FI62475B - FOERFARANDE FOER TILLVERKNING AV EN LEDNINGSTRAOD AV ALUMINIUM - Google Patents

Description

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Patant · och ragietaratyraltan 'AiwdkM uti ^ d och uti. »Krifwn pubikarad 30.09.82 (32) (33) (31) Pyrdtttjf« uollwui —fefird pr + orlm 01 + .03.69 Hungary-Hungary (HU) MA-19I + 7 (71) Hungarian Aluminum Industry Trust, Pozsony i ut 56, Budapest XIII,

Femipari Kutato Intlzet, FehervEri ut ll + l +, Budapest XI,

Hungary-Hungary (HU) (72) Andräs Domony, Budapest, Tibor Laar, Budapest, Endre Mucsy,

Budapest, Mihälyne Zakar, Budapest, Uhkari-Ungern (HU) (7 * 0 Oy Kolster Ab (5I +) Method for making a conductor from aluminum - Förfarande för tillverkning av en ledningsträd av Aluminum

The invention relates to a method for producing a conductor wire from aluminum, in which the annealed heat-treated raw wire is thinned cold by 60-98% by plastic treatment so that the temperature of the material does not rise above 100 ° C, finally heat-treated the final wire - depending on the composition - 80-220 ° C temperature.

For economic reasons, unalloyed aluminum wire is usually made of smelted aluminum with an aluminum content of 99.5 ... 99.9%. The foreign elements that remain in it for a few tenths of a percent degrade the conductivity of the wire, but at the same time they increase the durability, so that it is uneconomical to make the wire from 99.99% aluminum.

The electrical conductivity and durability of wire are greatly affected by the amount of foreign elements - especially Fe, Cu, Ti, V and B - present in aluminum. Elemental compositions suitable for yarn making have been developed in recent decades.

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It is known that the properties altered by cold working (e.g. strength, electrical resistance) in the subsequent heat treatment approach at different rates the values they had before the treatment.

It is further known that the conductivity of each metal - also aluminum - deteriorates less under the influence of foreign elements if they are in a different phase than if they formed a solid solution with the parent metal. Compared to the above, of course, the conductivity of metals can be improved by arbitrary compositions. Substantial success, i.e. a high quality conductor wire, can only be achieved if the composition of the parent metal is determined according to the aspects explained above and the element is treated by the method according to the invention.

The well-known, traditional technology of yarn production consists of two work stages, viz. thermal forming, which may be either rolling or pressing, and cold working, which is usually multi-stage drawing.

According to an earlier opinion, the conductivity of the wire is decisively affected by the temperature of the heat treatment, but its strength increases with the degree of cold working. It was later found that a higher working temperature would be more advantageous due to the improvement in conductivity and a lower working temperature due to the increase in strength. As a mediation between the two viewpoints, heat treatment between 400 and 450 ° C became common.

It follows from these ideas - and has already been implemented - that both properties can be improved if the ingot is first annealed to 450 ... 600 ° C to improve conductivity, then cooled by slow cooling to room temperature and then cold formed at a lower temperature. However, the fact that kiln capacity has to be set up for implementation and energy consumption is high has an unfavorable effect (see Figure 1).

In addition to the traditional (conventional) technology mentioned above, the casting method has recently become more common in the production of raw wire.

In this case, the time between solidification and shaping of the flowing metal is so short that even the change in conductivity that normally occurs during thermal shaping at the odd temperature or during pre-heating cannot occur.

That is why the casting method can be used to produce a wire with lower conductivity from the same element than with conventional technology. The productivity of the casting process and the elimination of bar casting costs make it possible to avoid a cleaner, i.e. more expensive, element for producing a final product of the same quality.

The object of the invention is to make better use of the possibilities of yarn production in the element than hitherto, i.e. to produce a yarn with higher conductivity and higher strength, at the lowest possible cost.

The above object is achieved according to the invention in that when an element with at least 99.0% aluminum is used, the degree of cold working is chosen so that the tensile strength of the wire in the final measure exceeds the final strength value by 5-20% and the final heat treatment continues until the wire strength drops to the final strength value of the wire. During plastic cold working, the strength of the wire - up to a very high degree of working - increases continuously, whereas its electrical conductivity decreases rapidly at first and then decreases or increases - measured between the drawing steps - alternately.

From this observation, it could be concluded that, after many drawing steps, there has been a premature stage of re-exposure (softening) in which the conductivity renewal already begins, but the strength is not yet substantially reduced. Fortunately, this spontaneous improvement in conductivity can occur in small amounts just after true drawing, but its uncertainty causes a considerable variation in the conductivity of the finished wire.

The latter step (method step) of the method according to the invention - nom. heat treatment in the final measure - reduces quality variation and improves the conductivity of the wire, but as a result of this heat treatment - simultaneously with an increase in conductivity - a slow decrease in strength also begins. It is therefore necessary to sacrifice part of the strength achieved by the modification in order to achieve a reduction in resistance of 0.4 2 ... 0.6 ohms mm / km. This sacrifice can thus be made possible so that in the preceding steps of the method according to the invention a 20-30% strength surplus can be achieved compared to the most stringent instructions without increasing the manufacturing costs.

In the description of the method according to the invention, it is not numerically defined how many kp / mm the strength of the wire must be increased by modification and how many must be reduced as a result of the heat treatment. The reason for this is that standard international guidelines dictate requirements for wire strength depending on the dimension.

