Plastic preform heater with preform neck protection device

Abstract

A heater (1) for plastic preforms (4), the preforms having a body (41) and a neck (42) separated by a hoop (43), the heater (1) comprising: a plurality of supports (6) each carrying a holding member (7) for holding the preform (4), the supports (6) being movable in the heater so as to enable each holding member to move along a preform conveying path; a plurality of covers (8) fixedly connected to the supports (6), each cover (8) being connected to at least one support (6) by an actuating member (9), the actuating member (9) being pivotally mounted on the support (6) about a pivot axis spaced a distance from the preform conveying path, the heater further comprising a pivoting device for the actuating member, the pivoting device tending to drive the cover (8) from an open position to a protective position when the support (6) connected to the cover enters a holding area from an input / release area.

Description

Technical Field

[0001] The field of the invention is that of the design and manufacture of plastic containers.

[0002] More specifically, the present invention relates to a preform neck restraint for a preform heater. Background Art

[0003] Typically, plastic containers are obtained by heating a plastic preform to above the glass transition temperature.

[0004] Preforms typically have:

[0005] - a body having a generally cylindrical shape of revolution about a central axis;

[0006] - a neck extending from the first end of the body in an extension of the body, the neck being separated from the body by a hoop;

[0007] - A bottom portion closing the body at its second end.

[0008] same:

[0009] - the body of the preform becomes the body of the container;

[0010] - The neck of the preform remains unchanged during the container forming process;

[0011] - The bottom of the preform becomes the bottom of the container.

[0012] The heated preform is inserted into a mold having a cavity for the finished or intermediate container to be blown therein by injecting a fluid. More precisely, air is injected into the preform to deform it and stretch the plastic material until it comes into contact with the mold walls.

[0013] To heat the preforms, a heater is used, which is also called an "oven".

[0014] The preforms pass in a row in the heater, they being held by spinners, ie fingers that engage with the neck, more precisely with the inside of the neck.

[0015] These heaters use an array of light sources, typically laser diodes or halogen lamps, which emit radiation intended to heat the plastic material and thereby soften it to facilitate its stretching and deformation in the mold.

[0016] When the preform is heated, the neck of the preform, which generally has the shape of the neck of the finished container, is not heated.

[0017] In fact, heating of the neck leads to a risk of deformation, which could prevent the proper use of the finished container, for example by preventing the placement of a closure to close the container after filling.

[0018] For this reason, when heating the preform, its neck must be protected from the radiation of the light source and the hot air from the light source. In other words, a cavity must be created to confine the light radiation and hot air present in the heater.

[0019] The commonly used technique is to position the preform neck downward so that the preform neck extends outside the heater.

[0020] A reflective screen may be used to reflect the optical radiation towards the interior of the heater, thereby confining the optical radiation within the heater.

[0021] Furthermore, it is ensured that the heat conduction from the bottom to the top of the heated material has no influence on this heating of the preform.

[0022] However, this positioning is not without flaws.

[0023] In practice, for blowing, the preform is introduced into the mold, positioned with the neck on top.

[0024] Therefore, the preform must be turned over between the heater and the mold, since in the heater the preform is positioned with the neck downwards.

[0025] In addition to the time and machinery required to flip the preform, the flipping process may lead to the risk of damaging the preform.

[0026] In fact, high manufacturing schedules require rapid turning of preforms whose plastic material is relatively softened to allow them to deform. Therefore, the centrifugal forces associated with the high speed turning of the preforms produce stresses on the preforms that may cause them to fall off the holding member that carries them.

[0027] Another known technique consists in positioning the preform neck-up in the heater.

[0028] This avoids the need for a preform turning operation and thus the risk of preform damage.

[0029] In order to avoid heating of the preform necks, a reflector, also called a hood, is inserted between the preforms, positioned below the hoop, ie on the side of the preform body.

[0030] However, this reflector requires that the preform be removed according to a translation movement along the axis of rotation of the body.

