DE102018104896B4 - Cartridge heater with thermocouple and method for manufacturing such a cartridge heater - Google Patents

Abstract

Heating cartridge (1,101) with a tubular metal casing (10,110), with a winding body (20,120) wound with an electric heating element (30,130), which is arranged inside the tubular metal casing (10,110) and is electrically insulated from the tubular metal casing (10,110), and with a thermocouple (40,60,140),wherein the thermocouple (40,60,140) has at least three thermocouple legs (41,43,45,61,63,65,141,143,145,147), and at least one first contact point (44,64,146) and either one second contact point ( 42,62) or further contact points (142,144) between two thermocouples (41,43,45, 61,63,65,141,143,145,147), wherein only the first contact point (44,64,146) is designed such that a change in the temperature of the contact point the measurement result of the thermocouple (40,60,140) is determined, characterized in that the winding body (20,120) wound with the electric heating element (30,130) has at least one bore (21,22,121,122), with at least two thermolegs ( 43,45,63,65), which are connected to one another by a contact point (44,64), the first contact point (44,64,146) being designed in such a way that a change in the temperature of the contact point (44, 64,146) influences the measurement result of the thermocouple (40,60,140), is located inside the winding body (20,120) and at least one second or further contact point (42,62,142, 144) is arranged on a side of the winding body (20,120) opposite the connections and at least Sections of thermal legs (41,43,45,61,63, 65,141,143,145,147) directly or indirectly connected to the second or further contact point (42,62, 142,144) arranged there through the bores in the winding body (20, 120) to a connection-side side of the winding body (20,120) so that the thermal legs (41,43,45,61,63,65,141,143,145, 147) are inserted during manufacture of the heating cartridge (1,101) from the connection side of the winding body (20,120) and then on the second or another contact point (42,62,142,144) can be connected.

Description

The invention relates to a heating cartridge with a thermocouple having the features of the preamble of claim 1.

Cartridge heaters are often provided with a temperature sensor in order to verify the heat output and, if necessary, to adjust it. It is known from the prior art to use thermocouples as temperature sensors. Such thermocouples usually have two metallic conductors made of different materials, the so-called thermolegs, which are connected at one end so that the thermoelectric effect occurring at this end can be used to measure temperature.

In practice, such a thermocouple is placed in the in a cartridge heater with a winding body on which the electrical heating element, e.g. a heating wire or resistance wire, is wound, by removing its thermoleg from the connection side of the heating cartridge are pushed through holes in the winding body and then the tips are connected to one another in an electrically conductive manner, in particular welded or crimped, in order to form the measuring point of the thermocouple. However, this means that the position of the measuring point of the thermocouple in a heating cartridge cannot be freely selected, but that it generally has to be arranged on the side of a winding body opposite the connection side.

As long as only one winding body is used, the thermocouple must be arranged at the tip of this winding body and thus at one end of the heating cartridge. For example, if you want to ensure temperature monitoring in the middle section of an electric heating cartridge for a given application, the only option left is to arrange two or more wound winding bodies one behind the other and to connect them to one another.

• Erstens wird die Fehleranfälligkeit spürbar erhöht, da die einzelnen mit dem elektrischen Heizelement bewickelten Wickelkörper jeweils miteinander kontaktiert werden müssen. Zweitens wird der Zusammenbau der Heizpatrone komplexer, was die Prozesssicherheit senkt. Und drittens verliert man Freiheitsgrade bei der Gestaltung eines Temperaturprofils, da die Übergangsbereiche zwischen den einzelnen Wickelkörpern quasi zwangsweise unbeheizte Zonen darstellen, was zudem auch noch die Bauraumerfordernisse für das Erreichen einer gegebenen Heizleistung erhöht. Die Oberflächenbelastung auf dem Mantel und auf dem Widerstandsdraht steigt. Darüber hinaus werden die Kosten wegen der signifikant größeren Zahl von Arbeitsschritten deutlich erhöht.

Although this increases the flexibility in terms of the position at which the measuring point of the thermocouple can be attached to some extent (even if free positioning is still not created), it brings with it several significant problems:

• Firstly, the susceptibility to errors is noticeably increased, since the individual winding bodies wound with the electric heating element must each be contacted with one another. Second, assembling the cartridge heater becomes more complex, which lowers process reliability. And thirdly, you lose degrees of freedom in the design of a temperature profile, since the transition areas between the individual winding bodies are almost inevitably unheated zones, which also increases the space requirements for achieving a given heating output. The surface load on the sheath and on the resistance wire increases. In addition, the costs are significantly increased because of the significantly larger number of work steps.

