EP2448744A2

EP2448744A2 - Apparatus for heating parisons of thermoplastic material

Info

Publication number: EP2448744A2
Application number: EP10740299A
Authority: EP
Inventors: Maurizio Borgatti; Paolo Dalle Vacche; Massimo Morovingi; Fiorenzo Parrinello; Emilio Re; Gabriele Stocchi; Andrea Zanardi; Stefano Cassani
Original assignee: Sacmi Imola SC
Current assignee: Sacmi Imola SC
Priority date: 2009-06-30
Filing date: 2010-06-28
Publication date: 2012-05-09
Also published as: WO2011001358A3; IT1398130B1; ITBO20090420A1; WO2011001358A2

Abstract

An apparatus (1) for heating parisons (2) of thermoplastic material comprises: a conveyor (3) defining a path along which the parisons (2) are fed; a plurality of supporting elements (6) having a structure (7) fixed to the conveyor (3) and a rod (8) rotatably associated with the structure (7) to rotate about a longitudinal axis and having a lower end that can be operatively inserted in a parison (2) in such a way as to retain it and drive it rotationally about its longitudinal axis; a linking element (11) kinematically coupled to rotary means (12) rotatably associated with the structures (7) and coupled to the rods (8) in such a way that the rods (8) are made to rotate about their longitudinal axes while they move as one with the conveyor (3); heating means (10) designed to heat the parisons (2) as the latter move along at least a part of their feed path. The linking element (11) is motor driven to enable it to control the speed at which the parisons (2) rotate about their longitudinal axes.

Description

Description Apparatus for heating parisons of thermoplastic material

Technical Field

This invention relates to an apparatus for heating parisons of thermoplastic material.

The parisons are used to make containers by blow-moulding.

The parisons are heated so that they are in the required thermal state when they are blown into the moulds of the blow-moulding machine.

For this reason, it is important to guarantee uniform temperature along the radial extension of the parison. Background Art

To do this, prior art apparatus comprises a conveyor used to transport the parisons along a feed path through a heating tunnel.

The conveyor is associated with a plurality of elements for supporting the parisons.

These supporting elements have a structure fixed to the conveyor and a rod rotatably associated with the structure to turn about a longitudinal axis.

Further, the rod is movable axially relative to the structure between a lowered position, where the bottom end of the rod is operatively inserted in a parison in such a way as to hold it and rotate it about its longitudinal axis, and a raised position, where the parison is disengaged from the rod. This allows the parison to be picked up by the heating tunnel feed carousel and to be delivered to the transfer carousels which carry it to the blow-moulding carousel.

Some prior art apparatuses comprise a chain or a toothed crown wheel which is integral with the frame of the apparatus and, hence, in a fixed position relative to the conveyor.

Each rod has keyed to it a toothed wheel which meshes with the chain or toothed crown wheel in such a way that its motion (of revolution) as one with the conveyor causes the rods to rotate about their longitudinal axes thanks to the interaction of the toothed wheels with the fixed toothed crown wheel or chain.

The chain or toothed crown wheel thus constitutes a linking element kinematically coupled to rotary means (that is, the toothed wheels) rotatably associated with the parison supporting structures and coupled to the rods in such a way as to drive them rotationally about their longitudinal axes as a result of the movement of the rods as one with the conveyor.

Thus, the pan sons engaged with the rods are rotated about their longitudinal axes as they move through the heating tunnel.

This favours uniform distribution of the temperature in the parisons.

These solutions are not, however, free of disadvantages.

First of all, the speed at which the parisons are driven rotationally about their axes as they move through the heating tunnel, is not ideal for uniformly heating the parisons themselves.

In fact, the rotation speed of the rods about their longitudinal axes is set by the gear ratio of the chain and sprockets and by the conveyor speed which is in turn set by the speed of the blow-moulding machine located downstream of the heating apparatus and is any in case linked to the required container output per hour of the blow-moulding equipment.

The problem of the non-optimal speed of rotation of the parisons about their longitudinal axes in the heating tunnel is worsened by the need to adapt to the type of heating means used in the tunnel and the type and size of the parisons.

Another shortcoming of prior art systems is described below.

The fact that the rods rotate about their longitudinal axes poses a problem for picking up the parisons.

