U.S. patent application number 13/150736 was filed with the patent office on 2011-12-08 for oven for the thermal conditioning of preforms and control method of an air cooling device fitted to such an oven.
This patent application is currently assigned to SIDEL PARTICIPATIONS. Invention is credited to Mikael DERRIEN.
Application Number | 20110300497 13/150736 |
Document ID | / |
Family ID | 43587211 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110300497 |
Kind Code |
A1 |
DERRIEN; Mikael |
December 8, 2011 |
OVEN FOR THE THERMAL CONDITIONING OF PREFORMS AND CONTROL METHOD OF
AN AIR COOLING DEVICE FITTED TO SUCH AN OVEN
Abstract
An oven (10) for the heat treatment of preforms and a method for
operating an air-cooling device (42) fitted to such an oven
includes controlling elements (58) to vary the cooling air flow
rate onto the body (18) and bottom (20) of the preforms (12) along
the heating path.
Inventors: |
DERRIEN; Mikael; (Octeville
sur Mer, FR) |
Assignee: |
SIDEL PARTICIPATIONS
Octeville sur Mer
FR
|
Family ID: |
43587211 |
Appl. No.: |
13/150736 |
Filed: |
June 1, 2011 |
Current U.S.
Class: |
432/1 ;
432/77 |
Current CPC
Class: |
B29C 35/0805 20130101;
B29C 49/04 20130101; B29C 49/68 20130101; B29C 49/6445 20130101;
B29C 2035/1658 20130101; B29K 2105/258 20130101; B29B 13/024
20130101; B29K 2067/003 20130101; F27D 15/0206 20130101; B29C 35/16
20130101; B29C 2035/0822 20130101; F27D 15/02 20130101 |
Class at
Publication: |
432/1 ;
432/77 |
International
Class: |
F27D 15/02 20060101
F27D015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2010 |
FR |
1054309 |
Claims
1. Oven (10) for the heat treatment of thermoplastic preforms (12)
each respectively comprising a first part (14, 16) in its
definitive shape and a second part (18, 20) intended to be heated
by heating means (30) arranged along at least part of a determined
heating path followed by the preforms (12) travelling through the
oven, the said oven (10) comprising a cooling system (36) capable
respectively of cooling the first parts (14, 16) and the second
parts (18, 20) of the preforms, characterized in that the cooling
system (36) comprises at least one cooling device (42) capable of
air-cooling at least the second part (18, 20) of the preforms (12),
the said cooling device (42) comprising at least ventilation means
(52) capable of delivering a given flow rate of cooling air and
means (58, 64) for selectively varying, along the heating path of
the preforms (12), at least the cooling air flow rate delivered by
the said ventilation means (52) for cooling the said second parts
(18, 20) of the preforms (12).
2. Oven (10) according to claim 1, characterized in that the said
means (58, 64) consist of at least one speed variator (58)
associated with at least one of the ventilation means (52) of the
said at least one cooling device (42) so that the variation in
cooling air flow rate along the path is obtained by selectively
operating the said speed variator (58) associated with the said
ventilation means (52) independently of the other ventilation means
(52) of the cooling device (42).
3. Oven (10) according to claim 2, characterized in that the speed
variator (58) is operated via at least one operating unit (60) to
act on a drive motor (56) that drives the said associated
ventilation means (52) so as selectively, along the heating path,
to vary the air flow rate delivered for cooling at least the second
parts (18, 20) of the preforms (12).
4. Oven (10) according to claim 1, characterized in that the means
(58, 64) at least consist of shut-off means (64) so that the
variation in cooling air flow rate along the path is obtained by
selectively operating each of the shut-off means (64) independently
of the other shut-off means (64) of the cooling device (42).
5. Oven (10) according to claim 4, characterized in that the
shut-off means (64) can be operated selectively in terms of their
position so as selectively, along the heating path, to vary the
air-flow rate delivered for cooling at least the second parts (18,
20) of the preforms (12).
6. Oven (10) according to claim 1, characterized in that the oven
(10) comprises temperature measurement means (62) capable of
measuring the internal temperature and/or the external temperature
of the wall of the second part (18, 20) of the preforms (12) at
least at a determined position along the heating path and of
supplying at least one signal representative of one of the said
measured temperatures or of the gradient corresponding to the
difference between the said internal and external temperatures of
the wall.
7. Oven according to claim 1, characterized in that the cooling
system (36) comprises at least one operating unit (60, 70) for
operating the said at least one cooling device (42) which is
capable of controlling the said means (58, 64) intended selectively
along the heating path to vary the air flow rate for cooling at
least the second parts (18, 20) of the preforms (12) so as to set
the heat treatment of the preforms (12) along the heating path
through real-time control of the said means (58, 64) of the cooling
device (42).
8. Oven (10) according to claim 1, characterized in that the oven
(10) is of modular design comprising at least a number [n] of
modules (M) in which the said heating means (30) are mounted
arranged along all or part of the heating path, and in that the
means (58, 64) for selectively varying the air flow rate for
cooling at least the second parts (18, 20) of the preforms (12) are
common to at least two modules (M) designed to form a series and/or
parallel unit.
9. Method for operating a cooling device (42) which, being fitted
to a heat treatment oven (10) according to claim 1, is intended to
air-cool at least the second parts (18, 20) of the preforms (12)
travelling through the oven (10) along a heating path,
characterized in that the operating method comprises at least one
step consisting in: operating the means (58, 64) in order
selectively to vary the cooling air flow rate delivered at least to
the said second parts (18, 20) of the preforms (12) along the
heating path.
10. Method according to claim 9, characterized in that the method
comprises at least one step consisting in: measuring the internal
temperature and/or the external temperature of the wall of the
second part (18, 20) of the preform (12) so as to produce at least
one signal representative of the internal and/or external
temperature of the wall or of the gradient corresponding to the
difference between the said internal and external temperatures.
11. Method according to claim 9, characterized in that the method
comprises at least one setting step consisting in: controlling the
said means (58, 60) in real time in order, as a function of at
least one data item such as at least one signal representative of
temperature, to set the air flow rate for cooling at least the
second parts (18, 20) of the preforms (12) which flow rate is
delivered variably along the heating path.
12. Method for heat treating preforms (12) in an oven (10)
comprising at least one operating step according to claim 9 which
is implemented in combination with at least one of the following
setting steps that consist in: setting the power of the heating
means (30) so as to vary, along the heating path, the heating power
delivered to the second parts (18, 20) of the preforms (12),
particularly so as to establish stabilization zones.
13. Method according to claim 10, characterized in that the method
comprises at least one setting step consisting in: controlling the
said means (58, 60) in real time in order, as a function of at
least one data item such as at least one signal representative of
temperature, to set the air flow rate for cooling at least the
second parts (18, 20) of the preforms (12) which flow rate is
delivered variably along the heating path.
14. Oven (10) according to claim 2, characterized in that the oven
(10) comprises temperature measurement means (62) capable of
measuring the internal temperature and/or the external temperature
of the wall of the second part (18, 20) of the preforms (12) at
least at a determined position along the heating path and of
supplying at least one signal representative of one of the said
measured temperatures or of the gradient corresponding to the
difference between the said internal and external temperatures of
the wall.
15. Oven according to claim 2, characterized in that the cooling
system (36) comprises at least one operating unit (60, 70) for
operating the said at least one cooling device (42) which is
capable of controlling the said means (58, 64) intended selectively
along the heating path to vary the air flow rate for cooling at
least the second parts (18, 20) of the preforms (12) so as to set
the heat treatment of the preforms (12) along the heating path
through real-time control of the said means (58, 64) of the cooling
device (42).
