FR3089446A1 - Device for manufacturing a container by blow molding or stretch blow molding - Google Patents

Abstract

The invention relates to a device (1) for the manufacture of a container by blow molding or stretch-blowing from a plastic blank, the device comprising a first half-mold (21) and a second half-mold (22) together defining an imprint (E) of the container to be formed, a first support (31) and a second support (32) respectively carrying the first half-mold and the second half-mold, and pneumatic compensation means for a blowing pressure, the compensation means comprising: - a first sealed chamber (41) interposed between the first support and the first half-mold; - a second sealed chamber ( 42) interposed between the second support and the second half-mold; - injection means (43) of pressurized air coupled to the first sealed chamber and to the second sealed chamber. Figure for the abstract: Fig. 1

Description

Description

Title of the invention: Device for manufacturing a container by blow molding or stretch blow molding

The field of the invention is that of the manufacture of containers by blow molding or stretch blow molding from a plastic blank.

The invention relates more particularly to the manufacture of containers by blowing or stretch-blowing using a device comprising a mold comprising two half-molds, and pneumatic compensation means of a blowing pressure at l inside the mold.

It is known to manufacture containers, in particular bottles, by blow molding or stretch blow molding from a plastic blank. A blank corresponds to a preform or to an intermediate form between the preform and the final container.

To do this, blanks are brought to a thermal conditioning station at a glass transition temperature such that they can be deformed. The hot blanks are then transferred to a mold, comprising assembled half-molds, where they are "blown" or "stretched and blown". The blowing is carried out by means of a pressurized gaseous fluid, generally air.

The pressures involved during blowing frequently reach 40 bars. As a result, during the manufacture of a container with a capacity of 1.5 l, which has a projected surface of approximately 250 cm2, a force of the order of 9,800 dN tends to separate the two half-molds. assemblies which constitute the blow mold.

A conventional device comprises:

- a mold comprising a first half-mold and a second half-mold which together define the imprint of the container to be formed;

- a support for each half-mold, each support carrying one of the half-molds. Despite all the care taken in producing the half-molds and their support, under the action of the force generated by the pressure of the blowing fluid, the two half-molds deviate from one another and an offset of a few tenths of a millimeter may appear at the joint plane of the half-molds.

A parting line with an offset of one tenth of a millimeter has the consequence that the container formed has poor visual quality.

In other words, although the structural strength of the container is intact, the offset induced by the blowing pressure at the joint plane degrades the appearance of the container.

It should be noted that this disappointing perceived quality can prevent the marketing of the container.

It is therefore important to avoid such play at the joint plane of the molds.

We know from the patent document published under the number FR2659265 a compensation system integrated into the device for manufacturing the container.

More specifically, the device comprises a sealed chamber interposed between one of the half-molds, the first half-mold, and its support. The first half-mold is thus partially mobile relative to its support.

Pressurized air injection means inject compressed air inside the sealed chamber during the blowing of the container. The injection of compressed air inside the sealed chamber allows the first movable half-mold to be pressed against the second half-mold to compensate for the blowing pressure inside the container.

Inherent in the locking system of such manufacturing devices, a set of unlocking and locking of the mold still exists. The injection of air into the sealed chamber thus makes it possible to compensate for the unlocking and locking play of the mold in order to press the first half-mold against the second half-mold.

The second half-mold is fixed integrally on its support, without the interposition of elastic means. This second half-mold serves as a reference point for centering the blank inside the mold and for making certain adjustments to the device.

This solution improves the visual appearance of the container obtained.

However, this solution does not provide complete satisfaction with the result obtained.

Indeed, it has been found that visual defects, although less significant, can still be observed on the containers produced with this type of device.

In addition, it has also been observed that the blowing pressure (up to 40 bars) can temporarily deform the material constituting the mold, and produce an undesirable ovalization of the container.

Finally, the pneumatically compensated half-mold has degraded cooling performance compared to the second half-mold secured to its support. Indeed, the sealed chamber between the first half-mold and its support induces the presence of an air knife preventing optimal transfer of the temperature from the half-mold to its support. This difference in cooling performance between the two half-molds can produce an absence of symmetry between the two parts of the container pressed against each of the half-molds during blowing. That is to say that, even if the container would have an unwanted ovalization, it would also have an absence of symmetry between the two parts previously described.