In effect, to pick up the parison, the rod is pressed down into the parison so that a pick-up end portion of it engages the interior of the parison. Since the vertical movement is accompanied by the rotation of the rod about its axis, there is a risk of damaging the parison and a risk of troubles in parison gripping action.

To overcome this problem, some apparatuses currently in use are designed in such a way that the toothed wheel of the rods mesh with the chain only along a specific part of the conveyor path (in particular, the part where the parisons are inside the heating tunnel) whilst the rods do not mesh when they are in the part of the path where they interact with the parisons in order to pick them up.

In this way, when the rods actually pick up the parisons, they rotate freely relative to the respective supporting structures.

This effectively avoids the risk of damaging the parisons but creates another problem, and that is the need to ensure that the toothed wheels integral with the rods mesh correctly with the toothed wheel or chain when they reach the end of the part of the path where the rods rotate freely. This problem involves a considerable complication in the drive mechanism of the apparatus in order to avoid unacceptable conditions of wear on the toothed wheels on the rods and undesired vibration during engaging phase .

From document US 5853775 it is known to provide two different chains, arranged at different locations in the apparatus, and to motorize each chain independently form the other.

This allows to heat the parisons in a way which is not uniform.

However, said solution enhances the problem of wear on the toothed wheels on the rods, because it entails a sequence of engagements and disengagements of the rods with respect to the chain.

Also from document US 4484884 it is known to provide a motorized chain arranged in such a way to engage with the rods only in a limited portion of the path defined by the parisons in their movement in the heating apparatus. Hence, said solution has analogous disadvantages with respect to those of US 5853775.

Indeed, neither US 5853775 nor US 4484884 are focused with the goal of obtaining a uniform heating of the parisons; rather, they face the problem of heating the parisons in a way which is inhomogeneous.

Aim of the Invention

This invention has for an aim to provide a thermoplastic parison heating apparatus that overcomes the above mentioned drawbacks of the prior art.

In particular, it is an aim of the invention to provide a thermoplastic parison heating apparatus that is constructionally very simple and allows parison heating conditions to be optimized.

Another aim of the invention is to provide a thermoplastic parison heating apparatus that allows to optimize the speed at which the heating apparatus processes the parisons, as a function of the speed of the line (for producing blow moulded containers from the parisons) where the apparatus is inserted, determined by the size of the containers, nevertheless guaranteeing optimum and uniform heating of the parisons.

These aims are fully achieved by the apparatus according to the invention as characterized in the appended claims and, more specifically, in that the linking element is motor driven.

In particular, the present invention makes available an apparatus for heating parisons of thermoplastic material, comprising:

- a conveyor having a ring-shaped configuration and defining a path along which the parisons are fed, said path forming a closed loop; - a plurality of supporting elements having a structure fixed to the conveyor and a rod rotatably associated with the structure to rotate about a longitudinal axis and having a lower end that can be operatively inserted in a parison in such a way as to retain it and drive it rotationally about its longitudinal axis;

- a linking element kinematically coupled to a rotary member rotatably associated with the structures and coupled to the rods in such a way that the rods are made to rotate about their longitudinal axes as a result of their movement as one with the conveyor;

- means for heating the parisons along at least a part of the parison feed path;

- a first motor, connected to the conveyor, and a second motor, connected to the linking element, characterized in that it comprises control means connected to the second motor for varying the speed of the linking element as a function of the speed of the conveyor, for setting the speed at which the parisons rotate about their longitudinal axes at a predetermined value independently of the speed of the conveyor.

Preferably, the linking element is configured as a ring, arranged in such a way that the rotary member is stably coupled to the linking element during a movement of the rotary member in said closed loop.

In this light, the linking element is configured as a single ring, arranged substantially in correspondence to the path along which the parisons are fed.

This allows to provide a thermoplastic parison heating apparatus which is of particularly robust construction.

In fact, the fact that rotary member (e.g. a sprinkle) is stably coupled to the linking element (e.g. a chain) advantageously allows to avoid damage of the rotary member caused by the succession of disengagements and subsequent engagements of the rotary member with respect to the linking element.

