CA2016032A1

CA2016032A1 - Injection moulding tool for synthetic plastics materials

Info

Publication number: CA2016032A1
Application number: CA002016032A
Authority: CA
Inventors: Wilhelm Reil
Original assignee: Individual
Current assignee: Tetra Laval Holdings and Finance SA
Priority date: 1989-05-09
Filing date: 1990-05-03
Publication date: 1990-11-09
Also published as: ATE126124T1; EP0396969B1; AU5477290A; AU628543B2; GR3017186T3; ES2075087T3; EP0396969A2; DE59009491D1; JPH02307721A; DE3915061A1; EP0396969A3; DK0396969T3

Abstract

Abstract Injection moulding tool for synthetic plastics materials An injection moulding tool is described which has a mould part (9) for the injection moulding of synthetic plastics material, with a carrier (3) for accommodating the mould part (9) and which, to form the injection moulding cavity (5) comprises a surface contour attachment, at least one cooling space (14, 15) being provided for connection to coolant supply and discharge lines (2).

In order to simplify such an injection moulding tool, rendering its production less expensive and increasing its effective life, it is envisaged that the mould part (9) be constructed as an insert carrying the surface attachment and mounted separably (10, 11) on the carrier (3) and to have a large part of its surface disposed in heat-conducting contact with the carrier (3), the cooling space (14, 15) being disposed in the carrier (3).

Description

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Injection moulding tool for synthetic plastics materials ___________________________________________________________ The invention relates to an injection moulding tool with a mould part for the injection moulding of synthetic plastics and with a carrier to hold the mould part which, in order to form the injection moulding cavity, comprises an attachment on the surface contour, at least one cooling space being provided for connection to coolant supply and discharge lines.

Injection moulding tools of this type for integrally moulding tops and/or bottoms onto the tube of a liquids package produced from a long paper tube coated on both sides with syn-thetic plastics material and so made liquid-tight are already known. The prior art injection moulding tool comprises a two-part outer mould, the two mould parts being fixed to carriers which are in turn articulatingly disposed on the machine and can be moved together mechanically by control drives along a common joint face and are pressed against each other under pressure so that the liquid synthetic plastics material is injected at high pressure into the mould cavity formed by the two mould parts. After cooling, the two mould parts are, by reason of the pivoting movement of the carrier, controlled by the drive, so moved apart from each other that the moulded product is freed. In the case of a prior art apparatus, an essentially cylindrical inner mandrel which constitutes the inner mould part is, after the separation of the two outer mould parts, freed together with the package which is closed at one end and can move out of the injection moulding tool.

Where these prior art injection moulding tools are concerned, it has been demonstrated repeatedly that the output cannot be increased as desired because the moulding has to be adequately cooled and so hardened through before the mould parts can be moved away from one another, particularly if for example the top comprises an opening with a tear-open tab or is provided with other parts which represent a certain mass of synthetic plastics material.
It always tal<es a certain time for this heated mass of synthetic plastics material to cool adequately.
Furthermore, another disadvantage which has been found ;s that the attachment to the surface contour on the injection moulding cavity is inevitably subject to wear and tear so that after a certain period of use the mould parts have to be tal<en out and replaced by new ones. This was expensive.

For adequate cooling, cooling spaces were disposed behind the surfaces forming the attachment on the surface contour and they were connected to coolant supply and discharge lines, the coolant being for example water. The man skilled in the art set out to take the cooling passages as closely as possible behind the mould faces and also to provide as many cooling passages as possible in order to reduce the cooling time and so increase the output from the injection moulding tool. In general, the cooling passages were made by bores, and it was necessary carefully to ensure sufficient stability of the surface attachment on the injection moulding cavity so that the high pressures of the synthetic plastics material during injection moulding could not damage the surface attachment. Therefore, the walls behind the surface attachment had to at least retain a certain thickness so that on the other hand a sufficiently rapid dissipation of temperature could never take less than a minimum time.

The man skilled in the art was faced with this difficulty of an excessive cooling time just as with the difficulty of achiev;ng the longest possible effective life of the mould part because after the surface - , . :, , "' ~, ~ ' ,. :

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attachment had become worn, the entire mould part had to be changed and thrown away.

Tog~ther with the disposal of the mould part, also the tool parts which contained the cooling space together with the surface attachment. Whether the cooling spaces were provided by bores or, according to other ideas, by metal cutting processes, provision of the relevant cooling space was expensive so that in any case a rapid exchange of injection mould parts was uneconomical.

Therefore, the invention is based on the problem of simplifying an injection moulding tool of the type described at the outset and of making its manufacture less expensive and of increasing its effective life.

