DE102014108553B4 - Serving tray heating pad, serving tray with a serving tray heating pad and method for controlling the temperature of a serving tray - Google Patents

Abstract

A serving tray heating insert in which a) the heating insert (7) consists of a nonwoven with heat conductors fixed to a heating conductor structure, b) the heating conductors consist of several filaments (1, 1 ') twisted into a stranded wire (2), c) the stranded wire (2) is provided with a thermally conductive plastic sheath (5) and d) the filaments (1, 1 ') of the two ends of the strand (2) are connectable to energizable contacts on the outer edge of a serving tray, characterized in that e) at least one filament (3) of the stranded wire (2) is provided with an electrically insulating and thermally conductive coating (4) and f) the at least one electrically insulated filament (3) of the stranded wire (2) is suitable when the electrically non-insulated filaments are energized (1, 1 ') of the stranded wire (2) to be miterwärmt over its entire length and thereby to change its ohmic resistance such that the resistance change is used as a temperature control signal and g) the at least one e dielectrically isolated filaments (3) and the non-insulated filaments (1, 1 ') of the stranded wire (2) at the ends of the stranded wire (2) are combined into separate groups and can each be connected to different contacts on the outer edge of the serving tray.

Description

The invention relates to a serving tray heating pad with electrical contacts on the outer edge of the tray, a serving tray with the heating pad and a method for controlling the temperature of a serving tray.

Serving trays are known in different embodiments. In particular, serving trays made of laminated pressed plastic films are known. They usually consist of several superimposed flow-compressed SMC films (SMC = Sheet Molding Compound) in a layer thickness of 2.8 to 3.2 mm. The material can be processed with a low reaction shrinkage and is dimensionally stable even with larger local temperature differences.

From the publication DE 101 19 104 A1 It is known to arrange on the tray as a heating means an electric heating plate. Such a heating plate must be inserted into a corresponding recess in the tray surface. Due to thermal stresses, cracks can occur at the transition edges.

It is also known to incorporate a heating pad into such serving trays to heat food trays placed on the tray. From the utility model application DE 20 2013 011 699 U1 is a serving tray with a continuous flat footprint is known, in which at least one localized, is integrated as a heating element electrically heatable heating zone over a heating element, wherein the heating conductors are connected to electrical contacts on the outer edge of the tray. The heating zones can be shown in different surface shapes. In the heating zones and temperature sensors for controlling the supplied heating energy can be integrated.

From the publication DE 42 31 341 A1 is known a serving tray, which consists of an upper and a lower impact-resistant plastic shell, the space is filled with a plastic foam. In the upper plastic shell receptacles for food dishes are incorporated, the recordings are provided with electrical contact surfaces for the transmission of electrical heating energy in specially trained food harnesses.

From the publication US Pat. No. 6,521,873 B1 is a heating pad for a blanket with electrical contacts on the outer edge known. The heating pad consists of a graphite fiber bundle, which is provided with a thermally conductive plastic sheath and fixed on a flexible, fiber-based layer by means of a thread in the form of a Heizleiterstruktur.

From the publication US 2011/0 278 280 A1 is known a warming system for food. In a bottom plate of the keep warm system, an electrical heating element is integrated, the ends of which are connected to electrical contacts on the edge of the warming system. The heating conductor consists of an electrically conductive, twisted fiber bundle which is mounted on a nonwoven material and pressed into the bottom plate.

From the pamphlets US 5 093 556 A and DE 27 58 805 A1 are known devices for heating food, which are arranged in containers on a serving tray. The serving trays have a foam insulation in their interior to prevent heat loss.

From the publication DE 10 2004 011 514 A1 For example, an electric heating element is known which has a thread with a plurality of electrical conductors. The electrical conductors consist of a thread-like core made of plastic, which is surrounded by a metal envelope. Several such conductors can be twisted into a thread.

From the publication DE 10 2006 017 732 A1 is a conductive fabric known for use in motor vehicles. The electrically or optically conductive filaments of the fabric may be suitable as a heating conductor, as a temperature sensor, as a pressure detection sensor or as an antenna.

