CH654496A5 - METHOD FOR CONTINUOUSLY PRODUCING A WIRE OF LOW CROSS SECTION AND LARGE LENGTH. - Google Patents

Description

The invention relates to a method for the continuous production of a wire.

In the conventional production of wire from metallic materials, it is usually assumed that a wire bar (rolled bar) is rolled down in a continuous rolling mill to a wire rod (semi-finished product) of a suitable cross-section. As a rule, this cross-section is limited at the bottom by the conditions to be observed during rolling. On the one hand, the rolling stock cools down at the start of the operations, i.e. surface enlargement relatively quickly during the first rolling passes, which cannot be compensated for by an increased starting temperature of the ingot due to the risk of exceeding the maximum permissible deformation temperature. On the other hand, towards the end of the operations, the temperature of the rolling stock rises again in the last rolling passes due to the high deformation work per unit volume. In addition, the wire speeds that have already reached over 50 m / s cannot be increased at will. Further processing of the semifinished product into smaller diameters in a second conventional roller mill is countered by the high cooling at the beginning of the operations. For steel, the usual lowest achievable diameter is approx. 5.5 mm. If smaller cross sections are to be achieved, the further reduction is carried out by repeated drawing, which usually has to be interrupted by intermediate annealing operations in order to restore the ductility of the material lost due to strain hardening. The technology of wire production by hot rolling and cold drawing is known from numerous publications (A. Pomp, production of steel wire, Verlag Stahleisen M.B.H. Düsseldorf 1969; J. A. Shey, Metal deformation processes, pp. 457-547, Marcel Dekker Inc. New York 1970).

The combination of the usual roller mills with the wire drawing devices and intermediate annealing stations represents a considerable investment. The perfect monitoring of the processes also often encounters difficulties. This primarily concerns the temperature control of the material to be deformed. Due to the tools, devices and apparatus to be coordinated, the block weight of the billets is limited. In order to counteract the cooling during the first rolling passes, the block has to be brought to a temperature which is often undesirable from the metallurgical point of view (uppermost limit temperature). On the other hand, when the thinner cross sections are reached, the wire has to be rolled at high speed (up to over 50 m / s) for economic reasons and due to the unfavorable cross section / circumferential ratio of the wire. Due to the deformation work converted into heat, the temperature of the rolling stock in the roll gap can rise again in such a way that it reaches the upper permissible limit. The monitoring of all these operating parameters, which are subject to strong fluctuations in space and time, is difficult and complex. The same applies to the wire drawing mill with its lubrication problems, with the reduced cross-sectional area per train and the need for frequent intermediate annealing.

There is therefore a need to increase the initial block weights and thus the associated length of the wire, to stabilize the deformation temperatures and to expand the rolling operations to smaller wire dimensions in order to dispense with drawing operations altogether, if necessary, or at least to significantly reduce the number thereof.

The invention has for its object to provide a manufacturing method for thin metal wires, which allows to increase the wire length arbitrarily in a continuous manner and significantly reduce the wire end cross-section with a considerable reduction in the number of drawing operations. The process control should be carried out in a simple manner and the product should have optimal metallurgical properties within predetermined limits.

According to the invention, this object is achieved by the features of claim 1.

The invention is described on the basis of the following exemplary embodiments explained by figures.

It shows:

The figure is a graphic representation of the temperature of the material to be deformed as a function of the successive shaping operations. The abscissa can also be interpreted qualitatively (with appropriate scale distortion) as a time axis. Curves a and b represent the temperature profile of the rolling stock over the number of passes for rolling by means of heated rolls for the start of the billet (a) and the end of the billet (b). For comparison, the temperature profile of the rolling stock is shown for conventional rolling (billet start: curve c; billet end: curve d), e means a number of drawing stitches (in the present case 5) to achieve an equivalent wire diameter for comparison with previous conventional rolls (continuation of

