Preform heat treatment unit comprising an element for blocking radiation towards the neck of the preforms

Abstract

Preform heat treatment unit comprising an element for blocking radiation towards the neck of the preforms The heat treatment unit comprises: - a first wall (26), comprising a first heating element (28), and a second wall (30), comprising a second heating element (32), - a first system for gripping and moving (34) a first plurality of preforms (1) on a first row (R1), - a second system for gripping and moving (36) a second plurality of preforms (1) on a second row (R2). The heat treatment unit comprises a blocking element (37) extending between the first and second rows (R1, R2) in order to block radiation emitted by the first heating element (28), respectively the second heating element (32), towards the second gripping and moving system (36), respectively towards the first gripping and moving system (34).Figure for abstract: Figure 3.

Description

Title of the invention: Preform heat treatment unit comprising an element for blocking radiation towards the neck of the preforms

[0001] The present invention relates to a heat treatment unit for preforms of a container manufacturing installation of the type comprising: an enclosure delimited by a first wall and a second wall extending on either side of the enclosure in a transverse direction, the first wall comprising at least a first heating element and the second wall comprising at least a second heating element, a first system for gripping and moving a first plurality of preforms on a first row adjacent to the first wall, said first gripping and moving system being arranged to cooperate with a neck of each preform of the first plurality of preforms to move said preforms along a predefined circulation path extending in a longitudinal direction, substantially perpendicular to the transverse direction, a second system for gripping and moving a second plurality of preforms on a second row adjacent to the second wall, said second gripping and moving system being arranged to cooperate with a neck of each preform of the second plurality of preforms to move said preforms along the circulation path.

[0002] Such a heat treatment unit, or oven, is generally equipped with a plurality of heating elements arranged to emit heat towards preforms made of synthetic material passing through the heat treatment unit while rotating on themselves in order to apply a heating profile to these preforms and allow their subsequent deformation, for example by stretch blow molding, so as to produce containers from the preforms.

[0003] For example, it has been proposed to provide that the enclosure of the heat treatment unit is delimited by two walls extending along the path of the preforms and each comprising heating elements emitting heat into the enclosure. Such an arrangement makes it possible to improve the energy distribution in the enclosure and to improve the efficiency of a heat treatment unit. Document EP 2 782 741 describes, for example, such a heat treatment unit.

[0004] According to one embodiment, this document proposes moving the preforms in two rows between the walls of the enclosure, which makes it possible to improve the efficiency of the heat treatment unit and the application of heat to the preforms while limiting the size of the heating unit.

[0005] When heating a preform, however, it is advisable to avoid heating the neck of the preform, since the neck already has its final shape, i.e. the shape it has in the finished container. It is therefore advisable not to make the neck malleable by heating it with the body of the preform, which will be deformed later during a blowing operation.

[0006] However, when the preforms circulate in two rows in the enclosure, the dispersion of the radiation emitted by the heating elements means that part of the radiation emitted by the heating elements of a wall is applied to the necks of the preforms of the row furthest from this wall and therefore causes heating of these necks.

[0007] To limit this unwanted heating, it may be provided to ventilate the neck of the preforms moving through the enclosure in order to cool it. However, such ventilation does not allow sufficiently targeted cooling of the neck of the preforms and the part of the body extending immediately under the neck also risks being cooled even though this is precisely a critical area undergoing significant deformation during the blowing of the containers and therefore requiring special heating.

[0008] One of the aims of the invention is to overcome these drawbacks by proposing a heat treatment unit which makes it possible to effectively avoid unwanted heating of the necks of the preforms circulating in the enclosure of the heat treatment unit.

[0009] For this purpose, the invention relates to a heat treatment unit of the aforementioned type, comprising at least one blocking element extending between the first row and the second row so as to block radiation emitted by the first heating element towards the second gripping and moving system and to block radiation emitted by the second heating element towards the first gripping and moving system so that the necks of the preforms of the first row and the second row are not heated by the first and second heating elements.

