IMPROVED DISTRIBUTION PLATE FOR A MOULD FOR THE INJECTION MOULDING OF PLASTIC MATERIALS

Technical field of the invention

This invention relates in general to the sector of injection moulding of plastic materials, and more closely it concerns a distribution plate, for a mould for the injection moulding of plastics, which includes significant improvements with respect to those ones currently used in the industry, particularly in terms of the capacity of sealing against leakage or outflow of fluid plastic material under pressure which is fed and distributed by the distribution plate in order to be injected into the mould. This invention also relates to a corresponding improved process for assembling a distribution plate for the injection moulding of plastic materials, and a mould that includes an improved distribution plate such as the one proposed herein.

Background art Distribution plates generally have the function, in a machine for the injection moulding of plastic material, of receiving a fluid plastic material under pressure and of distributing it to one or many injection nozzles, which are in turn intended for directly injecting the plastic material into the inner cavities of the mould.

Such a distribution plate may be made of a plurality of distinct distribution elements or modules, which are integrated in the structure of the mould and are traversed internally by a plurality of flow channels, or hot channels, along which the plastic material flows towards the injection nozzles.

These flow channels may extend from one distribution element to the next, or may traverse several adjacent distribution elements, and together make up a network of flow channels for distribution of the fluid plastic material to the injection nozzles.

A distribution plate exhibiting the general characteristics set out above is described in the international patent application PCT/EP2005/052821 , published

as WO2006/000541 A1 and having the same holder as that of the present application, such previous patent application being quoted here both as a document reflecting the known art and as a useful reference for any further information and/or clarification not found in the present one. One typical problem regarding the manufacturing of these distribution plates concerns the connections between the different flow channels or sections of flow channels which are formed, each continuing on from the other, in the distinct distribution elements of the distribution plate and in particular the requirement that these connections or junctions must be such as to allow the distribution elements, and in general the different parts that make up the distribution plate, to thermally freely expand with respect to one another and hence not cause dangerous stresses to arise in the distribution plate during use.

In this regard, the above-mentioned application PCT/EP2005/052821 proposes a distribution plate, for distributing the plastic material to a plurality of injection nozzles, comprising a plurality of plate elements, separate from one another, which internally define multiple channels for the flow of the fluid plastic material, in which a plurality of expansion joints is provided both for connecting one with another the sections of the flow channels which are formed in two adjacent plate elements, and for connecting the flow channels with the injection nozzles, in such a way as to permit relative expansion movements, in the event of temperature changes, among the different parts of the distribution plate.

The expansion joints described in this patent application, though allowing the single plate elements or distribution elements to expand freely without giving rise to dangerous stresses, appear conditioned however, at least in terms of their capability to ensure sealing against the outflow or leakage to the outside of the fluid plastic material that flows through them and in the respective flow channels, by the arrangements, characteristics and precision with which the various plate elements making the distribution plate are mounted.

In particular, it has been shown experimentally how an imprecise construction of the various distribution elements and/or how a lack of accuracy when they are mounted during assembly of the distribution plate on the mould can give rise to stresses and deformations likely in certain circumstances to compromise, or at least significantly limit, the capability of the junctions made with these expansion joints to seal against leakage of the molten plastic material that flows through them, in particular at the high pressure values, sometimes greater than 1400 bar, such as those present in the most modern injection moulding art.

In particular it is supposed that the occurrence of these leaks may in some way depend, possibly also by direct or indirect effect of the stresses and deformations mentioned above, on an incorrect and insufficiently precise alignment of the seats, formed in the two adjacent plate elements, in which the ends of the expansion joints are accommodated and mounted, or also by other, often concomitant causes, which are not always easy to identify. To sum up, the solution described in the above-mentioned patent application filed on behalf of the applicant appears in need of further improvements and enhancements in order to guarantee absolute and sure sealing against any leakage to the outside of the fluid plastic material flowing in the junction zones of the flow channels which extend through two distinct, contiguous and adjacent distribution elements.

Disclosure of invention

Therefore one object that this invention intends to achieve is that of overcoming the drawbacks set out above, by proposing a distribution plate for a mould for the injection moulding of plastic materials and of the type including several distribution elements defining a network of flow channels, which possesses improved characteristics and performances, and in particular is such as to allow the respective distribution elements to expand freely one with respect to the other, for the purposes of avoiding dangerous stresses being generated in the structure

of the distribution plate, and to ensure at the same time perfect sealing against any leakage of the molten plastic material in the connection zones between the flow channels formed in the various distribution elements.

