For special steel mills, producing large‑size wire rods above Φ21 mm has long been a technical challenge. Compared with small‑size products, large‑size high‑carbon and alloy steel wire rods face unique rolling difficulties: frequent carbide roll ring breakage, serious surface scratches, unstable loop shape, and poor coiling quality.
This article summarizes the core process pain points in actual production and shares targeted improvement measures that have been verified on site.
1. Overview of Process Difficulties
For large‑size special steel wire rods, the ideal production route is high‑speed bar mill + coiler. When using the traditional high‑speed wire rod mill + laying head route, the process characteristics lead to obvious problems:
- Low finishing speed, no temperature rise in pre‑finishing and finishing blocks
- Continuous temperature drop during rolling, especially serious head temperature loss
- High deformation resistance due to high alloy content
- Large rolling force and impact load on the reducing and sizing mill (RSM)
- Large self‑weight, high bending resistance, and serious friction damage
These factors directly cause roll ring breakage, surface scratching, and poor tail loops. Only systematic process optimization can achieve stable production.
2. Pain Point 1: Carbide Roll Ring Breakage
Roll ring breakage in the RSM is the most frequent failure in large‑size rolling.
Main Causes
- Serious head temperature drop
- Insufficient locking between roll ring, taper sleeve and shaft
- Excessive pass filling rate
Solutions
- Strictly control the bar head temperature; avoid continuous cooling and ensure sufficient re‑heating time.
- Carry out waterproof treatment at cooling equipment to prevent the head from cooling too fast.
- Ensure reliable locking; contact area ≥80%.
- Control pass filling rate between 90%–95% to avoid stress concentration.
3. Pain Point 2: Surface Scratches
Large‑size wire rods have large self‑weight and high bending resistance, so scratches are more likely to occur.
Key Scratch Positions
- Laying pipe, bending guides, pinch rolls
- Guide rollers and cooling conveyor rollers
- Worn inner grooves of laying pipe
Solutions
- Use guide‑wheel type bending units with good cooling and lubrication.
- Strictly align the laying pipe, guides and pinch rolls.
- Use customized large‑diameter laying pipes: Φ16–22 mm → ID 34 mm Φ23–28 mm → ID 38 mm
- Polish all guide rollers and air‑cooling rollers regularly.
- Optimize production sequence from large to small to avoid secondary scratches.
4. Pain Point 3: Poor Tail Loop Control
Poor tail loops lead to messy coils, difficult packaging and customer complaints.
Causes
- Large inertia; the tail speed cannot keep up with the acceleration of the laying head
- Speed mismatch between pinch roll and laying head
- Excessive drop height in the coiler
- Loose tail loops on the cooling conveyor
Solutions
- Adopt synchronous speed up of RSM, pinch roll and laying head.
- Optimize acceleration slope: slow start, then synchronous follow.
- Use tail pause mode on the cooling conveyor to avoid loose loops.
- Adopt high‑position coiling to reduce falling impact and tilt.
- Optimize oscillation parameters to avoid too small loops.
5. Root Cause & Summary
The core of the difficulties lies in the process characteristics of large‑size special steel wire rods:
- Rolling route skips pre‑finishing and finishing blocks
- No high‑speed temperature rise; continuous temperature drop
- High deformation resistance and high rolling force
- Low‑temperature laying increases friction resistance
- Large self‑weight and high bending resistance
To achieve stable rolling and good quality, targeted optimization must be carried out:
- Strictly control head temperature to avoid black heads
- Ensure roll ring locking and reasonable pass filling rate
- Optimize laying pipe diameter and guide conditions to reduce scratches
- Adjust speed synchronization to improve tail loop shape
- Maintain stable temperature, speed and tension parameters
Only through systematic tuning can large‑size special steel wire rods achieve stable quality, smooth production and low consumption.