[0010] By interposing a blocking element between a heating element of a wall and the system for gripping and moving the preforms of the row spaced from this wall, the neck of the preforms of this row is not heated due to the dispersion of the radiation from the heating element because the system for gripping and moving the preforms cooperates with this neck to transport the preforms into the enclosure. Thus, heating the neck of the preforms is effectively avoided without having to limit the heating of the part of the body of the preforms extending immediately under the neck.

[0011] The heat treatment unit according to the invention may further comprise one or more of the following characteristics, considered alone or in any combination: technically feasible: - the blocking element comprises a first face extending opposite and parallel to the first wall of the enclosure and a second face extending opposite and parallel to the second wall of the enclosure, said first and second faces being made or being coated with a material absorbing the radiation emitted by the first and second heating elements incident on said first and second faces; - the blocking element further comprises a reflective face extending between the first face and the second face substantially perpendicular thereto, said reflective face being arranged to reflect the radiation emitted by the first and second heating elements incident on said reflective face towards a body of the preforms of the first row and of the second row; - the blocking element comprises a body provided with a cooling channel extending in the longitudinal direction, said cooling channel being in fluid communication with a source of a cooling fluid, said cooling fluid circulating in said cooling channel; - the heat treatment unit comprises a plurality of first heating elements distributed at least in the longitudinal direction on the first wall and a plurality of second heating elements distributed at least in the longitudinal direction on the second wall, the blocking element extending in the longitudinal direction between all of the plurality of first heating elements and second heating elements; - the heat treatment unit comprises a plurality of first heating elements distributed at least in an elevation direction perpendicular to the longitudinal direction and to the transverse direction on the first wall and a plurality of second heating elements distributed at least in the elevation direction on the second wall, the blocking element extending in the elevation direction above or below the plurality of first heating elements and second heating elements; - the first and second heating elements each comprise a plurality of sources of monochromatic or pseudomonochromatic electromagnetic radiation; - the first and second heating elements emit radiation in the transverse direction with a divergence angle less than or equal to 15° around the transverse direction; - the first and second gripping and moving systems are arranged so that the preforms of the first row and the second row are offset in a staggered manner in the longitudinal direction relative to each other; and - the first and second walls of the enclosure and the blocking element are movable in an elevation direction, perpendicular to the longitudinal and transverse directions, relative to the first and second systems for gripping and moving the preforms.

[0012] Other aspects and advantages of the invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0013] [Fig-1] is a schematic representation from above of a part of a container production installation comprising a heat treatment unit according to the invention,

[0014] [Fig.2] is a schematic representation from above of a part of a heating section of the heat treatment unit of [Fig.l], in which the preforms circulate in two rows, and

[0015] [Fig.3] is a schematic sectional representation of the heat treatment unit of [Fig.2].

[0016] With reference to [Fig.l], an installation for producing containers from a succession of preforms 1 is described.

[0017] Such an installation generally comprises at least one heat treatment unit 2 arranged to heat the preforms 1 and a forming station 4 in which the heated preforms 1 are formed into containers, for example by stretch blow molding. As shown in [Fig.l], a transfer wheel 6 is for example provided between the heat treatment unit 2 and the forming station 4 to transfer the heated preforms 1 at the outlet of the heat treatment unit 2 to an inlet of the forming station 4, which is for example formed by a carousel carrying several forming units, each arranged to form a container from a preform 1 heated during the rotation of the carousel. Apart from the heat treatment unit 2 which will now be described in more detail, such a container production installation is known per se and will not be described in more detail here.

[0018] The heat treatment unit 2, or oven, is arranged to heat a succession of preforms 1 circulating in the heat treatment unit in order to apply a thermal profile to each preform 1 to make it malleable with a view to its subsequent deformation in the forming station 4.