[0031] Therefore, the preform must be grasped by the preform body, which may cause the body to deform. When the container is formed in the mold, this deformation may then produce the danger of the container being damaged, or in the worst case, make the formed container become impossible.

[0032] Furthermore, gripping the preform by its body may cause local cooling in the plastics material, such cooling being caused, for example, by a thermal gradient between the temperature of the gripping member and the temperature of the preform.

[0033] This local cooling can make blowing the plastic material in the mould difficult and, in the worst case, can result in the production of a container that is unsuitable for placement on the market, in particular if the container is intended for carbonated beverages.

[0034] In fact, the carbonation contained in the beverage causes the interior of the container to be pressurized. The fracture triggering zone, which results in an area of ​​low mechanical strength, can then turn into a crack in the container, causing it to burst.

[0035] In addition, taking out the preform with a single translation requires a large stroke in height, ie along the axis of the preform body. Therefore, the heater must have considerable dimensions to allow this stroke. Summary of the Invention

[0036] The present invention is particularly intended to remedy the deficiencies of the prior art.

[0037] More precisely, the present invention aims to propose a solution allowing to protect the neck of the preform while heating it, and to preserve the integrity of the body when the preform is removed from the heater.

[0038] The present invention also aims to provide such a solution that ensures easy removal of the preforms from the heater.

[0039] The present invention also aims to provide such a solution which maintains the high progress of the prior art while limiting the risk of damage to the preform during removal.

[0040] The present invention also aims to provide a solution which allows reducing the bulk dimensions of the heater relative to heaters according to the prior art.

[0041] These objects, as well as others which will appear hereinafter, are achieved by means of the present invention, which relates to a heater for heating preforms made of plastic, the preforms having a body and a neck separated by a hoop, the heater comprising:

[0042] - a light source for emitting radiation for heating the preform;

[0043] a plurality of supports, each carrying a holding member for holding a preform, the supports being movable in the heater so that each holding member is movable along the preform conveying path,

[0044] The heater has an input / release area in which the supports are separated from each other, and a holding area in which the supports are close to each other, and a light source is arranged near the holding area.

[0045] The heater also has a plurality of covers, which are fixedly connected to the support member and can move between the following positions:

[0046] a protective position in which the shells are butted against each other in order to form together a shroud intended to extend around the body below the collar of the preform in order to form a barrier against light radiation directed in the direction of the neck,

[0047] - an open position, in which the housings are separated from each other,

[0048] In the heater, each cover is connected to at least one support by an actuating member, which is pivotally mounted on the support about a pivot axis spaced a distance from the preform conveying path, and the heater also has a drive device for driving the actuating member to rotate relative to the support so as to drive the cover from the open position to the protective position when the support connected to the cover enters the input / release area as far as the holding area.

[0049] Such a heater allows the neck of the preform to be effectively protected when the body is heated, while facilitating the importation and exportation of the preform into and from the heater.

[0050] In fact, the open position of the housing allows for easy arrangement of transverse preform removal or insertion means for facilitating the removal of preforms from the heater or the insertion of preforms into the heater.

[0051] Furthermore, this makes it possible to reduce the volumetric dimensions of the heater relative to the prior art, since the holding member does not necessarily have to be moved together with the preform in order to reach a lateral removal or insertion device, for example located below or above the support.

[0052] Furthermore, this allows the production schedule to be increased, since the removal of the preforms can take place as the preforms are being fed forward, ie transversely.

[0053] According to a first preferred embodiment,

[0054] The heater comprises a chain with a plurality of links, one of each supporting element being mounted on a link, and a wheel for driving the chain of the supporting elements, said wheel having a main axis, and each housing having an inner edge and an outer edge, said inner edge extending relative to the preform transport path on the side of the main axis of rotation, and an outer edge situated opposite the inner edge. In this first embodiment, for each housing, the pivot axis is located near the inner edge of the housing, and the drive means for driving the actuating element in rotation comprise a direct mechanical connection between the actuating element and a second supporting element adjacent to the first supporting element.