The above object may be considered to be fully achieved by the distribution plate having the characteristics set out in the first, independent main claim.

Particular embodiments of the distribution plate of the invention are also defined in the dependent claims.

As will be better understood in the following description, the distribution plate proposed here has numerous advantages, such as that of guaranteeing, with simple arrangements and at low cost, perfect and sure sealing against any leakage of the plastic material distributed by it.

Accordingly with this innovative distribution plate there is no longer the need to have to provide, for the parts comprising it, an extremely accurate and precise assembly, which other than being expensive is never completely sure of guaranteeing the desired sealing results, as unfortunately is the case of the conventional distribution plates.

Brief description of drawings

These and other objects, characteristics and advantages of this invention will appear clearly from the following description of a preferred embodiment thereof, provided solely by way of a non-limiting example with reference to the accompanying drawings, where:

Fig. 1 is a plan view of a distribution plate, according to this invention, for a mould for the injection moulding of plastic materials;

Fig. 2 is a section view, along the line H-Il of Fig. 1 , that shows a distribution network comprised by hot flow channels made in the distribution plate of the invention;

Fig. 3 is a view, in an enlarged scale, of a connection zone between the hot flow channels of Fig. 2;

Fig. 4 is a view of some details of the connection zone of Fig. 3 under operating conditions, i.e. with the distribution plate hot; and

Figs. 5 and 6 are respectively a front view and a section view, along the line Vl-Vl of Fig. 5, of a sealing element, in the form of a Belleville spring, mounted in the connection zone of Fig. 3.

Best mode for carrying out the invention

With reference to the drawings, a distribution plate, also called "hot plate", having the characteristics of the present invention and intended for use in the field of moulding of plastic materials, is generically indicated with the numeral 10. Such a distribution plate 10 is typically provided for feeding and distributing a plastic material in the fluid or molten state to a mould 12, in turn fitted and used in a machine 13, shown schematically only in dot and dash lines in Fig. 1 , for the injection moulding of plastic materials.

The distribution plate 10 is integrated with the block that constitutes the mould 12, and in particular it is arranged between an outer plate 12a, also called end plate, and an inner plate 12b, also called nozzle-bearing plate, in which the end plate 12a defines an outer end or wall of the block comprising the mould 12, and the nozzle-bearing plate 12b supports and accommodates one or more injection nozzles having the function of directly injecting into mould 12 the plastic material distributed and received from the distribution plate 10.

An intermediate plate 12c, part of the mould block 12 and placed between the plates 12a and 12b, runs with an internal profile 12c' around the distribution plate 10, so as to form a kind of frame that accommodates the distribution plate 10.

The distribution plate 10 is essentially made of a plurality of distinct distribution or distributing elements which are arranged adjacently and beside one another, between the two plates 12a and 12b, and also comprises a plurality of flow channels, usually called "hot channels" or "hot flow channels" which are formed internally and extend,

through the various distribution elements, in continuation of one another, in particular according to a branch-like configuration so as to define a distribution network 14.

These flow channels have the specific function of distributing the fluid plastic material from a feeding or entrance zone of the distribution plate 10 to the injection nozzles, housed in plate 12b, so that it is injected into the mould 12, as said above.

The distribution elements comprising the distribution plate 10 have a flat or plate- like shape, in the direction of their extension along the two plates 12a and 12b of the mould block 12, and have, in plan, i.e. when observed in the normal direction to the plane of plate 12a or 12b, a profile that may variously shaped. In general both the number of these distribution elements and the plan configuration of their profile depends on the characteristics of the mould 12, and more in particular on the number and arrangement of the zones of mould 12 that the distribution network 14, formed therein, must reach for distributing and injecting therein the fluid plastic material. For example, in the non-limiting embodiment as illustrated in the drawings, the distribution plate 10 consists of three single distribution elements indicated with numerals 21 , 22 and 23, wherein the distribution element 21 is arranged in a central zone and has a branch-like configuration reminiscent of a cross, and the other two distribution elements 22 and 23, both of which have a T' configuration, are arranged laterally and at opposite sides with respect to the distribution element 21.

The distribution elements 21 , 22, 23 are arranged and configured in the distribution plate 10 in such a way as not to be in direct contact with one another, but instead leaving an empty space or gap between two adjacently arranged elements, thus enabling distribution elements 21 , 22, 23 to have free and unimpeded thermal expansions, as will be explained better below.