[0019] More particularly, as shown in [Fig. 3], each preform 1 comprises a body 8 and a neck 10 and the heat treatment unit 2 is arranged to heat the body 8 without heating the neck 10 of each preform 1, as will be described in more detail later. The body 8 extends along an axis A and has, for example, the shape of a test tube extending between a bottom 12 and the neck 10, which forms an open end of the test tube. The neck 10 comprises, for example, a collar 14 extending from a radial plane substantially perpendicular to the axis A projecting towards the outside of the body 8. Such a collar 14 forms for example a gripping surface for the preform 1 and the container made from the preform 1. The part of the preform 1 extending from the collar 14 to the open end comprises for example a thread making it possible to fix a cap on the container made from the preform 1. Thus, the neck 10 of the preform 1 has the same shape as the neck of the container made from this preform 1. This is why it is advisable not to heat the neck 10 of the preform 1 in the heat treatment unit 2 in order to avoid any deformation of the neck 10.Furthermore, keeping the neck 10 cold and rigid makes it possible to provide a non-deformable gripping zone for the preform 1 for moving it in the container production facility, in particular in the heat treatment unit 2 as will now be described.

[0020] The heat treatment unit 2 comprises a system for gripping and moving a succession of preforms 1 making it possible to grip the preforms 1 by the neck 10 and to move them in the heat treatment unit along a predefined circulation path T extending in a longitudinal direction. The movement gripping system comprises a plurality of gripping elements 15 arranged one after the other along the circulation path T, each gripping element 15 being arranged to cooperate with the neck 10 of a preform 1. According to one embodiment, the gripping elements 15 are further arranged to rotate the preforms 1 around their axis A when they are transported in the heat treatment unit 2.According to one embodiment, each gripping element 15 comprises a pin on which the neck 10 of a preform 1 is fitted by its open end, the pin being movable in rotation to rotate the preform around its axis A. Such a gripping element 15 is known as a “spinner”.

[0021] When the preforms 1 are in the heat treatment unit 2, their axis A extends in an elevation direction Z of the heat treatment unit 2, as shown in [Fig. 3], the elevation direction Z being substantially perpendicular to the longitudinal direction.

[0022] According to the embodiment shown in [Fig.l], the heat treatment unit 2 comprises a transport section 16, in which the preforms 1 are moved one after the other in a single row in the longitudinal direction, and a heating section 18, in which the preforms 1 are moved in two parallel rows RI, R2 extending in the longitudinal direction, as will be described in more detail later. The preforms 1 circulate in the heat treatment unit 2 from an entry point 20, to which they are brought for example by a transport wheel 22, in the transport section 16 then in the heating section 18 to an exit point 24, where the heated preforms 1 are recovered by the transfer wheel 6 to be brought to the forming station 4. According to the embodiment shown in [Fig.l], the gripping and moving system forms a loop between the transport section 16 and the heating section 18, that is to say that the gripping elements 15 released from the preforms which they were transporting to the exit point 24 return to the entry point 20 to recover new preforms to be heated.

[0023] In the remainder of the description, only the heating section 18 will be described in more detail with reference to Figures 2 and 3, the rest of the heat treatment unit 2 being known.

[0024] At least in the heating section 18, the heat treatment unit 2 comprises a first wall 26, comprising at least one first heating element 28, and a second wall 30, comprising at least one second heating element 32. The first and second walls 26, 30 are opposite each other on either side of the heat treatment unit 2 and define between them an enclosure within which the preforms 1 circulate along the circulation path T predefined on two rows RI and R2. The first and second walls 26, 30 are spaced from each other in a transverse direction substantially perpendicular to the longitudinal direction and to the elevation direction Z so as to extend on either side of the circulation path T. The height of the first and second walls 26, 30 is defined along the elevation direction Z.

[0025] In order to move the preforms 1 on two rows RI and R2 spaced from each other in the transverse direction, the gripping and moving system separates in the heating section 18 into a first gripping and moving system 34 moving a first plurality of preforms 1 on the first row RI in the longitudinal direction and into a second gripping and moving system 36 moving a second plurality of preforms on the second row R2 in the longitudinal direction. At the inlet of the heating section 18, the gripping and moving system is for example arranged so that every other preform passes over the first row RI, the other preforms passing over the second row R2. At the outlet of the heating section 18, the preforms 1 are for example grouped in a single row up to the outlet point 24 of the heat treatment unit 2, as shown in [Fig.l].

