Method for producing metallic components made of a copper alloy

Abstract

The present invention relates to a method for producing metallic components, preferably for media flow in drinking water systems, from a copper alloy, comprising melting an alloy with the constituents, conditioning the material before and / or during the solidification process, preferably by grain refinement, and hot forming the material at a temperature between 680 and 780 °C. The present invention aims to provide a method for producing metallic components, in particular for media flow in a drinking water system, which can be carried out economically.

Description

[0001] The present invention relates to a method for producing metallic components, preferably for media guidance in drinking water systems, from a copper alloy.

[0002] Water is an essential raw material for the survival of living organisms. When drinking water is drawn from the supply system for consumption, it must be of such a quality that it does not cause illness in humans. To achieve this, high standards are placed on the materials that come into direct contact with the drinking water. Copper is considered an indispensable material in industry and technology for water-conducting systems because, in addition to its high corrosion resistance, it also has antibacterial properties. In addition, copper also exhibits other positive material properties, which include good castability, high strength and toughness, and formability. However, not all copper alloys are suitable for the production of drinking water-conducting components.

[0003] DE 10 2019 106 131 A1 and DE 10 2019 106 136 A1 each describe lead-free copper alloys, one with 3.87 wt% Sn, 1.4 wt% Zn, 0.42 wt% S, 0.01 wt% Fe, and 0.01 wt% Ni, and one with 3.2 wt% Sn, 1.6 wt% Zn, 0.19 wt% S, 0.01 wt% Fe, and 0.02 wt% Ni, with the remainder being copper. This copper alloy is used to manufacture components for media-carrying gas or water pipes in a process that includes melting the alloy and producing a blank followed by pressing. The selected pressing temperature during pressing is in the range of 750°C to 900°C. The publications disclose setting temperatures of 800°C and 860°C or 880°C with a view to achieving good fine graining with positive forming properties.According to the disclosure of these publications, a lower forming temperature leads to significantly higher forming forces, which ultimately affects the economic efficiency of the process.

[0004] The production of shaped parts from a copper alloy containing 4.5 wt.% Sn, 5.4 to 13 wt.% Zn, 0.08 wt.% Pb, 0.01 wt.% Fe, and 0.4 wt.% Ni, the remainder being copper, is described in DE 10 2012 013 817 A1. The production process comprises melting the alloy, continuously casting semi-finished products and subsequently cutting them to length to form blanks, heating the blanks to a temperature between 750°C and 850°C, and then pressing them into shaped parts. Furthermore, mechanical preconditioning using electromagnetic stirring is carried out during the melting and casting processes. As a result, the material has an average grain size of less than 1 mm before the hot pressing process. Such mechanical preconditioning enables the formation of fine grains without the need to alloy additional elements such as B or Zr.

[0005] EP 3 225 707 A1 also discloses a component for media-carrying gas or water pipes made of a lead-free copper alloy. This document addresses the role of sulfides in ensuring sufficient machinability of the alloy.

[0006] EP 3 581 667 A2 discloses a copper alloy containing 2 to 6 wt.% Sn, 0 to 5 wt.% Zn, 0.05 to 0.6 wt.% S, less than 0.25 wt.% Pb, less than 0.6 wt.% Ni, and less than 0.25 wt.% Sb, with the remainder being copper. Said copper alloy is used to produce molded parts by means of a process comprising a hot-pressing operation at temperatures between 700°C and 900°C, followed by machining. For this purpose, an average grain size of 2 mm is achieved prior to the hot-pressing operation by adding between 0.005 and 0.03 wt.% Zr and / or B.

[0007] The present invention aims to provide a method for producing metallic components, in particular for media guidance in a drinking water system, which can be carried out economically.

[0008] To solve this problem, the present invention proposes a method having the features of claim 1.

