WO1991012135A1

WO1991012135A1 - Method of bonding metal sheet material to a core or base sheet material and also an apparatus for carrying out said method

Info

Publication number: WO1991012135A1
Application number: PCT/NL1991/000026
Authority: WO
Inventors: Johan Georges Joseph Berck
Original assignee: Beheersmaatschappij Buitendijk B.V.
Priority date: 1990-02-15
Filing date: 1991-02-15
Publication date: 1991-08-22
Also published as: AU7248391A; NL9000366A

Abstract

The invention relates to the field of bonding metal (6, 8) sheet material to a core or base sheet material with the aid of a fusible bonding layer (7). In this process, the metal sheet material is heated by electromagnetic radiation and the metal sheet material and the core or base sheet material are forcibly pressed against each other in the heating zone or immediately downstream of it. In this process, the heat necessary to fuse the said bonding layer is removed from the heated section of the metal sheet material. According to the invention, a limited section of the metal sheet material is now heated and the bonding layer is heated for a short time to a temperature which is appreciably above its melting point. As a result of this method, the temperature of the core or base sheet material itself will hardly increase and will consequently not be able to fuse. As a result of this it has become possible to laminate relatively thick plastic core material without making use of bonding films and without there being a danger of said core material being pressed out.

Description

Method of bonding metal sheet material to a core or base sheet material and also an apparatus for carrying out said method.

The invention relates to a method of bonding a metal sheet material to a core or base sheet material with the aid of a fusible bonding layer.

A method of this type is frequently used to bond metal sheets to all kinds of core or base sheets. This method is generally described as laminating and the product as a laminate. A known product is the so- called sandwich sheet in which a core sheet made of, for example, light or cheap material is clad on both sides with a metal sheet. Such sheets may be a light or cheap alternative to, for example, sheet steel. Products are also known in which a base sheet is clad on one side with a metal sheet. The metal sheet then has, for example, the function of protecting the base sheet. Conversely, it is also possible for the base sheet to protect the metal sheet. Finally, there are also sheet-like products known which are composed of an alternation of metal sheets and core or base sheets. In this connection, it is possible to think, for example, of a sandwich sheet which is clad on one or both sides with a base sheet. Such an outermost base sheet has, for example, the function of a protective layer for the metal sheet situated underneath it. Such a base sheet also often has a decorative function.

In the laminates discussed above, both the metal sheets and the core or base sheets can per se also be laminates in turn. In the case of aluminium, for example, a so-called cladding layer may be provided on a metal sheet. A core or base sheet often has relatively thin surface layers which are intended to achieve adhesion to a metal sheet. In addition, it is also possible for a separate bonding layer in the form of a film to be used or for the bonding layer to be provided on the metal sheet material. It is also possible for the core or base sheet material to be composed in its entirety of bonding material. In the known methods, the entire laminate is heated right through during assembly to a temperature at which the bonding layers fuse. The various layers of the laminate are then forcibly pressed onto one another and cooled in that state, after which the laminate forms a single whole. In this process, problems are to be expected if the bonding layer is relatively thick or if other relatively thick layers of the laminate are also fused. As a result of forcibly pressing the layers of the laminate onto one another, there is the danger, particularly in the case of relatively quite thick fused layers, of the fused material being pressed out of the laminate, with thickness variations also occurring. To avoid this problem, it is usual to use very thin bonding layers, the melting point of which is above that of the other materials in the laminate. Such a solution imposes limitations on the freedom of choice of material for the laminate. In another solution, the edges of the laminate are sealed off so that molten material is prevented from flowing away. In this case, however, the laminate has an insufficiently constant thickness. The present invention makes a contribution to the manufacture of laminates, in which the problem that relatively thick layers are in the molten state during the manufacture is solved.

According to the present invention, this problem is solved in that the bonding layer in a laminate is heated for a short time to a temperature which is appreciably above the melting point and in that a limited section of the metal sheet material is heated by electromagnetic radiation, in particular inductive heating, and the metal sheet material and the core or base sheet material are forcibly pressed against each other in the heating zone or immediately downstream of it, the heat necessary to fuse the said surface layer being removed from the heated section of the metal sheet material.

As a result of these measures, it -is possible to raise the temperature of the bonding layer which makes contact with the electromagnetically heated metal sheet very rapidly to above its melting point, in which process the other sections of the laminate such as the core or base sheet hardly increase in temperature. Because only a limited section of the metal sheet is heated, the heat thereof can be rapidly removed after the bonding layer has melted. This avoids the bonding layer being exposed for a prolonged time to the high temperatures which may possibly affect the surface. The possibility is also avoided that the remaining sections of the laminate such as the core or base sheet will still become too hot and may melt. In this method it is also possible for only a surface layer making contact with the metal sheet to be fused in the case of a relatively thick bonding layer. It is only with the aid of electromagnetic heating that it is possible to heat a limited section of the metal sheet to the desired temperature. It is also possible with electromagnetic heating to nevertheless force sufficient thermal calories into the surface layer of the core or base sheet in the case of a metal sheet material having low thermal capacity (for example, a relatively thin sheet) . It is then possible to press the metal sheet forcibly onto the core or base sheet without the danger of pressing out a section of the core or base sheet.

