PL206123B1 - Apparatus for manufacturing stick-like articles - Google Patents

Abstract

Device for use in cigarette filter production in which an encasing device (23) encases a material strand with encasing material (21). A heating device (28) for warming the material stand is positioned after the encasing device in terms of the production direction.

Description

Description of the invention

The present invention relates to a device for the production of rod-shaped articles from a web of material, especially in the tobacco processing industry, with a wrapping device with an endless belt conveyor or a formatting conveyor for wrapping the web in a sheath material, a heating device for heating the web or rod articles made of it, and a transport device for transporting the web or rod-shaped objects made therefrom through the above-mentioned devices, preferably in the axially longitudinal direction.

In the tobacco processing industry, such a device may be, inter alia, part of a machine for producing a strand of filters for producing filter plugs. In the manufacture of filter plugs, the filter material (tow) is prepared from an endless strand pulled from a bale, which consists of individual fibers or staple fibers (e.g. cellulose acetate), before it is folded into a filter web, it is wrapped in a web of casing material, the seam area of which is provided with glue and cut into filter plugs having a single usable length or a multiple of the usable length. In practice, the preparation takes place in such a way that the web of filter material, after being pulled out of the bale, is loosened and expanded and then stretched in the extraction zone in the longitudinal direction. In this state, the filter material web is in turn wetted with a plasticizer which makes the surface of the fibers or the staple fibers sticky, after which it is glued together. The web prepared in this way is immediately then folded into a web of staple fibers, wrapped and cut into individual filter plugs with a single usable length or a multiple of a single usable length.

Said plasticizer, which is usually triacetin, is a solvent for the filter material. When the surface of the staple fibers is moistened with the plasticizer, they dissolve and can be glued together at the points of contact. In order to cure the staple fiber connections thus formed, the softener concentration in the dissolved filter material must be reduced. This is done by diffusing the softener into the staple fibers, thereby distributing the softener over a much larger amount of material, and thus the desired dilution. As with most chemical processes, the rate of diffusion is temperature dependent, with elevated temperatures accelerating curing.

The wrapping device usually has an endless conveyor, also referred to as a format conveyor, by means of which the web of material and the separately supplied casing material are transported in an axially longitudinal direction through the wrapping device, also referred to as a formatter. In the wrapping apparatus, a strip of material for the sheaths is applied with stationary forming tools around the strip of material and glued accordingly.

A device of the initially mentioned type is known from US Pat. No. 4,357,188 A. In this known device, a filter band is guided through chamber resonators, which are supplied with microwave energy. The filter band is guided through the chamber resonators together with the formatting conveyor. Thus, when microwaves are exposed, the filter band is surrounded by a formatting conveyor. Only after exiting the chamber resonators, the formatting conveyor is moved back from the filter band, then wrapped with sheath material.

A similar device is disclosed in US 3,017,309. In this solution, a circular conveyor or a formatting conveyor runs through the wrapping device. Looking in the direction of transport, a heating device is located behind the wrapping device through which the formatting or belt conveyor passes. As soon as it leaves the heating device, the forming belt is again lifted from the web of material then surrounded by the sheath material. This leads to the heating of the formatting or circular conveyor. In practice, however, it turned out that increased wear occurs by heating the formatting or circular conveyor. A similar device is also disclosed in DE 29 36 490 C2.

In order to eliminate the undesirable successive heating of the formatting conveyor guided by the chamber resonators, it is necessary to cool it outside the chamber resonators during the return movement, as proposed in DE 2 443 056 B2. However, this countermeasure requires significant additional equipment investment, which negatively affects manufacturing and operating costs.

The object of the invention is to simplify the structure of the initially mentioned device.

PL 206 123 B1

This object is thus achieved by means of a device of the above-mentioned type, that the heating device is a microwave device for heating the web of material or rod-shaped objects made of it, and is arranged downstream of the circular conveyor belt when viewed in the transport direction of the material web or of rod-shaped objects made of it. or with the formatting conveyor of the wrapping device.

Preferably, in a device equipped with a cutting device for cutting the web of material into a rod-shaped object, the cutting device is arranged between the wrapping device and the heating device.

Advantageously, the device has a second transport device for transporting rod articles, in particular in the axial transverse direction, and a second transport device for transporting rod articles, in particular in the axially transverse direction, which is arranged downstream of the heating device, seen in the transport direction of rod articles.

