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Hot Strip Mill

Hot Strip Mill – Highest performance for new and existing steel mills

The demand for hot strip mill is growing in multiple ways. To remain competitive, new and existing mills must meet this challenge in the best possible way.

The production of hot strip is a key element of steel production. Since close to half of all steel produced is hot-rolled to strip, mills require maximum throughput and availability combined with geometrical precision and the ability to create optimum material properties.

 Slab Sizing

Slab sizing press (SSP)

Ever since Primetals Technologies was the first in the world to develop a SSP, we have maintained our position as a pioneer in the field. Since that time, we have enhanced the SSP based on our extensive experience in the steel industry to make numerous improvements like followings.

  • Increased width reduction: Maximum 350 mm
  • Improved slab caster efficiency
  • Improved yield
  • Structure which helps reduce the time required for modification (or installation)
 
Fig.1- Operating SSP  |  Fig.2- Difference with conventional edger  |  Fig.3- Structure of SSP  

 Coil Box

Advanced Coil Box

The coil box is located between the roughing mill and finishing mill to coil the transfer bars after roughing passes. The coil box enables a shorter distance between the roughing mill and the finishing mill in a new plant as well as minimizes the temperature drop of the transfer bar entering the finishing mill. The mandrelless coil box contributes further to reducing the temperature drop at the coil inner wraps in comparison with the mandrel-type coil box. The mandrelless coil box also makes space to install the side heat shields which contribute to reducing the temperature drop at the coil edge. Primetals Technologies designed the coil box to have two selectable coil transfer operations. One is passive coil transfer without any positive mechanical actions as a simple operation method. The other is forced coil transfer. The forced coil transfer system ensures smooth and quick coil transfer and enables higher productivity.
 
  • Prevention of temperature drop at the coil inner wrap through mandrel less coil transfer
  • Prevention of temperature drop at the coil edge through adjustable side heat shields
  • Short-pitch coiling operation through higher coiling speed operation and the forced coil transfer operation from coiling position to uncoiling position to enable the higher productivity
  • Stable operation of the finishing mill through higher temperature and uniform temperature over the whole length of the transfer bar. Due to this feature zoom rolling in the finishing mill is not required
  • Passing through the coil box without coiling is selectable according to the required production and operation methods
  • Large coil capacity for a wide range of transfer bar sizes to enable a wide rage of carbon steel production, as well as stainless steel production
 
Fig.1- Coiling by Coil Box  |  Fig.2- Coiled by  Transfer Bar  
 
 
Fig.3- Benefit of Mandrel-less type Coil Box  
 
 
Fig.4- Forced Coil Transfer Explained  

 Crop Shear

Differential Speed Crop Shear

Transfer bars rolled at roughing mill have shapes out of square, so-called tongue and fishtail, on their head and tail ends. The crop shear is located in front of the finishing mill to cut off such unsteady parts of the transfer bar as crops for stable threading. The differential-speed rotary crop shear is a unique product of Primetals Technologies. The design incorporates top and bottom drums with different diameters and peripheral speeds. During operating turn, the knife gap is transitionally changed from plus–zero–minus, which ensures several operational and economical advantages to customers.
 
  • Better profile at sheared bar ends created by the transitional chage in knife gap
  • Extended knife changing cycle through the insensitiveness to  the knife wear and extended knife gap
  • Capability to cut the end crops in very short pieces, from a minimum of 20mm. This feature, engaged with crop optimization system, will improve crop loss remarkably.
  • Robust design and high torsional rigidity with the application of synchronizing gears on the drum shaft ends between top and bottom
  • Quick knife changing with hydraulic unclamping system (Option)
  • Quick drum changing system (Option) 
 
Fig.1- In-Line Knife Replacement Type  |  Fig.2- Cassette Drum Replacement Type
 
 
Fig.3- Feature of Differential Speed

 Rolling

Advanced Pair Cross Mill

Primetals Technologies was the first in the world to develop a pair cross mill with high strip shape control capability. Since that time, we have maintained our position as a pioneer in the field, and Primetals Technologies have made numerous improvements to this system based on our extensive experience in the industry.

  • High strip shape control capability
  • Simplified structure
  • Achievement of high rolling reduction
  • Reduced mill vibration through the use of a mill stabilizing device (MSD)
 
Fig.1- Evolution of PC mill 
 
 
Fig.2- Front view of PC mill  

Smartcrown

SmartCrown work rolls feature a modified, sine-shaped contour. By selecting the correct contour coefficients and shifting the work rolls by the same amount in opposite directions, the resultant unloaded roll gap is always cosineshaped, regardless of the actual shifting position of the rolls.

