Method for the production of an electrically conductive resistive layer and heating and/or cooling device

Abstract

An electrically conductive resistive layer is produced by thermally spraying an electrically conductive material onto the surface of a non-conductive substrate. Initially, the material layer arising therefrom has no desired shape. The material layer is then removed in certain areas so that an electrically conductive resistive layer having said desired shape is produced.

Claims

1. A method for producing a heater, the steps comprising: applying an electrically conductive material onto a non-conductive substrate by accelerating and spraying unmolten particles of the electrically conductive material onto the non-conductive substrate at a temperature below a melting temperature of the electrically conductive material to cause micro-welding between the unmolten particles and the non-conductive substrate, wherein the electrically conductive material is applied to form an electrically conductive material layer having no desired shape; and removing a portion of the electrically conductive material layer in partially removed areas such that an electrically conductive resistive heating layer is formed having a desired shape.

2. The method according to claim 1 wherein the removing of the electrically conductive material layer is done via a laser beam, a water jet or a powder blasting process.

3. The method according to claim 1 further comprising the step of at least indirectly detecting the current value (WIST) of the electrical resistance for the electrically conductive resistive layer during the removing of the areas of the electrically conductive resistive heating layer.

4. The method according to claim 3 further comprising the step of comparing the current value (WIST) of the electrical resistance for the electrically conductive resistive heating layer with a target value (WSOLL) and removing additional area of the electrically conducting material to change the current value such that the difference between the current value (WIST) and the target value (WSOLL) is reduced.

5. The method according to claim 4 further comprising the step of simultaneously obtaining the current value (WIST) of the electrical resistance of the electrically conductive resistive heating layer and the reduction of the difference between the current value (WIST) and the target value (WSOLL).

6. The method according to claim 1 wherein the material layer is removed such that at least at one spot of the electrically conductive resistive heating layer possesses a predetermined melting spot that functions as a melting fuse.

7. The method according to claim 1 wherein the material layer is removed in such a way that the electrically conductive resistive heating layer is meander-shaped.

8. The method according to claim 1 further comprising the step of applying a non-conducting intermediate layer onto the electrically conductive resistive heating layer after the removed areas and subsequently applying another electrically conductive material layer over the non-conducted intermediate layer via thermal spraying and subsequently removing areas of the another electrically conductive material layer such that a second electrically conductive resistive heating layer is formed which has the desired shape.

9. The method according to claim 1 wherein the electrically conductive material comprises bismuth, tellurium, geranium, silicone and/or gallium arsenide.

10. The method according to claim 1 wherein the electrically conductive material is applied to fire plasma spraying, high-speed flame spraying, arc spraying, autogenously spraying, laser spraying or cold spraying.

11. The method according to claim 1 further comprising the step of sealing the electrically conductive resistive heating layer.

12. The method according to claim 11 wherein the sealing is performed via silicone, polyimide, or water glass.

13. The method according to claim 11 wherein the sealing is performed under vacuum.

14. The method according to claim 1 wherein the non-conductive substrate comprises glass.

15. A tubular flow heater comprising: a non-conductive tubular substrate; and an electrically conductive resistive heating layer applied onto the substrate, wherein the electrically conductive resistive heating layer comprises an electrically conductive material that is at first applied surrounding the tubular substrate by accelerating and spraying unmolten particles of the electrically conductive material onto the non-conductive tubular substrate at a temperature below a melting temperature of the electrically conductive material to cause micro-welding between the unmolten particles and the non-conductive tubular substrate, areas of the electrically conductive resistive heating layer being subsequently removed such that a desired shape is obtained.

16. A heating plate comprising: a non-conductive substrate; and an electrically conductive resistive heating layer applied onto the substrate, wherein the electrically conductive resistive heating layer comprises an electrically conductive material that is at first applied over the substrate by accelerating and spraying unmolten particles onto the non-conductive substrate at a temperature below a melting temperature of the electrically conductive material to cause micro-welding between the unmolten particles and the non-conductive substrate, areas of the electrically conductive resistive heating layer being subsequently removed such that a desired shape is obtained.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective layout of a tube on which an electrically conductive material is sprayed-on;

(2) FIG. 2 is the tube of FIG. 1. Its electrically conductive layer is worked-on with laser beams;

(3) FIG. 3 is a side view of the tube of FIG. 2 after completion;

(4) FIG. 4 is the top view on a plate-shaped part with a meander-shaped electrically conductive resistance layer;

(5) FIG. 5 is two diagrams. One shows the progression of time of the electrical resistance and the other shows the progression of time of the length of the electrically conductive resistance layer from FIG. 4 during manufacturing; and

(6) FIG. 6 shows a section through the plate-shaped part with 2 electrically conductive resistance layers arranged one above the other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) FIGS. 1 and 2 show the production of a tube shaped flow heater. On a high temperature resistant tube (12) with an electrically non-conductive material an electrically conductive layer is applied (FIG. 1). The application is conducted by means of a device (16) which is used to spray particles of Germanium (Ge) (18) on the tube (12). In this case, cold-gas-spray method is used.

(8) In the spraying process the unmolten particles of Germanium (Ge) are accelerated to speeds of 300-1200 m/sec and sprayed on to the tube (12). On impact the Ge-particles (18) as well as the surface of the tube get deformed. Because of the impact surface-oxides of the surface of the tube (12) get broken-up. Through micro-friction because of the impact the temperature of the contact area increases and leads to micro-welding.

(9) The acceleration of the Ge-particles (18) is done by means of a conveyor-gas whose temperature can be slightly increased. Although the Ge-powder (18) never reaches its melting temperature, the resulting temperatures on the surface of the tube (12) are relatively moderate so that for example the tube can be made from a relatively cheap plastic material.