Preferably, furthermore, the second transport device is arranged in a housing which is surrounded by thermal insulation and / or has a device for air conditioning the housing.

Preferably also, the heating device has a guide device along which the web of material or rod objects made of it are moved through the heating device.

The guide device is preferably fixed in relation to the movement of the material web or rod objects made of it and is designed for passively guiding the material web or rod objects made of it.

According to the invention, the guide device has a guide means in the form of a track for the slidably received receiving material web or rod articles made therefrom.

According to the invention, the guide device further comprises a lower section for a sliding abutment of the material web or rod articles made therefrom, and an upper section, and the spacing between the lower section and the upper section is dimensioned according to the thickness of the material web or rod objects made therefrom.

Preferably, the lower section forms a concave support surface in cross section.

According to a feature of the invention, the lower section has at least two support elements spaced apart from each other.

Advantageously, the support elements essentially provide a point support or a linear support for the material web or rod objects made of it in the direction of movement of the material web or rod objects made of it.

According to the invention, the upper section essentially forms a point contact or, in the direction of movement of the fabric web or rod articles made therefrom, a line contact with the fabric strip or rod articles made therefrom.

Preferably, the track guide means has an elongated shape.

According to a further feature of the invention, the supporting elements have slats which preferably extend parallel to each other in the direction of movement of the material web or rod objects made of it.

According to another feature of the invention, the upper section has at least one lath extending in the direction of the movement of the material web or rod-shaped objects made therefrom.

Preferably, the lath or slats have a circular cross section.

According to the invention, too, the guide means in the form of a track for guiding the material web or rod articles made therefrom is designed in the axially longitudinal direction.

Preferably, the distance in the transverse direction of the supporting elements is smaller than the thickness or diameter of the material web of rod articles made therefrom.

Preferably, the guide means is made of a heat-resistant material, preferably a ceramic material.

According to the invention, the guide means is made of a material with a low coefficient of friction.

According to the invention, in a heating device having a housing, a guide means is provided in the housing and the housing has an openable portion, the guide means being exposed when the housing is opened.

Preferably, the opening part comprises a housing cover.

PL 206 123 B1

Preferably, further, the openable part is pivotable about the axis of rotation.

Preferably, the axis of rotation substantially extends in the direction of movement of the fabric web or rod articles made therefrom.

According to the invention, the upper guiding means section is arranged on a portion of the housing to be opened.

Finally, the device preferably has a safety switch for switching off the heating device when the housing is opened.

The present invention leads to a considerable simplification of the structure of the device. This is the case in particular when the wrapping device has a circular conveyor or a formatting conveyor. In this case, the heat treatment takes place after the formatting conveyor has been moved away, so that the formatting conveyor is not heated and therefore also does not have to be cooled.

In the usual case, when a cutting device is provided for cutting the wrapped material web into rod articles, the cutting device may be arranged between the wrapping device and the heating device, so that in this embodiment the rod articles already made from the wrapped material strip are heat treated.

If a second transport device is provided for transporting the rod-shaped objects, preferably in the transverse direction, the second transport device, which, viewed in the direction of transport of the rod-shaped items, usually has a drum, should be arranged downstream of the heating device. This second transport device is placed in the casing and, in order to prevent rapid cooling of the rod-shaped objects heated by the heating device, thermal insulation is provided surrounding the casing and / or an air-conditioning device for the casing.

The heating device should have a guide device along which the material web or rod articles made therefrom are carried in the heating device. This guide device is preferably arranged stationary with respect to the movement of the fabric web or rod-shaped objects made of it, and is designed to passively guide the web of material or rod-shaped objects made therefrom, the material web or rod-shaped objects made therefrom being received from the first transport device. high kinetic energy that they can move independently along the guide device.

In a particularly preferred embodiment, the guide means, during its movement through the heating device, the fabric web or rod articles made therefrom, are positioned between the lower and upper sections of the guide means such that they move along the lower section and substantially adjoin the upper section.

The lower section preferably forms a concave support surface in cross section. As a result, a shape similar to a bathtub is created, which houses a cloth strip or rod-shaped objects made of it.

Additionally or alternatively, it is also possible that the lower section has at least two spaced-apart support elements.

