Abstract:
A heating device for tempering preforms before processing in a stretch blow device. The heating device includes a heating alley with a plurality of infra red emitters, arranged parallel to the longitudinal axis of the tempered preforms. At least one back reflector and/or one filter is assigned to the infra red emitters, whereby the at least one back reflector and/or the at least one filter is segmented.

Description:
This is a Continuation of U.S. patent application Ser. No. 13/317,494 and claims the benefit of German Patent Application DE 10 2010 049 136.5, filed Oct. 22, 2010. Both applications are hereby incorporated by reference herein. 
    
    
     The present invention relates to a heating device for tempering preforms, especially a heating device. The invention furthermore relates to the use of a back reflector or a filter in a heating device for tempering preforms. 
     BACKGROUND 
     So called preforms are used for the production of plastic bottles. The preforms are made of a thermoplastic material, especially PET. The preforms are first heated and then reshaped into the desired container shape in a stretch blow device. Usually the preforms are conveyed through a heating device on a conveyor path before being processed in the stretch blow device. 
     Each preform is already designed with an upwardly open mouth region, which usually comprises an external thread. This mouth region essentially corresponds to the mouth region of the finished bottle. The preforms are typically injection molded parts. The preforms are tempered to the required forming temperature in a heating device. The tempered preforms are then processed and reshaped into the final container or bottle shape in a stretch blow device. 
     The heaters for tempering the preforms via infrared radiation are arranged in heating boxes. The heating boxes are arranged on the outboard side of the straight long sides of the heating device. Usually reflectors are arranged on the inside and on the floor part of the heating boxes. Thereby the emitted infrared radiation can be used as much as possible because the infrared radiation is advantageously deflected in the direction of the preforms. 
     In most known systems the mouth region of the preforms is protected from excessive heating by an air stream. This is necessary because otherwise the mouth region might be deformed in the subsequent blow molding process. This would lead to the production of incorrect containers that need to be discarded. 
     Furthermore, the surface of the preforms needs to be protected from burning which might occur due to excessive local heating. This is usually done by injecting air into the heating system. The air is usually injected through slits in the reflectors that are arranged opposite to the heating elements. 
     A schematic representation of a heating device  1  for tempering preforms  20  according to the known state of the art is shown in  FIG. 1 . The preforms  20  are delivered by transport means or transporter  2 , then divided and spaced as required by a sawtooth starwheel  3   a  and fed into an oven or heating module  4 , where they are moved along a heating tunnel  5  in a transport direction F. 
     While moving through the oven  4 , the preforms  20  first pass through a first linear heating zone  5   a , whereby their circumferential surface is heated uniformly. After a deflection zone  6  at one end of the oven  4 , the movement of the preforms  20  continues through a second linear heating zone  5   b . In the second linear heating zone  5   b  the preforms  20  are tempered to the final temperature before being processed into the final shape in a stretch blow molding device. Multiple heating boxes  7  are arranged in the linear zones  5   a ,  5   b  of the heating tunnel  5 . The heating boxes  7  comprise infrared emitters and additional reflectors. 
     The reflectors are required in order to minimize radiation losses as much as possible. The radiation emitted by the infrared emitter, which does not enter the preforms  20 , is reflected back to the preforms  20  by the reflectors and therefore not lost. 
     While the preforms  20  pass through the oven  4 , they are preferably rotated to ensure a uniform heating of all sides. Then the heated preforms  20  are passed, for example, to an outlet starwheel  3   b  and fed into a stretch blow molding device or something alike. 
       FIG. 2  shows a heating box  7  known from prior art for use in a heating device according to  FIG. 1 .  FIG. 2  especially shows a heating alley  8  with a heating box  7  used in one of the linear heating zones  5   a ,  5   b  in the heating module  4 ,  5  (see  FIG. 1 ). The preform  20  is mounted on holding means or holder  16  and preferably rotated during its movement through the heating alley  8 . To prevent excessive heating of the mouth region  22  of the preform  20 , the mouth region  22  is shielded from direct radiation by a shielding plate  9 . Furthermore an outer cooling plate  10  is arranged in this region. This outer cooling plate  10  shields the mouth region  22  from upward radiation. 