The metal sheet therefore acts as a heat buffer which can be additionally heated in accordance with its nature during the contact with the core or base sheet.

This way of deforming is also economical because it is not necessary to heat the entire laminate.

Such a method can be used either in lamination in which at least the surface layer of the core or base sheet material facing the metal sheet material is formed by the bonding layer or in which the bonding material is situated on the surface layer of the metal sheet material facing the core or base sheet material or in which the bonding layer is provided as a separate film between the metal sheet material and the core or base sheet material.

In many cases it will be necessary to keep the metal sheet material pressed onto the core or base sheet material until the bonding has been achieved. This is necessary to prevent the metal sheet becoming detached from the core or base sheet immediately after it has been pressed onto it because the core or base sheet material are pressed into each other somewhat in the contact-pressure region as a result of which the metal sheet material is not flat and tends to become detached from the core or base sheet near the contact-pressure region as a consequence of its flexural stiffness. This tendency will be great, especially if a powerful pressing-on takes place in a small area (for example, if pressure rollers are used) . A fused bonding layer will usually not be capable of preventing this problem. It will once it has cooled sufficiently. Until that time a contact-pressure force is required.

It is preferable that the metal sheet material, the bonding layer and the base or core sheet material are passed together and at the same speed continuously past an inductive heater. As a result of this, a more or less continuous laminate manufacturing process is achieved.

Such a method will, for example, be very suitable for manufacturing a so-called sandwich sheet material in which a metal sheet material whose thickness is less than the thickness of the core sheet material, which is usual in this connection, is bonded to both sides of the core sheet material. Such a sandwich may, for example, be made up as follows: two aluminium layers each 0.2 mm thick with a plastic layer 0.6 mm thick in between. With a density of 2.73 kg/dm³ for aluminium and of 1.1 kg/dm³ for plastic, 1 square metre of this will weigh 1.752 kg whereas the same sheet made of 1 mm thick aluminium weighs 2.73 kg. In this way, a light sheet material is obtained.

As a result of heating a metal sheet, it will expand. Because a heated metal sheet section is adjacent to an unheated section in the present method, expansion differences arise. In the case of relatively thin sheets, folds may arise in the sheet as a result of this. This can be prevented by ensuring that the plane of the metal sheet material undergoes a bending or flexure in or near the heating zone. As a result of said bend or flexure, the stiffness of the sheet increases in the plane and folds can no longer occur.

The invention also relates to an apparatus for carrying out the present method which comprises means for heating the metal sheet material electromagnetically, in particular inductively, and contact-pressure means for pressing the metal sheet material in or near the heating zone onto the core or base sheet material.

It is preferable that the apparatus comprises means for placing the section of the metal sheet material which is in or near the heating zone at an angle with respect to the exit plane of the heating zone. As a result of this, folds in the plane of the material which arise as a consequence of expansion differences are prevented.

The invention will now be explained in greater detail with reference to a number of exemplary embodiments of apparatuses for carrying out the method according to the present invention. In these exemplary embodi- ments, a core of base sheet material is always used which is provided with a fusible bonding layer on the surface facing the metal sheet material. Of course, for the purpose of the invention, a bonding layer in the form of a separate film can be used in the same way, or the bonding layer can be provided on the surface of the metal sheet material facing the core or base sheet material. In this connection, use is made of the attached drawings, in which:

Figure 1 shows a diagrammatic view of the section of the apparatus in which the heating and contact-pressure zone for bonding the metal sheet to the core or base sheet are situated. Figure 2 shows in a view another embodiment of the heating and contact-pressure zone.

Figure 3 shows a final embodiment in a view of the region in which the heating and contact-pressure zone are located.

Figure 4 shows a temperature-time diagram of the metal sheet while passing the heating zone.