The invention particularly aims to overcome the drawbacks of the prior art. More specifically, the invention aims to provide a device for the manufacture of a container by blowing or stretch-blowing which allows to obtain a container having a higher visual quality than that of the containers obtainable by through devices according to the prior art.

The invention also aims to provide such a device which has a better joint plane than those of the devices according to the prior art which include pneumatic compensation.

These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to a device for the manufacture of a container by blow molding or stretch blow molding from a blank in plastic material, the device comprising:

- A mold comprising a first half-mold and a second half-mold together defining an imprint of the container to be formed;

- A first support and a second support respectively carrying the first half-mold and the second half-mold, the first support and the second support being movable between an open position and a blowing position of the container;

- pneumatic compensation means for a blowing pressure inside the mold, the compensation means comprising:

- A first sealed chamber interposed between the first support and the first half-mold, the first half-mold having a clearance relative to the first support;

- means for injecting pressurized air coupled to the first sealed chamber, characterized in that the compensation means comprise a second sealed chamber interposed between the second support and the second half-mold, the second half-mold having a travel relative to the second support, and the means for injecting pressurized air being coupled to the second sealed chamber.

Thanks to the device according to the invention, a double pneumatic compensation is achieved during the blowing or stretch-blowing of the plastic blank.

This double compensation makes it possible to obtain a better mold joint plane. The best parting line is obtained thanks to the two half-molds which are both pressed against each other, each by means of its sealed chamber during blowing. Thus, during the blowing of the container, the pressure exerted on the first half-mold and on the second half-mold is compensated on both sides of the mold, and the forces are distributed homogeneously, whether on the side of the first half-mold. or on the side of the second half-mold.

The device can thus be designed to avoid or reduce the ovalization phenomenon of the container.

In addition, the deformation of the mold halves under the effect of pressure and thus the deformation of the container, although inevitable, can then be anticipated.

Thanks to this anticipation of deformations, the design of the device can be provided to predetermine the phenomenon of ovalization of the container so as to minimize it.

More specifically, thanks to the double compensation, the two half-molds will touch but will not themselves keep their shape. For example, if they both define a shape of round section (each half-mold having a semicircle shape), then, under the effect of pressure, this round shape tends to be ovalized by the deformation of the metal and the opening of the half-molds under the effect of pressure.

In the case where only one of the half-molds is compensated, this ovalization is not the same on the side of the first half-mold compared to that occurring on the side of the second half-mold.

Double compensation thus allows to have a symmetrical deformation.

In addition, by incorporating compensation means taking the form of a sealed chamber between each of the half-molds and their support, then the cooling of the half-molds is homogeneous on both sides of the mold.

Thus, rather than having a mold having a second half-mold which cools more quickly than its first half-mold (because the first half-mold is separated from its support by an air knife which prevents or limits good transmission of the temperature from the half-mold to the support), then this characteristic (the air gap) is found on each of the half-molds and the temperature transfer takes place in a homogeneous manner.

Finally, the fact of having two movable half-molds allows the deflections of the half-molds relative to their support to be smaller than the deflection of the single movable half-mold of the device according to the prior art .

For example, compared to a device according to the prior art where the only movable half-mold relative to its support would have a travel of a tenth of a millimeter, then the two half-molds according to the invention each have a travel of five hundredths of a millimeter. That is to say that the travel is halved compared to the travel according to the prior art.

Advantageously, the first sealed chamber and the second sealed chamber are symmetrical with respect to one another.

This symmetry can be axial or planar.

Thanks to such symmetry between the two sealed chambers, the ability to obtain a better quality joint plane is increased. More specifically, the device can more easily produce a container that does not have a negative ovalization phenomenon.

This reduction in the negative ovalization phenomenon is obtained thanks to better control of the deformations of the materials constituting the device, as well as to better control of the cooling of the two half-molds.

This symmetry can be axial or planar, which makes it possible to standardize the forming parameters of the container and which contributes to obtaining a qualitative joint plane.