     In a heating alley  8  infrared emitters are arranged in a vertical row parallel to the longitudinal axis X of the preform  20 . Therefore the preform  20  gets irradiated and heated over its entire height. The term parallel refers to a plane, in which the majority of the radiant emitters  11  are arranged. The longitudinal axis of each rod-shaped radiant emitter  11  is perpendicular to the longitudinal axis X of the preform  20 . The electrical power of each radiant emitter  11  can be controlled separately. Thereby a temperature profile can be applied to the preform  20  along its longitudinal axis X. All radiant emitters  11  are arranged in the same distance from the longitudinal axis X of the preform  20 . Furthermore, a bottom radiant emitter  12  is arranged in the lower part of the heating alley  8 , which irradiates and thereby heats the preform  20  from below. 
     To ensure the best use of the radiation from the radiant emitters  11 ,  12 , the heating alley  8  comprises reflectors, especially a counter reflector  13 , a bottom reflector  14  and a back reflector  15 . The counter reflector  13  is arranged behind the preform  20 , opposite to the radiant emitters  11 . The back reflector  15  is arranged behind the radiant emitters  11  thus reflecting the radiation that could otherwise not be used for the heating of the preforms  20 . 
     It is necessary to have a certain minimal distance d 1  between the back reflector  15  and the infrared radiant emitters  11  to prevent damage of the back reflector  15  due to the high temperature fluctuations in the heating alley  8 . 
     EP1 278 619 B1 describes a heating assembly with elongated heaters. A single reflector is associated with each heater. The reflector has a parabolic shape, therefore the reflected radiation beams are generally parallel to each other which ensures a controlled tempering of the preforms. 
     DE 100 58 950 B4 shows a heating route for preforms with elongated halogen light sources. The reflectors are arranged around the preform and form a substantially closed radiation space. 
     SUMMARY OF THE INVENTION 
     Due to the high process temperatures and the temperature fluctuations occurring in the heating tunnel, the demand on the materials used in the heating tunnel is very high. For this reason reflector materials with advantageous properties regarding temperature resistance, thermal shock resistance, reflection of radiation, thermal conductivity and so on are preferably used. Especially ceramics and glass show very good properties. These materials are characterized by their low thermal expansion coefficients and low linear expansion coefficients. Therefore their temperature-dependent expansion is relatively low. By contrast, typical metallic materials exhibit a significantly higher thermal expansion coefficient and thus show a higher linear expansion. Examples of the linear expansion coefficients of various materials at 20° C. are listed in tabular form in  FIG. 3 . 
     With ever rising energy prices, the highest possible efficiency of machinery and equipment is becoming increasingly important. It is an object of the present invention to optimize the efficiency of heating tunnels or similar heating devices by using suitable reflectors. 
     The present invention provides a heating device for tempering preforms prior to processing in a stretch blow molding device. The used preforms comprise a mouth region and a longitudinal axis. The heating device comprises a heating alley with transport means or transporter for the movement of the preforms along a transport route. In the heating alley a plurality of infrared emitters are arranged in a vertical row parallel to the longitudinal axis of the preform. All the radiators have the same distance to the longitudinal axis of the irradiated preform. The infrared emitters are used for heating the preforms. To take full advantage of the radiation, at least one back reflector is associated with the infrared emitters. Any radiation that is emitted on the backside of the infrared emitters is reflected into the heating alley where it also serves to heat the preforms. 
     Furthermore at least one filter can be assigned to the infrared emitters, so that only radiation of a specific wavelength or a specific wavelength range is introduced or irradiated into the heating alley. This filter is preferably used for changing short-wave radiation emitted from the infrared emitters into long-wave radiation. Especially one filter can be assigned to each infrared emitter. 
     According to the invention the at least one back reflector and/or the at least one filter is formed in segments. Very strong temperature fluctuations occur in a heating alley. The infrared emitters produce temperatures of 800° C. or even more. Large back reflector tiles or filter tiles are usually made of a ceramic material, glass, glass ceramics, quartz glass, coated quartz glass or something alike. These materials are especially brittle. Therefore these materials tend to break easily when they are subjected to high temperature fluctuations and/or loads of pressure and/or tensile forces. The back reflector tiles or filter tiles then have to be replaced. This requires a stopping of the machinery and leads to a costly loss of production. Due to its segmented structure the at least one back reflector and/or the at least one filter can be arranged significantly closer to the infrared emitters without incurring damage, especially without the danger of breakage. 