[0009] The present invention presents the processing of a specific copper alloy which requires compliance with defined upper limits with regard to those components that can migrate from the component into the water. This also applies in particular to the control of impurities. Here, the present invention proposes compliance with fixed upper limits for certain impurities, namely impurities with Al, Cd, Cr and Si. This means that the corresponding elements may, but do not have to, be contained in the alloy up to the stated upper limit. Neither the impurities nor the other elements mentioned in the patent claim merely with upper limits are necessary components of the alloy. However, according to preferred developments of the present invention, they can be required as necessary elements with a minimum proportion in order to achieve certain properties within the alloy orof the resulting metallic component.

[0010] The alloy used in the present invention is melted in the inventive process with the alloy components according to claim 1. The material formed by the alloy is then conditioned before and / or during the solidification process. Conditioning is preferably carried out with the aim of grain refinement. Conditioning can be achieved through chemical-metallurgical influences, particularly during solidification by introducing foreign nuclei.

[0011] To produce the semi-finished product, the alloy is preferably cast or continuously cast. During casting, the melt is preferably superheated and poured at a temperature at least 15 °C above the melting temperature of the alloy. The so-called casting temperature is preferably between 20 °C and 70 °C, and particularly preferably between 30 °C and 50 °C above the melting temperature of the alloy. For the alloy according to the invention, casting temperatures can be between 1500 °C and 1100 °C or between 1070 °C and 1090 °C. These casting temperatures influence the resulting microstructure of the material and can lead to the formation of finer grains.

[0012] In the process according to the invention, the semi-finished product is then hot-formed at a temperature between 680 °C and 780 °C, preferably between 700 °C and 770 °C, particularly preferably between 710 °C and 740 °C, to produce the component. Furthermore, the hot-forming takes place at a temperature of at least 700 °C, preferably at least 710 °C, particularly preferably at a temperature between 720 and 730 °C.

[0013] At forming temperatures outside this range, the semi-finished product may tend to crack, for example at lower temperatures, or exhibit surface oxidation, for example at higher temperatures.

[0014] Surprisingly, it has been found that components of the aforementioned type can also be produced at a much lower hot forming temperature without the need for significantly higher forming forces. It has also been shown that the temperature for hot forming can be lowered with smaller grain sizes. However, with a view to reliable process control, an average grain size of between 0.5 mm and 3 mm is preferably produced in the semi-finished product and before hot forming. The grain size is preferably between 1.0 mm and 2.5 mm. More preferably between 1.5 mm and 2 mm. Further more preferably, the grain size is between 1.6 mm and 1.8 mm.

[0015] In view of economic requirements and other properties of the components to be manufactured, the process should be carried out with a hot forming temperature of between 720 °C and 730 °C, which, based on practical tests by the inventors, leads to a grain size in a range of between 1.5 mm and 2 mm, which is established before hot forming and after solidification of the alloy to form the semi-finished product.

[0016] Furthermore, it has been shown that the deformation rate during hot forming can influence the mechanical properties of the component being manufactured. For example, if the deformation rate is too high, the material may crack. However, if the deformation rate is reduced too drastically, this deformation rate may not be feasible even with positive forming results due to the resulting process duration and the resulting economic disadvantages. Therefore, hot forming should be carried out at a deformation rate between 1 1 / s and 1 / 10 1 / s.

[0017] Nickel should be added at between 0.05 and 0.4 wt.%, preferably within a range of between 0.1 and 0.3 wt.%, and particularly preferably within a range of between 0.15 and 0.25 wt.%. Nickel increases the strength after hot forming. However, an excessively high nickel content impairs the formability of the alloy for producing the semi-finished product.

[0018] The alloy according to the invention contains tin in a proportion of 3.5 to 4.8 wt.%. Tin acts as a solid solution strengthener in the alloy, thus increasing tensile strength, yield strength, and hardness. However, tin reduces elongation at break. Tin also has a positive influence on corrosion resistance. However, an excessively high tin content results in more pronounced segregations during hot forming, which complicates subsequent hot forming. While heat treatment is possible to break these segregations, heat treatment is time- and energy-intensive and leads to a coarsening of the microstructure, which the present invention aims to avoid.