From the publication WO 2007/099 019 A1 is known a heating conductor for textiles, which consists of a number of electrically mutually insulated filaments. The individual filaments are provided with a glass coating for electrical insulation. In the filament bundle also non-isolated filaments may be inserted. The filaments of the bundle may be twisted or aligned parallel to one another and combined by an outer envelope.

The invention has for its object to provide a serving tray heating pad, which can be integrated into different constructions of serving trays, without generating local stress cracks and distortions in the tray surface. The heating pad should be easily adaptable to different heating zone shapes and heating powers and be controllable via a temperature measurement in the temperature.

This object is achieved according to the invention in a serving tray heat insert of the type mentioned by the characterizing features of claim 1. Advantageous embodiments will become apparent from the features of the dependent claims 2 to 21. The object is further with a A serving tray according to claim 22 and a serving tray according to claim 26. Special Serviertablettausfaltungen arise from the features of claims 23 to 25. A method for temperature control is specified in claim 27.

By fixing the heating conductors on a nonwoven fabric, in particular by sewing, a flat heating pad is created, which can be glued to the underside of a serving tray shell or inserted as an intermediate layer during the compression of SMC plastic films in this. The heat conductors are advantageously made of several filaments twisted into a strand. Thin filaments or conductive fibers are referred to as filaments which give the strand a high degree of flexibility so that they can be fixed in the form of different heating conductor structures on the nonwoven. The ends of the heating conductors can be brought to prepared contacts on the outer edge of the tray and connected to them.

The nonwoven with the heating conductors can be made as an intermediate layer on a serving tray pressed from SMC films to a thickness that can be completely enclosed by the covering material layers of the tray during pressing in the SMC material.

To produce a larger cross-section of the heating conductor several strands can be twisted into a total strand. A heating pad with this heating conductor configuration is particularly suitable for fixing to the underside of a serving tray shell, which is subsequently foamed.

In order not to press the cross section of the heating conductor strand during compression or foaming, it is expedient that the strand is provided with an enveloping coating for stabilizing the cross section. For this coating, a material must be chosen which, on the one hand, enables mechanical and thermal stability and, on the other hand, good heat transfer, such as e.g. PP / PU / PE / PTF plastics.

The filaments forming the strand are preferably twisted together, so that the mutual twist of the filaments is maintained even at open ends of the strand. Remaining interstices between the twisted filaments are preferably filled with an electrically conductive powder, such as carbon or graphite. The already mentioned enveloping coating of the strand is expediently applied after the introduction of the powder in order to additionally avoid falling out of the powder during processing of the strand. The sheathed stranded wire with inclusion of the powder forms a uniform cross-section for power conduction and heating of the filaments.

Advantageously, at least one filament with an electrically insulating sheath is inserted into the strand and twisted with the remaining filaments. The electrical insulation should have a good thermal conductivity. The filaments with electrical insulation can also be provided as a core of a strand around which the strand is twisted with the remaining filaments.

The electrically insulated and uninsulated filaments of the strand are grouped together at the ends of the strand and connected to separate contacts on the outer edge of the tray. The filaments of the strand, which are not electrically insulated against each other, are energized and heat up. They form the actual heating conductor. The electrically isolated filaments of the strand are miterwärmt over its entire length and thereby change their ohmic resistance. The resistance change can be measured at the respective contacts and used as a temperature control signal.

The at least one electrically insulated filament for temperature measurement can also be wound on the outside of the envelope of the heating conductor strand. For this purpose, it is advantageously applied to the Verzwirnungsrichtung opposite winding direction to bridge unevenness in the cross section of the pure heat conductor strand can.

