EP0318895A2 - Tubular heating element - Google Patents

Abstract

The invention relates to a tubular heating element whose end (1a) has inside a jacket tube (1) an empty space which accommodates a protection element (36, 37, 38), a switching device being provided which, on reaching a specific temperature, is tripped by the protection element (36, 37, 38). It is furthermore provided that the protection element (36, 37, 38) is inserted into the end (1a) of the jacket tube (1) independently of the jacket tube (1) and that the switching device, on reaching the specific temperature, is tripped by the change of the shape of the protection element (36, 37, 38) pretensioned in the direction of a switching-off process. <IMAGE>

Description

The invention relates to a tubular heater according to the preamble of claim 1.

From EP 00 86 465 B1, a tubular heater with a heating coil made of resistance wire has become known, which is embedded in insulating material and housed in a jacket tube. In the jacket pipe end a piece of pipe is inserted, which is insulated from the jacket pipe and in which an overheating protection in the form of a PTC element, a heat sensor, a fuse or a thermostat is housed. The pipe section is connected to the heating coil in direct heat conduction. The overheating protection is interchangeably inserted into the pipe section from the outside.

The accommodation of a security element in the form of a fuse, a thermostat or a heat sensor in the tubular heater end has the great advantage that there is a direct flow of heat to the heating coil, so that an increase in temperature thereof very quickly reaches the securing element.

Since the securing element lies outside the heated part of the tubular heating element, the associated area of the casing tube no longer calcifies when water is heated, so that a defined heat flow and, accordingly, a defined response of the securing element is achieved regardless of the other degree of calcification of the tubular heating element.

However, securing elements such as e.g. To construct thermostats that can be accommodated in the limited space of a few millimeters in the tubular heater end, but which nevertheless ensure a safe switching operation with the operating voltage generally of 220 volts. In practice, only fuses have prevailed in practice. However, these have the disadvantage that the tubular heater is only switched off via a single voltage pole. In the event of a short-circuit of the heating coil to the tubular heating element jacket at a certain point in the course of the tubular heating element, current flows through the heating coil in spite of the single-pole disconnection, specifically as a result of the lower resistance of the heating coil resulting from the shortening of the live length of the heating coil with a relatively large heating power and corresponding Risk of fire.

Also the use of PTC elements in the tubular radiator end was not able to establish itself in the field of household machines because these circuits do not have the required reliability and responsiveness.

Alloys with shape memory are so-called "memory alloys" e.g. Known from Techn.Mitt.Krupp Research Reports, Volume 34 (1976), No. 1, which are sold under the name "NITINOL".

The invention is based on the object of improving the reliability and response characteristics of an excess temperature fuse for a tubular heater arrangement of the type in question, to enable two-pole disconnection and to significantly reduce the costs for the fuse element and the replacement thereof.

The solution to this problem results from the characterizing feature of claim 1. The subclaims describe preferred embodiments.

• Fig.1 eine Ansicht eines U-förmig gebogenen Rohrheiz­körpers mit zugehöriger Flanschplatte;
• Fig. 2 schematisch einen Schnitt durch ein Rohrheizkörper­ende mit einem stabförmigen Sicherungselement;
• Fig. 3 einen Schnitt längs der Linie III-III in Fig. 1 in vergrößertem Maßstab;
• Fig. 4 in weiterhin vergrößertem Maßstab eine Schnittan­sicht längs der Linie IV-IV in Fig. 3;
• Fig. 5 schematisch einen Schnitt durch das Rohrheizkörper­ende mit einem stabförmigen Sicherungselement aus einem Memory-Metall;
• Fig. 6 einen Schnitt ähnlich Fig. 5, bei dem das Siche­rungselement aus einer Schraubenwendel aus einem Memory-Metall besteht;
• Fig. 7 einen Schnitt ähnlich den Fig. 5 u. 6, bei der das Sicherungselement aus einem Schrumpfschlauch besteht;
• Fig. 8 ähnlich Fig. 7, bei der das Sicherungselement aus einem Feuchtigkeitsausdehnungsregler besteht;
• Fig. 9 eine Schnittansicht, bei der das Sicherungselement eine Salzfüllung enthält;
• Fig. 10 ein Sicherungselement mit einer Regelung durch Dampfdruck;
• Fig. 11 eine Ausführungsform mit einer bei Schmelz­temperatur ansprechenden Lötverbindung;
• Fig. 12 die Ausführungsform nach Fig. 11 nach Ansprechen des Sicherungselementes und Aufreißen der Löt­verbindung; und
• Fig. 13 eine gegenüber den Fig. 11 und 12 abgewandelte und 14 Ausführungsform.

