EP0750444B2 - Radiant heater and method for its manufacture - Google Patents

Abstract

The method involves pressing a heat barrier film (15) in a special form as a tablet (12) of disposable heat resistant material with an essentially flat surface. The heat conductor (17) is attached to the surface with partial embedding in the heat barrier material. The tablet is placed in an empty carrier shell (23) as a one-piece heat barrier. The partial embedding is performed in the vicinity of protruding attachment feet (22) of the heat conductor. The hear conductor is placed in an insertion tool (16) and pressed into the surface of the tablet with its embedded parts.

Description

Field of application and state of the art

The invention relates to a radiant heater with a carrier shell and an insulating layer inserted therein, on which a heating element is attached.

From DE 27 29 930 A, a radiant heating unit for glass-ceramic electric cooking appliances has become known in which lie in a carrier shell one or more insulating layers of non or weakly compacted bulk material. On these layers, a plate of fibrous insulating material is laid on which are fixed by embedding in the wet state heating coils. The plate is held down by a peripheral edge. Here, the attachment of the heating element is made in an ideal way, however, a two-layer structure needed.

From DE 28 06 367 A, a radiant heater has become known in which a pourable insulating material is filled in a carrier shell and compacted with a stamp, so that a surface is formed, are stapled to the heating coils by means of wire staples. The surface does not need to be flat.

A similar structure with embedded in deep grooves heating coils has become known from EP 35 280 B, wherein a lower, thin layer of pourable insulating material is pressed directly into the carrier shell, while over a thicker layer of bonded with inorganic adhesive aluminum silicate is over, thus the Heat conductor can "stick" can.

A radiant heater according to the first part of claim 1 is known from DE-U-9 419 922.

In order to ensure a stable position of the insulating layers, the surface of the lower layer and the lower surface of the upper layer are each arched away from each other.

A multilayer insulation structure is not only expensive, but at least inferior to a single-layer structure with regard to its insulating effect, if one of the layers consists of less good heat-insulating material. Therefore, the aim is to get along as possible with a layer of highly insulating material. It is pourable insulating material, which is pressed to cohesion accordingly.

Task and solution

The object of the invention is to provide a radiant heater, which allows a simple and uniform embedding of the heat conductor with ease of manufacture and high efficiency of the insulation.

This object is achieved by a radiant heater according to claim 1. The preparation of the entire insulation of pourable high temperature resistant thermal insulation material as a prefabricated tablet allows the production in a size and shape accurately sized form, in particular it can be ensured that after the compression of the insulating material, the surface of the tablet is flat. In this flat surface, the heating element, which are received in an otherwise flat punch In grooves, from which they protrude with their mounting feet, so press that the feet are pressed equally deep into the surface and, accordingly, the protruding part always is equally wide if this is intended.

When pressing the insulating layer directly into the carrier shell, this could not be realized. The support tray made as a sheet metal plate usually had a naturally convex bottom. In addition, the insulation also bulged upwards due to radial compressive stress. If the fixing feet were pressed into this upwardly curved surface, then either the attachment in the edge region was imperfect or too deep in the middle region, so that the radiating surface of the heating conductor became too small.

You could not buckle the stamp, because the curvature of the thermal barrier coating was unpredictable and uneven and also a curved shape of the heat conductor carrying surface would mean an unacceptable increase in the height of the radiant heater.

According to an advantageous embodiment of the invention, both the production of the thermal insulation molding as well as the attachment of the heating element is preferably carried out in a separate form outside the carrier shell and inserted the thus prepared, equipped with the heating conductor one-piece tablet in the empty sheet metal plate. At the same time, a convex bottom of the tin plate does not interfere, as it creates an additional air-insulating layer. The tablet is in one piece and preferably one-layered, but could also be formed as a multilayer pressed.

A secure and tilt-free attachment is ensured by the fact that the carrier shell has in its edge region a raised relative to the bottom, annular support shoulder on which a possibly corresponding remote edge of the tablet rests.

