HK1061997B - Temperature sensor and heating device for hot runner systems - Google Patents

Description

Temperature sensor and heating device for hot runner system

Technical Field

The invention relates to a temperature sensor for a hot runner system, comprising a resistive element connectable to a control circuit of a heating system by means of a connection point; and a heating device of the hot runner system having a heating element in thermal contact with the header or nozzle body and the temperature sensor described above.

Background

Hot runner systems are used for die casting moulds, where a plastic compound flowing at a predetermined temperature can be introduced under high pressure into a separable mould body (cavity). A heating system is usually provided to prevent premature cooling of the hot compounds in the distribution channel and the spout by maintaining the plastic fluid at a constant temperature. The temperature control requirements of hot runner molds are very high because the process window for most plastics being processed is very narrow and very sensitive to temperature fluctuations, especially in the nozzle and gate areas. This means that, for example, temperature changes of a few degrees occur in the region of the lance which are sufficient to lead to injection errors and to cause rejects. Therefore, accurate temperature control is important if the fully automatic hot runner mold is to operate without error.

Monitoring and controlling temperature is typically accomplished by temperature sensors (resistance sensors) in the form of resistive conductors. The temperature sensor is mounted as a separate element in a slot or hole in the material tube or heating block, as disclosed in european patent EP-a1-0927617 or german patent-U-20100840. Furthermore, german patent-a 1-19941038 and german patent-a 1-10004072 describe temperature sensors and entire heating devices, as achieved by applying thick film technology to the surface of the nozzle or header body, such as by direct coating.

Resistive sensors typically have a U-shaped or meandering resistive element made of a metal or metal alloy whose resistance changes with increasing or decreasing temperature. A disadvantage of the measurement technique associated therewith is that only average temperature values over a large spatial range can be recorded, despite careful positioning of the sensors on the hot runner system. Thus, it is difficult to achieve the desired level of temperature control over the temperature distribution at or near the end of the header, at the end of the lance, and the like. In particular, die casting moulds require the knowledge of the exact temperature of the nozzle tip, so that the temperature can be maintained exactly and changed if necessary.

Disclosure of Invention

It is therefore an object of the present invention to take a simple approach to improving the recording and influencing of the temperature of selected portions of a hot runner nozzle, header, or similar structure. In particular, the object of the invention is to achieve variable control of the operating temperature of the end region of a hot runner nozzle. Another important object of the invention is to propose a heating device of a hot runner system, the temperature of the runner being accurately recordable within a defined range, which is as narrow as possible.

The invention proposes a temperature sensor for a hot runner system, wherein the sensor is provided with a resistive element connected to an electronic control part of the heating system, the sensor being provided with at least two segments and at least one bottom segment in its longitudinal or transverse segment direction extension, the at least two segments being connected to each other via the at least one bottom segment at their bottom ends, the resistance of the bottom segment being greater than the resistance of the remaining area of the resistive element. This simple and low cost method allows the temperatures recorded on the header or hot runner nozzle to be much more accurate than previously possible.

This is due to the fact that the temperature change of the bottom section of the resistive element, which has a very large resistance, has a much faster and significant effect than the other parts of the resistive element. Furthermore, a properly positioned temperature sensor can track very accurately the temperature development changes at the precisely positioned location by accurately positioning the temperature sensor bottom section with higher resistance in the appropriate area of the heating system or hot runner. The recorded values can be evaluated with a higher degree of reliability to control the operating temperature and the operating state of the heated element. To this end, the resistance element is composed of at least one segment 22 and at least one base segment 24, the resistance of which is greater than the resistance of the segment at a specific temperature.

The resistance of the bottom segment is at least an order of magnitude higher than the segments, preferably 2 to 100 times higher. The sensitivity of the temperature sensor so formed means that temperature fluctuations will cause the bottom section of the thermal sensor to instantaneously experience a change in resistance, and a properly positioned bottom section (e.g., located in the end region of the hot runner nozzle) produces a much faster and improved temperature measurement.