[0055] A direct mechanical connection is a mechanical connection between a portion of the actuating member and a portion of the second support member that does not require the use of one or more mechanical components that move relative to one another. In other words, a direct mechanical connection does not pass through the links of a chain. However, a direct mechanical connection may be made through spacers, bearings, washers, intermediate surface coatings, or equivalent components.

[0056] This allows the housing to be positioned in its open or protective position in a mechanical and automatic manner when the support element is merely moved from the input / release area to the holding area.

[0057] Advantageously, for each housing, the mechanical connection mechanically connecting the actuating member to the second support comprises a sliding pivot connection situated near the outer edge of the housing.

[0058] In particular, the sliding pivot connection consists of a rotational movement and a translational movement of the actuating member relative to the second support about two different movement axes.

[0059] This pivot connection allows the shells to generate a curvilinear translational movement, which facilitates the opening of the shells and, in particular, allows, in the open position of the shells, a greater spacing between the outer edges of two adjacent shells than between the inner edges of two adjacent shells. This thus facilitates the lateral insertion or removal of preforms.

[0060] Advantageously, the sliding pivot connection is realized by an oblong hole made in the actuating member and a cylindrical finger received in the oblong hole and carried by the second support.

[0061] This structure allows to simply and accurately realize the sliding pivot connection.In addition, this purely mechanical connection is convenient to only move the cover shell by means of the support member.

[0062] According to an advantageous second embodiment, the heater has, for each housing, a drive member cooperating with the actuating member in order to move the housing from the protective position to the open position or vice versa.

[0063] In this case, the actuating member is then connected to the support only via its pivot connection, which allows ensuring the movement of the cover from its open position into the protective position or vice versa, independently of the position of the adjacent support.

[0064] In this case, each drive member has a cam track fixed to the base and a roller which moves along the cam track and is connected to the actuating member.

[0065] The cooperation between the cam track and the roller allows to initiate the rotation or implement the movement of the actuating member relative to the support on which it is rotationally mounted in a precise manner, depending on the position of the support on the base.

[0066] Preferably, each roller is rotatably mounted on its cooperating actuating member.

[0067] This pivoting mounting facilitates a curvilinear translational movement of the housings, which facilitates obtaining the open position of the housings relative to one another in a precise manner when required, in order to facilitate the lateral removal or insertion of preforms.

[0068] According to an advantageous aspect, each housing is mounted on an actuating member by removable fixings.

[0069] Thus, if necessary, for example if the preform neck also has to be heated or for example for maintenance of the machine, the housing can be removed from the heater.

[0070] Preferably, the detachable fixing member has:

[0071] - at least one fixing hole formed in the actuating member, and

[0072] - at least one arm fixed to the housing and adapted to be inserted into the fixing hole.

[0073] This structure is conducive to quickly installing the cover onto the heater, especially the actuating member, or quickly removing the cover from the heater, especially the actuating member.

[0074] Additionally, the installation may be provided with a poka-yoke feature to facilitate and ensure correct placement of the housing in the heater.

[0075] Preferably, the actuating member has at least one aperture which is transverse to the fixing hole and connected to the fixing hole, the arm has a groove which is used to be opposite to the aperture when the arm is inserted into the fixing hole, and the detachable fixing piece further has a retaining member which is inserted into the aperture, the retaining member being used to cooperate with the groove of the arm to prevent the arm from falling out of the fixing hole.

[0076] This allows for a quick mounting or dismounting of the cover on or from the actuating member by means of the retaining member and ensures a secure hold of the cover on the actuating member.