The heating conductors may preferably be a thin corrugated band of heating conductor material which is fastened upright on the insulating body by projecting with fastening feet formed on the band which protrude at a distance from one another, but possibly also over the entire heating conductor length go through and / or can be interrupted by perforations are pressed. These are curved according to the corrugation of the band and thus form spade-shaped and shaped by its curvature fastening elements that can be pressed into the finished tablet surface.

These and other features will become apparent from the claims and from the description and drawings, wherein the individual features each alone or more in the form of sub-combinations in one embodiment of the invention and in other fields be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections as well as intermediate headings does not restrict the general validity of the statements made thereunder.

Brief description of the drawing

Fig. 1

eine Form mit einem Stempel für einen ersten Herstellungsschritt,

Fig. 2

die Form mit einem Einpreßwerkzeug für einen zweiten Herstellungsschritt,

Fig. 3

eine perspektivische Detaildarstellung eines Heizleiterband-Abschnittes und

Fig. 4

in schematischer Darstellung wie Fig. 1 und 2, den fertiggestellten Strahlungsheizkörper.

An embodiment of the invention is illustrated in the drawings and will be explained in more detail below. In the drawings show:

Fig. 1

a mold with a stamp for a first production step,

Fig. 2

the mold with a press tool for a second production step,

Fig. 3

a detailed perspective view of a Heizleiterband section and

Fig. 4

in a schematic representation as shown in FIGS. 1 and 2, the finished radiant heater.

figure description

To produce a radiant heater 11 (FIG. 4), a flowable insulating material 31 is filled into a mold 12 shown in FIGS. 1 and 2 and, if necessary, smoothed for the purpose of comparison. The shape has one of the outer shapes of the radiant heater approximately matched shape, but does not have to match exactly. Instead, the mold cavity 33 may deviate from the final shape intended for the product produced therein so that the product finally obtains the desired final shape after being compressed and taking into account all further intermediate steps.

The insulating material is a silica airgel, which is produced pyrogenically and has a dust-like consistency when not pressed. This silica airgel is usually blended with additives such as opacifiers that reduce radiation transmission, binders and / or reinforcing agents to increase mechanical strength, such as fibers. However, it is desirable and an advantage of the invention that the separate thermal insulation molding can be made fiber-free.

In the form of a ram 13 can be retracted, which compresses the loose bulk material so that a manageable tablet is formed, which is not compressed to the extent that they lose their good thermal insulation properties. Except by the design of the mold cavity can also be ensured by the design of the press ram, possibly in deviation from the planar shape of the pressing surface 14, that the resulting, hereinafter also referred to as a tablet, thermal insulation molding 15 has a flat surface.

In the same form orggf. in another form of support or on a base a Heizleiterband 17 is now partially pressed into the surface 18 of the thermal insulation molding 15 by an insertion punch 16. For this purpose, the insertion die has 16 grooves 20 in its surface 18 facing surface 19. The grooves are arranged according to the desired installation (Macroform) of the heating element, for example, spiral or meandering. They are about as wide as the heating conductor.

In the example shown, the heating conductor 17 consists of a thin strip of heating conductor material shown in greater detail in FIG. The thickness is usually only a few hundredths of a millimeter, e.g. 0.04-0.07 mm, while the height is a few millimeters. At the lower edge of the continuous band-shaped portion 21 mounting feet 22 are arranged, which are made with the tape in one piece by appropriate punching or cutting. This e.g. rectangular or trapezoidal limited mounting feet are, like the band, curved in a wave, so that the band has a transverse to its main direction corrugation. The axes of curvature of the waves are thus perpendicular to the surface 18, 19.

The Heizleiterbänder 17 are held in the grooves 20 by appropriate design and resilient system or by introduced into the insert magnets, so that the mounting feet 22 protrude out of the grooves 20 on the lower surface 19 of the insert 16. Thus, the insertion punch is pressed against the flat surface 18 of the tablet 15, and that until the mounting feet 22 have penetrated into the pre-compressed material. The surface 19 of the insertion punch limits the punch movement, which however can also be adequately intercepted by a controller. This can be done a certain Nachverpressung, but this is not absolutely necessary. Then the punch 16 is raised while the heat conductors 17 remain on the tablet 15. This can be facilitated by e.g. a holding the heating element holding solenoid is turned off.