16. Oven (10) according to claim 2, characterized in that the oven
(10) is of modular design comprising at least a number [n] of
modules (M) in which the said heating means (30) are mounted
arranged along all or part of the heating path, and in that the
means (58, 64) for selectively varying the air flow rate for
cooling at least the second parts (18, 20) of the preforms (12) are
common to at least two modules (M) designed to form a series and/or
parallel unit.
17. Oven (10) according to claim 3, characterized in that the oven
(10) comprises temperature measurement means (62) capable of
measuring the internal temperature and/or the external temperature
of the wall of the second part (18, 20) of the preforms (12) at
least at a determined position along the heating path and of
supplying at least one signal representative of one of the said
measured temperatures or of the gradient corresponding to the
difference between the said internal and external temperatures of
the wall.
18. Oven according to claim 3, characterized in that the cooling
system (36) comprises at least one operating unit (60, 70) for
operating the said at least one cooling device (42) which is
capable of controlling the said means (58, 64) intended selectively
along the heating path to vary the air flow rate for cooling at
least the second parts (18, 20) of the preforms (12) so as to set
the heat treatment of the preforms (12) along the heating path
through real-time control of the said means (58, 64) of the cooling
device (42).
19. Oven (10) according to claim 3, characterized in that the oven
(10) is of modular design comprising at least a number [n] of
modules (M) in which the said heating means (30) are mounted
arranged along all or part of the heating path, and in that the
means (58, 64) for selectively varying the air flow rate for
cooling at least the second parts (18, 20) of the preforms (12) are
common to at least two modules (M) designed to form a series and/or
parallel unit.
Description
[0001] The present invention relates to an oven for the heat
treatment of preforms and to a method for operating an air-cooling
device fitted to such an oven.
[0002] The present invention relates more specifically to an oven
for the heat treatment of thermoplastic preforms each respectively
comprising a first part in its definitive shape and a second part
intended to be heated by heating means arranged along at least part
of a determined heating path followed by the preforms travelling
through the oven, the said oven comprising a cooling system capable
of cooling the first parts and the second parts of the
preforms.
[0003] In general, the invention relates to the field of the
manufacture of containers which are obtained by the conversion of
preforms, particularly by blow-moulding or by
stretch-blow-moulding, the preforms notably being obtained by the
injection-moulding of thermoplastic, for example of polyethylene
terephthalate (PET).
[0004] To do this, the preforms undergo a preliminary heat
treatment in an oven to raise them to a temperature above the glass
transition temperature of the material of which they are made.
[0005] The manufacture of containers such as bottles, vials or any
other type of hollow body is generally performed in installations
comprising such a preform heat treatment oven associated with at
least one machine for the conversion of preforms into containers
which machine is located downstream, for example a "blower".
[0006] Many preform heat treatment ovens, notably those
incorporated into installations for the manufacture of containers,
are known from the prior art.
[0007] Document WO-A-2004/062885, to which reference may be made
for fuller details, non-limitingly illustrates one example of a
heat treatment oven, more particularly an oven of the linear type
(as opposed notably to an oven of the circular type).
[0008] It will be recalled that a thermoplastic preform or parison
respectively comprises a first part in its definitive shape, which
consists of the neck and the flange, and a second part which is the
only part intended to be heat treated in the oven and which
consists of the body and the bottom.
[0009] The heat treatment of the second parts formed of the body
and of the bottom of the preforms is an operation that is
particularly tricky because of the importance that the temperature
of the material has in relation to the subsequent conversion
operations, for example conversion by blowing a gas (air) under
pressure or stretch-blow-moulding, or alternatively conversion
which is effected at least in part by filling with a pressurized
liquid.
[0010] On the one hand, the mean temperature of the second part of
the preforms needs to be higher than the glass transition
temperature of the material (around 80.degree. C. for PET) so as to
allow biorientation of the material during the conversion, but at
the same time needs to be lower than the crystallization
temperature (around 140.degree. C. for PET) above which there is a
risk that the material will crystallize, making the preform
unsuited to any further conversion.
[0011] Thus, too low a preform temperature may cause a whitish
pearlesence (pearlized appearance) of the end container as a result
of an overstretching of the preform which at molecular level leads
to breaks in the long polymerized chains.
[0012] By contrast, too high a preform temperature may cause
spherolitic crystallization of the constituent material, thus
rendering the preform unsuited to any further conversion, notably
involving blow moulding and/or filling.
[0013] What is more, the temperature distribution within the
preform itself has an impact on the quality of the end container,
and in particular on the transparency and distribution of material
in the body and bottom of the container.
[0014] The temperature distribution through the body and bottom of
the preform is multi-faceted, including the distribution around the
circumference of the preform (that is to say the angular
distribution about the main axis of the preform), the axial
distribution (that is to say that parallel to the said axis) and
also the distribution through the wall thickness of the body and of
the bottom of the preform.
[0015] Thus, in order to ensure a temperature distribution around
the entire circumference of the preform, the preforms are generally
rotated on themselves about their main axis at the same time as
they travel past the heating means arranged on all or part of the
heating path.
[0016] The rotating of the preforms in order to obtain a uniform
circumferential temperature distribution is, however, dependent on
the application, because for certain applications a non-uniform
circumferential distribution is likewise sometimes sought,
particularly on containers of complex shape.
[0017] For fuller details, reference may, for example, be made to
document WO-A-94/23932 regarding the heat treatment of a preform in
order to obtain an end container with a complex shaped body.
[0018] The preforms are rotated using gripper means that hold the
preforms in position, neck up or neck down, along the entire
heating path, the gripper means being connected for the purposes of
movement to the transport device that performs said looped heating
path.
[0019] Document WO-A-00/48819, to which reference may be made for
fuller details, illustrates one example of a transport device and
improved gripper means.
[0020] It is also possible to control the axial distribution of the
temperature, i.e. the heating profile parallel to the axis of the
perform, and to do so by controlling, for example, the power
radiated by the lamps (infrared radiation lamps) or diodes used as
heating means in such an oven, by using focusing means
(FR-A-2.732.924) or alternatively by selectively setting the
position of each lamp so as to vary the distance between each of
the lamps and the corresponding portion of the second part of the
preforms (FR-A-2.872.734).
[0021] The temperature distribution through the thickness of the
wall of the body and of the bottom of the preform is, on the other
hand, far more difficult to master even though it is this
distribution that is of key importance in mastering the subsequent
operation of converting the preform into a container.
[0022] The ideal outcome of the preform heat treatment is a
temperature gradient through the wall which is such that the
temperature of the internal surface of the wall is greater than, or
failing that at least equal to, the temperature of the external
surface of the wall.
[0023] This is because it has been found that a small gradient
between the temperature of the external surface of the wall and the
temperature of the internal surface of the wall, which is
comparatively higher than that of the external surface, makes it
possible to obtain an end container with good visual and structural
qualities, notably good transparency and a relatively consistent
wall thickness.
[0024] The reason for this is notably that, when the preform is
being converted into a container, the radial development of the
inside diameter of the preform is then greater than the radial
development of the outside diameter and it is therefore preferable
for the wall to have such a temperature gradient which favours the
wall surface that is effecting the greatest radial development.
[0025] What is more, it will be understood that obtaining such a
gradient is, in practice, all the more important when the wall is
very thick or when the container is obtained after a great deal of
radial development of the preform.
[0026] In a heat treatment oven, it is common practice to use an
air-cooling system to perform a dual cooling function.
[0027] The cooling system on the one hand cools the second parts of
the preforms and on the other hand cools the first parts of the
preforms and the constituent mechanical components of the oven to
prevent them from deteriorating.
[0028] Such a system for the air-cooling of preforms contributes,
in combination with the heating parameters, towards obtaining the
desired gradient in the wall of the preform by encouraging the
transmission of heat by convection through the thickness of the
material of the body and of the bottom and by limiting the surface
heating induced by the absorption of the emitted radiation.