With the method according to the invention, it is possible to arbitrarily produce a yarn from an ordinary element which has better conductivity and the same strength than the technologies used hitherto. Over the past decades, manufacturers have sought to improve conductivity primarily by raising the purity of the element. With the method according to the invention, a reduction in resistance of 0.4 to 0.6 ohm mm / km can be achieved more economically than by further increasing the purity of the element.

The conductivity-improving effect of this heat treatment according to the invention is also increased by the fact that the equilibrium concentration of the solid solution at low temperature approaches rapidly after strong cold working - due to the effect of a high cross-hard error concentration, while in the cast state it would require an impractically long heat treatment. In addition to the simultaneous improvement in conductivity, this phenomenon also results in a prescribed precipitation hardening. During cold working, heating must therefore be limited, as overheating between private drawing steps causes similar effects to heat treatment in the final measure, but - in contrast - the consequences here are detrimental because the conductivity improvement is eliminated by subsequent treatment, but the strength loss remains and may be true.

The present invention will be explained in more detail below with a few embodiments with reference to the drawings. They present:

Figure 1: Heat treatment according to a known method, schematically.

Figure 2: Heat treatment according to a method according to the invention, schematically.

Figure 3: Variation in characteristic electrical resistance and strength in an embodiment of the invention.

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Figure 4: Variation in characteristic electrical resistance and strength in another embodiment of the invention.

Figure 5: The above changes in another embodiment of the invention.

A comparison of Figures 1 and 2 clearly reveals the difference that the conventional method has two heatings, but the method according to the invention has only one heating.

As a result of the experiments, it has been found that the improvement in conductivity to be achieved and the rate of recooling depend on the temperature values realized in the first stage of heating in the method according to the invention. The best results could be achieved with a short heating between 500 and 550 ° C and a cooling rate of max. 40 ... 100 ° C / h. By lowering the heating temperature, the cooling rate can be increased, and extending the heating time is advantageous. The optimum heating conditions before heat treatment are significantly dependent on the composition of the element.

Another suitable embodiment of the method according to the invention is in that the raw wire produced by the casting roll method is heat-treated at a temperature of 150 to 300 ° C before cold working. This heat treatment partially replaces the thermal effects that increase conductivity, which - in traditional work - affect the ingot before modification. Since the distortions of the lattice caused by the modification accelerate the separation of the foreign elements, a corresponding improvement in conductivity can be achieved in this way even before the softening of the raw wire is completely softened.

In another embodiment of the method according to the invention, the heat treatment is actually related to the ratonization of the transport, so that the heat treatment is carried out on the transport track from the wire drawing plant to the cable manufacturing workshops or the warehouse. The wire rings taken from the wire drawing machine must be placed or suspended at most loosely connected to the conveyor track so that the heat transfer medium - which is suitably air - passes well through the bundle. The transport track must be enclosed in a heat-insulating liner. Inside the liner, it is appropriate to ensure a uniform temperature with artificial rotation and automatic temperature control.

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When the plant is stopped as planned, the wires that are still on the transport track for heat treatment must be removed. In the event of an unexpected plant shutdown, eg in the event of a power failure, harmful prolongation of the heat treatment must be prevented by opening the heat-insulating liner. The transport path for heat treatment must be conveniently set high, between the roof and other equipment.

A preferred possibility of the method according to the invention is that the heat treatment in real scale can be combined with the surface treatment of the yarn. Especially in yarns used under abrasive conditions, it may be important to increase the corrosion resistance of the yarns. In this case, it is expedient to carry out the heat treatment in the medium forming the etching layer or coating, which improves the conductivity.

The properties of the yarns produced by the method according to the invention will be explained in more detail below on the basis of exemplary embodiments in comparison with yarns produced by known methods.

Smelted aluminum samples comprising several compositions were treated by various methods similar to the method of the invention and finally examined how the resistance and strength of the wire change if it is heat treated in real scale.

Example 1

Two compression ingots were cast from EAl 99.8 (Fe 0.11, Si 0.09%), one of which was heated at 500 ° C for two hours to improve conductivity in a known manner, then slowly cooled to room temperature, then both ingots were compressed at 200 ° C. The compressed yarn was formed by 98% cold drawing.

Thus, the yarn samples were prepared in a modified state, and BY samples were performed soon after the heat treatment 120-140-160-180-200 ° C for half an hour electrical resistance measurements and strength measurements.

Figure 3 illustrated at the top the change in the characteristic electrical resistance (p20) and at the bottom the tensile strength as a function of the heat treatment temperature.

Crosses (+) show the values measured from heated ingot yarns and points (.) Show those values measured from unheated ingot yarns. In the figure, we have shown with a horizontal line the values specified in the then most stringent instructions.

Example 2

A wire was prepared from melt EA1 99.6 (Fe 0.25, Si 0.09%) as described in the previous example. The change in properties depending on the heat treatment temperature is shown in Figure 4. Example 3

The molten EAl 99.7 (Fe 0.18, Si 0.08%) was cold-formed from the ready-to-use, roll-rolled raw material 97%, then heat-treated and examined as described in the previous examples. Finally, the properties are divided in Figure 5.

It can be seen from these three examples that the resistance of the hardened wire depends on the composition of the material, the method of treatment, but in all three cases a characteristic 2 0.4 ... 0.6 Ω mm / km reduction in resistance can be achieved by heat treatment in the final dimension.

The working examples prove that the process according to the invention makes it possible to produce a better wire from the smelted aluminum of a similar composition than is required by the strictest instructions currently in force.