In particular, the distribution elements 21 , 22, 23 are separated from one another by a separating space or cut 17, defining a distance D (Figs. 3 and 4), in correspondence with respective adjacent portions that are traversed by two flow

channels, one continuing on from the other, i.e. by two contiguous sections of one flow channel.

Each of the distribution elements 21 , 22, 23 is mounted and exactly positioned and matched, i.e. centered, with respect to the mould block 12 through a respective centering pin or member 15, protruding from the distribution element itself and accommodated in a corresponding seat 15a produced on the nozzle-bearing plate 12b of the mould 12.

Furthermore spacing elements 41 , rigidly mounted on the distribution elements 21 ,

22, 23 but suitable for sliding along the surfaces 12a' and 12b' of the plates 12a and 12b of mould 12, have the function of holding and supporting at a given distance or space the distribution elements 21 , 22, 23 between the plates 12a and 12b, at the same time leaving them free to expand longitudinally with respect to these plates. Therefore the distribution elements 21 , 22, 23, thanks to this centered and supported assembly with respect to the mould block 12, together with the fact that, though adjacent, they are separated by a certain distance from one another, can expand freely, i.e. they can have limited movements relative to one another and with respect to the plates 12a and 12b when distribution plate 10 is subjected, during operation, to high temperature variations, without these thermal expansions triggering dangerous tensions in the structure of distribution plate 10. Again, suitable contrasting members 33, placed between the intermediate plate

12c of the mould 42 block 12 and the distribution elements 22 and 23, may be provided for receiving and contrasting at least a part of the stresses acting on the latter-named when distribution plate 10 is in operation, and in particular for reducing the extent of the stresses acting on the centering pins 15. In any event, these contrasting members 33 are not to be considered essential and can therefore not be present, in which case the centering pins 15 associated with the distribution elements 21 , 22 and 23 are suitably sized in order to receive and

contrast alone all the stresses that arise between the distribution elements 21 , 22 and 23 during operation of the distribution plate 10.

As already anticipated, distribution plate 10 is provided for receiving and being fed with molten plastic material, indicated MP, from other parts of the moulding machine 13.

In particular the fluid plastic material MP is received by the distribution plate 10 through an aperture 31a, provided in a feeding zone 31 and communicating with the interior of the central distribution element 21 , for being distributed from this feeding zone, along the flow channels of the distribution network 14 made in the three distribution elements 21 , 22 and 23, to a plurality of injection nozzles 32, housed in the plate 12b of the mould 12, from where the molten plastic material MP is then directly injected into mould 12.

In the non-limiting embodiment illustrated here, the distribution network 14 comprises four flow channels or flow channel sections, 14-1 , 14-2, 14-3, and 14-4, made internally in the central distribution element 21 , which branch out in a cross-like form from a common origin in the feeding zone 31.

This distribution network 14 also has two flow channels 14-5 and 14-6 which are made in the distribution elements 22 and 23 in continuation of and therefore in the same direction respectively as the flow channels 14-1 and 14-3 (Fig. 1 ), to receive from the latter the fluid plastic material MP.

There are further channels or flow channel sections 14-7, 14-8,.... 14-14, and still others, not indicated here for simplicity's sake, that are made in the distribution elements 21 , 22 and 23, and which continue from or branch out perpendicular to those mentioned above so as to complete the distribution network 14 on the periphery, in order to convey the plastic material received from the distribution plate 10 to the various injection nozzles 32.

Suitable connecting or connection elements, indicated with numeral 18 and also called expansion joints, are provided for connecting the flow channels which extend, in

continuation of one another, through two adjacent distribution elements, in order to establish continuity along the distribution network 14, despite the separating spaces 17 between the distribution elements 21 , 22, 23 in the connection zones of the flow channels. These connection elements 18 are substantially conforming to those described in patent application PCT/EP2005/052821 , already quoted above, having the same applicant as the present one.

In particular, each of these connection elements is made, as shown in Fig. 3 with reference to the specific connection element that connects the flow channels 14-1 and 14-5 formed respectively in the distribution elements 21 and 22, of a tubular coupling 18, which is accommodated and permanently fixed at a first end 18a, for instance in a planting operation, in a corresponding seat 21a formed in the distribution element 21 , and is slidingly accommodated at a second end 18b, opposite the first, in a corresponding seat 22a formed in the distribution element 22.