Thereafter, this is now the Heizleiterband firmly bonded heat-insulating molding 15 removed from the mold or its holder and can, if necessary, after an intermediate storage, are inserted as a prefabricated part in a sheet-metal carrier shell 23 of a radiant heater. This sheet-metal tray has the shape of a flat shell with a relative to the bottom 24 slightly raised edge 25, to which the vertically projecting outer edge 26 connects. The tablet 15 has a base formed in accordance with this shape, namely a recessed bottom portion 27, and a contrast edge section 28 which rests on the support shoulder 25 when the tablet 15 is inserted.

Although it would be possible for the heat-insulating molding subsequent to the flat surface 18 to form an upstanding edge in the outer region, which internally insulates the outer edge 26 of the sheet metal carrier shell 23, it is preferable to use a separate annular rim 30 made of a mechanically somewhat stronger and likewise highly heat-resistant insulating material. Material, for example of ceramic fibers or vermiculite insert, which projects slightly above the sheet-metal outer edge 26 and rests with its upper side to the underside of a glass ceramic plate 29, which forms the cooking surface. This edge 30 then also serves as a backup of the heat-insulating molding in the carrier shell and prevents, for example in transport lifting. Due to the large-scale hold-down and the fact that this edge 30 acts directly on the support shoulder 25, the heat-molded part 11 is charged only by low compressive forces when the radiant heater 11 is resiliently pressed against the underside of the glass ceramic plate. In diameter, i. in the horizontal dimensions, the separate thermal insulation molding 25 may be slightly smaller than the carrier shell, so that even heat, moisture or the like. Conditional expansions do not lead to a strain of the thermal insulation molding.

The resulting radiant heater is thus characterized by a heating element carrying flat to be designed surface with uniform embedding depth of the heating element, which is independent of the shape of the carrier shell, the bottom 24 could be quite random or deliberately curved to any jump glass effects in the Prevent heating. Due to the single-layer insulation made of highly heat-insulating and high-temperature-resistant material, the insulation is very effective and inexpensive to produce. Due to the low mechanical requirements can be largely dispensed with a reinforcement by fibers.

The surface 18 of the separate heat-insulating molding 15 is flat in the sense that it corresponds exactly to the desired shape. For example, the surface could also consist of two levels offset from each other in height, e.g. Heating conductors of different heights can be used in different areas. However, the flat version of the surface 18, which runs as exactly as possible parallel to the lower edge of the glass ceramic, is preferred, the upper edges of the heating conductors then also lying in a plane lying parallel to the glass ceramic surface.

Claims (3)

1. A radiant heater (11) comprising a carrier dish (23) and a thermally insulating layer (15) inserted therein to which a heating conductor (17), in being partially embedded in the thermally insulating material of said thermally insulating layer, is secured, wherein said thermally insulating layer (15) consists of a tablet, compressed in a separate mold from said thermally insulating material, wherein said carrier dish (23) being made from sheet metal comprises in said edge portion a supporting shoulder (25) which is raised with respect to its bottom (24) on which said tablet forming said thermally insulating layer (15) is supported, where required, by a suitable offset (28) directly substantially only in its edge portion (28), whilst in the region of the bottom a spacing exists between the bottom (27) of the tablet and the bottom (24) of the carrier dish (23).
2. The radiant heater as set forth in claim 1, wherein said heating conductor (17) is a thin, corrugated strip (21) of metallic resistive material standing upright on said surface (18) of said tablet (15) which comprises fastening feet (22) curved preferably to comply with the corrugation and protruding downwards which are embedded in said thermally insulating layer (15).
3. The radiant heater as set forth in claim 1 or 2, wherein said top surface (18) of said tablet (15) and/or the top edge of said heating conductor each lie in a plane, these planes being preferably parallel to each other.

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