The support elements essentially provide a point support or in the direction of movement of the material web or rod-shaped objects made of it, a linear support for the material web or rod-shaped objects made therefrom. In this way, a thrust bearing, for example a two-point bearing for the lower section, is formed at suitable points in cross-section, and thus the interface of the material web or rod objects made of it is minimized as much as possible. In this way, a reduction in friction can be achieved, which in turn favorably influences the movement of the fabric web or rod objects made therefrom. A further significant advantage of such a single support, in this connection, is that the fabric web or rod articles and supports made therefrom can be positioned mutually so that contact with the seam points on the casing or with the sticking points of the casing is eliminated. which also presents a risk of contamination. Accordingly, the fabric strip or the rod-shaped articles made therefrom can be positioned such that the point of the glue seam or the point of adhesion is between the support elements or outside the support elements, and therefore outside of interaction therewith.

Also, the upper section forms a substantially point contact, or in the direction of movement of the material web or rod objects made therefrom, a line contact with the material web, or

With rod-shaped objects made of it, so that in this case, in the same way as before, the already explained actions and advantages are achieved. In this way, for example when looking at the cross-section, a three-point thrust bearing is formed together with the lower section.

Typically, the track guide means should have an elongated shape. In a refinement of this embodiment, the support elements have slats extending in parallel to each other in the direction of movement of the material web or rod objects made of it. Also, the upper section has at least one flap extending in the direction of the movement of the material web or rod-shaped objects made therefrom. In order to achieve the aforementioned line contacts, the strip or strips should preferably have a circular cross section.

The distance in the transverse direction of the supporting elements must be smaller than the thickness of the material web or the diameter of the rod objects made of it.

The guide means is made of a heat-resistant material, preferably ceramic and / or low-friction material.

At this point, it should be noted that the previously described arrangement of the guide device in the heating device is also an independent aspect of the invention.

In a heating device having a housing in which the guide means is disposed, the housing has an opening portion which is made such that when the housing is opened, the guide means is substantially exposed. This embodiment provides easy and simple access to the transport path of the material web or rod-shaped articles made therefrom inside the heating device, which is advantageous not only for handling, but also when material accumulation could occur due to disturbances in the heating device.

The opened part is the housing cover. In this case, the housing can consist of two half-shells, of which the lower half-shell is stationary and the upper half-shell is used for opening. For ease of handling, the opening portion of the housing should be pivotable about the axis of rotation, the axis of rotation generally preferably extending in the direction of movement of the fabric web or rod-shaped objects made therefrom in order to allow easy access in the heating device over substantially the entire length to it. the way of transporting the material strand or the rod-shaped objects made of it.

The upper section of the guiding means is located on the opening portion of the housing. In this way, when the housing is opened, the transport route is also opened at the same time, so that particularly easy access to it is possible.

The safety switch, when opening the housing, switches off the heating device. In this embodiment, the user does not have to consider switching off the heating device as this is done automatically by means of a safety switch. This is especially advantageous when using microwaves.

The subject of the invention in an exemplary embodiment is shown in the drawing, in which fig. 1 shows a construction diagram of a filter-strand manufacturing machine, fig. 2 - partial sectional view of a microwave applicator in the filter-strand manufacturing machine according to fig. 1 and fig. 3 is a sectional view of the microwave applicator of Fig. 2 in the closed state (Fig. 3a) and in the open state (Fig. 3b).

Fig. 1 shows a schematic diagram of a machine for producing a filter band.

A preparation device as described in DE 42 09 606 A1 is attached to the filter strand manufacturing machine 2. In such a preparation device, the web of filter material is pulled from the bale and, inter alia, processed by expanding and drawing out and spraying a finely distributed liquid plasticizer such as, for example, triacetin. The web of material for the filters sprayed with the softener is finally transferred in a pleated strand in a preparation device and then transported to a filter strand making machine 2. Fig. 1 shows schematically the strand of material for filters prepared in the preparation device and identified by reference numeral 10. .