Brief Description of the Drawings

These and other characteristics of the invention will become more apparent from the following detailed description of a preferred, non-limiting embodiment of it, with reference to the accompanying drawings, in which:

- Figure 1 schematically illustrates an apparatus according to the invention in a perspective view;

- Figure 2 schematically illustrates the apparatus of Figure 1 in a plan view;

- Figure 3 is a perspective view illustrating one of the supporting elements of Figure 1; - Figure 4 illustrates the element of Figure 3 from a different angle;

- Figure 5 is a section view of the element of Figure 3 in a first operating position;

- Figure 6 illustrates the detail A from Figure 5;

- Figure 7 illustrates the element of Figure 5 in a second operating position;

- Figure 8 illustrates the detail B from Figure 7;

- Figure 9 is an exploded view of a portion of the element of Figure 3;

- Figure 10 is a section view of the portion of Figure 9. Detailed Description of the Preferred Embodiments of the Invention

With reference to the accompanying drawings, the numeral 1 denotes an apparatus according to this invention.

The apparatus 1 is an apparatus for heating parisons 2 made of thermoplastic material, used to make containers by blow-moulding.

In effect, the apparatus 1 receives the parisons at a feed station, heats them to the required temperature (typically to a temperature greater than its glass transition temperature) and transfers them, at an outfeed station, to a blow- moulding machine using a transfer star wheel.

The apparatus 1 comprises a conveyor 3 defining a path along which the parisons 2 are fed.

Preferably, the conveyor 3 has a ring-shaped configuration so that the path along which the parisons move forms a closed loop.

The conveyor 3 comprises, for example, a chain or a belt trained around wheels or pulleys driven by a motor 4.

The motor 4 that drives the conveyor 3 is preferably an electric motor,

In the example illustrated, the conveyor 3 comprises a first chain 5A and a second chain 5B kinematically connected to the same motor 4.

Thus, the first chain 5A and the second chain 5B rotate synchronously. Further, the first chain 5A and the second chain 5B are vertically spaced by a predetermined quantity.

The apparatus 1 also comprises a plurality of elements 6 for supporting the parisons 2, to enable the parisons 2 themselves to be moved by the conveyor 3 along the feed path. Note that Figure 1, for simplicity, illustrates only two of the supporting elements 6 forming part of said plurality.

The supporting elements 6 are connected to the conveyors and are preferably spaced uniformly along the conveyor 3. Each supporting element 6 comprises a structure 7 fixed to the conveyor 3 and a rod 8 rotatably associated with the structure 7 to turn about a longitudinal axis.

In the example illustrated, the structure 7 is equipped with a first arm 9A fixed to the first chain 5A and a second arm 9B fixed to the second chain 5B.

It should be noted that, in the example illustrated, the longitudinal axis of the rods 8 is vertical, that is to say, perpendicular to a horizontal surface that supports the apparatus 1.

Further, the rod 8 is movable axially relative to the structure 7 between a lowered position, where the bottom end of the rod 8 is operatively inserted in a parison 2 in such a way as to hold it and rotate it about its longitudinal axis, and a raised position, where the parison 2 is disengaged from the rod 8.

The apparatus also comprises a heating tunnel 10 in which the parisons 2 move along at least a part of the feed path defined by the conveyor 3.

Preferably, the heating tunnel 10 houses a plurality of infrared lamps, usually mounted only on the outside of the machine, towards the operator; on the opposite side there are deflectors for reflecting the rays emitted by the infrared lamps in order to optimize their effect.

Therefore, the heating tunnel 10 constitutes means for heating the parisons 2 during their movement as one with the conveyor 3 along at least a part of the feed path it defines.

The apparatus 1 further comprises a linking element 11 kinematically coupled to the rods 8 in such a way that the rods 8 are made to rotate about their longitudinal axes while they move as one with conveyor 3.

For this purpose, each supporting element 6 comprises a rotary member 12 mounted rotatably on the structure 7 to rotate about the longitudinal axis of the rod 8 and interacting with the linking element 11 in such a way as to rotationally drive the rod 8 about its axis.

Preferably, the linking element 11 is a chain and the rotary member 12 is a sprocket meshed with the chain. Alternatively, other known systems may be used instead of the chain, such as a toothed belt, for example, designed to enable the rotary member to move along a path defined by the linking element 11 itself, while remaining coupled to (and, more specifically, meshed with) the linking element 11, causing simultaneous rotation of the rotary member 12 about its axis of rotation.

According to the invention, at least one of the supporting elements 6 comprises a friction clutch 13 connected to the rod 8 and to the rotary member 12 to define a first operating position, where the rod 8 is engaged with the rotary member 12, and a second operating position, where the rod 8 is disengaged from the rotary member 12 and can therefore rotate freely about its longitudinal axis.

