FR2736582A1 - INSTALLATION FOR THE MANUFACTURE OF HOLLOW BODIES IN SYNTHETIC MATERIAL - Google Patents

Abstract

This installation comprises on the one hand, on each of the intermediate molds (40a, 40b) separating, in each of the chains (A and B) of molds (4a, 4b), two distinct imprints each corresponding to at least one blank (15) : - a semi-cylindrical axial channel (12) cooperating with the opposite mold channel (40a, 40b) to form an imprint making a junction duct (14) between two successive blanks (15), - a radial bore ( 13) of cylindrical section opening into the axial channel (12) and to the outside, - and a piston (16), mounted to slide in the bore (13) against the spring return means (19) on driving outwards, this piston having an internal head (16a), of diameter at least equal to that of the axial channel (12), and an external heel (16b) projecting from the back of the corresponding mold, and, on the other hand , and on either side of the parallel branches of the mold chains, two fixed ramps (22a, 22b) controlling the radial inward movement of the pi opposite stons (16) to crush, at least locally, the junction duct (14) between two blanks (5).

Description

The invention relates to the manufacture of hollow body blanks made of

  synthetic material and, more particularly, blanks which, after cooling, are heated and subjected to radial stretching, together with longitudinal stretching,

  to improve their mechanical or optical characteristics.

  Such blanks, made of polyvinyl chloride or polyethylene, are generally intended to form containers, and for example, containers

  transparent and brilliant highlighting their content.

  Currently, these blanks are obtained by injection blow molding in the

  same facilities as those producing bottles, flasks or various containers, that is,

  to say by complex installations, operating step by step, having a productivity

  limited and leading to a high manufacturing cost.

  Installations are known to manufacture continuously monolayer or multilayer sheaths with smooth or annular outer surface, by means of two chains of molds describing closed circuits in which two parts of trajectories are parallel, so that the impressions of the molds in screws screw form a tunnel whose longitudinal axis is coaxial with that of a tubular parison, delivered by an extruder. This parison is brought into contact with the imprints by the difference between

  its internal pressure and the external pressure prevailing in the fingerprints.

  This type of installation works continuously and provides tubular bodies which, at the output of the machine, are cut to the desired length. In this technique, it is known to locally produce sections of different diameters, for example, for

  constitute the tulips used for the end-to-end connection of duct sections.

  The object of the present invention is to overcome the drawbacks of the installations currently producing extrusion blow blanks in two-piece unit molds carried by a carousel, by modifying the installations continuously producing tubular bodies by means of mold chains. of which two parallel branches form, by the molds facing each other, a continuous impression. For this purpose, the installation according to the invention comprises, on the one hand, on each of the intermediate molds separating, in each of the mold chains, two distinct indentations each corresponding to at least one blank: a cooperating semi-cylindrical axial channel with the mold channel facing each other to form an impression forming a connecting duct between two successive blanks, - a cylindrical bore of cylindrical section opening into the axial channel and outside, - and a piston, slidably mounted in the radially sliding bore against spring return means driving it outwards, this piston having an internal head of diameter at least equal to that of the axial channel, and an external heel protruding from the back of the corresponding mold, and on the other hand, and on both sides of the parallel branches of the mold chains, two fixed ramps controlling the radial displacement towards the inside of the pistons

  opposed to crush at least locally the connecting duct between two blanks.

  Thus, each blank hollow body is first formed by the pressure differential exerted on the parison, and is completed by crushing the conduit connecting it to the next blank being formed. This crushing also closes the downstream end of the next blank, thus improving the effect of the pressure differential on the parison. The installation of the installation is inexpensive and reliable and allows to obtain, at low cost, continuously and with a high rate, blanks that can be taken as the current blanks in traditional extrusion blow molding facilities. Moreover, the plant can form synthetic materials with a higher viscosity than in current installations, without affecting the

  characteristics of the blanks and the final product.

  Other features and advantages will emerge from the following description

  with reference to the attached schematic drawing representing, by way of example, a form

execution of this installation.

  Figure 1 is a plan view from above with partial section of an installation for the manufacture of body blanks, Figure 2 is a partial side view showing an embodiment of the blanks obtained, Figure 3 is a side view. in cross section along III-III of Figure 1 showing, on an enlarged scale, the closing pistons when at rest, Figure 4 is a plan view from above with partial section showing the

  closing pistons at the beginning of the closing phase by two slides.

  As shown in FIG. 1, this installation comprises an extruder 2 delivering a tubular parison 3 of synthetic material between two mold chains A and B describing each of the continuous circuits, of which at least two branches are parallel to the direction of movement of the parison. 3, schematized by the dashed line D. Each mold chain A or B is composed of a succession of molds 4a, 4b each having semi-cylindrical cavities 5a, 5b facing each other and defining a continuous tunnel. The mold chains are, in known manner, associated with means ensuring their drive in translation, for example, a succession of toothed wheels arranged at a fixed position and cooperating with racks arranged on the

back on the base of the molds.

  The installation also comprises, as shown in FIG. 3, means 6 pressing the molds 4a, 4b against each other during their common trajectory and a lower frame 7a on which the molds slide and an upper plate 7b, crossed locally by ducts 8 bringing into a channel 9, a vacuum source. Each mold has internal channels 10 bringing this source of vacuum into the footprint

4a, 4b corresponding.

  These arrangements are well known to those skilled in the art and do not have to be

developed in more detail.