     In particular, the individual segments of the at least one back reflector and/or the at least one filter are interconnected by a tongue and groove joint. The advantage of such a joint is that a controlled expansion takes place. Due to the form-locking connection between the tongues and grooves no gaps are formed between the segments of one tile. In the case of the reflector such gaps would lead to a loss of radiation. In case of the filter such gaps would allow the passage of radiation of an unwanted wavelength. 
     In general, the at least one back reflector and/or the at least one filter is arranged in the heating alley in a mounting bracket. Such a mounting bracket is made for example from sheet steel or stainless steel or stainless steel plate or a similar suitable material. The mounting bracket thus has a different linear expansion coefficient than the at least one back reflector and/or the at least one filter. With the temperature fluctuations occurring in the heating alley, this can cause pressure or strain on the at least one back reflector and/or the at least one filter. This can in turn result in exceeding the allowable material limits and lead to a breakage of the material of the reflector or filter tile. 
     Traditionally, the reflectors and/or filter are fastened firmly or rigidly to the metallic material of the mounting bracket by screw connections, bonding, clamping, folding or riveting joints or something alike. The metallic materials are used as fastening or support elements for the installation of the reflectors and/or filters in the heating alley. The different linear expansion of the different materials leads to additional or increased stress on the different components, especially on the reflector or filter tile. The materials glass or ceramic used as reflector material are brittle and can take up only little pressure or tensile stress. Repeated temperature fluctuations therefore quickly lead to damages of the reflector, for example, by breakage. 
     According to a preferred embodiment, the at least one back reflector and/or the at least one filter is arranged in a so-called floating mount or floating bearing. The floating mount is required for fastening the reflector within the heating alley. Hereby, the ceramic material of the back reflector and/or the filter is decoupled from the mounting element. The floating mount is used for providing fastening means for fastening the reflector within the heating alley. The floating mount prevents additional stresses on the brittle material of the at least one back reflector and/or the at least one filter. The floating mount allows a free movement or extension of the brittle material in all spatial directions. 
     At least one recess is incorporated in the narrow side faces of each reflector, whereby at least one holding element or structural element of a frame member of the floating mount engages with the recess. The recess is wider and/or deeper than the engaging frame member. Particularly the width of the recess is wide enough to ensure that always an air gap remains between the reflector material and the frame material, even though the reflector and the frame expand differently. Furthermore the recess is deeper than the engaging frame member. Therefore free movement of the material is also possible in this spatial direction. In this construction the reflector is supported in the frame with sufficient precision. Especially no additional stress arises from the use of different materials. This is due to sufficient space in all directions, which allows an unhindered expansion of the different materials. 
     Preferably, the at least one back reflector and/or the at least one filter—hereinafter referred to as tile—is held in a rigid, torsion-resistant frame. Such a frame is particularly useful for thermal decoupling between the tiles and the frame, since the middle of the frame is free of material. Therefore no expansion or deformation of the frame takes place in this middle area. 
     To make an infrared emitter, first a glass tube is produced. Then halogen gas is introduced into the glass tube through a hole that is closed afterwards. At this so-called injection point, the material thickness of the emitter is increased. To be able to place the back reflector as close as possible to the infrared emitter, the reflector shows an exposure or groove in the area corresponding to the injection point of the emitter. According to an alternative embodiment the back reflector is segmented in this area. 
     Due to the segmented structure the tile can stand up to larger temperature fluctuations. It is therefore possible to minimize the distance between the infrared emitters and the back reflector. Preferably, the maximum distance between the infrared emitters and the back reflector is 50 mm. Even more preferably the maximum distance between the infrared emitters and the back reflector is 10 mm or even as low as 5 mm. 
