CH454935A - Process and installation for the heat treatment of steel wires - Google Patents

Description

Process and Installation for the first heat treatment of steel rods

The present invention relates to the heat treatment of steel wires and in particular, but not exclusively, to those steel wires intended for the manufacture of welded mesh panels.

Usually, the steel wire, which has been lattice or slatted, then spun and straightened, is welded into lattice panels which are treated in a large furnace. of mensions. The heat treatment lasts more than twenty minutes.

According to the invention, an has found that a rapid rise in temperature ap#plice to the steel wire before its assembly in trellis allows to remove 1.e tral ment au fou r of the trellis panels and thus to achieve a significant savings while obtaining finished products of such good quality.

The invention therefore relates to a process for the heat treatment of wires. of steel cut into Bars, said method consisting in inserting the Bar between jaws so as to close an electrical circuit and in passing an electric current through this Bar for a very short time, in such a way as to there. heat to a temperature not deepening -3000 C.

The invention also relates to an installation for the implementation of this method, this installation, intended to be mounted near a wire-draping machine, comprising in combination: ' de la Barre, this circuit being closed by La Barre itself; attached to this circuit, an opening and closing contactor and an auxiliary energy regulation circuit controlling the opening and closing of the heating circuit according to the energy passing through the baxre.

Thanks to this procedure and to this installation, it is possible to carry out the heat treatment of the yarn immediately after the straightening and straightening machine and even to adapt the installation to the straightening machine.

In addition, the first tathermic treatment according to the invention advantageously makes it possible to stop the phenomenon of aging of the steel baue when the disiries mechanical characteristics (resistance and Oastic limit) are reached.

Other advantages will appear during the description which will follow.

In the appended drawing, fig. 1 is a schematic plan view of an installation according to the invention for the first thermal treatment of steel wires; fig. 2 is a comparative diagram of the tensile curves of a thread treated in accordance with the invention and of an untreated thread with, on the abscissa, the elongations A% of the thread and, on the ordinate, the loads C to which the thread is subjected .

According to the example of execution reproduced in FIG. 1, the invention is applied to a wire F rolled or else to be spun, notched and finally straightened. 0n seen in fig. 1 the first wire F coming out of a straightening machine R of a known type, constituted for example by a rotary straightening frame, preceded and followed by driving rollers. The wire then passes under a shear C to be cut into a bar 1 of determined length which must undergo the heat treatment.

The Bar is transferred to a Resistance Heating Plant and, more precisely, is placed between two pairs of jaws which grip it at its ends. Each pair of metallic jaws, for example made of copper or copper alloy, comprises a fixed jaw 2, connected to an electric heating circuit, and a movable jaw 3, mounted at the end of the piston rod. a double-acting cylinder V, with pneumatic control. Each movable mädhoi! re 3 is suitably; t iso] ie- electrically from the piston rod of the corresponding virin V.

The control of the two cylinders V is constituted in the following manner: at the ends of the cylinders of these cylinders deboudhent, on either side of the piston, two conduits 4 and 5 serving alternately as a conduit for supplying fluid under pressure and for & charge. Lines 4 and 5 are connected to a four-way dispensing valve 6. Two of these routes are precisely conduits 4 and 5. The other two routes are, on the one hand, a pressurized fluid supply conduit 7 and, on the other hand, a discharge conduit B.

The electrical circuit used for the heat treatment of Bar 1 in accordance with the invention is constituted, for example, as follows: 2 through a contactor 10, a transformer 11 and conductors 12. The contactor 10 is controlled by an electromagnet 13, powered by an auxiliary circuit 14 for regulating the energy sent to the bar 1. This circuit 14 receives current induced from a wire of circuit 12 through an induction coil 15. Mounted on circuit 14 is a power regulator 16 of the commercial type commonly used in probing machines. This regulator essentially consists of a capacitor, the charge of which is a function of the intensity and the time and is such that the product of the intensity and the time is kept constant so that each bar receives a constant energy to ensure the r6 P <B >cr -</B> end of processing. The operation <B>of</B> this regulated tower 16 depends on the energy which has entered the berm 1. If the supply voltage of the line 9 varies, the energy passing through the busbar 1 varies the same direction but the first delay of intervention of the regulator 16 varies in the opposite direction, as well as, consequently, the duration of tensioning of the baue 1. This is why, the first energy regulator 16 ensures the regularity the heat treatment of the bars 1.

