GB1558418A - Wiredrawing machine - Google Patents

Description

(54) WIRE-DRAWING MACHINE (71) We, CROUZET, a French Corporate Body, of 128 Avenue de la Republique, 75011 Paris, France, and ELFIT, a French Body Corporate, of Port Fluvial, 71002 Macon, France, do hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns wire-drawing machines.

An object of the invention is to provide a wire-drawing machine using one or more traction capstans capable of maintaining a constant, but adjustable, tension on the wire being drawn, whatever may be the rotational speed of the capstans.

It is known that the resistant stresses (or efforts) of the wire-drawing dies do not vary very much for drawing speeds for fine wire, under adequate lubricant, in the range between 0 and 50 m/s.

If one pulls on the wire that is being drawn with a constant force, equal to a known percentage of the breaking load of the wire, which passes into successive dies whose resistance to the wire-drawing is known and does not vary very much with wire speed, one will have combined the best possible conditions for wire-drawing.

Various known proposals use known techniques to keep the drawing force constant and independent of the wire speed.

Such proposals use, for example, regulated d.c. motors, electromagnetic couplings, and fluid drives. The number of capstans necessary, in general between 5 and 20 on an ordinary machine, makes these techniques very expensive in construction and in use.

In an ideal machine, the peripheral linear speed of the various capstans should be strictly equal to the speed of the wire, that is to say that the rotational speeds of each capstan should be strictly controlled so that each capstan runs at a predetermined increased speed ratio relative to the preceding capstan. This ideal condition is never fulfilled, because it is very difficult to know strictly the ratios of the successive speeds and these ratios are capable of varying with wear of the dies. Usually the difficulty is avoided by causing the capstans to be rotated in such a way that the normal circumferential speed theerof is a little greater than the speed of travel of the wire. Thus, when the wire approach speed of a capstan becomes greater than the wire approach speed of the next capstan, the wire run departing from the first capstan slackens and the wire slips relative to the capstan which is generally provided with a frusto-conical rim in order to favour this mode of operation.

The disadvantages of this known technique are that the rim of the capstan wears out rapidly as a result of friction, and that the wire, which grips only periodically to the capstan, is subject to jerky traction, often suffiicent to cause breakage. For these reasons, the majority of the known devices are often ill-suited to the drawing of very fine wires for electrical windings of a diameter, for example, of several hundredths of a millimetre.

Certain known proposals have, in addition, the disadvantage that they possess a significant inertia due to the presence of the rotors of their motors and also the disadvantage of needing regulating means acting on the electrical or hydraulic power supply to the motor; as a result, the drawing force is subject to fluctuations the amplitude of which can exceed the limits permitted by the resistance to breakage of the fine wires being drawn.

To obviate these disadvantages, there have already been proposed wire-drawing machines comprising dies and capstans each driven by a respective magnetic coupling providing a constant couple, the coupling comprising a driving ring made of grainorientated magnetic material, having a strong coercive field and alternate permanent poles, the driving ring being integral with a quill shaft and serving to drive the capstan, integral with which is a driven disc which is made of magnetic alloy having a low coercive field and is coaxial with the driving ring, by way of the driven disc.

However, these machines cannot adapt automatically, without wear, to variations in speed of the wire. The drawing force cannot be regulated easily, nor with precision.

Pursuant hereto, the present invention provides a wire-drawing machine comprising dies and one or more capstans disposed for drawing a wire through said dies, the or each said capstan being driven through a respective magnetic coupling providing a substantially constant torque from a respective driving shaft mounted in a quill, the magnetic coupling comprising a driving ring carried by the driving shaft and made of grain-oriented magnetic material having a strong coercive field and alternate poles, and a driven annular disc carried by the capstan and made of magnetic alloy having a weak coercive field, said- capstan being mounted idle on said shaft so that said disc is coaxial with and adjacent to said ring and the air gap therebetween is adjustable.

Because the air gap is adjustable, the drawing force, which is substantially inversely proportional to the width of the air gap, can advantageously increase slightly with increase in the relative speed, since the force to be overcome to cause movement of the wire also increases with increase in speed.

