Continuous extrusion process for obtaining ultra-fine grain copper bar

Abstract

The invention relates to a continuous extrusion process for obtaining an ultra-fine grain copper bar, which relates to the technical field of metal processing, and comprises the following steps: up-drawing continuous casting: taking electrolytic copper as a raw material, preheating and drying the electrolytic copper, melting the electrolytic copper in a smelting device, covering the surface of copper liquid with charcoal and graphite flakes, up-drawing a copper rod with the diameter of 30mm by adopting a traction unit, the copper rod is prepared through continuous extrusion, the copper rod subjected to upward continuous casting serves as a raw material, a continuous extrusion unit is utilized, the preheating temperature of a mold is 400-500 DEG C, the preheating time is 2 h, the preheating temperature of blank extrusion is 740-760 DEG C, and the preheating time is 2 h. And producing a copper rod with the diameter of 20mm, continuously extruding to prepare the copper bar, and producing the ultra-fine grain copper bar by using the copper rod prepared in the previous step as a raw material and using a continuous extrusion unit again under the condition that the product outlet temperature is 350-400 DEG C. According to the method, through the mode of simplifying the technological process and reducing the working procedures, it is guaranteed that the surface quality of the prepared ultra-fine grain copper bar is high, energy consumption is reduced, and the production efficiency of the copper bar is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal processing, in particular to a continuous extrusion process for obtaining ultrafine-grained copper bars. Background Art

[0002] Copper busbars, also known as copper busbars or copper busbars, are made of copper and are long conductors with rectangular or chamfered rectangular cross-sections. They are used to transport current and connect electrical equipment in circuits. As an important material in electrical engineering, copper busbars have good electrical and thermal conductivity and high current carrying capacity. In some cases, it is necessary to enhance the strength and toughness of copper busbars. Increasing the strength by changing the metal composition will often affect the thermal and electrical conductivity of the copper busbars.

[0003] At present, the common solution to increase the strength of copper bars is the "cold deformation + heat treatment" process. This type of process is relatively mature and can fully improve the casting structure, but the copper bars produced by this process have many cracks, low yield rate, long process flow, high energy and resource consumption, and are not conducive to large-scale production.

[0004] For related technologies, please refer to the patent application with publication number CN107414408A, which discloses a method for preparing high-precision oxygen-free bright copper busbars; the application adopts the "upward continuous casting + continuous extrusion + drawing" process to prepare the copper busbars. However, this method has the following limitations: (1) The speed of the extrusion wheel for preparing the copper busbar is too high, and the average grain size of the prepared copper busbar is too large and has many defects.

[0005] (2) The copper rod prepared by upward continuous casting is directly used as the blank for extruding the copper busbar. The average grain size of the prepared copper busbar is too large, thereby reducing the mechanical properties of the copper busbar.

[0006] In view of the above-mentioned related technologies, a method for preparing ultrafine-grained copper busbars is urgently needed to ensure that the prepared copper busbars have smaller grain size, higher mechanical properties, and high surface quality, can meet the needs of industry use, have a simple process flow, can be suitable for large-scale production, and effectively reduce costs. Summary of the invention

[0007] In order to improve the production efficiency and product quality of copper busbars, the present invention provides a continuous extrusion process for obtaining ultrafine-grained copper busbars.

[0008] The present invention provides a continuous extrusion process for obtaining ultrafine-grained copper bars, which adopts the following technical scheme: A continuous extrusion process for obtaining ultrafine-grained copper bars, the process comprising the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it and then melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, using a traction unit to pull up a copper rod with a diameter of 30mm, and the speed of pulling up the copper rod is 200-300mm / min; S2: Continuously extruding to prepare copper rods, using the upward continuous casting copper rods prepared in S1 as raw materials, using a continuous extrusion unit, with a product outlet temperature of 350-400°C, a mold preheating temperature of 400-500°C, preheating for 2 hours, and an extrusion blank preheating temperature of 740-760°C, to produce copper rods with a diameter of 20 mm; S3: Continuously extrude to prepare copper bars, using the copper rod prepared in S2 as raw material, and again using a continuous extrusion unit, with a product outlet temperature of 350-400°C, a mold preheating temperature of 400-500°C, preheating for 2 hours, and an extrusion blank preheating temperature of 740-760°C to produce copper bars.