[0077] Therefore, in order to install or remove the cover, it is only necessary to retract the holding member to insert the cover arm into the fixing hole or remove it from the fixing hole, and then reposition the holding member. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Other characteristics and advantages of the invention will appear more clearly on reading the accompanying drawings and the following description of a preferred embodiment of the invention given as an illustrative and non-limiting example, in which:

[0079] Figure 1 is a top perspective view of a portion of a plastic preform heater according to the present invention;

[0080] Figure 2 is a top perspective view of a preform for heating by a heater according to the present invention;

[0081] Figure 3 is a bottom view of a portion of a heater according to the present invention, showing the protective cover in a first position, namely an input / release position;

[0082] Figure 4 is a bottom view of a portion of a heater according to the present invention showing the preform protection cover in a second position, i.e., a holding position;

[0083] Figure 5 is a top perspective view of the housing and the actuating member on which the housing is mounted;

[0084] Figure 6 is a bottom view of a portion of a heater according to the present invention showing a different embodiment of the drive actuation member. DETAILED DESCRIPTION

[0085] Figure 1 A heater 1 according to the invention is shown.

[0086] More precisely, this heater 1 has:

[0087] - a feed wheel 3 for feeding preforms 4 into the heater 1;

[0088] - a light source 5 for emitting radiation for heating the preform 4;

[0089] - a chain consisting of links meshing with the teeth of a wheel 2 driving the chain, said wheel 2 being driven in rotation relative to the main axis;

[0090] a plurality of supports 6, each carrying a retaining member 7 for retaining a preform 4, each support 6 being fixed to a link of the chain so as to be substantially parallel to one another when the corresponding link is a straight portion of the chain and to move away from one another when the link rotates about the wheel 2;

[0091] A plurality of housings 8 , which are fixed to the support 6 .

[0092] like Figure 2 As shown, each preform 4 generally has:

[0093] - a body 41 , substantially in the shape of a cylinder of revolution about a central axis X;

[0094] a neck 42 extending from a first end of the body 41 in the extension of the body 41 , the neck 42 being separated from the body by a hoop 43 ;

[0095] - A bottom portion 44 closing the body at its second end.

[0096] same:

[0097] - the body 41 of the preform 4 becomes the body of the container;

[0098] - the neck 42 of the preform 4 remains unchanged during the container forming process;

[0099] The bottom 44 of the preform 4 becomes the bottom of the container.

[0100] The holding member 7 , also known as a tournette, is in the shape of a core rod and is intended to be inserted into the neck 42 of the preform 4 .

[0101] The retaining member 7 is used to engage and hold each preform 4 by being firmly mounted in the neck 42 , so that the preforms are released from the supply wheel 3 and pass in sequence in front of the light source 5 .

[0102] In particular, each rotator is mounted on a support 6 .

[0103] Each support 6 is driven by the links of the chain to which it is fixed, and thus moves from one zone of the heater to another, namely:

[0104] - an input / release region, in which the supports 6 are separated from one another;

[0105] A holding area, in which the supports are brought close to one another.

[0106] In the import / release area, the holding member 7 and the support 6 are located near the supply wheel 3 .

[0107] In contrast, in the holding area, the support 6 is moved away from the supply wheel 3 , in particular so as to present the preforms 4 facing the light source 5 .

[0108] In particular, the support 6 is moved from one position to another in a conventional manner by means of a system of cam rollers and rollers running along the cam rollers.

[0109] Purely mechanically, these supports 6 are therefore advanced in sequence when the heater 1 is operated. The supports pass from the input / release area to the holding area and vice versa via cam rollers and rollers to which each support is attached.

[0110] The holding member 7 can move between a high position and a low position relative to the supporting member 6 .

[0111] In particular, in the high position, the retaining members 7 hold the preforms 4 at a height that is higher than the height at which they are situated when in the supply wheel 3 .

[0112] In the lowered position, the holding member 7 allows loading of the preforms 4 from the supply wheel 3 or releasing the preforms 4 at the outlet of the heater 1 .