Preferably, all the supporting elements 6 comprise the friction clutch 13 connected to the rod 8 and to the rotary member 12 to define a first operating position, where the rod 8 is engaged with the rotary member 12, and a second operating position, where the rod 8 is disengaged from the rotary member 12 and can therefore rotate freely about its longitudinal axis,

In the example illustrated, the friction clutch 13 comprises a block 14 integral with the rod 8 and shaped to match the shape of a cavity 15 made in the rotary member 12 to form a coupling between the block 14 and a surface of the rotary member 12 facing the cavity 15.

Thus, the rod 8 and the rotary member 12 are coupled by a tapered clutch; the contact angle made by the tapered clutch with the longitudinal axis is preferably between 5° and 30°.

In an alternative embodiment not illustrated, the tapered friction clutch is substituted by a flat friction clutch.

According to the invention, the rotary member 12 is a sprocket stably meshed with the chain 11; that is to say, all the rotary members 12 are coupled to the linking elements 11 for the full length of the feed path, without interruptions.

Figures 9 and 10 show how each rod 8 is equipped at a free end of it (that is, at its bottom end) with a plurality of pushers 81, preferably three in number.

Preferably, the pushers 81 are uniformly distributed around the longitudinal axis of the rod 8.

The pushers 81 are housed in respective slots 82 made in the rod 8 and are designed to slide radially inside the slots 82 between a withdrawn position where the pushers 81 are at least partly located inside the slots 82 (to enable the parison 2 to be inserted) to an extracted position where a part of each pusher 81 extends outside its slot 82 more than it does when it is in the withdrawn position, thereby defining the vertices of a polygon having a circumscribed circle of predetermined diameter (at least greater than the diameter of the cavity defined by the parison 2).

The pushers 81 are preferably dice shaped.

The pushers 81 are preferably fixed to elastic arms 83. The elastic arms 83 are equal in number to the number of pushers 81. One end of each elastic arm 83 is fixed to the rod 8 and the other end fixed to a respective pusher 81.

The elastic arms 83 are designed in such a way that when in the rest position, they place the respective pushers 81 in the extracted position, and when in a flexed position (inwards towards the longitudinal axis of the rod 8), place the pushers 81 in the withdrawn position.

Preferably, the elastic arms 83 are parallel to the axis of the rod 8.

Thus, the pushers, the elastic arms 83 and the slots 82 together constitute means for gripping the parisons 2.

In effect, when the rod 8 is in the lowered position, the pushers 81, being connected to the elastic arms 83, are positioned in contact with an inside wall of the parison 2 without damaging it and exert pressure on it (substantially radial, from the inside out) as a result of the interference between the parison 2 and the pushers 81 in the withdrawn position or in an intermediate position between the extracted and the withdrawn position.

In this way, the gripping means control the movement of the parison 2.

During the axial movement of the gripping means (as one with the rod 8) from the raised position to the lowered position, the pushers 81 are moved from the extracted position to the withdrawn position as a result of the parison 2 being placed on the free end of the rod 8 and the above mentioned interference.

In the light of the above, it should be noted that the pushers 81 preferably have a radiused or outwardly rounded surface in order to avoid damaging the parison 2.

Further, all the supporting elements 6 comprise a wheel 16 kinematically connected to the rod 8 and interacting with a cam 17 (of known type and only partly illustrated in the drawings) for moving the rod 8 axially, that is to say, for moving the rod 8 from the lowered position to the raised position and vice versa.

Preferably, each supporting element 6 comprises a sleeve 18 coaxial with the rod 8 and positioned round the outside of the latter in such a way as to cover a central portion of it.

In particular, the ends of the rod 8 are rotatably connected to the structure 7, while a central portion of the rod 8 is rotatably inserted in the sleeve 18.

The sleeve 18 is coupled to the structure 7 in such a way that it can move axially from a raised position to a lowered position and vice versa, without being able to rotate about its axis (that is, about the axis of the rod 8).

The wheel 16 is fixed to the sleeve 18. The wheel 16 therefore moves as one with the supporting element 6 under the action of the conveyor 3 and is free to move axially thanks to interaction with the cam 17 but cannot rotate about its axis.

This advantageously allows the apparatus to be further simplified.