[0029] In fact, the applicant has been able to establish that
mastering the temperature distribution in the body and the bottom
and obtaining a gradient of the abovementioned type in the wall of
this second part of the preform can more especially be achieved by
setting the following various parameters: [0030] the radiation
exposure time; [0031] the speed at which the preforms rotate on
themselves; [0032] the preform thermal stabilization time; [0033]
the ventilation cooling of the body and of the bottom.
[0034] These settings are generally made on the basis of
temperature measurements taken on the preforms as they leave each
heat treatment oven.
[0035] Thus, the optimization of the heat treatment method in order
to obtain the desired temperature distribution in the second parts
of the preforms in the oven is very particularly dependent on the
setting of these parameters.
[0036] In order to optimize the heat treatment of the preforms,
improvements have been made to the ovens but these improvements
essentially concentrate on the heating means arranged along at
least part of the heating path in order to form a heating
tunnel.
[0037] In terms of the cooling system by contrast, the improvements
made relate mainly to the quality of the air used in the oven for
cooling purposes, its cleanliness (dust, bacteria, etc.), its
temperature or its level of humidity.
[0038] In terms of the cooling system, the setpoint for the
ventilation means of the cooling system is therefore set in order
to obtain a cooling air flow rate capable of avoiding any
crystallization and also of safeguarding the mechanical components
of the oven.
[0039] Thus, and because of its dual function, the ventilation is
not a parameter that a person skilled in the art considers when
determining the settings for the preform heat treatment oven.
[0040] This is because the power of the ventilation means of the
cooling system is set initially to deliver a given flow rate of
cooling air capable of avoiding crystallization of the preform and
of safeguarding the mechanical components of the oven.
[0041] As a result, the cooling air flow rate is always constant
along the entire heating path followed by the preforms.
[0042] The cooling air is therefore delivered to the second parts
of the preforms always at the same flow rate, irrespective of the
position of the preform on the entirety of the heating path, where
it enters to where it exits the oven, the preforms receiving the
same amount of cooling air throughout the heating path.
[0043] It is an object of the present invention notably to improve
the method for heat treating preforms in an oven by optimizing the
cooling so as to improve the quality of manufacture of the
containers.
[0044] To this end, the invention proposes an oven for the heat
treatment of preforms, of the type described hereinabove,
characterized in that the cooling system comprises at least one
cooling device capable of air-cooling at least the second part of
the preforms, the said cooling device comprising at least
ventilation means capable of delivering a given flow rate of
cooling air and means for selectively varying, along the heating
path of the preforms, at least the cooling air flow rate delivered
by the said ventilation means for cooling the said second parts of
the preforms.
[0045] The invention therefore proposes that the cooling air flow
rate be varied along the heating path, preferably only the cooling
air for the second parts of the preforms, the air flow rate being
determined as a function of the position occupied by the preform
along the said path.
[0046] Advantageously, the cooling air is delivered to the second
part of a preform travelling along a given portion of the heating
path at a given air flow rate that is at least different from the
flow rate at which the cooling air is delivered to the said second
part of this same preform travelling along another portion of the
said path.
[0047] The principle underlying the invention, which involves
varying at least the cooling air flow rate delivered to the second
parts of the preforms that are to be heat treated, is counter to
the preconceptions of a person skilled in the art.
[0048] First of all, because the air ventilation cooling system
also has the function of safeguarding the mechanical components
rather than only having the function of preventing
crystallization.
[0049] Specifically, in the heat treatment ovens of the prior art,
the cooling system performs the dual function of cooling, on the
one hand, the body (and bottom) and, on the other hand, the neck
and the mechanical components such as the gripper means.
[0050] Thus, hitherto, the whole of the ventilation means of the
cooling system was initially set at a determined power setpoint so
as to deliver a preform cooling air flow rate that was constant
over the entirety of the heating path.
[0051] In the prior art, the ventilation means deliver a cooling
air flow rate to the preforms which is the same at every point on
the heating path so that each second part of a preform receives
cooling air perfectly uniformly along the entire heating path.
[0052] According to the invention, the cooling air flow rate
delivered to the second parts of the preforms advantageously varies
along the heating path in order to optimize the heat treatment and,
more particularly, in order to obtain a gradient in the wall which
gradient is such that the internal temperature is higher than the
external temperature, within the shortest possible heat treatment
time.
[0053] By virtue of the invention, the efficiency of the heat
treatment oven is improved, for example because the preforms, which
generally enter the oven cold, are no longer cooled or are cooled
with a low cooling air flow rate over the first portion of the
heating path that immediately succeeds the entry to the oven.
[0054] This is possible because the risk of crystallization of the
preform is then practically zero which means that the cooling air
hitherto delivered over such a first portion contributes only to
reducing the efficiency of the heating means and subsequently
increasing the total time needed for the preform to achieve the
desired heat treatment.
[0055] The invention therefore makes it possible, aside from
increasing the efficiency of the ovens, also to reduce the energy
consumption of the ovens, especially the consumption of electricity
used by the heating means.
[0056] This is because setting a low or zero cooling air flow rate
over the first portion of the path will incidentally make it
possible to reduce the power setting of the heating means so that
the electricity consumption will thereby be reduced, without the
start of the heating of the preforms thereby being affected.
[0057] Advantageously, the energy consumption of the ventilation
means is also reduced once the air flow rate has been optimized for
each portion of the heating path, whether or not the heating means
therein are active, as in the stabilization portions for
example.
[0058] Advantageously, the cooling system comprises at least a
first cooling device intended to cool the first part of the
preforms that are at their definitive shape and a second cooling
device, independent of the first cooling device, and intended to
air-cool the second part of the preforms.
[0059] Thanks to such a cooling system, the cooling functions can
be completely separated as compared with the solutions known from
the prior art, by cooling the second parts of the preforms
independently of the first parts of the preforms and of the gripper
means associated with the transport device.
[0060] Advantageously, the cooling air flow rate needed to
establish the desired gradient can be constantly optimized
throughout the heating path, while at the same time avoiding the
risks of crystallization of the second parts of the preforms.
[0061] According to other features of the invention: [0062] the
said means for selectively varying the cooling air flow rate on at
least the second part of the preforms along the heating path
consist of at least one speed variator associated with at least one
of the ventilation means of the said at least one cooling device so
that the variation in cooling air flow rate along the path is
obtained by selectively operating the said speed variator
associated with the said ventilation means independently of the
other ventilation means of the cooling device; [0063] the speed
variator is operated via at least one operating unit to act on a
drive motor that drives the said associated ventilation means so as
selectively, along the heating path, to vary the air flow rate
delivered for cooling at least the second parts of the preforms;
[0064] the means for selectively varying the cooling air flow rate
on at least the second part of the preforms along the heating path
at least consist of shut-off means so that the variation in cooling
air flow rate along the path is obtained by selectively operating
each of the shut-off means independently of the other shut-off
means of the cooling device; [0065] the shut-off means can be
operated selectively in terms of their position so as selectively,
along the heating path, to vary the air flow rate delivered for
cooling at least the second parts of the preforms; [0066] the
shut-off means, such as least one pivoting flap, are arranged in at
least one duct of the cooling device which duct is intended to
carry the cooling air to the second parts of the preforms; [0067]
the shut-off means, such as a sliding flap, are arranged upstream
of the reflectors facing the heating means and are mounted such
that they can move in terms of position in order selectively to
open or close all or some of the cooling air passage openings
formed in the region of the reflectors in order to deliver the
cooling air to the second parts of the preforms; [0068] the oven
comprises temperature measurement means capable of measuring the
internal temperature and/or the external temperature of the wall of
the second part of the preforms at least at a determined position
along the heating path and of supplying at least one signal
representative of one of the said measured temperatures or of the
gradient corresponding to the difference between the said internal
and external temperatures of the wall; [0069] the cooling system
comprises at least one operating unit for operating the said at
least one cooling device which is capable of controlling the said
means intended selectively along the heating path to vary the air
flow rate for cooling at least the second parts of the preforms so
as to set the heat treatment of the preforms along the heating path
through real-time control of the said means of the cooling device;
[0070] the said operating unit controls the said means as a
function of at least one data item such as the said at least one
signal representative of the internal and/or external wall
temperature or of the gradient corresponding to the difference
between the said internal and external temperatures; [0071] the
oven is of modular design comprising at least a number [n] of
modules in which the said heating means are mounted arranged along
all or part of the heating path, and the means for selectively
varying the air flow rate for cooling at least the second parts of
the preforms are common to at least two modules designed to form a
series and/or parallel unit;
[0072] The invention also proposes a method for operating a cooling
device which, being fitted to a heat treatment oven, is intended to
air-cool at least the second parts of the preforms travelling
through the oven along a heating path, characterized in that the
operating method comprises at least one step consisting in
operating the means in order selectively to vary the cooling air
flow rate delivered at least to the said second parts of the
preforms along the heating path.
