EP2305004A2

EP2305004A2 - Heating element of a heating comb for producing a honeycomb material

Info

Publication number: EP2305004A2
Application number: EP09702561A
Authority: EP
Inventors: Bernard J. Michels; Norbert Uebach
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-01-18
Filing date: 2009-01-06
Publication date: 2011-04-06
Also published as: DE102008005220B4; DE102008005220A1; WO2009090116A2; WO2009090116A3

Abstract

The invention relates to a heating element (18) of a heating comb made from an electrically conductive material (22) for producing a honeycomb material (10) from thermofusible material (14), said element having zones and different electrical resistors, as a result of which the zones are heated differently.

Description

Designation: Heating element of a heating comb for the production of a honeycomb material

The present invention relates to a heating element of a heating comb for producing a honeycomb material from a thermofusible material.

Honeycomb materials or elements are widely and increasingly used. Reasons for this are in particular the high compressive strength and rigidity of such structures. Honeycomb materials can be used, for example, as insulating material in cooling technology, as acoustic insulating materials or as lightweight building materials. The use of honeycomb materials in mechanical engineering, in rail and road transport, in scaffolding, in the aerospace industry, for high-performance sports equipment and in the construction of racing vehicles and high-sea yachts is well known. Furthermore, honeycombs of larger dimensions can be used for ground mounting, road construction, sports fields, horticulture, dam and thinnest attachment.

Honeycomb materials are known from the materials metal, in particular aluminum or steel, paper or cardboard and plastic. Aluminum honeycombs have the disadvantage that the raw material aluminum is relatively expensive and the production of aluminum honeycombs is expensive. Although honeycomb material made of paper or cardboard is lightweight and easy to produce by gluing, there is a lack of often necessary strength, resistance to moisture and fire resistance. For this reason, such honeycomb are primarily only as a commodity, z. B. used as packaging material.

Plastic honeycomb material, however, has a number of advantages, but in particular the production of the honeycomb structure is possible only with increased difficulty.

The production of honeycomb materials can be done, for example, starting from flat material (films).

In such a production films are fed to a welding device at room temperature. In this case, two opposite foil webs of a plastic material having a melting point, partially melted under the supply of heat, the melts then combined and cooled. The films form a monolithic block in the molten and then cooled areas, which is macroscopically homogeneous but may consist microscopically of very different structural phases. These two film webs are then bonded to a third web in the same manner, with the "welds" longitudinally of the film webs offset from the already existing welds, and then the bonded webs are pulled apart at an adequate temperature to the honeycomb body to be achieved ,

It is known that the heating combs used for the compound have individual heating elements, which may consist of steel, which is formed around an insulator. The insulator may for example consist of polyimide, a thermoplastic high-performance plastic from the group of polyimides. Since in the production of the honeycomb material, the insulator is briefly exposed to very high temperatures of more than 300 ⁰ C during the heating phases, there is usually a use of the polyimide Vespel®, which easily tolerates these temperatures, but ages under the influence of temperature and thus becomes unstable. Both the detection and the regulation of the temperature takes place via a thermo-sensor, which is housed in the insulator. However, this proves to be disadvantageous in that the heating elements are not very stable and are therefore easily destroyed if used incorrectly. Furthermore, the dead times occurring in this method lead to a complex PID parameterization in the individual temperature measurements and thus require special operation steps at the start of welding.

Furthermore, nonwovens or films with a density of less than 190 gr / m ² can not be processed because the heating elements currently used are too thick and a thinner construction is too unstable due to the mechanical properties of the Vespel®.

One area of application for honeycomb materials with low density would be, for example, the use as thermal insulation, and the production of clear optical translucent honeycomb or honeycomb materials. Also the then favorable light diffusion would be advantageous. Since no special strengths are required in the fields of heat and optics, but thermal and optical properties are important, thin films could be used in these areas. Furthermore, spunbonded nonwoven webs could be advantageously used in filtration applications. Also, a use in the field of soil attachment of, for example, non-accessible areas such as dams or slopes and noise barriers on highways would be advantageous.