The filaments of the strand can be formed by carbon fibers, but are preferably essentially made of a silver-copper alloy or a stainless steel-copper alloy into which dopants can be introduced to improve the heating power. It is also possible to twist filaments of different material together. The individual filaments of the strand preferably have a diameter of 5 to 120 μm. From the thinner filaments are preferably prepared strands with up to 250 individual filaments, from the thicker wires strands with up to 70 individual filaments. Strands of a number of thinner individual filaments are used in particular for covering heating zone structures of smaller diameter and strands made of a number of thicker individual filaments for covering heating zone structures of larger diameter.

The number and diameters of the individual filaments in a heat conductor strand affect the geometry of the laying structure of the strand on the nonwoven. It is preferable to provide a distance of 3 to 4.5 mm between the heating conductor strands.

Preferably, the laying structure of the heating conductor strands is meandering in a circular area. But there are also rectangular and triangular surface shapes possible. In the case of a meander-shaped laying, a crossing-free return of the heating conductor strand from the formed heating zone structure is possible, in particular also in the case of concentric heating zone structures which can be controlled separately.

In a meandering laying structure, the heating conductors are at certain points in due to a small bending radius parallel to the leading heating conductor at this. To produce a small bending radius, the heating conductor must have sufficient flexibility, which is influenced by the number and thickness of the individual filaments in the strand.

In contrast, a spiral laying structure of the heating conductor strand on the nonwoven has advantages. However, the inside of the spiral lying end of the strand must be embedded through the web through in a further intermediate layer in which the safe return to the contacts can be done without contacting with the Heizzonen structure forming heat conductors.

As the nonwoven preferably a fiberglass mesh fabric is used, which can be stored well in another glass fiber reinforced material by compression or foaming. However, it is also possible to use a non-woven of a natural fiber, e.g. Flax, to use. The upper or lower side of the non-woven fabric equipped with the heating conductor can be provided with an adhesive layer, by means of which an immediate localization on the underside of a suitable serving tray shell is possible. It has also been found that subsequent foaming or filling of a cavity by swelling under the e.g. glued nonwoven the mutual position of the heating conductors to each other on the non-woven changed.

In order to secure the heating pad against overheating, it is advantageous to have a thermal overload switch on the nonwoven fabric in an edge region of the structure pattern formed by the heating conductor, e.g. Bimetal switch, to fix and insert as a breaker switch for the energization of the heating element in the heating conductor.

In addition, a thermocouple, whose signal lines can be connected to separate contacts on the outer edge of the tray, can be fixed on the nonwoven within the structure pattern formed by the heating conductors. However, a disadvantage is the only locally measured temperature as a controlled variable for the heating element.

As already mentioned, the particular structure of the heating pad allows its use in different serving tray constructions, with necessary modifications e.g. in the choice of material for the tray are possible in a simple manner. In particular, in direct contact of the heating pad with the underside of a tray tray is to pay attention to the temperature resistance of the material of the tray to avoid distortions of the footprint of the serving tray.

Additional heat insulation of the tray to the bottom of the tray may be achieved by incorporating a heat insulating additive, e.g. fine glass beads, are reached in the lower tray layers and does not hinder the function of the heating pad.

In the drawing, an embodiment of the serving tray heating pad is shown schematically and will be described with reference to the figures. Show

1 a twisted strand,

2 a total strand braided from several strands,

3 a heat insert in a circular meander structure and

4 a heating pad with electrical safety elements.

1 shows one of several filaments 1 twisted strand 2 a heating conductor. One of the filaments 1' is led out of the twist. The individual filaments 1 . 1' are twisted together without mutual insulation and may consist of the same or different materials.

In the strand 2 is a filament 3 as a soul inserted around the other filaments 1 . 1' are twisted. The filament 3 is with an electrically insulating, thermally conductive coating 4 Mistake. The filament 3 serves as a temperature sensor. Instead of as a core, it can also be applied to the circumference of the strand, preferably in the opposite direction to the twisting direction 2 be placed. The filaments 1 . 1' can from the filament 3 separated into a common end. The group of filaments 1 . 1' and the filament 3 are connectable to different contacts on the outer edge of a serving tray, not shown.

