Method for manufacturing a heating element

Abstract

Method for manufacturing a heating element comprising the following steps: Arranging a heating element (8) in a tube, and providing the tube with cooling fins by peeling, wherein the heating element (8) is a ceramic element, the tube is a flat tube having broad sides and narrow sides, at least one of the broad sides of the tube has a convex inner surface, and after arranging the heating element in the tube the tube is compressed, thereby reducing the thickness of the flat tube.

Description

The present invention relates to a method for producing a heating rod, wherein a heating resistor is arranged in a tube and the tube is provided with cooling fins by peeling. A corresponding heating device is disclosed in JP H07-34 392 B2, JP H03-44 896 U and DE 90 03 832 U1.Peeled cooling fins are made by peeling fins from a metal surface, such as an aluminum tube, using a sharp and precisely controlled blade tool. The tool scrapings off a small layer of material, lifts it and bends it vertically to form the lamella. This process is referred to as peeling. The production of cooling fins by peeling is described in detail in US 2001 / 0030039 A1.Heating devices having heat sinks formed by peeling have substantial advantages compared to conventional heating devices with cooling fins which are cut out of sheet metal and are plugged onto a tube, as is known, for example, from DE 203 12 313 U1.Cutting cooling fins out of sheet metal and then placing them on a heating tube is expensive. In addition, thermal conduction between the cooling fins and the tube may be impaired by oxide layers or dirt. Forming fins by peeling provides excellent thermal contact and heat transfer. In addition, it reduces the number of parts from which heaters are assembled.An object of the present invention is to show how heat conduction of a heater with peeled cooling fins can be improved.This object is achieved by a method for manufacturing a heating rod according to claim 1.According to the invention, it is provided that the cooling body is part of a housing in which the heating resistor is arranged. The housing is a tube, namely a flat tube.According to the invention, it is provided that the heating resistor is a ceramic heating resistor, for example a PTC resistor (positive temperature coefficient). Such resistors can be made on the basis of barium titanate. Since PTC resistors show a sudden increase in their electrical resistance at a critical temperature, they are inherently protected from overheating beyond a critical temperature. The tube may include a single heating resistor or may include multiple heating resistors.A ceramic resistor can be electrically contacted in the tube by means of a contact plate. A suitable contact plate may be cut from sheet metal and protrude from the tube, thereby providing an electrical connection for connecting the heater to a power source. The tube itself can be used to connect the resistor to ground. It is also possible to arrange a second contact plate in the tube and to place the heating resistor between the contact plates.A further advantageous development of the invention provides that the resistor(s) and the contact plate(s) are held by a mounting frame. This makes it possible to simplify assembly.In principle, cooling fins can be produced by peeling before or after the arrangement of the heating resistor in the tube. An advantageous further development of the invention provides that the heating resistor is arranged in the tube after it has already been provided with peeled-off lamellae, and the tube is then plastically deformed by compression. Compressing the tube improves the thermal coupling of the heating resistor(s) to the tube. The tube is preferably provided with shoulders which run along the longitudinal edges of the tube. The fins are arranged between the shoulders and are thus less wide than the tube. The tube may then be compressed by applying pressure to the shoulders.According to the invention, a flat tube is used which has at least one convex inner surface, for example a curved inner surface. The ceramic resistor is disposed in the tube such that one of the contact sides of the ceramic resistor faces the convex inner side of the tube. The contact sides of a ceramic resistor are the sides at which electrical contact is made, for example, by a contact plate. As a rule, the ceramic resistor is plate-shaped. The two main sides of such a plate-shaped resistor are generally the contact sides.When the flat tube is compressed and thereby made even flatter, the thermal contact of the tube with the ceramic resistor is improved. The convex inner surface of the tube gradually deforms during pressing and improves the thermal contact. The convex inner surface of the tube may contact the resistor when the tube is used as an electrical contact of the resistor. As a rule, however, the convex inner surface of the tube does not contact the resistor, since a contact plate and electrical insulation lie between them.Two opposing inner surfaces of the tube may be convex, i.e., bulge