It is the object of the present invention to provide a heating element which makes it possible to weld honeycomb materials faster, easier and more reliable. In particular, a welding of low density material should be possible.

According to the invention the object is achieved by a heating element for producing a honeycomb material from a thermofusible material having the features of claim 1. In this case, the heating element according to the invention is characterized by zones with different electrical resistances, which cause a different heating of the zones when current flows. Advantageous embodiments of the invention are specified in the subclaims.

The zones can be produced according to the invention by at least one slot in the heating element. If a slot divides an electrical conductor and its width varies, the resistance varies inversely linearly with the width of the conductor, with the current flowing at its temperature, depending on the ambient temperature and the thermal conductivity. Take, for example, a transparent heating element that tapers from its base to the tip and introduces a slot, electrical resistance increases from the base to the tip. If the heating element at the base is connected to a thermal mass and the tip is exposed in the air, the temperature drops from tip to base.

In this way, it is possible that a heated heating element in the lower region has a lower temperature than in the upper region. If the heating element between two sheets of film is introduced to weld them, the contact between the heating element and the film web is formed only at the moment when the heating element is fully inserted. Accordingly comes the lower portion of the film web with the heating element when pulling out the longest in contact.

The contact thus arises only when the heating element is fully inserted. If a heating element with a length of 10cm is withdrawn at a constant speed, the lower centimeter of the film webs is heated 10 times more than the upper one with uniform heating temperature from top to bottom. Since the acceleration of the retraction is limited, the temperature of the heating element must fall from top to bottom to ensure a constant heat transfer to the webs. The different temperature zones of the heating element, which are particularly advantageous from top to bottom, thus ensuring a constant heat transfer to the film webs, so that all areas of the film webs are welded together at about the same time and the film webs in the lower area not by possibly too hot or too long Heating to be destroyed.

In a further particularly advantageous embodiment, the heating element has grooves for generating zones. By removing material also the electrical resistance is changed, there is only complete separation of the heating element.

The zones can be varied by the geometric dimensions of the slot of the groove, ie length, width and / or depth.

The division into temperature zones leads to a continuously occurring temperature topography starting from the upper very hot region of the heating element to the lower somewhat cooler region of the heating element and / or from a hot region in the middle of the heating element to colder temperature zones on the respective sides.

In a particularly advantageous embodiment, the groove is filled with an electrically conductive material having a different electrical conductivity than the material of the heating element. Since the entire geometry of the heating element is often predetermined in terms of process technology, filling the groove with an electrically conductive material provides another possibility for producing a wanted temperature topography, which is largely independent of the geometry of the heating element. Thus, for example, the groove filling be carried out such that a wire made of copper, aluminum, brass, silver, etc. introduced from a good electrically conductive metal in the groove and soldered by brazing and then the excess soldering bead is ground down to the heating element level. In this way, for example, a copper-filled 0.5mm wide groove behaves like a pure stainless steel heater that is 20mm wide, as the copper electrical resistivity is about 40 times smaller than that of stainless steel. Preferably, the resulting electrical circuit causes an electrical resistance change of at least 400ppm / ° C, preferably> 1000ppm / ° C.

In a third embodiment of the invention, the zones are defined by different geometry, e.g. Thickness (thickness) of the heating element itself generated over its course. For example, the heating element may be thinner at its tip than at its base.

The three methods mentioned for generating the zones are based on the shape of the heating element and thus the change in the electrical resistance per zone. The three shaping measures can be combined as desired with one another in order to achieve as exact a temperature distribution over the heating element as possible.

