FIELD OF THE INVENTION

The present invention relates to a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides directed to improve the quality of hot rolled strip coil. More particularly, the present invention is directed to providing a crop shear guide configuration and position comprising an additional ‘Out position’ involving transfer bar width and a ‘camber value’ wherein finishing mill entry guide sense the camber value of transfer bar as soon as the transfer bar head end is sensed so as to ensure that strip is not caught between crop shear and finishing mill entry guide. The crop shear guide design according to the invention is adapted to improve mill availability by reducing cobble occurrence and improving quality of coil avoiding head end necking.

BACKGROUND ART

In a hot strip mill, relatively wide steel slabs are rolled into very thin strips. Typically, a hot strip mill operation consists of three stages: roughing stage, finishing stage and coiling stage. In the roughing stage, the thickness of the slab is reduced from a typical dimension of 220 to 28 mm. The finishing mill further reduces the thickness of the strips to approximately 16 to 1.6 mm thick. Typically, a finishing mill consists of six closely spaced rolling mills. From the finishing mill, the strips are coiled for convenience of handling and further processing of the steel strip.
In a Hot Strip Mill (HSM), the slab travelling between the roughing mill and the finishing mill is called a ''transfer bar''. The irregularly shaped head and tail end of each transfer bar must be trimmed in a ''crop shear'' in order to avoid cobbles when the transfer bar is rolled into a very long strip and subsequently coiled.
Conventional finishing process in a hot strip mill operates satisfactorily only under normal conditions. But when an abnormal condition occurs, such as a cambered strip from coil box struck between finishing mill entry guide and crop shear guide, the consequence is cobbling of the strip or developing quality issue like head necking of the coil. The main function of the crop shear guide and first finishing mill entry guide is to feed the strip at center to the finishing mill, in case any cambered strip comes from coil box. Unless this is accomplished, the cambered strip may end up with cobble or if such a strip is allowed to pass through the finishing mill, it may lead to head end necking of the coil and low finishing temperature. Crop shear guides are operated by hydraulic system. Cobble occurrences delay the mill availability and head end necking results in quality issues. Apart from these difficulties in finishing mill, the cambered strip cut at crop shear will have taper head end which will result in non-uniform roll wear.

The design and positions according to the initial design of the crop shear guide and finishing mill-1 entry guides have three positions namely Ambush, Centering and Ingoing - all these positions of guides operate sequentially. “Ambush position” of crop shear guides its initial position, as transfer bar head end enters into the guides. “Centering position” is the force mode in which the crop shear guides touches the strip until it experiences load of 0.5 tons or less than 20 mm strip width and keeps strip in the center. “Ingoing position” refers to the crop shear guide with some offset value. The finishing mill-1 entry guide position has similar sequence of operation except the load experience in “Centering position”.

The crop shear guide “Ingoing position” triggers the “Centering position” of the finishing mill-1 entry guide. The “Ingoing position” of crop shear guide remains at the same position when the finishing mill-1 entry guides at “Centering position”. Due to this design and position of guides, the strip with head end camber used to get caught between finishing mill-1 entry guide (Centering) and crop shear guide (Ingoing) resulting in cobbles. Even if it passes through finishing mill entry guides, it leads to quality issue like head end necking of the coil. Cobble results in decreased mill availability and reduced productivity, whereas head end necking results in bad quality of the coil as well as non uniform roll wear.

There has been therefore a need in the art to developing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides adapted to avoid occurrence of cobble due to any cambered strip from coil box struck between finishing mill entry guide and crop shear guide resulting in cobbling of the strip or developing quality issue like head necking of the coil. The system and method of hot strip rolling process of the invention would ensure cambered strip cut at crop shear do not have taper head end to avoid non-uniform roll wear. The system will favour improved mill availability and higher productivity with consistent quality of the hot rolled steel strip products.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to providing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides adapted to avoid cobble occurrences before entry to the finishing mill in hot strip mill.

A further aspect of the present invention is directed to providing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides which would eliminate quality issue like head necking of the coil due to a strip with head end camber and also avoid low finishing temperature.

A still further aspect of the present invention is directed to providing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides which would ensure that a cambered strip cut at crop shear does not form a taper head end and does not result in non-uniform roll wear.

A still further aspect of the present invention is directed to providing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides which would enhance mill availability and improve productivity.

A still further aspect of the present invention is directed to providing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides which would improve hot strip rolling process by reducing cobble occurrence and improving the quality of the coil through innovating crop shear guide design and position.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is thus directed to a system for improving hot strip process in hot strip mills comprising:
roughing stage , finishing stage and coiling stage and involving crop shear guides and finishing mill entry guides ;
said crop shear guide comprising four positions involving Ambush, Centering ,Ingoing and an additional “Out Position” and said finishing mill entry guide comprising the positions Ambush, Centering and Ingoing.

A further aspect of the present invention is directed to a system for improving hot strip process in hot strip mills wherein said additional “Out Position” of the crop shear guide is adapted such that the strip with head end camber does not get caught between the finishing mill entry guide (centering) and the crop shear guide (Ingoing) and thus avoid the unwanted cobbles and in turn increased mill availability and productivity.

A still further aspect of the present invention is directed to a system for improving hot strip process in hot strip mills adapted such that when the finishing mill entry guide is at “Centering position” , the crop shear guide will be at “Out position”, said “Out position” involving transfer bar width and identified “Camber value”.