The strand 2 is with an outer cladding 5 provided, which is shown only over part of the circumference. Into the spaces between the twisted filaments 1 . 1' For example, an electrically conductive powder (not further shown) may be incorporated as filler through the enclosure 5 falling out of the strand 2 is prevented. The powder supports the power line in the overall cross section of the mutually non-isolated filaments 1 . 1' , The serving 5 also serves the mechanical strength of the strand 2 against deformation of the cross section when an external pressure is applied to the strand 2 ,

2 shows one of several strands 2 . 2 ' twisted total strand 6 , In the strands 2 . 2 ' are each isolated filaments 3 inserted. The total strand 6 is also with a wrapper 5 provided, which serves the same purpose as for 1 described.

3 shows a heating pad 7 with heating conductor strands 2 . 6 which are sewn on an unrecognizable fleece or otherwise fixed in a meandering structure. Shown is a circular area occupancy, due to the meandering arrangement of the strands 2 . 6 the end of a strand 2 . 6 without crossing radially from the interior of the heating pad 7 led out. The strands 2 . 6 are fixed substantially parallel to each other and due to their flexibility with a relatively small radius each recirculated bent, so that there is an unoccupied radial surface area, which is responsible for the return of the strand 2 . 6 or other lines is usable.

4 shows a heating pad 7 with inserted security elements. In the supply line of the heating conductor strand 2 . 6 is a bimetal switch as overload protection 8th inserted, which is closed in normal operation and jumps in case of overheating.

In the area of the heat insert 7 is additionally a thermocouple 9 with additional signal lines 10 inserted, which isolated from the leading out of the interior of the heating insert Heizleiter strand 2 . 6 are laid.

LIST OF REFERENCE NUMBERS

1, 1 '

 filament

2, 2 '

 Heating conductor strand

3

 isolated filament

4

 coating

5

 wrapping

6

 Total strand

7

 heating insert

8th

 Bimetallic switch

9

 thermocouple

10

 signal line

Claims (27)