By means of this installation, an.p, proceeds to the heat treatment of a Bar 1 in the following way: After having cut a Bar 1, it is brought between the jaws 2 and 3. The tap 6 is actuated so as to jaws 2 and 3. These are tightened on the beam 1. The corltator 10- is fixed in turn. The steel wire then receives an electrical current at low voltage, for example of the order of 10 volts under an electromagnetic current, from: Pomdine of 400 amperes at the frequency of the network for 20 to 30 seconds.

The processing time is a function of the energy which has passed through Bar 1. As always. top, the first regulator 16 sets the first tensioning time of the Bar 1, so that it is traversed by a predetermin@e energy. This energy is the same for all treated Bars of a given diameter.

If a higher heating power is used, the heating time can be reduced. With an appropriate power, one can, for example, reduce the heating time to a few seconds, i.e. 4 to 10 seconds, so as to adapt the heat treatment according to the invention to the handle of the madhi. thread.

The yarn is thus brought to a fordre temperature of 3000. It takes on a straw yellow color. At the end of the aforementioned time, the energy regulator 16 acting on the electromagnet 13 causes the opening of the contactor 10. Simultaneously with the opening of this contactor, the valve 6 is actuated so as to loosen the jaws 3 and Rod.

Following this heat treatment, if the Breaking load and the elastic limit of the wire F are practically not modified, on the other hand, the elongations are substantially increased. The increase in the elongation characteristics Paz compared to the untreated yarn can reach an order of magnitude of 40%.

If we now examine (fig. 2) the comparative tensile curves of a yarn treated in accordance with the end of the invention (curve I in full traft) and of an untreated yarn 6 (curve II in interrupted traft), the existence, for the wire, of a clear elastic limit at point a and the appearance of a horizontal plateau at b or Luders zone which corresponds to an elongation without an increase in load. This level is followed. of an elongation curve in an arc of a circle b c preceding the rupture which occurs at point c.

This plateau shows a considerable increase in the plastic deformation of the product.

n therefore finds quo the first wire heated uniformly to a temp6aature not exceeding 3000 presents very improved elongation characteristics without significant va riations of. elastic limits and breaking loads.

Thanks to its increased elongation characteristics, the yarn treated according to the invention is applicable to cold forming. It is therefore possible, in certain cases, to replace a Martin steel of cold trap quality with a Thomas steel of conventional composition, conforming to the invention. The ill-formed Tho steel, which is more economical than the aforesaid Martin steel, is strong enough for applications such as cold heading where enough plasticity is required to avoid tapures during deformation.

Thanks to the clamping jaws 2 and 3 which accept Bars 1 of different diameters and thanks to the energy regulator 16 which regulates the treatment energy to a constant value, the installation makes it possible to treat wires of all diameters. taken by @example between 2 and 12 mm.

Furthermore, the treatment installation itself is extremely economical since its cost price is one tenth of the cost price of a furnace. In addition, the floor space requirement is derisory compared to that of welded mesh panel treatment furnaces. Indeed, as shown in FIG. 1, the length of the installation does not exceed that of a bar 1 to be treated, whereas the dimensions of a furnace for mesh panels. The welded sections are much larger in width to accommodate the progressively tied lattice panels.

In addition, the first treatment is extremely fast, since it only lasts 5 to 30 seconds, much faster than the Tour treatment which takes about 20 minutes.

