During the coiling process of common carbon hot-rolled steel strip, controlling the coiling tension is a key factor in determining the quality of the inner ring of the coil. Tension setting requires a balance between material ductility, equipment load capacity, and process stability. Its impact spans the entire process, including stress distribution, deformation control, and defect prevention within the coil's inner ring.
When coiling tension is excessive, the inner ring of the common carbon hot-rolled steel strip experiences excessive radial pressure, leading to a sharp increase in interlayer friction. This high pressure can cause two typical defects: First, microcracks in the inner ring strip due to localized stress concentration, particularly when the strip's head is cambered or the side guides are misaligned, causing cracks to propagate along the rolling direction. Second, plastic deformation of the inner ring of the coil manifests as shrinkage in the strip's width or thickening in its thickness, resulting in "narrow gauge" or "flat coil" defects. Furthermore, excessive tension increases contact stress between the coil and the strip. Long-term operation can lead to surface wear or elastic deformation of the coil, further deteriorating the inner ring's coil shape.
Insufficient coiling tension can cause the inner ring of the coil to become loose, resulting in "bread roll" or "tower" defects. During the initial coiling of common carbon hot-rolled steel strip, if the tension cannot overcome the inherent rigidity of the strip, the inner ring will naturally sag due to gravity, resulting in uneven interlayer gaps. These gaps can be magnified by vibration during subsequent transportation or storage, causing interlayer shifting or overall coil deflection. More seriously, a loose inner ring can cause the strip surface to slide against the reel and auxiliary rollers, resulting in slip marks or scratches, and reducing surface quality. Furthermore, a loose inner ring can shift the coil's center of gravity, increasing the risk of unwinding on the transport chain or walking beam, and threatening production safety.
Coiling tension plays a decisive role in the stress distribution within the inner ring of the coil. Proper coiling tension ensures uniform elastic deformation within the inner ring, creating a self-locking structure through interlayer friction, preventing loosening or slippage. When the tension matches the strip's yield strength, the peak stress in the inner ring is below the material fatigue limit, preventing stress relaxation or creep under dynamic loads. Furthermore, uniform tension distribution reduces stress concentration at the strip edges, lowering the risk of edge cracking or delamination. This is particularly important for edge-quality-sensitive materials such as common carbon hot-rolled steel strip.
Dynamic control of coiling tension also significantly impacts inner ring quality. In the initial coiling phase, when the coil diameter is small, lower tension is required to prevent overloading of the inner ring. As the coil diameter increases, tension gradually increases to compensate for the moment of inertia and maintain stable interlaminar pressure. At the end of coiling, tail-dropping tension reduction control is implemented to avoid sudden changes in tension at the strip tail and prevent inner ring loosening or tucking. This segmented tension control strategy effectively balances inner ring stress and deformation. For example, after the strip tail leaves the final stand of the finishing mill, pinch roll pressure and coiling tension are reduced, allowing the strip to run at a stable lower tension until coiling is complete, thus preventing tail loosening.
The synergistic effect of equipment status and coiling tension also directly impacts inner ring quality. Accuracy deviations in equipment such as the reel, pinch rollers, and side guides can alter the tension transmission path. For example, if the side guides are significantly misaligned or severely worn, the strip head will be pushed toward the slower side, causing inner ring turbulence. If the pinch rollers are significantly misaligned or the roll gap is inconsistent, the strip head cannot pass parallel to the coil, causing inner ring misalignment. Therefore, measures such as regular calibration of the side guide position, adjustment of the pinch roller gap, and maintenance of the pinch roller parallelism are necessary to ensure uniform tension transmission.
Matching process parameters with coiling tension is key to optimizing inner ring quality. For example, the thickness, width, and hardness of common carbon hot-rolled steel strip must be consistent with the set tension value. Thinner strips require higher-precision tension control to prevent slip marks. The coiling speed and acceleration must be matched to the dynamic response of the tension to avoid tension fluctuations during acceleration and deceleration. The cooling process must be coordinated with the tension control to prevent uneven stress in the inner ring caused by temperature gradients. By establishing a multi-parameter coupling model of tension, speed, and temperature, accurate prediction and control of inner ring quality can be achieved.
When coiling common carbon hot-rolled steel strip, coiling tension is a key factor influencing the quality of the inner ring by influencing stress distribution, deformation control, and defect prevention. Proper tension setting requires comprehensive consideration of material properties, equipment status, process parameters, and dynamic control requirements. Through segmented tension control, equipment precision maintenance, and multi-parameter collaborative optimization, the tightness, flatness, and surface quality of the inner ring of the steel coil can be significantly improved, ensuring a stable raw material supply for subsequent processing.