Said section 22 and/or said bottom section 24 of the temperature sensor forms an arc or arch of a U-shape, which allows an optimal positioning or alignment of the bottom section with high electrical resistance. The segments 22 and bottom segments 24 may have a serpentine back and forth shape, providing a greater range of options for other designs.

For determining the resistance value, the geometry of the temperature sensor is preferably such that the segment 22 covers a large part of the length of the temperature sensor, the cross-section of the segment being larger than the cross-section of the bottom segment 24. The practical implementation can be achieved in a simple manner in that the segments and the bottom segment form a resistive track of uniform thickness, the width of the segments being greater than the width of the bottom segment.

The resistance path is composed of sintered conductive paste. The segment 22 and/or the bottom segment 24 can also be formed by at least two resistive tracks lying one above the other, which are separated by an insulating layer. This allows any particular resistance value to be formed in a very low structure. The segments 22 and the bottom segment 24 may also be covered by or embedded in an insulating layer. The insulating layer may be a ceramic dielectric layer, which ensures that a permanent solid connection is established between the temperature sensor and the wall of the object to be measured. Furthermore, the heating system and the temperature sensor are effectively protected against moisture absorption.

In addition, the inventive segment 22 and the bottom segment 24 have different material compositions. This facilitates the formation of various resistance values on the resistive traces, resulting in a spatially sensitive temperature recording.

The claimed invention is a particularly advantageous heating device for a hot runner system having a heating element and temperature sensor in thermal contact with the header or nozzle body. According to this embodiment, the temperature sensor is an integral part of the heating system, mounted as a measuring element on or in the header or nozzle body.

According to the invention, the heating element of the heating system is composed of electrically and thermally conductive paths that meet performance requirements. It can be mounted in the header or nozzle body in different densities and shapes depending on the relevant performance and temperature profile. In particular, the heat conduction path has at least in part a meandering form and/or is a double wire.

According to the invention, the resistance of the heat conduction path in the middle region of the header or nozzle body is lower than the resistance in the top or end region. Thus, energy may be released in the middle of the header or nozzle body to achieve a particular temperature profile. The temperature is in each case concentrated towards both ends, for example in the vicinity of the inlet or outlet of the header or nozzle body.

The heat conduction path forms at least one zone of greater electrical resistance than the remainder of the heat conduction path, and the sensitive bottom section of the temperature sensor is inserted into a recessed portion of said high resistance heat conduction zone, i.e. it may be set very close to the free end of the lance or header body. The temperature change in this critical region can be measured instantaneously, effectively avoiding injection errors. The bottom segment of the thermal sensor is surrounded by a tightly packed heat conduction path in the high resistance region.

The thermally conductive path may be positioned on the insulating layer and covered by another insulating layer. Further, the temperature sensor and the heat conduction path may be disposed on the same level of the insulating layer. This means that the arrangement of the temperature sensor and the heat conduction path can also be realized without difficulty with a low structural height.

The heat conduction path and the insulating layer are composed of sintered thin film and/or sintered thick film conductive paste. At least the insulating layer is a ceramic dielectric layer. The entire heating system, as well as the temperature sensor, can thus be manufactured in a simple and cost-effective manner. Furthermore, the integral connection with the lance or header body ensures an optimum heat exchange.

The dielectric coating is permanently applied to the body of the header or lance and is pre-stressed (toughened) with respect to the header or lance body after at least one sintering process. For example, due to the laminar bond formed with the hot runner nozzle and the arrangement of the heating elements, it has a very compact size compared to conventional arrangements, while still having the same performance.

Alternatively, the media coating may be permanently applied to a substrate that is bonded to the body of the header or nozzle by thermal contact.

