The raw material is C10200 oxygen-free copper billet. Upon arrival, strict incoming inspection is carried out. We use a spectrometer to test chemical composition to verify compliance with C10200 standard, ensuring extremely low oxygen content and high conductivity. Mechanical performance tests including tensile strength, elongation and hardness are conducted. Visual inspection checks the billet surface for cracks, inclusions, pores and oxidation layers. Dimensions, roundness and internal defects are examined by ultrasonic detection. Non-conforming billets will be marked, isolated and returned to the supplier to avoid mixing into production.
2.Hot Extrusion & Piercing:
Qualified copper billets are heated uniformly to the specified extrusion temperature in a heating furnace. The heated billet is sent to the extrusion press with piercing mandrel to form initial seamless copper tube shell. The extrusion speed and pressure are precisely controlled to guarantee uniform wall thickness and compact internal structure. After extrusion, the tube shell is air-cooled and straightened to eliminate obvious bending deformation.
3.Multi-pass Cold Drawing:
The extruded copper shell goes through repeated cold drawing on precision drawing machines with progressive-size diamond dies and internal mandrels. Each drawing pass reduces outer diameter and wall thickness gradually to approach capillary size. Lubricant is continuously supplied during drawing to reduce die wear and prevent surface scratching. Intermediate cleaning is arranged between drawing passes to remove residual drawing oil and copper chips.
4.Bright Annealing Heat Treatment:
After reaching the preliminary capillary dimension, the copper tubes are loaded into a closed bright annealing furnace filled with protective nitrogen-hydrogen mixed atmosphere. Controlled heating and slow cooling are performed to recrystallize the copper grain, eliminate cold working hardening and residual stress, restore ductility for coiling, while keeping the surface bright without oxidation and discoloration.
5.Precision Sizing, Coiling & End Protection:
Annealed capillary tubes go through final sizing drawing to strictly stabilize outer diameter, inner diameter and wall thickness within tolerance. The qualified straight capillary is continuously wound into standard coil size on automatic coiling machine, control coiling tension evenly to avoid flattening or kinking of thin-wall tube. Plastic end caps are installed on both tube ends to block dust, moisture and foreign particles from entering the inner bore.
6.Final Inspection, Cleaning & Packaging:
100% sampling inspection is implemented: dimensional measurement, wall thickness test, air tightness pressure test, surface inspection for scratches, pits and cracks. The coils are cleaned to remove residual lubricant and dried thoroughly. Each coil is wrapped with stretch film for protection, packed into cartons with moisture-proof material. Labels with material grade C10200, size, coil weight, batch number and inspection record are attached before shipment.