[0073] Advantageously, the method comprises a step consisting in
measuring the internal temperature and/or the external temperature
of the wall of the second part of the preform so as to produce at
least one signal representative of the internal and/or external
temperature of the wall or of the gradient corresponding to the
difference between the said internal and external temperatures.
[0074] Advantageously, the method comprises at least one setting
step consisting in controlling the said means in real time in
order, as a function of at least one data item such as at least one
signal representative of temperature, to set the air flow rate for
cooling at least the second parts of the preforms which flow rate
is delivered variably along the heating path.
[0075] By virtue of the method for operating the air-cooling device
according to the invention, the heat treatment of the preforms in
the oven is optimized.
[0076] Other features and advantages of the invention will become
apparent from reading the detailed description which follows, for
an understanding of which reference will be made to the attached
drawings in which:
[0077] FIG. 1 is a plan view schematically depicting one embodiment
of an oven for the heat treatment of preforms;
[0078] FIG. 2 is a cross section schematically depicting a module
of the oven according to FIG. 1 and illustrating a first embodiment
of means capable selectively along part of the heating path of
varying the flow rate of the cooling air which is at least
delivered to the said second parts of the preforms;
[0079] FIG. 3 is a cross section, similar to FIG. 2, schematically
depicting a module of the oven according to FIG. 1 and illustrating
a second embodiment of the means capable selectively along part of
the heating path of varying the flow rate of the cooling air which
is at least delivered to the said second parts of the preforms.
[0080] In the description and the claims use will be made,
non-limitingly, of the "longitudinal", "vertical" and "transverse"
orientations to denote respectively elements according to the
definitions given in the description and with respect to the (L, V,
T) trihedral frame of reference depicted in the figures.
[0081] By convention, the terms "upper" and "lower" will be used to
qualify the elements in relation to the vertical orientation of the
(L, V, T) trihedral frame of reference, this being with no
reference to the Earth's gravitational field.
[0082] Likewise, the terms "upstream" and "downstream" will be used
with reference to the direction in which the preforms circulate
along the heating path or, alternatively, with reference to the
direction in which the cooling air circulates through the oven.
[0083] The elements of the invention that are identical, similar or
analogous will be denoted by the same reference numerals.
[0084] FIG. 1 depicts one embodiment of an oven 10 for the heat
treatment of thermoplastic preforms 12.
[0085] Non-limitingly, the oven 10 is an oven of linear type having
a preform 12 heating path that describes the shape of a "U" from an
entry E of the oven to an exit S thereof.
[0086] As an alternative, the oven 10 is a circular oven, that is
to say an oven that has a heating path in the shape of a roughly
circular "C".
[0087] Advantageously, the oven 10 is an oven of modular design.
What is meant by a modular oven 10 is an oven that comprises at
least a determined number [n] of modules, one module for example
being defined with respect to the heating means, which heating
means are generally in the form of a subassembly or unit comprising
for example infrared radiation lamps which are superposed radially
one above the other.
[0088] In a known way, an oven 10 comprises more or fewer heating
modules according to the heating time needed for the application,
and this is what determines the length of the oven 10 or, more
generally, its size.
[0089] Specifically, the heat treatment time can vary from one
preform 12 to another, notably according to its wall thickness, its
material, etc.
[0090] The thermoplastic preforms 12, for example preforms made of
polyethylene terephthalate (PET), are intended to be converted into
containers after they have been heat treated in the oven 10.
[0091] In the remainder of the present description, the term
"preform" non-limitingly denotes either a parison or an
intermediate container, and likewise the term "blow-moulding" also,
for the purposes of simplification, covers a stretch-blow-moulding
operation.
[0092] One example of a preform 12 of vertical axis .largecircle.
and which here is in the overall shape of a test tube has been
depicted in detail in FIG. 1 using an enlargement.
[0093] For the purposes of heat treatment, an especial distinction
is made between two parts of the preform 12, namely, respectively,
a first part that is in its definitive shape, and that consists of
a neck 14 and a flange 16, and a second part which consists of a
body 18 and a bottom 20.
[0094] Specifically, the first part 14, 16 in its definitive shape
does not need to be heated, only the second part 18, 20 being
intended to be heat treated in the oven 10.
[0095] As illustrated by FIG. 1, the tubular body 18 of the preform
12 is closed at an upper end by the hemispherical bottom 20 and at
its lower end comprises a neck 14 which is already in the
definitive shape of the neck of the container, the annular flange
16 which extends radially outwards roughly delineating the said
first and second parts.
[0096] As explained in the preamble, the heat treatment performed
in the oven 10 is intended at preparing the preform 12 for
conversion, by blow-moulding and/or by filling with a fluid, so as
to shape each preform 12 into a container.
[0097] In the oven 10, each preform 12 is transported by a
transport device 22 along a heating path in the direction of the
arrows depicted in FIG. 1, i.e. from upstream to downstream from
the entry E to the oven where the preform generally enters "cold"
(at ambient temperature) to the exit S of the oven where each
preform 12, the second part of which has been heated, is then ready
to be converted into a container.
[0098] In a heat treatment oven 10 like the one depicted in FIG. 1,
the heating path comprises in succession, a first heating zone,
known as the entry zone, formed by the straight outbound portion of
the path starting at the entry E, a zone known as the first
stabilization zone, formed by the curved portion, a second heating
zone, known as the distribution zone, formed by the straight return
portion of the path ending at the exit S, and a second
stabilization zone consisting of the path followed by the preforms
between the exit S and the conversion unit such as a blowing
machine.
[0099] The first, entry, heating zone is intended to preheat the
second part 18, 20 of the preform 12, for example up to a
temperature of the order of 50.degree. C. to 80.degree. C., and the
second, distribution, heating zone is intended to effect the final
heating, for example to a temperature of the order of 90.degree. C.
to 110.degree. C.
[0100] The temperatures are given by way of non-limiting indication
and are notably dependent on the material of which the preform 12
is made, which in this instance is PET.
[0101] The first stabilization zone interposed between the first
and second heating zones is intended, by means of the resulting
time delay, to allow the heat to become evenly distributed
throughout the second part 18, 20 of the preform 12.
[0102] As may be seen in FIG. 2, the transport device 22 comprises
gripper means 24 capable individually of collaborating with the
neck 14 of each preform 12 in order to hold the preform 12 in a
determined position, in this instance vertically neck down (or, as
an alternative, neck up).
[0103] The gripper means 24 of the chuck type are connected in
terms of movement to the transport device 22 and are advantageously
able to rotate the preforms 12 on themselves about their main axis
.largecircle..
[0104] The transport device 22 for example consists of a link chain
or a belt which is driven in a closed loop between two wheels 26,
at least one of which is turned by motorized means (not
depicted).