In addition, the arrangement of the invention makes it possible to use notched belts and pulleys which are standardised, even if the speed ratios chosen are not exact; this contrasts with the machines having conventional fixed capstans and which have to have very taut flat belts with correspondingly large power consumption, which is a pure loss.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a part-sectional elevation illustrating the construction of a capstan arrangement in a wire drawing machine in accordance with a preferred embodiment of the invention; and Fig. 2 is a diagrammatic general view illustrating a wire-drawing machine incorporating a plurality of capstans as illustrated in Fig. 1.

The capstan arrangement shown in Fig.

1 comprises a driving shaft 1, mounted in a quill body 2 by roller bearings 3. Mounted on one end of the shaft 1 is a drive pulley 4, and mounted on its other end is a flanged plate 5 carrying a permanently-magnetic driving ring 6, made of grain-orientated material (e.g. a ferrite material) having a strong-coercive field (2,500 to 4,000 oersteds) magnetised in a direction parallel to the axis in order to form a multipolar permanent magnet having alternate poles.

A small diameter spindle 7, disposed coaxially with the driving shaft 1, and locating by one end in an axial bore in the end of the shaft 1 on which the pole 5 is mounted, rotates in bearings 8 located in a driven member 9 made of light alloy and playing the role of a capstan. This capstan 9 comprises a frusto-conical drum 9a having cheeks 9b to confine the wire to the frusto-conical surface of the drum 9a, which drum 9a, as shown, can advantageously be a separately-applied rim made of a material comprising carborundum particles bound together by a synthetic rubber (e.g.

nitrite rubber) and having a coefficient of friction of at least 0.4 with lubricated aluminium wire. This high coefficient of friction makes it possible to achieve adequate traction with less than two turns of wire around the capstan; this, coupled with the conicity of the drum which contributes to ensuring that the turns of the wire remain separated, eliminates the risk-of crossing of the wire and, accordingly accidental breakage.

However, in order to obtain the quality desired, experience has shown that the material of the wheel should have a grain size three times smaller than the diameter of the wire and a Shore Hardness index of 60 to 90.

An annular magnetic disc 10, made of magnetic alloy having a weak coercive field, for example 150 cersteds, such as a nickel- aluminium alloy known under the name of MALHYSTER, is fixed coaxially to the driven member 9 so as to face the driving disc 6, with an air gap 11 therebetween. A screw 12 arranged axially of the member 9 acts on a thrust ball 13, disposed in a housing on the axis of the capstan, to determine, adjustably, the extent of the air gap 11 and, therewith, the action of the lines of force of the magnet 6 extending between the opposite poles of said magnet 6 through the disc 10.

When the driving shaft 1 is caused to rotate, in the absence of resistance, the member 9 is entrained and rotates at the same speed as the shaft 1. If the drum 9a is used as a capstan to exert traction on a wire, relative slippage occurs between the driving ring 6 and the driven member 9, the magnetic poles which are produced in the magnetic disc 10 (which were fixed in the absence of slippage) having to shift in a continuous manner. The result is loss of energy through hysteresis, which gives rise to a couple or torque. This couple is substantially constant when the angular slippage between the driving ring 6 and the disc 10 remain low, that is to say for a relative rotational speed of about 500 r.p.m.

In fact, the couple is not absolutely constant and increases very slightly with increase in the relative speed, which is an advantage for the application to a wire-drawing machine capstan, since the force to be overcome in order to cause movement of the wire also increases with speed.

The couple is substantially inversely proportional to the air gap 11 and this latter can be varied within very wide limits by acting on the thrust ball 13 by means of the screw 12.

The couple is also proportional to the radii of the driving ring 6 and of the disc 10. Accordingly, it is possible to determine the maximum couple a particular capstan can transmit by selection of appropriate radii for its driving ring 6 and magnetic disc 10.

