In modern rolling mill production lines, rolled products such as strip steel or wire rod can reach lengths from tens to hundreds of meters. For efficient handling, transportation, and storage, these long products must be wound into compact coils. The equipment responsible for this process is called a coiler.
A coiler is a critical auxiliary unit in steel rolling plants. Its operating condition directly influences production stability, strip quality, and the overall throughput of the rolling mill. Coilers are widely used not only in rolling lines, but also in downstream processing units such as pickling, annealing, slitting, galvanizing, and coating lines.
Types of Coilers in Steel Rolling
Coilers can be categorized based on application into three main types:
1. Hot Strip Coiler
Hot strip coilers are used in hot rolling mills to coil steel at elevated temperatures (typically 550–750°C).
They are available in multiple configurations:
- Above-ground and underground types
- Mandrel (drum) and non-mandrel designs
In practice, underground coilers are commonly adopted for layout efficiency and operational safety. Controlled coiling tension is applied to ensure proper coil formation and strip quality.
2. Cold Strip Coiler
Cold strip coilers are used in cold rolling mills and continuous processing lines.
Key characteristics:
- Require higher coiling tension compared to hot coiling
- Typically adopt mandrel-type tension coilers
- Installed at the exit of processing lines (e.g., pickling, annealing, coating)
At the entry of such lines, decoilers and strip flattening devices are used to uncoil and prepare the strip.
3. Wire Rod Coiler
Wire rod coilers are used in wire rod mills and have evolved significantly.
- Early systems only performed basic coiling
- Modern systems integrate controlled cooling processes after rolling
- Typically work together with laying heads and cooling conveyors
This integration improves mechanical properties and ensures uniform coil quality.
Key Requirements for Coiling in Strip Production
To meet process and quality demands in both hot and cold rolling, coilers must satisfy several technical requirements:
- Controlled Tension Coiling
Coiling must be performed under appropriate tension to maintain strip shape, reduce rolling torque, and ensure coil integrity. - Stable Tension Throughout the Process
Constant tension must be maintained from the beginning to the end of coiling, requiring adjustable drum speed. - Easy Coil Discharge
Due to tight winding under tension, the coiler must allow efficient and safe coil removal. - High Structural Strength and Rigidity
The mandrel is subjected to significant radial forces, demanding robust mechanical design.
Main Components of a Strip Coiler
A typical strip coiler consists of two primary subsystems:
1. Coiling Unit
This is the core mechanism responsible for forming the coil.
- Two coiling modes exist: solid (tight) coiling and hollow coiling
- Modern strip production almost exclusively uses solid coiling due to better coil tightness, alignment, and speed capability
2. Drive System
The drive system ensures proper rotation and tension control.
- As coil diameter increases during winding, the rotational speed must gradually decrease to maintain constant tension
- Speed regulation methods include:
- Mechanical control
- Electrical control
- Hydraulic control
