METHOD AND APPARATUS FOR MANUFACTURING A HEATER

Abstract: Method for the preparation of a band, sheet, foil, fabric, mesh, or a similar plastic layer (1) that is heatable by means of an electric resistance wire. Thereat, having been heated by means of electric current, the resistance wire (2) is pressed into the said plastic layer (1) consisting of a thermoplastic when this layer is partly softened or molten by the effect of the hot wire (2) at the wire. The wire (2) remains inside the plastic (1) when the plastic is again cooled and receives its former state. Thereinafter, when the resistance wire (2) is heated to an appropriate extend by means of electric current, while the plastic (1) does not become excessively soft and while the resistance wire (2) remains in it, the plastic layer (1) can be used for heating the desired objects.

Description: Method and apparatus for manufacturing a heater The invention is concerned with a method for the preparation of a band, sheet, foil, fabric, mesh or a similar plastic layer that is heatable by means of an electric resistance wire. The invention is also concerned with an apparatus for the application of the method. A sheet or band heatable by means of an electric resistance wire and prepared by means of the method meant in the present invention can be used as such or as cut-off to primary elements of appropriate size for most varied purposes. They may be used as coated with a layer or layers of cloth in or on, e.g., seats, in particular car seats, covers, clothes, e.g. diver's suits, gloves, shoes, etc. for heating them and for other, corresponding purposes. The elements are heated by means of the resistance wires contained therein by means of electric current, preferably a low-voltage current. The method of preparation meant in the inven¬ tion is in particular characterized in that, having ■ been heated by means of electric current, theresistance wire is pressed into the said plastic layer consisting of a thermoplastic when this layer is partly softened or molten by the effect of the hot wire at the wire and that the wire then remains inside the plastic when the plastic is again cooled and receives its former state, whereinafter, when the resistance wire is heated to an appropriate extent by means of electric current, while the plastic does not become excessively soft and while the resistance wire remains in it, the plastic layer can be used for heating the desired objects. The apparatus in accordance with the inven¬ tion is characterized in that the apparatus comprises a drum and a roll pressing against the drum, the plastic layer being fed to between the drum and the roll, whereat the resistance wire heated by means of electric current is pressed into the plastic. An embodiment of the invention will be described in the following with reference to the attached drawings. They are sche atical illustrations: Figure 1 , of an apparatus for carrying out the method as viewed from behind, Figure 2, of the same as Fig. 1, but as a side view. Figure 3, of the apparatus on an enlarged scale as a partial sectional view. Figure 4, of a part taken apart from the apparatus, and Figure 5, of an element band manufactured in accordance with the method. The product shown in Fig. 5 is a band of uniform width, of a thickness, e.g., of 1 mm or less and of a width, e.g., of 5 to 10 cm. The material of the band is of a flexible thermoplastic plastic, as solid or perforated. It may also be of a mesh struc¬ ture, whereat the area of the meshes or openings in the net is, e.g., about one half or more than one half of the overall area of the net. The meshes in the net may be small, e.g. about 1 to 2 sq. mm. Into the band, a thin resistance wire 2 has been pressed as hot, the said wire winding back and forth in the band 1 in the way shown in Fig. 5. The resistance wire may be thin, e.g. 0 about 0.1 mm or less. Out of the continuous element band meant in Fig. 1, it is possible to make primary elements by cutting it into pieces of appropriate length, for being placed into the object of heating. Several primary elements may be connected electrically in parallel, and the supply of current into the resistance wires can be arranged, e.g., from a transformer, from a rectifier, from an accumulator, or from a battery via supply conductors common for the primary elements. Owing to the low voltage (e.g., 12 to 24 V), the connections do not require particular protections, and the heat that is generated does not melt the plastic. The resistance wires for the primary element may also be manufactured of an appropriate iron alloy, besides the usual metal alloys used for this purpose in prior art, in which case their cost is more favourable than the cost of wires made of a manganese alloy or equivalent. When an alloy of iron is used, a favour¬ able dependence on the temperature is obtained for the resistance wire: An increase in temperature increases the resistance value of the primary element and, with constant-voltage supply, the output is reduced. In this way, a local self-control property is obtained for the network, which causes a more isothermic distribution of temperature in the element itself. The apparatus for the preparation of the ele- ment band comprises a drum 3, which can be rotated on its shaft 4 attached to the frame of the machine (not shown in the drawing) , e.g., by means of a motor (not shown) . The end walls of the drum extend as a flange towards the centre to the circumference 5 of a circle inside which there are, at each end of the drum, centre pieces 6 stationarily mounted to the frame, the shape of the said centre pieces being shown in Fig. 4 as viewed in the direction of viewing of Fig. 2. In the mantle face of the drum, near its edges, there are uniformly spaced radial holes and pins 7 in the holes. Fig. 3 is an enlarged and partial view of an axial vertical section through Fig. 2, at the topmost pin 7 shown therein. The pin 7 is of circular section, and its bottom portion extends at the shoulder 8 downwards as thicker. Between the shoulder and the inside face of the drum, there is a spiral spring 9 around the pin, which spring presses the pin downwards, against a stationary guide piece 6 , and the pin is capable of moving in its longitudinal direction in the corresponding holes in the drum. When the drum revolves, the guide pieces 6 push the outermost ends of the pins 7 somewhat out of the mantle face of the drum, as is shown in Fig. 2, on the left-side portion of the drum. Correspondingly, on the right-side portion of the drum, by the effect of the springs 9, the outermost ends of the pins have been ■ pulled to the level of, or slightly inside, the outer face of the drum as the lower ends of the pins are placed against the guide piece 6. Underneath the drum 3, there is a cylindrical roll 10, which can revolve around its shaft 11 attached to the frame. The roll 10 is coated with a resilient layer 12, e.g., of rubber, which is compressed against the drum. In front of the roll, there is a feeding table 13. The upper part of the end of the table placed next to the roll is shaped as downwardly concave so that it runs along the mantle face of the roll and extends to the proximity of the contact point 14 between the roll and the drum. When element band is being prepared by means of the apparatus, the drum 3 is rotated, according to Fig. 2, anti-clockwise. The resistance wire 2 is threaded, e.g., by means of a separate threading device (not shown in the figure) around the pins 7 in the upper portion of the drum so that, on the face of the drum, the wire receives a form somewhat resembling the toothing of a saw, shown in Fig. 1. The wire is on the drum in this form even when the roll 10 presses the thermoplastic plastic band fed from the table 13 to between the drum 3 and the roll 10, 12. By means of electric conductors and connecting devices (not shown in the drawings) , an appropriate electric voltage is connected between two pins 7 placed on the drum. One of these pins is close to the face of the feeding table, or even in contact with it, and the other one of the pins is at an appropriate distance higher on the drum. Inside the drum, there are collec¬ tor means of a construction in itself known, e.g. similar to those in a DC motor, which, when the drum revolves and when the pins are in, and close to, the said locations, connect the voltage to the said pins. The current provided by the electric voltage in the resistance wire between the pins heats the resistance wire appropriately so that, being pressed by the roll 10, it is well pressed into the thermoplastic plastic film or net when it is fed in between the roll and the drum 3. The heated wire softens and melts the plastic layer only locally, so that this portion is, soon after the wire has been submerged into it, again stiffened after the band leaves the space between the drum and the roll, while the resistance wire remains inside the thermoplastic. In this way, this apparatus permits continuous production of long element bands. Owing to the elasticity of the material, they can be wound onto rolls, from which suitable pieces are then cut off when required. If it is so desired, an element band manu¬ factured in the above way may still be coated with an additional layer or layers of plastic. If required, the apparatus described above may be connected with control devices (not shown in the drawings) by means of which it is possible to control, e.g., at what positions on the drum the pins are between which the electric voltage is connected in each parti- cular case. As a rule, is is preferable that the resistance wire is heated rapidly only slightly before it is pressed into the plastic. In such a case, hardly any oxydizing has time to take place, and the extending of the wire by the effect of heat does not have time to become detrimental. If necessary, the position of the guide piece 6 may also be adjusted by turning it around its axis and by then locking it in its position. This has an effect on the position at which the pins are retracted into the drum and at what position they come out of the drum. Of course, other adjustments are also purposeful, such as adjustments of the voltage and of the intensity of the current, etc. The current may be adjusted in relation to the speed of rotation and to the position of the drum. The value of the current depends on the properties of the plastic band material and on the speed of rotation of the drum.