[0009] S4: Rapid cooling: The obtained billet is rapidly cooled at the outlet of the extrusion die by spraying liquid nitrogen. The nozzle spacing is 50-60 mm, and the distance between the nozzle and the billet surface is 10-20 mm. The billet is rapidly cooled from high temperature to room temperature to refine the grains. S5: Drawing, straightening and machining the copper busbar obtained in S4.

[0010] Preferably, the temperatures of the smelting furnace and the holding furnace are both 1150° C., wherein the smelting furnace is covered with charcoal with a thickness of 150-160 mm, and the holding furnace is covered with graphite flakes with a thickness of 100-120 mm.

[0011] Preferably, the channel length of the continuous extruder cavity is set to 80-100 mm.

[0012] Preferably, when the copper bar is prepared by continuous extrusion, the copper bar introduction speed through the continuous extrusion unit is 2.2-2.7 m / min, the lead-out speed is 0.23-0.28 m / min, and the extrusion ratio is 2-4.

[0013] By adopting the above technical solution, the electrical conductivity of copper square is ≥98.3%IACS; the grains in all directions are uniform and consistent, with an average grain size of ≤20um; the tensile strength is ≥450 MPa; the yield strength is ≥400MPa; and the elongation is ≥20%.

[0014] In summary, the present invention includes at least one of the following beneficial technical effects: The present invention adopts a special continuous extrusion process and die parameters to obtain an ultra-fine-grained copper busbar with an average grain size of ≤20um, which significantly improves the mechanical properties of the copper busbar; In the present invention, liquid nitrogen cooling is preferably used, because the temperature of the copper busbar can be quickly reduced, the formation of large grains is avoided, and the quality of the copper busbar is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to make the content of the present invention more clearly understood, the present invention is further described below according to specific embodiments and in conjunction with the accompanying drawings, wherein Figure 1 It is a cross-sectional view of the mold used in the process of the present invention.

[0016] Figure 2 It is a process flow chart of the present invention.

[0017] Figure 3 3 is a metallographic structure morphology diagram of the sample in the embodiment of the present invention.

[0018] Figure 4 This is a metallographic structure morphology diagram of the sample in Comparative Example 1 of the present invention.

[0019] Figure 5 This is a metallographic structure morphology diagram of the sample in Comparative Example 2 of the present invention.

[0020] Figure 6 This is a metallographic structure morphology diagram of the sample in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with all the accompanying drawings.

[0022] The embodiment of the present invention discloses a continuous extrusion process for obtaining ultrafine-grained copper bars.

[0023] A continuous extrusion process for obtaining ultrafine-grained copper bars, the process comprising the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it before melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, and using a traction unit to pull up the copper rod; the temperature of the smelting furnace is 1150℃, using dried charcoal for covering, the charcoal covering thickness is 160mm; the temperature of the holding furnace is 1150℃, using graphite flakes for covering, the covering thickness is 120mm; the speed of the upward copper rod is 240mm / min, and the diameter is 30mm; S2: Continuous extrusion to prepare copper rods, using the upward continuous casting copper rods prepared in S1 as raw materials, using a continuous extrusion unit, the product outlet temperature is 350-400°C, the mold is preheated at 400-500°C, preheated for 2 hours, the extrusion billet preheating temperature is 740-760°C, the continuous extruder speed is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S3: Continuously extruding to prepare copper bars, using the copper rods prepared in S2 as raw materials, and using the continuous extrusion unit again, the product outlet temperature is 350-400°C, the mold is preheated at 400-500°C, preheated for 2 hours, the extrusion billet preheating temperature is 740-760°C, the continuous extruder speed is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S4: Rapid cooling: The obtained billet is rapidly cooled at the outlet of the extrusion die by spraying liquid nitrogen. The nozzle spacing is 50-60 mm, and the distance between the nozzle and the billet surface is 10-20 mm. The billet is rapidly cooled from high temperature to room temperature to refine the grains. S5: Drawing, straightening and machining the copper busbar obtained in S4.