Figure 1 shows the inductive heating means of an apparatus 1 for carrying out the method according, to the present invention, which means are indicated below by inductors 2 and 3 which are situated opposite the pressure rollers 4 and 5- In this case, the heating zone is bounded by the influence region of the inductors 2, 3 and the contact-pressure zone by the influence region of the pressure rollers k , 5- With the aid of this apparatus, a metal sheet 6 is first provided on the core sheet 7 at the position of the inductor 2, after which the metal sheet 8 is subsequently bonded to the same core sheet 7 at the position of the inductor 3- In this case, the metal sheets 6, 8 and the core sheet 7 are fed at the same constant speed past the inductors 2, 3- The metal sheet 8 is brought to the desired temperature by the inductor 3_' Because the metal sheet 8 moves past the inductor 3 at a certain speed, the metal sheet 8 has to be irradiated by the inductor 3 over a certain length in the direction of movement in order to heat it for this purpose. In order to keep the heating constant if the speed is variable, a section of the inductor 3. for example, may make an angle with respect to the plane of the core sheet f . The distance between the metal sheet 8 and the inductor 3 can then be varied in said section by varying the angle at which the metal sheet approaches the core sheet 7. Thus, the distance between the metal sheet 8' and the inductor in the foremost region of the latter is greater than that between the metal sheet 8 and the foremost region of the inductor 3« As a result of this greater distance, the heating in said region is less because the degree of heating is inversely proportional to the square of the distance in the case of electromagnetic heating. The variation of the angle may, for example, be done by computer control. The inductor 3 then heats the metal plate 8 in a very short time to a tem¬ perature which is above the melting point of the surface of the core sheet 7 which in this case forms the bonding layer. Then the surface of the core sheet 7 also undergoes, in a very short time, a temperature increase which is sufficient to cause the surface to melt. As a result of the rate at which the temperature increase takes place, the temperature of the remaining section of the core sheet 7 will hardly be increased, as a result of which this section retains its solid form. There is therefore also no danger of a section of the core sheet 7 being pressed out when the metal sheet 8 is pressed at that instant onto the core sheet 7 by the inductor 3 which is in this case on a foundation 9 and the pressure roller 5 which exerts a force in the direction of the inductor 3» In this connection, the pressure roller 5 can be driven to rotate, as a result of which the feed-through of the various sheets is achieved. It is also possible that the pressure roller 5 rotates freely, the feeding of the various sheets through the apparatus being achieved elsewhere in the apparatus. The same applies to the application of the metal sheet 6 with the aid of the inductor 2 and the pressure roller 4 as for the metal sheet 8, with the proviso that in Figure 1 the distance between the metal sheet 6 and the inductor 2 is greater in the foremost region of the latter than that between the metal sheet 8 and the inductor 3- This may, for example, be necessary if, for example, the composition of the surface layer of the core sheet 7 with which the metal sheet 6 comes into contact has a different melting behaviour or if, for example, the thickness of the metal sheet is different from that of the metal sheet 8, as a result of which the heating behaviour is different. The metal sheet 6 is in this case pressed onto the core sheet 7 by an inductor 2 energised by a spring 10 and the pressure roller 4 which, for example, is mounted with respect to a foundation. Of course, there are other possibilities for generating a contact-pressure force between the inductor 2 and the pressure roller 4, or the inductor 3 and the pressure roller 5t respectively. It is usually necessary that, downstream of the heating zone after the metal sheet material has been pressed onto the core or base material, this pressure is more or less maintained until the surface layer has cooled sufficiently. This is to prevent the metal sheet material separating from the core or base material immediately after the contact-pressure zone. In Figure 1 unheated contact-pressure elements 13 which are arranged downstream of the inductors 2, 3 are provided for this purpose.

In Figure 2, the inductors 2, 3 are constructed as cylindrical rollers. The inductors 2, 3 then simultaneously form the contact-pressure means. In this case, the metal sheets 6, 8 are simultaneously applied to the core sheet 7- In order to place the metal sheets 6, 8 in or near the heating zone at an angle with respect to the exit plane of the heating zone, said sheets can, for example, be fed over guide rollers 11, 12. This causes the metal sheets 6, 8 to undergo a change in direction in or near the heating zone. This prevents folding as a consequence of the very local expansion of the metal sheets. This, also causes the metal sheet 6, for example, to be irradiated by the inductor 2 over a reasonable length. Normally, this distance will in fact be almost a line, which offers insufficient opportunity to heat the metal sheet 6 with the aid of the inductor 2. As a result of the arrangement shown, the metal sheet 6 touches the inductor 2 over a greater circumferential region. In order to increase the irradiation length between the metal sheet 6 and the inductor 2, the metal sheet can be brought into the position which is indicated by 6' by, for example, placing the guide roller 11 in the position 11'. Of course, such an apparatus with a few modifications can also be used to make a laminate composed of one metal sheet 6 and a base sheet 7« Moreover, the inductors 2, 3 con be driven to rotate, so that they provide the feed-through of the sheets. They may also be freely rotatable, the feed-through of the sheets being provided elsewhere in the apparatus. Here again contact-pressure elements 13 are used to keep the metal sheet material pressed onto the core or base sheet material until the molten bonding layer has cooled sufficiently.

