DE102018127305A1 - Electric heater element with an electrically operated heating element and an anode for cathodic corrosion protection - Google Patents

Abstract

The invention relates to an electric heater element (10) for use in a water reservoir, comprising a metallic fastening element (20) for attaching the electric heater element (10) to the water reservoir, an electrically operated heating element (26), an anode (12) for cathodic corrosion protection and a trimming resistance element (46), the heating element (26) being electrically contacted with the fastening element (20) and / or the water reservoir via the trimming resistance element (46), and the heating element (26) and the anode (12) in spatial proximity to one another on the fastening element ( 20) are arranged.

Description

The invention relates to an electric heater element with an electrically operated heating element and an anode for cathodic corrosion protection for use in a water tank, in particular in a water tank for hot water.

Such an electric heater element is used in practice, for example, for water storage tanks, such as storage water heaters. Storage water heaters are used to heat water for private or industrial purposes. The technical requirements for such storage water heaters are high. The systems should function properly over the longest possible service life without permanently influencing the quality of the water. They should be corrosion-resistant and, accordingly, should of course not show any leakage even after many years of operation. These requirements must be met at water temperatures up to 100 ° C, whereby the water quality can cover a wide range with regard to various parameters, such as water hardness, electrical conductivity and salinity.

Unalloyed or low-alloy steels are generally used as construction materials for water storage tanks and in particular storage water heaters. Contact with water would therefore result in the continuous supply of oxygen-containing fresh water to the corrosion processes on the DHW cylinder. To prevent or reduce such corrosion damage, enamelling of the inside of the DHW cylinder is often provided. With the proper execution of such an enamel coating, degrees of coverage of 99.9% and more are possible. However, there are always at least the slightest defects in the enamelling, so that even an enamel coating cannot provide 100 percent protection against corrosion processes. As an additional corrosion protection measure, enamelled storage water heaters are therefore generally additionally provided with a galvanic anode (sacrificial anode) or an external current anode. Such anodes are usually passed through an opening in the wall of the hot water tank and fixed in the wall. The use of these anodes serves to protect the steel construction material from cathodic corrosion in the area of enamelling defects with electrolyte contact.

By using the anode, a protective current flows from the anode to the enamelling defects (cathode), which prevents corrosion. The structural design of the storage water heater and the arrangement and number of anodes ensure that the protective current is sufficiently and as evenly distributed as possible. The anode is usually attached centrally, i.e. in the middle of the round storage water heater that is usually to be protected, so that the potential on all surfaces of the container takes on approximately the same value in order to enable a favorable protective current distribution over the storage water heater.

Due to the sometimes strongly fluctuating water temperatures with high relative temperature changes within the storage water heater, the varying pressure differences due to different water levels within the storage tank, the electrochemical processes due to cathodic corrosion protection and also the extremely high demands on the drinking water hygiene of the water from hot water storage tanks are very high , multiple requirements are placed on the materials of the heating element, the anode and the connection / sealing of the two elements with respect to the DHW cylinder.

Copper or copper alloys, such as brass, are generally used as construction materials for the heating elements of the electric heater element. Stainless steel is also used. However, the use of metal-conducting heating elements has an unfavorable influence on the distribution of the protective current over the water storage tank, since the construction of the water tank usually results in electrical contact between the anode and the heating element. If the anode is in close proximity to the heating element, the anode primarily protects the heating element instead of the imperfections in the enamel, since the heating element acts as a foreign cathode. In order to prevent this and to ensure an advantageous protective current distribution, the anode is generally mounted far away from the heating element, for example at a distance of approximately 30 to 50 cm from the heating element. The disadvantage of this is that generally two separate, spaced-apart openings must be present in the water reservoir. This means additional design effort and increases the manufacturing costs.

Based on this, it is the object of the invention to provide an electric heater element with an anode which is particularly compact and which enables effective corrosion protection of the water reservoir.

This object is achieved by the subject matter of patent claim 1. Preferred further developments can be found in the subclaims.

According to the invention, an electric heater element is therefore provided for use in a water reservoir, comprising a metallic one Fastening element for fastening the electric heater element to the water reservoir, an electrically operated heating element, an anode for cathodic corrosion protection and a balancing resistance element. It is provided that the heating element is electrically contacted with the fastening element and / or the water reservoir via the balancing resistance element and that the heating element and the anode are arranged in spatial proximity to one another on the fastening element.