     Furthermore, at least one counter reflector is arranged in the described heating alley. The counter reflector is located on the side of the heating alley opposite to the infrared emitters. Therefore the preform is moved between the infrared emitters and the at least one counter reflector. Minimizing the distance between the preform and counter reflector also leads to a significant improvement in energy efficiency because the reflection of the radiation onto the preform is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, embodiments of the invention illustrated by the accompanying figures are used to explain its advantages. The relative sizes of the individual elements in the corresponding figures are not always in real proportions. Some forms are simplified and other forms are enlarged in relation to other shown elements for the sake of clarity. 
         FIG. 1  shows a schematic representation of a heating device (prior art). 
         FIG. 2  shows a heating box that is used in a heating device according to  FIG. 1  (prior art). 
         FIG. 3  shows the linear expansion coefficients of various materials at 20° C. in a tabular form (prior art) (prior art). 
         FIG. 4  shows a heating box that is used in a heating device according to the invention. 
         FIGS. 5   a/b  show a back reflector according to the prior art. 
         FIGS. 6   a/b  show a back reflector according to the invention with a mounting bracket. 
         FIGS. 7   a/b  show a further embodiment of a mounting bracket for a back reflector. 
         FIGS. 8   a/b  show a further embodiment of a back reflector in a floating mount according to the invention. 
         FIGS. 9   a/b  show the temperature distribution on a reflector along the longitudinal axis of the reflector, whereby the reflector is arranged behind the emitter (prior art). 
         FIG. 10  shows an arrangement of several reflectors behind an emitter according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     For the same or equivalent elements of the invention, identical reference numerals are used. Furthermore, for the sake of clarity, only reference numerals are represented in the various figures, which are necessary for the description of each figure. The illustrated embodiments are merely examples of how the inventive device can be designed and do not constitute final limitations. 
       FIG. 4  shows a heating box  7  to be used in a heating device or heater according to the invention. According to the invention the back reflector  50  can be located in a very short distance d 1  to the infrared emitters  11 . Preferably, the distance d 1  is a maximum of 5 mm. Furthermore, the distance d 2  between the preform  20  and the counter reflector  30  is reduced, which also leads to a better use of the infrared radiation. 
       FIGS. 5   a / 5   b  show two different views of a back reflector  15  according to the known state of the art. This consists of a single tile  90 , which is for example made of ceramic material, glass, glass ceramics, quartz glass, coated quartz glass, polished sheet aluminum or any other suitable material. The back reflector  15  preferably has mounting devices  70  for facilitating the mounting and replacing of the back reflector  15  in the heating alley. This may for example be a notch or groove  72 . The back reflector  15  may then be inserted into corresponding mounting devices in the heating alley. 
       FIGS. 6   a / 6   b  show a back reflector  50  or a tile  92  according to the present invention in a mounting bracket  80 . The tile  92  is divided into three segments S 1 , S 2 , S 3 . The segments S 1 , S 2 , S 3  are connected to each other via interlocking tongue and groove joints  95 . A controlled expansion takes place when the tile  92  is heated. Due to the connection by interlocking tongue and groove joints no gaps occur between the segments S 1 , S 2 , S 3  of the tile  92 , which might lead—in the case of the back reflector  50 —to a loss of radiation. In the case of the filter such gaps would lead to the passage of radiation of unwanted wavelength. 
     A mounting bracket  80  particularly serves to facilitate the mounting and the replacement of the tile  92  in the heating alley. For this reason the mounting bracket  80  may, for example, be provided with mounting devices. 
     Furthermore, the tile  92  features a recess  96 . The position of the recess  96  is selected in a way that after installation of the tile  92  in a heating alley the recessed area  96  corresponds to the injection point of the infrared emitter. It is therefore possible to place the back reflector  50  very close to the infrared emitter. 
       FIGS. 7   a / 7   b  show a further embodiment of a mounting bracket  82  for a back reflector  50 . The design of the tile  92  corresponds to the tile  92  in  FIGS. 5   a/b.    
     The mounting bracket  82  is made of e.g. a steel sheet, stainless steel sheet or a similar suitable material. The mounting bracket  82  is designed as a so-called floating mount. The floating mount  82  prevents additional tension on the brittle material of the tile  92  and allows a free movement and extension of the tile  92  in all spatial directions. 
