FR2489645A1 - Induction heat treatment plant for non:ferromagnetic wire - using electromagnet coil on ferrite yoke with narrow air gap through which wire travels - Google Patents

Abstract

The plant includes a C-shaped yoke which leaves a narrow air gap along which the wire is fed; and an electromagnet coil is wound on the yoke. The a.c. fed through the coil is pref. between 2 kHz and 1 MHz; and the yoke is pref. made of ferrite. The two ends of the C-profile forming the yoke are pref. tapered towards the air gap or, alternatively, are widened or unaltered so several parallel wires may be heated simultaneously while travelling along the gap. When heating Cu or stainless steel wires, the thermal efficiency of a conventional solenoid using 15 kHz is only 34-40%. The invention increases this efficiency to 70-75%, or more if two wires are heated simultaneously.

Description

 The present invention relates to the induction heat treatment of wires, in particular non-magnetic (non-ferromagnetic) metallic wires.

 It is known to carry out such a heat treatment using a solenoid inductor through which the wire to be treated passes. Although not without advantages - simplicity in particular - this process is subject in some cases to a low yield.

 The present invention proposes a device capable of higher efficiency.

 In the proposed device, the inductor winding is wound on an almost closed magnetic circuit, defining an elongated air gap along which the wire to be treated passes.

 Preferably, the magnetic circuit is made of ferrite. Advantageously, the induction frequency is established between 2000 Hz and 1 MHz approximately.

 In a first alternative embodiment, the opposite ends of the magnetic circuit leading to the air gap become thinner towards the air gap.

 In another variant, the opposite ends of the magnetic circuit giving onto the air gap are widened or of the same section, this authorizing the simultaneous heating of several wires.

 Compared to the solenoid, an open system such as the one described is advantageous for handling due to the ease of inserting the wire into the heating zone.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings, given to illustrate, without limitation, various embodiments of the present invention, and in which
Figure 1 schematically illustrates a conventional solenoid inductor
. Figure 2 illustrates a first embodiment of the present invention; and
FIGS. 3 and 4 respectively illustrate two variants of the preferred embodiment of FIG. 2.

 Figure 1 therefore illustrates a solenoid inductor, designated by the general reference 1; surrounding a section of wires, designated by 2. It has been observed that the heating of a non-magnetic material of small section requires a high frequency. However, even when an adapted frequency is used, the efficiency of a solenoid inductor according to FIG. 1 often remains low.

 A new arrangement has been devised which makes it possible to significantly improve the yield, by moving the inductor away from the wire to be treated, subject to providing between them an almost closed magnetic circuit in the air gap of which the eye is located.

 FIG. 2 illustrates a first embodiment of this kind, where we see an inductor section 10, constituted for example of copper tube, wound on a magnetic circuit designated by the general reference 30. This circuit 30 comprises a vertical upright 31 on which most of the circuit 10 is wound; the upright 31 is completed by two opposite horizontal uprights 32 and 34, which in turn are joined on two vertical uprights opposite 33 and 35, the ends of which face each other to define a gap 40. In the gap 40, comes move the wire 20 to be treated.

The experiments were carried out with a ferrite magnetic circuit, sized to a sufficient size. These experiments were carried out for induction frequencies established between 2000 and 20000 Hz approximately. More particularly, the experiments were conducted at the frequency of 15,000 Hz, on non-magnetic materials (copper and stainless steel). The results obtained were as follows - for stainless steel, the yield is 70%,
against 34% at 15,000 Hz with a solenoid inductor
classic.

- for copper, the yield is 75%, against
40% at 15000 Hz with a conventional solenoid inductor.

The tests were carried out in particular with an inductor assembly the dimensions of which, as defined in FIG. 2, were
A = 28 mm L = 90 mm H = 152 mm G = 93 mm.

A 6 mm diameter stainless steel wire was tested at a frequency of 15,000 Hz. The size of the air gap D was 10 mm.

As previously indicated, the yield is close to 70%. This yield reaches 82% when two wires are heated simultaneously in the same air gap. A copper wire of the same diameter heated at a frequency of 15000 Hz, in a 10 mm air gap, made it possible to reach a yield of 0.75, a figure which is raised to 0.85 when two wires are heated simultaneously.

 Other experiments have been carried out with a magnetic circuit, the opposite ends of the magnetic circuit leading to the air gap 40, illustrated at 36 and 37 in FIG. 3, have been bevelled, in order to gradually thin towards the air gap, up to having a size which corresponds substantially to the width of the useful air gap. Unlike the first, this circuit only heated one wire.

These experiments have brought to light even better experimental yields than those indicated above. The heating efficiency of a 6 mm diameter stainless steel wire is then close to 80%.

 Of course, the present invention is not limited to the embodiment described, but it extends to any variant in accordance with its spirit, such as for example the variant shown in FIG. 4 in which the opposite ends (38, 39 ) of the magnetic circuit (30) overlooking the air gap (40) are widened.

Claims (5)

 1. Device for the heat treatment of non-magnetic wires by induction, of the type comprising an inductor winding (10) in electromagnetic cooperation with the wire to be treated (20), characterized in that said inductor winding is wound on a magnetic circuit (30 ) almost closed, defining an elongated air gap (40) along which the wire to be treated passes.  2. Device according to claim 1, characterized in that the magnetic circuit (30) is made of ferrite.  3. Device according to one of claims 1 and 2, characterized in that the induction frequency is established between 2000 Hz and 1 MHz approximately.  4. Device according to one of claims 1 to 3, characterized in that the opposite ends (36, 37) of the magnetic circuit giving on the air gap (40) thinner towards the air gap.  5. Device according to one of claims 1 to 3, characterized in that the opposite ends (38, 39) of the magnetic circuit (30) overlooking the air gap (40) are widened or of the same section, which allows the simultaneous heating of several wires.