The disc 10 must not have permanent magnetic poles which would result in periodic fluctuation of the couple. When the apparatus is stopped with a very small air gap 11, permanent poles may form. If, whilst the apparatus is stopped, one sets a very large air gap, the induction in the disc 10 is insufficient to destroy this permanent magnetisation upon starting-up. The apparatus contains its own demagnetisation means formed by the adjustable air gap 11 and by the adjusting screw 12 action on the thrust ball 13.

Demagnetisation is effected by adjusting the air gap 11 so as to be as small as possible, setting the shaft 1 rotating while keeping the capstan 9 stopped, and slowly increasing the air gap 11 by means of the screw 12.

The shaft 1 bears a second pulley 14 which is available for driving with a suitable ratio another identical device.

The quill body 2 has a collar (or flange) 2a associated with a cheek 15 allowing the mounting of the capstan arrangement in a respective one of a pair of parallel slots 20 of a framework (Fig. 2) formed, for example, with a plurality of uprights 16, 16'. Each slot 20 slidably accommodates the collars or flanges 2a and the cheeks 15 of its respective capstans so that they are adjustable within their slots 20, the positions of the capstans being determined by the positions of respective wire-drawing dies 17 which are accommodated adjustably in a slot 20t disposed midway between and parallel to the two slots 20, and by the lengths of standard belts 18, 18' used to transmit rotational movement from the arrangement, as described, having hysteresis friction, to another identical capstan arrangement from a driving motor 19. The dies 17 may advantageously be rotating dies Finally, by mounting appropriate detectors on the driving shafts and the capstans, it is possible to compare the respective speeds of the shaft and the capstan and control the relative slippage occurring at each capstan and, therefore, the elongation of the wire and also to check the wear of the dies.

In fact, if any one of the dies wears away, the diameter of the outlet wire will increase and its length will decrease, which will have the effect of slowing down the respective capstan. Its relative speed in relation to its respective driving shaft will increase, which will have the effect of increasing slightly the hysteretic couple, without any disadvantage to the general behaviour of the apparatus.

The arrangement according to the invention can be used in wire-drawing machines for fine aluminium wire.

WHAT WE CLAIM IS: 1. A wire-drawing machine comprising dies, and one or more capstans disposed for drawing a wire through said dies, the or each said capstan being driven through a respective magnetic coupling providing a substantially constant torque from a respective driving shaft mounted in a quill, the magnetic coupling comprising a driving ring carried by the driving shaft and made of grain-oriented magnetic material having a strong coercive field and alternate poles, and a driven annular disc carried by the capstan and made of magnetic alloy having a weak coercive field, said capstan being mounted idle on said shaft so that said disc is coaxial with and adjacent to said ring and the air gap therebetween is adjustable.

2. A machine as claimed in Claim 1, in which the said air gap is adjustable by means of a thrust ball which bears on one end of the driving shaft and cooperates with a screw in a housing on the axis of the capstan.

3. A machine as claimed in Claim 1 or 2, in which the capstan comprises a frustoconical drum provided with cheeks to con- fine the wire to its frusto-conical surface.

4. A machine as claimed in Claim 3, in which the drum and the cheeks constitute a rim made of a material comprising carborundum particles bound together with a synthetic rubber and having a coefficient of friction with a lubricated drawn wire of at least 0.4.

5. A machine as claimed in any preceding claim having a plurality of the capstans and comprising a frame having a pair of parallel slots each serving slidably to accommodate the quills of respective ones of the capstans the distance between which is adjustable.

