Mold with an insert for a container blow molding machine

The invention relates to a mould (1) for a machine that is used to blow mould containers. The invention comprises: a wall (3) defining a cavity (4) which is distributed around a main axis, said wall (3) being equipped with passages (6, 7) for the circulation of a heat-transfer fluid inside the wall (3); and at least one mould insert (8) which is mounted to the wall (3), said insert being equipped with at least one conduit (17, 23) which is connected to a passage in the wall (3).

The invention relates to container blow molding. More particularly, it relates to a mold for a container blow molding machine, which blow molding is carried out by introducing a pre-heated parison (generally formed from thermoplastic material) into the mold, then placing the parison under pressure to provide it with the desired shape in the mold.

The skilled person is aware that blow molding is not carried out in the abstract, but that the operations carried out during blow molding (such as whether or not the container in the mold is heat treated, optionally cooling the container on leaving the mold, etc) and the machine parameters (such as the temperature of the mold) depend on the intended use of the container.

Thus, certain applications require the mold to be cooled: this applies, for example, when fabricating containers intended to receive still water.

In contrast, other applications require the mold to be heated: hence, hot filling (for example, with liquids such as tea, pasteurized fruit juice, etc) or pasteurizing the contents assumes that the mold is heated to a predetermined temperature to heat fix the material, the parameters for adjusting the temperature of the mold depending on the temperature of the filling liquid or the pasteurization conditions.

The temperature of the mold (cooling or heating) is adjusted by circulating a heat transfer fluid (for example city supply water or cooled water when cooling; hot water or oil when heating, the choice of fluid depending on the temperature to be reached) in passages provided in the wall of the mold, around the molding cavity.

Further, the skilled person is aware that hot filling or pasteurizing may cause substantial deformation of the container, which depends on the temperature of the liquid on filling or the pasteurization parameters, even if the container has previously undergone heat fixing treatment to render it heat resistant, which deformation may be irreversible to a greater or lesser extent, so that it does not completely disappear after the liquid has cooled. Hence, a liquid at (or heating the container to) a temperature of 80° C. causes the container to expand more than it would with a liquid at a temperature of 60° C.; further, even if the hot-filled or pasteurized container does not deform during filling or pasteurization, the internal pressure drop which accompanies cooling of the contents (after sealing) could cause a reduction in the volume of the container, which may result in contraction of certain zones of the container walls.

In order to at least partially overcome these disadvantages, it has in the past been proposed to anticipate residual deformation of the container following hot-filling or pasteurization and/or cooling by providing a molding insert in the mold, which insert can form deformation zones (panels or the like) on the container and may be positioned differently depending on the envisaged variation in the volume of the container during filling, to compensate for that deformation.

That solution means that the same mold can be used for containers that have similar shapes but that are intended to receive liquids at different temperatures or that undergo different heat treatments: under such circumstances, the containers are different at the end of blow molding, but become identical or similar following filling and/or cooling.

The use of inserts in applications other than hot filling or pasteurization is known, namely for containers which, a priori, are not susceptible of undergoing a treatment that might result in their deformation after their fabrication. That applies, for example, when, starting from a common basic shape, a manufacturer wishes to diversify in order to produce different series of containers with differences that may lie in details regarding the shape (the position of molded patterns such as logos, which differ from one series to another) and/or in volume: a known example relates to producing series of promotional containers of volume that is greater than the basic volume, so that inserts are used to increase the height of the containers of such series.

However, especially in the zone of the inserts, the use of inserts for any reason suffers from problems with the uniformity of thermal regulation of the mold. Such an absence of uniformity can in all configurations result in a problem with forming the containers properly, i.e. containers in which the distribution of material is optimized. Further, with containers intended to be hot filled or pasteurized, such problems with thermal regulation may result in the appearance of residual stresses in the container that are expressed during filling or pasteurization by non-recoverable deformation that deleteriously affects the behavior and/or final appearance of the container.

The aim of the invention is to overcome the above-mentioned disadvantages, by proposing a solution that can optimize thermal regulation of the mold during blow molding.

To this end, the invention proposes a mold for a container blow molding machine, said mold comprising:a wall defining a cavity distributed about a main axis, said wall being provided with passages for circulating a heat transfer fluid within the wall;at least one molding insert mounted on the wall, said insert being provided with at least one duct that communicates with a passage of the wall.

In this manner, heat transfer fluid can circulate in the molding insert, which is thus brought to substantially the same temperature as the wall of the mold.

Thus, it is possible to obtain a substantially uniform temperature of the mold during blow molding. This is beneficial to the mechanical stability of the container during hot-filling, since the mold can be heated substantially uniformly.