[0105] The drive by the transport device 22 thus determines the
speed V of travel through the oven of the preforms 12 supported by
the gripper means 24, and also, incidentally, determines the total
duration of the heat treatment or, more particularly, the duration
of the time delay corresponding to the length of time taken by a
preform 12 to pass through the first stabilization zone.
[0106] In order to avoid any deformation of the first part 14, 16
of the preform 12 during the heating in the oven, the neck 14 and
the flange 16 of each preform 12 are protected by protection means
28 (FIGS. 2 and 3), such as manifolds, which extend longitudinally
over at least part of the heating path, particularly over the first
and second heating zones.
[0107] The oven 10 comprises heating means 30 which are preferably
associated with reflectors 32.
[0108] The first and second heating zones respectively form a
heating tunnel which is formed longitudinally on one side by a
heating wall comprising the heating means 30 and on the other side
by a reflective wall formed of the reflectors 32 which are arranged
transversely facing the said heating means 30.
[0109] As can be seen in FIG. 1, the heating means 30 and the
reflectors 32 are arranged along at least part of a heating path,
here, along the first and second heating zones, the first
stabilization zone having no heating means 30.
[0110] The heating means 30 are formed for example of diodes or
infrared radiation lamps referenced IR1, IR2, IR3, . . . IRn in
FIGS. 2 and 3, which are usually used in this field of application
for heating the preforms 12.
[0111] For preference, the reflectors 32 are perforated with
openings 34 to allow the passage of the cooling air that cools the
second parts 18, 20 of the preforms 12, which air is delivered by a
cooling system 36.
[0112] According to a first feature of the invention, the cooling
system 36 comprises at least one cooling device capable of
air-cooling at least the second part 18, 20 of the preforms 12.
[0113] Advantageously, the cooling system 36 is, however, capable
respectively of cooling the first parts and the second parts of the
preforms 12.
[0114] Specifically, the necks 14 of the preforms 12 are outside
the tunnel comprising the heating means 30 and, although they are
protected from radiation and heat by the means 28, the necks 14 do
need to be kept below a certain temperature, by cooling.
[0115] To do this, the cooling of the first part 14, 16 of the
preforms 12 is also performed by the air cooling system 36 with
which the oven 10 is equipped, alone or in combination with
additional cooling means.
[0116] Advantageously, the cooling system 36 comprises cooling
means 38, for example the circulation of a heat transfer fluid
(water) through pipes incorporated into the protective manifolds
that make up the means 28.
[0117] The first parts 14, 16 of the preforms 12 are preferably
cooled by at least one cooling device of the cooling system 36 and
by such heat transfer fluid cooling means 38.
[0118] Advantageously, the cooling system 36 comprises at least a
first cooling device 40 intended to cool the first part 14, 16 of
the preforms 12 which are in their definitive shape, and a second
cooling device 42 intended to air-cool the second part 18, 20 of
the preforms 12.
[0119] As may be seen from FIG. 2, the second cooling device 42 of
the cooling system 36 is advantageously independent of the first
cooling device 40 so that the cooling of each of the first and
second parts of the preforms 12 can be disconnected.
[0120] As an alternative, the cooling system 36 comprises a single
air-cooling device intended to cool the first and second parts of
the preforms 12 respectively.
[0121] For preference, the cooling system 36 comprises, for cooling
the first parts 14, 16 of the preforms 12, a first cooling device
40 (independent of a second device 42) and cooling means 38.
[0122] The first air-cooling device 40 comprises ventilation means
44 which are arranged in a duct 46, known as the first duct, and
which are rotationally driven by a motor 48.
[0123] For preference, the ventilation means 44 are arranged at the
entrance to the first duct 46 and are able to draw in a stream A of
ambient air through filtration means 50.
[0124] The first duct 46 carries the cooling air stream A as far as
the first parts 14, 16 of the preforms 12 circulating through the
oven 10 and the gripper means 24.
[0125] The second cooling device 42, which is independent of the
first cooling device 40, comprises ventilation means 52 which are
arranged in a second duct 54 and rotationally driven by a motor
56.
[0126] For preference, the second ventilation means 52 are arranged
at the entrance to the second duct 54 and are able to draw in an
ambient air stream B through filtration means 50.
[0127] The second duct 54 carries the cooling air stream B as far
as the second parts 18, 20 of the preforms 12 circulating through
the oven 10, in order to cool them.
[0128] The ventilation means 44, 52 here are arranged upstream of
the preforms 12 so that the cooling air is respectively blown onto
the first and second parts of the preforms 12.
[0129] As an alternative, the ventilation means 44 and/or 52 are
arranged downstream of the preforms 12 so as to cause cooling air
to circulate through the tunnel by depression.
[0130] According to the invention, the cooling system 36 comprises
at least one cooling device 42 capable of air-cooling at least the
second part 18, 20 of the preforms 12, the said cooling device 42
comprising at least ventilation means 52 capable of delivering a
given cooling air flow rate and means 58, 64 for selectively, along
the heating path of the preforms 12, varying at least the cooling
air flow rate delivered by the said ventilation means 52 for
cooling the said second parts 18, 20 of the preforms 12.
[0131] Advantageously, the flow rate at which the cooling air is
delivered to the second part 18, 20 of a preform 12 travelling
along a given portion of the heating path is at least different
from the flow rate with which the cooling air is delivered to the
second part 18, 20 of this preform 12 travelling along another
portion of the said path.
[0132] As a result and according to the invention, the flow rate of
cooling air delivered to the second parts 18, 20 of the preforms 12
via the second cooling device 42 of the system 36 is not constant
along the entire length of the heating path followed through the
oven 10 from the entry E to the exit S.
[0133] Advantageously, the second cooling device 42 comprises
ventilation means 52 which are distributed along the entire length
of the heating path and which are capable of being operated
individually so as selectively to vary the cooling air flow rate as
a function of the position occupied by the preform along the
heating path.
[0134] For preference, the oven 10 is of modular design and
comprises at least a number [n] of modules M comprising at least
the said heating means 30 arranged along all or part of the heating
path, and the associated reflectors 32.
[0135] As illustrated in FIG. 1, the oven 10 thus comprises modules
M1, M2, M3 . . . Mi to form the first and second heating zones in
the heating path.
[0136] By convention, a unit of a first type (in series) is defined
as comprising at least two modules M arranged in series one after
the other in the direction of the heating path followed by the
preforms 12 through the oven 10 so that the second parts 18, 20 of
the preforms 12 are heated consecutively by the heating means 30 of
each module M of the unit of the first, "series", type.
[0137] Advantageously, the means for selectively varying the
cooling air flow rate over the second parts 18, 20 of the preforms
12 are common to at least two heating modules M forming a unit of
the first type (a series unit).
[0138] Thus, the flow rate of cooling air delivered to the preforms
12 passing through the two modules M that make up the unit of the
first type is therefore the same.
[0139] By convention also, a unit of a second type (a parallel
unit) comprising at least two modules M arranged in parallel and
through which the preforms 12 pass in opposite directions is
defined for the modular oven 10.
[0140] Typically, that will be the case of two modules M which are
transversely aligned and respectively belong to the first, entry,
heating zone in the case of one of them, and to the second heating
zone in the case of the other.
[0141] A first embodiment of the means for selectively varying the
cooling air flow rate on at least the second part of the preforms
along the heating path will now be described with reference to FIG.
2.
[0142] Advantageously, the means for selectively varying the
cooling air flow rate consist of at least one speed variator 58
which is associated with at least one of the ventilation means 52
of the second cooling device 42.
[0143] In this first embodiment, the variation in cooling air flow
rate along the heating path is obtained by selectively operating
the said speed variator 58 associated with the said ventilation
means 52, independently of the other ventilation means 52.
