GB2474124A

GB2474124A - Heating preforms

Info

Publication number: GB2474124A
Application number: GB1016372A
Authority: GB
Inventors: Peter Reginald Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-09-30
Filing date: 2010-09-30
Publication date: 2011-04-06
Also published as: WO2011039295A3; GB201016372D0; WO2011039295A2; GB0917174D0; GB2474027A

Abstract

An apparatus for reheating and conditioning an elongate preform for forming a blow moulded container comprises a heated receiver having a surface in uniform contact, preferably by the application of vacuum, with an outer surface of the preform to conductively heat it. The surface may comprise a cylindrical elongate portion 13 and a hemispherical concave portion 15 defining a cavity 8 for receiving a preform. The receiver may comprise a block (202, figure 4), which is one of a plurality mounted on a closed loop conveyor for delivering preforms to a stretch-blow-moulding station. Each block has a plurality of cavities (218) defined between split halves (220, 222) and pivotable to open the cavities to allow insertion or removal of preforms. The block halves may comprise spaced heaters (226, 230) allowing a temperature gradient to be established along the length of the preforms which may be controlled in dependance on the block orientation which may be determined by a proximity switch. Heating of each heater block may be controlled by a thermostatic control system in wireless communication with a central control unit. A busbar and pick-up arrangement (236, 234) may provide electrical connection to the blocks on the conveyor and a plug and socket arrangement (240, 242) allows blocks to be removed for servicing.

Description

HEATING PREFORMS

The present invention relates to an apparatus and method for reheating and conditioning a preform, in particular an elongate preform for stretch 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 andlor damaging the surface of the preform to introduce blow moulding

I

irregularities or visible defects in the blow moulded container andlor 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 including 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 and said surface portions are adapted to engage in substantially uniform contact with an outer surface of an elongate preform to transfer heat thereto by conduction from said surface portion; and means for heating said receiver.

A preferred heating means is a thermostatically controlled electric resistance heater.

Optionally, the cavity has a closed end and an open 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 cavity.

Preferably, a plurality of the receivers are serially mounted around a continuous conveyer having a closed loop configuration.

Typically, the conveyor is driven by an indexing motor which sequentially delivers heated preforms to a stretch blow moulding station.

In one embodiment, each receiver comprises a heater block for reheating and conditioning a preform therein. Preferably, each heater block comprises a plurality of heated cavities spaced along a length of the heater block. Optionally, each cavity is disposed between split halves of the block, the split halves being separated by a longitudinal split extending between the halves, Preferably, the split halves of the block extend transverse to the direction of movement of the conveyor. Preferably, each split half has at least one heater and at least one thermocouple associated therewith.

Optionally, each split half has a radially outer electric resistance heater and a radially inner electric resistance heater which are controllable to establish a desired temperature gradient therebetween. Preferably, the radially outer heater is located relative to the cavity for heating an open end of the preform and the radially inner heater is located relative to the cavity for heating a closed end of the preform. Preferably, a first pair of the radially outer and radially inner heaters and a second pair of the radially outer and radially inner heaters are on opposite sides of the preform-receiving cavity in the block.

Preferably, each heater block has an electrical pick-up assembly mounted at a radially inner edge of the heater block which is slidably electrically connected to an elongate busbar for electrical power which extends along the conveyor path to provide electrical power to the means for heating.

Preferably, each heater block has a thermostatic control system. Optionally, the thermostatic control system includes a wireless control unit mounted on the respective heater block. The apparatus may further comprise a central control unit which wirelessly monitors the wireless control units. The thermostatic control system may be adapted to control the heating gradient along the height of the heater block to enable the temperature profile along the length of a preform located in the cavity to be controlled. Typically, the means for heating is adapted to provide different heating gradients along the cavity dependent upon the orientation of the receiver.

Preferably, a proximity switch is mounted relative to the conveyor which is adapted to detect the position of each receiver as the conveyor rotates so as to provide a signal indicative of the orientation of the receiver. The orientation signal may be communicated to a control unit which adjusts the temperature profile of the means for heating of the respective receiver.