Preferably, the device comprises means for locking the first support and the second support in the blowing position of the container, the device having a play of locking and unlocking between the first half-mold and the second half-mold for allow the locking means to pass from an unlocked state to a locked state and vice versa, the locking and unlocking clearance being equal to the sum of the deflections of the first half-mold and of the second half-mold.

The locking means define the locking / unlocking clearance required between the two half-molds. This locking and unlocking game is essential for the operation of the locking means, and cannot be lowered below a certain value.

Consequently, thanks to the deflections between each of the half-molds and their support, the sum of which is equal to the locking and unlocking clearance, then the stroke and the pressures exerted on the two half-pieces can be optimized. molds during the injection of a blowing pressure inside the sealed chambers.

According to an advantageous characteristic, the sum of the deflections of the first half-mold and of the second half-mold is between 0.07 mm and 0.2 mm, and is preferably equal to 0.1 mm.

According to an advantageous solution, the movement of the first half-mold is equal to the movement of the second half-mold.

According to a preferred embodiment, the first sealed chamber is delimited between the first support and the first half-mold by a first elastically deformable peripheral seal, and the second sealed chamber is delimited between the second support and the second half mold by a second elastically deformable peripheral seal.

Such elastically deformable peripheral seals ensure the tightness of the sealed chambers.

Advantageously, the first peripheral seal and the second peripheral seal are identical.

In this way, the manufacture and assembly of the peripheral seals is simplified. In addition, this allows to participate in the functional and structural symmetry between the two half-molds, and to optimize the formation of a qualitative joint plane.

According to a preferred design, the first peripheral seal and the second peripheral seal are lip seals, each peripheral seal having:

- a first lip bearing against the half-mold;

- a second lip pressing against the support, the first lip and the second lip being oriented towards the inside of the sealed chamber delimited by the peripheral seal.

Such lip seals have high reliability.

The reliability of these elastically deformable peripheral seals is particularly important because of the production rates of the devices for the manufacture of a container by blow molding or stretch blow molding (this rate can be from 2,600 to 2,800 bottles per hour per mold).

According to a first alternative embodiment:

- The first half-mold has a groove housing the first peripheral seal;

- The second half-mold has a groove housing the second peripheral seal. According to a second alternative embodiment:

- The first support has a groove housing the first peripheral seal;

- The second support has a groove housing the second peripheral seal.

The peripheral seals can be completely housed in the grooves when the two half-molds are pressed against their support.

The symmetrical design of these grooves makes it possible to have reduced deformation of the peripheral joints, which induces an increase in their service life.

According to an advantageous embodiment, the device comprises first elastic return means of the first half-mold and second elastic return means of the second half-mold each in a position pressed respectively against the first support and the second support .

Such elastic return means allow, in the absence of air injection into the sealed chambers or into the mold, to ensure that the two half-molds are spaced from each other to present a set of locking and unlocking allowing the opening of the mold.

Other features and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment of the invention, given by way of illustrative and non-limiting example, and of the accompanying drawings among which :

[Fig.l] is a cross-sectional representation of a device for manufacturing a container by blow molding or stretch blow molding, according to the invention, passing through the middle of the imprint defined by the mold;

[Fig.2] is a horizontal section of the device passing through the center of the air injection nozzles inside the sealed chambers;

[Fig.3] is an exploded perspective view illustrating a half-mold and its support, the support being shown in a section passing through the air injection nozzle inside the sealed chamber;

[Fig.4a] is a schematic representation of a peripheral seal between a half-mold and a support in an exploded view;

[Fig.4b] is a schematic representation of a peripheral seal between a half-mold and a support according to an assembled view illustrating the sealed chamber formed;

[Fig.5] is a side view of a support.

Figure 1 illustrates a device 1 according to the invention for manufacturing a plastic container by blow molding or stretch blow molding from a blank.

The device 1 comprises:

- a mold 2;

- a mold support 3.

The mold 2 comprises a first half-mold 21 and a second half-mold 22. For the blowing of a container, the first half-mold 21 and the second half-mold 22 are applied one against the other. 'other and define between them a cavity having an imprint E of the container to be formed.