[0144] For preference, each of the ventilation means 52 is
associated with a variator 58 so that it can be operated
independently of the other ventilation means 52 for ventilating the
heating path.
[0145] As may be seen from FIG. 1, a ventilation means 52/variator
58 assembly is advantageously fitted to each of the modules M of
the oven 10.
[0146] The speed variator 58 acts on the drive motor 56 that drives
the ventilation means 52 with which it is associated so that the
said ventilation means 52 delivers cooling air at a flow rate which
differs from the air flow rate delivered by the other ventilation
means 52.
[0147] Because the maximum cooling air flow rate which corresponds
to 100% is determined by the maximum power of the drive motor 56
driving the ventilation means 52, it is possible, by using the
speed variator 58, selectively to operate the ventilation means 52
associated with it in order to achieve delivery of a cooling air
flow rate ranging between 0 and 100%, for example an air flow rate
equal to 30%, 50% or 80%, over a given portion of the heating
path.
[0148] Through independent operation of each of the oven 10
ventilation means 52 that deliver the cooling air, it is possible
selectively and precisely to vary the cooling air flow rate
delivered by the ventilation means 52 to the second parts 18, 20
along the heating path.
[0149] By way of non-limiting example, the heating path through the
oven 10 has been broken down into a succession of portions in order
to illustrate the implementation of the invention according to the
first embodiment.
[0150] As may be seen from FIG. 1, the heating path for example
comprises a first portion T1 comprising the modules M1 and M2, then
a second portion T2 comprising the modules M3 to M6.
[0151] The first and second portions T1 and T2 correspond to the
said first, entry, heating zone in which the second parts 18, 20 of
the preforms 12 are heated.
[0152] The heating path then continues in the form of a third
portion T3 which here corresponds to the first stabilization zone
and has no heating means 30.
[0153] Depending on the application, cooling air may or may not be
applied to the second parts 18, 20 of the preforms 12 in this first
stabilization zone.
[0154] For preference, the oven 10 here has no such ventilation
means 52 in the first stabilization zone.
[0155] After the third portion T3, the heating path in this example
comprises another, fourth, portion T4 and a fifth portion T5 which
together correspond to the second, distribution, heating zone.
[0156] The fourth portion T4 contains the modules M7 to M10 while
the fifth portion T5 comprises the last modules M11 and M12 before
the exit S from the oven 10.
[0157] For preference, each module M of the oven 10 is individually
equipped, in addition to the heating means 30, with ventilation
means 52 driven by a motor 56 capable of being operated by a speed
variator 58 in order, via a duct 54, to deliver cooling air to a
portion of the heating path.
[0158] By way of non-limiting example of the variation in cooling
air flow rate along the length of the heating path, the variator 58
associated with the motor 56 of the ventilation means 52 of the
first module M1 is set to a setpoint corresponding to a power of
between 0 and 30% of the maximum power, for example 10%, so that
the associated duct 54 delivers a near-zero or low cooling air flow
rate.
[0159] Advantageously, the same setpoint between 0 and 30% is
applied for setting the variator 58 associated with the motor 56 of
the ventilation means 52 of the second module M2.
[0160] In this case, the cooling air flow rate is then identical
over the first portion T1 comprising the said modules M1 and
M2.
[0161] The variator 58 associated with the motor 56 of the
ventilation means of each of the modules M3 to M6 that the second
portion T2 comprises is set to a different setpoint, for example a
higher one, corresponding to a power of between 30 and 60% of
maximum power, such as 40% of maximum power.
[0162] Likewise, the variator 58 associated with the motor 56 of
each of the ventilation means 52 of the next modules M7 to M10 that
the fourth portion T4 comprises is also set to a setpoint different
from those of the first, entry, heating zone (T1+T2), for example a
setpoint corresponding to a power of between 50% and 80% of maximum
power, such as 70%.
[0163] Finally, the variator 58 associated with the motor 56 of
each of the ventilation means 52 of the modules M11 and M12 that
the fifth portion T5 comprises is set with a setpoint corresponding
to a power of 80% or 100% of maximum power.
[0164] To sum up, for the above example, the cooling air flow rate
will, by comparison with the maximum flow rate that determines the
100% reference obtained with maximum power of the motor 56 that
drives each of the ventilation means 52, vary successively along
the length of the heating path such that it is equal to: [0165] 10%
in the first portion T1 (modules M1 and M2) [0166] 40% in the
second portion T2 (modules M3 to M6) [0167] 0% in the third portion
T3 which is the stabilizing portion [0168] 70% in the fourth
portion T4 (modules M7 to M10) [0169] 90% in the fifth portion T5
(modules M11 and M12).
[0170] Advantageously, the cooling air flow rate delivered in the
first modules, here M1 and M2 in the abovementioned example, is
near-zero or low once the preforms 12 have entered the entry E of
the oven 10 "cold", generally at an ambient temperature of the
order of 20.degree. C.
[0171] The risks of crystallization of the second parts 18, 20 of
the preforms 12 are therefore considered to be equal to zero when
the heating of the heat treatment begins.
[0172] Be that as it may, in ovens 10 according to the prior art,
cooling air was blown by the cooling system 36 with a flow rate
that is constant from the entry to the exit.
[0173] As a result, because of the absence of flow rate or low flow
rate of cooling air on this first portion T1, referring to the
aforementioned example, the heating power of the heating means 30
is advantageously reduced without the heat treatment being
ultimately affected.
[0174] Advantageously, the electrical energy consumption in these
modules such as M1 and M2 is thus reduced, and in so doing, the
efficiency of the oven 10 is improved.
[0175] Advantageously, the set of means such as the ventilation
means 52, the motors 56 and the variators 58 can therefore be
omitted from the first modules such as M1 and M2 in the heating
path, to the notable benefit of a reduction in cost, particularly
of hardware and upkeep thereof.
[0176] When the ventilation for the air cooling of the second parts
18, 20 of the preforms 12 is omitted, for example but
non-limitingly on the first modules M or a determined first portion
T1, the reflectors 32 are then advantageously replaced.
[0177] This is because there is then no need--in the absence of
ventilation for air cooling--to have a "blowing" reflector 32, that
is generally one which is perforated with numerous openings 34 to
allow the passage of the cooling air.
[0178] Advantageously, use is made of reflectors which notably have
a solid surface which are able to increase the reflection of
radiation and, through their greater effectiveness, increase the
overall efficiency of the oven 10.
[0179] Advantageously, the materials used for such reflectors are
determined in order to optimize the reflection, notably of the
infrared radiation, of the heating means 30, and to do so while
also setting aside any compromise in also performing the
ventilation function.
[0180] For preference these reflectors are made of materials such
as fibrosil or alternatively of ceramic, rather than of aluminium
which is the material used for the conventional reflectors 32 of
the "blowing" type.
[0181] In addition, it will be noted that in the absence of
cooling, reflectors 32 made for example of aluminium, are likely
not to be able thermally to withstand the high temperatures
encountered in such an oven 10.
[0182] Advantageously, reflectors made of the abovementioned
materials (fibrosil, ceramic, etc.) have excellent thermal
withstand, even with little or no cooling.
[0183] Of course, the use of such reflectors is not in any way
restricted to cases in which the cooling ventilation is omitted,
and such reflectors can even be used with any cooling system
36.
[0184] By comparison, although because of their solid surfaces they
are less ventilating than the "blowing" reflectors 32 that have
openings 34 in them, such reflectors can be arranged leaving
passages for the cooling air between two consecutive
reflectors.
[0185] For preference, special means are then implemented to
improve the diffusion of cooling air from such a passage opening
between two reflectors.
