TITLE:

METHOD AND EQUIPMENT FOR PREVENTING UNDESIRED MOVEMENT OF PARISONS WHEN PLACED IN THE MOULD BEFORE BLOW MOULDING

DESCRIPTION

The invention relates to machines for thermoforming by blow moulding bottles, flasks or other hollow products in general from thermoplastic material. In particular, the invention relates to machines for thermoforming by blow moulding which have at least one vertical extrusion head which extrudes a parison, or a plurality of pahsons simultaneously, in a downward direction, a mould and counter-mould unit being positioned cyclically to the side of these parisons with the interposition of a transverse guide and slider unit and corresponding self-centring drive means, on a principal carriage which can carry said mould and counter-mould unit, by means of other guide and slider units and corresponding drive means, from the parison supply station to a neighbouring station where blow moulding means operate. The mould and counter-mould unit is presented in the open state at said extrusion and parison supply station, where at the correct time the unit is made to carry out a closing movement which is usually self-centring, in order to grip the opposite ends of precisely measured portions of parison which by suitable means are cut and separated from the continuous formations discharged from the extrusion head, after which the mould and counter-mould unit is transferred to said neighbouring station where needles are inserted into the upper end of each thermoforming cavity to blow pressurized gas into each portion of parison, thus inflating it and making it adhere to the corresponding thermoforming cavity which forms the product. The needles are designed to keep the product suspended on them when, in a following stage of operation, the mould and counter-mould unit is opened by a self-centring movement and is returned to the extrusion station to collect new portions of parison and repeat the cycle which has been described. In known machines for thermoforming by blow moulding, the principal carriage which

carries the mould and counter-mould unit in the reciprocating movement between the parison extrusion station and the blow moulding station is generally associated with a set of ghppers which, when said unit is in the extrusion station, are positioned in the blow moulding station to grip the containers held therein and to enable the blow moulding needles to be disengaged from the containers, in such a way that, when the mould and counter-mould unit loaded with portions of parison is translated to the blow moulding station, the containers formed in the preceding cycle are transferred by said ghppers to a neighbouring station where container finishing means operate and where the containers are picked up by other means and transferred to other stages of the machine's operating cycle, thus releasing said grippers which can thus repeat the stages described. In general, the closing and opening movement of the grippers is provided by the means which also provide the closing and opening movement of the mould and counter-mould unit, in other words by the sliders which carry the components of this group. An example of a machine of this type is described in Italian patent 1 260 295 (corresponding to EP 0597385 and to U.S. 5,458,479) in the name of the present applicant.

In this type of machine for thermoforming by blow moulding, or in similar or other types of machines, which may be rectilinear or oscillating or rotating, the following technical problem is encountered. During the closure of the mould and counter-mould unit, the portions of parison trapped therein, and especially the outermost portions of the row, tend to diverge downwards from each other and to oscillate, in such a way that it becomes difficult to grip them in a centred way in the thermoforming cavity of the mould and counter-mould unit. This problem is presumably caused by the large body of air displaced by the mould and counter-mould unit in the movement by which it closes on to the pahsons, and by the fact that this body of air tends to flow out of the decreasing volume of space between the mould and the counter-mould, with mainly horizontal movements. In order to overcome this drawback, it is necessary to carry out said closing movement of the mould and the counter-mould at a moderate speed, but this retards the production cycle of the machine and can never fully resolve the problem.