It should also be noted that when the treatment is applied to a rolled yarn, the yarn obtained is perfectly clean. In fact, reheating <B>of</B> the yarn to straw yellow (less than 30011 C) requires distilling the rolling oil. The tiny layer of oxide covering the wire has no detrimental role in welding for the fabrication of welded mesh.

Subsequently, for the manufacture of the welded mesh, this results in a much more regular run of the probing machines which require less energy to perform the welds. exhibiting less dispersion and less reject batches of acceptance tests. This treatment therefore provides a very high quakte product. Finally, the welded mesh obtained from wires treated in accordance with the invention no longer exhibits any significant aging phenomenon. The same is true for the. upright bars: 1 saddles are used: as they are without being subsequently mounted as a trellis.

In fact, the aging phenomenon, which lasts about a month, can be stopped at any time. I#1 suffices to subject the fi<B>l</B> to the heat treatment <B>of</B> the invention. Aging can therefore be stopped when the desired mechanical characteristics (strength and elastic limit) are reached. They remain unchanged after treatment. Only the plasticity and the elongation values of the metal increase, as seen above.

A few numerical examples will illustrate the application of the method of the invention.

<I>Example 1</I> Untreated control sample. Sample of rolled steel wire, notched, straightened, diameter 6 mm. Breaking strength .................. 51.5 to 57 kg/me Elastic limit . <B>------------- -----------</B> 47.6 to 54.5 kg/mm2 Elongation measured over a length of 5 diameters 11 at 18.3% Elongation measured over a length of 10 .diameters 9.2 to 10.8% <I>Example 2</I> Sample of the same rolled steel wire, notched, straightened and treated according to invention by resistance heating by Joule effect, by applying an electric current for 20 seconds (10 volts - 400 amps - network frequency).

Tensile Strength <B>.............. . .</B> 51.5 to 55.8 kg/mm. Elastic limit .. <B>............ - ..........</B> 46 to 52 kg/m Elongation measured over a length of 5 diameters. 17 to 21.7% Elongation measured over a length of 10 diameters 11.6 to 15 0/0 <I>Example 3</I> Identical length of rolled wire, notched, straightened and treated by passing an electric current through it of the same characteristics as in Example 2, for 25 seconds.

Breaking Strength <B>... - - ---- -----</B> 50.8 to 55.5 kg/mid Yield Strength <B>........ .... ............ _</B> 46.7 to 51.5 kg/min-2 Elongation measured over a length of 5 diameters 13.3 to 21.7 % Elongation measured over a length of 10 diameters 10 to 15% <I>Example 4</I> Sample of the same wire drawn, notched, straightened and heated by an electric current with the same characteristics as in example 2, for 30 seconds .

Tensile strength ............................ 50.6 to 55 kg/me Yield strength <B>--------------- ----- ---------</B> 45.8 to 51.2 kg/m Elongation measured over a length of 5 diameters 13.5 to 21 11/o Elongation measured over a length of 10 diameters 11 to 16

Claims (2)

CLAIMS I. Process for the heat treatment of steel wire in bars, intended in particular for the manufacture of welded mesh panels, said process being characterized in that it consists in clamping the bar between jaws so as to close a electrical circuit and passing an electric current through this bar for a very short time, so as to heat it to a temperature not exceeding 3000 C. II. Heat treatment installation for carrying out the method according to claim I, characterized in that it comprises in combination: an electric circuit for heating the bar, this circuit being closed by the bar itself; in series on this circuit, an opening and closing contactor and an auxiliary energy regulation circuit controlling the opening and closing of the heating circuit according to the energy passing through the bar. III. Steel wire obtained by the process according to claim I and characterized in that it has a clear elastic limit and the appearance of a plateau or Luders zone which corresponds to an elongation without an increase in the load. SUB-CLAIMS 1. Process according to claim I, characterized in that the bar is heated by resistance by the Joule effect by passing it through an electric current of high intensity, under low voltage, at<B>there</B> normal network frequency, for less than 30 seconds. 2. Installation according to claim II, characterized in that there are provided clamping jaws of the bar to be treated.