Work Roll Shift Mill

Primetals Technologies have been a pioneer in the field ever since we developed the world's first Work Roll Shift Mill and have enhanced this technology based on our extensive experience in steel industry. Primetals Technologies utilizes the Work Roll Shifting at hot strip rolling field for different two purposes:

  • Dispersion of wear of work roll
  • Strip shape control (SmartCrown), as described in detail below:

Mill stabilizing device (MSD)

At today's demanding condition, maintaining stable operation of rolling mill is becoming difficult. MSD is a hydraulic cylinder installed to mill housing window and press a roll chock against the opposite side with constant force. MSD eliminates gap between roll chocks and mill housing, keep rolls in proper position and stabilize rolls.

  • Enables stable rolling at demanding rolling condition.
  • Stabilizes threading.
  • Reduces housing window gap control work. (Easier maintenance)
  • Prevents problems occurring from roll skew between WR and BUR.
  • Can be applied to existing mill

Online Roll Profiler (ORP)

Primetals Technologies have been a pioneer in the field ever since we developed the world's first system capable of roll grinding inside the mill stand (ORP), and have enhanced this technology based on our extensive experience in the industry.

  • Extending the roll life
  • Eliminating roll surface defects
  • Extending the length of same-width rolling
  • Permitting to widen out without roll change
 
Fig.3- Diagram of ORP  |  Fig.4- Grinding wheel

 Shape measuring

Looper Shape Meter (LSM)

The measurement of strip shape between mill stands on a Hot strip mill has previously been rather difficult and unreliable. Primetals Technologies has developed a looper shape meter (LSM) for continuous and accurate measurement of interstand shape. LSM has superior advantages as follows:
 
  • The load on the segment roll is measured by a torque meter without any influences of hysteresis of mechanism, unlike a load cell 
  • Measurement by torque meter enables higher accuracy and increased measurement reliability without any influences caused by changing mechanical condition
  • Easily interchangeable with existing loopers. Because LSM has small moment of inertia, existing looper drive system can be reused
  • Easy replacement of segment roll for maintenance
 
Fig.1- Diagram of LSM  |  Fig.2- LSM Operation 
 
Fig.3- Conversion from Measured Torque to Strip shape (I-unit) of each order

 Cooling

​Power cooling (Enhanced strip cooling system)

Hot strip mills often reach their limits in terms of power and flexibility for production of advanced high strength steel grades (AHSS) like API X80/X100, dual-phase, martensitic and complex-phase grades. For cooling and advanced “in-line” metallurgical treatment of new materials, Primetals Technologies developed “Power Cooling” technologies. This combines the advantages of normal laminar cooling or “low pressure cooling” and “high power cooling” with the highest cooling rates for flexible operation.

Equipment – Power Cooling Technology

In addition to applying Power Cooling Technology to the early stages of cooling it can also be applied between the roughing mill and the finishing mill, between the finishing mill stands and in the late part of the cooling area. This is necessary to make different production strategies possible as they are shown in the diagram below. The Power Cooling unit can be retrofitted into existing plants using the existing water treatment plant, tank and piping infrastructure. The Power Cooling units are supplied with water via a booster pump generating the required operation pressure. Alternatively the pump can be bypassed to supply the Power Cooling headers directly from the overhead tank for operation in laminar cooling mode.Thus, the full operation spectrum which requires laminar cooling on the total cooling length can be kept after installation of Power Cooling

Fig.1- Power cooling unit  

Application

The working area of Power Cooling is not only dedicated to thick strips (> 18mm) with high cooling rates. Due to the extended control of water flow and therefor control of heat flux it is also used for strips with a critical combination of thickness-speed ratio and required cooling rates and for standard steel grades, e.g. using the Power Cooling in laminar mode. The combination of Power Cooling with laminar cooling is a perfect solution for cooling lines which offers a wide range of applications as well as for optimizing the current product mix and future metallurgical requirements.

Typical Physical Characteristics of Power Cooling

  • Significantly increased cooling rates compared to laminar / turbo laminar cooling
  • High heat flux rates up to 5 MW/m²
  • Wide flow-rate control range for maximum metallurgical flexibility

Alloying

Power Cooling opens the door for reduction of alloying costs by substitution of hardening elements with hardening effects of higher cooling rates.