[0186] As an alternative, it is also possible to reduce costs--not
by omitting means such as a ventilation means 52, a motor 56 and a
variator 58--but by making such means common to at least two
consecutive modules forming a series unit, such as the modules M1
and M2, or alternatively a parallel unit such as the modules M5 and
M8.
[0187] As an alternative, the means 52, 56, 58 are shared between a
series unit and a parallel unit, i.e. between a group of at least
four modules M which are adjacent to one another in pairs.
[0188] Thus, the means 52, 56, 58 of the second cooling device 42
are advantageously common to or shared by two or more modules in
the following portions T2 to T5.
[0189] The resulting cost reduction achieved by such commonality of
means will be more particularly sought after when the oven 10 is
fitted with a first air-cooling device 40 independent of the second
device 42 for cooling the first parts 14, 16 of the preforms
12.
[0190] However, when the first cooling device 40 consists of at
least one air-cooling device, the means 44, 48 are advantageously
common to series and/or parallel units once the cooling air flow
rate delivered for cooling the first parts 14, 16 of the preforms
12 is constant along the entire length of the heating path.
[0191] As an alternative, the cooling air flow rate delivered by
the first cooling device 40 for cooling the first parts 14, 16 of
the preforms 12 also varies along the heating path, notably but not
exclusively if the oven 10 cooling system 36 comprises just one
single device for air-cooling the entire preform 12, the said first
device 40 then consisting of the second device 42 and vice
versa.
[0192] However, it will be understood that the options of
selectively varying the cooling air flow rate for the second parts
18, 20 of the preforms 12 along the heating path will be all the
greater than will be the means 52, 56, 58 of the second cooling
device 42 with which the oven 10 is fitted.
[0193] Thus, by comparison with the abovementioned example, the
number of portions T1 to T5 can vary for each application, just as
it will be recalled that the number of modules M in an oven 10 can
also vary according to the application.
[0194] In the example given previously, the cooling air flow rates
vary increasingly as the preforms 12 progress along the heating
path, although it is recalled that that is merely one non-limiting
example given for explanatory purposes.
[0195] In addition, the fact that in at least one given module M or
that in one determined portion of the heating path air-cooling of
at least the said second parts of the preforms 12 is performed does
not necessarily lead to a consequence that the heating means 30 are
active therein given that the stabilization portions can
advantageously be arranged all along the heating path, to alternate
with the heating portions, and therefore not only in the third
portion T3 corresponding to the bend in the oven 10 depicted in
FIG. 1.
[0196] Advantageously, each speed variator 58 is operated via at
least one operating unit 60 to act on a drive motor 56 that drives
the said associated ventilation means 52 so as to obtain the
selective variation in air flow rate for cooling the second parts
of the preforms 12 along the heating path.
[0197] According to the method for operating the second cooling
device, the various setpoint values corresponding to the desired
cooling air flow rates along the heating path are input into the
operating unit 60.
[0198] For preference, the operating unit 60 is also capable of
operating the ventilation means 44 of the first cooling device 40,
which means are driven by the motor 48.
[0199] Advantageously, the first cooling device 40 comprises a
variator (not depicted) which is associated with the drive motor 48
that drives the ventilation means 44, the said variator therefore
being operated by the operating unit 60 or, as an alternative, by a
separate operating unit.
[0200] Indeed according to the invention, the method for operating
the cooling device 42 with which the heat treatment oven 10 is
fitted, is intended to allow the second parts 18, 20 of the
preforms 12 circulating through the oven 10 along the heating path
to be air-cooled selectively.
[0201] Advantageously, the operating method comprises at least one
step consisting in selectively operating the means 58 associated
with the ventilation means 52 of the said device in order to vary
the cooling air flow rate delivered to the said second parts of the
preforms 12 along at least part of the heating path.
[0202] Advantageously, the method for operating the cooling device
is further improved and is not restricted to operating the cooling
device 42 as a function only of the setpoints initially entered
into the operating unit 60 for varying the flow rate along the
heating path.
[0203] Advantageously, the oven 10 comprises temperature
measurement means 62 capable of measuring the internal temperature
and/or the external temperature of the wall of the second part 18,
20 of the preforms 12 at least at a determined position along the
heating path and of supplying at least one signal representative of
one of the said measured temperatures or of the gradient
corresponding to the difference between the said internal and
external wall temperatures.
[0204] The operating method is therefore capable of closed-loop
feedback control over the cooling air flow rate, using notably the
internal and/or external temperature of the wall of the second part
of the preforms 12.
[0205] For preference, the signals corresponding to the internal
and external temperatures are transmitted to the said at least one
operating unit 60 which then determines the gradient (or delta)
corresponding to the difference between the said internal and/or
external temperatures of the wall.
[0206] The temperature measurement means 62 consist for example of
at least one pyrometer, or as an alternative, a thermal camera,
which are used in particular for measuring the external temperature
of the wall.
[0207] Advantageously, the temperature measurement means 62 used
further comprise, especially for measuring the internal
temperature, means of the type of those (probes) described in
document WO-A1-2010/031923 to which reference can be made for
fuller details.
[0208] Advantageously, the operating unit 60 is capable of
controlling the said means consisting of the speed variators 58 in
order selectively to vary the cooling air flow rate delivered to
the second parts of the preforms along the heating path and do so
as a function at least of the said signal representative of the
internal and/or external temperature, so as to set the heat
treatment of the preforms 12 along the heating path through
real-time control over the said means and subsequently the
ventilation means 52.
[0209] A second embodiment of the means for selectively varying the
cooling air flow rate over at least the second part of the preforms
12 along the heating path will now be described with reference to
FIG. 3.
[0210] The description of the second embodiment will advantageously
be given by comparison with the first embodiment.
[0211] Advantageously, the means according to the invention for
varying the cooling air flow rate consist at least of the shut-off
means 64 which can be operated in terms of their position in order
selectively, as a function of the portion of the heating path, to
vary the cooling air flow rate delivered to the second parts 18, 20
of the preforms 12.
[0212] In the first embodiment, the variation in cooling air flow
rate is obtained by acting, via the variator 58 coupled to the
motor 56, directly on the ventilation means 52 which first create
the cooling air stream.
[0213] In this second embodiment, each ventilation means 52 causes
a given cooling air flow rate to circulate along the associated
duct 54 of the second cooling device 42, which flow rate the said
shut-off means 64 can selectively vary.
[0214] Thus, the shut-off means 64 are selectively operated in
terms of their position in order to control the cooling air flow
rate intended to be delivered to the second parts 18, 20 of the
preforms 12.
[0215] Advantageously, the shut-off means 64 are arranged at least
in the duct 54 of the second cooling device 42 intended to carry
the cooling air as far as the second parts 18, 20 of the preforms
12.
[0216] For preference and as illustrated in FIG. 3, the shut-off
means 64 are produced in the form of at least one flap.
[0217] Advantageously, the shut-off means 64 are arranged upstream
of the reflectors 32 facing the heating means 30 and are mounted
such that they can move in terms of position in order selectively
to open or close all or some of the cooling air passage openings 34
through which the cooling air is delivered to the second parts of
the preforms 12.
[0218] As illustrated in FIG. 3, the shut-off means 64 for example
consist of at least one flap arranged in the duct 54 associated
with at least one module M of the oven 10, preferably as close as
possible to the reflectors 32.
[0219] The flap 64 is mounted such that it can rotate between at
least two extreme positions, a first position P1 in which the flap
does not shut off the cross section of the duct 54 and a second
position P2 in which the flap completely shuts off the duct 54, the
said positions P1 and P2 being represented in dotted line in FIG.
3.
[0220] The first position P1 corresponds to the position in which
all, that is to say 100%, of the cooling air flow rate generated by
the ventilation means 52 is delivered, whereas the second position
P2 corresponds to the position of the flap 64 that prevents any air
from circulating along the duct 54 downstream of the flap 64 so
that the cooling air flow rate delivered at least to the second
parts 18, 20 of the preforms 12 is equal to zero, namely 0%.