The sleeve 18 is coupled to the rod 8 by a ring 19 (illustrated in Figure 8) fixed to the rod 8 and connected to a top end of the sleeve 18 (forming a stop for the top end of the sleeve 18). Preferably, the ring 19 is a snap ring. It should also be noted that the ring 19 is inserted in an annular groove made in the rod 8.

Preferably, the supporting element 6 also comprises a spring 20 which operates on the sleeve 18 in such a way as to apply on the latter an axially directed force opposing the action of the cam 17 on the wheel 16.

In particular, the spring 20 has a first end fixed to the structure 7 and a second end connected to the rod 8 (preferably to the bottom end of the rod 8) to apply a downwardly directed axial force on it.

Thus, when the wheel 16, upon interaction with the cam 17, causes the sleeve 18 to move upwards (that is, towards the raised position, the sleeve 18 pushes the rod 8 upwards (to the raised position), overcoming the force of the spring 20.

It should be noted that the cam 17 is set up to move the rod 8 upwards when it is at a station for releasing the pan sons 2.

The spring 20 has the effect of ensuring that the wheel 16 follows the cam profile, pushing the rod 8 downwards, which in turn drags the sleeve 18 and the wheel 16 downwards along with it.

It should be noted that the spring 20 is also designed to push the block 14 towards the rotary member 12, thus creating friction between the matching surfaces of block 14 and rotary member 12, in such a way that the rotary member 12 rotationally drives the block 14 and the elements engaged with it.

It should also be noted that all the supporting elements 6 also preferably comprise a tubular limit stop element 21 connected to a bottom portion of the structure 7 to protrude axially downwards relative to it.

The limit stop element 21 is set up in such a way that when the rod 8 is in the lowered position (Figure 4), the end portion of the rod 8 equipped with the gripping means protrudes downwardly relative to the limit stop element 21 and the parison 2 coupled to it is in contact (at an upper annular surface of it) with the limit stop element 21; and when the rod 8 is in the raised position (Figure 5), the end portion of the rod 8 equipped with the gripping means is positioned inside the limit stop element 21 and the parison 2 is uncoupled from the rod 8.

It should be noted that the limit stop element 21 opposes the parison 2 in such a way that the latter can be removed from the conveyor 3 during exchange with the grippers of the transfer carousels; the limit stop element 21 abuts the parison, stopping its upward axial movement together with the conveyor 3 and thereby causing the conveyor 3 to be pulled off the parison. The raised position of the rod 8 thus constitutes a parison releasing configuration for the respective supporting element 6.

It should be noted that preferably the friction clutch 13 is designed to be set in the first operating position (where the rod 8 is rigidly connected to the rotary member 12 and rotates as one with it about its longitudinal axis) when the rod 8 is in the lowered position, and in the second operating position (where the rod 8 is disengaged from the rotary member 12 and can rotate freely about its longitudinal axis) when the rod is in the raised position.

This further simplifies the apparatus 1 since the cam and wheel 16 system used to move the rod from the lowered position (where the parison 2 is picked up) to the raised position (where the parison 2 is released) is advantageously also used to move the friction clutch 13 from the first operating position (where the rod 8 is engaged with the rotary member 12) to the second operating position (where the rod 8 is disengaged from the rotary member 12).

Preferably, the friction clutch 13 is designed to be set in the second operating position when the rod is in an intermediate position between the lowered and raised positions.

This advantageously avoids the risk of the rod 8 creating a drill effect that would damage the parison during the axial downward movement of the rod 8 (when the gripping end portion of the rod 8 is inserted into the parison).

According to another aspect of the invention, the linking element 11 is movably connected to a frame of the apparatus 1.

As mentioned above, the linking element 11 preferably comprises a chain.

Hence, the toothed chain 11 is movably connected to the frame and is motor driven. In particular, the toothed belt 11 is trained around pulleys so that it can rotate while remaining kinematically coupled to the rotary members 12 of the supporting elements 6.

According to the invention, the apparatus 1 comprises control means configured for varying the speed of the linking element 11 as a function of the speed of the conveyor 3, for setting the speed at which the parisons 2 rotate about their longitudinal axes at a predetermined value independently of the speed of the conveyor 3.

Preferably, the apparatus 1 comprises a first motor 4, connected to the conveyor 3, and a second motor, connected to the linking element 11.

In this light, the control means is connected to the second motor for varying the speed of the linking element 11. That means the rotation speed of the parisons 2 about their longitudinal axes is advantageously independent of the speed of the conveyor 3.

