The invention relates to an infrared light source device for heating an object, during a thermal treatment process, in particular a thermal deformation process, for example in a production line.
For industrial heating applications such as thermal deformation processes like bottle blowing, drying, hardening, rapid thermal processing, etc., light sources like incandescent, Xenon or halogen lamps have typically been in use until now.
For example, the current bottle blowing process uses halogen burners to heat PET pre-forms beyond 100° C., before they are blown.
However, the broad spectra of these lamps makes a skin effect appearing at the outer side of preform due to high absorption of long wavelengths, with the apparition of a corresponding significant thermal gradient between inner and outer preform sides which would lead to a inhomogeneous temperature over the preform volume and thus to an incorrect blowing.
To speeding up the production line, the thermal homogeneity is found rapidly by cooling the outer side (e.g. with a fan or a cooling fluid circuit) until the inner side reaches the right process temperature.
But such cooling systems are cumbersome, noisy and costly.
To overcome this problem, WO 2006/056673 discloses the use of high power density of infrared lasers as well as the selection of emitted wavelength in a shorter range (between 800 nm and 1064 nm) where the absorption by the PET preform is low. The advantage is that the radiation is then absorbed in the whole volume rather than just in a skin.
Nevertheless, this requires a reflector arrangement allowing many passes of laser light through the PET form.
Furthermore, even if such lasers are a promising technology to be used, they are still not efficient enough and still expansive.
The invention overcomes the previous drawbacks by providing, in a first aspect, an optical interface for transmitting at least some infrared rays emitted from at least one light source so as to heat an object above a threshold temperature, wherein the object has a low transmission and a high absorption for infrared wavelengths greater than an infrared wavelength threshold, the optical interface comprising:
According to a second aspect, the invention proposes an optical interface for transmitting at least some infrared rays emitted from at least one light source so as to heat an object above a threshold temperature, wherein the object has a low transmission and a high absorption for infrared wavelengths greater than an infrared wavelength threshold, the optical interface comprising:
Therefore, the invention according to first or second aspect optimises the efficiency of heating processes by selecting appropriate emission bandwidth depending on the optical properties of the object to be heated.
For example it is recommended for the heating stage of objects like PET preforms to have a maximum of supplied infrared energy between the near/medium infrared region (around 1000 nm), a bandwidth presenting a high transmission being suited to minimise the temperature gradient over the preform thickness of such a poor thermal conductive material.
Optional features of the invention according to the first or second aspect of the invention are either of the following features:
According to a third aspect, the invention proposes a set of optical interfaces dedicated to be placed in front of at least one light source which emits some infrared wavelengths for heating an object having a determinate thickness placed at a determinate distance from the light source, each optical interface being according to said first or second aspect and having an interference filter with an optical transmitting spectrum different from those of the other optical interfaces, each transmitting spectrum corresponding to a thickness of an object so as to provide an optimum heating of an object having this determinate thickness.
According to a fourth aspect, the invention proposes an optical device comprising:
Optional features of this optical device are either of the following features:
According to a fifth aspect, the invention proposes an arrangement of light sources according to a line or matrix of light sources such that the light emitting from the light sources heat a determinate volume placed at a determinate distance from the arrangement, the arrangement further comprising at least one optical interface according to said first or second aspect of the invention.
This arrangement of light sources may further comprise at least one back light reflector placed at one side of the light sources so as to reflect radiations back to the determinate volume.
According to a sixth aspect, the invention proposes an equipment for blowing preforms, comprising the said arrangement of light sources for heating the preforms prior to or during the blowing step, a preform defining the said determinate volume.
According to a seventh aspect, the invention proposes a method of heating a preform, comprising an infrared radiation using at least one optical device according to said fourth aspect of the invention.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
a and 3b show a double-ended lamp in accordance with the invention;
a and 4b show a double-ended lamp in accordance with an advantageous embodiment of the invention;
This object 300 may be any object needed to be heated, for different applications, e.g. for industrial heating applications such as thermal deformation processes like bottle blowing, drying, hardening, rapid thermal processing. This object 300 can also be a human being, an animal, a plant or a part thereof, who necessitates the application of a thermal energy corresponding to a certain threshold temperature brought to the whole body, for well-being or medical purpose.