The invention is intended to overcome this serious technical problem in such a way as to ensure the correct vertical positioning of the parisons when the mould and counter-mould unit closes on them, while enabling the speed at which this unit closes on the parisons to be sustained, using a method and equipment as summarized in Claim 1 and in the subsequent dependent claims, based on the following idea. Before the stage of the closure of the mould and counter-mould unit or during this stage, the free space between the mould and the counter-mould, which is occupied by the extruded parisons, is closed laterally by suitable means, on both opposing sides or fronts, in such a way that it remains open only above and below. During the closure of the mould and counter-mould unit, the air trapped within this unit can be discharged freely by vertical and essentially downward movements only, since said space is substantially blocked in its upper part by the close proximity of the extrusion head and of the parisons which move downwards, and the combination of these conditions causes the parisons to remain vertical and substantially immobile, even if the speed of closure of the mould and counter-mould unit is, at least initially, high. Further characteristics of the invention, and the advantages resulting therefrom, will be made clearer by the following description of a preferred embodiment of the invention, illustrated purely by way of non-limiting example in the figures of the attached sheets of drawing, in which: - Fig. 1 is a schematic lateral view of the equipment according to the invention, in the two successive stages of operation;

Fig. 2 is a schematic view of the equipment from above, showing the stage in which the mould and counter-mould unit is closing on to the parisons produced by the extrusion head; - Fig. 3 shows further details of the equipment in a view taken through the section line Ill-Ill of Figure 2.

In Figures 1 and 2, the number 1 indicates in a summary way the principal carriage of the machine which is made to slide on its own sliders by means of its own actuators (not shown) on the guide means 2, which may for example be inclined, in such a way that the carriage is positioned alternately at a station S1 or at a neighbouring station

S2, at which stations, respectively, a head 3 for extruding the parisons 103 of thermoplastic material or the needles 4 of the blow moulding station are positioned above the carriage.

The carriage 1 carries guides 5 orthogonal to the guides 2, on which pairs of sliders 6, 106 move, a mould 7 and a counter-mould 107 being mounted on each of these pairs, the mould and counter-mould being moved by an actuator and by synchronizing means, which are indicated schematically by 8 and are not illustrated in detail since they are also known, in a self-centring movement for the closure and opening of the mould and counter-mould 7, 107. In Figures 2 and 3, the numbers 9 and 109 indicate the opposing and complementary cavities of the mould and counter- mould unit 7, 107, in which the vertical portions of the parisons 103 supplied by the extrusion head 3 are to be positioned and gripped in a cyclic way. In Figures 1 and 2, the numbers 10 and 110 indicate the known complementary ghppers, which, when the mould and counter-mould unit is at the station S1 , as shown in solid lines in Figure 1 , are positioned at the station S2 to grip the containers P2 which have been formed in a preceding cycle and which are retained by the blow moulding needles 4. By contrast with the procedure in the known art, in which said ghppers 10, 110 derive their closing and opening movement directly from the sliders 6, 106 of the mould and counter-mould unit 7, 107, in the present case these ghppers 10, 110 are mounted on corresponding sliders 11 , 111 which run on guides 12, 112 mounted on a single beam 13 which is parallel to the guides 5 and which is fixed to the carriage 1 by means of supports 14. The number 15 indicates schematically an actuator unit for the synchronized self-centring operation of the sliders 11 , 111 , to produce the closing and opening movement of the ghppers 10, 110 independently of the opening and closing movement of the mould and counter-mould unit 7, 107, although the ghppers are fixed to this unit in the movement of translation along the guides 2 which may for example be inclined.

The equipment according to the invention is completed by at least one plate 16 with which the mould and counter-mould unit 7, 107 comes substantially into contact with its front face when it completes its movement of entry into the station S1 , as shown in

