Heater

Abstract

A heating device for thermal joining of plastic materials having a base body, which is penetrated by a cooling recess and on which an electrically insulating support surface is configured, on which at least one electrically conductive heat conductor is arranged, which is provided with an electrically insulating coating on a contact surface facing away from the support surface. The support surface has at least one curved or angled support surface section and that the heat conductor overlaps the curved or angled support surface section at least in parts.

Claims

1. A heating device for thermal joining of plastic materials having a base body, which is penetrated by a cooling recess and on which an electrically insulating support surface is configured, on which at least one electrically conductive heat conductor is arranged, which is provided with an electrically insulating coating on a contact surface facing away from the support surface, wherein the support surface has at least one curved or angled support surface section and wherein the heat conductor overlaps the curved or angled support surface section at least in parts.

2. The heating device according to claim 1, wherein the electrically insulating support surface is defined by a ceramic coating, which is applied to a pressing surface configured on the base body.

3. The heating device according to claim 2, wherein a wall thickness of the base body between the cooling recess and the pressing surface below the electrically insulating support surface is constant.

4. The heating device according to claim 2, wherein a first wall thickness of the base body between the cooling recess and the pressing surface below a concave support surface section is configured to be less than a second wall thickness of the base body between the cooling recess and the pressing surface below a flat or convex support surface section.

5. The heating device according to claim 2, wherein a neutral axis of the heat conductor has a spatial design that can be preset and/or wherein the pressing surface has a surface geometry corresponding to a spatial design of a neutral axis of the heat conductor.

6. The heating device according to claim 5, wherein a layer thickness of the ceramic coating, which is applied to the pressing surface, is constant.

7. The heating device according to claim 2, wherein the pressing surface is configured as flat and wherein a layer thickness of the ceramic coating, which is applied to the flat pressing surface, is configured as variable in order to create the at least one curved support surface section.

8. The heating device according to claim 1, wherein the heat conductor is configured spatially such that it extends in a spatial direction in which a cross-sectional extent of the heat conductor is minimal, between two planes aligned parallel to each other, the distance between which is greater than the cross-sectional extent in said spatial direction.

9. The heating device according to claim 1, wherein the heat conductor is configured spatially such that it extends in a spatial direction in which a cross-sectional extent of the heat conductor is maximal, between two planes aligned parallel to each other, the distance between which is greater than the cross-sectional extent in said spatial direction.

10. The heating device according to claim 1, wherein the heat conductor has different cross-sections in cross-sectional planes, which are aligned at right angles to a neutral axis of the heat conductor.

11. The heating device according to claim 5, wherein the pressing surface has a surface geometry geometrically similar to a spatial design of the neutral axis of the heat conductor.

Description

[0017] Advantageous embodiments of the invention are shown in the drawings.

[0018] FIG. 1 shows a purely schematic, cut-away front view (not to scale) of a first embodiment of a heating device,

[0019] FIG. 2 shows a top view of the heating device according to FIG. 1,

[0020] FIG. 3 shows a side view of the heating device according to FIG. 1,

[0021] FIG. 4 shows a purely schematic (not to scale), cut-away front view of a second embodiment of a heating device,

[0022] FIG. 5 shows a top view of the heating device according to FIG. 4, and

[0023] FIG. 6 shows a side view of the heating device according to FIG. 4.

[0024] A first embodiment of a heating device 2 shown in FIGS. 1 to 3 is provided for use with a pressing device (not shown) for forming a welding or sealing tool and can be employed, for example, in an electrically driven welding or sealing machine (also not shown), in particular for positively bonded, thermal joining of open end regions of plastic sleeves to plastic bags.

[0025] For this purpose, the heating device 1 comprises a base body 2, which can be configured in the form of a rectangular profile and which comprises a cooling recess 3. For illustration purposes only, provision is made that the base body 2, in cross-sectional planes, which are aligned at right angles to a profile axis 4, has the same cross-section over the entire length thereof. Furthermore, provision is made for example that cross-sections of an external geometry of the base body 2 and the cooling recess 3 are each configured as rectangular. Preferably, the base body 2 is made of metal, in particular aluminium or a ceramic material.

[0026] A ceramic coating 6 is applied to an external surface of the base body 2, also called the pressing surface 5, which is attached in a positively bonded manner to the pressing surface 5 and which is a ceramic glass layer in particular. Together with an outer side facing away from the pressing surface 5, the ceramic coating 6 defines a support surface 7, which, for illustration purposes only, is configured as a plane with two rectangular sunken recesses 8. A strip-shaped heat conductor 9 is applied to the support surface 7. The heat conductor 9 can be made from a metallic strip material, for example, which is attached to the support surface 7 in a positively bonded manner, for example by soldering, or the heat conductor 9 is applied to the support surface 7 using a suitable method from an electrically conductive amorphous material, which can contain metal particles in a thermosetting binder for example, and hardens there.