6. A machine as claimed in claim 5

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. energy through hysteresis, which gives rise to a couple or torque. This couple is substantially constant when the angular slippage between the driving ring 6 and the disc 10 remain low, that is to say for a relative rotational speed of about 500 r.p.m. In fact, the couple is not absolutely constant and increases very slightly with increase in the relative speed, which is an advantage for the application to a wire-drawing machine capstan, since the force to be overcome in order to cause movement of the wire also increases with speed. The couple is substantially inversely proportional to the air gap 11 and this latter can be varied within very wide limits by acting on the thrust ball 13 by means of the screw 12. The couple is also proportional to the radii of the driving ring 6 and of the disc 10. Accordingly, it is possible to determine the maximum couple a particular capstan can transmit by selection of appropriate radii for its driving ring 6 and magnetic disc 10. The disc 10 must not have permanent magnetic poles which would result in periodic fluctuation of the couple. When the apparatus is stopped with a very small air gap 11, permanent poles may form. If, whilst the apparatus is stopped, one sets a very large air gap, the induction in the disc 10 is insufficient to destroy this permanent magnetisation upon starting-up. The apparatus contains its own demagnetisation means formed by the adjustable air gap 11 and by the adjusting screw 12 action on the thrust ball 13. Demagnetisation is effected by adjusting the air gap 11 so as to be as small as possible, setting the shaft 1 rotating while keeping the capstan 9 stopped, and slowly increasing the air gap 11 by means of the screw 12. The shaft 1 bears a second pulley 14 which is available for driving with a suitable ratio another identical device. The quill body 2 has a collar (or flange) 2a associated with a cheek 15 allowing the mounting of the capstan arrangement in a respective one of a pair of parallel slots 20 of a framework (Fig. 2) formed, for example, with a plurality of uprights 16, 16'. Each slot 20 slidably accommodates the collars or flanges 2a and the cheeks 15 of its respective capstans so that they are adjustable within their slots 20, the positions of the capstans being determined by the positions of respective wire-drawing dies 17 which are accommodated adjustably in a slot 20t disposed midway between and parallel to the two slots 20, and by the lengths of standard belts 18, 18' used to transmit rotational movement from the arrangement, as described, having hysteresis friction, to another identical capstan arrangement from a driving motor 19. The dies 17 may advantageously be rotating dies Finally, by mounting appropriate detectors on the driving shafts and the capstans, it is possible to compare the respective speeds of the shaft and the capstan and control the relative slippage occurring at each capstan and, therefore, the elongation of the wire and also to check the wear of the dies. In fact, if any one of the dies wears away, the diameter of the outlet wire will increase and its length will decrease, which will have the effect of slowing down the respective capstan. Its relative speed in relation to its respective driving shaft will increase, which will have the effect of increasing slightly the hysteretic couple, without any disadvantage to the general behaviour of the apparatus. The arrangement according to the invention can be used in wire-drawing machines for fine aluminium wire. WHAT WE CLAIM IS:

1. A wire-drawing machine comprising dies, and one or more capstans disposed for drawing a wire through said dies, the or each said capstan being driven through a respective magnetic coupling providing a substantially constant torque from a respective driving shaft mounted in a quill, the magnetic coupling comprising a driving ring carried by the driving shaft and made of grain-oriented magnetic material having a strong coercive field and alternate poles, and a driven annular disc carried by the capstan and made of magnetic alloy having a weak coercive field, said capstan being mounted idle on said shaft so that said disc is coaxial with and adjacent to said ring and the air gap therebetween is adjustable.

2. A machine as claimed in Claim 1, in which the said air gap is adjustable by means of a thrust ball which bears on one end of the driving shaft and cooperates with a screw in a housing on the axis of the capstan.

3. A machine as claimed in Claim 1 or 2, in which the capstan comprises a frustoconical drum provided with cheeks to con- fine the wire to its frusto-conical surface.

4. A machine as claimed in Claim 3, in which the drum and the cheeks constitute a rim made of a material comprising carborundum particles bound together with a synthetic rubber and having a coefficient of friction with a lubricated drawn wire of at least 0.4.

5. A machine as claimed in any preceding claim having a plurality of the capstans and comprising a frame having a pair of parallel slots each serving slidably to accommodate the quills of respective ones of the capstans the distance between which is adjustable.

6. A machine as claimed in claim 5

wherein there is a third slot disposed mid way between and parallel to the slots of the pair, this third slot adjustably accommodating a plurality of dies.

7. A machine as claimed in any preceding claim in which in the or each capstan, the shaft and the capstan are provided with detectors permitting comparison of the speeds of the sheath and the capstan, and control of the elongation of the wires, as well as checking of the wear of the dies.

8. A wire-drawing machine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.