Figures 1 and 2, and the extension of this plate is such that it substantially covers the whole height of the space V between the opposing faces of the mould 7 and counter- mould 107, on which faces said thermoforming cavities 9, 109 open. The plate 16 can, for example, be formed from a suitable plastics material and/or other suitable strong light material, and can be supported with the interposition of suitable removable support and registration means 17, for example by at least one suitable upright structure 18 fixed to the base of the machine. The structure 18 can also be positioned in an easily removable way, to allow easy inspection of the opposing inner walls of the mould and counter-mould unit when necessary. The plate 16 can be provided, on its face turned towards the mould and counter-mould unit, with suitable recesses, in which any projecting lateral parts of the mould and counter-mould, and/or other neighbouring parts associated with the carriage 1 , can move freely. The grippers 10, 110 are provided, at their end facing the mould and counter-mould unit, with complementary plates 19, 119, also made, for example, from suitable plastics material and/or other suitable material, which are substantially in contact with the rear face of the mould 7 and counter-mould 107, opposite the face which contacts said plate 16. The plates 19, 119 are coplanar with each other and extend in such a way that, when the grippers 10, 110 are in the closed position, they touch each other as shown in figures 2 and 3, and substantially cover the whole height of the other end of said space V. The vertical and opposing sides of the plates 19, 119 which come into contact with each other during the closure of the grippers 10, 110 can be flat and parallel to each other, or can have a sinuous profile so as to form a closure of the labyrinth type which provides a good seal. The faces of the plates 19, 119 turned towards the mould 7 and the counter-mould 107 can also be provided with recesses to prevent interference with any projecting parts of the mould and counter-mould unit and/or of other parts.

The operation of the equipment as described is simple and evident. The carriage 1 moves by translation towards the left-hand side of Figures 1 and 2, with the sliders 6, 106 and 11 , 111 open, in such a way that the mould and counter-mould unit 7, 107 is positioned in the station S1 , without interfering with the parisons 103 which

progressively occupy their open intermediate space V, while the ghppers 10, 110 are positioned at the sides of the containers P2 produced in the preceding operating cycle of the machine and retained by the blow moulding needles 4. At the end of this translational movement, the space V of the mould and counter-mould unit is closed at the front by the fixed plate 16, while it is closed at its rear face by the complementary plates 19, 119 carried by the ghppers 10, 110 which are made to close at the correct time to grip said containers P2 and to enable the blow moulding needles 4 to disengage from the containers. Figures 1 and 2 clearly show that, when the mould 7 and the counter-mould 107 are brought towards each other and closed in order to trap corresponding portions of the pahsons 103 in the corresponding cavities 9, 109, the space V between the mould and counter-mould, the volume of which decreases progressively, is closed at the front and rear by the plates 16 and 19, 119, and is substantially blocked in its upper part by the proximity of the extrusion head 3 and is freely open in its lower part, so that the air tends to flow out of said space V with vertical and essentially downward movements, thus ensuring that the parisons 103 remain in the vertical position and substantially immobile, being in this way correctly gripped between the mould and counter-mould 7, 107, even when the speed of closure of this unit is, at least initially, high. After the closure of the mould and counter-mould 7, 107, the carriage 1 is translated towards the right-hand side of Figures 1 and 2 and moves away from the fixed plate 16, while the plates 19, 119 remain close to each other because the grippers 10, 110 are transferring the containers P2 from the station S2 to a neighbouring station S3 where, for example, the containers have their lower and upper sprues M1 , M2 removed, and where they are picked up by subsequent removal means 20 which are not described in detail here since they are known and are not necessary for the understanding of the invention.

When the unit consisting of the mould 7 and counter-mould 107 reaches the station S2, the portions of parison trapped in the cavities 9, 109 are penetrated and inflated by the needles 4 at the correct time, so that they take on the shape of these cavities.

At the end of this stage of thermoforming by blow moulding, the mould 7 and the counter-mould 107 are opened so as to release the thermoformed containers suspended on the needles 4 and, with the ghppers 10, 110 also open, the carriage 1 is translated towards the left-hand side of Figures 1 and 2, for the repetition of the cycle which has been described. At this stage, the grippers 10, 110 and the plates 19, 119 are open and do not interfere with the containers suspended on the needles 4, while the mould and counter-mould unit 7, 107 has its space V open both at the front face or side which enters the parison supply station and at the rear face or side, since the rear plates 19, 119 are separated from each other. At the end of this movement, the space V is closed at its front face or side by the fixed plate 16 and is closed at the opposing rear face or side by the plates 19, 119 which close on each other as a result of the closure of the grippers 10, 110 on to the containers of the preceding cycle which are suspended on the needles 4, and the aforesaid operating cycle is repeated from this point.