[0026] The first row RI is adjacent to the first wall 26 and the second row R2 is adjacent to the second wall 30. In other words, the preforms 1 moved on the first row RI are closer, in the transverse direction, to the first wall 26 than to the second wall 30 and the preforms moved on the second row R2 are closer, in the transverse direction, to the second wall 30 than the first wall 26. According to one embodiment, the first and second gripping and moving systems 34, 36 are advantageously arranged so that the preforms 1 are arranged in a staggered pattern in the enclosure. By staggered pattern, it is meant that the preforms 1 of one row RI are offset in the longitudinal direction relative to the preforms 1 of the other row R2. Such a staggered arrangement ensures that the preforms 1 of the first row RI are also exposed to the radiation emitted by the second heating element 32 between two preforms 1 of the second row R2 and that the preforms 1 of the second row R2 are also exposed to the radiation emitted by the first heating element 28 between two preforms 1 of the first row RI. Thus, the heating of the preforms 1 of the two rows RI, R2 is uniform.The spacing in the transverse direction between the rows RI, R2, and the spacing in the longitudinal direction between the preforms 1 can be adjusted in particular as a function of the diameter of the preforms 1.

[0027] The first heating element 28 and the second heating element 32 are for example associated with each other to form a pair of heating elements. As described in more detail later, the heat treatment unit 2 comprises for example several pairs of heating elements, each formed of a first heating element 28 extending on the first wall 26 and a second heating element 32 extending on the second wall 30. The first and second heating elements 28, 32 extend at least partly opposite each other on either side of the enclosure. By "extend at least partly opposite each other on either side of the enclosure", it is meant that the first and second heating elements 28, 32 extend substantially at the same height in the elevation direction Z and at least partly opposite each other in the transverse direction. According to an embodiment shown in [Fig.2], the first and second heating elements 28, 32 of a pair of heating elements are however offset relative to each other in the longitudinal direction so that the second heating element 32 extends only partly opposite the first heating element 28. Such an embodiment is for example described in document EP 2 782 741 and those skilled in the art may refer to this document to obtain more details on such an embodiment, in particular in terms of dimensioning and positioning of the heating elements relative to each other.

[0028] The first heating element 28 and the second heating element 32 of a pair of heating elements are identical. Thus, only the first heating element 28 will now be described in more detail.

[0029] The first heating element 28 comprises for example a plurality of sources of monochromatic or pseudo-monochromatic electromagnetic radiation. More particularly, the first heating element 28 is for example a laser emitter and the radiation sources are laser chips arranged to emit laser radiation in the infrared range in an emission direction E substantially parallel to the transverse direction. The radiation sources are for example arranged next to each other on a support so as to form at least one row of radiation sources extending in the longitudinal direction. According to one embodiment, the radiation sources form at least one upper row and at least one lower row arranged one above the other in the elevation direction. The radiation sources are electrically connected in series with each other between a positive connection terminal and a negative connection terminal.

[0030] Such heating elements are for example described in document FR 3 124 030 and those skilled in the art may refer to this document to obtain more details, in particular with regard to the structure of each radiation source, the arrangement of the radiation sources on a support, the connection of the radiation sources to each other and the cooling of the heating elements. It is understood that the invention is not limited to heating elements formed by laser emitters and also applies to other types of heating element, such as halogen-type incandescent tubular lamps.

[0031] It should be noted that the radiation emitted by such a heating element is not strictly rectilinear and exhibits a certain divergence. More particularly, the radiation emitted by each radiation source rather has the shape of a cone whose angle α at the apex is for example less than or equal to 15°. Such divergent radiation emitted by several radiation sources is represented in [Fig. 3] by the different oblique lines going from one wall to the other of the enclosure. Thus, the radiation emitted by the heating elements arranged opposite the upper parts of the bodies 8 of the preforms 1, adjacent to the necks 10 of the preforms 1, is likely to strike the necks 10 of the preforms 1 located in the row furthest from these heating elements due to the divergence of the heating elements.Thus, for example, the radiation emitted by a first heating element 28, located opposite the upper part of the body 8 of the preforms 1 located on the first row RI, is likely to strike the neck 10 of the preforms 1 located on the second row R2, as can be seen in [Fig. 3]. Similarly, the radiation emitted by a second heating element 32, located opposite the upper part of the body 8 of the preforms 1 located on the second row R2, is likely to strike the neck 10 of the preforms 1 located on the first row RL. Thus, the neck 10 of the preforms 1 is likely to be heated. in the heating section 18 when this is not desirable.