Serving tray heating pad in which a) the heating pad ( 7 ) consists of a nonwoven with thereon to a Heizleitererstruktur fixed heating conductors, b) the heating conductors of several to a strand ( 2 ) twisted filaments ( 1 . 1' ), c) the stranded wire ( 2 ) with a thermally conductive plastic sheath ( 5 ) and d) the filaments ( 1 . 1' ) of the two ends of the strand ( 2 ) are connectable to energizable contacts on the outer edge of a serving tray, characterized in that e) at least one filament ( 3 ) of the stranded wire ( 2 ) with an electrically insulating and thermally conductive coating ( 4 ) and f) the at least one electrically isolated filament ( 3 ) of the stranded wire ( 2 ) is suitable, when energizing the electrically non-insulated filaments ( 1 . 1' ) of the stranded wire ( 2 ) to be miterwärmt over its entire length and thereby to change its ohmic resistance such that the resistance change is used as a temperature control signal and g) the at least one electrically isolated filaments ( 3 ) and the non-isolated filaments ( 1 . 1' ) of the stranded wire ( 2 ) at the ends of the strand ( 2 ) are combined into separate groups and each connectable to different contacts on the outer edge of the serving tray. A serving tray heating pad according to claim 1, characterized in that a plurality of strands ( 2 ) to a total strand ( 6 ) are twisted. A serving tray heating pad according to claim 1 or 2, characterized in that the filament ( 3 ) with electrical insulation as a core in the strand ( 2 ) is arranged around which the strand ( 2 ) is twisted. A serving tray heating pad according to claim 1 or 2, characterized in that the filament ( 3 ) with electrical insulation to the twisting direction of the strand ( 2 ) opposite winding direction on the strand ( 2 ) is arranged. A serving tray heating pad according to claim 1, characterized in that the intermediate spaces of the strand ( 2 ) forming filaments ( 1 . 1' ) within the envelope ( 5 ) are filled with an electrically conductive powder. Serving tray heating pad according to claim 1, characterized in that the fleece is provided on its underside with an adhesive layer. Serving tray heating insert according to claim 1, characterized in that the nonwoven fabric is provided with an adhesive layer covering the heating conductor structure. A serving tray heating pad according to claim 1, characterized in that the filaments ( 1 . 1' ) of the stranded wire ( 2 ) consist of a carbon fiber. A serving tray heating pad according to claim 1, characterized in that the filaments ( 1 . 1' ) of the stranded wire ( 2 ) consist of a silver-copper alloy. A serving tray heating pad according to claim 1, characterized in that the filaments ( 1 . 1' ) of the stranded wire ( 2 ) consist of a stainless steel copper alloy. A serving tray heating pad according to any one of claims 8 to 10, characterized in that the stranded wire ( 2 ) of a mixture of filaments ( 1 . 1' ) of different materials is twisted. Serving tray heating pad according to claim 1, characterized in that the nonwoven consists of a glass fiber mesh. A serving tray heating pad according to claim 1, characterized in that the nonwoven fabric consists of a natural fabric. Serving tray heating pad according to claim 1, characterized in that the heating conductors form a meandering structure pattern on the nonwoven, wherein the heating conductors are fixed without crossing on the nonwoven. Serving tray heating pad according to claim 1, characterized in that the heating conductors are fixed with a distance between 3 and 4.5 mm from each other on the fleece. A serving tray heating pad according to claim 1, characterized in that the filaments ( 1 . 1' ) of the stranded wire ( 2 ) have a diameter of 5 to 120 microns. A serving tray heating pad according to claim 1, characterized in that the stranded wire ( 2 ) consists of up to 250 filaments with a diameter of 5 to 50 microns. A serving tray heating pad according to claim 1, characterized in that the stranded wire ( 2 ) consists of up to 70 filaments with a diameter of 50 to 120 microns. Serving tray heating pad according to one of the preceding claims, characterized in that at least two heating conductors are arranged on the nonwoven to separate structural patterns arranged concentrically to each other. A serving tray heating pad according to any one of the preceding claims, characterized in that on the nonwoven in a peripheral region of the structure pattern formed by the heating conductors, a thermal overload switch ( 8th ) is fixed and inserted as a breaker switch in the heating conductor. A serving tray heating pad according to any one of the preceding claims, characterized in that on the nonwoven within the pattern formed by the heat conductors, a thermocouple ( 9 ) whose signal lines ( 10 ) are connectable to separate contacts on the outer edge of the tray. A serving tray of layered pressed plastic comprising a serving tray heating pad according to any one of claims 1 to 21, wherein the nonwoven is pressed with the heating conductors as an intermediate layer in the interior of the serving surface of the tray. Serving tray according to claim 22, characterized in that the heating pad is connected under pressure and heat to above and below the heating layer arranged material layers of the tray with the material of the tray, so that the heating conductors extend within the serving surface of the tray. Serving tray according to claim 22, characterized in that the heating conductors form a spiral pattern on the nonwoven fabric, wherein the inside of the spiral end of the heating conductor is passed through the nonwoven and a material layer lying below the nonwoven material of the tray and separated by this material layer the heat conductor Spiral crossing in the serving area runs. Serving tray according to claim 22, characterized in that a lying in the use position under the heating layer material layer of the tray is provided with a heat-insulating additive. Serving tray of two plastic trays and interposed foam insulation comprising a serving tray heating pad according to one of claims 1 to 21, wherein the heating pad attached to the underside of serving as a serving surface plastic shell and the foam insulation between the plastic shells is introduced. A method of controlling the temperature of a serving tray with a serving tray heating pad according to any one of claims 1 to 21 comprising the steps of: a) energizing the filaments not isolated from each other ( 1 . 1' ) of the stranded wire ( 2 ), wherein the electrically isolated filaments ( 3 ) of the stranded wire ( 2 ) be mitwärwärt over its entire length and thereby change their resistance, b) measuring the change in resistance at the respective contacts and c) Use of the resistance change as a temperature control signal.

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