Title of Invention

A SHIELD FOR REDUCING HEAT LOSS IN HOT ROLLED BARS IN STEEL PLANTS

Abstract

A shield for reducing heat loss in hot rolled bars in steel plants, characterised in that the shield comprises one outer rectangular metallic plate (9) and one inner rectangular metallic plate (10), which are held in position parallel to each other by anchor bolts and are of adjustable dimensions, such as herein described, with a gap (11) between the plates, which is packed with heat insulating materials, such as herein described, the plates being held together firmly along the periphery, length, width and diagonal thereof by means of mild steel structural angles (12), nuts and bolts, the shield being supported on beam (7) disposed before the finishing stand housing (6) and arranged to be held at a varying height above the roller table (4) used for hot rolling of bars.

Full Text

The present invention relates to a shield for reducing heat loss in hot rolled bars in steel plants. Considerable heat losses occur during hot rolling and transfer stages of producing hot strips from bars/slabs in the rolling mill of a steel plant. The maximum heat loss takes place, however, during the transfer of break-down bars from the last roughing stand to the finishing stand in a rolling mill, causing a temperature run down from the front end of the bar to its tail end, which may be as high as 80-100°C. This temperature run down leads to non-uniformity in hardness and affects also the other quality parameters of the rolled strips appreciably. At present, no suitable means is available for reducing the said heat loss in the rolling mill of a steel plant. The objective of the present invention is to provide a shield by using which the temperature run down of bars during their transfer from the last roughing stand to the finishing stand in a rolling mill can be reduced to 20-25°C. The other objective is to minimise the percentage of the kick backs of blooms (due to temperature drop) in Blooming and Billet Mills, thereby improving the productivity and quality of rolled products. The invented shield has been designed by optimising the following operating parameters of the laboratory modules: - 2 - (i) dimensions of the shield; (ii) height of the shield above the roller table; (iii) material used for fabricating the shield; (iv) type and thickness of heat insulating materials used in the shield. The invention is described fully and particularly in an unrestricted manner with reference to the accompanying drawings in which - Figure 1 is a view of the general arrangement of the heat shield disposed in different position over the roller table of a hot strip mill; Figure 2 is the front elevation of one embodiment of the invented shield mounted over the roller table in a hot strip mill; Figure 3 is the view of Section A-A in Figure 2; and Figure 4 is the graph showing the variation in temperature run down of bars with retention time over the roller table, with and without using the shield. Referring to Fig. 1, the heat shield (1) is in the fully raised position, heat shield (2) is in partly raised position and heat shield (3) is in fully lowered position with respect to the upper surface of roller table (4). Referring to Figs. 2 and 3, the invented heat shield module is shown to be in the fully raised position (1); it can be in the partly raised position (2). The shield is supported on beam (7) disposed near the finishing stand housing (6). The - 3 - bars to be rolled are allowed to move from the last roughing stand (5) towards the finishing stand housing (6) over the roller table (A) and to be covered by the shield module for reducing the temperature run down of the bars during their transfer from the last roughing stand to the finishing stand housing. The heat shield module comprises one outer plate (9) made of rectangular mild steel sheet and one inner plate (10) made of rectangular stainless steel sheet of type SS 310S. which are held in position parallel to each other by anchor bolts. The gap (3.1) between the outer and inner plates is packed with heat insulating materials (not shown). The typical thickness of the outer plate is 8.0 mm and that of the inner plate is 0.8 to 1.2 mm. The outer and inner plates are held together firmly along the periphery, length, width and diagonal thereof by means of mild steel structural angles (12) of typical sectional dimensions 75 x 75 x 5 mm, and nuts and bolts. The shield is designed to accommodate heights between 250-400 mm above the roller table during the normal rolling operation at Hot strip mills. Different modules of the shield were fabricated and their effectiveness in reducing the temperature run down of the rolled bars was studied for determining the optimum design parameters for construction of the shield. Module 1 was made by sandwiching the gap between the outer and inner plates with 5.0 mm thick ceramic fibre as the heat insulating material. - 4 - Module 2 was made by providing 10.0 nun thick air gap as the heat insulating material between the outer and inner plates. Module 3 was made by sandwiching the gap between the outer and inner plates with 10.0 mm thick ceramic wool as the heat insulating material. Experimental bars of dimensions 750x250x20 mm were rolled using the modules 1, 2 and 3 of shields. Holes for inserting thermocouples were made in the bars for recording the surface temperature thereof. At