The accompanying drawings serve to further explain the subject matter of the invention. Show it:

• 1 shows a view of a U-shaped tubular heater with associated flange plate;
• Figure 2 shows schematically a section through a tubular heater end with a rod-shaped securing element.
• 3 shows a section along the line III-III in FIG. 1 on an enlarged scale;
• FIG. 4 shows a sectional view along the line IV-IV in FIG. 3 on a further enlarged scale;
• 5 schematically shows a section through the tubular heating element end with a rod-shaped securing element made of a memory metal;
• 6 shows a section similar to FIG. 5, in which the securing element consists of a screw spiral made of a memory metal;
• Fig. 7 shows a section similar to Fig. 5 u. 6, in which the securing element consists of a shrink tube;
• FIG. 8 is similar to FIG. 7, in which the securing element consists of a moisture expansion regulator;
• 9 is a sectional view in which the securing element contains a salt filling;
• 10 shows a securing element with regulation by vapor pressure;
• 11 shows an embodiment with a soldered connection which is responsive at the melting temperature;
• FIG. 12 shows the embodiment according to FIG. 11 after the securing element has responded and the soldered connection has been torn open; and
• Fig. 13 a modified compared to Figs. 11 and 12 and 14 embodiment.

With reference to FIG. 2, a tubular heater consists of a casing tube 1, in which a heating coil 2 is housed embedded in insulating material 3. In the end region 1 a of the tubular heating element which is no longer heated by the heating coil 2, a piece of pipe 4 is inserted which is surrounded by the insulating material 3 over at least part of its length. The heating coil 2 is welded onto the conically tapering end 5 of the pipe section 4. Furthermore, the pipe section 4 is held by a terminating bead 6.

Since the pipe section 4 is electrically connected to the heating coil 2, it serves as a connection pole 7. Since the end region 1 a of the casing tube 1 is no longer heated by the heating coil 2, it cannot calcify either, so that there is a heating element over the entire operating life of the tubular heating element constant heat flow from the heating coil 2 via the welded connection at the conical end 5 to the pipe section 4 and concentrically through the insulating material 3 to the unheated area 1a. This heat flow remains the same regardless of the position in which the tubular heating element is installed, due to the concentric heat flow. Accordingly, a constant temperature occurs in the pipe section 4 during normal operation.

A rod 8 is now inserted into the pipe section 4 and is pressed by a spring 9 of a switching device 10 on the inner bottom of the pipe section 4.

The rod 8 consists of a metal or plastic material that melts at a certain temperature or changes its structure in the sense of a contraction or dilation. This temperature is somewhat higher than the temperature which arises in the tube 4 during normal operation. If the temperature of the tubular heating element rises inadmissibly, for example due to falling dry due to lack of water or coverage, for example due to a piece of laundry or excessive calcification, then it rises the temperature in the pipe section 4. The end of the rod 8 protruding into the pipe section 4 begins to melt, the spring 9 pivoting the movable contact of the switching device 10. Switching device 10 accordingly switches off the power supply to the heating coil 2.

In the embodiment shown in FIG. 1, the ends of the tubular heating element 1 are seated in a flange 11 which closes an opening in a container wall 12. The flange 11 carries a switching device 13 common to both tubular radiator ends, the switching contact 14 of which is bridged by a rod 15 which engages in the rods 8. In the event that the rods 8 consist of a melting material, a spring, not shown, is provided which presses on the rod 15. When one of the rods 8 melts, the contact 14 of the switching device 13 is accordingly pressed in and the power supply to both tubular heater ends is interrupted.

In the embodiment shown in FIGS. 3 and 4, a snap disk 16 is provided, on which a piston 17 acts. An element 18, which expands greatly at the critical temperature, acts on the piston 17 against the pretension of the snap disk 16. When a certain one is exceeded Temperature, the snap disc, as shown in FIG. 4 with dashed lines, reaches its critical equilibrium point and snaps out, the contact 14 of the switching arrangement 13 then being opened via the rod 15.

This embodiment has the particular advantage that "sticking" of the contact is avoided. The response accuracy is very high.

