What should be paid attention to in the process of processing different types of copper wires?
Different types of copper wires are different in material (pure copper, brass, bronze, white copper, etc.), alloy composition, diameter and performance requirements (such as conductivity, wear resistance and elasticity), so it is necessary to adjust the process parameters and operation points in processing. The following are the precautions for processing all kinds of common copper wires:
A, pure copper wire (such as T2, TU1, T3)
Features: purity ≥99.9%, excellent electrical and thermal conductivity, good ductility, low hardness and easy oxidation.
Matters needing attention in processing
Stretching process
Die selection: use diamond or cemented carbide die (surface roughness Ra≤0.2μm) to avoid surface scratch caused by die sticking.
Lubrication requirements: Soap liquid or synthetic oil (such as PEG lubricant) shall be used, and the drawing speed shall be ≤5m/s to prevent annealing softening caused by heat generated by friction.
Annealing treatment: bright annealing (temperature 300-400℃, nitrogen protection) is carried out every 3-5 passes to prevent oxidation and restore plasticity.
surface treatment
Avoid using sulfur-containing cleaning agents (such as sulfide) to prevent copper sulfide (Cu₂S) black spots, and give priority to ultrasonic cleaning with deionized water.
Long-term storage needs to be coated with acid-free vaseline or antirust oil and wrapped with moisture-proof paper to prevent the formation of "verdigris" (basic copper carbonate).
High precision requirement
Ultra-fine copper wire (≤0.05mm) should be processed in a constant temperature and humidity workshop (temperature 20 2℃, humidity 45%-55%) to reduce electrostatic dust adsorption.
Second, brass wire (such as H62, H65, H80)
Features: Copper-zinc alloy, containing 5%-40% zinc, with high strength and easy cutting, but easy to produce stress corrosion (quarter crack).
Matters needing attention in processing
stress control
Stress relief annealing (temperature 200-250℃, heat preservation for 1 hour) is required for every 2-3 passes of stretching during processing, so as to avoid cracking during bending caused by residual stress.
Avoid contact with ammonia (such as ammonia in coolant) and prevent zinc corrosion. Mineral oil or semi-synthetic cutting fluid can be used.
Mould and equipment
The drawing die should be cleaned regularly (soaked in 10% hydrochloric acid solution for 10 minutes) to prevent zinc from adhering to the die and affecting the dimensional accuracy.
When stamping, the die gap should be 10%-15% larger than that of pure copper (for example, the gap of 0.5mm brass wire is 0.05-0.06mm), so as to reduce the punching force and prevent die wear.
surface treatment
Before nickel plating or chromium plating, cyanide pre-copper plating (thickness 2-3μm) is needed to enhance the bonding force of the coating and avoid the preferential dissolution of zinc in brass to cause foaming.
Three, bronze wire (such as QSn6.5-0.1, QAl9-4)
Features: Containing tin, aluminum, lead and other elements, it has good wear resistance and elasticity, but its plasticity is low and it is difficult to process.
Matters needing attention in processing
Temperature control
Preheat the blank (150-200℃) before drawing to improve plasticity and reduce tensile force (for example, the tensile force of QSn6.5-0.1 is 20%-30% higher than that of pure copper).
Monitor the mold temperature during machining. If it exceeds 60℃, stop cooling (cooling by circulating water) to prevent tin segregation from affecting performance.
mold design
Large-angle drawing die (entrance angle is 12-15, and the length of sizing belt is 2-3mm) is adopted to reduce the scratch on the wire surface and the tensile stress.
When bending, the bending radius should be ≥3 times the line diameter (for example, the bending radius of 1mm line diameter should be ≥3mm) to avoid internal cracking.
anticorrosion treatment
After machining, it is necessary to clean the cutting fluid residue with ethanol immediately to prevent the oxidation of aluminum and tin components, and subsequent passivation treatment (such as chromate passivation) can be carried out.
Four, white copper wire (such as B10, B30, BMn40-1.5)
Features: Copper-nickel alloy, excellent corrosion resistance and heat resistance, high resistance and obvious work hardening tendency.
Matters needing attention in processing
Annealing process
The intermediate annealing temperature should be increased to 600-700℃ (air or vacuum furnace), and the holding time should be extended to 2-3 hours to fully eliminate work hardening (for example, the hardness of B30 white copper can be reduced from HV200 to HV120 after annealing).