The web of filter material 10 then enters the filter web manufacturing machine 2 via the funnel 17, where it is joined together and applied to a web of sheath material 21 pulled from the reel 18 and by means of an adhesive coating device coated with a thermally activatable adhesive. The sheath material web 21 and the associated filter material web 10 reach an endless format conveyor 22, which both components pass through a formatting device 23, which places the sheath material web 21 around the filter material web 10 and forms a filter web 24 without end. With its adhesive joint, it runs over a cooling bar 26, on which the adhesive seam is hardened. Then, using a knife apparatus 27 sukce6

Filter plugs are cut off from the filter web 24, which are conveyed by the microwave applicator 28 in the axially longitudinal direction and transferred by means of an accelerator 29 to a depositing drum 31, whereby they are further transported in the axially transverse direction. From the depositing drum 31, the filter plugs, which are not shown in more detail in FIG. 1, reach the depositing belt 32, from which they are led to a further processing, also not shown, or to an intermediate store.

The microwave generator 28 is associated with a microwave generator 34 with an integrated control device, which, like the microwave applicator 28, is arranged in the auxiliary device 36. The microwave generator 34 comprises a control device 38 which, in the illustrated embodiment, is arranged in the filter-band forming machine. 2 and further controls the drive of the format conveyor 39 by the operating speed information of the filter strand forming machine and controls the microwave power generated accordingly. The drive of the format conveyor 39 drives the circular format conveyor 22.

In the exemplary embodiment shown, the acceleration device 29, the discharge drum 31 and the lengthwise delivery belt 32 are surrounded by a housing 40, the wall of which is provided with insulation 40a to prevent rapid cooling of the filter plugs heated in the microwave applicator 28. additionally or alternatively also, not shown in FIG. 1, a device for air-conditioning the housing 40, in particular by means of supplied warm air, can be provided. In addition, a temperature sensor 42 is housed in the housing 40, which is connected to the microwave generator 34, whereby the microwave energy produced by the microwave generator 34 in the microwave applicator 28 is controlled or regulated to a predetermined value by means of the integrated control, so that the filter plugs are transported through the microwave applicator. 28 heat to a certain temperature.

Thus, the housing 40 forms a storage device that is connected to the attachment 36 and to the filterband forming machine 2 or may be a component of the attachment 36.

Fig. 2 is a detail sectional side view of the microwave applicator 28, while Fig. 3 is a sectional view of the microwave applicator 28 in a closed state (Fig. 3a) and in an open condition (Fig. 3b).

The microwave applicator 28 has a housing 50 that can be opened using a cover 50a. As can be seen from Fig. 3, the lid 50a is the tiltable upper half-shell of the housing 50 and the lower portion of the housing 50 is its fixed lower half-shell. By opening the cover 50a, free access to the inside of the housing 50 and the built-in components therein is obtained. During operation of the microwave applicator 28, the lid 50a of the housing 50 is kept closed by the lock 52. As can be seen in particular in Figure 3, the lid 50a is secured to the remainder of the housing 50a by a hinge 53, the pivot axis 53a of the hinge 53 runs in the direction of the longitudinal extent of the housing 50. In Fig. 2, it can be seen that the cover 50 extends almost the entire length of the housing 50.

As can also be seen in FIG. 2, a safety switch 54 is provided which, when opening the housing 50, causes the microwave generator 34 (FIG. 1) to be switched off due to the tilting of the cover 50a. The safety switch 54 is connected to the microwave generator 34 or to the control circuit 38 via a cable 54a.

A feed pipe 56 is provided on one of the front sides of the housing 50, through which the cut-off and thus individual filter plugs coming out of the knife apparatus 27 enter the housing 50 of the microwave applicator 28 (FIG. 1). On the opposite side of the front housing 50 is a discharge pipe 57 through which the filter plugs heated in the microwave applicator 28 enter the associated acceleration device 29 (FIG. 1). As can moreover be seen in Fig. 2, the feed pipe 56 and the discharge pipe 57 lie in a line in the axial direction.

The microwave applicator 28 has a guide device 60 that is disposed within the housing 50. In the illustrated embodiment, the guide device 60 is formed by three guide rails 61, 62 and 63 that are arranged parallel to each other and extend in the longitudinal direction of the housing 50. Three The guide strips 61, 62 and 63 end before the supply tube 56 and before the discharge tube 57 and extend parallel to the common axis of the supply tube 56 and the discharge tube 57.

As can be seen in particular in Fig. 3a, in the illustrated embodiment, the first and second guiding bars 61 and 62 form a pair and lie in an imaginable horizontal plane.

While the third guiding bar 63 is positioned in the center above the first and second guiding bars 61 and 62. Thus, the first and second guiding bars 61 and 62 form the two lower guiding bars and the third guiding bar 63 forms the upper guiding bar.