[0032] In order to avoid this unwanted heating, the heat treatment unit 2 according to the invention comprises at least one element 37 for blocking the radiation emitted by the first and second heating elements 28, 32 towards the necks 10 of the preforms 1 located in the enclosure. More particularly, the blocking element 37 is arranged between the two rows RI, R2 in the transverse direction opposite the first and second gripping and movement systems 34, 36 of the preforms 1, more particularly opposite the pins of the gripping elements 15, that is to say opposite the necks 10 fitted onto these pins when preforms 1 circulate in the heating section 18 so as to protect these necks 10 from the radiation emitted by the first and second heating elements 28, 32.

[0033] Thus, according to one aspect, the invention also relates to a blocking element 37 for radiation emitted by a heating element comprising a body 39 comprising a first face 38 and a second face 40 made of or coated with a material absorbing the radiation emitted by the heating element. The first face 38 extends opposite the first wall 26 substantially parallel to the latter and the second face 40 extends opposite the second wall 30 substantially parallel to the latter, at a lower or upper end of these first and second walls 26, 30 in the elevation direction Z. Indeed, when the preforms 1 circulate in the enclosure, their neck 10 extends opposite one of the ends of the first and second walls 26, 30 in the elevation direction Z. The end opposite which the necks 10 extend depends on the way in which the preforms 1 are transported.If they are transported “head up” as shown in [Fig. 3], the neck 10 of the preforms and the body 39 of the blocking element 37 extend opposite the upper end of the first and second walls 26, 30 in the elevation direction Z. If the preforms 1 are transported “head down”, the neck 10 of the preforms and the body 39 of the blocking element 37 extend opposite the lower end of the first and second walls 26, 30 in the elevation direction Z. Thus, the first face 38 extends in the path of the radiation emitted by a first heating element 28 arranged opposite the upper part of the body 8 of the preforms 1, as can be seen by the radiation interrupted by the first face 38 in [Fig. 3], and the second face 40 extends in the path of the radiation emitted by a second heating element 32 arranged opposite the upper part of the body 8 of the preforms 1.According to one embodiment, the first and second faces 38, 40 are painted black to absorb the radiation emitted by the first and second heating elements 28, 32.

[0034] According to one embodiment, the body 39 further comprises a reflective face 42 extending between the first face 38 and the second face 40, substantially perpendicular cularly to these at one end of the body 39 in the elevation direction Z. As shown in [Fig.3], the reflecting face 42 is oriented towards the bottom 12 of the preforms 1 circulating in the enclosure so as to reflect the radiation emitted by the first and second heating elements 28, 32 and incident on the reflecting face 42 towards the body 8 of the preforms 1 of the first row RI and the second row R2. Thus, part of the radiation emitted by the first and second heating elements 28, 32 oriented towards the blocking element 37 due to the divergence of this radiation can be returned towards the body 8 of the preforms 1, which improves the heating power of these heating elements by reducing the radiation loss due to the divergence.Depending on the end of the first and second walls 26, 30 opposite which the blocking element 37 extends, the reflective face 42 forms a lower face (when the blocking element 37 extends opposite the upper end of the walls, as shown in [Fig. 3]) or an upper face (when the blocking element 37 extends opposite the lower end of the walls) of the body 39 of the blocking element 37. The reflective nature of the reflective wall 42 is for example obtained by polishing the lower or upper face of the body 39 of the blocking element 37 until a mirror polish is obtained.

