suitable synthetic material. Of course, the process and apparatus are not restricted to the production of shaped articles with perpendicularly branching sections, but can be applied iitr example to produce any kind of brunch pipe fitting with a branch making nn arbitrary angle with the main portion of the pipe.

For the production o the beads 5a , 25b and 25c , which are in the form of undercut beads, on to the core elements 26a, 26b and 26 there is placed a respective ring, around which moulding takes place. After separation of the core elements from the beads, the ring is removed from the bead or recess. Thus a subsequent reshaping of the shaped article is avoided; and the article is produced completely in one moulding process. Flanges or the like for example can also be formed by injection moulding on the article, or moulding can take place around such flanges, if these are put onto the core elements 26 With the process and apparatus described above, it is possible to produce a pressure pipe plug-in fitting for releasable pipe connections, from synthetic material, the difficulties of previously known fittings being? to some extent mitigated. Furthermore, the production of a shaped article may take place by injection moulding in economical maimer.

The mould halves are opened at the beginning of the shrinking process setting in by reason of the material-dependent expansion quotients or coefficients, but before the time when the possible freezing-in of tensions might be expected to start. The cooling of the shaped article takes place quickly by the cooling means described above, and thereafter the cores are retracted. Shortly after this, the core element necessary for the formation iii t!ie branch section is retracted wholly or partially from the shaped article, and after termination of the .shrinking process of the shaped article in axial and radial direction the remaining core element or elements or core j. ts are retracted. it may be regarded as of advantage in relation to the shrinkuge problem In particular in the case of preasure pipe fittings with branch sections, for example a T-piece, to withdraw initially the vertically running core element sufficiently early that a free shrinkage of the shaped article xially in relation to the branch section can take place, and thus no additional tensions can be frozen in. A consequence is a uniform shrinking process with uniform distribution of possibly remaining residual tensions.

The early retraction of this core element is achievable by larger dimensioning of the brunch core element by the amount, which by the shrinkage of the diameter of the branch section reduces the latter.

The shrinkage in axial direction on each side of the branch section is to lie adapted to the radial shrinkage of the branch section. Also this ia achievable by corresponding dimensioning of the core elements and of the injection mould. Of course, the respective steps and the computing and dimensioning of the core elements and of the injection mould are dependent on the properties of the material to be worked.

The temperatures in the injection mould are significantly lower than in the case of known injection moulds. The core elements are permanently cooled, and only the injection mould or the mould parts are temperable, i.e. arranged to be heated and/or cooled, A possible difficulty with known processes, that they are not fully - Ik - automatable, is at least to some extent mitigated by the above described process and apparatus, if an automatically operable displacing means in the form of a core element movemen unit is provided, which permits the shaped a ticle with its associated cove elements to be taken out from the mould parts laterally. While the shaped article situated on the core elements is directly -intensively cooled with a cooling medium, by moving a second pair of core elements into the warm mould a new shaped article is produced. The mo v.Lni.j of the new pair of cove elements takes place at the same time as the la t al moving-out of the first pair of core elements. Of course, further cove elementa may be provided if required. This process may be designed to be completely automatable.

The cooling time may be reduced by the employment of impact nozzles or the like, which permit an intense cooling effect.

The above described process and apparatus may be used to produce tension-free fittings, for example thick-walled, large pressure pipe plug-in fittings from synthetic materials. If desired, the mould halves and all the core i": l.emeuts may be temperable.

I desired, after opening of the mould halves the core unit being removed from the mould parts may execute firstly a movement in the vertical direction (position to position D) and then a movement in the horizontal direction, in relation to the plane of separation of the mould parts. It is desirable that the initial movement should be in a direction substantially perpendicular to the plane of separation, and that the subsequent movement should be in a direction substantially parallel to the plane of separation.

Referring to Figs. 8 and 9 of the drawings, the core element of the injection moulding machine is designated by reference numeral 1, and is provided with one or more depressions, distributed over the periphery, to receive one or more electromagnets or permanent magnets 2 to 5. If desired, a combination of electromagn La and permanent magnets may be employed, liotween- the magnets and the core, insulating sleeves 6 to 9 ore disposed. An insert piece or core component 10 of f rromagnetic material is pushed on to the core element 1 and located at the desired position determined by the magne s 2 to 3, by the magnetic .field. If desired, the core component 10 may lie put oge her from .several individual parts, as shown in Pig. 2, to facilitate u simpler mode ot! removal from the undercut or recessed portion. The individual segments of the core component 10, after removal of the finished shaped article from the mould, are removed from the recessed portion, the two pieces 10a and 10b initially being withdrawn inwardly, followed by the pieces 1.0c and lOd.

In place of fittings, of course other parts may be produced using the described process, with undercut' portions or recesses, these being produced together with the shaped article in the master moulding process.

V.'ith th ' above described process and apparatus, it is possible to produce hollow bodies with undercut portions during an injection moulding process, i.e. in the master moulding process, together with the whole of the shaped article. Possible difficulties with known processes of this kind may at least to some extent be mitigated.

The core element is provided with one or more magnets or polepiect!s of uii electromagnet, which co-operate with the ferromagnetic core component applied over the main core element to locate the core component on the core element. The core component, in dependence upon the material employed for this, can be constructed in one or more pieces. In one embodiment, the core 'component is permanently magnetised. f desired, the described process may be eraployed with advantage also in reshaping proceasea, i.e. process steps taking place subsequently to t main moulding operation, for example in the case of blowing, foaming or casting. Suitable articles to be produced by the process are for example 1:'i 1.1 i na , containers and pipe sections.

Claims (4)

43040/2 CLAIMS V^<

1. A process for the injection moulding of hollow articles from thermoplastic synthetic materials by injection of a mass of synthetic plastic material into a temperature controlled mould consisting of mould parts and mould cores, subsequent cooling of the cores, removal of the injection moulding on the core from the mould, coding of the injection moulding on the core in a cooling means and subsequent complete withdrawal of the core after the injection moulding has reached the required stability of shape, characterized in that for the production of a thick-walled pressure pipe fitting a machine consisting of one mould and two mould cores is used, of which the mould parts and the mould cores are maintained by temperature controlling media at temperatures below the temperature of fl wability of th injected mass of synthetic material, that the cores ar partially retracted in the closed mould, which is placed in the cooling means, shortly before or after the mould is opened, and that the injection moulding is cooled in the cooling means by a cooling medium viich is applied to it from the outside after the temperature of the outer surface of the injection moulding has reached by heat conduction a value which is above the temperature of flowability of the injected mass of synthetic material.

2. A process according to Claim 1 , characterized in that first one part of the core forming a branch is partially retracted, thereafter the other parts of the core are partially retracted and subsequently, after the cooling of the injection moulding is completed to an average temperature of the injection moulding which is below the temperature of flowability of the injected mass of synthetic material, the cores are completely retracted. 43040/2

3. A mould for the production of hollow synthetic articles such as fittings, containers, pipe sections and the like having one or more undercuts by the method according to Claim 1 or 2, comprising several ferromagnetic mould parts detachable from the core at the place at which the undercut is to be produced o the injection moulding and a core provided with a number of electro-magnets, permanent magnets or electro and/or permanent magnet groups which correspond to the number of mould parts, embedded in the core opposite each mould part.

4. A mould according to Claim 3, characterized in that each of the magnets is surrounded by an insulating sleeve. HE :mr