Without limitation to the scope of the invention, the object 300 in the subsequent description is a preform to be heated and blown (simultaneously and/or after the heating) into a final container (e.g. a bottle). “Preform” means any preform as well as any intermediary container between the preform and the final container. Indeed particular industrial process may comprise a first step of forming an intermediary container from the preform, then, after a determinate time, a second step of forming a final container from the intermediary container. To perform such blowing or part of blowing, a certain thermal energy has to be brought to the preform (or to the intermediary container) 300. In this example, the preform 300 comprises an outer surface 301 and an inner surface 302 defining an outer wall with a specific thickness.
The optical systems of
Due to efficiency of such an industrial process, it is desirable to obtain a heating efficient and rapid: this is the main purpose of the optical system of the invention.
The optical system of
The light source 100 is able to emit infrared lights with energy sufficient to heat the preform 100 according to industrial requirements. Possibly, the light source 100 emits other kinds of wavelengths, such as for example wavelengths in the visible range. The light source 100 can be of any kind, such as for example an incandescent, halogen, Xenon lamp, or a LED.
Light source 100 is located so as to heat homogeneously the preform 300, i.e. on the whole length, on the whole circumference, on the whole thickness.
The substrate 202 is preferably transparent to at least near infrared. It can be made for example of amorphous, polycrystalline, nanocrystalline glass or quartz.
The interference filter 201 is arranged for cutting-off some wavelengths from the emitting spectra so as to optimise the heating of the preform 300 according to the invention. Preferably the interference filter 201 reflects the undesirable wavelengths back to the light source 300. The interference filter 201 is designed to heat homogeneously, quickly and sufficiently the preform 300, and especially to obtain a rapid thermal equilibrium between the inner side 302 and of the outer side 301 of the preform 300 necessary for blowing.
Alternatively, the heating of the preform 300 may be provided with a plurality of light sources 100′, 100″, 100′″ (
A single optical interface 200 may be provided for all the light sources 100′, 100″, 100′″ (
One infrared reflector 400′, 400″, 400′″ may be provided at the backside of each light source 100′, 100″, 100′″ (
On
The interference filter 201 may be formed either on a substrate 202 separate from the light source 100 or on a part of the light source 300 such as for example the vessel of an incandescent lamp or on the optics of a LED.
An example of a double-ended lamp coated with an interference filter 201 in accordance with the invention is depicted in
The incandescent body 102, which is for example a tungsten wire, has its extremities connected to the foils 107, which are for example pieces of molybdenum to which the extremities of the incandescent body 102 are welded.
Current supply conductors 103 are also welded to the foils 107. The current supply conductors are connected to the current wires 109. This can be done by welding a current supply conductor 103 to a current wire 109, through a hole of a cap 105.
Such a cap 105 is described in patent EP 0345890. Alternatively, the extremity of the incandescent body 102 serves as current supply conductor and is directly connected to the current wire 109. The incandescent body 102 is maintained in position inside the lamp vessel 101, by means of the supports 108, which permit a right positioning of the incandescent body 102 in the lamp vessel 101.
The lamp vessel 101 is filled with a high-pressure discharge gas, such as argon, and comprises a small quantity of a halide substance in order to prevent darkening of the lamp vessel 101, due to deposition of gaseous tungsten.
As the lamp of
It should be noted that the interference filter 201 can be deposited on an external face of the outer envelope 104, or on an inner face of the outer envelope 104, or can be a combination of a reflective film deposited on the external face of the outer envelope 104 and a reflective film deposited on the inner face of the outer envelope 104.
Moreover, the outer envelope 104 is particularly advantageous. In case of lamp failure or even explosion of the lamp vessel, thanks to the outer envelope 104, any glass pieces that may fall off safely remain inside the outer envelope 104, so that the persons using such a lamp cannot be injured.
In
It can be noticed that the lamp of
A double-ended lamp in accordance with another embodiment of the invention is depicted in
Such a ceramic reflective layer is used, for example, in a halogen lamp sold by the applicant under reference 13195Z/98.
Such a ceramic reflective layer 400 has the advantage that it resists at relatively high temperatures, such as 2000° C. This is particularly advantageous in the lamps in accordance with the invention, which operating temperatures can be above 1000° C., depending on the linear power density.
Such a reflective layer 400 provides focalization of the radiation beams emitted by the incandescent body 102, which is necessary in order to direct the radiation beam to a person or an object to heat. As a consequence, no external reflector is required, which is an advantage, because such an external reflector is bulky and limits the compactness of the lamp system.
