EP3993562A1 - Heating cartridge with ceramic casting compound - Google Patents

Abstract

A heating cartridge is described with a ceramic core (11), a heating wire which surrounds the ceramic core (11) as a heating coil (12), and a metal sleeve (13) in which the ceramic core (11) and the heating coil (12) are arranged, wherein the heating coil (12) is embedded in a ceramic casting compound which fills a gap between the ceramic core (11) and the inside of the metal sleeve (13).

Description

The invention relates to a heating cartridge, in particular for heating a spray nozzle. Such heating cartridges contain a heating wire which is arranged as a heating coil in a metal sleeve.

Out of DE 20 2007 010 865 A1 a heating cartridge is known which has a continuous central fitting bore for receiving a plastic injection nozzle. This cartridge heater has an annular interior that is enclosed by a metal jacket. A heating coil, which is wound onto a ceramic winding body, is embedded in ceramic powder in this interior space. The metal jacket is assembled from two parts, between which there is a gap enclosed by an annular wall. All parts are compressed together by radial pressing. The annular wall forms a bead on the outer metal jacket, from which the connections of the heating coil are led out and which is filled with casting compound or insulating granules.

Cartridge heaters for spray nozzles and other applications must be compact and enable high heat outputs, which requires good thermal coupling of the heating coil to the surrounding metal sleeve. The interior of the metal sleeve is therefore usually filled with ceramic powder such as magnesium oxide and the metal sleeve is then plastically deformed, with the ceramic powder being compacted. After the metal sleeve has been plastically deformed and recompacted, the outside of the metal sleeve often has to be reworked, in particular ground down. In addition, not all metal sleeves are suitable for this procedure. Thus, the metal sleeve may have a shape, material, thickness, or coating unsuitable for compaction. In addition, the process is very complex.

It is the object of the present invention to show a way in which a heating cartridge that enables a high power density can be created with less effort.

This object is achieved by a heating cartridge with the features specified in the claim. Advantageous developments of the invention are the subject of subclaims.

In a heating cartridge according to the invention, the metal sleeve in which the heating coil is arranged is filled with ceramic casting compound. A space between a ceramic core, which surrounds the heating coil, and the inside of the metal sleeve is therefore filled with ceramic casting compound. Since a ceramic casting compound is filled into the metal sleeve as a liquid, post-compacting by plastic deformation of the metal sleeve can be dispensed with. Post-processing of the outside of the metal sleeve is therefore not necessary.

Since plastic deformation of the metal sleeve is no longer necessary with a ceramic casting compound, there is no risk of damage to components inside the heating cartridge. The heating coil can therefore easily be wound around a ceramic core containing one or more channels contains, in which, for example, a lead of the heating coil is arranged. It is also possible to initially insert the heating coil into the metal sleeve without a core and then to fill the interior of the metal sleeve with ceramic casting compound. In this way, the ceramic casting compound then forms a ceramic core, which the heating coil surrounds and also fills the space between the core and the inside of the metal sleeve. The ceramic core is preferably designed in one piece, for example through the casting compound or as a separate component. However, individual segments such as discs that are joined together are also conceivable.

Furthermore, a temperature sensor can be arranged directly in the potting compound, which conducts heat very well, since no mechanical pressure is exerted on it. A protective housing can therefore be dispensed with. A very precise temperature measurement can advantageously take place in this way. The temperature sensor is preferably arranged between a bottom of the metal sleeve and the ceramic core in order to measure the temperature directly at the spray opening. Its connections can be routed together in one or separately in two channels of the ceramic core. However, it is also possible to arrange at least one temperature sensor itself in a channel, in particular in the center of a channel, of the ceramic core. In an advantageous embodiment, the heating cartridge also has several temperature sensors, e.g. to record both the temperature at the spray nozzle and inside the ceramic core.