The first half-mold 21 and the second half-mold 22 also define a joint plane at their faces which are in contact with each other during the blowing of the container.

The first half-mold 21 more precisely comprises a first half-shell 211 and a first shell support 212.

Similarly, the second half-mold 22 includes a second half-shell 221 and a second shell support 222.

The first shell support 212 and the second shell support 222 are for example made of aluminum. Aluminum in particular improves the cooling and the mass of the mold 2.

This mold structure is described in European patent EP0821641.

The mold support 3, meanwhile, comprises a first support 31 and a second support 32. This first support 31 and this second support 32 are conventionally designated by the term of brackets.

The first support 31 and the second support 32 respectively carry the first half-mold 21 and the second half-mold 22. In other words, the first support and the second support 32 embed the mold 2.

The first support 31 and the second support 32 are designed to take up and distribute the blowing forces exerted inside the mold 2 during blowing.

Referring to Figures 2, 3 and 5, the first support 31 and the second support 32 are movable between an open position (not shown) and a blowing position of the container, illustrated by Figure 2, position in which the mold is closed, by means of a hinge 33.

Referring to Figure 5 which illustrates a second support 32, the device 1 comprises means for locking the first support 31 and the second support in the blowing position of the container.

The locking means are known and are in particular of the type comprising:

- Legs 34 presented by the first support and by the second support 32, pierced with concentric bores, the legs 34 overlapping one another in the blowing position of the container, and being distributed over the entire height of the supports 31 , 32;

- fingers (not shown), controlled by a common shaft, locking two successive lugs 34 by fitting into the bores.

To this end, the device 1 has a locking and unlocking clearance between the first half-mold 21 and the second half-mold 22 allowing the locking means to pass from an unlocked state to a locked state and vice versa.

Referring to Figures 1, 2, 3, 4a and 4b, according to the principle of the invention, the device 1 comprises pneumatic compensation means of a blowing pressure inside the mold 2.

These pneumatic compensation means include:

- A first sealed chamber 41 fitted to the first half-mold 21 and the first support 31;

- A second sealed chamber 42 fitted to the second half-mold 22 and the second support 32;

- means 43 for injecting pressurized air coupled to the first sealed chamber 41 and to the second sealed chamber 42.

The first half-mold 21 is movable relative to the first support 31. The first half-mold 21 has in particular a clearance relative to the first support 31.

Similarly, the second half-mold 22 is movable relative to the second support 32 and the second half-mold 22 thus has a clearance relative to the second support 32.

With reference to FIGS. 1 and 5, these deflections are limited by stops 36 with screws. These screw stops 36 can be adjusted to modify the travel of the first half-mold 21 and of the second half-mold 22.

With reference to FIG. 3, these screw stops 36 are coupled to the second half-mold 22 on fixing points 360. The mounting is identical for the stops 36 with screws of the first half-mold 21.

According to the present embodiment, each of the deflections is 0.05 mm, and the sum of the deflections of the first half-mold 21 and the second half-mold 22 is equal to 0.1 mm.

The locking and unlocking game is, according to the present embodiment, equal to the sum of the deflections of the first half-mold 21 and the second half-mold 22.

The small 0.05 mm clearance of the first half-mold and the second half-mold prevents the appearance of a phenomenon of corrosion by contact wear (also described by the English term "fretting") at the stops. 36 with screws and other parts impacted by the displacement of the half-molds 21, 22 relative to the supports 31, 32.

With reference to FIGS. 1 and 5, the device 1 also includes return means 37 for the half-molds 21, 22 in a position pressed against their support, of which:

- First elastic return means of the first half-mold 21 in a position pressed against the first support 31;

- elastic return means of the second half-mold 22 in a position pressed against the second support 32.

These return means 37 include return springs. According to a possible embodiment, a return spring can be coupled on a rod extending from a half-mold through the support to a head of the rod spaced from the support. The return spring is then located between the rod head and the support and tends to move apart from one another, thus tending to bring back or maintain the half-mold in its position pressed against the support.

In the absence of other constraints, the return means thus allow the half-molds 21, 22 to be moved away from one another.