Preferably, the split halves of each heater block are adapted mutually to pivot between an open position, in which upper ends of the split halves are separated and have a gap therebetween to provide an enlarged upper open end of the cavity, and a closed position, in which the upper ends of the split halves are in contact. Optionally, the split halves of each heater block are provided with a pivot line extending along the length of the heater block for pivoting the split halves on opposite sides of the pivot line between the open and closed positions. The apparatus may further comprise an actuator system selectively to drive the split halves between the open and closed positions by rotation about the pivot line. Preferably, a longitudinal vacuum duct is located beneath the pivot line to enable connection of the cavity to a source of vacuum when the split halves are in the closed position. Typically, the vacuum duct is part of a vacuum system which is adapted to hold a closed end of the preform securely in the cavity independent of the orientation of the combination of the preform and the cavity.

The present invention further 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 outer surface, the method comprising the steps of: i) contacting the 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 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, said surface of the receiver defines a cavity which has a closed upper end and an open lower end.

Optionally, said outer surface of the preform and said surface of the receiver are held in contact with one another by means of a vacuum.

Typically, 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 preferred embodiment, a plurality of the receivers are serially mounted around a continuous conveyer having a closed loop configuration, Preferably, the conveyor is driven by an indexing motor which sequentially delivers heated preforms to a stretch blow moulding station.

Preferably, the receiver is heated by a radially outer electric resistance heater and a radially inner electric resistance heater which are controllable to establish a desired temperature gradient therebetween. Typically, the radially outer heater is located relative to the cavity for heating an open end of the preform and the radially inner heater is located relative to the cavity for heating a closed end of the preform. Optionally, the heating of each receiver is controlled wirelessly.

Preferably, the heating gradient along the height of the receiver is controlled to enable the temperature profile along the length of a preform located in the cavity to be controlled. Optionally, different heating gradients along the cavity are provided dependent upon the orientation 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. soflening 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, or a high temperature in the neck area to achieve a level of crystallinity for heat set applications; 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 side view of a preform reheating and conditioning apparatus in accordance with a second embodiment of the present invention coupled to a stretch blow moulding apparatus for manufacturing bottles from the preforms.

Figure 4 shows a schematic perspective view of a heater block of the preform reheating and conditioning apparatus of Figure 3.

Figures 5(a) and (b) show schematic perspective views of the heater block of Figure 4 in an open position and a closed position respectively.

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 optionally coated with a non-stick material, which may be PTFE (polytetrafluoroethylene). Such a non-stick material may be omitted if low heating temperatures are used, typically less than 100CC for polyethylene terephthalate (PET) preforms.

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 preforni 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 moulded 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.

Another preferred embodiment of a receiver is illustrated in Figures 3 to 5. A continuous chain conveyer 200 includes a plurality of heater blocks 202 which are serially mounted around an endless loop 204 in an oval configuration. The conveyor 200 comprises a preform reheating and conditioning station. The heater blocks 202 are typically composed of a metal having high thermal conductivity, such as aluminium.

As shown in Figure 3, the continuous chain conveyor 200 is located adjacent to a stretch blow moulding apparatus 300 for stretch blow moulding the preforms heated by the heater blocks 202 carried by the conveyor 200. The conveyor 200 is driven by an indexing motor 302 which sequentially delivers heated preforms 308 to an unloading station 304 at which the heated preforms 308 in a plurality of selected heater blocks 202 are unloaded from the heater blocks 202 and subsequently conveyed to a stretch blow moulding station 306.

An upper conveyor section 206 and a lower conveyor section 208 are provided between opposed end sections 210, 212 which are mounted on drive rollers 214, 216 which engage chain links 220 of the conveyor 200, shown in detail in Figure 4. The conveyor includes an endless chain 201 coupled to a respective end 203 of the heater block 202, Alternatively, the conveyor 200 may includes spaced endless chains, each coupled to a respective end of the heater blocks 202. Typically, sixty heater blocks 202 are mounted on the conveyor 200 in a closed loop configuration. Each heater block 202 comprises a plurality of heated cavities 218, spaced along the length of the heater block 202. Each cavity 218 is disposed between split halves 220, 222 of the block 202. The longitudinal split 224 extends between the halves 220, 222 which also extend transverse to the direction of movement of the conveyor 200 Each split half 220, 222 has a radially outer electric resistance heater 226 and an associated thermocouple 228, and a radially inner electric resistance heater 230 and an associated thermocouple 232. The radially outer electric resistance heater 226 and the radially inner electric resistance heater 230 are controllable to establish a desired temperature gradient therebetween. The individual heaters 226, 230 and their respective thermocouples 228, 232 are individually controlled so as to maintain the precise temperature required for the stretch blow moulding of the preform into a bottle at the stretch blow moulding station 306. The thermocouples 228, 232 provide temperature measurement of the block regions heated by the associated heaters 226, 230. There are, in the preferred embodiment, four heaters associated with each heating block 202, comprising two radially outer heaters 226 for heating the open end (i.e. the neck finish portion) of the preform 308 and two radially inner heaters 230 for heating the closed end (i.e. the base forming portion) of the preform 308, with each of the pair of upper heaters 226 and of the pair lower heaters 230 being on a respective split half 220, 222 and therefore on opposite sides of the preform cavity 218 in the block 202. This provides uniform heating across the diameter of the preform 308, and a desired temperature gradient along the length of the preform 308.