From the U.S. 6,104,011 A a heating cartridge with the features of the preamble of patent claim 1 is known. More cartridge heaters reveal the EP 2 966 933 A1 and the DE 10 2013 212 205 A1 .

The object of the invention is therefore to provide a cost-effective design for a heating cartridge with a thermocouple with increased process reliability, in which the measuring point of the thermocouple can be positioned more freely without the disadvantages mentioned above occurring.

This object is achieved by a heating cartridge having the features of patent claim 1 and a method for producing such a heating cartridge having the features of patent claim 15. Advantageous developments of the invention are the subject matter of the dependent claims.

A cartridge heater according to the present invention has a tubular metal shell, a bobbin wound with an electrical heating element disposed inside the tubular metal shell and insulated from the tubular metal shell, and a thermocouple. For the sake of completeness, it is pointed out that a tube can have different cross-sectional geometries, in particular cross-sectional geometries that deviate from the circular shape.

It is essential to the invention that the thermocouple has at least three thermocouples and at least a first contact point and a second contact point or further contact points between two thermocouples, with only the first contact point being configured such that a change in the temperature of the contact point affects the measurement result of the thermocouple.

For the sake of completeness, it is pointed out that the terms "first" and "second" used here do not define a specific order or sequence of these contact points, but serve to categorize or refer to the different types of contact points. For example, if there are three contact points are, so the middle contact point can definitely be the first contact point.

By using a thermocouple with at least one additional contact point, which ensures that additional contact points do not affect the measurement result, you get at least one additional point where, after inserting individual thermocouples or thermocouples preconfigured by connecting them to one another, you can two separate bores of the wound bobbin can make the thermocouple functional by contacting, in particular welding to the additional contact point. According to the invention, an additional contact point that is not required for the function of the thermocouple but also does not impair it is used in order to achieve an additional degree of freedom in assembly.

The first contact point can be made between thermolegs of one of the typical material pairings for thermocouples, e.g. nickel-chromium/nickel, iron/copper-nickel, platinum-rhodium/platinum and provides the actual functionality of the thermocouple.

One way to make the second contact point non-functional so that it does not affect the measurement result is that two thermocouples made of the same material or a pair of materials with essentially the same thermoelectric coefficients are in contact with each other at the second contact point, so that a Changing the temperature of the second contact point does not affect the measurement result of the thermocouple.

It would therefore be conceivable, for example, to use a first nickel thermocouple and second and third nickel-chromium thermocouples and to connect them to one another at two contact points. A standard Type K thermocouple is then practically present at the first contact point. At the second contact point, the metal pairing is nickel-chromium/nickel-chromium, which of course does not falsify the measurement result for the first contact point. Of course, further contact points can be provided according to this principle if further thermocouples made of identical material are added and connected with contact points, which then always connect thermocouples of the same material and are therefore insensitive to temperature changes.

An alternative possibility, which always requires the thermocouple to be broken down into more thermocouples and more contact points, is that two thermocouples made of different materials, which have different thermoelectric coefficients, are also in contact with one another at the first additional, i.e. a second, contact point and that there is a second further, i.e. third, contact point which compensates for the effect of a change in temperature of the second contact point. The simplest way to achieve this is to use a sequence of material transitions of opposite direction relative to each other, then ensuring that the contact points so corresponding are located at locations where the temperature can be considered equal.

A conceivable example would be a system with a first thermal leg made of Fe, a second and fourth thermal leg made of CuNi and a third thermal leg made of NiCr. A Type J thermocouple is obtained at the first point of contact between the first and second thermolegs. At the second contact point between the second and the third thermal leg and at the third contact point between the third and fourth thermal leg, the material pairings correspond to type E thermocouples, which, however, compensate each other because of the swapped material sequence, if it is ensured that the temperature at these contact points is the same is. In the case of a heating cartridge, this condition is usually easy to meet if the contact points are arranged at the same axial position of the heating cartridge.

It is particularly preferred if the first contact point, viewed in the axial direction of the tubular metal jacket, lies between the two ends of the winding body on which the electrical heating element is wound.

If at least one thermal limb, preferably all thermal limbs, are formed, there are manufacturing advantages. In particular, contact points can then be easily formed by providing the flat strip with an overlap and then carrying out a spot welding process.