[0035] According to one embodiment, the blocking element 37 further comprises a cooling channel 44 extending in the body 39 and in fluid communication with a source of a cooling fluid (not shown). The cooling fluid circulates in the cooling channel 44 so as to dissipate the heat absorbed by the first and second faces 38, 40 of the body 39 of the blocking element 37 under the effect of the divergent radiation of the first and second heating elements 28, 32. According to variants, the cooling fluid is the same or is different from the cooling fluid used to cool, in a known manner, the first and second heating elements 28, 32. According to one embodiment, the cooling fluid circulating in the cooling channel 44 is glycolated water. The cooling channel 44 extends over the entire length of the body 39 in the longitudinal direction.

[0036] As described above, the enclosure comprises a plurality of first and second heating elements 28, 32 distributed in the enclosure to expose the entire heating section 18, outside the zone in which the necks 10 of the preforms 1 extend, to the heat emitted by the heating elements. Thus, the first heating elements 28 are for example distributed at least in the longitudinal direction on the first wall 26 and the second heating elements 32 are for example distributed at least in the longitudinal direction on the second wall 30, the first and second heating elements 28, 32 of a pair of heating elements extending at least partly opposite one another in the longitudinal direction transverse. Alternatively or additionally, the first heating elements 28 are for example distributed at least along the elevation direction Z on the first wall 26 and the second heating elements 32 are for example distributed along the elevation direction Z on the second wall 30, the first and second heating elements 28, 32 of a pair of heating elements extending at least partly opposite each other along the transverse direction.

[0037] When the first and second heating elements 28, 32 of a pair of heating elements are offset relative to each other in the longitudinal direction, the first heating element 28 extends at least partly opposite a reflective section 46 of the second wall 30 and the second heating element 32 extends opposite a reflective section 46 of the first wall 26, as shown in [Fig. 2]. The reflective sections 46 extend for example between adjacent heating element columns so that the first and second walls 26, 30 are both heat-emitting and heat-reflecting. As previously indicated, such an arrangement of a heat treatment unit 2 is already known per se and will not be described in further detail here. Those skilled in the art may refer to document EP 2 782 741.

[0038] In this case, the blocking element 37 advantageously extends in the longitudinal direction between all the pairs of first and second heating elements 28, 32 distributed in the longitudinal direction, that is to say in the entire heating section 18 in the longitudinal direction. Alternatively or additionally, the blocking element 37 extends opposite a part of the upper or lower pair of first and second heating elements 28, 32 or above or below this pair in the elevation direction Z so as to block only the part of the radiation oriented towards the neck 10 of the preforms 1.

[0039] According to one embodiment, the assembly formed by the first and second walls 26, 30 and the blocking element 37 is movable in the elevation direction Z relative to the first and second gripping systems 34, 36 and for moving the preforms in order to adapt the position of this assembly to the different models of preforms 1 likely to circulate in the enclosure, in particular to the different heights of these preforms 1. According to one embodiment, the first and second walls 26, 30 and the blocking element 37 are movable together in the elevation direction Z so that the modification of the position of one of the elements of this assembly causes the modification of the position of the other elements of this assembly. Alternatively, the locking element 37 is movable independently of the first and second walls 26, 30, i.e. the position of the locking element 37 can be adjusted independently of that of the first and second walls 26, 30.

[0040] The blocking element 37 described above makes it possible to effectively prevent the heating of the neck 10 of the preforms 1 in the heating section 18 without requiring specific ventilation for the necks 10 and without having to reduce the heating power supplied to the upper area of ​​the body 8 of the preforms 1 adjacent to the neck 10. This is particularly advantageous because the upper area of ​​the body 8 of a preform 1 is generally an area that must undergo significant deformation during the production of a container. Indeed, this area generally forms a flare or shoulder of the container in which the diameter of the container increases to make a transition between the neck and the rest of the body of the container. Thus, it is essential that this area be efficiently heated in order to control such deformation.

