The tantalum tubes are made from pure tantalum or tantalum alloys (such as Ta-2.5W, Ta-10W). Due to the excellent corrosion resistance (resistance to hydrochloric acid, sulfuric acid, aqua regia, and strong alkalis at high temperatures), plasticity, and high-temperature stability of tantalum, they are the core heat exchange / fluid transportation components in extreme conditions of fields such as chemical engineering, semiconductors, wet metallurgy, and power. The core difficulty in their manufacturing lies in the high reactivity of tantalum (easily oxidized, hydrogen and nitrogen absorption), large cold working deformation, strict welding requirements, and the need to strictly control environmental and process parameters throughout the process.
Sintering and forging: The tantalum ingot is melted in a cold bed furnace by an electron beam, and then undergoes high-temperature forging (1200 - 1400℃, protected by argon gas) to cut off the billet, resulting in solid rods, which eliminate the porosity and segregation in the cast state. Extrusion into rough tubes: After drilling the rods, they are hot extruded in a vacuum / argon gas protected extrusion machine (1000 - 1200℃) to form rough tubes with a large diameter, achieving the initial shaping of the tube body. Multiple passes of cold rolling / cold drawing: The rough tubes undergo multiple passes of cold rolling (two-roll / multi-roll cold rolling machines) or cold drawing (fixed mold / movable mold drawing), gradually reducing the wall thickness and reducing the diameter. The deformation amount per pass is controlled within 15% - 25% (to avoid excessive processing hardening and cracking). Intermediate vacuum annealing: After 2 - 3 passes of cold processing, perform vacuum annealing (temperature 800 - 1000℃, vacuum degree ≥ 1×10⁻³Pa, holding for 1 - 2 hours), eliminating processing stress, restoring plasticity, and preventing subsequent bending cracking. Finishing and initial inspection: Straighten the billet tubes (roller straightening machine, straightness ≤ 0.5mm/m), cut the head and tail, polish the inner and outer surfaces, and then conduct ultrasonic testing (UT) to check for internal defects, penetrant testing (PT) to check for surface micro-cracks. If qualified, enter the coil forming process.
The room-temperature plasticity of tantalum is excellent (elongation ≥ 30%). More than 90% of tantalum tubes are formed by cold bending (no heating required, avoiding oxidation); only large-diameter (Φ ≥ 50mm), thick-walled (wall thickness ≥ 3mm) or high-strength tantalum alloy tubes are bent at low temperatures (200 - 300℃, protected by inert gas). The key lies in controlling the three major issues of tube flattening, rebound and cracking.
Cold bending forming (main process, high precision, high efficiency) for small diameter pipes (Φ ≤ 20mm, closely arranged heat exchange pipes): CNC pipe bending machine (three-roll / four-roll rolling, capable of precisely controlling the diameter, pitch, and number of loops); medium and large-sized pipes (Φ 20 - 50mm, long-distance transportation pipes): CNC mandrel-type bending machine (with flexible mandrel / ball mandrel, preventing thin-walled pipes from flattening).
Special bending tooling for non-standard pipe coils (tool + hydraulic drive, suitable for irregular pipe diameters and variable pitch). Key process parameters: minimum bending radius for pure tantalum tubes R ≥ 3D (D is the outer diameter of the pipe), for tantalum alloy tubes R ≥ 4D (smaller R is prone to flattening and cracking); rebound control: tantalum has a low elastic modulus (186 GPa), the cold bending rebound angle is approximately 3° to 8°, a pre-added rebound compensation angle (adjusted according to pipe diameter, wall thickness, and bending diameter) is required; post-forming correction after shaping; anti-flattening measures (thin-walled pipe core): insert a flexible core rod (nylon/rubber core rod, adapted to the bending arc) or a ball core rod (multiple ball sections, rotates with the bending pipe); fill the pipe with dry high-purity quartz sand or low-melting-point alloy (remove after bending / melt and remove), the filling must be dense to avoid local collapse; control the bending pipe speed (≤ 5mm/s), bend at a constant speed, avoid impact deformation.
Pre-treatment of the blank pipe: Wipe the inner and outer surfaces with alcohol to remove oil stains and dust (to prevent surface scratches during bending or carbonization pollution at high temperatures);
Workpiece positioning: Fix the blank pipe on the bending machine / coil machine, set the circle diameter according to the drawing (such as Φ200, Φ500), pitch (such as 20mm, 50mm), and continuously bend the total length: Start the equipment, uniformly roll / bend, and monitor the roundness of the pipe body in real time (flattening rate ≤ 5%, that is, the short axis / long axis ≥ 0.95); After the initial shaping and bending are completed, use special molds to correct the circle diameter and pitch, and eliminate local springback.