According to the invention, the winding body on which the electric heating element is wound has at least one bore. In this case, a thermocouple or at least two thermocouples, which are connected to one another by a contact point, can be guided through the bore. Two bores which are arranged parallel and symmetrically to one another are particularly preferred. A preconfigured "half" of the thermocouple, each with one or more thermocouples and the corresponding number of contact points, can then be inserted into each of these bores from the connection side of the winding body and that Thermocouple can then be made ready for use by creating the missing contact point in the tip area, while at the same time the "active" first contact point can be arranged in particular at any point in the bore, so that according to the invention the contact point, which is designed in such a way that a change in the Temperature of the contact point influences the measurement result of the thermocouple, is inside the winding body.

If one ensures that a contact point is accessible through a window or a recess in the bobbin, further manufacturing advantages can be achieved because this allows the contact point to be made at a given point only after threading. The threading in of long sections of thermal legs or of several thermal legs that are already connected to one another by contact points can thus be simplified or avoided.

It is advantageous if the winding of the electrical heating element varies in the area of the first contact point and in particular in the area of such a window compared to the winding in other areas of the winding body.

Of course, if desired, an electric heating cartridge designed according to the invention can also have a plurality of winding bodies which are electrically connected to one another, in particular connected in parallel or in series.

According to the invention, there is an embodiment in which at least one second or further contact point is arranged on a side of the winding body opposite the connections and in which at least sections of the thermal legs directly or indirectly adjoining the second or further contact point arranged there are connected through openings in the winding body to form a connection-side side of the bobbin are guided, so that the thermal legs can be plugged into the production of the heating cartridge from the connection-side side of the bobbin and then connected to the second or further contact point.

The method according to the invention for the production of such a heating cartridge differs from the previously known procedure for the production of heating cartridges in that during the production of the heating cartridge the thermal legs are inserted through openings from the connection side of the winding body and then at a second or further contact point, the on the opposite side of the winding body to the connection-side side.

• 1: eine geöffnete Ansicht einer ersten elektrischen Heizpatrone mit Thermoelement,
• 2: einen Querschnitt durch den Wickelkörper der Heizpatrone aus 1,
• 3: eine Ansicht eines alternativ ausgestalteten Thermoelements,
• 4: einen Querschnitt durch eine zweite elektrischen Heizpatrone mit Thermoelement,
• 5: den Wickelkörper der Heizpatrone aus 4, und
• 6: eine Ansicht des Thermoelements aus 4.

The invention is explained in more detail below with reference to figures that represent exemplary embodiments. Show it:

• 1 : an opened view of a first electrical cartridge heater with thermocouple,
• 2 : a cross section through the coil body of the heating cartridge 1 ,
• 3 : a view of an alternatively configured thermocouple,
• 4 : a cross section through a second electric heating cartridge with thermocouple,
• 5 : the coil body of the heating cartridge 4 , and
• 6 : a view of the thermocouple 4 .

1 shows an opened view of an electric heating cartridge 1 with a tubular metal casing 10, which in this case is equipped with a base 11. Inside the tubular metal jacket 10 is a winding body 20, onto which the electrical heating element 30 designed as a resistance wire is wound, which can be supplied with electricity via an electrical supply line 31 and electrically by optionally compacted MgO powder 50 opposite the tubular metal jacket 10 is isolated. A thermocouple 40 is arranged inside the winding body 20 . Further details on the structure of the thermocouple 40 and its arrangement in the bobbin 20 can be the 2 remove.

how to get in 2 recognizes that the thermocouple 40 differs from previously conventional thermocouples in three thermolegs 41,43,45, which are electrically conductively connected to one another at two contact points, a first contact point 44 and a second contact point 42, for example by welding. The materials of the thermolegs 43 and 45 are selected in such a way that they form a thermocouple of a desired type with the first contact point 44, with which the temperature at this contact point can be determined in the usual way. The material of the thermal leg 41 is identical to the material of the thermal leg 43, which means that the contact point 42 between the thermal legs 41, 43 does not affect the result of the temperature measurement with the first contact point 44. The purpose of the additional second contact point 42 becomes clear when one realizes that the thermal legs 43, 45 with the contact point 44 between them are arranged in a first bore 21 penetrating the winding body 20 in its interior in the axial direction and on the connection-side end of the bobbin 20 in an insulated, preferably flexible connecting element 47 go over and the Thermolegs 41 are arranged in a second bore 22 penetrating the winding body 20 in its interior in the axial direction and merges into an insulated, preferably flexible connecting element 46 at the connection-side end of the winding body 20 . This means that the components of the thermocouple 40 must be threaded into the bores 20, 21 from the connection side of the winding body 20, which is only possible if the thermocouple 40 is separated. In other words, it is therefore absolutely necessary to provide a contact point of the thermocouple 40 on the side of the winding body opposite the connections, even if the actual measuring point is to be at a different point.