This is particularly important because the speed of the conveyor 3 depends on the overall speed of the production line where the apparatus 1 is inserted, i.e. the line for producing blow moulded containers from the parisons.

In particular, the apparatus 1 feeds a blow moulding machine; the speed of said blow moulding machine (which varies significantly when the shape or the size of the containers to be blown is changed, e.g. by substituting single cavity moulds with double cavity moulds designed to blow two containers at the same time) determines the speed at which the apparatus 1 must supply the heated parisons 2, and thus it determines the speed of the conveyor 3.

The speed of the conveyor 3 itself effects the speed at which the parisons 2 rotate around their axes.

However, given a parison typology, it is possible to find said predetermined speed (of rotation of the parison around its axis) which is optimized for a uniform and correct heating of the parison 2 itself in the heating apparatus 1.

Hence, the control means acts on the speed of the linking element 11, to compensate undesired variations in the speed of rotation of the parisons 2, caused by variations in the speed of the conveyors 3.

Preferably, the motor 4 connected to the conveyor 3 constitutes said first motor and the apparatus 1 comprises said second motor (not illustrated) connected to the chain 11. The second motor is preferably an electric motor.

The first and second motors are preferably independent of each other.

Said control means (for example, in the form of a suitably programmed electronic card connected to an inverter that drives the motor) are preferably connected to the second motor to control the speed at which the parisons rotate about their longitudinal axes.

In particular, said control means are programmed to control the speed at which the parisons rotate about their longitudinal axes.

More specifically, the apparatus preferably comprises means for regulating the speed of the second motor (embodied, for example, by the control means and the inverter that drives the second motor) which also constitute means for regulating the linear speed of the linking element 11.

That means the rotation speed of the parisons about their longitudinal axes can advantageously be reversed or cancelled as required, making the toothed belt 11 to move in the opposite direction relative to the conveyor 13. For this purpose, the invention also contemplates the provision of means (embodied, for example, by the control means and the inverter that drives the second motor) for reversing the motion of the second motor.

Thus, the apparatus 1 enables the rotation speed of the rotary member 12, and hence of the conveyor 3, to be varied as required, even cancelling or reversing the direction of motion relative to the direction of motion due solely to the feed motion of the member 12 on the linking element 11. That means the rotation speed of the motor that controls the movement of the chain 11 is acted upon.

The invention offers the following advantages.

Firstly, the apparatus 1 enables the parisons 2 to be heated uniformly and, at the same time, is particularly robust and simple in construction.

In effect, the rotary members 12 are always coupled to the linking element

11 which means the problem of guaranteeing that the teeth of the rotary members

12 correctly mesh with the teeth of the linking element 11 is solved at the root.

Moreover, the fact that the friction clutches 13 are controlled by the same cam that controls the mechanism that grips and releases the parisons 2 constitutes a further simplification.

Also, the apparatus 1 is particularly flexible and optimizes the way the parisons 2 are rotated about their longitudinal axes inside heating tunnel.

This is made possible by the fact that the linking element 11 is motor driven.

Further advantages derive from the presence of a control system that regulates the rotation speed of the parisons about their longitudinal axes according to the parameters connected with the characteristics of the parisons and with the heating means.

It has also to be observed that the linking element 11 is configured as a ring

(i.e. has an annular shape); it is arranged in such a way that each rotary member 12 is stably coupled to the linking element 11 during the movement of the rotary member 12 in said closed loop.

Preferably, the linking element 11 is configured as a single ring, arranged substantially in correspondence to the path along which the parisons 2 are fed.

Said shape and arrangement of the linking element 11 (which allows the rotary members 12 to be always coupled thereto) is advantageous because avoids engagements and disengagements of the rotary members 12 with respect to the linking element 11, thus making the apparatus 1 more reliable and robust.

Furthermore, the following is observed.

The presence of the friction 13 allows to avoid damaging the parisons during the coupling between the rods 3 and the corresponding parisons 2. In fact, it allows the rod 8 to be idle, while the rod 8 is inserted in the parison 2.

In this light, it has to be underlined that, according to a further aspect of the present invention, the apparatus 1 comprises supporting means (not illustrated) configured for rotating the parison 2 around its axis while it is engaged by the rotating rod 8. In particular, said supporting means are configured to rotate the parison 2 at the same speed at which the rod 2 rotates.