Thanks therefore to this mounting configuration, the tubular coupling 18 is suitable for sliding along the respective axis, that is to say for having, local to the end 18b, limited relative movements with respect to the adjacent distribution elements 21 and 22, when, due to the effect of the thermal expansions produced by the temperature variations, the distance D, defined by the cut 17 between the two adjacent distribution elements 21 and 22, tends to vary over time.

The injection nozzles 32 that receive the fluid plastic material distributed by the distribution plate 10 for directly injecting into mould 12 can be made and coupled with mould 12 according to various arrangements, and can also be of various operating types, substantially non-influential and irrelevant for the purposes of this invention.

Other parts are provided to complete the construction of the distribution plate 10 and the relative mounting on the mould 12, between the plates 12a and 12b, while ensuring its complete operating functionality, such as for instance electrical

heating resistances, indicated with numeral 42, which are arranged in a coil configuration adjacently to the various flow channels 14-1 , 14-2, 14-3, etc. of the distribution network 14, in order to heat and keep them constantly at the required temperature. Again distribution plate 10 may include, among its parts, a number of reference elements 43, also called transport guides, which have the purpose simply of keeping the distribution elements 21 , 22, 23 assembled during transport, and thus of facilitating their mounting and final positioning and matching on the mould 12.

It should however be pointed out that these reference elements 43, where provided, leave the distribution elements 21 , 22 and 23 full freedom to expand, once assembled on mould 12, in response to the heat variations they are subject to in operation.

According to an essential characteristic of this invention, distribution plate 10 also comprises, in correspondence with each of the zones joining or connecting the hot flow channels between two adjacent distribution elements, sealing means, generically indicated with numeral 24, which are associated with the connection element 18 to ensure under all conditions perfect and sure sealing against any outflow to the outside of plastic material MP flowing through the flow channel joining zone. In particular the sealing means 24 are suitable for producing a hermetical seal around the connection element 18, in the area of the separating space 17 between the two adjacent distribution elements, by cooperating in a pressure relationship with the portions of the two adjacent distribution elements, facing the separating space 17, when the distribution plate 10 expands on account of the heating it is subject to during operation.

In construction terms, as represented in detail in Fig. 3, these sealing means 24 are composed of at least one pair of Belleville springs, respectively 26, 27, truncated cone shape, also commonly called using expressions that have come

into technical jargon "Bauer sprigs" and "Belleville spring washers", wherein these Belleville springs 26, 27 are mounted, one beside the other, on the external cylindrical surface of the tubular coupling 18 and are then accommodated in the separating space or cut 17, defined by the distance D, that separates the two adjacent distribution elements 21 and 22 in the joining zone between the channels 14-1 and 14-5.

As illustrated in Figs. 5 and 6, these Belleville springs 26, 27 each define a central circular hole, respectively 26a, 27a, an external circular profile or edge, respectively 26b, 27b, and adjacently to the latter a ring-shaped pressure plane, indicated respectively with 26c, 27c, produced in a grinding or lapping operation.

In the assembly configuration such as represented in Figs. 3 and 4, the two Belleville springs 26 and 27 are arranged and accommodated in the space 17 that separates the two distribution elements 21 and 22, whereby the respective central holes 26a, 27a axially receive the tubular coupling 18. Moreover the ring-shaped pressure planes 26c, 27c provided in the Belleville springs 26 and 27 are arranged in contact with the facing surfaces, respectively 22b e 21 b, of the adjacent distribution elements 22 and 21 , and the internal edges, adjacent to the holes 26a, 27a of the same springs 26 and 27, are arranged in contact with one another, along respective ring-shaped surfaces 26d, 27d. Preferably, to facilitate mounting of the distribution plate 10 on the mould 12, these Belleville springs 26, 27 are sized so that they can be accommodated essentially free and unimpeded in the space 17, though with a slight clearance, of for instance 0.1 í 0.2 mm, with respect to the walls 21 b and 22b of the distribution elements 21 and 22, in cold conditions, i.e. when the distribution plate 10 is not yet hot as under operating conditions.

To advantage Belleville springs 26 and 27 may be produced in determined normalized dimensions, so as to be suitable for meeting the usual requirements,

shapes and dimensions in the field of distribution plates and their assembly and integration in the moulds currently employed in injection moulding.