The snap disk 16 can consist of a composite metal or a bimetal in order to achieve the most accurate response characteristic possible. In the illustrated embodiment, the snap disc is schematically integrated into the tubular heater end. The snap disk can of course also be arranged at another location on the flange 11. For example, replace the contact 14 of the switching device 13 or be combined with it.

In the embodiment shown in FIGS. 5 and 6, the "memory effect" of certain metals is used. "Memory metals" are alloys, for example with 52 to 57% nickel, a few% cobalt and the rest titanium. The metals are deformed at low temperatures. At a certain transition temperature that at a titanium content of about 46% is 120 ° C, then the memory metal returns to its original shape. This area is therefore extremely cheap for the present purpose.

In the embodiment shown in Fig. 5, a rod 20 made of a memory metal is inserted into the pipe section 4, which was bent at low temperature. When the transition temperature of 120 ° is reached, the rod 20 returns to its original straight shape and releases a contact 20a. Of course, the opposite way can also be followed, i.e. that a bent rod is made that is straightened at low temperature. This rod then bends at the transition temperature and actuates a corresponding contact.

In the embodiment shown in FIG. 6, a coil spring 21 made of a memory metal is inserted into the pipe section 4. When the transition temperature is reached, the wire of the helix 21 tries to return to its original straight shape, i.e. it expands. A piston 22 is pressed onto a contact 23.

In the embodiment shown in Fig. 7, a tubular member 24 made of a shrinkable material. When the critical temperature is reached, the material shrinks. The hose 24 then actuates a contact 14 of the switching arrangement 13 via a rod 15. With these shrink films or shrink sleeves, the memory of plastics is used for their condition before deformation. These are cold-stretched thermoplastic foils based on PETP, PE, PVC, which contract back to their original state when heat-treated. The shrink sleeves can also be pushed onto a rod and fastened at their front end to a ring sliding thereon, which actuates the switching device, for example via a connecting wire.

8 shows a moisture expansion regulator 25 which actuates a piston 26. Instead of a piston 26, an elastic, rubber-like material can also be provided. When a permissible temperature in the tube 4 is exceeded, a contact 27 is then actuated by the piston 26.

In the embodiment shown in FIG. 9, the effect of recrystallization or growth of crystal nuclei is used. A salt filling 28 in turn acts a piston 29 which actuates a contact of a switching device 30. The effect of the recrystallization or the growth of crystal nuclei at a certain temperature is thus exploited.

Certain chemical volatile compounds can also be used in a tube with a piston or in a tube whose jacket is stretchable, for example made of an elastic rubber-like material. The heating increases the vapor pressure in the tube until it overcomes the resistance of the snap disk 16 and the contact is thus actuated.

In the embodiment according to FIG. 10, a switching arrangement is inserted into the pipe section 4, which contains an liquid 32 boiling at approximately 120 ° C. in an elastic sleeve 31. In accordance with the vapor-liquid equilibrium, the membrane 33 bulges out and assumes the shape shown in broken lines when the temperature rises above the normal value, a contact 34 of a switching device 35 being actuated.

In the embodiment shown in FIGS. 11 and 12, a cylindrical metal body 36 is provided, to which the heating coil 2 is welded. An outwardly leading rod 38 is soldered to the front end face of the metal body 36 by means of a solder connection 37. The rod 38 is guided through the inner bore of an insulating bead 40 which closes the tubular heating element. The insulating bead 40 is recessed in a trough-like manner on its front side, so that it can receive a spherical rubber bead 39 which is held in the compressed state by a disk 38a spread out on the rod 38. The rod 38 also serves to supply current to the heating coil 2. If, as a result of an excess temperature, for example when a temperature of 150 ° C. is exceeded, the solder connection 37 tears open, the elastic ball 39 relaxes, so that the current supply to the heating coil 2 is interrupted, as shown in FIG Fig. 12 is shown.

In the embodiment shown in FIGS. 13 and 14, the rubber ball 39 is replaced by a helical spring 41 which is housed in a housing 42 which consists of two box-shaped parts sliding into one another. The mode of operation is otherwise the same as in the embodiment according to FIGS. 11 and 12.

It is expedient if both connections of the tubular heater are switched off when the switching device 10 responds.

If the overheating is due to a burnout of the tubular heater, i.e. by arcing between the heating coil 2 and the tubular heater 1, the arc continues to burn when voltage is supplied from the other connection of the tubular heater. This also means that the water filling of the device is under tension with the corresponding dangers for the operator.