  According to the invention, to allow the manufacture of blanks 15 of hollow bodies by means of the molds 4a, 4b of the installation, it also comprises intermediate molds 40a, 40b. Each of these is disposed between two molds 4a or two molds 4b, corresponding to the imprints of two separate blanks. In addition, each of these intermediate molds 40a, 40b comprises, as shown in more detail in Figure 4, a semi-cylindrical axial channel 12 and a radial bore 13 opening therein. The semi-cylindrical channels 12 of two molds 40a, 40b arranged opposite each other form a cylindrical imprint making it possible to produce a connecting duct 14 (in FIG. 3) between the two upstream and downstream blanks 15 formed by the imprints of the molds 4a and 4b and partly by the imprints 42a, 43a, 42b, 43b formed in the intermediate molds 40a, 40b. These footprints are also connected by channels

  suitable not shown in the vacuum supply circuit.

  The radial bore 13 of each mold 40a, 40b forms a slide for a piston 16 whose inner head 16a has a diameter at least equal to that of the channel 12. This piston 16 is integral with a flange 17 sliding in a housing 18 extending the radial bore 13. This collar is constantly subjected to the elastic return of a spring 19, interposed between it and the bottom of the housing 18. Its outward movement is limited by abutment on a rod 20. Finally, the piston 16 is secured to an outer bead 16b which, when in the rest position, protrudes outside the mold 40a or

b, as shown in Figure 3.

  According to another characteristic, the installation is provided, on either side of the parallel branches of the two mold lines A and B of two fixed ramps 22a, 22b which control the radial displacement towards the inside of the pistons 16. These ramps are arranged downstream of the closure zone of the molds of the two chains and at a distance from this zone which is less than the length of the tubular hollow body to be produced. In the embodiment shown, the hollow body being constituted by two blanks 24 arranged in opposition, the ramps 22a, 22b are separated from the closing zone F of the molds, shown in FIG. 1, by a distance S which is smaller than to the

length L of the two blanks.

  The ramps 22a and 22b are extended by slides 23a and 23b which are intended to hold the pistons in the pinching position for the duration of

gelation of the material.

  With this installation and as the introduction of the parison 3 in the mold tunnel, and thanks to the pinch made by the downstream pistons, but also thanks to the pressure differential between the pressure in the parison, and the vacuum brought into the footprints of the two mold chains, this parison is pressed against the cavities of the mold and gradually forms the two blanks 15 hollow bodies. For example, the pressure inside the parison is 0.2 bar higher at atmospheric pressure while the pressure in the cavities is 0.2 to 0.4 bar lower than atmospheric pressure. When the two pistons 16, arranged upstream of the two hollow bodies formed, come into contact with the ramps 22a, 22b, they are moved radially towards each other thus crushing the junction channel 14 with the next blank. This crushing, taking place while the material is still well below its gel point, ensures a tight seal between the blanks 15,

respectively downstream and upstream.

  In a preferred embodiment, when the parison 3 delivers between the channels 12 of the molds 40a, 40b, the running speed of the mold chains A and B is reduced to increase the thickness of the material forming a connecting duct. 14 between two blanks 15, and improve the subsequent resistance of the shutter

drafts.

  As indicated above, the pistons are kept pressed against each other until the material has reached its gel point, that is to say practically to the downstream end of the molding tunnel. When the pistons 16 escape the ramps 23a, they are biased outwardly by the return spring 19, so as to allow the free formation of a new connecting duct 14 and especially to have external heels 16b overflowing the back of the mold in anticipation of a

  next meeting with ramps 22a, 22b.

  The blanking line thus manufactured is cooled by dipping in a bath.

  At the outlet of the bath, the blanks 4 are cut at 25, other downstream and upstream blanks, then are separated from each other by sectioning at 26. Each of these blanks is stored until it is recovery in an extrusion plant

  blowing to form a container.

  The development required to transform this facility is inexpensive and uses reliable means to make the most of continuous production. Moreover, such an installation makes it possible to produce blanks in highly viscous synthetic materials, without this disturbing the manufacturing conditions, since it is simply necessary to reduce the speed of displacement.

two chains of mussels.

Claims (2)

  1. Installation for the production of synthetic hollow body blanks comprising an extruder (2) delivering a tubular parison (3) of synthetic material, two chains (A and B) of molds (4a, 4b) describing continuous circuits whose two branches are parallel to the exit trajectory of the parison and delimit a tubular cavity by a series of semi-cylindrical cavities (Sa, 5b) facing each other, translational drive means for the molds, and means controlling the difference between the pressure prevailing in the parison (3) and the hollow bodies and the pressure prevailing in the tubular cavity, characterized in that it comprises, on the one hand, on each of the intermediate molds (40a, 40b) separating, in each of the chains (A and B) of molds (4a, 4b), two distinct indentations each corresponding to at least one blank (15): - a semi-cylindrical axial channel (12) cooperating with the mold channel (40a , 40b) in facing relation to form an impression forming a connecting duct (14) between two successive blanks (15), - a radial bore (13) with a cylindrical section opening into the axial channel (12) and outside, and a piston (16) slidably mounted in the bore (13) against spring biasing means (19) driving it outwards, said piston having an inner head (16a) of at least equal diameter to that of the axial channel (12), and an external heel (16b) projecting from the back of the corresponding mold, and, on the other hand, and on either side of the parallel branches of the mold chains, two fixed ramps (22a). , 22b) controlling the inward radial displacement of the opposed pistons (16) to crush, at least locally, the connecting pipe (14) between two blanks (15).   2. Installation according to claim 1, characterized in that the ramps (22a, 22b) are extended by slides (23a, 23b) holding the pistons (16) in position.   pinch position during the gelling time of the material.