GB2474027A

GB2474027A - Apparatus and method for heating preforms

Info

Publication number: GB2474027A
Application number: GB0917174A
Authority: GB
Inventors: Peter Reginald Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-09-30
Filing date: 2009-09-30
Publication date: 2011-04-06
Also published as: WO2011039295A3; GB2474124A; GB201016372D0; WO2011039295A2; GB0917174D0

Abstract

An apparatus for reheating and conditioning an elongate preform for forming a blow moulded container such as a bottle, comprises a heater 20, 22 and a receiver 4 with a cylindrical elongate surface 6, (102, figure 3) which engages with a surface of an elongate preform to transfer heat to the preform by conduction. The cylindrical surface 6 may comprise the inner surface of a cylindrical cavity one end of which is in the form of a concave hemispherical surface 15 which may have a vacuum duct 30 opening. Vacuum may be applied to hold outer surfaces of the preform in contact with the receiver. At least two spaced heaters may be provided which allows for a temperature profile to be established along the length of the receiver and so the preform. Alternatively the cylindrical surface (102) may comprise the outer surface of a pin (100) which is internally heated by a fluid such as oil flowing through duct (118), preferably a baffled bore, in the pin. A thermal insulator (108) may be provided in part of the pin around the duct to prevent heating of the neck finish of the preform.

Description

V

HEATING PREFORMS

The present invention relates to an apparatus and method for reheating and conditioning a preform, in particular an elongate preform for blow moulding into a container such as a bottle.

In the packaging industry, the process of blow moulding is often used in the manufacture of containers, particularly bottles for carbonated beverages. This process involves the initial formation of a preform, typically by injection moulding, which preforms are subsequently blow moulded to form the containers. Such preforms are typically formed of thermoplastic material, particularly polyethylene terephthalate (PET).

PET preforms need to be at the correct temperature for stretch blow moulding when introduced into the mould cavity of a blow moulding machine. The desired temperature may vary along the length of the preform. To achieve this, there are currently four known methods: 1. Latent heat within the preform, the latent heat resulting from solidification of the preform during the injection moulding process; 2. Latent heat, together with additional radiated heat from a radiation heater; 3. Radiated heat; or 4. Microwave energy emitted from a source of microwave energy.

These known methods can suffer from one or more of the following problems, namely: the temperature control of various regions of the preform can be inaccurate, the energy consumption may be high, and the heated preform may be subjected to stresses causing deformation prior to blow moulding.

It is currently generally accepted within the blow moulding industry that any form of contact to the surface on the hot preform will have a detrimental effect on the stretch-blow phase, for example inadvertently introducing a temperature gradient within the preform and/or damaging the surface of the preform to introduce blow moulding

F

irregularities or visible defects in the blow moulded container and/or causing off-axis blow moulding.

The present invention aims at least partially to overcome these problems of known heating methods and apparatus. There is a need in the art for a method and apparatus for preform heating in which there is very accurate temperature control, for example in which the neck area of the preform is not overheated, in which there is low energy consumption and in which the preform is allowed to relax without bending.

The present invention provides an apparatus for reheating and conditioning an elongate preform for forming a blow moulded container, said apparatus comprising: a receiver which comprises a substantially cylindrical elongate surface portion, wherein said surface portion is adapted to engage in substantially uniform contact with a surface of an elongate preform and is further adapted to transfer heat thereto by conduction from said surface portion; and means for heating said receiver.

In first embodiment, the receiver has a first, substantially cylindrical elongate inner surface portion and a second, substantially hemispherical concave inner surface portion, wherein the first surface portion and second surface portion define a cavity. Preferably, the cavity has a closed upper end and an open lower end and the receiver further comprises a vacuum duct which opens into the second, substantially hemispherical concave inner surface portion. Preferably, the means for heating the receiver comprises at least two heaters, wherein the heaters are spaced from each other in a direction along the length of the receiver.

In a second embodiment, the receiver has a first substantially cylindrical elongate outer surface portion and a second, substantially hemispherical convex outer surface portion.

Preferably, the means for heating the receiver comprises a conduit extending substantially along the length of the receiver for flow of heated fluid therethrough.

Preferably, the conduit is formed as a common bore of the receiver and has parallel inlet and outlet portions separated by a baffle. Preferably, the apparatus further comprises a mount fitted to the receiver, the mount comprising an annular thermal, insulator surrounding the conduit.

The present invention also provides a method for reheating and conditioning an elongate preform for forming a blow moulded container, wherein said preform is formed from a thermoplastic material and has an inner surface and an outer surface, the method comprising the steps of: i) contacting one of the inner and outer surface of the preform with a surface of a receiver, wherein said surface of the receiver is adapted to engage in substantially uniform contact with one of said inner surface and said outer surface of the preform, and said receiver is adapted to transfer heat conductively from said surface of the receiver to the preform; ii) heating the receiver such that heat is transferred conductively from the receiver to the preform.

