1.What are the hazards of burrs on the edge of cold-rolled coils? Why must they be strictly controlled?
Risks of strip breakage during rolling: In cold continuous rolling, burrs on the strip edges can easily scratch the roll surface, even leading to strip breakage and production stoppage.
Surface indentation defects: Burrs that fall off onto the strip surface can be pressed into the rolls, forming periodic indentations, causing product downgrading or scrapping.
Zinc plating quality issues: For products requiring galvanizing, burr areas often have uneven or incomplete plating, affecting corrosion resistance.
Subsequent processing obstacles: During stamping, burrs can scratch the die, and the burrs themselves can become stress concentration points, inducing stamping cracks. Therefore, high-standard cold-rolled coils typically require burr height control within 0.02mm (20μm), and precision applications even require ≤15μm.
2.What are the main causes of edge burrs?
Inappropriate disc shear process parameters: This is the most critical factor. Improperly set shear blade gap and overlap directly lead to burrs. Studies show that the shear blade gap has a significantly greater impact on edge quality than the overlap. If the gap is too large, the material will be pulled apart rather than sheared, resulting in large burrs; if the gap is too small, shear blade wear will accelerate, also easily leading to secondary shearing.
Poor shear blade condition: Wear and dulling of the shear blade, chipping, or axial vibration of the shear blade during shearing due to loose hydraulic nuts will all cause uneven shearing surfaces and burrs.
Defects in hot-rolled raw materials: Severe defects such as edge waviness, camber, and cracks in the incoming material will cause uneven force during shearing, impacting the shear blade, causing "blade slippage" or incomplete shearing in certain areas, thus producing burrs.
Inaccurate calibration: If the shear blade gap calibration method is too simplistic (such as relying on only one or two measurements with a feeler gauge), it will fail to accurately reflect the actual gap, also causing process parameters to deviate from the optimal value.
3.How can burrs be controlled by optimizing the process parameters of a disc shear?
Shear blade clearance: The clearance is typically taken as 8% to 12% of the strip thickness, but the specific amount needs to be calculated using formulas based on material strength and thickness. For ultra-low carbon steels such as IF steel, Shougang's research has provided a specific calculation formula for continuous annealing and galvanized products, which significantly reduces burr height after application. An excessively large clearance increases the proportion of the fracture zone, resulting in higher burrs; an excessively small clearance leads to an excessively large shear zone, resulting in good cross-sectional quality but rapid shear blade wear.
Shear blade overlap: The overlap also needs precise control. Too little overlap results in incomplete shearing; too much overlap exacerbates shear blade wear and generates extruded burrs. It is typically set between -3mm and +3mm (negative values indicate a larger clearance) based on the strip thickness.
Dynamic adjustment: Modern control requires dynamic fine-tuning based on the actual shape and strength fluctuations of the incoming material, rather than using fixed parameters indefinitely.
4.Besides shearing, what other auxiliary methods can effectively remove or reduce burrs?
Deburring Rolls (Extrusion Rolls): One or more pairs of deburring rollers are installed after the disc shear. By pressing down on the edge of the strip, burrs are flattened or removed through extrusion.
Coating Optimization: Using laser cladding coating instead of traditional chrome plating significantly improves the wear resistance of the roller surface and extends its service life.
Roll Shape Optimization: Optimizing the traditional flat roller into a curved roller not only improves the deburring effect but also avoids the "bright edge" defect caused by excessive extrusion.
Edge Grinding Machine: For high-quality requirements (such as automotive panels) or thick products, grinding wheels can be used to actively grind away a layer from the strip edge, thoroughly removing burrs and micro-cracks. Advanced edge grinding equipment can track the strip speed and position in real time, automatically adjust the grinding amount, and compensate for the effects of roller wear and strip edge waviness, achieving constant pressure precision grinding.
5.How to inspect and control the quality of burrs on the production site?
Online Monitoring: Utilizing laser scanners or high-speed cameras, the edges of the sheared strip are inspected online to monitor burr height and morphology in real time. An alarm is immediately triggered or shearing parameters are automatically adjusted if any exceedances are detected.
Offline Sampling Inspection: The machine is periodically stopped to measure the shear blade clearance using feeler gauges or microscopes, and burr height is measured using a roughness tester or 3D profilometer. For example, burr morphology is observed using a digital microscope with 2000x magnification, and burr height is quantified using a laser scanner with a resolution of 0.01μm.
Standardization: Enterprises should establish strict inspection procedures, such as specifying that the amount of burrs on the cut edge is controlled within 0.02mm, and regularly checking the wear of the deburring rollers to ensure they are in good working order.
Record Tracking: The start and end positions of each steel coil are recorded along with the burr inspection results. Areas with large performance fluctuations at the start and end, and prone to burr generation, are given special attention or appropriately removed in subsequent processes.