Drawings

Other features, details and advantages of the invention will become more apparent from the following description of embodiments thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a heating device having a thermally conductive path and a temperature sensor;

FIG. 2 is a plan view of a temperature sensor;

FIG. 3 is a cross-sectional view taken along section A-A of FIG. 2;

FIG. 4 is another embodiment of a temperature sensor;

FIG. 5 is another embodiment of a heating device with a temperature sensor; and

fig. 6 is another embodiment of a heating device with a temperature sensor.

List of reference numerals

B middle part E end region

K header/lance body L Length

O top region

10 temperature sensor 20 resistance element

22 segment 24 bottom segment

26 insulating layer 30 connection contact

40 heating system/heating device 42 heating element

44 heat conduction path 46 region

47 recess 50 connection

52 zigzag tape 53 joint

54 where the longitudinal conductors 55 converge

56 zigzag return band 58 insulating layer

59 insulating layer

Detailed Description

In fig. 1, the temperature sensor, designated by the reference numeral 10, is a component of a heating device 40 of a hot runner system (not shown in detail in the drawings), and in particular a hot runner nozzle (also not shown). The temperature sensor has a resistance element 20 made of a material whose resistance changes with an increase or decrease in temperature. These constitute the basis for registering and suitably regulating the temperature generated by the heating means 40 by means of a suitable electronic control circuit (not shown).

The resistive elements 20 extend primarily longitudinally along the hot runner nozzle or heating system 40. It can be divided into three segments 22, 24, 22 which together form a narrow U-shaped arc. The sections 22 form two identical resistive branches that extend in parallel along the body K of the hot runner nozzle, the bottom ends of which are connected to the bottom section 24. The resistance of the bottom segment 24 at a particular temperature is greater than the resistance of the segment 22 and may be 2 to 100 times greater. This can be achieved by making the cross-sectional dimension of each segment 22 at least twice that of the base segment 24. But the best arrangement is to have the segments 22 and the bottom segment 24 have U-shaped resistive traces of uniform thickness. As shown in fig. 2, the width of the segment 22 area is greater than the width of the base segment 24. The length L of the temperature sensor 10 or resistive element 20 is substantially equal to the length of the hot-runner nozzle body K.

Connection contacts 30 are provided for connecting the temperature sensor 10 to an electronic evaluation and control circuit. These contacts may be in the form of solder contacts. To these soldering contacts 30, connecting wires or cables are fixed, which emerge through the spout body or the connecting flange.

The heating means 40 preferably includes a heating element 42 which is an electrically conductive path 44. The connecting portion 50 of the serpentine return strip 52 is located at the top region O, which may be located in front of the base or flange of the hot runner nozzle (not shown). The parallel thermally conductive paths of the ribbon are separated from each other by a distance approximately equal to the width of each conductive path. The upper strip 52 changes at a junction 53 into a frame-like branch or longitudinal wire 54, which wire 54 extends in the middle part B of the heating device 40 or the nozzle body k. These longitudinal wires or branches 54 converge at their lower ends 55 to form a lower zigzag return band 56 in the end region E of the nozzle body K, in particular in the nozzle end region (not shown). The width of the thermally conductive path 44 in the region of the upper meandering band 52 and the regions of the branch and longitudinal leads 54 is greater than the width of the thermally conductive path 44 of the lower meandering band 56, and thus the electrical resistance of the thermally conductive path 44 of the lower meandering band 56 is higher than the electrical resistance of the remainder of the thermally conductive path 44. The heating function is thus concentrated in the region E of the end of the lance.

As can be seen in fig. 1, the thermally conductive paths 42, 44 are symmetrically arranged with corresponding halves thereof surrounding the centrally located temperature sensor 10. Which together with the bottom segment 24 constitutes a hairpin-like curvature as highly sensitive measurement region. The bottom segment is surrounded by a tight heat conduction path 44 of the lower serpentine return band 56 in the recess 47 of the high resistance heat conduction zone 46 and, therefore, in the nozzle end region E of the hot runner so that any temperature fluctuations in this region will greatly affect the resistive element 20.

