Online Measurement and Quality Control in High-speed Wire Rod Mills
After the final rolling pass, ensuring consistent product quality becomes critical. In modern molinos de alambrón de alta velocidad, this is achieved through real-time monitoring systems placed right at the exit of the sizing or reducing mill stand.
Two key devices are used: an online eddy current flaw detection system and a laser-based diameter measurement gauge. These tools work together to monitor every inch of the moving wire rod as it travels at speeds up to 120 EM.
The eddy current probe detects surface defects such as cracks, costuras, or folds with high sensitivity—often identifying flaws smaller than 0.1 mm deep. Mientras tanto, the laser micrometer measures the outer diameter continuously, capturing data hundreds of times per second. Any deviation beyond ±0.15 mm from the target size triggers an automatic alert for operators.
This level of precision ensures that only material meeting strict dimensional tolerances moves forward into downstream processing. It also reduces scrap rates and improves overall yield by catching issues before large volumes of defective coils are produced.
Controlled Cooling Process: From Water Quenching to Air Cooling
Once the wire rod exits the last stand, it enters a precisely managed cooling path designed to control its microstructure and mechanical properties. The process starts with a water cooling section, followed by controlled air cooling on a Stelmor-type conveyor.
The primary goal of water cooling is to regulate the temperature at which the wire rod is laid down into coils—a parameter known as 吐丝温度 (吐丝 means “spitting silk,” referring to how the wire forms coiled loops). This temperature typically ranges between 850°C and 950°C depending on steel grade and final application requirements.
The number of active water boxes and flow rate are automatically adjusted based on real-time feedback from infrared pyrometers. Por ejemplo:
| Steel Grade | Target Delivery Temp (°C) | Water Box Stages Used | Flujo de agua de refrigeración (m³/h) |
|---|---|---|---|
| SWRH82B (Prestressed Concrete Steel Wire) | 880 ± 20 | 6 stages | 420 |
| ML08AL (Low Carbon Cold Heading Steel) | 920 ± 20 | 3 stages | 280 |
| 65Mn (Spring Steel) | 860 ± 20 | 7 stages | 480 |
These parameters are stored in the production recipe database and recalled automatically when switching grades. Closed-loop control adjusts pump output and valve positions dynamically to maintain stable cooling intensity even under fluctuating plant conditions like water pressure drops or ambient temperature changes.
Coiling and Spacing: How the Wire Takes Shape
After water cooling, the hot wire rod is gripped by pinch rolls and fed into the turbine-type laying head (also called a吐丝机). This high-speed device rotates at over 1,000 rpm, guiding the wire into uniform spiral loops.
The standard coil diameter formed is approximately Φ1075 mm, though some lines can adjust between Φ900–1150 mm depending on rod size and cooling needs. Each loop is spaced evenly across the width of the conveyor to ensure optimal airflow during cooling.
The laying head must synchronize perfectly with the rod speed. Por ejemplo, at a delivery speed of 105 m/s and a rod diameter of 6.5 mm, the turbine spins at around 980 rpm with a lay pitch (distance between adjacent turns) set to about 8.2 mm. Misalignment here can cause overlapping coils or uneven stacking, leading to poor heat dissipation and internal stress buildup.
Para evitar esto, advanced systems use servo-driven laying heads with real-time position correction. Sensors detect minor variations in incoming rod speed and instantly adjust the rotation angle and radial extension of the guide tube.
Air Cooling Conveyor System and Microstructure Development
The coiled wire then travels along a long-delay air-cooling conveyor, commonly referred to as a Stelmor line. This conveyor plays a crucial role in determining the final metallurgical structure of the wire rod.
The line described here features 16 high-capacity axial fans, each delivering up to 180,000 m³/h of air. The upper section includes insulated hoods that can be opened or closed automatically based on the required cooling rate.
Cooling strategies vary significantly by steel type:
- Standard Cooling: Hoods open, full fan power – used for low-carbon steels needing ferrite-pearlite structures.
- Delayed Cooling: Hoods closed, reduced airflow – applied to medium-carbon or boron-treated steels to promote fine pearlite or bainite formation.
- Fast Cooling: Maximum airflow, no hood insulation – used for hard-drawn wire applications requiring higher strength.
The conveyor speed is another adjustable factor. Typical transport times range from 40 seconds for thin rods (5.5 mm) to over 120 seconds for thicker sizes (16 mm). By the time the coil reaches the end of the line, phase transformation is complete, resulting in a homogeneous microstructure and uniform tensile properties throughout the coil.
Coil Collection and Handling: From Loose Coil to Final Bundle
At the tail end of the cooling conveyor, the spiral-shaped wire falls into a coiling basket (mandrel). A coil distributor ensures even layering to keep the final package height manageable—typically below 1400 mm.
The resulting coil has an outer diameter of about Φ1250 mm, inner diameter of Φ850 mm, and weighs between 1.8 a 2.5 tons depending on rod size and winding density. During collection, the wire temperature remains between 350°C and 600°C, still warm enough to avoid thermal shock but cool enough for safe handling.
Once full, a “shutter” plate supports the leading end (called the “nose”) of the coil while the central mandrel lowers and tilts the entire coil from vertical to horizontal position. Al mismo tiempo, a second empty mandrel swings into place to begin collecting the next coil—enabling continuous operation without downtime.
A transfer cart then moves the loose coil sideways onto a hanging hook of the PAG&F line (Pinch & Fold transport system). This overhead conveyor transports the coil slowly through inspection, agrupar, and weighing stations.
Final Processing: Inspección, agrupación, and Storage
As the coil moves along the P&F line, it passes through several key stations:
- Visual Inspection Station: Operators examine the surface condition, check for kinks or misalignment, and take samples for lab testing if needed.
- Cropping Station: The front and tail ends (which may have irregular dimensions) are cut off using hydraulic shears.
- Bundling Station: The coil is compressed radially by a horizontal press to reduce looseness, then tightly bound with two or three high-tensile steel wires using automatic strapping machines.
- Weighing & Marking: Each bundle is weighed, and a label is attached indicating heat number, grade, diámetro, weight, and production date.
The facility uses three fully automatic bundlers—one dedicated to each production line and one shared unit for flexibility. An additional space is预留 (reserved) for future expansion. This setup allows uninterrupted bundling even during maintenance.
After labeling, the finished coil is delivered to the unloading station where a small trolley removes it from the hook and places it into a storage bin. Empty hooks return automatically to the coiler area for reuse.
Finalmente, large electromagnetic cranes lift multiple coils at once and transport them to the finished goods yard. Aquí, they await shipment to customers—whether for drawing into fine wire, cold heading into fasteners, or further processing in spring manufacturing.
Why These Details Matter for Producers and Buyers
Understanding the full journey—from online gauging to final bundling—helps both mill operators and end users appreciate what goes into producing reliable, high-performance wire rod.
For producers, optimizing water cooling settings, maintaining precise laying head alignment, and ensuring consistent bundling force directly impact product consistency and customer satisfaction.
For buyers—especially those in wire drawing, pre-stressed concrete, or automotive parts manufacturing—knowing the cooling pattern and coiling temperature helps predict drawability, ductilidad, and final strength more accurately.
En el competitivo mercado actual, even small improvements in cooling uniformity or defect detection rates can lead to significant gains in yield, lower rejection rates, and better compliance with international standards like ISO 16120 or ASTM A510.