In particular, the heating element may be made of steel, in particular of stainless steel. Stainless steel is significantly more robust than polyimide Vespel®, which results in improved stiffness of the heating element. In this way, the heating elements may be substantially thinner than heretofore (for example, 1.5 mm from the original 3.2 mm), whereby honeycomb materials can be made from materials with lower thicknesses. In this way, the periphery of the heating element can be made simpler and more robust by the improved rigidity of the heating elements, which on the one hand the production of larger raw honeycomb and on the other hand an increase in the welding cycle is possible.

It is possible to regulate the temperature zones by the respective temperature coefficient of the resistance (TCR), since the different temperature zones of the Heating element to change its resistance with the temperature. The properties of a TCR control are known, for example, from sensor technology, in which PCT and NCT resistance alloys are used. The average resistance specifies the actual value for the control. Furthermore, the temperature coefficient (TCR) depends on the materials used, so that an absolute temperature determination is possible. The dead times of the TCR control in relation to the dead times of currently used temperature measurements are much lower.

Advantageously, during welding, the groove receives the melt of the polymer to be welded. The polymer degrades very slowly because it is exposed to a very small groove surface. Furthermore, the welding process is initiated more quickly when the sheets to be joined are wetted with liquid polymer, whereby the heat transfer is considerably accelerated. In contrast to the conventional heating elements, which can accommodate the polymer only on its surface, fill in the Heizkämmen invention, the grooves with the polymers. At temperatures above the melting point, the liquid polymer degrades rapidly on the heating comb surface because it is exposed to a large air surface, which is not the case for the polymer in the groove.

A device with heating elements according to the invention is particularly suitable for welding nonwovens. For the purposes of the invention, the term nonwoven is understood to mean a coherent thread layer and / or continuous thread layers. For example, spunbonded nonwovens which are produced directly from a dope are also suitable. On a conveyor belt, the scrim is deposited and subsequently optionally chemically or thermally solidified. Subsequently, the fleece can still be dyed and / or printed. As raw materials are predominantly polypropylene, but also polyester, polyamide or copolymer threads in question.

The production of different hot zones across the width of the heating element improves the production of nonwoven honeycombs because, for example, the threads in the middle can be very strongly welded, while the degree of Welding to the sides is less. The brittleness at the honeycomb edges is significantly reduced.

Also, the heating elements can be coated many times. For example, a copper layer can further reduce the electrical resistance in the lower region and / or improve the electrical contacts. Furthermore, as an additional layer, a material with low surface energy can be applied, whereby the adhesion to a metal surface is substantially reduced.

According to the invention, any number of heating elements can be connected either in parallel or in series. Wherein the resistance R can be determined by U / I or with a Wheatstone bridge and is independent of the current regime.

Furthermore, welding methods are possible which are based on the principle of external heating and / or the principle of internal heating.

In a method according to the principle of external heating, heat is introduced from outside into the film webs with the aid of heating elements according to the invention until both film webs have reached the melting temperature. The heat is thus passed through film webs until the surfaces facing each other are sufficiently heated. The heat can be introduced only through a film web, but it is also possible to heat both to be joined film webs.

In a method according to the principle of internal heating, however, a heating element according to the invention is brought between the film webs to be joined. The film webs are therefore heated only on the sides, which are to be connected later.

But it is also possible a combination of the two methods. Especially with honeycomb materials with large cells and thick or thick material, it makes sense to heat the film webs from the outside and from the inside. The heat then reliably reaches all threads. The methods mentioned are only to be understood as examples; it is only essential for the production of a honeycomb material that a sufficiently stable welded joint is formed.

In the following the invention will be explained with reference to the accompanying figures. Further advantages and embodiments will become apparent from this description and the appended claims.

Show it :

FIG. 1 is a schematic representation of a honeycomb material;

2 shows a schematic diagram of the production of a honeycomb material by heating the films to be joined from the outside,

Figure 3 is a schematic diagram of the production of a honeycomb material by

Heating the foils to be joined from the inside,

Figure 4 is a schematic view of a heating element according to the invention.

FIG. 1 shows, in a simplified basic representation, a detail of a honeycomb material 10. In the present exemplary embodiment, this has hexagonal cells 12.

