This invention relates to a method for preparing high-performance copper/titanium bimetallic capillary tubes, belonging to the field of bimetallic capillary material preparation technology. The invention employs a hot-spinning method to prepare metallurgically bonded copper/titanium composite tubes with dimensions of Φ (7.0～15.0) mm × (0.5～2.0) mm. After pickling the inner and outer surfaces, the tubes undergo direct multi-pass drawing, combined with intermediate annealing, to obtain copper/titanium bimetallic capillary tubes with dimensions of Φ (0.5～6.1) mm × (0.1～0.8) mm. This invention uses hot-spinning to prepare small-sized copper/titanium composite tubes, followed by direct drawing, resulting in simple processes and equipment, long die life, and low production costs. The combination of floating mandrel drawing and air drawing, along with necessary intermediate annealing, further facilitates the deformation processing of the copper and titanium layers, resulting in composite capillary tubes with high dimensional accuracy and good surface quality.
Copper and copper alloy capillary tubes are a type of tubing with a relatively small diameter and thin wall thickness, ranging from Φ (0.5～6.1) mm × (0.1～0.8) mm (outer diameter × wall thickness, the same below). They are important raw materials widely used in central air conditioning, modern household appliances, instruments, and meters. Their characteristics include high processing difficulty and high added value. With the rapid development of my country's equipment manufacturing, home appliance, and marine industries, the market demand for copper and copper alloy capillary tubes is increasing. However, in highly corrosive seawater environments such as ships, desalination plants, and coastal power plants, the service life of copper and copper alloy capillary tubes is shortened due to seawater corrosion, reducing the reliability of instruments. Pure titanium capillary tubes have extremely excellent corrosion resistance, but titanium has low thermal conductivity, thick-walled capillary tubes have poor heat exchange performance, and the mechanical properties of thin-walled capillary tubes are difficult to meet the application requirements. Copper/titanium bimetallic capillary tubes are a new type of composite capillary tube made by coating the inner wall of a copper tube with a layer of titanium. Combining the advantages of titanium (low density, high specific strength, and excellent corrosion resistance) with the excellent thermal conductivity of copper, copper/titanium composite capillary tubes possess excellent overall performance. Therefore, copper/titanium bimetallic capillary tubes have broad application prospects in shipbuilding equipment, marine industry, large-scale refrigeration systems, home appliance industry, and instrumentation, and are of great significance for improving the safety and reliability of ship equipment and industrial machinery.
Currently, the main methods for preparing copper/titanium composite tubes include: drawing composite, hydraulic bulging composite, and explosive welding. Cold working composite methods such as drawing (see: Yu Jiazheng, Metal Composite Pipe and its Manufacturing Method and Pipe Connection Structure, Chinese Invention Patent, CN1186921A, 1998-07-08) and hydraulic bulging (see: Wang Xuesheng, Li Peining, Manufacturing Technology of Hydraulically Expanded Seamed Stainless Steel Pipe Lined Composite Pipe, Pressure Vessel, 2001, 18(4): 50-52) typically achieve composite by a small amount of plastic deformation of the base material or the base and cladding materials to obtain an interference fit. The resulting composite pipes have low interfacial bonding strength, poor coordination of deformation between the two metal layers, and are difficult to manufacture into capillary tubes. Explosive welding relies on the large pressure generated by explosive explosions to achieve solid-state welding of two metals at the interface, resulting in high interfacial bonding strength. However, it is highly dangerous to operate, has low production efficiency, and uneven titanium layer thickness, making it difficult to guarantee the required titanium layer thickness after manufacturing capillary tubes.
To address the problems existing in the above-mentioned processes, the purpose of this invention is to provide a method for preparing copper/titanium bimetallic capillaries using a combination of hot spinning (high-temperature rotary forging, hereinafter referred to as "hot spinning") and drawing. This method utilizes the triaxial compressive stress deformation generated during rotary forging to achieve multiple deformation passes, while simultaneously achieving metallurgical bonding of the composite tube under high temperature. Subsequently, a floating mandrel drawing and/or air drawing process is used, combined with intermediate annealing, to obtain a high-performance copper/titanium bimetallic capillary.
To achieve the above objective, the technical solution of this invention is as follows: A metallurgically bonded copper/titanium composite tube with dimensions of Φ (7.0～15.0) mm × (0.5～2.0) mm is prepared using the hot spinning method. After pickling of the inner and outer surfaces, it is directly subjected to multiple drawing passes, combined with intermediate annealing, to obtain a copper/titanium bimetallic capillary with dimensions of Φ (0.5～6.1) mm × (0.1～0.8) mm. The multi-pass drawing process can employ direct drawing or disc drawing, including moving mandrel drawing and/or air drawing; the cross-sectional area reduction rate per drawing pass is between 10% and 40%; when the cumulative cross-sectional area reduction rate reaches approximately 70%, an intermediate annealing is required; the intermediate annealing process involves an annealing temperature of 500℃ and an annealing time of 1 hour; lubrication is applied during the drawing process, and mineral oil or vegetable oil can be used as the lubricant; the drawing speed is 1–20 mm/min.
It has the following advantages:
1. Small-sized copper/titanium composite tubes are prepared by hot spinning, followed by direct drawing, resulting in simple processes and equipment, long die life, and low production costs.
2. The copper/titanium composite tubes prepared by hot spinning have a metallurgical bond at the interface and lack brittle intermetallic compounds, which is beneficial for the coordinated deformation of the two metal layers during the drawing process, resulting in copper/titanium bimetallic capillaries with high interfacial bonding strength.
3. The combination of floating core drawing and air drawing, along with necessary intermediate annealing, is more conducive to the deformation processing of copper and titanium layers, resulting in composite capillaries with high dimensional accuracy and good surface quality.