The lower bars, the first and the second guiding bars 61 and 62 are precisely fixed on the first brackets 64 which are fixed on the fixed part of the housing 50. The upper bar, the third guiding bar 63, on the other hand, is precisely located on the second brackets 66 which are fixed on the cover 50a. of the housing 50. The latter has the effect that, when the cover 50a is opened, the top bar, the third guiding bar 63, is taken away and thus, as shown in Fig. 3, is moved away from the bottom strips, the first and second guiding bars 61 and 62.

In the illustrated embodiment, three guide bars 61, 62 and 63 are positioned at the apex of an imaginary isosceles triangle that surrounds the common axes of feed pipe 56 and discharge pipe 57. Accordingly, feed pipe 56, a space formed by three spaced bars. the guide 61, 62 and 63 and the discharge pipe 57 constitute the transport path along which the filter plugs move in the longitudinal to axial direction.

Thus, the three guide strips 61, 62 and 63 form linear or, when viewed point-by-point cross-section, three-point support bearings.

The inside diameter of the supply pipe 56 and the discharge pipe 57 are dimensioned according to the outside diameter of the filter plugs to be applied. The same also applies to the spacing of the three guide strips 61, 62 and 63.

After passing through the supply pipe 56, the filter plugs reach the two lower strips, the first and the second guiding strips 61, 62, along which they slide along until the microwave applicator 28 exits the discharge tube 57 again. As they move along the lower strips, the first and the second guiding bars 61 and 62 an overlying top bar, the third guiding bar 63 ensures that the filter plugs cannot leave the track formed by the bottom bars, the first and second guiding bars 61 and 62. Thus, the bottom bars, the first and second guiding bars 61 and 62 serve as supports, while the upper bar, the third guiding bar 63 is intended to limit the transport path thus formed. The spacing between the three guide bars 61, 62 and 63 is chosen such that the filter plugs can only move axially in the longitudinal direction with a relatively little play, the spacing between the lower bars, the first and second guide bars 61 and 62 being smaller than the diameter of the filter plugs.

As can be seen in Fig. 3, all three guide bars 61, 62 and 63 are circular in cross-section. This results in an approximately only linear contact (support) of the filter plugs with the lower strips, the first and second guiding strips 61 and 62, and also only approximately linear contact of the filter plugs with the upper strip, the third guiding strip 63. Thus minimized there is a contact between the filter plugs and the guide strips 61, 62 and 63 and therefore the friction that arises therefrom. Moreover, the filter plugs entering through the supply pipe 56 can be arranged such that the adhesive joint does not come into contact with the guide strips 61, 62 and 63, but is positioned therebetween.

In the illustrated embodiment, no conveyor drives are provided in the microwave applicator 28 for the active transport of the filter plugs. On the contrary, the kinetic energy that the filter plugs have when entering the feed tube 56 must be sufficient for the filter plugs to slide without any difficulty through the feed tube 56, along the guide bars 61, 62 and 63 and through the discharge tube 57 up to the accelerator. 29 (fig. 1). Therefore, the feed pipe 56, the guide bars 61, 62 and 63 and the discharge pipe 57 should be made of a material with a low coefficient of friction. Moreover, due to the effect of heat, the material of the three guide bars 61, 62 and 63 should be heat-resistant, for which a ceramic material, for example, is suitable.

Claims (26)