The heat conduction paths 42, 44 of the heating device 40 are planar strips of uniform thickness, between 0.02 and 0.5 mm thick. The heat conduction path is preferably formed by a conductive film or paste sintered on an insulating layer 52 which is previously bonded to the body K of the header or nozzle. The insulating layer is preferably a ceramic dielectric coating that is pre-stressed against the header or nozzle body K after at least one sintering process. The resistive element 20 of the temperature sensor 10 is also secured to the dielectric coating 58, preferably at the same level as the thermally conductive paths 42, 44, using thick film technology. The temperature sensor 10 may be made of platinum or other suitable metal alloy having a resistance that varies with temperature. An additional insulating layer 59 is provided to protect the heating system 40 and the temperature sensor 10 from external influences. The insulating layers form a common protective insulating compound that can be applied to the lateral surfaces of the hot runner nozzle or the surface of the cylindrical sleeve.

The formation and positioning of the individual bottom sections 24 of the resistive elements 20 in the end regions E of the hot-runner nozzles (regions sensitive to temperature variations) allows for accurate and instantaneous recording of the thermal spread. Deviations from the nominal temperature can result in the temperature sensor 10 of the present invention producing a much faster and more pronounced change in resistance than conventional temperature sensors, i.e., deviations from the nominal temperature can be quickly and accurately recorded, resulting in instant adjustment of the heating system 40.

Fig. 3 shows a cross-sectional view of the temperature sensor 10 of fig. 2. The heating system 40 is located on the outer wall of the lance body K. The heating system is designed in a planar layer form with a ceramic dielectric coating 58 applied directly to the metal layer as an insulating layer, the heating layer 42, which may include a heat conduction path 44, is then applied to the ceramic dielectric layer in a serpentine and/or frame form (as shown in fig. 1), with an outer coating 59 covering the heat conduction path 44 and the underlying dielectric layer 58 providing external shielding and electrical insulation. An insulating layer 26 is also applied to the overcoat layer 59, in which the temperature sensor 10 is embedded.

In the embodiment shown in fig. 4, the bottom section 24 of the temperature sensor has a meandering shape, forming a very sensitive measuring zone. It is located in a region of the hot runner nozzle where the temperature of the location can be recorded as quickly as possible. Fig. 5 and 6 show different options for the design of the heat conduction path 44 and the arrangement and position of the temperature sensor 10, respectively, in which the measuring end 24 is always located in the desired temperature measuring zone.

The invention is not limited to the embodiments described above but can be modified in many ways. For example, the segment 22 and the bottom segment 24 of the temperature sensor 10 may be formed by stacking two resistive paths 20 separated by a thin insulating layer on top of each other, which may enable higher resistance values, such as those required when higher temperatures are required to be measured. It is also important that the resistance value of the resistive element 20 in the area where the temperature fluctuations need to be recorded instantaneously and accurately should be much higher, i.e. 2 to 100 times higher, than the rest of the area on the resistive path 20. The result is that the thermal sensor 10 will measure and affect the temperature change of the selected area with minimal thermal delay.

In an advantageous development, the entire device, which is connected in a suitably insulated manner to the conducting header or lance body, has a uniform thickness. This enables easy and reliable embedding of thick films. Thick films can be sintered using known methods, the glass-ceramic-metal system containing at least one glass, glass-ceramic or ceramic component which wets the metal surface at the respective sintering temperature and at least a portion of which can be converted into a crystalline state.

All the features and advantages disclosed in the description and the drawings, including design details and spatial arrangements, are essential to the invention and can be implemented alone or in varying combinations.

Claims (25)

1. A temperature sensor (10) for a hot runner system, the resistive element (20) of which is connectable to a control circuit of a heating system (40) by means of connection contacts (30); it is characterized in that the preparation method is characterized in that,

the resistor element has at least two segments (22) and at least one base segment (24) in the longitudinal or transverse segment direction extension thereof,

the at least two segments (22) are connected to each other at their bottom ends via the at least one bottom segment (24),

the resistance of the at least one bottom segment (24) is greater than the resistance of the remaining area of the resistive element (20).