[0113] Accordingly, when the support member 6 is in the holding position, the clamping member 7 is in a high position. And when the support member 6 is in the input / release position, the clamping member 7 is in a low position.

[0114] In order to allow the clamping member 7 to be moved from its upper position to its lower position, a mechanical device such as a cam / cam raceway connection can in particular be provided.

[0115] In a variant, a pneumatic actuator, an electric actuator, or an electro-pneumatic actuator may also be provided for allowing the holding member 7 to be movable.

[0116] Now, refer to Figures 3 to 6 The cover 8 and its working conditions are described.

[0117] The cover 8 allows the light radiation emitted by the light source 5 to be reflected in the direction of the body 41 of the preform 4 , in order to protect the neck 42 of the preform 4 .

[0118] To this end, each housing 8 advantageously has a coating reflecting light radiation. In a variant, the constituent material of the housing can have light-reflecting properties.

[0119] like Figure 3 、 4 5 , each housing 8 has an inner edge 81 which, as in the non-limiting embodiment shown, can extend substantially parallel to the preform conveying path. The inner edge 81 is located on the side of the preform conveying path closest to the main axis of rotation of the wheel 2. Each housing 8 also has an outer edge 82 opposite the inner edge 81.

[0120] For connection to the preform 4 , each shell 8 has two mutually opposite circular cutouts 83 , which are located between the inner edge 81 and the outer edge 82 .

[0121] Each housing 8 is mounted on at least one support 6 .

[0122] Advantageously, each housing 8 is movable relative to its support 6 between the following positions:

[0123] a protective position in which the shells are butted against each other in pairs so as to form together a housing intended to extend around the body 41 and under the collar 43 of the preform 4 ;

[0124] an open position in which the housings are separated from one another.

[0125] In the protective position, the housing 8 then forms a barrier against light radiation directed in the direction of the neck 42 .

[0126] To allow this movability, each housing 8 is connected to at least one support 6 by an actuating member 9 .

[0127] The actuating member 9 is pivotably mounted on the support 6 near the inner edge 81 of the housing 8 .

[0128] As will be described later, the actuating member 9 tends to drive the cover 8 from the open position to the protective position, or vice versa, when the support 6 to which it is connected is moved from the input / release position to the retaining position.

[0129] according to Figure 3 、 4 5 , for each housing 8 , the actuating member 9 is pivotably mounted on a first support 6 , connected to a second support 6 adjacent to the first support 6 , near the outer edge 82 of the housing 8 .

[0130] More precisely, the actuating member 9 is connected to the second support 6 by a sliding pivot connection.

[0131] It is to be clarified that, here, a sliding pivot connection is understood to mean a connection which simultaneously allows not only a pivoting but also a translation of the actuating member 9 relative to the second support 6 .

[0132] However, contrary to the mechanical definition of a sliding pivot connection, the translation axis and the rotation axis of the actuating member 9 are in this case different from one another.

[0133] Therefore, although the movement of the actuating member 9 relative to the second support 6 is a curvilinear translation movement mechanically comparable to a planar support connection, in this case the connection between the actuating member 9 and the second support 6 is considered to be a sliding pivot connection.

[0134] like Figure 3 and 4 As shown, the sliding pivot connection is realized by an oblong hole 91 made in the actuating member 9 and a cylindrical finger 92 received in the oblong hole 91 and carried by the second support 6 .

[0135] According to an alternative embodiment not shown in the drawings, the oblong hole 91 could be made in the support 6 , the finger 92 being carried by the actuating member 9 .

[0136] When two adjacent supports 6 pass from the input / release zone into the holding zone or vice versa, the sliding pivot connection and the pivot connection connecting the actuating member 9 to each of the two adjacent supports 6 cause the housing 8 to move in a curvilinear translational movement.

[0137] Reference Figure 3 , the cover 8 is shown in its open position.