According to yet another aspect of the present invention is directed to a system for improving hot strip process in hot strip mills wherein the “Camber value” is derived from the finishing mill entry guide as soon as transfer bar head end is sensed.

The objects and advantages of the present invention are described in greater details with reference to the following non limiting accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: is the schematic diagram of finishing mill entry guides and crop shear guide configuration involving three positions in conventional hot strip mill process.

Figure 2: is the schematic diagram of crop shear guide configuration involving four positions according to the present invention in order to avoid cobble occurrence and improve quality of coils.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

The present invention relates to a system of crop shear guide and positions directed to reducing cobble occurrence and improve the quality of hot rolled and finished strip coil.

Reference is first invited to the accompanying Figure 1 that schematically illustrates the finishing mill entry guides and crop shear guide configuration involving three positions in conventional hot strip mill process.

The design and positions according to the initial design of the crop shear guide and finishing mill-1 entry guides have three positions namely Ambush, Centering and Ingoing - all these positions of guides operate sequentially. “Ambush position” of crop shear guides its initial position, as transfer bar head end enters into the guides. “Centering position” is the force mode in which the crop shear guides touches the strip until it experiences load of 0.5 tons or less than 20 mm strip width and keeps strip in the center. “Ingoing position” refers to the crop shear guide with some offset value. For example, Ingoing position, as shown in Figure-1, shows width of the strip 1000 mm an offset value of 250 mm. The finishing mill-1 entry guide position has similar sequence of operation except the load experience in “Centering position”. Figure-1 shows the schematic of crop shear and finishing mill-1 entry guides design and position before innovation.

The crop shear guide “Ingoing position” triggers the “Centering position” of the finishing mill-1 entry guide. The “Ingoing position” of crop shear guide remains at the same position when the finishing mill-1 entry guides at “Centering position”. Due to this design and position of guides, the strip with head end camber used to get caught between finishing mill-1 entry guide (Centering) and crop shear guide (Ingoing) resulting in cobbles. Even if it passes through finishing mill entry guides, it leads to quality issue like head end necking of the coil. Cobble results in decreased mill availability and reduced productivity, whereas head end necking results in bad quality of the coil as well as non uniform roll wear.

Reference is now invited to the accompanying Figure 2 that illustrate crop shear guide configuration involving four positions according to the present invention in order to avoid cobble occurrence and improve quality of coils. Additional one more position of the crop shear guide has been introduced in the new design to ensure the strip should not catch between crop shear and finishing mill-1 entry guides. The innovation involved by changing the crop shear guide design and position by introducing “Out position”. Under new design, the finishing mill-1 entry guide will be at “Centering position” and the crop shear guide will be at “Out position”. The “Out position” involves transfer bar width and newly innovated “Camber value”. This “Camber value” has been derived from the finishing mill entry guide as soon as transfer bar head end is sensed. For example, “Out position” which is indicated in Figure 2 shows width of the strip of 1000 mm and 350 mm Camber value. Figure 2 shows the schematic crop shear guides design and position after innovation.

The result of the invention as obtained by way of implementing the system of the invention is shown as comparison of mill availability and quality before, during and after innovation in the following Table 1.

Table 1.

Parameters Before innovation During Innovation After Innovation
Mill availability In 1 yr. In 1 yr. In 1 yr.
Cobbles 1000 1023 695
Number of slab extracted 139040 128173 165264
Mill utilization index,% 81.5 81.9 84.8
Quality
Number of coils produced 135229 124788 190211
Number of coils with Head end necking 583 408 537
%, improvement in head end necking 0.43 0.33 0.28

It is thus possible by way of the present invention to providing a system for improving hot strip process in hot strip mills involving crop shear guide and finishing mill entry guides by introducing a new position i.e. “out position” in crop shear guide other than the three conventional positions e.g. Ambush, Centering and Ingoing positions, in relation to the finishing mill-1 entry guide so as to feed a cambered strip at center to the finishing mill and thereby avoid occurrence of cobble and also head end necking of coil. The system of the invention would thus enhance mill availability and improved quality of coil in hot strip mill.

We Claim:

1. A system for improving hot strip process in hot strip mills comprising:
roughing stage , finishing stage and coiling stage and involving crop shear guides and finishing mill entry guides ;
said crop shear guide comprising four positions involving Ambush, Centering ,Ingoing and an additional “Out Position” and said finishing mill entry guide comprising the positions Ambush, Centering and Ingoing.

2. A system for improving hot strip process in hot strip mills as claimed in claim 1 wherein said additional “Out Position” of the crop shear guide is adapted such that the strip with head end chamber does not get caught between the finishing mill entry guide (centering) and the crop shear guide (Ingoing) and thus avoid the unwanted cobbles and in turn increased mill availability and productivity.

3. A system for improving hot strip process in hot strip mills as claimed in anyone of claims 1 or 2 adapted such that when the finishing mill entry guide is at “Centering position” , the crop shear guide will be at “Out position”, said “Out position” involving transfer bar width and identified “Camber value”.

4. A system for improving hot strip process in hot strip mills as claimed in claim 3 wherein the “Camber value” is derived from the finishing mill entry guide as soon as transfer bar head end is sensed.

5. A system for improving hot strip process in hot strip mills substantially as hereindescribed and illustrated with reference to the accompanying figures.

Dated this the 21st day of June, 2011
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)