It should be noted that the reflective layer 400 can be deposited on an internal face of the lamp vessel 101, instead of being deposited on an external face, as depicted on
In some lamps, it is not possible to provide such a reflective layer 400 on the lamp vessel, because the lamp vessel already comprises a reflective film. As a consequence, in order to focus the heat, these lamps can be used in combination with an external reflector 400.
Whatever its configuration and the substrate on which it is formed, the interference filter 201 is preferably a multilayer comprising layers of, alternately, a first layer of a material having a comparatively high refractive index and a second layer of a material having a comparatively low refractive index.
Optionally the second layer of the interference filter comprises predominantly silicon oxide, and the first layer of the interference filter comprises predominantly a material having a refractive index which is high as compared to a refractive index of silicon oxide.
Preferably, the first layer of the interferential filter comprises a material chosen from the group formed by titanium oxide, tantalum oxide, zirconium oxide, niobium oxide, hafnium oxide, silicon nitride and combinations of said materials. Preferably, the material of the first layer of the interferential filter predominantly comprises titanium oxide or niobium oxide.
Preferably, the interference filter 201 is TiO2/SiO2 type-films or Nb2O5/SiO2-type films.
The interference filter 201 may be provided in a customary manner by means of 1. physical vapor depostion (PVD), e.g. reactive magnetron sputtering or evaporation, 2. chemical vapor deposition (CVD), e.g. low pressure CVD (LPCVD), plasma enhanced CVD (PECVD), plasma impulse CVD (PICVD), 3. wet chemical deposition techniques, e.g. sol gel coating by spraying and dipping.
The interference filter 201 may have typically a thickness around 5 micrometers.
This graph shows that the PET plastic becomes nearly completely opaque for wavelengths above 2250 nm. This is due to the high absorption level of PET above this range.
So, when heating a plastic PET preform with wavelengths greater than 2250 nm, the high absorption leads to overheat the outer side 301 and to under-heat the inner side 302 (see
This graph shows also that the transmission curve of PET comprises a 1st level of transmission (at around 90 a.u.) in the range 400-1600 nm much higher than an intermediary level of transmission (at around 40 a.u.) in the range 1600-2250 nm.
This intermediary level of transmission shows an intermediary level between transparency (1st level) and total opacity (for wavelengths greater then 2250 nm) for which absorption and transmission of the wavelengths through the preform 300 are moderate.
To properly blow a plastic container (such as a bottle) the PET should be homogeneously heated between 100° C. and 130° C., since above 130° C.: the PET cristallizes.
Instead of cooling the outside surface 301 of the PET preform, by using fans, the invention proposes to provide an interference filter 201 that removes most of the light emission above 2250 nm and keeps as much as possible below 2250 nm. This is depicted by
The advantage of these intermediary wavelengths for preparing the blowing of a PET preform 300 is shown on
It is shown that:
This example shows that the filter no 2 optimises the heating of the preform 300, by speeding up the homogeneous heating (between inner and outer sides of the preform 300) while ensuring a sufficient heating temperature for blowing issue.
Furthermore the interference filter 201 according to the invention can be designed so as to keep an appropriate transmission rate beyond the cut-off wavelength (i.e. 2000 nm here) so as to reach a temperature equal to or greater than the threshold temperature (i.e. 100° C. here) and to obtain rapidly (i.e. 21 seconds here) a homogeneous heating (i.e. between inner side 302 and outer side 301 of the preform 300), and therefore optimising the industrial heating of the preform 300 in view of the next and/or simultaneous blowing step. To this purpose, and in view of
Example of a 42 layered-interference filter 201 according to the invention (those from which the corresponding curve on
Optionally, the interference filter 201 is also configured to filter out (e.g. by reflection) a large part of the visible radiation emitted by the light source 100.
Indeed, this visible radiation reflected back by the interference filter 201 can be reabsorbed by a halogen lamp for being reemitted later on through infrared radiation. This allows saving energy. This energy saving is enhanced if a reflector 400 is provided on the backside of the light source 100.
Moreover, the non-emission of visible wavelengths may be desirable, e.g. for avoiding any glaring effect that may affect people close to the optical system.
The interference filters 201 corresponding to the spectrum of
Any reference sign in the following claims should not be construed as limiting the claim. It will be obvious that the use of the verb “to comprise” and its conjugations does not exclude the presence of any other elements besides those defined in any claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.
Number | Date | Country | Kind |
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08300244.4 | Jul 2008 | EP | regional |
08300273.3 | Sep 2008 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2009/053090 | 7/16/2009 | WO | 00 | 2/17/2011 |