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Endless Rolling Mill

Endless Rolling Mill - Advanced solutions from the market pioneers

The concept of endless hot rolling was introduced to meet the increasing demands for hot-rolled steel sheet using a cost-effective process compared to the conventional batch-type process.

Endless rolling involves the joining of the tail end of a preceding transfer bar with the head end of the following transfer bar after the roughing stands but prior to the finishing stands. Primetals Technologies was the first company in the world to develop the related equipment for induction-heating joining (IHJ) and super deformation joining (SDJ) to enable endless rolling. Furthermore, the dynamic Pair Cross mill can also be installed to deal with flying strip-thickness changes and increasing thermal crown resulting from continuous rolling.

 Bar Joining

The concept of the endless hot rolling was introduced to meet demands for diverse products of hot rolled steel sheets using a cost-effective process compared to the conventional batch-type process. Endless rolling involves joining of the tail end of a preceding bar and the head end of a following bar after rough rolling. The repetitively joined hot bars are subsequently finish-rolled, which results in the endless rolling. This process has the following advantages over the conventional batch-type process:

  • Expansion of product lineup: Production of thinner, wider and harder steel sheets; Stable rolling of thin and hard-to-roll materials
  • Increase in productivity: Great reduction in mill idle time, and constant rolling speed with reduction of mill acceleration and deceleration time
  • Improvement of product quality: Improvement in accuracy and uniformity of strip thickness, crown, and width
  • Energy savings: Reduction of the mill acceleration and deceleration frequencies
  • Improvement of yield: Minimizing of miss-rolling by applying tension at head and tail parts of strip

Fig.1- Comparison of IHJ and SDJ

Induction Heating Joining (IHJ)

JFE Steel Chiba No.3 HSM is the first HSM in the world to realize endless hot strip rolling. The Key to Endless Rolling is the Induction Heating Joining Machine that was developed by Primetals Technologies jointly with JFE Steel. 

Fig.2- IHJ explained  |  Fig.3-  IHJ design image 

Super Deformation Joining (SDJ)

The Super Deformation Joining Machine that was developed by Primetals Technologies jointly with POSCO was installed in 2006 and is now in operation at No.2 Hot Strip Mill in Pohang Works, POSCO. The procedure of SDJ consists of four steps: partial descaling, overlapping, joining, and crop disposal.

  • Partial descaling by high-pressure water is first performed on the area to be joined before overlapping
  • The head of the following bar is partially overlapped on the tail of the preceding bar by increasing the speed of the following bar
  • Both bars are joined by shearing action of the stationary pendulum type-joining machine
  • Crops on both sides are pushed off from the joint and disposed

SDJ doesn't require a special heating process and the joining process is very quick. Also, the equipment size is smaller than IHJ type.

Fig.4- Layout of SDJ  |  Fig.5- Design image of SDJ 

Fig.6- SDJ operation  |  Fig.7- SDJ process

 Key Technologies

Following items are key technologies to implement the successful endless rolling.

  • Dynamic APFC (Automatic Profile & Flatness Control)
  • Shear to split long strip before coiling
  • Dynamic switching over of coilers during high- speed rolling and coiling

Primetals Technologies is the only supplier in the world that can supply a complete endless rolling system, and five hot strip mills are under operation with our endless rolling technology, with remarkable accomplishments. Primetals Technologies offers, in connection with the above, the following proven technologies for the customer.

  • Dynamic Pair Cross Mill
  • High-speed shear
  • Advanced down coilers with switch-over function (Option: Carrousel coiler)

Fig.1- Dynamic APFC  |  Fig.2- High-speed shear |  Fig.3- Coilers with switch-over function

Dynamic Pair Cross Mill

Dynamic Pair Cross Mill is a Pair Cross Mill which is able to change cross angle of the rolls during the rolling process. The feature allows the control of strip crown and strip shape during rolling (Dynamic APFC) in order to deal with flying strip thickness changes and growing of roll thermal crowns which occur at the continuous rolling.
Application and number of Dynamic Pair Cross Mill stands are customized in accordance with product range and other requirements.
Dynamic Pair Cross Mill can also be effective for normal batch rolling for compensation of thermal expansion of work rolls and changes in other rolling conditions in one bar.

High Speed Shear

High Speed Shear splits long strip before coiling at endless rolling. It is a rotary-type shear equipped with eccentric mechanism. Before shearing, drums are rotating with a gap in order to let strip go through. And at shearing the eccentric mechanism narrows the gap and has knives approach to shearing position. The speed of drum is set synchronized with the speed of strip at shearing.

High-Speed Down Coiler with Threading Direction Change Function

Endless rolling requires coiling facility special features. Threading starts immediately after the preceding strip had passed. And the threading speed is higher than normal batch rolling. In order to continue coiling without gap time, coiler is equipped with switch-over function which can change threading direction in high speed. Pinch roll with offset adjustment system is the core technology for the function. To ensure stable threading at carry-over table between No. 1 and No. 2 coilers, Pneumatic strip feeding system is introduced. Also, the down coiler it's self has a special configuration of 4 wrapper rolls which enables the smooth and quality coiling under the demanding condition.

Carrousel Coiler

Primetals Technologies were the first in the world to develop a hot rolling carrousel coiler. This is an alternative option to down coiler.

 

Fig.4- Carrousel Coiler  |  Fig.5- Carrousel Coiler Operation

 ‭(Hidden)‬ Automation

Under construction

 ‭(Hidden)‬ Services

Under construction

Reference Story

A unique solid-state joining process

Customer

POSCO Pohang Works

Type of plant

Full-scale endless hot rolling

Our solution

Joining bars very quickly (in less than 0.5 seconds) and reliably without a special heating process. An apparatus using this new joining process has been incorporated into the No. 2 hot rolling mill at the POSCO Pohang Works, where full-scale endless hot rolling is in operation. Here the other key technologies for endless rolling, such as High speed shear and Advanced down coilers with switch-over function are also applied. This project was a revamping of the existing, conventional batch hot rolling mill.

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