3 shows a view of an alternatively configured thermocouple 60. Like the thermocouple 40 discussed above, the thermocouple 60 has three thermocouples 61,63,65, which differ from the previously customary thermocouples and are connected to two contact points, a first contact point 64 and a second contact point 62, for example by Welding are electrically connected to each other. The materials of the thermolegs 63 and 65 are selected in such a way that they form a thermocouple of a desired type with the first contact point 64, with which the temperature at this contact point can be determined in the usual way. The material of the thermal leg 61 is identical to the material of the thermal leg 63, which means that the contact point 62 between the thermal legs 61, 63 does not affect the result of the temperature measurement with the first contact point 64.

A first significant difference between the thermocouple 40 and the thermocouple 60 is that the thermolegs 61,63,65 are made of a flat strip material, which leads to flat contact points 62,64. As the contact point 62 in particular shows, a very significant overlap of thermal legs can be used to form a contact point 62 here.

A second major difference is that the thermal leg 63 is bent into a U-shape. This makes it particularly easy to insert the thermocouples 61, 65 already connected to the connecting elements 67 or 68 from one side and the U-shaped thermocouple 63 from the other side of the winding body.

4 shows a cross section through a second electric heating cartridge 101 with a tubular metal jacket 110, which is equipped with a base 111 in this case. Inside the tubular metal jacket 110 is a winding body 120, onto which the electrical heating element 130 designed as a resistance wire is wound, which can be supplied with electricity via an electrical supply line 131 and electrically by optionally compacted MgO powder 150 opposite the tubular metal jacket 110 is isolated. A thermocouple 140 is arranged inside the winding body 120 . More details about the structure of the thermocouple 140 can be particularly good 6 remove.

6 shows another alternative embodiment for a thermocouple 140 with which the invention can be implemented. The thermocouple 140 has a first thermocouple 141, a U-shaped second thermocouple 143, a third thermocouple 145 and a fourth thermocouple 147 with a first contact point 146 and two further contact points 142,144 and has insulated, preferably flexible connecting elements 148,149. The first thermal leg 141 and the third thermal leg 145, which together with the second thermal leg 143 form the further contact points 142,144, are made from the same material, while the materials from which the second thermal leg 143 and the fourth thermal leg 147 are made differ from each other and differ from the material of the first thermal leg 141 and of the third thermal leg 145 and are selected such that a material pairing for a thermocouple of the desired type results, in particular at the first contact point 146 .

two in 4 Aspects shown should be particularly emphasized: First, it can be seen that all thermal legs 141,143,145,147 are designed in the form of a flat strip, which makes it particularly easy to manufacture the contact points 146,144,142 by spot welding overlapping flat strip sections, which results in a very good, reproducible contact leads.

Second, the structure of the thermocouple 140 ensures that the effect of the other contact points 142, 144 is compensated because they are positioned so symmetrically to one another that it can be safely expected that they will be exposed to the same temperature in the installation situation and a material transition AB from a material transition BA is followed. This structure also ensures that the further contact points 142, 144 do not falsify the results of the temperature measurement at the contact point 146.

In addition, the provision of the U-shaped second thermal leg 143 allows the threading path through bores in the winding body 120 to be further shortened, which has a positive effect on the production time flows. For this purpose, windows are then advantageously arranged in the winding body 120, which allow the contact points 142, 144 to be produced after the insertion of the thermal legs into the bores, for example by spot welding. However, contact points can also be produced by pressing without windows, particularly in the case of thermal legs made of flat material.

Another significant difference between the heating element 1 and the heating element 101 can be seen particularly well 4 in synopsis with the 5 If you look at the winding of the electrical heating element 130 in the area of the contact point 146, which is responsible for the actual measurement, it is noticeable that this measuring point is overwound with a larger helix pitch.

This makes it clear that with a heating cartridge 1,101 designed according to the invention, an adjustment of the power in this area is possible and thus the response/behaviour of the thermocouple can be adjusted to the respective installation situation of the respective application and/or the respective surface load, which according to the prior art that was not possible.

