(11) EP 0 300 517 B1


(45) Mention of the grant of the patent:
17.03.1993 Bulletin 1993/11

(21) Application number: 88200978.0

(22) Date of filing: 17.05.1988
(51) International Patent Classification (IPC)5H01C 17/00, B21F 1/04


Machine for shaping undulations in resistance wire

Maschine zur Herstellung von Meandern in Widerstandsdraht

Machine pour la formation d'ondulations dans un fil de résistance

(84) Designated Contracting States:

(30) Priority: 21.05.1987 IT 2062087

(43) Date of publication of application:
25.01.1989 Bulletin 1989/04

(73) Proprietor: A.G.A. S.r.l.
I-29022 Bobbio Piacenza (IT)

(72) Inventor:
  • Agogliati, Andrea
    I-20097 San Donato Milanese Milano (IT)

(74) Representative: Riccardi, Sergio 
Riccardi & Co. Via Macedonio Melloni, 32
20129 Milano
20129 Milano (IT)

(56) References cited: : 
GB-A- 1 515 071
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    [0001] The invention relates to a machine for shaping resistance wire which permits a high quality product to be obtained and is based on an original shaping principle which is highly innovative compared to techniques in current use and eliminates the relative disadvantages.

    [0002] The machines which are currently used to shape resistance wire into undulations for the construction of electrical resistances for electrical household appliances generally employ a shaping system constituted by gears or disks into which wedges have been inserted. When they rotate, these gears or disks with inserted wedges drag and pull the resistance wire and shape it in accordance with the parameters of the resistance to be constructed.

    [0003] Generally, the action of pulling the resistance wire causes stretching and also buckling of the wire, creating considerable disadvantages during the construction stage because of cracks in the wire and during utilisation in an electrical household appliance because of the production of hot spots and a consequent interruption in the flow of electricity in said appliance.

    [0004] The machine according to the present invention eliminates the disadvantages of the technique currently used, since it is based on the original principle of injecting the resistance wire instead of pulling it and thus does not use gears or disks with wedges for shaping

    [0005] Thus the technical problem is solved by the invention, in which the wire is pushed and not pulled, feeding it in at a speed higher than the speed at which it exits from the machine, so that the wire is forced to bend at a precise point, determined by the parameters which can be changed as requested, and defined by the conformation of the elements which guide the wire inside the machine, and thus the wire does not come into contact with any mechanical part which can damage it at the point at which it undergoes bending.

    [0006] These and other advantages of the invention of the invention will be more clearly understood and made more evident by the following description of an example of one embodiment, provided purely as an illustration of the working principle of the machine and with reference to the attached highly schematic drawings, in which:

    Figure 1 is a schematic representation of the working principle of the machine for shaping wire according to the invention of this claim; and

    Figure 2 is a diagram of the detail of the wire guide and the bending area of the machine in question.

    [0007] Referring now to the figures in the attached drawings, the machine according to the invention basically consists of an injection system constituted by two counter-rotating disks S and S' of a suitable shape, which form the thrust wheels for the resistance wire R coming from an appropriate feeding system which is not shown in the drawings; a wire guide G provided with a channel C for the injection of the wire R into a formation zone Z at the terminal part of the guide which is shaped to form a chamber of free outlet zone in which the bending of the wire R takes place. This zone has a dimension D equal to the distance between the exit of channel C of wire guide G and a point of tangency with the braking system, constituted by two braking rollers or cylinders F and F' which are also counter-rotating at a peripheral speed which is appropriately lower than that of the direction of rotation of counter-rotating thrust disks S and S'. The direction of rotation of counter-rotating disks S and S' is indicated by the arrows Vs, that of counter-rotating rollers F and F' is indicated by the arrows Vf, the direction in which the wire R is fed and the thrust direction is indicated by the arrows A, the direction of the resistance forces which are created on the wire R inside the formation zone Z are indicated by the arrows Dr, E is the elastic spring-back of the wire at the exit from the braking rollers F and F' and R' is the shaped wire which is obtained as the end product of the machine.