It is therefore an essential aspect of the invention that the anode and the heating element are arranged together and in spatial proximity to one another on the fastening element. Surprisingly, the spatial proximity of the anode to the heating element does not result in less corrosion protection. The fastening element enables the electric heater element to be fastened to the water reservoir, in particular in a wall of the water reservoir. The tubes of the electric heater that extend into the interior of the memory are partially insulated from the fastening element via a potential equalization resistor, and the sacrificial anode is passed through the fastening element to the outside in an electrically insulated manner. Due to the spatial proximity between the anode and the heating element, the expansion of the fastening element is small. Thus, due to the small extent of the fastening element, only a small installation opening in the water reservoir is required. A large opening, which would then have to be closed, for example, with an expensive and structurally complex flange connection, can thus be dispensed with according to the invention. Furthermore, it is also not necessary for the anode and the heating element to have two separate openings in the wall of the water reservoir. The extension of the fastening element is preferably between 3 and 20 cm.

Another essential aspect of the invention is that the heating element is electrically conductively connected to the fastening element and / or the water reservoir via the balancing resistance element. Dispensing with the balancing resistance element would lead to a short circuit between the heating element and the water reservoir or fastening element. As a result, the cathode protective effect of the anode for the enamelled water reservoir would be greatly reduced. If the resistance in the balancing resistance element is correctly dimensioned, on the other hand, the heating element is partially included in the cathodic protection of the water storage tank, which prevents so-called current leakage corrosion on the copper electric heater element, for example, and on the other hand improves the cathodic protection potential on the enamelled container - because it is more cathodic. An improved wall potential of the water reservoir ensures advantageous corrosion protection, especially for water with low conductivity. Furthermore, the structure of the electric heater element reduces the protective current, which leads to an increase in the life of the anode in the case of a sacrificial anode. So that the corrosion protection for the water reservoir is also possible when the heating element is electrically contacted via the balancing resistance element with the fastening element, it is a metallic fastening element. The fastening element preferably consists of a copper alloy, such as brass. In principle, stainless steel is also possible.

An electric heater element constructed in this way is then particularly suitable for use in water storage tanks, for example in a storage water heater. The construction of the electric heater element improves the cathodic protection of the water reservoir and reduces the protective current. The construction of the electric heater element according to the invention is particularly compact and only one opening in the wall of the water reservoir, preferably a sleeve or flange, is required for mounting on the water reservoir.

The spatial proximity of the anode to the heating element is understood to mean a distance between the anode and the heating element which is in the range from a few millimeters to a few centimeters. In particular, this means a distance between 1 mm to 50 mm.

An anode in the sense of the present invention comprises any corrosion protection anodes, such as sacrificial anodes made of magnesium alloys or aluminum alloys, or extraneous current anodes, which are used for the cathodic corrosion protection of liquid-containing containers or water reservoirs, in particular of water reservoirs for heated drinking water.

An electrically operated heating element in the sense of the present invention comprises any type of heating elements, such as heating rods, heating pipes or heating coils, which are supplied with electrical energy for heating the water in the water reservoir. In addition, built-in parts that serve to regulate and control the temperature, such as a temperature probe, are also recorded.

According to a preferred development of the invention, the fastening element has a thread and can be screwed directly into the water reservoir. This makes it easy to install the electric heater element in a wall of the water reservoir. The fastening element preferably has a standardized external thread, which is used for screwing in the sanitary Heating and air conditioning technology is suitable, such as a Whitworth pipe thread. For example, the fastener has a cylindrical thread in sizes G1 to G3 Inches on. The fastening element preferably has a cylindrical thread of the size G1 ¼ inch, which corresponds to a thread diameter of approximately 41.91 mm. Both pipe threads and conical threads can be used.

According to a preferred development of the invention, the anode comprises an anode body and a contact element which is electrically conductively connected to the anode body, the contact element passing through the fastening element in an electrically insulated manner through an insulating bushing. Depending on the type of anode - external current anode or sacrificial anode - the anode body can consist of different materials. For example, the anode body for a sacrificial anode can be made of magnesium or aluminum or for an external current anode made of titanium with a mixed oxide coating. The contact element can in principle be connected to the anode body in various ways. For example, it can be provided that the contact element is connected to a core running through the anode body, for example by means of welding, soldering and / or pressing, or that the contact element is cast into the anode body.

The contact element can be designed as a metal pin, which has a thread, for example. Such a configuration of the contact element as a metal pin is particularly simple to produce and has also proven to be easy to handle during operation of the sacrificial anode. In order to ensure an advantageous distribution of protective current at the water reservoir, the contact element is passed through the fastening element in an electrically insulated manner. The insulation feedthrough is provided for this. The insulation feedthrough can be realized, for example, as an injection molded part, the sealing preferably being carried out by press fitting. Furthermore, the insulating bushing can be designed as a turned part with an external and internal thread. The external thread of the turned part can for example be an M8 thread and the internal thread an M4 thread.