The honeycomb material 10 is formed from a material 14 or from interconnected film webs 14 a, 14 b, 14 c. In the embodiment shown, three contiguous film webs 14 a, 14 b, 14 c are shown differently for better understanding, but this does not mean that it is film webs 14 a, 14 b, 14 c made of different materials. The film webs 14 a, 14 b, 14 c are partially interconnected via connecting cuts 16, wherein the connecting portions 16 are offset from film web to film web by an amount H to each other. Depending on the choice of the size of the offset H, the shape of the cells 12 can be adapted to desired conditions. H is the distance from composite center to composite center. Furthermore, a cell division A is shown, which essentially means a height of a cell 12. The cell division A depends on the application and can vary from a few millimeters to the meter range.

The material 14 may be formed by a thermofusible or weldable material such as films, non-woven and / or textile material.

This heating of the material to be welded 14 can be done on the one hand according to the principle of internal heating (Figure 3) and on the other hand according to the principle of external heating (Figure 2) or by a mixed form.

FIG. 2 illustrates the principle of external heating. A first film web 14 a is in contact with a second film web 14 b and heating elements 18 according to the invention are brought into contact with the first web portion 14 a. The heating elements 18 heat them in such a way that heat is transferred first from the heating elements 18 to the first film web 14 a and then from the first film web 14 a to the second film web 14 b. The result is a heating area 20. Usually, the two film webs 14 a, 14 b pressed against holding stamp 22, which leads in this area in nonwoven fabric to a targeted Nachkalandrierung. Subsequently, the heating elements 18 are withdrawn, the film webs 14 a, 14 b are welded.

After the two film webs 14 have been joined together, a third film web 14 c (see Fig. 1) is added to these two film webs. It is necessary for the execution of the honeycomb structure that the connecting portions 16 between the first film web 14 a and the second film web 14 b offset from the then following connecting portions between, for example, the second film web 14 b and the third film web 14 c are arranged.

FIG. 3 illustrates the principle of internal heating. The heating elements 18 according to the invention are arranged between the first film web 14 a and the second film web 14 b. As a result of the heating, the heating region 20 is simultaneously formed in both film webs 14 a, 14 b, the heat transfer takes place starting from the heating elements 18 via the facing surface. nenflächen the film webs 14 a, 14 b in this. Overall, the heating can take place very quickly up to or above the melting temperature, taking into account the heat diffusion rate. It is essential for the heating that the melting temperature of the film lasts as short as possible in order to avoid or restrict recrystallization. The goal is, for example, in films, only a minimal area of the film webs 14 a, 14 b physically to change, so only a small area of the heating area 20 as possible.

After the two film webs 14 a and 14 b have reached the welding temperature, the heating elements 18 are removed and the two film webs 14 a, 14 b, for example, by means of movable cylinders, not shown, compressed. The movable cylinders may be covered with a soft material to form the film webs 14a. 14b as gently as possible to compress.

In a particularly advantageous embodiment, the movable cylinder clamp the heating elements 18 when they are between the film webs 14 a, 14 b, so they press the film webs 14 a, 14 b against the heating elements 18 After reaching the welding temperature, the heating elements pull 18 back.

After the two film webs 14a, 14b have been joined together, a third web section 14c (see Fig. 1) is added to these two film webs 14a, 14b. It is necessary for the formation of the honeycomb structure that the connecting portions 16 between the first track portion 14 a and the second track portion 14 b offset from the then following connecting portions between, for example, the second track section 14 b and the third Bahnabschnittl4 c are arranged.