[0221] Advantageously, the flap 64 is made to rotate between its
positions P1 and P2 by an actuator 66 in order to position the flap
64 in a determined intermediate position somewhere between the said
positions P1 and P2 and corresponding to the desired cooling air
flow rate of between 100% and 0%.
[0222] For preference, the flap 64 is mounted so that it can pivot
about hinge means 68.
[0223] Thus, by setting the position of each flap 64 for example
associated with one of the modules M, the variation of cooling air
flow rate along the associated portion of the heating path can be
determined.
[0224] According to an alternative form that has not been depicted,
the flap 64 is slideably mounted so that it slides between at least
extreme positions P1 and P2 respectively corresponding to a cooling
air flow rate of 100% and of 0%, and for preference the flap 64 is
mounted with the ability to affect a translational movement in a
longitudinal direction parallel to the heating zones of the heating
path.
[0225] The sliding flap 64 is, for example, positioned transversely
to the rear of the reflector 32 and is shaped to shut off one or
more openings 34 formed in the said reflector 32 so as to allow the
cooling air that is to be delivered to the second parts 18, 20 of
the preforms 12 to pass at a determined flow rate dependent on the
relative position of the flap 64.
[0226] For preference, each module M of the oven 10 comprises at
least one duct 54 for delivering cooling air and the said at least
one duct 54 (or as alternative, the reflector 32) comprises a
shut-off means 64 capable of varying the air flow rate according to
its position.
[0227] By comparison with the first embodiment, the shut-off means
64, such as a flap, are independent of the ventilation means 52
that create the cooling air flow rate, which means that the
ventilation means 52 and/or the motors 56 can be shared, in series
and/or in parallel, between at least two modules M, and so that
this can be done while at the same time retaining the option of
individually setting the flow rate for each of the modules M using
just the one flap 64.
[0228] Specifically, assuming that the power setpoint for the motor
56 that drives the ventilation means 52 is equal to the maximum,
namely to an air flow rate of 100%, the cooling air flow rate
ultimately delivered to the second parts 18, 20 of the preforms 12
is then determined merely by the position of the shut-off means
64.
[0229] The variation in cooling air flow rate along the heating
path is thus obtained by selectively setting the various positions
of the shut-off means 64 as a whole, each advantageously being
associated with one module M of the oven 10.
[0230] Of course, the flap is just one non-limiting example of the
type of shut-off means 64 that can be employed for varying the flow
rate along the heating path and as an alternative use could even be
made of a valve gate or some other similar means.
[0231] The shut-off means 64 of the second cooling device 42 are
thus capable of being set initially each to a determined position
by virtue of the actuator 66 so as thereafter in operation to
achieve the desired variation in air flow rate along the heating
path.
[0232] Advantageously, an operating unit 70 of the second device 42
is capable of controlling the said means 64 in order selectively to
vary the cooling air flow rate on the second parts 18, 20 of the
preforms 12 according at least to a signal representative of the
temperature, so as to set the heat treatment of the preforms 12
along the heating path through real-time control of the position of
the said means 64.
[0233] For preference, the said at least one signal is
representative of the internal and/or external wall temperature,
advantageously of the temperature gradient between the external and
internal surfaces of the wall of the body 18 and of the bottom 20
that form the second part.
[0234] Of course, the first and second embodiments just described
are merely non-limiting examples of how the teachings of the
invention can be implemented.
[0235] The invention further relates to a method for operating a
cooling device 42 which, being fitted to a heat treatment oven 10,
is intended to air-cool at least the second parts 18, 20 of the
preforms 12 travelling through the oven 10 along a heating
path.
[0236] The operating method comprises at least one step that
involves operating means 58, 64 in order selectively to vary the
cooling air flow rate delivered at least to the said second parts
18, 20 of the preforms 12 along the heating path.
[0237] In the first embodiment, the operating step therefore
consists in individually setting each variator 58 in order to
determine the cooling air flow rate that will be produced by the
associated ventilation means 52, driven by a motor 56, so as
advantageously to vary the said air flow rate along the heating
path in a sequence determined by the setting of each variator
58.
[0238] Specifically, by selectively setting the setpoint for each
variator 58, the cooling air flow rate that will be delivered to
the second parts 18, 20 of the preforms when the said preforms 12
are travelling along the corresponding portion of the heating path
is determined.
[0239] Likewise in the second embodiment, the operating step
consists in individually operating each shut-off means 64, such as
a flap or a valve gate, to set the cooling air flow rate desired
for the corresponding portion of the heating path and thus, by
selectively setting each means 64, varying the said cooling air
flow rate along the heating path in a sequence determined by the
setting of each actuator 66 of the shut-off means 64.
[0240] Advantageously, the operating method comprises at least one
setting step consisting in real-time control of the said means 58,
60, 66, 70 in order, as a function of at least one data item, to
set the air flow rate for cooling at least the second parts 18, 20
of the preforms 12, which varies along the heating path.
[0241] For preference, the said at least one data item used for
operation consists of at least one signal representative of the
internal and/or external temperature of the wall or of the gradient
corresponding to the difference between the said internal and
external temperatures.
[0242] Advantageously, the method comprises a measurement step
consisting in measuring the internal and/or external temperature of
the wall of each preform 12. For preference, a measurement is taken
at multiple points, notably in the vertical direction along the
height of the body 18 as far as the bottom 20 of the preform 12,
and this is done using temperature measurement means of the type
described hereinabove, such as a pyrometer, a thermal camera or
probes.
[0243] Advantageously, the steps in the operating method are
integrated into the more general method for heat treating the
preforms 12 in such an oven 10. Advantageously, a step of setting
the heating means 30 in order selectively to vary the heating power
over at least part of the heating path is also implemented.
[0244] The step of setting the heating means 30 consists in
determining the heating power delivered to the second parts 18, 20
of the preforms 12 over a given portion of the heating path through
the oven 10, particularly the variation in power is obtained by
selectively setting the strength of the current passing through
each heating means 30 and preferably for each module M.
[0245] Thus, the heating power can vary in the direction of the
axis .largecircle. of the preform 12, in this instance vertically,
in order to establish a determined heating profile, and the heating
power also varies along the heating path, notably between the first
and second heating zones.
[0246] However, the heating power delivered may further vary from
one module M to another along the heating path, namely in the
longitudinal direction, particularly in order to establish a
stabilization zone or stabilization zones in which the heating
means 30 are not active.
[0247] Advantageously, the ventilation means 52 are able
selectively to deliver a determined cooling air flow rate in such a
stabilization zone which forms one of the portions of the heating
path.
[0248] As an alternative, the ventilation means 52 are inactive in
such a stabilization zone in which the air then circulates only
naturally by convection.
[0249] For preference, the setting of the heating power is
determined in combination with the variations in cooling air flow
rate along the path according to the invention in order to optimize
the heat treatment method.
[0250] Advantageously, an exposure time for exposure to the
radiation of the heating means 30 is determined by setting the
power and the speeds of travel of the preforms 12 along the heating
path and in rotation on themselves.
[0251] The method for the heat treatment of preforms 12 in the oven
10 comprises at least one step of operating the air-cooling device
of the system according to the invention so as to vary the cooling
air flow rate delivered along the heating path, which operating
step is advantageously performed in combination with at least one
of the following setting steps which consist in: [0252] setting the
power of the heating means 30 so as to vary, along the heating
path, the heating power delivered to the second parts 18, 20 of the
preforms 12, particularly so as to establish stabilization
zones.
[0253] Advantageously, real-time setting, as a function of at least
one signal representative of the temperature, of the setting of the
parameters concerned with the power delivered by the heating means
30 is also carried out.
* * * * *