Continuous method for producing capillaries made of nonferrous alloys

Abstract

A method for producing capillaries from nonferrous alloys, in particular of Al, which includes the continuous cold rotary extrusion of a blank having a solid cross-section, obtained by casting, in order to produce a tube having a hollow cross-section. The deformation of the blank to be extruded is achieved only by using friction force. The method further includes at least one step of cold drawing of the extruded tube in order to reduce its diameter to the diameters corresponding to a capillary.

Claims

1. A method for producing capillaries from nonferrous alloys, the method including the following steps: a continuous cold rotary extrusion of an initial blank having a solid cross-section, produced by casting, in order to obtain a tube having a hollow cross-section, wherein a deformation of the blank to be extruded is achieved only by friction force, a cooling of the extruded tube to ambient temperature, and at least one step of cold drawing of the extruded tube in order to reduce a diameter thereof to diameters corresponding to a capillary, and a plurality of steps of cold drawing performed in succession until an inside diameter of the capillary in the range from 0.2 mm to 4.5 mm and a length of the capillary exceeding 10,000 mm with substantially constant inner diameters are obtained, wherein the initial blank is a wire rod with an initial external diameter of 9.5 mm-15 mm.

2. The method according to claim 1, further comprising a step of winding the extruded tube in the form of a coil before feeding to the step of cold drawing.

3. The method according to claim 1, wherein said nonferrous alloy is an aluminum alloy selected from the UNI EN 573-3 standard series from 1000 to 6000.

4. The method according to claim 1, wherein the alloy is an aluminum alloy of the UNI 3103 series.

5. The method according to claim 1, wherein the continuous cold rotary extrusion is achieved by using a wheel with an endless perimetric external groove in which said blank is accommodated and is fed to an extrusion chamber by a contact with protrusions in the extrusion chamber configured to generate sufficient friction to reach the deformation configured for the extrusion of the blank.

Description

DETAILED DESCRIPTION OF THE DISCLOSURE

(1) The method according to the disclosure comprises therefore a first step of continuous cold rotary extrusion according to a technique described e.g. in U.S. Pat. No. 3,765,216 or U.S. Pat. No. 4,055,979, in which the blank to be extruded is fed cold, without heating beforehand, and it reaches the necessary deformation solely by way of a friction force generated in the extruder. In particular, according to such technique, an initial blank, which is commonly a wire rod having a solid cross-section, obtained conventionally by way of casting and cold rolling in a production line, is fed cold to a rotary extruder that comprises a steel rotating wheel, actuated by motor and reduction gear. The wheel is provided with an external, perimetric, endless groove, into which is inserted the wire rod which is entrained through an extrusion chamber and subjected therein to high friction force developed by friction between the wheel and a section of the wall of the chamber, e.g. by virtue of protrusions or spikes positioned thereon which make contact with the groove of the wheel during rotation. Then, in the friction zone the wire rod in the groove reaches the level of yield or deformation of the alloy of which it is made, permitting the extrusion thereof through a die plate, e.g. bridge-like, which is arranged in the extrusion chamber. Thus, in this first step of the process, a continuous rotary extrusion takes place in which the level of deformability is reached in any case and the extrusion of the wire rod occurs without applying external heat or induced heating.

(2) In practice, a starting wire rod can be used in the form of a skein of weight that can be considerably greater than that usable in a hot extrusion process. For the purposes of illustration, a skein of 2000 kg can be used, placed e.g. on a pallet, which is unrolled and cleaned on the outer surface by way of brushing or passing in aqueous solutions, in the production line, and which is then fed to the continuous rotary extrusion. The wire rod can have an initial external diameter e.g. of 9.5-15 mm. While the process can be applied to various non-ferrous metals and alloys, e.g. including of copper, it is particularly advantageous in the manufacture of capillaries from alloys of aluminum in widespread demand, e.g. in the field of thermal expansion valves, by virtue of their low cost compared to copper and alloys of copper. It has in fact been found, advantageously, that the method of the present disclosure can be used with a wide range of alloys of aluminum with mechanical characteristics suitable for an easy deformability by extrusion, without other constraints or limitations in terms of chemical composition. Therefore the alloys of aluminum defined by the UNI EN 573-3 standard, series 1000 to 6000, can be used, for example the alloys of series 3000, for example the EN-AW 3103 alloy containing Si, Fe and Mg, which are far superior to the alloys of Al described in EP 1 840 487.

(3) The tube exiting from the cold rotary extrusion machine is passed through a cooling and drying vat in order to cool it to ambient temperature.

(4) The resulting extruded tube is then sent for induced current quality control, e.g. through guide loops, for the marking of any line defects, and then it can be sent to the subsequent steps of cold drawing, either immediately or after winding by way of winders to await such subsequent processes.

(5) The method of the disclosure finally comprises at least one final stage of cold drawing, but, preferably, a succession of drawing stages for a gradual reduction of the diameter of the extruded tube until it reaches the desired diameter of the capillary, usually an inside diameter in the range of 0.2 to 4.5 mm. In practice the cold drawing is conventional, in which one or more cold reductions of the cross-section of the tubes are carried out with drawing lines, through conveniently dimensioned dies and spindles.

(6) As can be seen from the foregoing, the method according to the disclosure presents considerable advantages by virtue of the use of a continuous cold rotary extrusion that does not make use of induced heating, in combination with the final cold drawing. By substituting the conventional hot extrusion for cold rotary extrusion, in which the heating is supplied by the friction force and the deformation is carried out by the wheel in rotation, the consumption of electricity is appreciably reduced, with a kw/ton ratio of consumption to product equal to a third of the common process of producing capillaries based on hot extrusion. Furthermore, the continuous cold extrusion process, in addition to not using induced heating, by virtue of its method of deformation on the rotating wheel, reduces the formation of oxides and does not require lubricating substances on the production utensils, so making the washing of the capillary tube optional and non-essential. In fact, in the hot extrusion process it can be necessary, in addition to the utensils, to lubricate the billet container with graphite, oil or specially-formulated polymers.

(7) The environmental impact is appreciably mitigated in that the consumption of water resources is reduced below 50 m.sup.3/h of water, and of hydraulic oil for actuating the machines below 1 m.sup.3, and at the same time carbon emissions are reduced. In fact, with induced heating not being necessary, no heating oven is needed, which conventionally would be an electric induction oven, and therefore would require a cooling system with consequent increase in the necessary volume of water. Alternatively, the consumption of methane gas used for methane-fueled heating ovens is eliminated.

(8) Finally, the method of the disclosure makes it possible to produce capillaries of unlimited length, in any case exceeding 10000 mm and with substantially constant inner diameters that make possible minimal variations of flow-rate of fluid, and with optimal outer and inner roughness.

(9) The disclosures in Italian Patent Application No. 102018000006938 from which this application claims priority are incorporated herein by reference.