     The mounting bracket  82  is preferably designed as a rigid, torsion-resistant frame  84 . The frame  84  particularly serves for thermally decoupling the tile  92  from the frame  84 . Since the middle of the frame  84  is free of material, no expansion or deformation can take place in this middle part. Therefore no strain or pressure is applied to the tile  92 . 
       FIGS. 8   a / 8   b  show further views of a back reflector  50  according to the invention. The back reflector  50  is arranged in a floating mount  82 . A recess  100 , particularly a slot  102  or something alike, is incorporated in the reflector  50 . At least one holding element  86 ,  87  engages with the mount  82 . Preferentially all four narrow sides of the reflector  50  show corresponding recesses  100 ,  102 , so that the reflector  50  can be supported by the frame  84  of the mount  82  on all four sides. 
     The dimension of the recesses  100  is specifically chosen to ensure that always a gap remains between the reflector  50  and the mount  82 , even when they expand differently. Thus there is no or only a slight contact between the reflector  50  and the mount  82 . 
     The reflector  50  is held in the support frame  84  of the mount  82  with sufficient accuracy. But still sufficient space is available in all three spatial directions for material changes, especially for expansions. This construction reliably prevents the development of additional tension on the reflector  50 . 
       FIGS. 9   a / 9   b  show the temperature distribution in a heating alley along the longitudinal axis XS of an emitter and along a reflector arranged behind the emitter according to the prior art. The temperature profile is uneven over the length L11 of the emitter  11 . The length L11 of the emitter  11  is measured and shown in mm. No heating coil is incorporated into the ends  11   b  of the emitter  11 . Additionally the ends  11   b  of the emitter  11  are supplied with cooling air  17  to increase the lifetime of the emitter  11 . This results in a maximum temperature Tmax in the middle part of the emitter  11 . The temperature decreases towards the ends  11   b  of the emitter  11 . The reflector  15  that is arranged behind the emitter  11  especially tends to break in the areas B 1 , B 2  of the temperature increase or decrease. 
       FIG. 10  shows an advantageous arrangement of several reflectors  50  according to the invention behind an emitter  11 . Hereby the reflectors  50  are arranged parallel to each other, whereby the segments S 1 , S 2 , S 3  of each reflector  50  are arranged perpendicular, e.g. one above the other. The size of the reflectors  50  is especially selected. In the areas with increased susceptibility to breakage, the adjacent reflectors are arranged at a small distance d 50  from each other. 
     This so-called vertical positioning of the reflectors  50  in comparison to the emitter longitudinal axis XS is particularly advantageous. The development of additional internal stress over long lengths of the ceramic or glass material of the reflectors  50 —which usually arises due to large temperature differences—can be avoided with this additional segmentation, which is accomplished by the arrangement of several reflectors beside each other. 
     The invention has been described with reference to preferred embodiments. However, it is conceivable to one skilled in the art that variations or modifications of the invention can be made without departing from the scope of the following claims. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               1  heating device 
               2  transport means 
               3   a  sawtooth starwheel/infeed starwheel 
               3   b  outlet starwheel 
               4  heating module/oven 
               5  heating tunnel 
               5   a / 5   b  linear heating zone 
               6  deflection zone 
               7  heating box 
               8  heating alley 
               9  shielding plate 
               10  cooling plate 
               11  infra red emitter 
               11   b  emitter end 
               12  bottom emitter 
               13  counter reflector 
               14  bottom reflector 
               15  back reflector 
               16  holding means 
               17  cooling air 
               20  preform 
               22  mouth region 
               30  counter reflector 
               50  back reflector 
               70  mounting device 
               72  notch/groove 
               80  mounting bracket 
               82  mounting bracket/floating mount 
               84  frame 
               86  holding element 
               87  holding element 
               90  tile 
               92  tile 
               95  tongue and groove joint 
               96  recess 
               100  recess 
               102  slot 
             B 1 /B 2  breakage sites 
             d 1  distance between infrared emitters and back reflector 
             d 2  distance between preform and counter reflector 
             d 50  distance between two reflectors 
             S 1 , S 2 , S 3  segments 
             X longitudinal axis 
             XS emitter longitudinal axis 
             F transport direction