    [0008] To obtain this undulated form, forces Dr are induced on the wire R in such a way as to oblige the wire to bend at a precise point. The wire is pushed by two thrust wheels S and S' into an obligatory path, in other words channel C of guide G and carried in proximity to the braking wheels F and F' which are also rotating and constitute a partial obstacle because their peripheral speed is lower than that of the thrust wheels S and S'. This obstacle can be fixed or mobile according to the shaping requirements of the wire.

    [0009] This obstacle impedes the linear passage of the wire R, which is thus forced to discharge its surplus from the opposite formation zone Z of the guide, situated between the guide and the braking rollers F and F'.

    [0010] Now the wire R will acquire the special undulating shape, which is produced by the combined forces of the speed and the bending resistance of the wire which come into play at all the points involved in the formation zone, as well as the walls of the guide.

    [0011] The bending parameters or variables can be simply stated in the following equation:

    Vs = the peripheral speed of the thrust wheels
    Vf = the peripheral speed of the braking wheels
    Let E = the spring-back due to the elasticity of the wire
    Vr-E = determines the quantity of the final product of undulated wire R' in m⁻¹ Finally, since D is the bending distance it determines the magnitude of the undulation produced and these parameters are directly proportional one to another. Therefore if the parameters are changed, undulated wire R' of a different pitch and depth is produced, according to what is required.

    [0012] This description clearly shows that the machine according to the invention fully solves the problems outlined above and allows a resistance wire to be bent into waves without introducing stretching and/or buckling but using only axial thrust.


    1. Machine for the shaping into waves of resistance wire for making electric resistors, comprising: a wire injecting system, constituted by two counter-rotating disks (S, S') which impart an axial thrust onto said wire; a wire guide (G) with a channel (C) for the injection of the wire into a formation zone (Z), said formation zone being formed by a free outlet zone of said wire guide; a braking system constituted by two counter-rotating rollers (F, F' ) with a lower peripheral velocity than the counter-rotating disks of the wire injection system; and whereby the wire is shaped in said formation zone (Z) in which the surplus wire created by the difference in speed of the injection system and the braking system is forced to bend itself taking on the form of an undulation.


    1. Maschine zum Formen von Widerstandsdraht in eine wellenförmige Mäanderform zum Herstellen von elektrischen Widerständen, wobei die Maschine versehen ist mit: einem Drahteinspeissystem, welches sich aus zwei in entgegengesetzter Richtung rotierenden Scheiben (S,S') zusammensetzt, welche eine axiale Schubkraft auf den Draht übertragen; einer Drahtführung (G) mit einem Kanal (C) zum Einspeisen von Draht in eine Formgebungszone (Z), wobei die Formgebungszone durch eine freie Auslaßzone der Drahtführung ausgebildet ist; einem Bremssystem, weiches sich aus zwei in entgegengesetzte Richtung rotierenden Walzen (F,F') zusammensetzt, welche mit einer geringeren Umfangsgeschwindigkeit als derjenigen der in entgegengesetzter Richtung rotierenden Scheiben des Drahteinspeissystems rotieren; und wobei der Draht in der Formgebungszone (Z) geformt wird, in welcher überschüssiger Draht durch die Differenz der Geschwindigkeit des Einspeissystems und des Bremssystems geschaffen wird, und der Draht infolgedessen dazu gezwungen wird, sich selbst zu biegen und so die Form von wellenförmigen Mäandern einzunehmen.


    1. Machine pour la formation d'ondulations dans un fil de résistance électrique comprenant : un système d'injection de fil constitué par deux disques (S, S') tournant en sens contraires qui appliquent une poussée axiale sur ledit fil; un guide-fil (G) avec un canal (C) pour l'injection du fil dans une zone de formation (Z), ladite zone de formation étant constituée par une zone de sortie libre dudit guide-fil; un système de freinage constitué par deux rouleaux (F, F') tournant en sens contraires avec une vitesse tangentielle inférieure à celle des disques tournant en sens contraires du système d'injection de fil, le fil étant conformé dans ladite zone de formation (Z) dans laquelle le surplus de fil créé par la différence de vitesses entre le système d'injection et le système de frein est forcé de se plier en prenant la forme d'une ondulation.