Usually, a fanning of the assembled film webs 14a, 14b to the final honeycomb material 10. This can also be done later, for example, at the site of the honeycomb material. Thus, after sufficient foil webs 14 have been joined, they are mechanically pulled apart so that the honeycomb cells open and, after cooling, the desired honeycomb material 10 is formed. FIG. 4 shows an embodiment of a heating element 18 according to the invention. The heating element 18 consists of an electrically conductive material into which two slots 20 are made in the exemplary embodiment shown. The slots 20 cause the current flow depending on the geometric dimension of the remaining material different electrical resistances are opposed. In the exemplary embodiment shown, connections 22 are shown in a foot region of the heating element 18, via which electrical current is introduced into the heating element 18.

The slots 20 effect in the embodiment shown, the hot zones 34 and colder zones 36 are generated. These zones 34, 36 extend both in the longitudinal direction of the heating element and in the transverse direction. The arrangement and geometry of the slots 20 is freely selectable for each individual case or for each honeycomb manufacturing device to be manufactured. It can also be seen that the geometric dimensions of the heating element 18 itself produce the desired zones 34, 36 with different electrical resistances and thus different temperatures. The heating element 18 shown tapers in this example in the direction of its free end, in order to achieve a better mechanical stability.

Furthermore, FIG. 4 shows that the zones 34, 36 of different temperature can also be created or influenced by introducing a groove 30. For the purposes of this invention, the term groove 30 describes a recess in the material of the heating element 18. Advantageously, the groove can be filled with a selected material, wherein the filling material has a different electrical resistance than the material of the heating element. By filling with different materials, it is possible to vary the temperature zones in the heating element 18.

The division into temperature zones leads to a continuously occurring temperature topography. The use of the heating element 18 ensures that the material 14 to be welded can be welded to a temperature and time adapted to its position. If the heating element 18 is inserted between two film webs in order to weld them together. Shen, the contact between the heating element 18 and the film web is formed only at the moment when the heating element 18 is fully inserted. Accordingly, the lower portion of the film web comes with the heating element 18 the longest in contact, because the heating element 18 is guided over its entire length from top to bottom of this. The upper portion of the film webs 14 a, 14 b, 14 c comes so only briefly and only with the hot upper portion of the heating element 18 in contact, while the lower portion of the film webs 14 a, 14 b, 14 c when running with all temperature zones the heating element 18 comes into contact. The different temperature zones of the heating element 18 thus ensure the desired optimum heat transfer to the film webs, so that all areas of the film webs are welded together as desired and the lower portion of the film webs 14 a, 14 b, 14 c not by possibly too hot or too long heating or treatment is destroyed by the heating element 18 with the heating comb.

The heat transfer according to the invention can also be influenced by an adaptation of the speed of movement of the heating element when pulling out. For example, it may be useful to increase the pull-out speed during the pull-out operation.

Claims

claims

1. heating element (18) of a heating comb made of an electrically conductive material (22) for producing a honeycomb material (10) from thermofu- sionable material (14) characterized by zones (34, 36) with different electrical resistances, resulting in different heating of the zones (34, 36) leads to current flow.

Second heating element (18) according to claim 1, characterized in that the zones (34, 36) by a geometric shape of the heating element (18).

3. heating element (18) according to claim 2, characterized in that the shaping by at least one slot (20).

4. heating element (18) according to one of claims 1 to 3, characterized by the shaping by at least one groove (30) is formed ..

5. heating element (18) according to one of claims 1 to 4, characterized in that the heating element (18) consists of metal.

6. heating element (18) according to one of claims 1 to 5, characterized in that the groove (30) is filled with electrically conductive material.

7. heating element (18) according to claim 6, characterized in that, the electrically conductive material (22) causes an electrical resistance change of at least 400 ppm / ° C, preferably> 1000 ppm / ° C causes

8. Heating element (18) according to one of claims 1 to 7, characterized by a plurality of slots (20) and / or grooves (30).

9. heating element (18) according to one of claims 1 to 8, characterized in that the shaping is formed by different thicknesses of material.

10. heating element (18) according to one of claims 1 to 9, characterized in that the shape over its course has different geometric dimensions.

11. Heating element (18) according to one of claims 1 to 10, characterized by a coating with low adhesion potential.