[0138] In the open position, the distance between the inner edges 81 of two adjacent shells 8 is smaller than the distance between the outer edges 82 of two identical adjacent shells 8 .

[0139] This makes it possible in particular to facilitate the loading of the holding member 7 with the preforms 4 and in particular to allow the housing 8 to be almost completely blanked out in order to be able to load / unload the preforms 4 in order to allow them to be introduced into the heater 1 or removed therefrom.

[0140] like Figure 4 , two adjacent housings 8 are shown in their protective position.

[0141] In the protection position, the inner edges 81 of two adjacent shells 8 and the outer edges 82 of two adjacent shells 8 are parallel to each other.

[0142] In other words, the distances between the inner edges 81 and the outer edges 82 of two adjacent casings 8 are the same.

[0143] This makes it possible for the housings 8 to surround the preforms 4 two by two, thus forming a barrier that shields the light radiation emitted by the light source 5 in the direction of the neck 42 .

[0144] The light radiation is then reflected on the cover 8 and redirected towards the body 41 of the preform 4 to avoid also heating the preform neck 42. In fact, this increases the efficiency of heating the body 41.

[0145] like Figure 5 As shown, each housing 8 is mounted on an actuating member 9 by a detachable fixing member.

[0146] To this end, the removable fixing has:

[0147] - at least one fixing hole 10 made in the actuating member 9, and

[0148] At least one arm 11 , fixed to the housing 8 , intended to be inserted into the fixing hole 10 .

[0149] More precisely, if Figure 5 As shown, the detachable fixing element has two fixing holes 10 opened in the actuating member 9 and two arms 11 fixed to the cover 8, each of which is used to be inserted into one of the fixing holes 10.

[0150] In order to avoid any accidental release of the housing, the actuating member 9 has at least one orifice 12 which is transverse to the fixing hole 10 and communicates with the fixing hole.

[0151] In particular, the removable fixing and actuating member 9 has one transverse orifice 12 opening into only one of the fixing holes 10 .

[0152] Advantageously, each arm 11 has a groove 111 intended to be opposite the orifice 12 when the arm 11 is inserted in the fixing hole 10 .

[0153] The removable fixing also has a retaining member 13 for insertion into the transverse opening 12 .

[0154] The retaining member 13 is used to cooperate with the groove 111 of the arm 11 to prevent the arm 11 from falling out of the fixing hole 10 .

[0155] Such a removable fixing allows in particular an easy and rapid replacement of the cover 8 when it is intended to be replaced, or allows a temporary removal of the cover to gain easy access to the support or retaining member 7 during maintenance operations or operations to change the preform format.

[0156] Preferably, if Figure 5 As shown, each housing 8 has a housing barrel 14 carrying the arms 11. The reflective part of the housing 8 is advantageously fixed to the housing barrel 14 using rivets 15.

[0157] according to Figure 6 In the second embodiment shown in FIG, the heater 1 has a drive member 93 which is fixed to the base and is adapted to cooperate with the actuating member.

[0158] More precisely, the driving member 93 comprises a cam track 931 fixed to the base and a roller 932 connected to the actuating member 9 for moving along the cam track 931. More precisely, each roller 932 is rotatably mounted on the actuating member 9 with which it cooperates.

[0159] Thus, when the support 6 moves from its input / release position to its retaining position, the roller 932 causes the cover 8 to rotate about the pivot connection by moving along the cam track 931 to allow passage from the open position to the protective position, or vice versa.

[0160] The heater 1 just described allows ensuring the protection of the neck 42 when heating the body 41 of the preform 4 , while ensuring easy loading and unloading of the preform 4 before and after heating it.

[0161] More precisely, in the open position, the spacing of the outer edges 82 of the cover 8 facilitates the output of the preforms 4 from the heater 1 or the input thereof, in particular allowing the preforms to enter or leave in a transverse manner, i.e. perpendicularly or almost perpendicularly to the axis of rotation of the rotor.

