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.
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 such as:
- Increased width reduction: Maximum 350 mm
- Improved slab caster efficiency
- Improved yield
- Press design which helps reduce the time required for retrofitting (or installation)
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 mandrel-less coil box contributes further to reducing the temperature drop at the coil inner wraps in comparison with the mandrel-type coil box. The mandrel-less coil box also provides space to install 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 method of operation. 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 through higher coiling speed and forced coil transfer from coiling position to uncoiling position to enable 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 range of carbon steel production, as well as stainless steel production
Transfer bars rolled at the roughing mill have ends out of square, so-called tongue and fishtail, on their head and tail ends respectively. The crop shear is located in front of the finishing mill to cut off these parts for stable threading. The differential-speed rotary crop shear is a unique product of Primetals Technologies. The design incorporates top and bottom drums of different diameters and peripheral speeds. During a rotation, the knife gap is transitionally changed from plus–zero–minus, which ensures several operational and economic advantages to customers.
- Better profile at sheared bar ends created by the transitional change in knife gap
- Extended knife changing cycle through reduced knife wear and extended knife gap
- Capability to cut end crops, to high tolerances from a minimum of 20mm. This feature, along with the crop optimization system, will reduce crop loss markedly.
- 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)
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)
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
The measurement of strip shape between mill stands on a 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. The LSM has superior advantages as follows:
- The load on the segment roll is measured by a torque meter without any influences of hysteresis of the mechanism, unlike when using 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 low moment of inertia, existing looper drive system can be reused
- Easy replacement of segment roll for maintenance
Hot strip mills often reach their limits in terms of power and flexibility for production of advanced high strength steel grades (AHSS) such as 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 later part of the roller table cooling section. 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 operating 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.
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
Power Cooling opens the door for reduction of alloying costs by substitution of hardening elements with hardening achieved by higher cooling rates.
Primetals Power Cooling is an advanced strip cooling technology
- Providing extremely 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 two 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 two-step cooling patterns e.g. needed for DP-grades
- Perfect for de-bottlenecking of short cooling lines
Primetals Technologies have developed an advanced down coiler, incorporating improvements derived from our vast amount of experience.
- 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- SSP in action
Fig.2- Comparison with conventional edger
Fig.3- Structure of SSP
Fig.4- Coiling by Coil Box
Fig.5- Coiling the Transfer Bar
Fig.6- Benefit of Mandrel-less Coil Box
Fig.7- Forced Coil Transfer Explained
Fig.8- In-Line Knife Replacement
Fig.9- Cassette Drum Replacement Option
Fig.10- Feature of Differential Speed
Fig.11- Evolution of PC mill
Fig.12- Front view of PC mill
Fig.13- Diagram of ORP
Fig.14- Grinding wheel
Fig.15- Diagram of LSM
Fig.16- LSM in operation
Fig.17- Conversion from Measured Torque to Strip shape (I-unit) of each order
Fig.18- Power cooling unit
Fig.19- "Alloying" with water = saving money
Fig.20- Hot coil being extracted from coiler
Fig.22- Advanced mandrel design
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.
Slab Sizing Press Control
The Slab Sizing Press (SSP) is able to improve productivity at continuous casting by organizing the slab width. But without proper control, the performance of SSP will not be maximized. The advantages of the 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 highly-accurate 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.
Critical components such as mandrels, roll force cylinders, spindles, hydraulics blocks, crop shears, require special attention to assure your plant’s optimum performance.
Thanks to the knowledge of Primetals Technologies experts, their long experience, and as an Original Equipment Manufacturer; Primetals Technologies Services Division is able to assess, repair and improve your Hot Strip Mills’ critical components.
At Primetals Technologies Services Division, the dedicated experts work day after day to improve the quality of their services. The satisfaction of the customers is the main concern. The Services Division has a dedicated area and an experienced team to give you the best answer for your hot strip mill’s components maintenance. Thanks to the collaboration with the engineering department and scientific office, Primetals Technologies Services Division can give you the best solution to increase the lifetime of your equipment.
Fig.1- Critical components requiring special attention for maintenance
Fig.2- Spindles before and after maintenance