In the case of tubular heaters which are operated with three-phase current, all connections should expediently be switched off when the switching device 10 responds.

The particular advantage of the new overload protection is that the rod 8 can be replaced very easily and that it is much cheaper than a fuse or a bimetallic switch. The rod is generally 3 to 5 cm in length and 3 mm in diameter. Its melting temperature can be 150 ° C in devices in which the tubular heating element is used for heating water, for example in washing machines, dishwashers, coffee machines or the like, i.e. at a temperature which is not exceeded as long as the tubular heating element passes through the water is cooled, but on the other hand there is still no risk of fire.

The plastic material of the rod 8 can be precisely adapted to the particular application of the tubular heater.

If an already manufactured series of tubular heaters is required for another purpose, then other rods 8 are used accordingly. In contrast to tubular heaters, where e.g. Fuses are provided in the course of a tubular heater, which are no longer interchangeable after manufacture, this ensures that corresponding large series can be produced, which are then divided according to the different types of devices.

The rod 8 can consist of a metal or an alloy that melts at the response temperature. Furthermore, it can consist of a base body, on which a metal tip is placed, which melts at the response temperature. This training has the advantage that only the corresponding metal tips have to be plugged in to adapt a series of radiators to a specific purpose.

Claims (19)

1. tubular heater, the end of which has a cavity inside the casing tube, which receives a securing element by means of which the tubular heater is switched off in the event of overheating,
characterized,
that in the cavity (4) at least one element (8) is inserted, the dimensions and / or shape of which change at a certain temperature, and that the element (8) acts on a switching device (10) which, when a certain temperature is reached is actuated by the element (8). 2. tubular heater according to claim 1,
characterized,
that the element (8) is rod-shaped. 3. tubular heater according to claims 1 to 2,
characterized,
that the element (8) consists of a memory alloy. 4. tubular heater according to claims 1 to 3,
characterized,
that the rod-shaped element (8) acts on a snap disc (16). 5. tubular heater according to claim 4,
characterized,
that the snap disc (16) consists of a bimetal alloy. 6. tubular heater according to claim 5,
characterized,
that the element (8) works on the principle of a moisture expansion controller. 7. tubular heater according to claim 6,
characterized,
that the element (8) contains a salt filling. 8. tubular heater according to claim 7,
characterized,
that the element (8) contains a plastic or metal bolt that softens or melts at a certain temperature. 9. tubular heater according to claim 8,
characterized,
that the element (8) consists of a shrink bolt or an arrangement with a shrink tube. 10. tubular heater according to claim 9,
characterized,
that the rod-shaped element (8) bends at a certain temperature or changes from a curved shape to a rectilinear shape. 11. tubular heater according to claims 1 to 10,
characterized,
that in the jacket pipe end of the tubular heater an electrically insulated pipe section is inserted, to which the end of a heating coil embedded in insulating material is attached in a heat-conducting and electrically conductive manner and that the element (8) is accommodated in this pipe section. 12. tubular heater according to claim 11,
characterized,
that the switching device (10) is arranged at the outer end of the pipe section (4). 13. tubular heater according to claim 12,
characterized,
that the switching device (10) is arranged outside the pipe section (4). 14. tubular heater according to claim 13,
characterized,
that the switching device (10) is fastened to a flange, through which a container wall opening is closed, through which the tubular heater protrudes into the container. 15. tubular heater according to claim 14,
characterized,
that the switching device (10) is designed with two poles or multiple poles and that with an appealing switching device (10) all mains lines are switched off by the tubular heater. 16. tubular heater according to claim 15,
characterized,
that the element (8) consists of a coil spring-shaped winding, the slope of which changes due to a memory effect. 17. tubular heating element, the end of which has a cavity inside the tubular casing, which receives a securing element by which the tubular heating element is switched off in the event of overheating,
characterized,
that the securing element contains a metal body (36), to which a rod (38) leading to the outside is soldered by means of a solder connection (37) melting at the response temperature, which rod is under a spring force that acts in the sense of separation from the metal body (36) acts on the rod (38). 18. tubular heater according to claim 17,
characterized,
that the spring force is exerted by an elastic ball (39) through which the rod (38) is guided and which is supported on an insulating bead (40) which closes off the tubular heating element. 19. tubular heater according to claim 17,
characterized,
that the spring force is exerted by a helical spring (41) which is arranged concentrically around the rod (38).

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