Copper strip peeling refers to the separation, lifting or falling off of a thin surface metal layer from the substrate. It falls into three categories: inherent peeling of cast slabs from smelting & casting (large-area long strip peeling), secondary peeling generated in rolling processes (spotty, fine peeling), and peeling after stamping forming. Below is a full breakdown of causes, improvement solutions and on-site emergency treatment.

I. Smelting & Casting Process (Root Cause, Mainly Large-area Long Strip Peeling)

Core Causes

1. Insufficient deoxidation of molten copper leading to brittle oxide inclusionsThe molten copper absorbs oxygen and generates brittle cuprite (Cu₂O), which distributes along grain boundaries in a mesh structure. During rolling deformation, the brittle layer directly separates and peels off. This defect occurs frequently in brass and copper-iron alloys.

2. Melt inclusions, furnace slag and foreign contaminantsIncomplete slag skimming during smelting, peeling lining refractory slag, oil stains or sediment carried by recycled scrap. The contaminants have vastly different ductility from the copper substrate, causing interface cracking and peeling during rolling elongation. Black slag layers can be seen in the interlayer of peeled areas.

3. Internal pores, looseness and subcutaneous bubbles in cast slabsHydrogen dissolved in molten copper and excessive cooling speed create subcutaneous pores on the slab surface. After rolling compression, the pores stretch, and the surface metal loses support from the base material, forming continuous long-strip peeling.

4. Cold shuts and overlaps on the surface of horizontal continuous cast slabsUneven cooling of the crystallizer and fluctuating casting speed cause overlapping metal cold shuts on the slab surface. These defects cannot be fully welded during hot rolling, resulting in peeling after cold rolling.

Solutions for Smelting & Casting

1. Strengthen deoxidation and oxygen removalAdd phosphor copper for deoxidation of pure copper; melt brass rapidly to reduce oxygen absorption, and cover the molten metal surface with charcoal or graphite powder to isolate air. Argon shielding melting can be adopted for copper-iron alloys to strictly control oxygen content.

2. Purify molten copper through thorough slag removalAdd refining agent and stir fully, then let the molten metal stand for 10–20 minutes for slag floating. Double slag skimming is required before pouring. Regularly clean the melting furnace and replace aged furnace linings to reduce aluminum dissolution into molten copper.

3. Eliminate slab pore defectsDry raw copper rods and scrap materials to remove water vapor; stabilize pouring temperature and casting speed, and ensure uniform cooling of the crystallizer. Conduct full inspection of off-line cast slabs and cut off head and tail sections with bubbles.

4. Eliminate cold shuts and overlaps on slab surfacesGrind graphite crystallizer molds regularly to maintain smooth inner cavities; stabilize traction speed and avoid frequent startup and shutdown. Rough mill the slab surface before rolling to remove the subcutaneous defective layer.

II. Hot Rolling & Cold Rolling Processes (Spotty, Fine Peeling, Accounting for 60% of On-site Failures)

Core Causes

1. Scale and oil residues pressed into the surface from previous processesHot rolling scale incompletely removed by pickling, thick oxide layers generated during intermediate annealing, and rolling oil residues on strip surfaces. Oxides are pressed into the copper strip surface during rolling; the oxides fall off in subsequent rolling or stamping, creating pits accompanied by peeling.

2. Excessive reduction per rolling passExcessive reduction rate in a single pass leads to excessive local stress on the metal surface, tearing the surface metal and causing peeling. This issue is more prominent for thin copper strips (thickness below 0.2 mm).

3. Damaged work rolls and foreign object indentationsCracks, pits or chrome peeling on roll surfaces; failed multi-stage filtration of rolling oil allows metal debris and dust to enter the roll gap, pressing indentations on the surface, which expand into peeling during subsequent stretching.

4. Deep scratches and abrasions on strip surfacesBurrs on roller tables and guides, friction between coiled layers caused by uneven tension. Stress concentrates at the bottom of deep scratches, and metal at scratch edges lifts and peels during processing.

Improvement Measures for Rolling

1. Complete pickling and surface grinding pretreatmentFully pickle hot rolling blanks to remove scale; add a brush grinding process (400–800 mesh grinding rolls) after annealing to eliminate surface oxide films. Control the concentration of cleaning liquid and ensure complete water washing and drying without water residue.

2. Optimize rolling reduction parametersReduce reduction per pass and adopt multi-pass small-deformation rolling; reserve a temper pass before finished products to release internal stress. Lower rolling speed for thin strips to reduce surface friction stress.

3. Maintain roll systems and rolling oilPolish and repair work rolls regularly; replace rolls immediately if surface damage is detected. Equip rolling oil with multi-stage filters and replace oil periodically with filtration accuracy controlled within 5 μm. Clear burrs on guide rolls and guide plates.

4. Adjust tension to reduce surface abrasionMatch tension of uncoiling, rolling and recoiling to avoid layer shifting and friction. Install wear-resistant plastic liners on guide paths to separate copper strips from hard metal surfaces.

III. Peeling Caused by Alloy Material & Stamping Forming (Peeling Occurs After Customer Stamping)

Causes

1. Brittle second-phase alloy particlesBrittle iron-rich particles inside copper-iron and phosphor copper alloys fall off during stamping stretching and form spot peeling. Zinc segregation in brass leads to local poor ductility.

2. Excessive internal stress in copper stripsFinished products without sufficient stress relief annealing generate surface stress cracking and peeling under stamping stretching.

3. Tiny subcutaneous defects in raw materialsMicro pores and inclusions in cast slabs are concealed after rolling and only exposed as peeling under heavy stamping deformation.

Improvement Measures

1. Homogenize alloys during meltingExtend the holding and standing time of molten copper to homogenize alloy elements and reduce agglomeration of brittle second phases; adjust the addition ratio of iron and phosphorus.

2. Conduct stress relief annealing for finished stripsPerform low-temperature stress relief annealing before the final rolling pass to release rolling internal stress; control the cooling rate after annealing to avoid secondary oxidation.

3. Inspect incoming raw materialsConduct stamping tensile tests on sampled incoming strips to screen hidden subcutaneous defects in advance. Isolate raw materials with peeling risks and send them back for remelting.

IV. On-site Emergency Treatment for Quick Production Loss Control

1. Partial peeling at strip heads and tails: Cut off defective sections on the production line, and process qualified sections normally.

2. Continuous long-strip peeling across the whole coil: Judge it as an inherent defect from cast slabs and send the entire coil back for remelting.

3. Scattered spot peeling (caused by pressed-in rolling scale): Add a light temper grinding pass to remove surface oxidized peeling layers.

4. Mass peeling during stamping: Prioritize replacing copper strip raw materials, meanwhile adjust stamping stretching clearance and reduce stretching speed.

V. Quick Identification of Peeling Sources for Fast Fault Location

1. Continuous long-strip peeling running through the whole strip → Pores, inclusions or surface overlaps of cast slabs from smelting & casting.

2. Random scattered spot peeling → Pressed-in rolling scale or brittle alloy particles.

3. Peeling only emerging after stamping (invisible on raw strips) → Tiny subcutaneous defects or excessive internal stress of raw materials.

4. Peeling distributed along rolling scratches → Surface scratches caused by guide path burrs or foreign object indentations from work rolls.

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