Claims: WHAT IS CLAIMED IS: 1. Method for the preparation of a band, sheet, foil, fabric, mesh, or a similar plastic layer (1) that is heatable by means of an electric resistance wire, c h a r a c t e r i z e d in that, having been heated by means of electric current, the resistance wire (2) is pressed into the said plastic layer (1) consisting of a thermoplastic when this layer is partly softened or molten by the effect of the hot wire (2) at the wire and that the wire (2) then remains inside the plastic (1) when the plastic is again cooled and receives its former state, whereinafter, when the resistance wire (2) is heated to an appropriate extent by means of electric current, while the plastic (1) does not become excessively soft and while the resistance wire (2) remains in it, the plastic layer (1) can be used for heating the desired objects. 2. Method as claimed in claim 1, c h a r - a c t e r i z e d in that, when the resistance wire (2) is pressed into the plastic layer (1), by means of the electric current, only the portion of the wire is heated that is being pressed,and/or a relatively short portion of the wire ahead of the said portion, which is not yet being pressed. 3. Method as claimed in claim 2, c h a r ¬ a c t e r i z e d in that the portion of the said wire (2) that is being heated and pressed into the plastic layer is shifted periodically or continuously relative the plastic layer (1) and the wire (2), or the other way round, the plastic layer (1) and the wire (2) are correspondingly shifted relative the devices that heat the wire and perform its said pressing. 4. Apparatus for carrying out the method as claimed in claims 1 to 3, c h a r a c t e r i z e d in that the apparatus comprises a drum (3) and a roll (10, 11) pressing against the drum, the plastic layer (1) being fed to between the drum and the roll, whereat the resistance wire (2) heated by means of electric current is pressed into the plastic. 5. Apparatus as claimed in claim 4, c h a r a c t e r i z e d in that, before the resistance wire (2) is pressed into the plastic, the wire is threaded into contact with metal pins (7) projecting out of the face of the drum (3) and thereby brought into a winding form on the face of the drum by means of the said pins, and that the wire (2) receives the electric current heating it from the pins. 6. Apparatus as claimed in claim 5, c h a r a c t e r i z e d in that the wire (2) receives the electric current heating it from the pins (7) only shortly before the wire is pressed into the plastic (1). 7. Apparatus as claimed in claims 4 to 6, c h a r a c t e r i z e d in that, after the pressing, the pins (7) are pulled for a period of time by means of automatic control into the drum (3) , whereat the detaching of the finished product from the drum (3) becomes easier, and, correspondingly, by means of auto¬ matic control, the pins (7) are pushed out of the drum (3) at an appropriate position.

Inventors: MELA MARTTI, MELA, MARTTI
Applicants: MELA MARTTI, MELA, MARTTI
Application year: 1984
Main classification: H05B3
IPC codes: B29C70, H05B3