2. The temperature sensor according to claim 1, wherein the resistance of the bottom segment (24) is greater than the resistance of the segment (22) at a predetermined temperature.

3. A temperature sensor according to claim 1, wherein the resistance of the bottom segment (24) is at least an order of magnitude higher than the segment (22).

4. The temperature sensor according to claim 1, wherein the base (24) has a resistance 2 to 100 times higher than the segment (22).

5. Temperature sensor according to claim 1, characterized in that the segment (22) and/or the bottom segment (24) form an arc or arch of a U.

6. Temperature sensor according to claim 1, characterized in that the segment (22) and/or the bottom segment (24) are at least partially in meandering back and forth.

7. The temperature sensor according to claim 1, characterized in that the segment (22) has a cross section covering a substantial part of the length (L) of the temperature sensor (10), said cross section being larger than the cross section of the bottom segment (24).

8. The temperature sensor according to claim 1, wherein the segments (22) and the bottom segment (24) form a resistive track of uniform thickness, the segments (22) having a width greater than the width of the bottom segment (24).

9. The temperature sensor of claim 8, wherein the resistive traces are comprised of sintered conductive paste.

10. Temperature sensor according to claim 8, characterized in that the segment (22) and/or the bottom segment (24) are formed by at least two resistive tracks lying one above the other, which are separated by an insulating layer.

11. The temperature sensor according to claim 8, wherein the segment (22) and the bottom segment (24) are covered by an insulating layer (26) or embedded in the insulating layer (26).

12. The temperature sensor of claim 11, wherein the insulating layer is a ceramic dielectric layer.

13. The temperature sensor according to claim 1, wherein the segment (22) and the bottom segment (24) have different material compositions.

14. Heating device of a hot runner system having a heating element (42) in thermal contact with a header or nozzle body (K) and a temperature sensor (10) according to any of the preceding claims 1 to 13, wherein said temperature sensor (10) is a measuring element located on or in said header or nozzle body (K).

15. The heating device according to claim 14, characterized in that the heating element (42) consists of an electric heat conducting path (44) that meets performance requirements.

16. Heating device according to claim 15, wherein the heat conducting path (44) has at least partly a meandering form and/or is a double wire.

17. A heating device according to claim 15, characterized in that the resistance of the heat conduction path (44) in the middle part (B) of the header or nozzle body (K) is lower than the resistance of the top zone (O) or the end zone (E).

18. A heating device according to claim 15, wherein in an end region (E) of the header or nozzle body (K) the heat conduction path has or forms at least one zone (46) with a resistance greater than the resistance of the rest of the heat conduction path (44), the bottom section (24) of the temperature sensor (10) being inserted into a recess (47) of the high resistance heat conduction zone (46).

19. The heating device according to claim 18, wherein the bottom section (24) of the thermal sensor is surrounded by closely packed heat conduction paths (44) in a high resistance zone (46).

20. A heating device according to claim 15, characterized in that the heat conducting path (44) is applied to an insulating layer (58) and is covered by a further insulating layer (59).

21. The heating device according to claim 20, wherein the temperature sensor (10) is arranged at the same level as the heat conduction path (44) on the insulating layer (58).

22. The heating device according to claim 20, wherein the heat conducting path (44) and the insulating layer (58, 59) consist of sintered thin film and/or sintered thick film conductive glue.

23. Heating device according to claim 20, characterized in that at least the insulating layer (58) is a ceramic dielectric layer.

24. Heating device according to claim 20, characterized in that the insulation layer (58) is permanently applied to the body (K) of the header or lance and is prestressed or toughened against the body of the header or lance after at least one sintering process.

25. Heating device according to claim 20, characterized in that the insulating layer (58) is permanently applied to a substrate which can be bonded by thermal contact to the body (K) of the header or spout.