In addition, the metal sleeve can have a helical flow channel on its outside. Flow channels can extend around the metal sleeve like a thread and—if the heating cartridge is inserted into a spray nozzle—specify the flow path of a liquid to be heated, so that heat generated by the heating cartridge is absorbed well. Alternatively, a metal helix can also be arranged on the outside of the metal sleeve. Together with the outside of the metal sleeve and the inside of a housing of the spray nozzle, this can also specify a helical flow path for a liquid to be heated. If a flow channel is present, this can be located, for example, in a cylindrical portion of the metal sleeve.

Such a flow channel can be formed by one or more grooves on the outside of the metal sleeve. Grooves can also be provided on the outside of the metal sleeve in order to increase the surface area and thus improve heat dissipation. For this purpose, grooves can be provided which run in the longitudinal direction of the metal sleeve and whose side walls are designed as ribs.

The ceramic casting compound preferably contains aluminum oxide, magnesium oxide or aluminum nitride as a component, in particular as a main component. The casting compound can contain a binder, for example silicone resin, as a further component. Water-soluble silicone resins are preferred as binders. Using a binder increases moisture resistance. The casting compound can advantageously be mixed with water before use. After casting the metal sleeve, the casting compound can be dried and hardened by the action of temperature.

Potting compounds are preferably used which have a thermal conductivity of at least 15 W/mK, preferably at least 30 W/mK. Casting compounds with a viscosity of at least 11000 mPas, in particular at least 15000 mPas, are also preferred. In addition, the potting compound advantageously has a volume resistance of at least 10 ⁹ ohms/cm at room temperature, preferably at least 10 ¹³ ohms/cm at room temperature, in order to ensure electrical safety. A value of at least 5 · 10 ^-6 /K is advantageous as the coefficient of thermal expansion in order to prevent the formation of a gap on the inner wall of the metal sleeve.

An advantageous development of the invention provides that a spacer, preferably made of ceramic, is arranged between the heating coil and the inside of the metal sleeve. The spacer can, for example, be ring-shaped or sleeve-shaped. However, partial ring-shaped spacers are preferred, that is to say spacers which only bear against part of the circumference of the heating coil. Several partially ring-shaped spacers, which are in contact with different circumferential sections of the heating coil, can together center the heating coil in a coil area.

Advantageously, the spacers can have a projection pointing radially inward, which sits between adjacent turns of the heating coil, for example is clamped there. Depending on the length of the heating coil, the number of spacers can be varied, for example two, three or more spacer areas can be provided in which two or more spacers each lie against a peripheral section of the heating coil. Spacers are particularly advantageous if the heating coil is initially inserted into the metal sleeve without a core and the interior of the metal sleeve is then filled with ceramic casting compound in order to form the core. A spacer or a plurality of spacers can stabilize the heating coil when the casting compound is poured in. The axial extent of the spacers is preferably one to two times the coil pitch, ie the distance from one turn of the heating coil to the adjacent turn, measured from wire center to wire center.

• Fig. 1 eine Sprühdüse mit einer Heizpatrone in einer Schnittansicht;
• Fig. 2 die Heizpatrone von Fig. 1;
• Fig. 3 eine Schrägansicht auf das untere Ende der verbauten Heizwendel; und
• Fig. 4 eine Schrägansicht auf das obere Ende der Heizpatrone;
• Fig. 5 ein weiteres Ausführungsbeispiel einer Heizpatrone in einer Schnittansicht;
• Fig. 6 vergrößerte Teilansicht zu Fig. 5;
• Fig. 7 vergrößerte Abstandshalter aus Fig. 5;
• Fig. 8 ein weiteres Ausführungsbeispiel einer Heizpatrone; und
• Fig. 9 eine Schnittansicht zu Fig. 8.

Further details and advantages of the invention are explained using exemplary embodiments with reference to the accompanying drawings. Components that are the same and that correspond to one another are denoted by the same reference numbers. Show it:

• 1 a spray nozzle with a heating cartridge in a sectional view;
• 2 the cartridge heater from 1 ;
• 3 an oblique view of the lower end of the installed heating coil; and
• 4 an oblique view of the upper end of the heating cartridge;
• figure 5 another embodiment of a heating cartridge in a sectional view;
• 6 enlarged partial view figure 5 ;
• 7 enlarged spacers figure 5 ;
• 8 another embodiment of a heating cartridge; and
• 9 a sectional view 8 .