Basically, an external current anode or sacrificial anode can be used as the anode. When using a sacrificial anode, it is provided according to a further development of the invention that the sacrificial anode is connected to the fastening element and / or the water reservoir in an electrically conductive manner for cathodic corrosion protection. This creates an electrical contact between the sacrificial anode and the device to be protected. The electrical connection can be made, for example, via a nut with the fastening element. Alternatively, an electrical contact to the wall of the water reservoir can also be established via an electrically conductive connection. This provides a possibility of determining the electrical potential of the anode body from outside the water reservoir, so that a conclusion can be drawn about the emitted protective current via a voltage measurement between the potential of the anode body and the potential of the water reservoir. If this falls below a predetermined value, it must be assumed that the sacrificial anode has “worn out” and must be replaced. There is also the possibility that the consumption of the sacrificial anode can be slowed down by connecting an ohmic resistor between the contact element and the fastening element or the water reservoir. Completely in accordance with the presented method of voltage measurement, the measurement of the absolute protective current between the anode and the container construction enables conclusions to be drawn about the condition of the sacrificial anode.

As an alternative to using a sacrificial anode, an external current anode can be used. When using an external current anode, it is provided according to a preferred development of the invention that the contact element for cathodic corrosion protection (titanium anode with MMO coating) is electrically conductively connected to an external voltage source. External current anodes thus permanently supply protective current. To regulate and control the protective current, external current anodes can be equipped with a potentiostat which is connected on the one hand to the water reservoir and / or the fastening element and on the other hand to the contact element (in particular Ti anode).

The insulation bushing is provided for the purpose of isolating the contact element of the anode from the fastening element. Basically, the insulation bushing can be made from any insulating polymeric material. According to a preferred development of the invention it is provided that the insulating bushing is made at least in part from cross-linked polyethylene. Furthermore, the insulation bushing can also be made exclusively from cross-linked polyethylene. The use of cross-linked polyethylene (PE-X) has several advantages. PE-X can provide both an insulating effect between the contact element and the water reservoir and a sealing effect between the annular gap of the push-through opening for the contact element in the fastening element. Material made of PE-X is characterized in particular by the fact that the material is essentially hygienically harmless in accordance with the generally recognized rules of technology, such as the approval guidelines, and is therefore Application in the field of water storage, in particular water storage for heated drinking water, is suitable.

Furthermore, PE-X has a high chemical resistance to bases and acids as well as a high electrochemical resistance to current influences. The thermal material resistance at temperatures up to 95 ° C and briefly up to 110 ° C and the thermal long-term resistance of up to approx. 20 years under the relevant operating conditions of water storage tanks, especially water storage tanks for heated drinking water, is another advantageous property of PE- X. Furthermore, PE-X can be manufactured in such a way that there is no complete electrical insulation, but that PE-X has an adjustable electrical conductivity. This provides a possibility for the insulating bushing to be used simultaneously as an ohmic resistance between the contact element of the anode and the fastening element. This reduces the protective current delivered to the sacrificial anode, thereby extending the life of the sacrificial anode.

In principle, the heating element can only comprise one heating tube. According to a preferred development of the invention, however, the heating element comprises a temperature sensor, at least one heating tube, an intermediate piece and a connecting element which is electrically conductively connected to the intermediate piece, the connecting element passing through the fastening element in an electrically insulated manner through a sealing body. The water in the water tank can be heated using the heating pipe. The temperature sensor is provided for regulating and / or checking the temperature. The heating tube and the temperature sensor preferably consist partly of copper or a copper alloy, such as brass, or of a nickel-based alloy. More preferably, they consist in part of stainless steel or enamelled non-alloy steel. The heating tube can be U-shaped or have another shape. The diameter of the heating tube is preferably between 5 and 15 mm and the length between 200 and 500 mm; However, lengths beyond this are also possible. The diameter of the temperature sensor is preferably between 5 and 15 mm and the length between 150 and 350 mm.