Electrical power is supplied to the split cavities 218 via a continuous bus bar assembly.

In particular, the heaters 226, 230 and thermocouples 228, 232 are electrically connected to a pick-up assembly 234 mounted at the radially inner edge of the heater block 202.

The pick-up assembly 234 is slidably electrically connected to an elongate busbar feed rail 236 which extends along the conveyor path to provide electrical power and coupling to the heaters 226, 230 and thermocouples 228, 232 as the heater blocks 202 move around the endless path of the conveyor 200.

Individual thermostatic control of the heater blocks 202 is achieved using individual wireless control units 238 mounted on each pair of split halves 220, 222, each wireless control unit 238 controlling the four upper and lower heaters 226, 230 in the split halves 220, 222. A central control unit 239 wirelessly monitors the wireless control units 238.

The wireless control unit 238 comprises a wireless transmitter/receiver module 238 which is connected to the pick-up assembly 234. A electrical plug connector 240 of the block 202 interfaces with an electrical socket connector 242 of the conveyor 200 which is mounted on a transversely extending stretcher support 244 which is affixed to the chain conveyor 200. The heater block 202 and the plug connector 240 affixed thereto can be unplugged from the socket connector 242 for removal from the conveyor 200 for replacement or servicing.

The control system for the heaters of the heater blocks 202 is adapted to control the heating gradient along the height of the heater block 202 to enable the temperature profile along the length of the preform 308 located in the cavity 218 to be controlled.

The heating control system is adapted to provide different heating gradients dependent upon the orientation of the respective heater block 202 and the preforms 308 located therein. Since convective heat rises, in order to provide uniform heating of s selected part of a preform irrespective of the orientation of the preform 308, the temperature gradient of the heating system is modified dependent upon the orientation of the respective heater block 202.

A proximity switch 250 is mounted to the conveyor frame (not shown). The proximity switch 250 detects the position of each heater block 202 so as to provide a signal indicative of the orientation of the heater block 202. The orientation signal is communicated to the central control unit 239, which then adjusts the temperature profile of the heaters 226, 230 of the respective block 202 to ensure that the correct upper and lower temperatures are maintained.

In the event that the conveyor 200 is stopped, the central control unit 239 reduces the temperature of the heaters 226, 230 to a default setting to ensure no overheating and easy restart of the preform heating step, As shown in detail in Figures 5(a) and 5(b), the split halves 220, 222 of each heater block 202 are adapted mutually to pivot between an open position shown in Figure 5(a) and a closed position shown in Figure 5(b). In the open position, the upper ends 400, 402 of the split halves 220, 222 are separated and have a gap 403 therebetween to provide an enlarged upper open end 404 of the enlarged cavity 406 to permit ready insertion of a preform 308 into the cavity 406 and removal of a preform 308 from the cavity 406. In the closed position, the upper ends 400, 402 of the split halves 220, 222 are urged together into contact to provide an ilmer surface 407 of the cavity 406 substantially corresponding to the outer surface 409 of the preform 308 for high thermal coupling between the heater block 202 and the preform 308 to enable accurate and efficient heating of the preform 308.

The closed end 408 of the preform 308 is located above a pivot line 410 extending along the length of the heater block 200, and opposed pivot drive rods 412 pass through the respective split halves 220, 222 on opposite sides of the pivot line 410. The pivot drive rods 412 are actuatable selectively to drive the split halves 220, 222 between the open and closed positions by rotation about the pivot line 410 as shown by the arrows in Figure 5.