inwardly toward the contact surfaces of the ceramic resistor. It is also possible that only a single inner surface of the tube facing a contact side of the resistor is convex, while the other side is flat. In both cases, the height of the inner space of the tube decreases from the narrow sides of the tube toward the center because of the convex shape of the inner surface of the tube. The height of the interior of the tube is measured from one broad side carrying fins to the opposite broad side. This height is reduced when the tube is compressed.The invention is explained in more detail on the basis of an exemplary embodiment with reference to the appended drawings. FIG. 1 shows a side view of a heating device, FIG. 2 is a plan view of the heating device, FIG. 3 is a front view of the tube housing of the heating device; and FIG. 4 shows a mounting frame with a contact plate and a heating resistor of the heating device,FIGS. 1 to 3 show a heating device, more precisely the tube housing of a heating device, which is designed as a cooling body. The housing is a flat tube 1 which has cooling fins 2. The cooling fins 2 are peeled fins formed integrally with the tube 1. This means that the plates 2 were formed by peeling from a flat tube. During peeling, lamellae are scraped from the flat tube by means of a sharp and precisely controlled blade. The blade scrapings a small layer of material from the tube surface one after the other, lifts it and vertically positions it to form the blades 2. Two opposite sides of the tube are provided with fins 2. The fins 2 are arranged on broad sides of the tube 1. These broad sides are connected by narrow sides which have no lamellae. The tube 1 and the fins 2 are integral, for example made of aluminum.The fins 2 are corrugated fins and thus have a corrugated shape, as can be seen in FIG. 2. Each blade 2 has a plurality of shafts, e.g., four or more shafts, which extend from a proximal end, at which the blades 2 are connected to the tube 1, to a distal end of the blades 2. Corrugated fins are made by peeling with a corrugated blade.The flat tube 1 has two opposite broad sides, which have lamellae 2, and narrow sides, which connect the broad sides. As shown in FIG. 3, the width of the tube 1 is greater than the width of the fins 2. on both sides of the fins 2 there is a shoulder 3 against which a pressing tool can be applied to compress the tube 1 after a ceramic PTC resistor has been placed in the tube 1.In the tube 1 is a mounting frame 5 which holds a contact plate 6 and one or more ceramic resistors 8, e.g. PTC heating resistors. The mounting frame 5 is shown in FIG. 4 with only a single ceramic resistor 8. The other three compartments 9 of the mounting frame 5 are empty for the sake of simplicity, but could of course also be filled with heating resistors 8. The mounting frame 5 may be provided with lugs 10 to retain the ceramic heating resistors 8 in the compartments 9.The heating resistors 8 are electrically contacted by the contact plate 6 which projects from the tube 1 and constitutes a terminal for connection to a power source. The contact plate 6 is electrically insulated from the tube 1. A second contact plate may be arranged in the tube 1 or the tube 1 itself may be used to provide a ground connection for the heating resistors 8.The resistors 8 are plate-shaped. They are electrically contacted on their large front and rear sides, where they each face one of the two lamella-carrying broad sides of the tube 1. The front and back sides of the resistors 8 are the contact sides of the resistors.The heater can be manufactured by disposing the heating resistors 8 together with the mounting frame 5 and the contact plate 6 in the tube 1. The tube 1 is then plastically deformed by compression. In this case, the thermal contact between the heating resistors 8 and the tube 1 is improved.Both broad sides of the tube 1 have an inner surface 4 which is convex. Consequently, the inside of the tube 1 bulges toward the contact sides of the resistors 8. Thus, the height of the inner space of the tube 1 decreases from the narrow sides toward the center. The height of the interior space is measured in a direction from one of the broad sides carrying the slats to the broad side carrying the opposite slats. The inwardly curved inner surface of the broad side facilitates the compression and leads to an improved thermal coupling between the tube 1 and the resistor 8.List of reference characters1 Tube 2 Slat 3 Shoulder 4 Convex surface 5 Mounting frame 6 Contact plate 8 Resistor 9 Compartment 10 Tab

Claims

A method of manufacturing a heating rod, comprising the steps of: disposing a heating resistor (8) in a tube; and providing the tube with fins by peeling, wherein the heating resistor (8) is a ceramic resistor, the tube is a flat tube having wide sides and narrow sides, at least one of the wide sides of the tube has a convex inner surface, and after disposing the heating resistor in the tube, the tube is compressed, thereby reducing the thickness of the flat tube.

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