The heating pipe and the temperature sensor are connected to the adapter for assembly. The intermediate piece can be mounted on the fastening element via the connecting element. The connecting element can be a pin, a screw or the like. It can have an external thread for easy attachment. The connecting element can in principle be connected to the intermediate piece in various ways. One possibility is that the intermediate piece has, for example, a blind hole with a cut thread, in which the connecting element can engage. In order to ensure an advantageous protective current distribution on the water reservoir, the connecting element is passed through the fastening element in an electrically insulated manner. For this purpose, the sealing body isolates the connecting element from the fastening element and seals the annular gap between the connecting element and the fastening element. Furthermore, the sealing body can also isolate and seal the intermediate piece from the fastening element. The sealing body preferably consists of a polymeric material.

According to a preferred development of the invention, the connecting element passes through the adjustment resistance element and is electrically contacted with the fastening element and / or the water reservoir via the adjustment resistance element. The heating element is electrically conductively connected to the fastening element and / or the water reservoir for improved cathodic corrosion protection via the balancing resistance element. This can be realized in that the connecting element passes through the trimming resistance element and is electrically contacted with the fastening element and / or the water reservoir via the trimming resistance element.

In this context, it is provided according to a preferred development of the invention that the trimming resistance element is ring-shaped, has a contact surface on each of the top and bottom sides for electrical contacting, and an ohmic resistor is interposed between the contact surfaces. Due to the annular configuration, the connecting element can pass through the trimming resistance element. The electrical contact between the connecting element and the fastening element can be established through the contact surfaces. Furthermore, according to a further preferred development of the invention, it is provided that the trimming resistance element is designed as a miniaturized circuit board in SMD construction. This enables safe and production-friendly series assembly. The ohmic resistance in the balancing resistance element is preferably between 500 and 1000 ohms, so that the heating element is included in the cathodic corrosion protection. This integration of the (copper) tubular element in the cathodic protective circuit serves to prevent current leakage corrosion on the same. The resistance is more preferably 620 ohms.

In the following, the invention is explained by way of example with reference to the drawings using a preferred exemplary embodiment.

• 1 eine schematische Darstellung eines Elektroheizerelements, gemäß einer bevorzugten Ausführungsform der Erfindung,
• 2 eine weitere schematische Darstellung des Elektroheizerelements aus 1, gemäß einer bevorzugten Ausführungsform der Erfindung,
• 3 eine schematische Darstellung eines Elektroheizerelements, gemäß einer weiteren bevorzugten Ausführungsform der Erfindung und
• 4 eine schematische Darstellung eines Elektroheizerelements, gemäß einer weiteren alternativen Ausführungsform der Erfindung.

Show in the drawing

• 1 1 shows a schematic illustration of an electric heater element according to a preferred embodiment of the invention,
• 2nd a further schematic representation of the electric heater element 1 , according to a preferred embodiment of the invention,
• 3rd is a schematic representation of an electric heater element, according to a further preferred embodiment of the invention and
• 4th is a schematic representation of an electric heater element, according to a further alternative embodiment of the invention.

The 1 and 2nd show two schematic representations of a first preferred embodiment of an electric heater element according to the invention 10th . The electric heater element 10th has an anode 12th on. The anode 12th has an anode body 14 Made of magnesium, which is electrical with the contact element 16 , in the exemplary embodiment shown here, a metallic threaded pin 18th , is contacted. So that the metallic grub screw 18th no direct contact with a fastener 20th has an insulation feedthrough 22 intended. With the fastener 20th the electric heater element 10th Mount in a wall of a water storage tank. The fastener 20th is made of brass and has a thread for assembly 24th on, in the embodiment shown here, an external thread with which it can be screwed into a wall of the water reservoir. The insulation bushing 22 is designed as a turned part, consists of cross-linked polyethylene (PE-X) and has an external thread of the size M8 and an internal thread of size M4 on.

On the fastener 20th a heating element is also mounted (insulated via 34 ). The heating element 26 has a U-shaped heating tube 28 , a temperature sensor 30th and an adapter 32 on. The temperature sensor 30th and the heating pipe 28 are with the adapter 32 connected via the attachment to the fastener 20th he follows.

The intermediate piece 32 exists like the fastener 20th made of brass. As a seal and insulation between the fastener 20th and the adapter 32 is a sealing body 34 made of polymer. The fastener 20th has a central inner bore, not shown, via which a connecting element is provided from the outside 36 , here as a screw 38 executed, in a blind hole of the intermediate piece 32 can intervene. The heating element is screwed in 26 towards the sealing body 34 tightened and against the fastener 20th sealed. The sealing body also acts as an insulating body. The heating element 26 is via two electrical crimp connectors 40 energized.