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Curves c and d) and f the soft annealing treatment after the previous drawing. A represents the point where, when using heated rollers, a wire cross-section of 86 mm2 (corresponding to 10.5 mm 0) is reached and the 1st sequence of continuous process steps is completed with one and the same connected workpiece. B is the point after further processing in a second continuous roll stand and corresponds to a wire cross-section of 7 mm2 (3 mm 0). In comparison, C represents the point that can be reached in conventional rolling with unheated rolls, where the rolling process must definitely be stopped. This limit is generally around 28 mm2 wire cross-section (corresponding to 6 mm 0). T is the temperature in ° C and n is the number (consecutive number) of the shaping operations. T0 and Tu indicate the upper and lower temperature limits of the hot deformation for a given material.

Exemplary embodiment A wire with a final diameter of 1.5 mm was produced from semi-finished products (bars, billets) with a square cross section with a side length of 100 mm and an axial length of 6000 mm. The material was thermoformed down to a diameter of 3 mm using a new method and from then on conventionally subjected to cold forming (drawing) or patenting. The latter operations were mainly used to establish a certain structural state with desired preferred properties (strength) and are not the subject of this invention. An approximately pearlitic carbon steel according to German material number 1.1262 with the following composition was used as the material.

chooses:

C:

0.80-0.84%

Si:

0.10-0.25%

Mn:

0.35-0.55%

P:

<0.030%

S:

<0.030%

N:

<0.007%

Fe:

rest

The upper hot deformation limit for this steel is the temperature T0 and is 1050 ° C, while the lower limit Tu is 850 ° C. The billet temperature at the first roll pass was between approx. 900 and 925 ° C (see curves a and b). However, this temperature can be up to 950 ° C. The temperature of the rolling stock decreased somewhat until the tenth pass, and then rose to just below T0 due to the transformation of the deformation work into heat. After a total of 16 stitches, the originally 10,000 mm2 cross-section had been reduced to 86 mm2, which corresponds to a wire diameter of 10.5 mm (point A in the figure). With a rolling stock speed of 30 m / s for the 16th pass, this corresponded to a throughput of 2.6 dm3 / s. The average decrease in cross-section per roll pass was thus approx. 26%. Since at point A the temperature interval given for this steel was exhausted, the deformation process of the first roller mill was stopped here, the rolled material was cut into suitable lengths and further rolled in a heat in a second roller mill with the interposition of a holding furnace. Here the average decrease in cross-section per stitch was approx. 30%. The wire was rolled down in a total of 7 further passes plus a calibration pass (omitted in the figure) to a cross section of 7 mm 2 (corresponding to 3 mm 0) (point B in the figure). The wire rod was then patented in a conventional way to achieve the desired mechanical properties (ductility, cold formability). The one in others

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5 drawing stitches reached a final diameter of 1.5 mm (cross-section: 1.8 mm2), the decrease in cross-section per drawing stitch was 24% on average. These operations have been omitted from the figure for the sake of clarity, since they are not part of the actual invention.

In the conventional rolling method, the highest rolling temperature T0 must be started immediately, with the material cooling relatively strongly in the course of the first 10 passes. For this reason, curves c and d (see figure) diverge for the start and end of the stick. After a total of 19 passes plus a calibration pass (not shown), the operation must be terminated because the upper temperature limit is reached and the speed of the rolling stock is limited by the dimensioning of the continuous rolling stand. This limit is reached in point C (see figure), which is assigned to a wire cross-section of 28 mm2 (corresponding to 6 mm 0). At a rolling stock speed of 50 m / s for the 19th pass, this corresponds to a throughput of 1.4 dm3 / s. The production is therefore comparatively lower than with the new process with heated rollers. It is also indirectly limited by the temperature drop at the start of rolling, which has a disadvantageous effect on the billet dimensions (cross section, length). After the calibration stitch following the 19th stitch, the wire rod must be processed using a suitable technique, e.g. the known Steelmoore process can be cooled from the rolling temperature to room temperature with a monitored cooling rate in order to produce a structure which is advantageous for the subsequent drawing. In order to arrive at the comparison cross-section of 7 mm2 (3 mm 0), 5 drawing stitches, each with a reduction in cross-section of approx. 24%, are required, which must be followed by a soft annealing process at 640 to 680 ° C (e and f in the figure). The further processing to wire of 1.5 mm 0 then takes place in the conventional manner described above by means of an additional 5 drawing stitches.