In one embodiment, said duct is in the form of a groove hollowed into a face of the insert turned towards the wall; it may meander, to enhance heat exchange.

In one embodiment, the position of the insert can be adjusted perpendicular to the main axis of the wall, and to this end the mold also comprises at least one adjusting shim, interposed between the wall and the insert, said shim being pierced by at least one port that opens onto a passage in the wall and onto a duct in the insert.

Thus, for the same insert, it is possible to adjust the position thereof as a function of the needs defined above, without deleteriously affecting the circulation of the heat transfer fluid.

Said shim is, for example, in the form of a plate having a contour that follows that of the insert, which may be provided with projecting pins that pass through positioning holes pierced in the shim.

In one embodiment, the wall of the mold is provided with at least two passages, namely a primary passage and a secondary passage, the insert being provided with at least two ducts, namely a primary duct and a secondary duct.

In one embodiment, the shim is pierced by at least two ports, namely a primary port that opens onto the primary passage and onto the primary duct, and a secondary port that opens onto the secondary passage and onto the secondary duct, the ports providing a properly dimensioned cross section of flow for the heat transfer fluid.

The primary port is, for example, in the form of an oblong hole, while the secondary port may be in the form of a circular hole.

The wall of the mold is, for example, hollowed by a recess in which the shim and insert are received, and into which at least one passage in the wall may open, facing a port in the shim.

Further, in one embodiment, the shim may be in the form of a set of laminated peel-off shims.

FIG. 1shows a portion of a mold1intended to equip a blow molding machine (not shown), to blow-mold containers (not shown).

The portion of mold1which is shown is in fact a portion of a half-mold2, intended to satisfy a particular requirement for the container to be formed, said need (an example of which is given below) possibly varying from one container to another and requiring adjustments that are difficult to make with a one-piece mold.

As explained below, the half-mold2shown comprises an attached insert; it is assembled with another half-mold (not shown) which, to form the body of the container, may be either identical with the half-mold2(i.e. it may also include an attached insert) or it may be different (i.e. it is a single piece, for example), the two half-molds being completed by a mold base element to form the base of the container, the assembly thus forming a complete mold.

The mold1includes a wall3that is made of steel or, as is preferable, of an aluminum alloy, and defines a cavity4(produced by precision machining) intended to receive a parison (not shown)—also termed a preform—of thermoplastic material, which has been heated to a temperature sufficient to allow it to deform during blow molding before introducing it into the mold1.

As can be seen inFIG. 1, the cavity4, which is shown in part in this figure, is generally distributed about a main axis X which, in defining a longitudinal direction, extends along the largest dimension of the cavity4(i.e. of the container), with the exception of a zone5in which a ribbed profile intended to facilitate gripping is to be formed on the container during blow molding.

As can also be seen inFIG. 1, the wall3of the mold1is provided with passages6,7intended to allow circulation of a heat transfer liquid within the wall3to regulate the temperature of the mold1.

Said passages6,7are in the form of a plurality of parallel bores pierced longitudinally into the wall3, and distributed over the periphery thereof.

Continuity of the heating circuit formed by passages6,7is ensured by perforations (not shown) connecting the passages6,7and produced in an upper portion of the mold, intended, it should be recalled, to form the shoulder of the container, not shown in the figures.

Said passages include a primary passage6in which the heat transfer fluid circulates from bottom to top of the mold1, for example, and a secondary passage7, adjacent to the primary passage6and connected thereto in the upper portion of the mold1, in which secondary passage7the heat transfer fluid flows in the reverse direction, from top to bottom of the mold1.

In the zone5where the profile is to be produced in the container, the mold1includes a molding insert8mounted on the wall3, in a position relative thereto that can be adjusted transversely, i.e. perpendicular to the main axis X.

In one embodiment, to allow the position of the insert8to be adjusted, the mold1also includes an adjusting shim9interposed between the wall3and the insert8.

The thickness of said shim9, which is in the form of a plate having a contour that substantially matches that of the insert8, is selected as a function of the envisaged variation in volume of the container during its subsequent filling.

Thus, depending on the temperature of the filling liquid, the thickness of said shim9may be selected to be 1 mm [millimeter], 1.5 mm, or 2 mm, said thickness in practice increasing with increasing temperature of the liquid.

Said shim9may be machined as a function of a particular defined requirement for the container to be formed. However, instead of fabricating the shim, it may be opportune to form the shim as a set of peel-off shims in the form of laminated sheets that are peeled off as a function of the desired size.

Such peel-off shims are commercially available and the skilled person could simply have a set of shims fabricated with the desired dimensions.