In the 1 The spray nozzle shown can be used, for example, to heat or vaporize reducing agent before it is introduced into the exhaust system of a motor vehicle. The spray nozzle has a housing 1 with a spray opening 2, a connection 3 for the electrical lines and a connection 4 for liquid. In the housing 1, a heating cartridge 10 is arranged in the Figures 2 to 4 is shown and explained in more detail below.

The heating cartridge 10 has a ceramic core 11, a heating coil 12 consisting of one or more heating wires which is wound around the ceramic core 11, and a metal sleeve 13 in which the ceramic core 11 and the heating coil 12 are arranged. The interior of the metal sleeve 13 is cast with a ceramic casting compound. The space between the heating coil 12 and the inside of the metal sleeve 13 is therefore filled with ceramic casting compound, preferably over the entire length of the heating coil 12, so that good thermal coupling of the heating coil 12 to the metal sleeve 13 results.

The ceramic casting compound is filled into the metal sleeve 13 as a pasty liquid and consists predominantly of aluminum oxide, magnesium oxide or aluminum nitride. In addition, the ceramic casting compound can also contain silicon oxide and, in particular when it is filled in, also water and/or a binder, for example a silicone resin. Both water-insoluble and water-soluble silicone resins are suitable. After filling, the ceramic casting compound is dried and hardened by heat treatment. Any binder initially present can burn in the process.

The ceramic core 11 contains a plurality of channels 6. A connection section 14 of the heating wire, which also forms the heating coil 12, runs in one of these channels 6. Connecting lines 9 of a temperature sensor 15, which is arranged between a base 16 of the metal sleeve 13 and the ceramic core 11, run in two other channels 6. The temperature sensor 15 can, for example, be an electrical resistor, such as an NTC resistor. However, the connecting lines 9 can also be combined in a common channel 6 run. The ceramic core 11 can contain one or more additional channels 6 in which no lines run. These additional channels 6 are filled with ceramic casting compound, but they can also be empty. The ceramic core 11 can consist of ceramic disks stacked on top of one another.

The metal sleeve 13 has a cylindrical section with an external thread. In this way, a helical flow channel 17 is formed on the outside of the metal sleeve 13 . A helical flow channel ensures that the liquid to be heated in the spray nozzle is guided along a helical path along the heating cartridge 10 and can therefore easily absorb heat from the heating cartridge 10 .

The end of the heating coil 12 facing the bottom 16 of the metal sleeve 13 is surrounded by a ceramic ring or a ceramic sleeve 18 . In particular, if the bottom 16 of the metal sleeve 13, as in the embodiment shown, has a conical shape or forms a dome and thus there is a space between the bottom 16 and the ceramic core 11, the heating coil 12 can be fitted with a ceramic ring or a ceramic sleeve 18 their bottom end are advantageously supported. The ceramic ring or the ceramic sleeve 18 therefore preferably has at its bottom end a radially inwardly projecting annular shoulder for supporting the heating coil 12, while a cylindrical side wall of the ceramic ring or the ceramic sleeve 18 centers the heating coil 12. A further function arises in relation to the temperature element 15. As the ceramic sleeve 18 increases the distance between the ceramic core 11 and the base 16 of the metal sleeve with its annular shoulder, it creates space for the arrangement of a temperature sensor 9.

The ceramic ring or the ceramic sleeve 18 thus surrounds an end section of the ceramic core 11 or the heating coil 12 and can be supported on the bottom 16 of the metal sleeve 13 . The ceramic ring or the ceramic sleeve 18 can be provided with slits or openings so that the ceramic potting compound can more easily fill all cavities in the heating cartridge 10 .