Reference List

1.101

cartridge heater

10.110

tubular metal jacket

11.111

Floor

20.121

winding body

21,22,121,122

drilling

30,130

electric heating element

31,131

supply line

40,60,140

thermocouple

41, 43, 45, 61, 63, 65, 141, 143, 145, 147

thermal legs

42.62

second point of contact

44,64,146

first point of contact

47,48,67,68,148,149

fastener

50,150

MgO powder

142,144

more contact points

Claims (11)

Heating cartridge (1,101) with a tubular metal casing (10,110), with a winding body (20,120) wound with an electric heating element (30,130), which is arranged inside the tubular metal casing (10,110) and is electrically insulated from the tubular metal casing (10,110), and with a thermocouple (40,60,140), wherein the thermocouple (40,60,140) has at least three thermolegs (41,43,45,61,63,65,141,143,145,147), and at least one first contact point (44,64,146) and either one second contact point ( 42,62) or further contact points (142,144) between two thermocouples (41,43,45, 61,63,65,141,143,145,147), wherein only the first contact point (44,64,146) is designed such that a change in the temperature of the contact point the measurement result of the thermocouple (40,60,140) is determined, characterized in that the winding body (20,120) wound with the electric heating element (30,130) has at least one bore (21,22,121,122), with at least two thermolegs ( 43,45,63,65), which are connected to one another by a contact point (44,64), the first contact point (44,64,146) being designed in such a way that a change in the temperature of the contact point (44, 64,146) affects the measurement result of the thermocouple (40,60,140), is located inside the winding body (20,120) and at least one second or further contact point (42,62,142, 144) is arranged on a side of the winding body (20,120) opposite the connections and at least Sections of thermal legs (41,43,45,61,63, 65,141,143,145,147) directly or indirectly connected to the second or further contact point (42,62, 142,144) arranged there through the bores in the winding body (20, 120) to a connection-side side of the winding body (20,120) so that the thermal legs (41,43,45,61,63,65,141,143,145, 147) are inserted during manufacture of the heating cartridge (1,101) from the connection side of the winding body (20,120) and then on the second or another contact point (42,62,142,144) can be connected. Heater cartridge (1.110) after claim 1 , characterized in that connecting lines are led out flexibly on one side of the heating cartridge (1.101) from the heating cartridge (1.101), so that an insertion direction when assembling the heating cartridge (1.101) is specified. Heater cartridge (1.101) after claim 1 or 2 , characterized in that all contact points (42,44,62,64,142,144,146) are arranged within the tubular metal jacket (10,110) and preferably embedded in an insulating material, preferably MgO powder (50,150), and optionally compacted. A heating cartridge (1,101) according to any preceding claim, characterized in that at the second contact point (42,62) two thermocouples (41,43,61,63) of the same material or of a pair of materials having substantially the same thermoelectric coefficients are in contact with each other stand, so that a change in the temperature of the second contact point (42,62) does not affect the measurement result of the thermocouple (40,60). Heater cartridge (1.101) according to one of Claims 1 until 3 , characterized in that at a first further contact point (142) two thermal legs (141,143) made of different materials which have different thermoelectric coefficients are in contact with one another and that there is a second further contact point (144) which has the effect of a change in the Temperature of the first further contact point (142) compensated. Heating cartridge (1,101) according to a preceding claim, characterized in that the first contact point (44,146) viewed in the axial direction of the tubular metal jacket (10,110) lies between the two ends of the winding body (20,120) wound with the electric heating element. A heating cartridge (1, 101) according to any preceding claim, characterized in that at least one thermo leg (41, 43, 45, 61, 63, 65, 141, 143, 145, 147) is formed from flat strip. Heating cartridge (1,101) according to one of the preceding claims, characterized in that at least one contact point (44,64,142,144) is accessible through a window in the winding body (20,120) or a recess in the winding body (20,120). Heater cartridge (1.101) after claim 8 , characterized in that the winding of the electrical heating element (30,130) in the area of the window varies in comparison to the winding in other areas of the winding body (20,120). Heating cartridge (1,101) according to a preceding claim, characterized in that thermo-legs (41,43,45,61,63,65,141,143,145,147), which form a contact point (42,44,62,64,142,144,146), overlap and are preferably fixed, in particular soldered or welded, especially spot welded. Method for producing a heating cartridge (1.101) according to one of Claims 1 until 10 , characterized in that during the manufacture of the heating cartridge (1,101) the thermal legs (41,43,45,61,63,65,141,143,145,147) are inserted through openings from the connection side of the winding body (20,120) and then at a second or further contact point ( 42,62,142,144), which is on the opposite side of the winding body (20,120) to the connection side.

Images