According to the invention, this problem is resolved in that the mould part is constructed as an insert mounted separably on the carrier and comprising the surface attachment, a major part of its surface being in heat-conductive contact with the carrier and in that the cooling space is disposed in the carrier.

The novel idea underlying the invention lies in the idea of using the carrier solely for cooling and of producing the mould part separately from the carrier and disposing it on the latter, because the mould part is the tool part which is most at risk in terms of wear and tear and the funGtional errors which these cause. Therefore, the invention envisages no longer providing the mould part itself with a cooling space but of so mounting it ~lat on the intensely cooled carrier that the attachment on the surface contours of the mould part is adequately cooled, although the mould part itself has no cooling space. When the mould part is worn, it can be thrown away with little hesitation and replaced by a new one, because it is cheaper to produce and the construction of the entire .. :,.:~:. . .~

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injection moulding tool is thus simplified. The tool part comprising the cooling spaces and which is necessarily subject ko high production costs is now, according to the r ' =: invention, the carrier which does not need to be exchanged -:~ because it does not have any parts which are subject to a high level of wear and tear. Therefore, according to the invention, the main parts of the injection moulding tool can be used for longer, i.e. they have a substantially increased effective life.

In this respect, it is expedient if the mould part consists of steel while the carrier consists of a material having a greater heat conductivity level than steel and is preferably a metal such as for example aluminium. The fact that aluminium has a greater capacity for heat conductance than steel is well known; also, thoroughly developed techniques for machining aluminium are available. According to the invention, the carrier may preferably be constructed as a casking, because casting aluminium is similarly a well controlled technique. The attachment on the surface contour can easily be produced on the mould part by a process of cutting metal from the surface and since the insert-like mould part is supported so that it is in heat-conveying contact with the carrier, the surface attachment is not only perfeckly supported mechanically but also the high temperatures from the injection moulding cavity can be readily dissipated by the surfaces of mould part on the one hand and carrier on the other which are in heat-conductive contact with one another. :

According to the invention, it is furthermore expedient for the carrier to have an angular shape in at least one cross-sectional plane. In the past, a carrier was produced in a weaker thinner and smaller configuration because it only had to transfer the mokional forces of the mould parts, because the supply and d;scharge lines for : , :

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cooling water and the mould parts wikh the cooling spaces themselves had to be accommodated, supported and moved by the carrier. Pressure forces during operation on the other hand were accommodated by the mould parts -exclusively and via joints and levers on the carrier and were dissipated through the machine frame. This very basic concept meant that an average man skilled in the art had doubts about disposing cooling spaces in a carrier.
The new idea underlying the present invention is a more solid and stable construction of the carrier into which cooling spaces can be incorporated without coming too close to critical limits in terms of stability and strength. As a result of the angular construction envisaged in at least one cross-sectional plane, the carrier can be of very stable manufacture so that it is then thick enough and has sufficient mass to provide outstanding cooling properties for inserts mounted on it.

It is furthermore advantageous according to the invention for the mould part to comprise a thin plate, preferably 1-5 mm and espec;ally preferably 2-3 mm thick and fixed to the carrier by screws. In practice, initial tests have shown that it is actually sufficient if the surface contour attachment is for example provided on a thin plate which is screwed to the carrier and is by interaction with the high working pressures from the injection moulding cavity pressed rigidly against corresponding surfaces on the carrier, so that the surface attachment enjoys cooling as if cooling spaces were provided a few millimetres behind its heat-exposed surface. The mould part with the surface attachment is actually the component which is most subjected to wear and tear during operation and by reason of the fact that it is constructed as an insert which can be removed by means of screws it can easily be replaced by a new mould part.

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According to the invention, it is particularly favourable for support if the mould part comprises, set at an angle to each other, two plates each of which has a surface attachment, these preferably together enclosing an angle of 90. In the case of packages for liquids, it is expedient to produce the top from synthetic plastics material with no carrier material, the top being integrally moulded onto the narrow end edges of the paper tube. Furthermore, it is advantageous if khis top has at the same time an opening device and it is part~cularly expedient for this to carry a tear-open tab. Such attachments produce shapes of top member, particularly by reason of the opening device and the tear-open tab, which extend in various planes, e.g. the main plane of the top in a horizontal plane when a liquids package is placed on the table, and the tear-open tab in a plane at right-angles thereto. Thus there are two different surface contour attachments, one for the main plane of the top and the other for the tear-open tab. Therefore, it is expedient for two plates to be disposed at an angle to each other and for each to carry a surface attachment and to have its thin-walled structure anchored rigidly to the carrier.