Patent claims 1. Device for the production of rod-shaped articles from a material strand, especially in the tobacco processing industry with a wrapping device with a circular belt conveyor or a formatting conveyor for wrapping the material strand in a sheathing material, a heating device for heating the material web or objects made of it And a first transport device for transporting the web of material or rod objects made of it through the above-mentioned devices, preferably in the axially longitudinal direction, characterized in that the heating device (28) is a microwave device for heating the web or made of it of the rod-shaped items and, as viewed in the transport direction of the material web or rod-shaped items made of it, is positioned downstream of an endless belt conveyor or a formatting conveyor (22) of the wrapping apparatus (23). 2. The device according to claim The cutting device of claim 1, characterized in that in the device provided with a cutting device (27) for cutting the web of material into rod-shaped articles, the cutting device (27) is arranged between the wrapping device (23) and the heating device (28). 3. The device according to claim 1 A transport device according to claim 1 or 2, characterized in that it has a second transport device (31) for transporting rod articles, in particular in the axially transverse direction, and a second transport device (31) for transporting rod articles, in particular in the axially transverse direction, which is arranged when viewed in the direction of transport of rod objects, downstream of the heating device (28). 4. The device according to claim 1 A device according to claim 3, characterized in that the second transport device (31) is housed in a housing (40) which is surrounded by thermal insulation (40a) and / or has a device for air-conditioning the housing (40). 5. The device according to claim 1 The device of claim 1, characterized in that the heating device (28) has a guide device (60) along which the web of material or rod-shaped objects made therefrom are moved through the heating device (28). 6. The device according to claim 1 The device according to claim 5, characterized in that the guide device (60) is stationary with respect to the movement of the fabric web or rod objects made therefrom and is designed for passively guiding the fabric web or rod objects made therefrom. 7. The device according to claim 1 A material according to claim 5 or 6, characterized in that the guiding device (60) has a guiding means (61, 62, 63) in the form of a track for a sliding receiving of a web of material or rod-shaped objects made therefrom. 8. The device according to claim 1 The device as claimed in claim 7, characterized in that the guide device (60) has a lower section (61, 62) for a sliding abutment of the fabric web or rod articles made therefrom, and an upper section (63), and a spacing between the lower section (61, 62) and the upper section (63) is dimensioned according to the thickness of the material web or the rod objects made therefrom. 9. The device according to claim 1 A device according to claim 8, characterized in that the lower section forms a concave support surface in cross-section. 10. The device according to claim 1 Device according to claim 8 or 9, characterized in that the lower section has at least two spaced-apart support elements (61, 62). 11. The device according to claim 1 10. A device as claimed in claim 10, characterized in that the support elements (61, 62) provide a substantially point support or in the direction of movement of the material web or rod objects made therefrom, a line support for the material web or rod objects made therefrom. 12. The device according to claim 1, A device as claimed in claim 8, characterized in that the upper section (63) forms a substantially point contact or in the direction of movement of the material web or rod-shaped objects made of it, in line contact with the material web or rod-shaped objects made therefrom. 13. The device according to claim 1, The track guide means (61, 62, 63) as claimed in claim 7, characterized in that the track has an elongated shape. 14. The device according to claim 1 The material according to claim 10 or 13, characterized in that the support elements have slats (61, 62) which preferably extend parallel to each other in the direction of the movement of the material web or rod-shaped objects made of it. 15. The device according to claim 1, 8. The apparatus as claimed in claim 8, characterized in that the upper section (63) has at least one flap extending in the direction of the movement of the material web or rod objects made therefrom. 16. The device according to claim 1, 14. The apparatus of claim 14, characterized in that the lath or slats have a circular cross-section. 17. The device according to claim 1 The device according to claim 7, characterized in that the guide means (61, 62, 63) in the form of a track for guiding the fabric strip or rod articles made therefrom is made in the axially longitudinal direction. PL 206 123 B1 18. The device according to claim 1 The material according to claim 10 or 17, characterized in that the distance in the transverse direction of the support elements (61, 62) is smaller than the thickness or diameter of the material web of rod articles made therefrom. 19. The device according to claim 1 The method of claim 7, characterized in that the guide means (61, 62, 63) is made of a heat-resistant material, preferably a ceramic material. 20. The device according to claim 1 7. The method of claim 7, characterized in that the guide means (61, 62, 63) is made of a material with a low coefficient of friction. 21. The device according to claim 1 A guide means (61, 62, 63) is provided in the housing (50) in the heating device (28) having a housing (50) and the housing (50) has an openable portion (50a), when opening housing (50), the guide means (61, 62, 63) is exposed. 22. The device according to claim 22 21, characterized in that the opening portion is a lid (50a) of the housing (50). 23. The device according to claim 1 21 or 22, characterized in that the opening portion (50a) is pivotable about the pivot axis (53a). 24. The device according to claim 24 23, characterized in that the axis of rotation (53a) substantially extends in the direction of movement of the fabric web or rod objects made therefrom. 25. The device of claim 1 The device of claim 8, characterized in that the upper guiding means section (63) is provided on the openable portion (50a) of the housing (50). The device of claim 26 21, characterized in that it has a safety switch (54) for switching off the heating device (28, 34) when opening the housing.