Referring to Figures 1 to 4b, the sealed chambers are interposed, or created, between the first support 31 and the first half-mold 21 for the first sealed chamber 41, and between the second support 32 and the second half mold 22 for the second sealed chamber 42.

According to this embodiment, the device 1 also includes a first peripheral seal 51 elastically deformable as well as a second peripheral seal 52 elastically deformable.

The first peripheral seal 51 delimits the first sealed chamber 41 between the first support 31 and the first half-mold 21.

Similarly, the second peripheral seal defines the second sealed chamber 42 between the second support 32 and the second half-mold 22.

During the blowing, air is injected into the sealed chambers 41, 42 which causes an increase in the pressure therein. This pressure tends to move the half-mold away from its support. The elastically deformable peripheral seals provide a sealed connection between each of the half-molds 21, 22 and their respective supports 31, 32.

The first peripheral seal 51 and the second peripheral seal 52 are advantageously lip seals which have a substantially U-shaped section.

With reference to FIGS. 4a and 4b, each peripheral seal 51, 52 has:

- a first lip 511, 521;

- a second lip 512, 522.

The first lip 511, 521 is intended to be in abutment against the half-mold 21, 22. The second lip 512, 522, in turn, is intended to be in abutment against the support 31,32.

These first lips 511, 521 and these second lips 512, 522 are intended to be oriented towards the inside of the sealed chambers 41, 42 delimited by the peripheral seals 51, 52.

With reference to FIGS. 4a and 4b, each peripheral seal 51, 52 is housed in a groove 35.

In fact, the mold 2 comprises two grooves 35, or the first support 31 and the second support 32 each include a groove 35.

According to this embodiment illustrated in Figures 1, 2 and 3, the first half-mold 21 and the second half-mold 22 each have a groove 35 in which are housed respectively the first peripheral seal 51 and the second peripheral seal 52.

More specifically, the first shell support 212 and the second shell support 222 respectively have a groove 35.

Advantageously and with reference to FIG. 2, the first sealed chamber 41 and the second sealed chamber 42 are symmetrical with respect to each other. More specifically, the first sealed chamber 41 and the second sealed chamber 42 are symmetrical with respect to a plane P passing through the joint plane.

This symmetry, illustrated by FIGS. 1 and 2, allows a homogeneous distribution of the forces of compensation of the forces generated on the half-shells by the blowing pressure of the container inside the mold.

[YES] According to the present embodiment, it is a planar symmetry.

Referring to Figure 2, it can be noted that, in addition to being symmetrical, the projections on the plane P of the first sealed chamber 41 and the second sealed chamber 42 are more important than the projection of the footprint E on plane P.

Referring to Figures 2, 3 and 5, the first support 31 and the second support 32 have air intake pipes 310, 320 inside the sealed chambers 41, 42.

These air intake pipes 310, 320 open outside the first support 31 and the second support 32 on a coupling plate 311, 321.

As shown schematically in FIG. 2, the means for injecting pressurized air 43 comprise a source 430 of pressurized air, an air outlet 433, as well as a pipe 432.

The means 43 for injecting pressurized air also include injection nozzles 434 coupled to the air intake pipes 310, 320. These injection nozzles 434 are covered by a housing (not shown ) assembled on the coupling plate 311, 321.

The injection means 43 further comprises a distributor 431. The distributor 431 is in this case of the "3/2" type, that is to say that it has three orifices and two positions.

The source 430 of pressurized air, the air outlet 433, as well as the piping 432 are coupled to the distributor 431. The piping 432 couples the distributor 431 to the injection nozzles 434.

In a first position of the distributor, illustrated in FIG. 2, the air source 433 feeds the piping 432 and the first sealed chamber 41.

Referring to Figures 1 to 5, the operation of the device 1 according to the invention is described below.

For the forming of a container, the mold 2 is closed while being loaded with a preform. The mold 2 is closed by passing the first support 31 and the second support 32 from their open position to their position for blowing the container.

The locking means make it possible to ensure that the mold 2 does not open during the blowing.

[0123] During the blowing phase, a fluid such as air is injected into the preform at the same time as the means 43 for injecting pressurized air are activated.