In this way, the friction between the rod 8 and the parison 2 during their coupling is avoided, even if the rod is still motorized during the coupling (thus providing an alternative to the friction 13).

Claims

1) An apparatus (1) for heating parisons (2) of thermoplastic material comprising:

- a conveyor (3) having a ring-shaped configuration and defining a path along which the parisons (2) are fed, said path forming a closed loop;

- a plurality of supporting elements (6) having a structure (7) fixed to the conveyor (3) and a rod (8) rotatably associated with the structure (7) to rotate about a longitudinal axis and having a lower end that can be operatively inserted in a parison (2) in such a way as to retain it and drive it rotationally about its longitudinal axis;

- a linking element (11) kinematically coupled to a rotary member (12) rotatably associated with the structures (7) and coupled to the rods (8) in such a way that the rods (8) are made to rotate about their longitudinal axes as a result of their movement as one with the conveyor (3);

- means (10) for heating the parisons (2) along at least a part of the parison feed path;

- a first motor (4), connected to the conveyor (3), and a second motor, connected to the uniting element (11), characterized in that it comprises control means connected to the second motor for varying the speed of the linking element (11) as a function of the speed of the conveyor (3), for setting the speed at which the parisons (2) rotate about their longitudinal axes at a predetermined value independently of the speed of the conveyor (3). 2) The apparatus according to claim 1, wherein the linking element (11) is configured as a ring, arranged in such a way that the rotary member (12) is stably coupled to the linking element (11) during a movement of the rotary member (12) in said closed loop. 3) The apparatus according to claim 2, wherein the linking element (11) is configured as a single ring, arranged substantially in correspondence to the path along which the parisons (2) are fed.

4) The apparatus according to any of the foregoing claims, wherein the rotary member (12) is a sprocket stably meshed with the linking element (11). 5) The apparatus according to any of the foregoing claims, wherein said first motor (4) and second motor are independent of each other, whereby the linking element (11) is motor driven independently from the conveyor (3). 6) The apparatus according to any of the foregoing claims, comprising means for regulating the speed of the second motor, connected to said control means, for controlling the speed at which the parisons (2) rotate about their longitudinal axes.

7) The apparatus according to any of the foregoing claims, wherein each of the supporting elements (6) comprises a friction clutch (13) connected to the rod (8) and to the rotary member (12) to define a first operating position, where the rod (8) is engaged with the rotary member (12), and a second operating position, where the rod (8) is disengaged from the rotary member (12), the rod (8) being axially movable relative to the structure (7) between a lowered position, where the lower end of the rod (8) is operatively inserted in a parison (2) in such a way as to retain it and drive it rotationally about its longitudinal axis, and a raised position, where the parison (2) is disengaged from the rod (8).

8) The apparatus according to claim 7, wherein the friction clutch (13) is designed to be set in the first operating position when the rod (8) is in the lowered position, and in the second operating position when the rod (8) is in the raised position.

9) The apparatus according to claim 8, wherein the friction clutch (13) is designed to be set in the second operating position when the rod (8) is in an intermediate position between the lowered and raised positions.

10) The apparatus according to any of the foregoing claims from 7 to 9, wherein each of the supporting elements (6) comprises a wheel (16) kinematically connected to the rod (8) and interacting with a cam (17) for moving the rod (8) axially from the lowered position to the raised position.

11) The apparatus according to claim 10, wherein, in each of the supporting elements (6), the wheel (16) is kinematically connected to the rod (8) for moving the friction clutch (13) from the first operating position to the second and vice versa by interacting with the cam (17). 12) The apparatus according to claim 10 or 11, wherein each supporting element (6) comprises:

a sleeve (18) coaxial with the rod (8), movable axially but without being able to rotate about its longitudinal axis, and coupled to the rod (8) in such a way that the rod (8) is constrained to move axially as one with the sleeve (18) but can rotate freely relative to it about its longitudinal axis, the wheel (16) being fixed to the sleeve (18).

13) The apparatus according to any of the foregoing claims, wherein each of the supporting elements (6) comprises at least one pusher (81) housed in a slot (82) made in a bottom end of the rod (8) and radially movable in the slot between an extracted position and a withdrawn position, the pusher (81) being connected to an elastic arm (83) designed to keep it in the extracted position when there are no forces applied to the pusher (81) itself.