To assist the mounting of the mould part, it is expedient to mount on the plate of the mould part at least one anchoring point. For example, the mould part could be produced by forging or casting, the part of the plate of the mould part which is remote from the injection moulding cavity being provided with the said anchoring points. In this way, the anchoring of the mould part on the carrier can be accessible from outside for speedier exchange in the event of repairs.

According to the invention, it is particularly favourable to use the iniection moulding tool of the type described above for integrally moulding a top and/or . : ., bottom onto the paper tube of a liquids package. If, namely, the conventional package producing machines are provided with a tool of the afore-described type which has one or other feature - possibly all the features - then .the .output from the package producing machine is increased because the cooling time can be reduced. Nevertheless,-.it is not necessary once the surface attachment --on the injection moulding cavity has become worn, to dispose of a complicated and expensively constructed cooling system.

The invention has been compared with the outer mould parts of a prior art type of injection moulding tool and also the advantages achieved have been so described that they are particularly favourable in conjunction with a two-part outer mould. However, a man skilled in the art knows that the inner mould can also be provided with corresponding inserts, plates and anchorage points, whereas the cooling passages extend in the carrier part of the inner mould so that when the relevant surface attachment has become worn, only the insert, the plate and its anchorage point have to be exchanged, while .the cooling spaces are separate and are also fluid-tightly separated therefrom, in the supporting part of the inner mould and do not have to be thrown away together with the worn surface attachment.

Further advantages, features and possible applications of the present invention will emerge from the ensuing description of a preferred example of embodiment.
In the accompanying drawings:

Fig. 1 is a cross-sectional view of a part of. the injection moulding tool of a preferred embodiment according to the invention, Fig. 2 is a rear view of the carrier of the-injection moulding tool, showing the rear anchorage point and the cooling water lines, ;' ~
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Fig. 3 is a perspective view of the carrier with the insert compris;ng the surface attachment, Fig. 4 is a plan view of the insert looking down on the carrier in Fig. 3 and ;magining that the parts of tha carrier concealing the insert are not there, Fig. 5 is a rear view of the insert look;ng down in relation to Fig. 4, Fig. 6 is a front view o~ the insert loo~;ng upwards ;n relation to Fig. 4, 0 Fig. 7 is a side view of the carrier looking from left to right in Fig. 4 and Fig. 8 is a tube for a l;quids package, closed at one end by a top comprising an open;ng device.

A part of the injection moulding tool is shown in Fig. 1 where a carrier 3 provided with a cooling water outlet 2 is mounted on the frame 4 to rotate about an axis 1. The carrier 3 assumes the position in which it defines half the injection moulding cavity. This ;njection mould;ng cavity 5 is indicated in Fig. 1 and is formed by cooperation of the two outer mould parts on the carriers 3 and the inner mould part which ;s not shown. Not shown is the ;nner mandrel wh;ch is capable of pivoting on the hub 6 of a mandrel wheel, not shown but rotatable about the ax;s 7, the sa;d inner mandrel therefore, as v;ewed in Fig. 1, moving out of or into the space between the two carriers 3 in the direction of the parting plane 8.

The carrier 3 supports the mould part 9 without clearance and is secured without clearance by screws 11 and an anchorage point 10. For pushing and withdrawing the mould part 9, the carriers 3 must be pivoted away ~rom each other. These pivot about the axis l when the ties are rotated about the axis 12 by a dr;ve engaging at 13.
After this opening of the injection moulding cavity 5, then, the screws 11 must be unscrewed from the anchorage points 10.

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g Fig. 1 also shows cooling passages 14, the inter;or volume of which -is connected by a system of passages, not shown, to the through-flow passages 15 and finally to the cooling water supply 17 (Fig. 2) or cooling water discharge 2. -- Fig. 1 shows how closely to the surface of the mould part ~ the cooliny-passages 14 are situa-ted in order rapidly to dissipate the heat present in the mould part. - - -In its shape and configuration, the mould part 9 can be more clearly seen in Figs. 4 to 7. It consists-of a thin main plate 17 from the main plane of which the anchorage point 10 projects to one side, here referred to as "downwardly", preferably at one end, here referred to as "rear", while at the opposite end, in this case the "front", the front plate 18 projects from the main plane of this plate 17 but in the direction opposite to that of the anchorage point 10, here referred to as "upwardly"
guides 27 being integrally moulded on the sides thereof and being adapted to slide in corresponding guide grooves 28 in the carrier 3.- The main plate 17 and the front- -plate 18 enclose- an angle of- 90. From the front, as shown in Fig. 6,--one sees the front plate-18 and-can see the surface contour attachment 19, particularly the gripper tab 20 of the moulding shown in Fig. 8; when looking upwards onto the main plate, i.e. if one is looking from left to right in Fig. 7 or from the bottom up in Fig. 6, it is possible to see the surface attachment 21 for the top 22 as is shown on the top of the tube in Fig. 3. When looking down onto the package, this top is circular which is why the surface attachment 21 for the top in Fig. 4 appears to be a dash-dotted circle. Of this second surface attachment 21, Fig. 4 shows, apart from the broken semi-circular - line,- -also the broken line -23 denoting the opening device 24 on the top 22 according to F;g. 8. In a drawing representing a definite embodiment, there will of course be further edges and surfaces which .. ..
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2~1 6~32 do not however need to be shown here. For understanding the invention, it is sufficient to know that the surface attachment 19, when looking at the front plate 18 from the front, i.e. in Fig. 6 when looking at the paper plane and in Fig. 7 when looking in an upwards direction, and the other surface attachment for the top is disposed under the main plate 17, i.e. when looking at the paper plane in Fig. 4 in an upwards direction or when looking from left to right in Fig. 7.