Claims

Claims

1. A preform heat treatment unit (1) of a container manufacturing facility, the heat treatment unit comprising: - an enclosure delimited by a first wall (26) and a second wall (30) extending on either side of the enclosure in a transverse direction, the first wall (26) comprising at least one first heating element (28) and the second wall (30) comprising at least one second heating element (32), - a first system (34) for gripping and moving a first plurality of preforms (1) on a first row (RI) adjacent to the first wall (26), said first system for gripping and moving (34) being arranged to cooperate with a neck (10) of each preform (1) of the first plurality of preforms (1) to move said preforms along a predefined circulation path (T) extending in a longitudinal direction, substantially perpendicular to the transverse direction,- a second gripping and moving system (36) of a second plurality of preforms (1) on a second row (R2) adjacent to the second wall (30), said second gripping and moving system (36) being arranged to cooperate with a neck (10) of each preform (1) of the second plurality of preforms (1) to move said preforms (1) along the circulation path (T),- the heat treatment unit being characterized in that it comprises at least one blocking element (37) extending between the first row (RI) and the second row (R2) so as to block radiation emitted by the first heating element (28) towards the second gripping and moving system (36) and to block radiation emitted by the second heating element (32) towards the first gripping and moving system (34) so ​​that the necks (10) of the preforms (1) of the first row (RI) and of the second row (R2) are not heated by the first and second heating elements (28, 32).,

2. A heat treatment unit according to claim 1, wherein the blocking element (37) comprises a first face (38) extending opposite and parallel to the first wall (26) of the enclosure and a second face (40) extending opposite and parallel to the second wall (30) of the enclosure, said first and second faces (38, 40) being made or being coated with a material absorbing the radiation emitted by the first and second heating elements (28, 32) incident on said first and second faces (38, 40).

3. A heat treatment unit according to claim 2, wherein the blocking element (37) further comprises a reflective face (42) extending between the first face (38) and the second face (40) substantially perpendicular thereto, said reflective face (42) being arranged to reflect the radiation emitted by the first and second heating elements (28, 32) incident on said reflective face (42) towards a body (8) of the preforms (1) of the first row (RI) and of the second row (R2).

4. A heat treatment unit according to any one of claims 1 to 3, wherein the blocking element (37) comprises a body (39) provided with a cooling channel (44) extending in the longitudinal direction, said cooling channel (44) being in fluid communication with a source of a cooling fluid, said cooling fluid circulating in said cooling channel (44).

5. A heat treatment unit according to any one of claims 1 to 4, comprising a plurality of first heating elements (28) distributed at least in the longitudinal direction on the first wall (26) and a plurality of second heating elements (32) distributed at least in the longitudinal direction on the second wall (30), the blocking element (37) extending in the longitudinal direction between all of the plurality of first heating elements (28) and second heating elements (32).

6. A heat treatment unit according to any one of claims 1 to 5, comprising a plurality of first heating elements (28) distributed at least in an elevation direction (Z) perpendicular to the longitudinal direction and to the transverse direction on the first wall (26) and a plurality of second heating elements (32) distributed at least in the elevation direction (Z) on the second wall (30), the blocking element (37) extending in the elevation direction (Z) above or below the plurality of first heating elements (28) and second heating elements (32).

7. A heat treatment unit according to any one of claims 1 to 6, wherein the first and second elements of heating (28, 32) each comprise a plurality of sources of monochromatic or pseudomonochromatic electromagnetic radiation.

8. A heat treatment unit according to any one of claims 1 to 7, wherein the first and second heating elements (28; 32) emit radiation in the transverse direction with a divergence angle (a) less than or equal to 15° around the transverse direction.

9. Heat treatment unit according to any one of claims 1 to 8, in which the first and second gripping and moving systems (34, 36) are arranged so that the preforms (1) of the first row (RI) and of the second row (R2) are offset in a staggered manner in the longitudinal direction relative to each other.

10. Heat treatment unit according to any one of claims 1 to 9, in which the first and second walls (26, 30) of the enclosure and the locking element (37) are movable in an elevation direction (Z), perpendicular to the longitudinal and transverse directions, relative to the first and second systems for gripping and moving the preforms (34, 36).

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