Metal deforming – With cleaning – descaling – or lubrication of work or product
Reexamination Certificate
2000-02-11
2001-07-10
Butler, Rodney A. (Department: 3725)
Metal deforming
With cleaning, descaling, or lubrication of work or product
C072S201000
Reexamination Certificate
active
06257034
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system and a method for preventing scale defects on a finish rolling line of hot rolling equipment by descaling or cooling a surface of a material to be rolled (hot rolled steel plate) to suppress the formation of scale (oxide film).
2. Description of the Related Art
In hot finish rolling, oxide film may grow after scale removal at an entry side of a row of finishing mills. Depending on the thickness of the oxide film, scale defects occur in a hot rolled steel plate to decrease the yield of the product and deteriorate its surface quality. To suppress the growth of oxide film, it has been performed empirically to set the temperature of the steel plate surface, or to control the temperature of the steel plate surface at the entry side of the row of finishing mills. When the growth of oxide film was suppressed by any of these conventional methods, the hot rolled steel plate was overcooled, or occurrence of scale defects was not fully prevented.
FIG. 8
is a view showing another conventional method for preventing scale defects. In this drawing, a hot rolled steel plate
1
, as a material to be rolled, passes, while being rolled, between a first stage rolling mill F
1
and a seventh stage rolling mill F
7
from an entry side to a delivery side (from left to right in the drawing). At a stage forward of the first stage rolling mill F
1
, a scale breaker FSB is placed for removing oxide film of the hot rolled steel plate
1
rough rolled by a roughing mill (not shown). High pressure water from a header
2
of the scale breaker FSB removes oxide film on the surface of the hot rolled steel plate
1
. At an entry side of each of the second stage rolling mill F
2
and the third stage rolling mill F
3
, descaling devices
12
,
13
are placed. These descaling devices
12
,
13
jet spray water when the thickness of oxide film on the surface of the steel plate is more than 10 &mgr;m. After being so descaled, the steel plate is rolled.
However, when the descaling devices are arranged between the rolling mills as in
FIG. 8
to perform descaling for oxide film more than 10 &mgr;m thick, the thickness of oxide film at the entry side of the third stage rolling mill F
3
may exceed 5 &mgr;m as shown in FIG.
9
. Finish rolling performed at an oxide film thickness of more than 5 &mgr;m results in the occurrence of scale defects on the surface of the hot rolled steel plate
1
, debasing the quality of the product. A thermometer
11
is provided at the entry side of the row of finishing mills so that the thickness of oxide film is predicted from the temperature of the steel plate detected, as well as the speed of the steel plate. Actually, the distance from the position of temperature detection to the descaling devices is so short that descaling control tends to be performed with some delay.
SUMMARY OF THE INVENTION
The pre sent invention controls an operating state of a descaler or a cooler placed between finishing mills. By so doing, the invention aims to restrict the thickness of oxide film, which occurs on a material to be rolled, to not more than a limiting oxide film thickness, thereby preventing the occurrence of scale defects of the material to be rolled. The invention also intends to suppress overcooling of the material to be rolled. Through these measures, the invention is to improve the quality of the product.
According to a first aspect of the present invention designed to attain the above-described objects, there is provided a system for preventing scale defects during hot rolling by hot rolling equipment having a scale breaker provided at an entry side of a finishing mill line composed of a plurality of rolling mills arranged in tandem, comprising:
a descaler provided between a first stage rolling mill and a second stage rolling mill of the finishing mill line;
a cooler, provided between the second stage rolling mill and a third stage rolling mill of the finishing mill line, for cooling a material to be rolled; and
a control device for controlling the descaler and the cooler to be selectively driven such that neither of the descaler and the cooler is actuated, one of the descaler and the cooler is actuated, or both of the descaler and the cooler are actuated, according to rolling conditions,
whereby the material to be rolled is rolled, with an oxide film thickness of the material at an entry side of the third stage rolling mill being restricted to not more than a limiting oxide film thickness.
Since rolling is performed, with the thickness of oxide film at the entry side of the third stage rolling mill being restricted to the limiting oxide film thickness or less, scale defects of the material to be rolled can be prevented, and a drop in the plate temperature of the material to be rolled can be minimized. Furthermore, the absence of scale defects can lead to an improved quality and an increased yield of a rolled product.
According to a second aspect of the present invention, there is provided a system for preventing scale defects during hot rolling by hot rolling equipment having a scale breaker provided at an entry side of a finishing mill line composed of a plurality of rolling mills arranged in tandem, comprising:
a descaler provided between a first stage rolling mill and a second stage rolling mill of the finishing mill line;
a descaler provided between the second stage rolling mill and a third stage rolling mill of the finishing mill line; and
a control device for controlling the descalers to be selectively driven such that neither of the descalers is actuated, one of the descalers is actuated, or both of the descalers are actuated, according to rolling conditions,
whereby a material to be rolled is rolled, with an oxide film thickness of the material at an entry side of the third stage rolling mill being restricted to not more than a limiting oxide film thickness.
According to this aspect of the invention, the same effects as those obtained by the first aspect of the invention are obtained.
In the above aspects, the limiting oxide film thickness may be 5 &mgr;m. Thus, scale defects of the material to be rolled can be prevented reliably. Moreover, water at a low pressure of at least about 70 kgf/cm
2
may be jetted by the descaler. Thus, economic descaling can be performed.
Besides, the control device may function as follows:
The control device computes the oxide film thickness of the material at the entry side of the third stage rolling mill based on a temperature of the material at a delivery side of a roughing mill, and if the computed oxide film thickness is not more than the limiting oxide film thickness, the control device actuates neither of the descaler and the cooler;
if the computed oxide film thickness is more than the limiting oxide film thickness, the control device incorporates the descaler into operating conditions and computes the oxide film thickness, and if the computed oxide film thickness is not more than the limiting oxide film thickness, the control device actuates only the descaler;
if the oxide film thickness computed after incorporating the descaler into the operating conditions is more than the limiting oxide film thickness, the control device incorporates both the descaler and the cooler into the operating conditions and computes the oxide film thickness, and if the computed oxide film thickness is not more than the limiting oxide film thickness, the control device actuates both the descaler and the cooler; and
if the oxide film thickness computed after incorporating both the descaler and the cooler into the operating conditions is more than the limiting oxide film thickness, the control device actuates both the descaler and the cooler while increasing the ability of both the descaler and the cooler.
Thus, the descaler and the cooler are controlled to be efficiently operative according to rolling conditions, so that scale defects in the material to be rolled can be prevented reliably.
Alternatively, the control device may have the following functions: The control d
Choi Woon Yong
Fukumori Junso
Kawamizu Tsutomu
Kaya Akira
Lee Jong Won
Butler Rodney A.
Mitsubishi Heavy Industries Ltd.
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