Preferably, the receiver is heated when said surface of the receiver and said surface of the preform are in substantially uniform contact.

In a first embodiment, said surface of the receiver is adapted to engage in substantially uniform contact with the outer surface of the preform. Preferably, said surface of the receiver defines a cavity which has a closed upper end and an open lower end.

Preferably, said surface of the preform and said surface of the receiver are held in contact with one another by means of a vacuum. Preferably, the vacuum is applied to the base of the preform only. Preferably, the receiver is heated such that there is a temperature gradient in a direction along the length of the receiver.

In a second embodiment, said surface of the receiver is adapted to engage in substantially uniform contact with the inner surface of the preform. Preferably, the receiver is heated by a flow of heated fluid through a conduit, wherein the conduit extends substantially along the length of the receiver.

The present invention on predicated on the finding by the present inventor that excellent results can be obtained by using conductive heat to reheat and condition preforms.

It has been found in particular that if the surface temperature of the receiver is kept lower than the higher end of the thermoplastic material's reheat temperature range for blow moulding (i.e. softening point), the preform does not adhere to the receiver and therefore there is no detrimental effect, for example as discussed above with respect to the state of the art, on the stretch-blow phase of the container manufacturing process resulting from the direct thermally conductive contact between the receiver and the preform.

The present invention employs conductive heat to reheat and condition preforms.

Particular benefits achievable by the preferred embodiments of the present invention are: 1. the preform is allowed to relax with its shape controlled, with no bending during stress relief; 2. "knife-edge" temperature change (i.e. a large temperature drop/increase can be controllably established over a short distance), with no overheating of the neck area; 3. very accurate temperature control due to surface contact of the receiver and preform; and/or 4. very low energy consumption due to direct heat transfer by conduction.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross-section through an apparatus for reheating and conditioning a preform in accordance with a first embodiment of the present invention.

Figure 2 is a schematic representation of the temperature distribution within different sections of a preform which is heated by the apparatus of the present invention.

Figure 3 shows a schematic cross-section through an apparatus for reheating and conditioning a preform in accordance with a second embodiment of the present invention.

Referring to Figure 1, there is shown an apparatus 2, according to a first embodiment of the present invention, for reheating and conditioning an elongate preform 50. The preform 50 which is to be heated comprises a thermoplastic material, such as PET. The preform 50 has a conventional hollow structure and comprises a threaded neck finish 52, including an annular closure seating flange 54, at an open end 56 of the preform 50, a main body section 58 and a closed end 60 having a convex outer surface 62, and a corresponding concave inner surface 64, which are typically substantially hemispherical.

The main body section 58 is substantially cylindrical, but with a small taper towards the closed end 60. The main body section 58 has an inner surface 66 and an outer surface 68.

The apparatus 2 comprises an elongate receiver 4 which has a preform-engaging surface 6 adapted to mate with a complementary outer surface of the preform 50. The preform-engaging surface 6 defines a cavity 8 shaped and dimensioned to provide a uniformly close contact with the outer surfaces 62, 68 of the preform 50 located towards the closed end 60 with respect to the flange 54. The receiver 4 has an end face 10 against which the flange 54 can abut in use when the preform 50 is received in the cavity 8. During heating, the finish 52 of the preform 50 is not in contact with the preform-engaging surface 6, and remains outside the cavity 8.

The receiver 4 is composed of a main body 12, which surrounds a first, substantially cylindrical, cavity portion and has an elongate inner surface 13 which is shaped and dimensioned to receive the main body section 58 of the preform 50, and an end body 14, mating with the main body 12, which surrounds a second, substantially hemispherical, cavity portion and has a concave inner surface 15 which is shaped and dimensioned to receive the closed end 60 of the preform 50. The main body 12 and the end body 14 are respectively mounted within main and end blocks 16, 18 which abut. The preform-engaging surface 6 defining the cavity 8 is coated with a non-stick material, which may be PTFE (polytetrafluoroethylene).

A first annular heater 20 surrounds the main block 16 and a second annular heater 22 surrounds the end block 18. The first and second heaters 16, 18 are spaced from each other in a direction along the length of the receiver 4. A respective thermocouple 24, 26 is located within each of the main and end blocks 16, 18 to measure the temperature for control of the heating of the preform 50.