(10) In other, not displayed construction examples, methods other than cold-gas-spraying can be used such as plasma-spraying, high-speed-flame-spraying, arc-spraying, autogenious-spraying or laser-spraying to apply the electrically conductive material to the substrate. Instead of Germanium (Ge), also Bismuth (Bi), Tellurium (Te), Silicon (Si) and/or Gallium Arsenide can be used, depending on the desired technical effect.

(11) The coating of the tube (12) with particles of Germanium (Ge) is done at first in a way that bit by bit the entire surface of the tube (12) is covered with the Germanium-layer (14) (compare FIG. 1). This material layer however does not have the desired shape yet: To be able to manufacture a tubular shaped flow heater an electrically conductive resistance layer must be produced which surrounds the tube (12) in a circumferential direction in a spiral shape. To achieve this, as can be seen in FIG. 2, a laser beam is directed to the “unshaped” material layer in a way that a spiral-shaped area (24) around the tube (12) is created in which the sprayed-on electrically conductive material (14) is not present any more.

(12) This is achieved by having the material in the material layer (14) met with the laser beam so that it heats and immediately evaporates that part of the layer (14). The laser device on one side and a—in the figure not shown—device which holds the tube (12) is one the other so that a continuing work process by the laser device (20) is possible.

(13) As can be seen from FIG. 3, an electrically conductive layer (26) is created, that stretches spirally from one axial end of the tube (12) to the other. The flow heater (28) is formed by the electrically conductive resistance layer (26) and the tube (12).

(14) In FIG. 4 a flat heat plate (28) is shown from a top view. This consists of a—in this view not visible—non conductive substrate on which, analog to the described process of FIGS. 1 and 2 at first a sheet-shaped layer of material (14) gets applied, out of which certain areas (24) are being evaporated with a laser beam (for simplicity only one area (24) was marked). Hereby a meander shaped electrically conductive resistance layer (26) was created that stretches from one end of the plate (28) to the other. This, however, has two specialties:

(15) On the upper end of FIG. 4 the material layer (14), from which the electrically conductive layer was produced, was evaporated in a way that the conductive track (26) shows a narrowed section. This creates a melting fuse (30) in such a way that the use of the heater plate (28) is protected.

(16) The second specialty is that the heating capacity or as the case may be the density of the heat flow was corrected during manufacturing that it corresponds to the desired heat capacity or as the case may be the desired heat flow to very high precision. This is achieved as follows: A voltage is applied to the ends 32 and 34 of the electrically conductive resistance layer (26) during the evaporation process so that the electrical resistance of the electrically conductive layer (26) can be measured continuously. The material layer (14) will be evaporated by the laser beam at first in only small sections (24). The horizontal layers of the evaporated areas (24) of FIG. 4 stretch only from a corner (dashed lines) (36) to the horizontal corner (38) of the electrically conductive layer (26) which lies above. (Also here because of illustration purposes only one area (24) is shown). In addition to this, the material layer (14) is processed by the laser beam in a way that the lower electrical end area (34) becomes relatively broad. This is shown with a dotted line with the mark 40.

(17) During the evaporation of the areas (24) of the material layer (14) of our present example, it is noted by measuring the resistance of the created layer (26), that the actual electrical resistance WIST (compare FIG. 5) of the electrically conductive layer is lower than the desired electrical resistance WSOLL. Shown in FIG. 4, the lower connection area (34) of the electrically conductive resistance layer (26) is processed by the laser beam in a way that his width decreases. Additional material is evaporated. Herewith the length of the electrically conductive resistance layer (26) increases with the dimension dl (compare FIGS. 4 and 5) thus increasing the electrical resistance WIST until it corresponds exactly with the desired electrical resistance WSOLL. The final position of the limiting line of the lower connection (34) is marked in FIG. 4 with the number 42.

(18) To adjust the density of the heat flow the evaporated areas (24) shown in FIG. 4 are increased. The final limitation at which the desired density of the heat flow corresponds to the desired density of the heat flow of the electrically conductive layer (26) is marked in FIG. 4 with the number 44 [for simplicity reasons only shown once in evaporated area (24)].

(19) FIG. 6 shows a plate-shaped heating device in a cross section. In contrary to the examples described above, it does not only show one electrically conductive resistance layer but two electrically conductive resistance layers (26a and 26b). Between these layers an electrically non conductive intermediate layer (46) is positioned. The manufacturing process of these electrical heating plates (28) is described as follows:

(20) At first an electrically conductive material is applied to the plate shaped substrate (12) as described above. The material is surface-applied by thermal spraying it in a way that at first the material layer does not show the desired shape in general yet. Following this process the material layer (24a) gets evaporated by laser beam in such a way that an electrically conductive resistance layer (26a) is created which does show the desired shape.

(21) On top of the finished electrically conductive resistance layer 26a an electrically isolating intermediate layer (46) gets applied in a following work step. Then the procedure described above gets repeated which means that, again, electrically conductive material is surface-applied by thermal spraying on top of the non conductive intermediate layer (46) in a way that the so created second material layer does not show the desired shape yet. This layer is then processed by a laser beam in certain areas (24b) in such a way that a second electrically conductive resistance layer (26b) is created which does show the desired shape.

(22) The material in a non shown example was chosen in a way that—instead of an electrical heating layer—an electrical cooling layer is created.

(23) In another not illustrated example, the temperature of the heating layer is controlled by a ceramic switch. In this case, it is understood to mean a non mechanical switch, which consists of an element, whose conductivity is highly dependent on its temperature. Alternatively, a bimetal switch can be used as well.