 

Fig.2- Alloying with water = saving money

Benefits

Primetals Power Cooling is an advanced strip cooling technology

  • Providing extreme high cooling rates (up to 40K/s @ 25.4mm)
  • Providing extreme flexibility with an adjustment range from 10% to 100%
  • Used for the complete product mix by operating in 2 modes, laminar and Power CoolingInstalled in running mills and new mills in combination with laminar cooling or as transfer bar cooling or as interstand cooling
  • Perfect solution for 2 step cooling patterns e.g. needed for DP-grades
  • Perfect for de-bottlenecking of short cooling linesProviding extreme high cooling rates 

 Coiling

​​​Advanced Down Coiler

Primetals Technologies have developed an advanced down coiler, incorporating improvements derived from our vast amount of experiences.

  • Wedge & link step less expanding type Mandrel for better coiling quality & reliability
  • Plug-in design for quick mandrel replacement
  • Automatic Jumping Control for preventing top-marks on inner wraps
  • Accurately controlled side guide & pinch rolls for stable operation & coil quality
 
Fig.1- Hot coil extracted from coiler  |  Fig.2- Mandrel  |  Fig.3- Advanced mandrel design

 Automation

Automatic Profile & Flatness Control (APFC)

APFC controls the entire length of strip profile and shape in the hot rolling finishing mill by means of high-precision setup functions and dynamic control (dynamic profile setup, dynamic shape control). The superior characteristics of the APFC include: 

  • The use of online physical models for highly-accuracy predictions of strip profile and shape, for optimal setup.
  • The dynamic control functions are not simple feedback control; they use models to consider both the profile and shape, and coordinate control in each of the stands.
  • Adjusting the model is simple for rapid set-up.

 

Fig.1- Example of APFC System Configuration  |  Fig.2- Sample of Crown and Shape Performance Results  

 

Fig.3- Quick setup by APFC

Slab Sizing Press Control 

Slab Sizing Press  (SSP) is able to improve productivity at continuous casting by organizing the slab width. But without the proper control, the performance of SSP will not be maximized. The advantages of SSP control include the following:

  • The use of step press functions corrects the loss of width at the front and rear ends of the slab, and can create a high-accuracy slab width along the full length of the strip after a single roughing pass.
  • Tapered slab press functions correct variations in the tapered slab width, and can create a uniform slab width through the full length of the slab after a single roughing pass, helping to improve yield.
 
 
Fig.4- SSP  |  Fig.5- Tapered Slab Press
 
 

Fig.6- Example of Step Press Use

 ‭(Hidden)‬ Technology

 

Primetals Technologies has consistently supplied a wide range of advanced hot rolling mills, including conventional hot strip mills, semi-endless and endless rolling mills. In particular, Primetals Technologies as a pioneering company has developed many world-renowned hot rolling technologies, key of which are listed below. Download the brochure for a more detailed review of each of the benefits and a dozen more supporting technologies and services. 

  • Slab Sizing Press (SSP): To improved slab caster efficiency and increase yield
  • Advanced Coil Box (Mandrel-less type): To reduce temperature loss of the rolled bar and shorten mill footprint
  • Differential Speed Crop Shear: High cutting performance
  • Advanced Pair Cross Mill: High strip shape control, reduced vibration and simplified construction
  • Work Roll Shift Mill: Even wear of work roll and improved strip shape with Smart Crown
  • Mill Stabilizing Device (MSD): Enables stable rolling under demanding rolling conditions  
  • Online Roll Profiler (ORP): Extends roll life 
  • Looper Shape Meter (LSM): For continuous and accurate measurement of inter-stand shape
  • Power Cooling (Enhanced Strip Cooling): Providing extremely high cooling rates for precise temperature control
  • Advanced Down Coiler: Wedge and link type step-less expanding mandrel for better coiling quality & reliability  

 

Fig.1- The sizing press can reduce the cast slab width by up to 350mm 

Reference Story

Customer

Dragon Steel Corporation, a member of CSC Group, Taiwan

Our solution

Dragon Steel Corporation decided to construct a hot strip mill to produce flat steel products as a core project. Primetals Technologies provided the hot strip mill to produce strip up to 1,880 mm wide employing state of the art technologies.

Line Specification

Production Capacity: 4 million tons/year
Steel Grades: Low-carbon, High-strength and Stainless steel
Slab Thickness: 250 mm (Stainless steel: 200 mm)
Slab Width: 900 mm to 1,880 mm (Stainless steel: up to 1,550 mm)
Slab Length: Max.. 10 m
Strip Thickness: 1.2 mm to 25.4 mm (Stainless steel: 2.0 mm to 6.5 mm) Strip Width: 700 mm to 1,880 mm (Stainless steel: 900 mm to 1,524 mm)
Coil Weight: Max.. 35,500 kg

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