[0019] A certain amount of sulfur combined with zinc promotes the alloy's solidification behavior and chip-breaking properties during subsequent machining of the semi-finished product. However, the zinc content must be controlled due to zinc's tendency to accumulate inhomogeneously and concentratedly in the microstructure, which complicates subsequent hot forming. Accordingly, 1.0 to 2.5 wt.% Zn and 0.02 to 0.5 wt.% S are added to the alloy.

[0020] Lead acts as a chip breaker, but its harmful effects on health are only tolerable within narrow limits, not least because of the risk of lead migrating from the metallic components into drinking water during long-term use. The same applies to the Sb content. For both alloys, there is an upper limit of 0.1 wt.%.

[0021] Zr, Fe and B promote grain refinement. Fe and B should be added in combination. The Fe content is between 0.005 and 0.3 wt.% and the B content is between 0.005 and 0.02 wt.%. The sole addition of between 0.005 and 0.02 wt.% Zr is preferable and more effective in terms of grain refinement. If the amount of zirconium in the alloy is not sufficiently matched or becomes too high, zirconium-rich sulfides can form along the grain boundaries. These precipitates can reduce the amount of dissolved zirconium in the solid solution and thus inhibit the resulting grain refinement effect. The mechanical properties of the material, e.g., strength and toughness, can also be impaired by such precipitates.

[0022] The copper alloy described above is particularly suitable for the production of media-carrying metal components used in drinking water pipes. Such components include fittings, end caps, and pipe connectors. The forming of these components is typically achieved solely by hot forming, preferably extrusion. However, hot forming can also be performed using pressing or stamping processes. Eccentric presses or hydraulic presses can be used for this purpose.

[0023] After hot forming, the components can be turned to length or machined, particularly to produce threads or connecting or sealing surfaces.

Claims

1. A process for producing metallic components, preferably for media guidance in drinking water systems, from a copper alloy, comprising (a) melting an alloy with the constituents 3.5 - 4.8 wt.% Sn 1.0 - 2.5 wt.% Zn 0.02 - 0.5 wt.% S ≤ 0.10 wt.% Pb < 0.1 wt.% Sb 0.05 - 0.4 wt.% Ni 0.01 - 0.06 wt.% P and unavoidable impurities, comprising < 0.01 wt.% Al < 0.01 wt.% Cd < 0.02 wt.% Cr < 0.01 wt.% Si and the remainder Cu, (b) conditioning the alloy before and / or during the solidification of a semi-finished product formed from the alloy, preferably by grain refining, and (c) hot forming the semi-finished product at a temperature between 680 and 780 °C to produce the component.

2. A process for producing metallic components from a copper alloy according to claim 1, characterized by a Zr content between 0.005 - 0.02 wt.%.

3. A process for producing metallic components from a copper alloy according to claim 1, characterized by an Fe content between 0.005 - 0.3 wt% and a B content between 0.005 - 0.02 wt%.

4. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized in that the Zn content is between 1.0 - 2.4 wt.%.

5. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized in that the Ni content is between 0.1 - 0.3 wt.%, preferably between 0.15 - 0.25 wt.%.

6. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized in that the hot forming takes place at a temperature of at least 700 °C, preferably at least 710 °C, particularly preferably at a temperature between 720 and 730 °C.

7. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized in thatthe average grain size of the semi-finished product before hot forming is between 0.5 - 3 mm, preferably between 1.0 - 2.5 mm, more preferably between 1.5 - 2.0 mm and particularly preferably between 1.6 - 1.8 mm.

8. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized in that hot forming is extrusion.

9. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized by a machining operation after hot forming.

10. A process for producing metallic components from a copper alloy according to one of the preceding claims, characterized in that Hot forming can be carried out at a deformation rate between 1 1 / s and 1 / 10 1 / s.

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