[0024] In the actual processing, when the copper bar is prepared by continuous extrusion of S3 of the present invention, the relationship between the extrusion temperature and the introduction speed is calculated. When the introduction speed is 2.2-2.7 m / min, It is 0.65-0.71. It can be calculated by formula 1 that the product temperature is 360-400℃. (In the formula, η=70%, i=80, d=30mm, D=630mm, P=600KW, n=1000rpm, T0=20℃.) (Formula 1) In the formula T ——Temperature of the extruded product at the die outlet (℃); ——Temperature of the extruded product at the die outlet (℃); i ——speed ratio of reducer; —— The total efficiency of converting the power consumed by the motor into product heat, including the mechanical efficiency of the main machine and the heat removed by the equipment; d —— Copper rod diameter (mm); D —— Extrusion wheel diameter (mm); P —— Rated power of main motor (kW); n —— Rated speed of main motor (rpm); ——Actual armature current of the main motor during production (A); ——Rated armature current of main motor (A).

[0025] In the step of preparing the copper busbar by continuous extrusion in S3 of the present invention, the parameters of introduction speed of 2.2-2.7 m / min, extrusion ratio of 2-4 and channel length of 80-100 mm are set to ensure that the product outlet temperature during the extrusion process is maintained between 350° C. and 400° C. This precise control effectively avoids the formation of cold deformation structure and large grains, thereby ensuring that the copper busbar has excellent electrical conductivity and thermal conductivity while significantly improving its strength and toughness.

[0026] In addition, liquid nitrogen cooling technology is used immediately after the copper busbar is extruded to quickly cool it down, further refining the grain structure inside the copper busbar. This not only enhances the microscopic uniformity of the material, but also promotes the overall improvement of mechanical properties.

[0027] The present invention adopts the process route of "upward continuous casting + continuous extrusion" to prepare the average grain size of the sample ≤ 20um, and improves the strength and plasticity of the copper bar through fine grain strengthening; the present invention adopts ultrafine crystal oxygen-free copper rods prepared by low introduction speed and low extraction speed as the original billet of extruded copper bar, in order to further refine the grain size of the extruded copper square billet. Subsequently, copper squares are prepared by low introduction speed and low extraction speed. The ultrafine crystal copper bar prepared in this way has good surface quality and simple process, reduces energy consumption, has high product utilization rate, and can be processed later after a little cleaning, which is conducive to improving production efficiency.

[0028] In order to better understand the effect of the present invention, the following comparative example experiments were also carried out: Comparative Example 1: A continuous extrusion process for obtaining ultrafine-grained copper bars, the process comprising the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it before melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, and using a traction unit to pull up the copper rod; the temperature of the smelting furnace is 1150℃, using dried charcoal for covering, the charcoal covering thickness is 160mm; the temperature of the holding furnace is 1150℃, using graphite flakes for covering, the covering thickness is 120mm; the speed of the upward copper rod is 240mm / min, and the diameter is 30mm; S2: Prepare copper rod by continuous extrusion, using the copper rod prepared by continuous casting in S1 as raw material, and using a continuous extrusion unit to produce copper rod with a diameter of 20 mm; the rotation speed is 350℃-400℃ for the product outlet temperature; the mold is preheated before use, the preheating temperature is 500℃, and the preheating time is 2 hours; the preheating temperature of the extruded billet is 750℃, the preheating time is 2h, and the continuous extruder speed is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S3: Prepare copper bars by continuous extrusion, using the continuously extruded copper rods prepared in S2 as raw materials, and using a continuous extrusion unit to produce ultrafine-grained copper bars; the mold is preheated before use, the preheating temperature is 500°C, and the preheating time is 2 hours; the preheating temperature of the extruded billet is 750°C, and the preheating time is 2 hours; the speed of the continuous extruder is 5r / min; the channel length of the continuous extruder cavity is 90mm; S4: Rapid cooling: The obtained billet is rapidly cooled at the outlet of the extrusion die by spraying liquid nitrogen. The nozzle spacing is 50-60 mm, and the distance between the nozzle and the billet surface is 10-20 mm. The billet is rapidly cooled from high temperature to room temperature to refine the grains. S5: Drawing, straightening and machining the copper busbar obtained in S4.