The comparison between the new rolling process and the conventional rolling / drawing technique shows that considerable heat energy can be saved by keeping the temperature of the furnace required to heat the rolling stock (billets, billets) lower. In addition, the energy is also better utilized in that the temperature differences between the start and end of the billet are significantly smaller and the deformation work is better utilized than in conventional rolling. Furthermore, the temperature difference between the start and end of the billet, which is considerably lower than that of conventional rolling, has a narrower cross-sectional tolerance along the rolling stock, since the deformation forces and the elastic deformations of the rolls are more uniform. There is no need for drawing operations and the intermediate annealing process (soft annealing) is eliminated. In general, hot rolling should also be cheaper than cold drawing, if you only want the shape and not a specific structure. In addition, hot rolling is the faster process than cold drawing, which results in a direct increase in production. The fact that the continuous rolling process with heated rolling in the first rolling mill is stopped at the 16th pass (86 mm2 cross-section) and not only at the 19th pass (28 mm2 cross-section) as in conventional rolling, results in a further increase in production in the present case Ratio 2.6 dm3 / s: 1.4 dm3 / s, i.e. by approx. 85%. The system is therefore used much better.

The heat radiation from the rolling stock and the heated rollers can be largely prevented by means of radiation shields acting as reflectors, which results in further energy savings. The for the isother3

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thermal energy required or quasi-isothermal rolling process can advantageously be provided by inductive heating of the rolls.

According to the new process with heated rolls, the cross-sectional decrease per roll pass can be set to be at least 5% larger than that of conventional rolling or drawing. This also applies to any other reduction process with unheated tools. This increased value can be maintained unabated as the number of stitches increases. It corresponds to a cross-sectional decrease of at least 26%.

The method can equally be applied to unalloyed or alloyed steels in such a way that the final cross-section of the wire rod is at most 24 mm2, with a reproducibility with respect to the tolerance of the rolling stock temperature below this cross-section of less than + 10 C. This ensures uniform and high quality products. Furthermore, the method can optionally also be applied to aluminum and its alloys, the final cross section of the wire rod advantageously being at most 15 mm 2 (approx. 4.5 mm 0).

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1 sheet of drawings

Claims (8)

654 496 PATENT CLAIMS 1. A process for the continuous production of a wire of small cross-section by rolling down a wire bar in a continuous rolling mill, characterized in that isothermal or quasi-isothermal rolling is carried out in at least one first continuous rolling mill with heated rollers. 2. The method according to claim 1, characterized in that the rolling stock is rolled down in a second continuous rolling train with heated rolls to a cross-section from which the final cross-section can be achieved by subsequent drawing operations without intermediate annealing. 3. The method according to claim 1, characterized in that the heat radiation of the rolling stock and the rollers is largely prevented by radiation shields acting as reflectors. 4. The method according to claim 1, characterized in that the thermal energy required for the isothermal or quasi-isothermal rolling process is provided by inductive heating of the rolls. 5. The method according to claim 1, characterized in that the cross-sectional decrease per roll pass is at least 26% and that this value is maintained unabated essentially with increasing number of passes. 6. The method according to claim 1 or 2, characterized in that the material to be processed is an unalloyed or alloyed steel and that the final cross section of the wire is at most 24 mm2. 7. The method according to claim 6, characterized in that the rolling process in the cross-sectional area below 24 mm2 with a reproducibility regarding tolerance of the rolling stock temperature of less than + 10 "C is carried out. 8. The method according to claim 1 or 2, characterized in that the material to be processed is aluminum or an aluminum alloy and that the final cross section of the wire is at most 15 mm2.