What are the requirements for metal copper strip processing?
The processing requirements of metallic copper strip involve many aspects, such as material selection, processing technology, dimensional accuracy, surface quality, performance index, etc. The specific requirements will vary according to the uses of copper strip (such as electronics, electricity, machinery, aerospace, etc.) and standards (such as national standard GB and international standard ISO, etc.). The following is a detailed introduction:
A, material selection requirements
Grade and composition of copper alloy
Choose the appropriate copper alloy type according to the purpose, which usually includes:
Pure copper (red copper): such as T1 and T2, with high purity (≥99.9%) and excellent electrical and thermal conductivity, used for conductive parts.
Brass: Copper-zinc alloy (such as H62 and H65), with high strength and good corrosion resistance, is used for structural parts and shrapnel.
Bronze: copper-tin alloy (such as QSn6.5-0.1), aluminum bronze (such as QAl9-4), etc., with outstanding wear resistance and corrosion resistance, used for bearings, springs, etc.
White copper: Copper-nickel alloy (such as B10 and B30), resistant to seawater corrosion, used in marine engineering and precision instruments.
Composition control: strictly follow the standards, and the content of impurities (such as Fe, Pb, S, etc.) should be lower than the specified value to avoid affecting the processing performance and finished product quality.
Raw material state
Usually, hot-rolled coils or ingots are used as raw materials, and it is necessary to ensure that there are no defects such as cracks, scales and inclusions on the surface and the internal structure is uniform.
Second, the processing technology requirements
Copper strip processing mainly includes rolling, annealing, surface treatment, finishing and other processes, and the requirements of each link are as follows:
1. Rolling process
Rolling mode:
Cold rolling: It is used to produce high-precision and high-surface quality copper strip, and the thickness tolerance is strictly controlled (such as ±0.005mm), which needs to be rolled and annealed alternately for many times.
Hot rolling: used for preliminary forming, reducing thickness and improving processing rate, but the surface accuracy is low, so it needs to be corrected by subsequent cold rolling.
Rolling accuracy:
Thickness uniformity: longitudinal thickness deviation ≤ 1%, transverse thickness deviation (such as middle crown) ≤ 0.5%.
Shape control: avoid waves, edge wrinkles or intermediate buckling, and realize it by adjusting roll crown and rolling force.
Rolling speed and lubrication:
High-speed rolling needs high-efficiency lubrication (such as rolling oil) to reduce friction heat and prevent surface scratch or adhesion.
2. Annealing process
Objective: To eliminate work hardening, restore plasticity and adjust grain structure.
Annealing type:
Intermediate annealing: annealing several times during cold rolling to reduce hardness and facilitate subsequent processing.
Annealing of finished products: final heat treatment to control hardness (such as soft state, semi-hard state and hard state) and mechanical properties.
Process parameters:
Temperature: the annealing temperature of pure copper is about 500-700℃, and the alloy copper needs to be adjusted according to its composition (for example, brass is about 600-750℃).
Holding time: determined according to the strip thickness and furnace type to ensure uniform annealing.
Cooling mode: generally cooling with furnace (soft state after annealing) or air cooling (semi-hard state).
3. Surface treatment
Cleaning: remove rolling oil, oxides and impurities, and usually use alkali cleaning, acid cleaning (such as dilute sulfuric acid) or electrolytic cleaning.
Anti-oxidation: clean and dry, and can be coated with anti-rust oil or passivated (such as chromate passivation, which should meet the requirements of environmental protection).
Coating treatment: nickel plating, tin plating, silver plating, etc. as required to improve conductivity or corrosion resistance.
4. Finishing process
Cutting and slitting:
Width accuracy: deviation ≤±0.1mm (high-precision strip ≤±0.05mm), with neat edges and no burrs.
Length accuracy: cut-to-length shear deviation ≤ 1 mm.
Straightening: eliminate the wave shape or sickle bend of the strip, and the flatness is ≤ 1-2mm/m..
Coiling: the winding diameter is uniform, the tension control is stable, and the loose winding or tower shape is avoided.
Third, the dimensional accuracy requirements
thickness deviation
Conventional accuracy: if the thickness is less than or equal to ≤0.5mm, the tolerance is ±0.01mm；; When the thickness is 0.5-3mm, the tolerance is ±0.02mm.
High precision (such as electronic grade copper strip): thickness tolerance 0.003-0.005 mm.
Width tolerance
When the conventional width is ≤300mm, the tolerance is ±0.1mm；; When the width is greater than ＞300mm, the tolerance is ±0.2mm.
inequality
Soft strip ≤3mm/m, hard strip ≤ 5 mm/m.
Fourth, the surface quality requirements
Prohibited defects:
There shall be no cracks, holes, folds, serious scratches, oxidation color, oil stains, etc. on the surface.
Slight scratches and roll marks are allowed, but the depth/height shall be less than or equal to half of the thickness tolerance.
roughness
General purpose: surface roughness ra ≤ 1.6 μ m; Precision electronic applications (such as FPC substrate): Ra ≤ 0.8 μ m..
Five, the performance index requirements
mechanical property
Tensile strength, yield strength and elongation shall meet the standards (such as GB/T 2059-2017 Copper and Copper Alloy Strip).
Example: The tensile strength of H62 brass strip (semi-hard state) is ≥345MPa, and the elongation is ≥15%.
Electrical/thermal conductivity
The conductivity of pure copper strip is ≥100% IACS (international annealed copper standard), and the alloy copper decreases according to the composition (for example, brass is about 20-40% IACS).
corrosion resistance
When used in wet or corrosive environment, it is necessary to pass the salt spray test (such as no corrosion for 24 hours) or intergranular corrosion test.
technological properties
Formability: If cracking is not allowed during stamping and bending, it should be evaluated by Erichsen test.
Weldability: the electronic copper strip should meet the requirements of brazing or resistance welding, and the surface should be clean and free of oxide film.
Six, environmental protection and safety requirements
Restriction of harmful substances
Comply with environmental protection standards such as RoHS and REACH, and limit the content of heavy metals such as lead (Pb) and cadmium (Cd) (such as Pb≤0.01%).
Processing environment
Rolling oil and cleaning liquid need to be recycled to avoid pollution; Annealing furnace waste gas needs to be purified and then discharged.
safe operation
It is necessary to prevent scalding when rolling or annealing at high temperature, and the rolling equipment should be equipped with protective devices to avoid the risk of being involved in coiling.
VII. Inspection and Standards
Test item
Size measurement (micrometer, laser thickness gauge), surface visual inspection, mechanical property test (tensile testing machine), composition analysis (spectrometer).
executive standard
Domestic: GB/T 2059 (copper and copper alloy strip), GB/T 1527 (copper and copper alloy drawn tube), etc.
International: ISO 4370 (copper and copper alloy strip), ASTM B152 (American pure copper strip standard), etc.
summary
The processing of metal copper strip needs to comprehensively consider the factors such as use, performance, accuracy and cost, and ensure that the products meet the customer's needs by strictly controlling the materials, process parameters and testing procedures. Different industries (such as new energy batteries, 5G communication) have increasingly strict requirements for copper strip, and the future processing trend will be ultra-thin (such as ≤0.01mm), high precision, low roughness and environmental protection.