[0029] Comparative Example 2: A continuous extrusion process for obtaining ultrafine-grained copper bars, the process comprising the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it before melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, and using a traction unit to pull up the copper rod; the temperature of the smelting furnace is 1150℃, using dried charcoal for covering, the charcoal covering thickness is 160mm; the temperature of the holding furnace is 1150℃, using graphite flakes for covering, the covering thickness is 120mm; the speed of the upward copper rod is 240mm / min, and the diameter is 30mm; S2: Prepare copper rods by continuous extrusion, using the copper rods prepared by continuous casting in S1 as raw materials, and using a continuous extrusion unit to produce copper rods with a diameter of 25 mm; the mold is preheated before use, the preheating temperature is 500°C, and the preheating time is 2 hours; the preheating temperature of the extruded billet is 750°C, and the preheating time is 2 hours; the speed of the continuous extruder is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S3: Prepare copper bars by continuous extrusion, using the continuously extruded copper rods prepared in S2 as raw materials, and using a continuous extrusion unit to produce ultrafine-grained copper bars; the mold is preheated before use, the preheating temperature is 500°C, and the preheating time is 2 hours; the preheating temperature of the extruded billet is 750°C, and the preheating time is 2 hours; the speed of the continuous extruder is 2.7r / min; the channel length of the continuous extruder cavity is 150mm; S4: Rapid cooling: The obtained billet is rapidly cooled at the outlet of the extrusion die by spraying liquid nitrogen. The nozzle spacing is 50-60 mm, and the distance between the nozzle and the billet surface is 10-20 mm. The billet is rapidly cooled from high temperature to room temperature to refine the grains. S5: Drawing, straightening and machining the copper busbar obtained in S4.

[0030] Comparative Example 3: A continuous extrusion process for obtaining ultrafine-grained copper bars, the process comprising the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it before melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, and using a traction unit to pull up the copper rod; the temperature of the smelting furnace is 1150℃, using dried charcoal for covering, the charcoal covering thickness is 160mm; the temperature of the holding furnace is 1150℃, using graphite flakes for covering, the covering thickness is 120mm; the speed of the upward copper rod is 240mm / min, and the diameter is 30mm; S2: Prepare copper rods by continuous extrusion, using the copper rods prepared by continuous casting in S1 as raw materials, and using a continuous extrusion unit to produce copper rods with a diameter of 20 mm; the mold is preheated before use, the preheating temperature is 500°C, and the preheating time is 2 hours; the preheating temperature of the extruded billet is 750°C, and the preheating time is 2 hours; the speed of the continuous extruder is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S3: Prepare copper bars by continuous extrusion, using the continuously extruded copper rods prepared in S2 as raw materials, and using a continuous extrusion unit to produce ultrafine-grained copper bars; the product outlet temperature is 350℃-400℃, and the cavity is preheated before use, the preheating temperature is 750℃, and the preheating time is 2 hours; the speed of the continuous extruder is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S4: Rapid cooling, the resulting billet is water-cooled at the exit of the extrusion die; S5: Drawing, straightening and machining the copper busbar obtained in S4.