The contact element is for cathodic corrosion protection 16 the anode 12th , in the simplest embodiment shown here, the metallic threaded pin 18th , about a mother 42 with the fastener 20th contacted. Alternatively, an electrically conductive connection can also be used 44 an electrical contact to the wall of the water reservoir can be made. To also the heating element 26 The connecting element must be included in the cathodic corrosion protection 36 , here the screw 38 , via a trimming resistor element 46 with the fastener 20th contacted. The trimming resistor element 46 is a miniaturized circuit board with an SMD (surfacemounted device) resistor 48 educated. So the screw 38 through the trimming resistance element 46 can reach through, is the trimming resistance element 46 ring-shaped. The board has contact surfaces on the top and bottom, the resistance value is 620 ohms.

3rd shows a sectional view of a further embodiment of the invention. In comparison to the embodiment in 1 and 2nd extend in the embodiment shown here, the sealing body 34 and the intermediate piece 32 over a larger area of the fastener 20th . The contact element breaks through accordingly 16 , in the exemplary embodiment shown here, the metallic threaded pin 18th , not just the fastener 20th , but also the intermediate piece 32 and the sealing body 34 . The insulation bushing 22 isolates the metallic grub screw 18th also from the adapter 32 and the sealing body 34 .

In 4th a sectional view of a further alternative embodiment is shown. In contrast to 3rd is the contact element 16 however, it is not designed as a threaded pin, but as a metallic pin 50 without thread. The intermediate piece is also corresponding 32 and the insulation bushing 22 customized. The intermediate piece 32 points in the area of the anode 12th an extension 52 on that of the insulation bushing 22 is enclosed. The insulation bushing 22 is designed as an injection molded part. As a seal between the extension 52 and insulation bushing 22 serves a sealing ring 54 . Between the metallic pin 50 and the insulation bushing are also two sealing rings 54 appropriate.

Reference list

10th

Electric heater element

12th

anode

14

Anode body

16

Contact element

18th

Grub screw

20th

Fastener

22

Insulation bushing

24th

thread

26

Heating element

28

Heating pipe

30th

Temperature sensor

32

Spacer

34

Sealing body

36

Fastener

38

screw

40

Crimp connection

42

mother

44

electrically conductive connection

46

Trimming resistance element

48

resistance

50

metallic pin

52

Continuation

54

Sealing ring

Claims (10)

Electric heater element (10) for use in a water reservoir, comprising a metallic fastening element (20) for fastening the electric heater element (10) to the water reservoir, an electrically operated heating element (26), an anode (12) for cathodic corrosion protection and a trimming resistance element (46), characterized in that the heating element (26) is electrically contacted with the fastening element (20) and / or the water reservoir via the balancing resistance element (46) and the heating element (26) and the anode (12) are spatially close to one another on the fastening element (20) are arranged. Electric heater element (10) after Claim 1 , characterized in that the fastening element (20) has a thread (24) and can be screwed directly into the water reservoir. Electric heater element (10) according to one of the preceding claims, characterized in that the anode (12) comprises an anode body (14) and a contact element (16) which is electrically conductively connected to the anode body (14), the contact element (16) being provided with an insulating bushing (22) passes through the fastening element (20) in an electrically insulated manner. Electric heater element (10) after Claim 3 , characterized in that the contact element (16) for cathodic corrosion protection is electrically conductively connected to the fastening element (20) and / or the water reservoir. Electric heater element (10) after Claim 3 , characterized in that the contact element (16) for cathodic corrosion protection is electrically conductively connected to an external voltage source. Electric heater element (10) after Claim 3 to 5 , characterized in that the insulating bushing (22) is at least partially made of cross-linked polyethylene. Electric heater element (10) according to one of the preceding claims, characterized in that the heating element (26) comprises a temperature sensor (30), at least one heating tube (28), an intermediate piece (32) and a connecting element (3) which is electrically conductively connected to the intermediate piece (32). 36), the connecting element (36) passing through the fastening element (20) in an electrically insulated manner through a sealing / insulating body (34). Electric heater element (10) after Claim 7 , characterized in that the connecting element (36) passes through the trimming resistance element (46) and is electrically contacted via the trimming resistance element (46) with the fastening element (20) and / or the water reservoir. Electric heater element (10) according to one of the preceding claims, characterized in that the trimming resistance element (46) is ring-shaped, has a contact surface on each of the top and bottom sides for electrical contacting, and an ohmic resistor (48) is connected between the contact surfaces. Electric heater element (10) according to one of the preceding claims, characterized in that the balancing resistance element (46) is provided as a miniaturized circuit board in SMD construction.

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