A ceramic bushing 19 centers the ceramic core 11 at the upper end. A metal head sleeve 21, which as in the exemplary embodiment is wider than the metal sleeve (13) and can have a stepped, cylindrical side wall, is materially connected to the upper end of the metal sleeve 13, for example by a circumferential weld seam 22 or by connecting the head sleeve 21 and the metal sleeve 13 are formed in one piece. The potting compound is preferably dimensioned such that the entire heating wire with heating coil 12 and heating wire connections 14 is embedded in the potting compound. In the present example, at least part of the interior of the head sleeve 21 is therefore also filled with the casting compound, in particular at least to the extent that the heating wire connections 14 are completely embedded therein.

figure 5 shows another exemplary embodiment of a heating cartridge 10 for a spray nozzle according to FIG 1 . In this exemplary embodiment, the ceramic core, around which the heating coil 12 is arranged, is made of casting compound. In contrast to the embodiment of 2 the ceramic core is therefore not a separate component here that is inserted into the metal sleeve 13 together with the heating coil 12 . Instead, the heating coil 12 is initially inserted into the metal sleeve 13 without a core and then the interior of the metal sleeve 13 is filled with ceramic casting compound. In this way, the ceramic casting compound then forms a ceramic core, which the heating coil 12 surrounds and also fills the space between the core and the inside of the metal sleeve 13 .

In order to stabilize the heating coil 12 when the casting compound is poured in, further spacers 24 are provided along the heating coil 12 between the end regions, in addition to centering aids or spacers in the end region, as represented by the ceramic sleeve 18 and the ceramic bushing 19, which surround the heating coil 12. In 6 the heating coil 12 is shown together with spacers 24 . 7 shows spacer 24 in a detailed view.

The spacers 24 are made of ceramic and are partially ring-shaped, for example. In the exemplary embodiment shown, two almost semicircular spacers 24 support the heating coil 12 in all directions along one turn. However, other spacers are also conceivable, which extend completely around the heating coil 12 or around more or less than half the circumference of the heating coil 12. In the exemplary embodiment, the spacers 24 each have a contact surface 26 which is in contact with the inside of the metal sleeve 13 stands. However, just a linear or multi-point contact is also conceivable.

The spacers 24 can have one or more radially inwardly directed projections 25, for example in the form of an annular bead, which protrude between adjacent windings of the heating coil 12 and thus prevent or at least make it more difficult for the spacers 24 to move axially when pouring in sealing compound. In an embodiment that is not shown, the projections 25 can also be thickened at their ends, so that they form a latching function and are fixed between the windings during assembly, which greatly facilitates assembly. If the spacers 24 have projections 25, they usually follow the course of the winding. In this case, the spacers 24 are therefore not aligned exactly on a radial plane, but are slightly inclined thereto, so that individual sections of the spacers 24 are not directly radially opposite one another. the Figures 6 and 7 show enlarged partial views figure 5 , in which only the heating coil 12 with spacer 24 or only the spacer 24 are shown. This trend is clearly visible in it. The contact surface 26 in the example thus has an axial displacement along the circumference corresponding to the helix height. This would also be the case with only linear or even multi-point support between the spacer 24 and the inside of the metal sleeve 13 .

In addition to the in Figures 1 to 4 shown version has the in figure 5 The version shown also has a guide 27 for guiding the temperature sensor (in figure 5 not shown) on. In the exemplary embodiment, this has a base part adapted to the ceramic sleeve 18 with a central opening for the temperature sensor and a tubular section for guidance the electrical supply line to the temperature sensor. The guide aid 27 can also be made in one piece with the ceramic sleeve 18 .

In the figures 8 and 9 another exemplary embodiment of a heating cartridge 10 is shown. Like the sectional view of the 9 shows, the internal structure of the heating cartridge 10 essentially corresponds to the embodiment of FIG figure 5 . A heating coil 12 is arranged in the metal sleeve 13 and the interior of the metal sleeve is filled with ceramic casting compound. Just like in the embodiment of figure 5 the potting compound thus forms a ceramic core around which the heating coil 12 is arranged and fills the space between the core and the inside of the metal sleeve 13 . The heating coil 12 is when filling the potting compound by spacers 24, as in the Figures 6 and 7 are shown, and stabilized by a ceramic sleeve 18 into which one end of the heating coil 12 protrudes.

