1.What are the general rules governing the accuracy range?
High-precision rolling mills (such as Sendzimir mills and advanced six-high mills for producing ultra-thin strip or silicon steel):
Static accuracy: ±0.3% ~ ±0.5%.
Dynamic accuracy (acceleration/deceleration, threading process): Controllable within ±1%.
This requires a high-performance hydraulic servo system, a high-response drive motor, a high-precision tension gauge, and an advanced control model.
Ordinary single-stand/multi-stand cold continuous rolling mills (producing carbon steel, appliance panels, etc.):
Mainstream accuracy: ±0.8% ~ ±1.5%.
This is a generally achievable level that meets the quality requirements of most products.
Accuracy may only be maintained within ±2% ~ ±3% or even wider, which often leads to significant thickness fluctuations or shape problems.
2.What are the key factors affecting the accuracy of tension control?
Tensile Gauge: The core sensor. High-precision strain gauge or piezomagnetic tensile gauges should have a measurement accuracy better than ±0.25%. Their installation location, calibration, and maintenance are crucial.
Encoder: Used to measure roll diameter and linear speed; its resolution directly affects tension calculation.
Winder/Unwinder Motor: Must be a vector-controlled AC or DC motor with rapid torque response.
Looper: In continuous rolling mills, the looper is a key device for buffering and regulating tension; the response speed of its hydraulic or electrical system directly affects the stability of tension between stands.
Control Algorithm: Traditional PID control is insufficient. Modern rolling mills commonly employ advanced algorithms such as feedforward control, adaptive control, fuzzy control, or neural networks to predict and compensate for disturbances during rolling (such as speed changes, sudden thickness changes, and fluctuations in friction coefficient).
System Integration and Communication: Fully digital, high-speed bus communication (such as EtherCAT) ensures synchronized and delay-free signals between controllers and sensors.
3.What are the consequences of insufficient tension control precision?
Thickness deviation: Tension is a crucial factor affecting rolling force and thus thickness. Tension fluctuations lead to longitudinal thickness variations.
Strip shape defects: Such as waviness, warping, and tapered coils. Uneven or unstable tension is one of the main causes of poor strip shape.
Strip misalignment and breakage: Uneven tension on both sides can cause strip misalignment; excessive tension can easily break the strip, while insufficient tension may lead to stockpiling or folding.
Surface quality: Unstable tension can cause slippage between the rolls and the strip, resulting in vibration marks or scratches.
4.How is accuracy measured and verified?
The fluctuation range during steady-state constant-speed rolling.
The maximum deviation and recovery time during acceleration and deceleration.
Control capability during threading and tail-wagging.
5.What should be considered when controlling the tension of cold-rolled coils?
Tension control accuracy in cold-rolled coils is one of the core competitive advantages of modern cold rolling mills. ±1% can be considered a watershed moment, a crucial indicator differentiating mid- to high-end mills. Achieving and maintaining high accuracy requires a perfect combination of high-precision sensing, high-speed execution, and intelligent control.
For production operators and technicians, understanding the target value and influencing factors of tension control accuracy is fundamental for equipment maintenance, process optimization, and problem diagnosis. When thickness or shape issues arise, the state of the tension system is often the first area to investigate.