Shear Cutting Machine for Steel Rolling Mills Details
The shear cutting machine consists of a pair of circular blades. Typically used in small workshops, it is installed before the cooling bed to perform rough shearing on long rolled stock, ensuring the material entering the cooling bed is not excessively long. Alternatively, it can be positioned before the finishing mill to trim the ends of rolled stock, guaranteeing smooth operation of the finishing mill process.
The ability of shear cutting machine to shear moving rolled stock transversely stems primarily from the blade disc axis being inclined at a specific angle relative to the stock's direction of travel. This design ensures the tangential component of the disc blades' circumferential velocity equals the stock's movement speed. Stock entry and exit from the disc blades is achieved via guide plates.
A drawback of the shear cutting machine is that it produces an inclined shear surface. However, this has minimal impact when trimming heads or performing rough shearing before the cooling bed. Due to its reliable operation, simple structure, and suitability for rolling speeds exceeding 10 meters per second, this shear cutting machine finds widespread application in small-scale workshops. It can operate continuously or in a start-up mode.
1. Purpose:
Length Cutting: The primary function is to cut continuous or long-length steel products into specified shorter lengths for further processing, transport, or direct customer use.
Defect Removal: Shears can also be used to crop off irregular ends (head and tail ends) of the rolled product that may have defects or inconsistent dimensions.
Sampling: Occasionally, small samples might be cut for quality control checks.
2. Types of Shears:
There are several types of shear cutting machines, each suited for different applications and steel product types:
Flying Shears: These are high-speed shears used in continuous rolling mills where the steel product is moving at high speeds. The shear blades move with the product during the cut, ensuring a precise cut without stopping the rolling process.
Start-Stop Flying Shears: The shear accelerates, cuts, and then decelerates.
Continuous Flying Shears: The shear's motion is synchronized with the material speed throughout the cutting cycle.
Rotary Shears: Often used for lighter sections or wire rods, these have rotating blades that create a continuous cutting action.
Cold Shears (or Bar Shears/Plate Shears): These are used to cut steel that has cooled down to ambient temperature. They are typically robust machines capable of cutting thick bars, billets, or plates.
Cropping Shears: Located at the entry of a mill to cut the front end of a hot billet or slab.
Dividing Shears: Used to cut the rolled product into predetermined lengths.
Guillotine Shears: Common for cutting plates and sheets, where a top blade descends past a fixed bottom blade.
Hot Shears: Used to cut steel while it is still hot (after the rolling process but before cooling). This is common for initial cropping or dividing larger sections like blooms, slabs, or heavy plates. Hot steel is easier to cut, requiring less force.
3. Key Components:
Shear Blades: Made from high-strength, wear-resistant tool steel. The design and angle of the blades are crucial for clean cuts and long life.
Shear Housing/Frame: A robust structure that holds all components and withstands the immense cutting forces.
Drive System: Typically hydraulic or electric motor-driven, providing the power for the cutting action.
Measuring System: Essential for accurate length control, often involving encoders, laser sensors, or limit switches that feed data to a control system.
Pinch Rolls/Roller Tables: To guide and hold the steel product firmly in place during the cutting operation.
Control System (PLC/HMI): Modern shears are highly automated, with Programmable Logic Controllers (PLCs) managing the timing, speed, and positioning for precise cuts based on operator input or production schedules.
4. Operating Principles:
The steel product (e.g., a continuous bar or a moving plate) is fed into the shear.
A sensor detects the leading edge of the product or measures its length.
Based on pre-set parameters, the shear's cutting cycle is initiated.
The blades engage, cutting the steel with a shearing action (similar to scissors).
The cut pieces are then conveyed away for further processing or stacking.
5. Advantages:
High Production Rates: Especially flying shears, which allow continuous operation.
Accuracy: Modern shears offer high precision in length cutting.
Versatility: Capable of cutting a wide range of steel grades and product dimensions.
Automation: Reduces manual labor and improves safety.
6. Challenges/Considerations:
Blade Wear: Blades need regular maintenance, sharpening, or replacement due to wear.
Noise and Vibration: Shearing can be a noisy and high-impact operation.
Maintenance: Regular lubrication and inspection of mechanical and hydraulic systems are critical.
Safety: Due to the high forces and moving parts, safety interlocks and procedures are paramount.
