Continuous-flow heater, and a method for the manufacture of a continuous-flow heater

Abstract

A continuous-flow heater is described, with a housing made from an aluminium-based alloy, in which a flow channel for a fluid to be heated extends from an inlet to an outlet, and a heating plate which is arranged in the housing, with a substrate made from steel, which carries heating conductor tracks, a frame embedded in a wall of the housing, wherein the heating plate forms one wall of the flow channel in the housing, and is welded to the frame.

Claims

1. A continuous-flow heater, comprising: a housing made from an aluminium-based alloy; a flow channel for a fluid to be heated extending in the housing from an inlet to an outlet; a heating plate arranged in the housing and having a substrate made from steel that carries heating conductor tracks; and a frame embedded in a wall of the housing, wherein the heating plate forms a wall of the flow channel and is welded to the frame; wherein the frame is formed from a material having a coefficient of thermal expansion between the coefficient of thermal expansion of the aluminium-based alloy of the housing and the coefficient of thermal expansion of the steel of the substrate of the heating plate.

2. The continuous-flow heater according to claim 1, wherein the frame is embedded in the wall of the housing by overmolding.

3. The continuous-flow heater according to claim 1, wherein the frame is made from steel.

4. The continuous-flow heater according to claim 3, wherein the frame is made from a steel having a nickel content of at least 5% by weight.

5. The continuous-flow heater according to claim 1, wherein the frame is made from a material that has a coefficient of thermal expansion of at least 17 ppm/K.

6. The continuous-flow heater according to claim 1, wherein the frame is made from a steel that has a coefficient of thermal expansion that is less than the coefficient of thermal expansion of the aluminium-based alloy by not more than 2 ppm/K.

7. The continuous-flow heater according to claim 1, wherein the frame has apertures for positioning pins.

8. A method for the manufacture of a continuous-flow heater, the method comprising: inserting a frame into a mold, the frame having a first coefficient of thermal expansion; casting an aluminium-based alloy in the mold and thereby making the frame embedded in a housing section, the housing section having a second coefficient of thermal expansion different than the first coefficient of thermal expansion; and providing a heating plate having a steel substrate carrying heating conductor tracks and welding the heating plate to the frame, wherein the heating plate has a third coefficient of thermal expansion that is different from the first and second coefficients of thermal expansion, wherein the first coefficient of thermal expansion has a value between the second and third coefficients of thermal expansion.

9. The method according to claim 8, further comprising: engaging positioning pins in the mold with apertures in the frame during the casting process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 shows a section of the housing of an inventive continuous-flow heater; and

(3) FIG. 2 shows the housing section together with a heating plate.

DESCRIPTION

(4) The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

(5) The housing section 1 of a continuous-flow heater shown in FIG. 1 is made from an aluminium-based alloy, and has an inlet 2 and an outlet 3 for the fluid to be heated. A frame 4 is embedded in the housing section 1, which forms an inwardly projecting strip, preferably a peripheral strip. In the example shown, the frame 4 is a rectangular ring, but in the case of a different housing shape can also have a correspondingly different shape.

(6) The frame 4 is embedded in the housing section 1 by an overmolding process. During manufacture, the frame is therefore inserted into a mold, in which the housing section 1 is then formed by a casting process, for example injection molding. The frame 4 can be provided with apertures 5, with which positioning pins engage as the housing section is being cast.

(7) FIG. 2 shows the housing section 1 of FIG. 1, together with a heating plate 6 positioned on the frame 4, which forms one wall of a flow channel that leads from the inlet 2 to the outlet 3. The heating plate 6 can therefore transfer heat very efficiently to a fluid flowing through the continuous-flow heater. The heating plate 6 has a substrate made from steel, which is covered on its side facing away from the flow channel by an insulating layer, on which heating conductor tracks are arranged. The heating conductor tracks are not shown in FIG. 2. Only contact fields 7 are shown, onto which connecting wires of the heating conductor tracks can be attached, for example welded.

(8) The substrate of the heating plate 6 is welded to the frame 4, so that any sealing elements between the substrate of the heating plate 6 and the frame 4, and between the frame 4 and the housing section 1, can be dispensed with.

(9) A further housing section (not shown) can be positioned on the housing section 1, for example so that heat generated by the heating plate 6 is dissipated to a greater proportion of the fluid in the flow channel, and does not flow away unutilized.

(10) The material of the housing section 1, the frame 4 and the heating plate 6 are matched to each other with respect to their thermal expansion coefficients. Gap formation as a consequence of different thermal expansion coefficients can usually be avoided if the thermal expansion coefficient of the aluminium-based alloy of the housing section 1 is greater than or equal to the thermal expansion coefficient of the material of the frame 4. However, large differences in the thermal expansion coefficients are unfavorable, since severe mechanical stresses can then form as a result of differential thermal expansion, which in extreme cases can lead to damage. For example, it is advantageous if the frame 4 is made from a steel that has a coefficient of thermal expansion that is less than the coefficient of thermal expansion of the aluminium-based alloy, but not less by more than 2 ppm/K.

(11) Steel alloys containing 5% by weight or more of nickel and/or manganese are particularly suitable for the frame 4 and the substrate of the heating plate 6. Steel alloys with a nickel content of 10% by weight or more are even more suitable. For example, the nickel steel NiMn 20 6 (coefficient of expansion 20.0 ppm/K) can be used for the frame 4 and the aluminium-based alloy A13 (coefficient of expansion 20.4 ppm/K) for the housing section 1. The substrate of the heating plate 6 can be made from the same material as the frame 4, or from a steel with a coefficient of expansion which deviates from the coefficient of expansion of the material of the frame 4, for example by 10% or less, preferably by 5% or less.

(12) While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF REFERENCE SYMBOLS

(13) 1 Housing section 2 Inlet 3 Outlet 4 Frame 5 Apertures 6 Heating plate 7 Contact fields