In the case of the preferred embodiment chosen here, the mould part is constructed from steel while the carrier 3 is produced from aluminium so that the heat conductivity in the carrier is greater than that of the mould part 9.

Already from the foregoing description of the mould part 9 which according to Fig. 7 is of Z-shaped cross-section, its character as an insert can be appreciated. With its surface attachments 19 and 21, the mould part 9 is the actual wearing part which is exchanged after a certain working life. The mould part 9 has no cooling spaces of any kind and there~ore is of comparatively simple form and can be inexpensively produced, in any event less expensively than a mould which comprises not only the surface attachment but also cooling spaces and corresponding sealing-tight connections.

Fig. 3 shows a perspective view of the position in which the mould part 9 with the main plate 17 and the front plate 18 is inserted. If in Fig. 3 one looks from the rear left to the right front, i.e. looking at the back 24 of the carr;er 3, then one has the view shown in Fig. 2, indicating the anchorage point 10 and the screws 1 1 .

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Looking at the finished product in Fig. 8, it is possible to see the useful possibility afforded by the afore-described tool with carrier 3 and mould plate 9 for the injection moulding of the top 22 shown at the top in Fig. 8 or of a (not shown) bottom onto the paper tube 25 which in its upper portion is of circular cross-section and which in its bottom portion is sealed in per se known manner by folded tabs and is of tetragonal cross-sec-tion (after it has been filled).

In operation, for cooling of the mould part 9, there is the advantage that the pressure of applicat;on of the synthetic plastics material which ;s introduced into the injection moulding cavity ~ during the injection moulding process causes the plates 17 and 18 to be firmly and intimately applied against the corresponding surfaces on the carrier, behind and at a very close distance from which the cooling passages 14 extend. Thus, a satisfactory transfer of heat from the steel mould part 9 to the carrier 3 or cooling passages 14 is guaranteed.

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Claims

1. An injection moulding tool with a mould part (10) for the injection moulding of synthetic plastics and with a carrier (3) to hold the mould part (9) which, in order to form the injection moulding cavity (5), comprises an attachment (19, 21) on the surface contour, at least one cooling space (14, 15) being provided for connection to coolant supply (17) and discharge lines (2), characterised in that the mould part (9) is constructed as an insert mounted separably (10, 11) on the carrier (3) and comprising the surface attachment (19, 21), a major part of its surface being in heat-conductive contact with the carrier (3) and in that the cooling space (14, 15) is disposed in the carrier (3).

2. An injection moulding tool according to Claim 1, characterised in that the mould part (9) consists of steel while the carrier (3) consists of a material which has a greater heat conductivity than steel, preferably a metal such as for example aluminium.

3. An injection moulding tool according to Claim 1 or 2, characterised in that the carrier (3) is angularly shaped in at least one cross-sectional plane.

4. An injection moulding tool according to one of Claims 1 to 3, characterised in that the mould part (9) comprises a thin plate (17, 18) preferably with a thickness of 1 to 5 mm and especially preferably a thickness of 2 to 3 mm, and is attached to the carrier (3) by screws (11).

5. An injection moulding tool according to one of Claims 1 to 4, characterised in that the mould part (9) comprises two plates (17, 18) set at an angle to each other and each of which (17, 18) carries a surface contour attachment (19, 21) and which preferably together enclose an angle of about 90°.

6. An injection moulding tool according to one of Claims 1 to 5, characterised in that at least one anchoring point (10) is provided on the plate (17) of the mould part (9).

7. Use of the injection moulding tool according to one of Claims 1 to 6 for integrally moulding a top (22) and/or bottom on the paper tube (25) of a liquids package.