Copper Alloy Pipe Production: From Extrusion to Finishing

Manufacturing Process for Copper Alloy Tubes (C44300, C61400, C68700, C70600, C71500) via Extrusion & Cold Drawing

Copper alloy tubes are widely used in marine, heat exchanger, automotive, and industrial applications due to their corrosion resistance, strength, and thermal conductivity. The extrusion and cold drawing process varies slightly depending on the alloy composition. Below is a detailed breakdown for each major alloy group.

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1. Raw Material Preparation

Alloy Types & Key Properties

Alloy	Composition	Key Properties	Common Applications
C44300	Cu-Zn-Sn (Admiralty Brass)	Excellent corrosion resistance	Condensers, heat exchangers
C61400	Cu-Al (Aluminum Bronze)	High strength, wear resistance	Marine hardware, pumps
C68700	Cu-Zn-As (Arsenical Brass)	Biofouling resistance	Heat exchangers, seawater
C70600	Cu-Ni 90/10	Seawater corrosion resistance	Desalination, ship piping
C71500	Cu-Ni 70/30	Superior strength, thermal stability	Offshore oil & gas

Billet Preparation

- Casting: Billets are cast via continuous casting or direct chill casting to ensure homogeneity.

- Heating:

- Brass (C44300, C68700): 650–750°C

- Aluminum Bronze (C61400): 750–850°C

- Cu-Ni Alloys (C70600, C71500): 800–950°C

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2. Hot Extrusion Process

Key Steps

1. Billet Lubrication:

- Graphite or glass lubricant for high-Ni alloys (C70600, C71500).

- Oil-based for brass (C44300, C68700).

2. Extrusion Press Setup:

- Die & Mandrel: Tungsten carbide or H13 tool steel.

- Extrusion Ratio:

- Brass (C44300, C68700): 10:1 to 20:1

- Aluminum Bronze (C61400): 8:1 to 15:1 (higher pressure needed)

- Cu-Ni (C70600, C71500): 12:1 to 25:1

3. Extruded Tube Output:

- Rough dimensions (OD: +10–20%, wall: +15–30% oversize).

- Surface may have oxide scale (removed in next step).

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3. Descaling & Cleaning

- Pickling:

- Brass (C44300, C68700): Dilute sulfuric acid (H₂SO₄).

- Aluminum Bronze (C61400): HNO₃ + HF (caution: aggressive).

- Cu-Ni (C70600, C71500): HNO₃ or H₂SO₄ + inhibitor.

- Mechanical Descaling: For tough oxides (e.g., C61400), abrasive blasting may be used.

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4. Cold Drawing Process

General Steps (All Alloys)

1. Pointing: One end is tapered for drawing.

2. Lubrication:

- Brass: Soap or oil-based.

- Aluminum Bronze/Cu-Ni: Phosphate coating + soap.

3. Drawing Setup:

- Dies: Tungsten carbide or PCD (polycrystalline diamond).

- Mandrels: Fixed (for precision) or floating (for long tubes).

4. Reduction per Pass:

- Brass (C44300, C68700): 25–35% area reduction.

- Al Bronze (C61400): 15–25% (higher strength).

- Cu-Ni (C70600, C71500): 20–30%.

5. Intermediate Annealing:

- Brass: Every 2–3 draws (400–600°C).

- Al Bronze: Every 1–2 draws (650–750°C).

- Cu-Ni: Every 1–2 draws (700–850°C).

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5. Final Heat Treatment & Finishing

Annealing (Recrystallization)

Alloy	Annealing Temp (°C)	Atmosphere	Purpose
C44300	400–550	Air or Nitrogen	Soften for bending
C61400	650–750	Nitrogen/Hydrogen	Stress relief, prevent oxidation
C68700	450–600	Air	Restore ductility
C70600	700–800	Hydrogen/Nitrogen	Prevent Ni oxidation
C71500	750–850	Hydrogen/Nitrogen	Optimize grain structure

Final Processing

- Straightening: Roller or stretch straightening.

- Cutting: Sawing or rotary cutting to length.

- Surface Treatment:

- Polishing (for heat exchangers).

- Passivation (HNO₃for Cu-Ni alloys).

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6. Quality Control & Testing

- Dimensional Checks: Laser micrometers, ultrasonic wall thickness gauges.

- Mechanical Testing:

- Tensile strength (ASTM B111, B584).

- Hardness (Rockwell B or Vickers).

- Corrosion Testing:

- Salt spray (ASTM B117) for marine alloys (C70600, C71500).

- Mercury nitrate test (ASTM B154) for C44300 (Admiralty Brass).

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Comparison of Key Alloy Processing Differences

Parameter	C44300 (Brass)	C61400 (Al Bronze)	C68700 (Arsenical Brass)	C70600 (Cu-Ni 90/10)	C71500 (Cu-Ni 70/30)
Extrusion Temp	650–750°C	750–850°C	650–750°C	800–900°C	850–950°C
Cold Draw Passes	3–5	4–6	3–5	5–8	6–10
Annealing Freq.	Every 2–3	Every 1–2	Every 2–3	Every 1–2	Every 1
Final Strength	300–400 MPa	500–700 MPa	350–450 MPa	300–400 MPa	400–550 MPa

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Final Notes

- Cu-Ni Alloys (C70600, C71500): Require tighter process control due to work hardening.

- Al Bronze (C61400): Needs higher extrusion forces and careful annealing.

- Brass (C44300, C68700): Easier to process but sensitive to dezincification (C44300 requires inhibitors).

Would you like details on alternative methods (e.g., continuous casting + pilgering) for specific alloys?