As can be seen inFIGS. 2 to 4, a recess10is hollowed into the wall3of the mold1and receives the shim9and the insert8together, the contour of said recess10being complementary to that of the insert8.

As shown inFIG. 3, the primary passage6opens, into the recess10via two openings, namely a lower primary opening11which is extended by a lower groove12, hollowed obliquely in the wall3, and an upper primary opening13, which is extended by an upper groove14, also hollowed obliquely into the wall3; as described below, these openings11,13are placed in communication when the shim9and the insert8are put into position.

Similarly, the secondary passage7opens into the recess10via two openings, namely an upper secondary opening15and a lower secondary opening16which are also placed in communication when the shim9and insert8are put in position.

In order to produce a uniform temperature in the mold1when blow-molding the parison, the shim9and the insert8are arranged to allow a heat transfer fluid to circulate inside the insert8. In fact, the passages6,7, interrupted in the recess10, are extended into the shim9and the insert8.

To this end, the insert8is provided with a primary duct17in the form of a groove pierced in one face18of the insert8termed the back face, turned towards the shim9(i.e. towards the wall3), which is pierced by a lower primary opening or port19in the form of an oblong hole which, when the shim9is in place in the recess10between the wall3and the insert8, is facing the lower primary opening11and thus opens onto the primary passage6produced in the wall3, said lower primary port19also opening onto a lower, oblique, portion20of the primary duct17.

The shim9is also provided with an upper primary opening or port21in the form of an oblong hole which, when the shim9is in place in the recess10between the wall3and the insert8, is facing the upper primary opening13and thus opens onto the primary passage6produced in the wall3, said upper primary port21also opening onto an upper, oblique, portion22of the primary duct17.

Further, as can be seen inFIG. 5in particular, the insert8is provided with a secondary duct23in the form of a groove pierced in the rear face18of the insert8, the shim9being pierced by an upper secondary port24in the form of a circular hole which, when the shim9is in place in the recess10between the wall3and the insert9, is facing the upper secondary opening15and thus opens onto the secondary passage7formed in the wall3, said upper secondary port24also opening onto an upper portion25of the secondary duct23.

The shim9is also provided with a lower secondary port26in the form of a circular hole which, when the shim9is in place in the recess10between the wall3and the insert8, is facing the lower secondary opening16and thus opens onto the secondary passage7, said lower secondary port26also opening onto a lower portion27of the secondary duct23.

As can clearly be seen inFIGS. 5 and 9, the ducts17,23in the insert8meander, to allow better distribution of the heat exchange between the heat transfer fluid and the bulk of the insert8.

Further, as can also clearly be seen inFIG. 5, the ducts17and23are not uniform in depth: this is due to the shape of the insert8, the thickness of which is not uniform measured perpendicularly to the main axis X: it is thinner in its upper and lower portions (ducts17and23thus being shallower), and it is thicker in the center (ducts17and23thus being deeper). The oblong ports formed in the shim9, which follow the shallowest portions of ducts17and23, can thus guarantee a minimum flow cross section for the heat transfer fluid to avoid head losses along the fluid circuit.

When the shim9and the insert8are in place in the recess10, the lower groove12is facing the lower primary port19and the lower portion20of the primary duct17, while the upper groove14is facing the upper primary port21and the upper portion22of the primary duct17.

Further, the upper secondary opening15is facing the upper secondary port24and the upper portion25of the secondary duct23, while the lower secondary opening16is facing the lower secondary port26and the lower portion27of the secondary duct23.

Thus, while ensuring continuity, the circulating heat transfer fluid circuit is diverted into both the primary passage6and the secondary passage7, the diverted fluid being used to advantage to bring the insert8to the same temperature as the wall3.

This diversion occurs regardless of the thickness of the shim9, with the ports19,21,24,26that are formed therein ensuring transit of heat transfer fluid from the wall3to the insert8, and vice versa.

Further, as shown inFIGS. 5 and 7, the insert8is provided with projecting pins28,29that pass through holes30,31pierced in the shim9, to allow precise positioning thereof relative to the insert8when positioning them together in the recess10.

Precision machining of the mold1and more particularly of the recess10, the shim9, and the insert8, can avoid having to position seals between the wall3and the shim9, and between the shim9and the insert8.

Although the description illustrates an embodiment in which the position of the insert8is adjusted using a shim, the invention is also applicable when a set of inserts of different depths (i.e. perpendicular to the axis X) is used to accommodate variations in the desired shape from one container to the other, in which case adjustment shims do not need to be used. Clearly, when the insert simply functions to allow production of a container shape which differs from a common basic shape, then shims no longer appear to be required.

However, even in the circumstances discussed here, shims may be used (in particular peel-off shims) to compensate for clearances linked to machining tolerances.