The air injection means 43 are controlled, thanks to the distributor 431, so as to coordinate the rise in pressure in the mold cavity 2 with that of the sealed chambers 41, 42. The compensation is then carried out symmetrically at the two half-molds 21, 22.

Advantageously, the blowing pressure inside the mold 2 is equal to the air injection pressure inside the first sealed chamber 41 and inside the second sealed chamber 42.

The injection of air into the sealed chambers 41, 42 makes it possible to separate the first half-mold 21 from the first support 31 and the second half-mold 22 from the second support 32, and thus to press one against the other the first half-mold 21 and the second half-mold 22.

At the end of the blowing of the container, the pressure is released in the mold 2 and the distributor 431 changes position to allow the air contained in the sealed chambers 41, 42 to escape.

The first support 31 and the second support 32 then pass from their blowing position of the container to their open position to open the mold 2, allow the extraction of the container formed, and start a forming cycle of a container.

Claims (1)

Claims [Claim 1] Device (1) for manufacturing a container by blow molding or stretch blow molding from a plastic blank, the device comprising: - A mold (2) comprising a first half-mold (21) and a second half-mold (22) together defining an imprint (E) of the container to be formed; - A first support (31) and a second support (32) respectively carrying the first half-mold and the second half-mold, the first support and the second support being movable between an open position and a blowing position of the container; - pneumatic compensation means for a blowing pressure inside the mold, compensation means including: - A first sealed chamber (41) interposed between the first support and the first half-mold, the first half-mold having a clearance relative to the first support; - means for injecting (43) pressurized air coupled to the first sealed chamber, characterized in that the compensation means comprise a second sealed chamber (42) interposed between the second support and the second half-mold, the second half-mold having a clearance relative to the second support, and the means for injecting pressurized air being coupled to the second sealed chamber. [Claim 2] Device (1) according to the preceding claim, characterized in that the first sealed chamber (41) and the second sealed chamber (42) are symmetrical with respect to each other. [Claim 3] Device (1) according to any one of the preceding claims, characterized in that it comprises means for locking the first support (31) and the second support (32) in the blowing position of the container, the device having a play locking and unlocking between the first half-mold (21) and the second half-mold (22) to allow the locking means to pass from an unlocked state to a locked state and vice versa, the locking and unlocking being equal to the sum of the deflections of the first half-mold and of the second half-mold. [Claim 4] Device (1) according to any one of the preceding claims, characterized in that the sum of the deflections of the first half-mold (21) and the second half-mold (22) is between 0.07 mm and 0.2 mm. [Claim 5] Device (1) according to any one of the preceding claims, characterized in that the movement of the first half-mold (21) is equal to the movement of the second half-mold (22). [Claim 6] Device (1) according to any one of the preceding claims, characterized in that the first sealed chamber (41) is delimited between the first support (31) and the first half-mold (21) by a first peripheral seal (51) elastically deformable, and in that the second sealed chamber (42) is delimited between the second support (32) and the second half-mold (22) by a second elastically deformable peripheral seal (52). [Claim 7] Device (1) according to the preceding claim, characterized in that the first peripheral seal (51) and the second peripheral seal (52) are identical. [Claim 8] Device (1) according to any one of claims 6 and 7, characterized in that the first peripheral seal (51) and the second peripheral seal (52) are lip seals, each peripheral seal having: - A first lip (511, 521) bearing against the half-mold (21, 22); - a second lip (512, 522) bearing against the support (31, 32), the first lip and the second lip being oriented towards the inside of the sealed chamber (41, 42) delimited by the peripheral seal. [Claim 9] Device (1) according to any one of claims 6 to 8, characterized in that: - The first half-mold (21) has a groove (35) housing the first peripheral seal (51); - The second half-mold (22) has a groove (35) housing the second peripheral seal (52). [Claim 10] Device (1) according to any one of claims 6 to 8, characterized in that: - The first support (31) has a groove (35) housing the first peripheral seal (51); - The second support (32) has a groove (35) housing the second peripheral seal (52). [Claim 11] Device (1) according to any one of the preceding claims, characterized in that it comprises first return means elastic of the first half-mold (21) and of the second elastic return means of the second half-mold (22) each in a position pressed respectively against the first support (31) and the second support (32).