Figure 3 shows another embodiment of an apparatus in which the metal sheets 6, 8 are fed between two inductors 2, 3 and are heated at that point, after which said sheets are subsequently pressed onto the core sheet 7 with the aid of contact-pressure means 4, 5- Placed downstream of the inductors 2, 3» which serve as a heating and contact- pressure zone, are contact-pressure means 4, 5 which form a double strip press. As a result of this, pressure can be exerted on the sheets with the aid of, for example, compressed air, over a certain length in the direction of movement thereof, while cooling can also be carried out over a certain path length with such a press. Of course, other contact- pressure means are also possible. The double strip press 4, 5 may, for example, also be designed to provide the heating. For this purpose, the foremost rollers (the left one in Figure 3) can be constructed as inductors. The contact-pressure elements 13 are then no longer necessary because the strip of the double strip press 4, 5 pressed onto the sheet material 6, 7, 8 is now able to perform this function completely on its own. In the apparatus according to Figures 1-3, the sheets move with respect to the apparatus. The converse is, of course, also possible. With an apparatus as shown in Figures 1-3, or a variant thereof which falls within the scope of the invention, it is also possible, for example, to give the laminate a profile. The laminate thus formed can then, for example, be cut into strips or rolled up.

Figure 4 shows the change in temperature of a metal sheet while the latter is being fed through the heating zone. The metal sheet enters the heating zone at temperature T₀ at time instant t₀. In a very short time, the inductor heats the temperature of the metal sheet to T₂. This temperature is above the melting point Tj of the bonding layer which, in this example, forms the surface layer of the base or core sheet to which the metal sheet will be bonded. At the time instant t_lt the metal sheet comes into contact with the base or core sheet. The temperature of the metal sheet will consequently drop rapidly and it is usually necessary to keep the temperature of the metal sheet at T₂ with the aid of heating. At time instant t₂, the heating of the metal sheet is terminated, as a result of which the temperature of the metal sheet will rapidly drop and at time instant t₃ will drop below the melting point Tj of the respective surface layer of the core sheet or base sheet. The surface layer is thus fused with the aid of "shot heating". These time instants are all so short that only a small thickness of the respective surface layer of the base or core sheet is fused. As a result, for example, of choosing the heating temperature of the metal sheet at T₃, it is possible to heat the metal sheet for a shorter time. Such a path is shown by a broken line in Figure 4. As a result of this it is possible to feed the sheet materials past the heating zone at greater speeds. It should be clear that the present invention is not limited to what has been described above. Characteristic of the invention is that, to bond a metal sheet material to a core or base sheet material with the aid of a fusible bonding layer, the latter is heated and fused so rapidly that the remaining section of the laminate, including the core or base sheet material has still hardly increased in temperature. This very rapid temperature increase is caused by heating the metal sheet material over a limited region with the aid of electromagnetic heating, in particular induction.

Claims

. CLAIMS

1.Method of bonding metal sheet material to a core or base sheet material with the aid of a fusible bonding layer, in which the metal sheet material is heated by electromagnetic radiation, preferably inductive heating, and the metal sheet material and the core or base sheet material are forcibly pressed against each other in the heating zone or immediately downstream of it, and in which the heat necessary to fuse the said bonding layer is removed from the heated section of the metal sheet material, characterised in that a limited section of the metal sheet material is heated and in that the bonding layer is heated for a short time to a temperature which is appreciably above the melting point.

2.Method according to Claim 1, characterised in that at least the surface layer of the core or base sheet material facing the metal sheet material is formed by the bonding layer.

3.Method according to Claim 1, characterised in that the bonding material is situated on the surface layer of the metal sheet material facing the core or base sheet material.

4.Method according to Claim 1, characterised in that the bonding layer is provided as a separate film between the metal sheet material and the base or core material.

5.Method according to Claims 1-4, characterised in that the metal sheet material is kept pressed onto the core or base sheet material until the bonding has been achieved.

6.Method according to Claims 1-5. characterised in that the metal sheet material, the bonding layer and the base or core sheet material are passed together and at the same speed continuously past an inductive heating device.

7.Method according to Claims 1-6, characterised in that metal sheet material is bonded to both sides of the core sheet material, the thickness of the core sheet material being greater than the thickness of the metal sheet material.

8.Method according to one of the preceding claims, characterised in that the plane of the metal sheet material undergoes a bending or flexure in or near the heating zone.

9.Apparatus for carrying out the method according to Claims 1 to 8 inclusive, characterised in that it comprises means for heating the metal sheet material electromagnetically, in particular inductively, and con¬ tact-pressure means for pressing the metal sheet material in or near the heating zone onto the core or base sheet material.

10.Apparatus according to Claim 3. characterised in that said means comprise placing the metal sheet at an angle with respect to the exit plane of the heating zone in or near the heating zone.

11.Apparatus according to Claim 10, characterised in that the angle is variable.