Unheated preforms 308 are loaded at a loading station 310 into the split halves 220, 222 which are in the open position. The split halves 220, 222 are then actuated so as to be in the closed position, and the preforms 308 are reheated as they progress towards the unloading station 320. For clarity, only a preform at the unloading station 320 is illustrated, The conveyor 200 moves in a clockwise direction, as shown by the arrows in Figure 3, passing along the top and then along the bottom of the conveyor path. The preforms 308 are conveyed along substantially the entire length of the annular path of the conveyor 200, a typical residence time being 2.5 minutes. At the unloading station 320, the split halves 220, 222 are actuated so as to be in the open position, and the heated preforms are removed. A batch of preforms 308 is removed from the line of cavities 218 extending across the split halves 220, 222 of the conveyor 200. In the embodiment shown there are six preforms 308 in the batch. The batch of preforms 308 is rotated about an angle of 90°, and then the batch is fed as a sequential line of preforms through the stretch blow moulding apparatus. Thereafter, the split halves 220, 222 return, in an indexed manner, to the loading station 310 at which a subsequent batch of preforms 308 is loaded for a subsequent reheat cycle.

Beneath the pivot line 410 the split halves 220, 222 are separable to form a longitudinal vacuum duct 416 to enable connection to a source of vacuum (not shown), located beneath the heater block 200, when the split halves 220, 222 are in the closed position of Figure 5(b). The vacuum holds the closed end 408 of the preform 308 securely in the cavity 406 independent of the orientation of the combination of the preform 308 and the cavity 406 as the preform 308 moves circumferentially around the conveyor 200 during the preform reheating and conditioning step.

The opposing faces of the split halves 220, 222 may be provided with a hermetic sealing surface 418 to assist maintaining the vacuum within the cavities 406.

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.