[0027] Due to the recesses 8 introduced into the plane, the support surface 7 has a plurality of, for illustration purposes only, angled support surface sections 10, which according to the illustrations in FIGS. 1 to 3, are at least partly covered by the heat conductor 9.

[0028] Thus, the heat conductor 9 has a spatial design in which a neutral axis 11 lies in the sectional plane of FIG. 1, which can therefore also be called the heat conductor plane. For illustration purposes only, the heat conductor plane is aligned at right angles to a support surface plane (not shown in detail) defined by outer edges 15, 16 of the support surface 7 and can, for example, comprise the intersecting line 18 plotted in FIG. 2 and at the same time be aligned at right angles to the representation plane of FIG. 2.

[0029] As can be seen from the illustration in FIG. 1, the neutral axis 11 presented in a schematic manner is created by a sequence of linear sections aligned at right angles to each other and, according to the illustration in FIG. 1, follows the course of the support surface 7 in a geometrically similar way. As can also be seen from FIG. 1, a wall thickness 19 between the cooling recess 3 and the pressing surface 5 is configured as constant, whereby the base body 2 has a simple design. The geometry of the support surface 7 and of the heat conductor 9 applied to the support surface 7 is defined by layer thicknesses 20, 21 of the ceramic coating 6 that are different in sections for illustration purposes only.

[0030] Furthermore, provision is made for illustration purposes only that the heat conductor 9 has the same cross-section in cross-sectional planes (not shown), which are aligned at right angles to the neutral axis 11, which does not necessarily have to be the case in other embodiments of heat conductors (not shown). In fact, the heat conductor can have varying cross-sections along the neutral axis as well as along its course.

[0031] The support surface 7 and the heat conductor 9 are covered by an insulating layer 17, which firstly guarantees electrical insulation for the heat conductor 9 and secondly, can be configured preferably as a non-stick coating or with an additional non-stick coating. Provision is made, for illustration purposes only, that the insulating layer 17 has the same layer thickness on the unspecified, flat surfaces of the support surface 7 and of the heat conductor 9, and preferably high thermal conductivity. The insulating layer 17 ends respectively at a distance from the shorter outer edge 15 of the support surface 7, whereby connecting surfaces 22, 23 of the heat conductor 9 remain free, on which a supply of electrical energy to the heat conductor 9 is made possible. For illustration purposes only, the insulating layer 17 is configured as a ceramic glass layer.

[0032] When electrical energy is supplied to both connecting surfaces 22, 23 of the heat conductor 9, an electrical current flows through the latter, which results in a heating of the heat conductor 9. The heat provided by the heat conductor 9 can be delivered through the electrically insulating layer 17 to a plastic material (not shown in detail) in order to enable local plasticisation and a welding together of several layers of the plastic material. The supply of electrical energy to the heat conductor 9 is then switched off and consequently the latter provides no further heat. In fact, heat is transferred from the plastic material (not shown) via the insulating layer 17, the heat conductor 9, the ceramic coating 6 and the base body 2 into the cooling fluid that has collected in the cooling recess 3. The plastic material can be cooled quickly as a result.

[0033] Reference signs increased by 30 respectively are used in the second embodiment of a heating device 31 shown in FIGS. 4 to 6 for those components that have the same functions as heating device 1 and a further description of said components is dispensed with.

[0034] In the illustration in FIG. 4, the cutting line follows the neutral axis 41 of the heat conductor 39, as shown in FIG. 5.

[0035] Unlike in the heating device 1, provision is made in the heating device 31 that a wall thickness 49 of the base body 32 between a cooling recess 33 and an outer surface called a pressing surface 35 is configured as variable, whereas a layer thickness 50 of the ceramic coating 36 applied to the pressing surface 35 is constant. This guarantees a particularly advantageous cooling effect by the cooling fluid collected, in particular flowing into the cooling recess 33, in the region of the recesses 38 in the support surface 37, in which particularly high energy density occurs owing to the angled course of the heat conductor 39 as well as the concave indentation caused by the recesses 38.

[0036] As can be seen from FIGS. 4 and 5, the neutral axis 41 of the heat conductor 39 runs along a three-dimensional joint path since the heat conductor 39 is angled in all three spatial directions of a Cartesian coordinate system.