In particular, with reference to Fig. 6, the Belleville springs used in assembling a distribution plate according to this invention may be of two distinct normalized types, having the dimensions defined in the following table, where:

01 is the outer diameter of the Belleville spring,

02 is the diameter of the central hole of the Belleville spring;

D is the thickness or height at rest, i.e. in non-deformed configuration, of the pack formed by two Belleville springs (therefore D corresponds substantially, and is therefore indicated with the same symbol as it, to the distance that defines under cold conditions the separating space 17 between two adjacent distribution elements in which the two Belleville springs are accommodated)

In operation, a distribution plate 10 according to this invention is fed with the molten plastic material MP, which then flows at high temperatures, generally above 200 ⁰ C, and pressures, even higher than 1400 bar, through the hot flow channels 14-1 , 14-2, 14-3, etc. of the distribution network 14, as indicated by arrow f1 in Fig. 3

This produces heating of the distribution plate 10, so that its parts, in particular the distribution elements 21 , 22, 23, expand, causing a contraction from D to D', as indicated in Figs. 3 and 4, of the distance separating them in the flow channel connection zones.

Because of this contraction, Belleville springs 26, 27 are compressed and elastically deformed in the axial direction, whereby they react accordingly by exerting, through the respective ring-shaped planes 26c e 27c, a corresponding pressure P against the walls 21b and 22b of the distribution elements 21 and 22, as indicated in Fig. 4, so as to hermetically seal the space around the tubular coupling 18 and thus

guarantee sealing against any leakage to the outside of the molten plastic material MP flowing through the zone of the tubular coupling 18.

In other words, when distribution plate 10 is hot, Belleville springs 26 and 27 exert both in the area of contact between one another and also, through the peripheral ring- shaped pressure planes 26c and 27c, against the facing walls 21 b and 22b of the two adjacent distribution elements 21 and 22, a pressure P of an entity suitable to prevent in all operating situations the material MP, flowing in the joining zone, from leaking to the outside, in particular also in the event of a non-perfect sealing, caused for instance by defective and imprecise mounting, between the tubular coupling 18 and the adjacent distribution elements 21 , 22.

In this regard, it should be noted how the two Belleville springs 26 and 27 operate in such a way as to produce, when the distribution plate 10 is in operation, a positive and automatic compensation effect for providing the above sealing around the tubular coupling 18. In fact, when the temperature of the distribution plate 10 tends to increase, particularly in presence of more critical operating conditions, such as an increase in the temperature of the fluid plastic material MP flowing in it, and consequently the distance D in the zone of the cut 17 tends to decrease on account of the higher thermal expansions of the distribution elements 21 and 22, the pressure P exerted by the Belleville springs 26 and 27 against the respective walls 21b e 22b also tends to increase correspondingly, due to the further elastic deformations in the axial direction of the same Belleville springs 26 and 27.

Therefore; as a result, the Belleville springs 26 and 27 react to compensate with a more efficacious sealing action for these more critical conditions, thereby always and in all operating situations guaranteeing sealing of the plastic material, that is preventing it from leaking to the outside in the flow channel joining zones.

In particular the forces which, during operation and heating of the distribution plate 10, are inducted on the distribution elements 21 , 22 and 23 by the pressure exerted by

Belleville springs 26 and 27 are received and supported by the centering pins 15, by means of which the distribution elements 21 , 22 and 23 are centered with respect to the mould 12, in such a way as to allow Belleville springs 26 and 27 to fully exert their sealing action against the outflow of fluid plastic material in the flow channel joining zones.

From the description provided, it will therefore be clear that this invention fully achieves the objects that it was intended to achieve.

Naturally, without prejudice to the basic principle and concepts of this invention, the embodiments and manufacturing details of the distribution plate proposed here may be abundantly varied with respect to what has been described and illustrated thus far, without departing from the scope of the invention itself.

For instance the Belleville springs mounted in the separating space between two adjacent distribution elements may be more than two, or they could be mounted overlapping one another along the respective conical surfaces. Still the Belleville springs could be mounted in this separating space in the direction opposite that described in the foregoing, i.e. in such a way as to press with their respective inner edges against the facing walls of the two adjacent distribution elements, instead of with their outer edges and respective ring-shaped bearing planes.

Again the Belleville springs could be associated with seats, made in the two adjacent distribution elements, in which they are suitably housed in the zone of the separating space, or the Belleville springs could be mounted in the separating space with a certain initial, cold pre-loading.