[0162] This then avoids any risk of damaging the preform 4 which is at its glass transition temperature, ie softened and susceptible to deformation, for example in the event of a crash.

[0163] At this time, a collision or a slight deformation may cause the risk of defects in the finished container after molding, or even make it impossible to mold a container from the deformed preform 4.

Claims

1. A heater (1) for heating a preform (4) made of plastic, the preform having a body (41) and a neck (42) separated by a hoop (43), the heater (1) comprising: - a light source (5) for emitting radiation for heating the preform (4); a plurality of supports (6), each carrying a holding member (7) for holding a preform (4), the supports (6) being movable in the heater so that each holding member is movable along the preform conveying path, The heater has: an input / release region in which the supports are separated from one another; a holding area in which the supports are close to one another and in which the light source is arranged near the holding area, The heater (1) further comprises a plurality of covers (8), the covers being fixedly connected to the support member (6), and the covers (8) being movable between the following positions: a protective position in which the shells are butted against each other in order to form together a housing which is intended to extend around the body (41) below the collar (43) of the preform (4) in order to form a barrier against light radiation directed in the direction of the neck (42), - an open position, in which the housings are separated from one another, It is characterized by: Each cover (8) is connected to at least one support (6) by an actuating member (9), the actuating member (9) being pivotally mounted on the support (6) about a pivot axis spaced a distance from the preform conveying path, the heater also comprising a drive device for driving the actuating member to rotate relative to the support so as to drive the cover (8) from the open position to the protective position when the support (6) connected to the cover enters from the input / release area to the holding area; The heater has a chain with a plurality of links, each support being mounted on a link, and a wheel for driving the chain of the supports, the wheel having a main axis of rotation, each housing (8) having an inner edge (81) and an outer edge (82), the inner edge extending on the side of the main axis of rotation relative to the preform conveying path, the outer edge being opposite the inner edge (81); For each housing (8), the pivot axis is located near an inner edge (81) of the housing (8), and the drive means for driving the actuating member in rotation have a direct mechanical connection between the actuating member and a second support (6) adjacent to the first support (6); Furthermore, for each housing (8), the direct mechanical connection of the actuating member (9) to the second support (6) comprises a sliding pivot connection located near the outer edge (82) of the housing (8).

2. The heater (1) according to claim 1, characterized in that The sliding pivot connection is realized by an oblong hole (91) made in the actuating member (9) and a cylindrical finger (92) received in the oblong hole (91) and carried by the second support (6).

3. The heater (1) according to claim 1, characterized in that For each cover (8), the heater (1) has a drive member (93) cooperating with the actuating member (9) to move the cover (8) from the protective position to the open position or vice versa.

4. The heater (1) according to claim 3, characterized in that Each driving member (93) has a cam roller (931) and a roller (932), wherein the cam roller is fixed to the base, the roller moves along the cam roller (931), and the roller is connected to the actuating member (9).

5. The heater (1) according to claim 4, characterized in that Each roller (932) is rotatably mounted on its associated actuating member (9).

6. A heater (1) according to any one of the preceding claims, characterised in that Each housing (8) is mounted on a corresponding actuating member (9) by a detachable fixing.

7. The heater (1) according to claim 6, characterized in that The removable fixings have: - at least one fixing hole (10) formed in the actuating member (9), and - at least one arm (11) fixed to the housing (8) for insertion into the fixing hole (10).

8. The heater (1) according to claim 7, characterized in that - the actuating member (9) has at least one orifice (12) which is transverse to the fixing hole (10) and communicates with the fixing hole (10); - the arm (11) has a groove (111) which is intended to be opposite to the orifice (12) when the arm (11) is inserted into the fixing hole (10); Furthermore, the detachable fixing piece further comprises a retaining member (13) inserted into the aperture (12), the retaining member (13) being used to cooperate with the groove (111) of the arm (11) to prevent the arm (11) from falling out of the fixing hole (10).

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