different preheating temperatures of the bars, the effect of the shield in reducing the temperature run down of the bars during their movement from the last roughing stand to the finishing stand housing was evaluated by recording the variation in temperature along their length during their movement. From the analysis of the test results it is found that module 3 experienced minimum temperature run down of the bars. The module 4 of the shield was then designed and constructed having the features given below s (i) Dimensions of the shield - 1500 x 1000 x 120 mm (ii) Thickness of heat insulating ceramic wool - 50 mm (iii) Height of the shield above the roller table - 350 mm. Thermocouples were mounted at three different positions on the shield, namely, at the inner plate, at the side panel and at the outer plate. Temperature was recorded continuously during rolling of 25/27.2 mm thick bars. Altogether 100 coils were monitored during the experimental runs. - 5 - The results obtained were found to be very encouraging. Based on the results obtained with module 4 shield, the design and construction of an industrial module of the shield were undertaken for heat conservation during double-piece rolling of blooms of length 5.5 m (max) supplied from 602/601 mm sq ingots wherein during processing of the first piece, the second piece is kept waiting on the roller table for 2 to 3 or 10 minutes defending upon the mill operating conditions. The temperature drop of the second piece during this waiting period was as high as 80 to 100°C. The features of module 5 of the shield designed are stated below s (i) Dimensions of the shield - 6000 x 1500 x 500 mm (ii) Thickness of the heat insulating ceramic wool - 75 mm (iii) Height of the shield above the roller table - 350 mm. The performance of the module 5 shield was studied under industrial production conditions in the rolling mill of a steel plant. The variation in temperature run down of rolled bars with time of their retention on the roller table, with and without using the shield, is shown in Fig. 4 from which it is found that while the temperature run down is 60 to 90°C without using the shield, it could be reduced to 20 to 25°C by using the shield. - 6 - We Claim :- 1. A shield for reducing heat loss in hot rolled bars in steel plants, characterised in that the shield comprises one outer rectangular metallic plate (9) and one inner rectangular metallic plate (10), which are held in position parallel to each other by anchor bolts and are of adjustable dimensions, such as herein described, with a gap (11) between the plates, which is packed with heat insulating materials, such as herein described, the plates being held together firmly along the periphery, length, width and diagonal thereof by means of mild steel structural angles (12), nuts and bolts, the shield being supported on beam (7) disposed before the finishing stand housing (6) and arranged to be held at a varying height above the roller table (4) used for hot rolling of bars. 2. The shield as claimed in claim 1, wherein the outer plate is made of thick mild steel sheet, the inner plate is made of thick stainless steel sheet of type SS 310 S, the heat insulating material used is ceramic wool and the shield is capable of being held at a varying height of 250-400 mm above the roller table during the rolling operation. 3. The shield as claimed in claim 1 or 2, wherein the shield is provided with heat insulating material of thickness 50 mm and held at a height of 350 mm above the roller table during the rolling operation. - 7 - - 8 - 4. The shield as claimed in claim 1 or 2, wherein the shield is provided with heat insulating material of thickness 75 mm and held at a height of 350 mm above the roller table during the rolling operation. A shield for reducing heat loss in hot rolled bars in steel plants, characterised in that the shield comprises one outer rectangular metallic plate (9) and one inner rectangular metallic plate (10), which are held in position parallel to each other by anchor bolts and are of adjustable dimensions, such as herein described, with a gap (11) between the plates, which is packed with heat insulating materials, such as herein described, the plates being held together firmly along the periphery, length, width and diagonal thereof by means of mild steel structural angles (12), nuts and bolts, the shield being supported on beam (7) disposed before the finishing stand housing (6) and arranged to be held at a varying height above the roller table (4) used for hot rolling of bars.

Documents:

01395-cal-1997 abstract.pdf

01395-cal-1997 assignment.pdf

01395-cal-1997 claims.pdf

01395-cal-1997 correspondence.pdf

01395-cal-1997 description(complete).pdf

01395-cal-1997 drawings.pdf

01395-cal-1997 form-1.pdf

01395-cal-1997 form-2.pdf

01395-cal-1997 form-3.pdf

01395-cal-1997 pa.pdf

1395-cal-1997-granted-abstract.pdf

1395-cal-1997-granted-assignment.pdf

1395-cal-1997-granted-claims.pdf

1395-cal-1997-granted-correspondence.pdf

1395-cal-1997-granted-description (complete).pdf

1395-cal-1997-granted-drawings.pdf

1395-cal-1997-granted-examination report.pdf

1395-cal-1997-granted-form 1.pdf

1395-cal-1997-granted-form 2.pdf

1395-cal-1997-granted-form 3.pdf

1395-cal-1997-granted-letter patent.pdf

1395-cal-1997-granted-pa.pdf

1395-cal-1997-granted-reply to examination report.pdf

1395-cal-1997-granted-specification.pdf