After annealing, it needs to be cooled quickly (such as water cooling) to prevent the uneven composition caused by the diffusion of nickel.
surface treatment
Before silver plating or gold plating, electrolytic polishing (electrolyte: 50% nitric acid+30% sulfuric acid+20% water, voltage 8-12V, time 30-60 seconds) is needed to remove the oxide film and improve the surface smoothness.
Avoid using cleaning agents containing chloride ions (such as NaCl solution) to prevent pitting corrosion.
High precision resistance wire machining
Constant tension control (error 1%) is adopted during stretching to ensure the uniformity of resistivity (for example, the resistivity fluctuation of BMn40-1.5 resistance wire is ≤ 0.01μ ω m).
Five, special function copper wire (such as phosphor copper, tin-plated copper, enamelled copper)
1. Phosphor copper wire (such as C5210 and C5191)
Key points: It contains 0.03%-0.3% phosphorus and has high elastic limit. It is used for springs.
Note: after stretching, aging treatment (120-150℃, heat preservation for 2-4 hours) is needed to improve elasticity; Avoid contact with acidic substances to prevent phosphorus oxidation.
2. Tin-plated copper wire (such as TS and TXRH)
Key points: the thickness of tin plating layer is 1-5μm, which improves the weldability.
Note: Before tin plating, it needs activation treatment (immersion in 1% sulfuric acid solution for 30 seconds), and the coating should be uniform to avoid oxidation caused by missing plating; Storage temperature ≤30℃ and humidity ≤60% to prevent the growth of tin whiskers.
3. Enamelled copper wire (such as QZ and QA)
Key points: the thickness of insulating paint layer is 0.01-0.1mm, which is used for motor winding.
Note: Before painting, the surface roughness of copper wire should be controlled within Ra≤0.4μm, and the baking temperature should be accurately controlled according to the paint type (for example, 200-220℃ in polyester paint and 180-200℃ in polyurethane paint) to avoid bubbles or cracks in the paint layer.
Six, general processing matters needing attention
1. Diameter and tolerance control
Fine copper wire (≤0.1mm): Multi-mode continuous drawing machine (for example, more than 20 dies) is adopted, and the reduction rate of each pass is ≤15%, which is matched with online laser caliper (accuracy ±0.001mm).
Thick copper wire (> ＞2mm): peeling treatment (mechanical or electrolytic) is required before drawing to remove the oxide scale to avoid breaking during drawing.
2. Environment and safety
When brass and bronze are processed, zinc smoke and tin smoke may be generated, so it is necessary to equip with local exhaust system, and the operators should wear dust masks (such as N95).
The cyanide electroplating process should strictly follow the safety regulations, set up an independent operation room and be equipped with emergency washing equipment.
3. Quality inspection
Material verification: X-ray fluorescence spectrometer (XRF) is used to quickly detect alloy components to prevent mixing.
Performance test:
Elastic copper wire: use a spring testing machine to detect the attenuation of elasticity (e.g. the elasticity decreases by ≤ 5% after 100,000 cycles);
Conductive copper wire: The resistivity of pure copper shall be ≤ 0.01724 μ Ω m (20℃) when measured by four-probe method.
Summary: Model-Process Matching Table
The key processing points of typical uses of copper wire models are easy to make mistakes
T2 pure copper wire cables and electronic leads are highly lubricated, and the tensile speed of oxidation annealing is too fast to cause wire breakage.
H65 brass wire screws and connectors are stress-relieved, annealed, and protected from ammonia corrosion. Cracking is caused by direct bending without annealing.
QSn6.5-0.1 Tin bronze precision spring preheating and stretching, mold temperature control, too high mold temperature leads to tin segregation.
B30 High-temperature Annealing and Chloride Ion Corrosion Prevention Cleaning Agent for White Copper Wire Seawater Equipment Parts Causing Pitting Corrosion
Aging treatment of C5210 phosphor copper wire electronic spring to avoid insufficient elasticity caused by aging in acidic environment.
Through the above targeted measures, the processing quality of different types of copper wires can be effectively controlled to ensure that their key properties such as conductivity, elasticity and corrosion resistance meet the design requirements.