In this embodiment, the cavity 8 has an open lower end and a closed upper end, and the preform 50 is, in use, inserted upwardly into the cavity 8 in an inverted orientation The end body 14 includes a vacuum duct 30 extending therethrough which opens into the concave surface 15 and is connected to a conduit 32 for connection to a source of vacuum (not shown). The vacuum duct 30 and conduit 32 are provided to apply a negative pressure onto the convex outer surface 62 of the preform 50 when the preform is received within the cavity 8, which acts, in use, to hold the outer surfaces 62, 68 of the preform 50 in contact with the preform-engaging surface 6 against the action of gravity.

In the preform heating method, the main body section 58 and closed end 60 of the preform 50 are is inserted into the cavity 8, such that the outer surfaces 62, 68 of the preform 50 engage in substantially uniform contact with the preform-engaging surface 6.

The primary holding force is the vacuum applied at the axial centre of the closed end 60 which form the base of the blow inoulded container and so is not visually important. In this embodiment, the preform 50 is held within the cavity 8 by the vacuum applied to the closed end 60 by the duct 30. Preferably, the preform 50 is held within the cavity 8 by a vacuum at the preform closed end 60 only. The first and second heaters 20, 22 are operated to heat the blocks 16, 18 which in turn conductively heat the receiver 4 which in turn conductively heats the preform 50. The spaced arrangement of the first and second heaters 16, 18 along the length of the receiver 4 allows for a temperature profile to be established along the length of the receiver 4, said length being parallel with the longitudinal axis of the inserted preform, which in turn provides an accurate temperature profile along the heated preform 50. Such a temperature profile assists in achieving good stretch-blow control in the subsequent stretch blow moulding stage of the container manufacturing process.

As is known in the art, the material of the preform which is to be stretch blow moulded is heated to be within a temperature range which is above the glass transition temperature range but below the melting temperature of the thermoplastic resin. Typically, the temperature of the preform-engaging surface 6 of the receiver 4 which defines the cavity 8 is kept lower than the higher end of the thermoplastic material's blow moulding temperature range, so that the preform 50 does not inadvertently adhere to the receiver 4 and so that there is no consequential detrimental effect on the subsequent stretch-blow phase of the manufacturing process.

It will be appreciated by those skilled in the art that heating means other than the above-mentioned first and second heaters, but which still allow for a temperature profile to be established, may be employed which are within the scope of the present invention. For example, as disclosed for the second embodiment, a coil carrying heated fluid may be embedded within the blocks.

In a second embodiment of the present invention, as illustrated in schematic cross-section in Figure 3, the receiver 100 is in the form of an elongate pin. In this embodiment, an outer surface 102 of the pin-shaped receiver 100 is adapted to mate with the inner surfaces 64, 66 of the preform 50. The preform 50 fits over the receiver 100, which is upwardly oriented, such that the inner surfaces 64, 66 of the preform 50 are in uniform contact with the outer surface 102 of the receiver 100. The outer surface 102 is coated with a non-stick material, which may be PTFE (polytetrafluoroethylene). The preform 50 is again in an inverted orientation when heated on the receiver 100.

The threaded neck finish 52 of the preform is, in use, supported on a lower mount 104 for the receiver 100. The receiver 100 is fitted onto the mount 104. A heating means 106 extends through the mount 104 and into the receiver 100. An annular thermal insulator 108 extends through the mount 104 and separates a radially outer part 110 from a radially inner part 112, the radially inner part 112 including the heating means 106.

The upper end 114 of the insulator 108 terminates beneath the receiver 100 and has an outer annular surface 116 which has the same outer diameter as that of the adjacent receiver surface and so, in use, engages the inner surface of the neck finish 52.

Accordingly, the insulator 108 substantially prevents inadvertent heating of the neck finish 52 by the receiver 100 or the heating means 106.

In this embodiment, the heating means 106 comprises a heated fluid, preferably a liquid, more preferably an oil, which flows through at least one duct 118 defined within the receiver 100. The heated fluid flows into the mount 104 via a fluid inlet 120; then flows through the mount 104, into the adjacent receiver 100 and along the receiver 100 towards the free end 122 thereof along an inlet conduit 124. The fluid then returns from the free end 122, along the receiver 100 and through the mount 104 along a return conduitl26, and exits the mount 104 via a fluid outlet 128.

Preferably, the inlet and outlet conduits 124, 126 comprise a common blind bore 130 separated by a central elongate baffle 132, the free end 134 of which is spaced from the inner surface 136 of the closed end of the common bore 130.

The receiver 100 is heated by the heating means 106. The receiver 100 transfers heat by conduction from the heated outer surface 102 to the mated inner surfaces 64, 66 of the preform 50. Again, the temperature of the surface of the receiver is kept lower than the higher end of the thermoplastic material's softening point.

Although various embodiments of the invention have been described in detail, it will be apparent to those skilled in the art that other modifications of the apparatus and method for reheating and conditioning a preform may be employed that are within the scope of the invention as defined in the appended claims.