[0031] Embodiment 1: A continuous extrusion process for obtaining ultrafine-grained copper bars, the process comprising the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it before melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, and using a traction unit to pull up the copper rod; the temperature of the smelting furnace is 1150℃, using dried charcoal for covering, the charcoal covering thickness is 160mm; the temperature of the holding furnace is 1150℃, using graphite flakes for covering, the covering thickness is 120mm; the speed of the upward copper rod is 240mm / min, and the diameter is 30mm; S2: Prepare copper rods by continuous extrusion, using the copper rods prepared by continuous casting in S1 as raw materials, and using a continuous extrusion unit to produce copper rods with a diameter of 20 mm; the mold is preheated before use, the preheating temperature is 500°C, and the preheating time is 2 hours; the preheating temperature of the extruded billet is 750°C, and the preheating time is 2 hours; the speed of the continuous extruder is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S3: Prepare copper bars by continuous extrusion, using the continuously extruded copper rods prepared in S2 as raw materials, and using a continuous extrusion unit to produce ultrafine-grained copper bars; the product outlet temperature is 350℃-400℃, and the cavity is preheated before use, the preheating temperature is 750℃, and the preheating time is 2 hours; the speed of the continuous extruder is 2.7r / min; the channel length of the continuous extruder cavity is 90mm; S4: Rapid cooling: The obtained billet is rapidly cooled at the outlet of the extrusion die by spraying liquid nitrogen. The nozzle spacing is 50-60 mm, and the distance between the nozzle and the billet surface is 10-20 mm. The billet is rapidly cooled from high temperature to room temperature to refine the grains. S5: Drawing, straightening and machining the copper busbar obtained in S4 The performance comparison of the copper busbars made in the three comparative examples and the embodiment is shown in the following table: Table 1 Performance comparison of copper busbars produced by the process of the present invention It can be seen from the above table that the copper busbar produced by the process and parameter ratio of the embodiment has significantly higher performance than other comparative examples, achieving uniform grains in all directions, an average grain size of ≤20um, tensile strength ≥450 MPa, yield strength ≥400 MPa, and elongation ≥20%. In addition, the ultrafine-grained copper busbar prepared by the present invention has good surface quality and simple process, low energy consumption, and high product utilization rate. It can be processed later after a little cleaning, which is beneficial to improving production efficiency.

[0032] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A continuous extrusion process for obtaining ultrafine-grained copper bars, characterized in that: The process includes the following steps: S1: Upward continuous casting, using electrolytic copper as raw material, preheating and drying it and then melting it in a smelting device, using charcoal and graphite flakes to cover the surface of the molten copper, using a traction unit to pull up a copper rod with a diameter of 30mm, and the speed of pulling up the copper rod is 200-300mm / min; S2: Continuously extruding to prepare copper rods, using the upward continuous casting copper rods prepared in S1 as raw materials, using a continuous extrusion unit, with a product outlet temperature of 350-400°C, a mold preheating temperature of 400-500°C, preheating for 2 hours, and an extrusion blank preheating temperature of 740-760°C, to produce copper rods with a diameter of 20 mm; S3: Continuously extruding to prepare copper bars, using the copper rod prepared in S2 as raw material, again using a continuous extrusion unit, the product outlet temperature is 350-400°C, the mold is preheated at a temperature of 400-500°C, preheated for 2 hours, the extrusion blank preheating temperature is 740-760°C, and the copper bars are produced; S4: Rapid cooling: The obtained billet is rapidly cooled at the outlet of the extrusion die by spraying liquid nitrogen. The nozzle spacing is 50-60 mm, and the distance between the nozzle and the billet surface is 10-20 mm. The billet is rapidly cooled from high temperature to room temperature to refine the grains. S5: Drawing, straightening and machining the copper busbar obtained in S4.

2. A continuous extrusion process for obtaining ultrafine-grained copper bars according to claim 1, characterized in that: The temperatures of the smelting furnace and the holding furnace are both 1150° C., wherein the smelting furnace is covered with charcoal with a thickness of 150-160 mm, and the holding furnace is covered with graphite flakes with a thickness of 100-120 mm.

3. The continuous extrusion process for obtaining ultrafine-grained copper bars according to claim 1, characterized in that: When the copper bar is prepared by continuous extrusion, the copper bar introduction speed through the continuous extrusion unit is 2.2-2.7 m / min, the lead-out speed is 0.23-0.28 m / min, and the extrusion ratio is 2-4.

4. A continuous extrusion process for obtaining ultrafine-grained copper bars according to claim 3, characterized in that: The channel length of the continuous extruder cavity is set to 80-100 mm.

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