The difference from the exemplary embodiments described above consists essentially only in the design of the outside of the metal sleeve 13. How 8 shows, the metal sleeve 13 of this heating cartridge 10 on its outside in the longitudinal direction running grooves, the side walls are formed as ribs 28 and thus improve the heat dissipation. However, other configurations of grooves and ribs, for example running transversely, are also conceivable. A separate head sleeve has also been dispensed with in this exemplary embodiment, i.e. the head sleeve is an integral part of the metal sleeve 13.

The in the figures 8 and 9 The heating cartridge 10 shown can be used, for example, for a hydrogen tank in fuel cell technology or hydrogen combustion. A pressure of up to 600 bar can occur in such tanks. Since the heating cartridge 10 was filled with ceramic casting compound and thus contains no cavities, compression or deformation of the metal sleeve 13 due to static pressure of a few hundred bar is practically impossible, so that the heating cartridge 10 can easily withstand such pressure loads.

Reference List

1

Housing

2

spray opening

3

connection

4

connection

6

channel

9

Connection cable of the temperature sensor

10

cartridge heater

11

ceramic core

12

heating coil

13

metal sleeve

14

Connection section of heating wire

15

temperature sensor

16

bottom of the metal sleeve

17

flow channel

18

ceramic sleeve

19

ceramic bushing

20

contact pins

21

head sleeve

22

Weld

23

spot weld

24

spacers

25

head Start

26

contact surface

27

Guide for temperature sensor

28

ribs

Claims (15)

Heating cartridge, in particular for heating a spray nozzle, with a ceramic core (11), a heating wire arranged as a heating coil (12) around the ceramic core (11), and a metal sleeve (13) in which the ceramic core (11) and the heating coil (12) are arranged, characterized in that the heating coil (12) is embedded in a ceramic casting compound which fills a space between the ceramic core (11) and the inside of the metal sleeve (13). Heating cartridge according to Claim 1, characterized in that the ceramic core (11) contains a channel (6) in which a connecting section (14) of the heating wire runs. Heating cartridge according to one of the preceding claims, characterized in that a temperature sensor (15) is arranged between a bottom (16) of the metal sleeve (13) and the ceramic core (11). Heating cartridge according to one of the preceding claims, characterized in that the ceramic core (12) contains a plurality of channels (6), in at least one of these channels (6) an electrical line (9) of a temperature sensor (15) or a temperature sensor (15) itself is arranged. Heating cartridge according to one of the preceding claims, characterized in that the ceramic core (11) has at least one continuous channel (6) which is only filled with ceramic casting compound. Heating cartridge according to one of the preceding claims, characterized in that grooves are formed in the outside of the metal sleeve (13). Heating cartridge according to one of the preceding claims, characterized in that at least one helical flow channel (17) is formed in the outside of the metal sleeve (13). Heating cartridge according to one of the preceding claims, characterized in that the ceramic casting compound contains aluminum oxide, magnesium oxide or aluminum nitride as the main component. Heating cartridge according to one of the preceding claims, characterized in that a bottom end of the heating coil (12) is surrounded by a ceramic ring or a ceramic sleeve (18). Heating cartridge according to one of the preceding claims, characterized in that the ceramic ring or the ceramic sleeve (18) has slots or openings. Heating cartridge according to one of the preceding claims, characterized in that the metal sleeve (13) is materially connected to a head sleeve (21) which is wider than the metal sleeve (13) and within which connecting sections (14) of the heating wire are connected to contact pins (20). are. Heating cartridge according to one of the preceding claims, characterized in that the heating wire with heating coil (12) and connection sections (14) is completely embedded in casting compound Heating cartridge according to one of the preceding claims, characterized in that a spacer (24) is arranged between the heating coil (12) and the inside of the metal sleeve (13), preferably several spacers (24) are arranged. Heating cartridge according to Claim 13, characterized in that the spacer (24) has a radially inwardly directed projection (25), which is arranged between adjacent turns of the heating coil (12), is preferably clamped between adjacent turns. Heating cartridge according to Claim 13 or 14, characterized in that the spacer (24) rests against only part of the circumference of the heating coil (12).

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