Claims

Claims 1. An apparatus for reheating and conditioning an elongate preform for forming a blow moulded container, said apparatus comprising: a receiver including 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 and said surface portions are adapted to engage in substantially uniform contact with an outer surface of an elongate preform to transfer heat thereto by conduction from said surface portion; and means for heating said receiver.
2. The apparatus according to claim 1 wherein the cavity has a closed end and an open end and the receiver further comprises a vacuum duct which opens into the second, substantially hemispherical concave inner surface portion.
3. The apparatus according to claim 1 or claim 2 wherein 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 cavity.
4. The apparatus according to any preceding claim wherein a plurality of the receivers are serially mounted around a continuous conveyer having a closed loop configuration.
5. The apparatus according to claim 4 wherein the conveyor is driven by an indexing motor which sequentially delivers heated preforms to a stretch blow moulding station.
6. The apparatus according to any preceding claim wherein each receiver comprises a heater block for reheating and conditioning a preform therein.
7. The apparatus according to claim 6 wherein each heater block comprises a plurality of heated cavities spaced along a length of the heater block.
8. The apparatus according to claim 6 or claim 7 wherein each cavity is disposed between split halves of the block, the split halves being separated by a longitudinal split extending between the halves.
9. The apparatus according to claim 8 when appendant on claim 4 wherein the split halves of the block extend transverse to the direction of movement of the conveyor.
10. The apparatus according to claim 8 or claim 9 wherein each split half has at least one heater and at least one thermocouple associated therewith.
11. The apparatus according to claim 10 wherein each split half has a radially outer electric resistance heater and a radially inner electric resistance heater which are controllable to establish a desired temperature gradient therebetween.
12. The apparatus according to claim 11 wherein the radially outer heater is located relative to the cavity for heating an open end of the preform and the radially inner heater is located relative to the cavity for heating a closed end of the preform.
13. The apparatus according to claim 12 wherein a first pair of the radially outer and radially inner heaters and a second pair of the radially outer and radially inner heaters are on opposite sides of the preform-receiving cavity in the block.
14, The apparatus according to any one of claims 6 to 13 when appendant on claim 4 wherein each heater block has an electrical pick-up assembly mounted at a radially inner edge of the heater block which is slidably electrically connected to an elongate busbar for electrical power which extends along the conveyor path to provide electrical power to the means for heating.
15. The apparatus according to any one of claims 6 to 14 wherein each heater block has a thermostatic control system.
16. The apparatus according to claim 15 wherein the thermostatic control system includes a wireless control unit mounted on the respective heater block
17. The apparatus according to claim 16 further comprising a central control unit which wirelessly monitors the wireless control units.
18. The apparatus according to any one of claims 15 to 17 wherein the thermostatic control system is adapted to control the heating gradient along the height of the heater block to enable the temperature profile along the length of a preform located in the cavity to be controlled.
19. The apparatus according to any preceding claim wherein the means for heating is adapted to provide different heating gradients along the cavity dependent upon the orientation of the receiver.
20. The apparatus according to claim 19 when app endant on claim 4 wherein a proximity switch is mounted relative to the conveyor which is adapted to detect the position of each receiver as the conveyor rotates so as to provide a signal indicative of the orientation of the receiver.
21. The apparatus according to claim 20 wherein the orientation signal is communicated to a control unit which adjusts the temperature profile of the means for heating of the respective receiver.
22. The apparatus according to any one of claims 8 to 13 wherein the split halves of each heater block are adapted mutually to pivot between an open position, in which upper ends of the split halves are separated and have a gap therebetween to provide an enlarged upper open end of the cavity, and a closed position, in which the upper ends of the split halves are in contact.
23. The apparatus according to claim 22 wherein the split halves of each heater block are provided with a pivot line extending along the length of the heater block for pivoting the split halves on opposite sides of the pivot line between the open and closed positions.
24. The apparatus according to claim 23 further comprising an actuator system selectively to drive the split halves between the open and closed positions by rotation about the pivot line,
25. The apparatus according to claim 23 or claim 24 wherein a longitudinal vacuum duct is located beneath the pivot line to enable connection of the cavity to a source of vacuum when the split halves are in the closed position.
26, The apparatus according to claim 25 wherein the vacuum duct is part of a vacuum system which is adapted to hold a closed end of the preform securely in the cavity independent of the orientation of the combination of the preform and the cavity.
27. 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 outer surface, the method comprising the steps of: iii) contacting the 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 said outer surface of the preform, and said receiver is adapted to transfer heat conductively from said surface of the receiver to the preform; iv) heating the receiver such that heat is transferred conductively from the receiver to the preform.
28. The method according to claim 27 wherein said surface of the receiver defines a cavity which has a closed upper end and an open lower end.
29. The method according to claim 27 or claim 28 wherein said outer surface of the preform and said surface of the receiver are held in contact with one another by means of a vacuum.
30. The method according to claim 29 wherein the vacuum is applied to the base of the preform only.
31. The method according to any one of claims 27 to 30 wherein the receiver is heated such that there is a temperature gradient in a direction along the length of the receiver.
32. The method according to any one of claims 27 to 31 wherein a plurality of the receivers are serially mounted around a continuous conveyer having a closed ioop configuration.
33. The method according to claim 32 wherein the conveyor is driven by an indexing motor which sequentially delivers heated preforms to a stretch blow moulding station.
34. The method according to claim 31 wherein the receiver is heated by a radially outer electric resistance heater and a radially inner electric resistance heater which are controllable to establish a desired temperature gradient therebetween.The method according to claim 34 wherein the radially outer heater is located relative to the cavity for heating an open end of the preform and the radially inner heater is located relative to the cavity for heating a closed end of the preform.36 The method according to claim 32 wherein the heating of each receiver is controlled wirelessly.37. The method according to claim 34 wherein the heating gradient along the height of the receiver is controlled to enable the temperature profile along the length of a preform located in the cavity to be controlled.38. The method according to claim 32, claim 36 or claim 37 wherein different heating gradients along the cavity are provided dependent upon the orientation of the receiver.39. The method according to claim 38 wherein the position of the receiver is detected as the conveyor rotates so as to provide a signal indicative of the orientation of the receiver.40. The method according to claim 39 wherein the orientation signal is communicated to a control unit which adjusts the temperature profile of the heating of the respective receiver, 41. The method according to any one of claims 27 to 40 wherein the receiver is adapted to pivot between an open position, in which upper ends of the receiver are separated and have a gap therebetween to provide an enlarged upper open end of the cavity, and a closed position, in which the upper ends of the receiver are in contact.42. The method according to claim 41 wherein the cavity is connected to a source of vacuum when the receiver is in the closed position.43. The method according to claim 42 wherein the vacuum holds a closed end of the preform securely in the cavity independent of the orientation of the combination of the preform and the cavity.