JPS5890386A - Manufacture of hot coil for welded pipe - Google Patents

Abstract

PURPOSE:To save energy required for heating skelp by cooling hot rolled band steel at a specified cooling rate and coiling at specified coiling tension to a loose coil and thereby making the whole surface of the band steel black. CONSTITUTION:Hot rolled band steel is cooled to <=500 deg.C, preferably <=300 deg.C, at a cooling rate of >=20 deg.C/sec by a hot plate. Cooling of central part of the plate width is accelerated and the part is made as black as the edge part. Then, the steel is coiled to a loose coil at coiling tension of <=1kg/mm.<2>. Cooling of inside of the coil is quickened to restrain decarbonization and whitening is prevented to make the whole surface of the band steel balck. Consequently, the rate of heat absorption at the time of heating of skelp is improved and heating energy can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a hot coil for forge-welded pipes, which saves energy required for heating the skelp in the manufacture of forge-welded pipes.

Conventionally, hot coils μ for forge-welded pipes are rolled by a hot rolling mill (3) as shown in FIG.

After cooling to a temperature of ~j, tO℃, it is wound into a tight coil with a winding tension exceeding lt, and then the tight coil is rewound and slit into multiple strips. After forming the skeleton, a forge-welded pipe is manufactured as shown in FIG. That is, first, the skelp (6) is heated in a heating furnace (7), and then heated in a heating furnace (7).
After exiting the mold, air is blown onto both edges using a scalp blower (ε) to remove surface scale, and then passed through a vertical forming row/L/(9)K to form an oven tube (65).Then, this open tube ( 1) Welding-
While blowing air or oxygen from the horn V4 to both edge parts to further raise the temperature of the part, forge welding low yv (Il
1 to obtain a crimped tube, and then squeeze this tube by Jiro/
I/ (12,), (/12.)... to reduce the diameter to the desired diameter to form a finished product.

By the way, in the production of the above-mentioned hot coil, when the hot-rolled copper strip is cooled by hot run spray, the edge part of the steel strip, which tends to cool down, has a blackish surface compared to the center part of the strip width; The central part is white.

If the copper strip 1 with this color tone is then wound into a tight coil and cooled to room temperature, the inside of the coil (the central part of the plate for copper strips) will be less cold than the sides (edges for copper strips). The inside of the coil is decarburized and takes on a whiter color. The hot carp μ with this color tone was rewound, and the skelp, which was slit into multiple strips, was heated to an edge temperature of approximately /' J! in a heating furnace for forged welded pipes. Heating was carried out to ensure a temperature of 0°C, but there was a drawback that a large amount of energy had to be spent to heat the white squelp.

This MFi eliminates these drawbacks as much as possible, and is a hot coil 5! ! ! The purpose of this invention is to make it possible to save the energy required for heating by making the entire surface of the steel strip black in the manufacturing process.

In general, heating furnaces for forge-welded pipes are mainly heated by thermal radiation, but when heating with such a heating furnace, it is said that it is advantageous for the steel material to be heated to be darker in color in order to reduce energy consumption. I can do it. The blacker it is, the more
The heat absorption rate becomes good and the heating efficiency is increased.

Focusing on these points, the present inventors conducted experiments and studies on a method for blackening the surface of the skeleton 1, which is a steel material to be heated. It has been discovered that a copper strip with a black surface can be obtained by increasing the cooling rate of the steel strip after stripping and suppressing decarburization on the surface of the copper strip as much as possible, and that such a method is economical. The conclusion was reached that it is the most advantageous.

That is, the gist of the present invention is to cool a hot-rolled copper strip to a temperature of 500°C or less at a cooling rate of 20 ns or more, and then wind it into a μm tin coil shape with a winding tension of 'Z or less. , a method for manufacturing a hot coil for forge-welded pipes, which is characterized in that decarburization of the steel strip after winding is suppressed as much as possible, and the surface of the copper strip is made black.

In conventional hot coils for forge-welded pipes, the edges of the copper strip are black and the center of the width is white, as described above, but in the present invention, the copper strip after hot rolling is cooled at a cooling rate of 2004 or more. By doing so, the cooling of the central part of the board is also accelerated, resulting in the same black color as the edge part. Furthermore, by winding the steel strip at a temperature of 500°C or less, more preferably 300°C or less, unraveling becomes difficult to occur, and by winding the steel strip into a loose coil with a winding tension of 1 or less The internal cooling becomes faster, decarburization is suppressed, whitening can be prevented, and the entire surface of the copper strip becomes black. As a result, the heat absorption rate during squelp heating is improved and heating energy can be saved.

If the cooling rate of the foam band is less than 2o''786, the cooling of the central part of the copper band will be slow and the desired color tone will not be achieved, and the SOO
It is difficult to maintain the winding temperature below ℃.

If the winding temperature exceeds SOO℃, decarburization will be accelerated in the hot coil after winding, which is undesirable, and if the winding tension exceeds 1, the coil will become tight and the inside of the hot coil after winding will deteriorate. The cooling rate is as slow as 20"/@ or less, which is not preferable because the effect of suppressing decarburization is small.

According to the inventor's experience, hot rolled steel strip (J * thickness x / j
00 wm width), the steel strip was cooled in advance to ≠00 °C at a cooling rate of 3/1E7e by cooling water injection from a hot run spray, and then wound as a loose coil with a winding tension of 0.6~. When left to cool to room temperature,
A copper strip with a completely black surface could be obtained. Furthermore, these copper strips were cut into three 500 ts wide skelps, and each skelp was heated in a heating furnace in the forge-welded pipe manufacturing process to bring both edges of the skelp to t3jo°C. Also, about 3≠OX toJ
It was possible to make the fuel (C gas) basic unit of Kca Ton. This value is the fuel consumption rate in the case of 3r o K0
t compared to at/Ton.

% less. Therefore, the present invention can be said to be an extremely effective measure for saving the energy required for squelp heating in the manufacture of forge-welded pipes.

[Brief explanation of the drawings] Figure 1 is an explanatory diagram showing the hot coil manufacturing process, Figure 2 is an explanatory diagram showing the hot coil manufacturing process,
The figure is an explanatory diagram showing a forge-welded pipe manufacturing process. l: copper strip, 2: hot coil, 3: hot rolling mill, ≠: hot spray,! : Winder 1. t: Skelp, 7: Heating furnace, r: Skelp proa, Ri: Forming roll, lO: Welding horn, //: Forged M roll, 12: Squeezing roll

Claims (1)

[Claims] (/l) After cooling the copper strip after hot rolling to a temperature below SOO℃ at a cooling rate of 201 or more, it is wound into a loose coil shape with a winding tension of 1z or less, and the copper strip is removed after winding. A method for manufacturing a hot coil for forge-welded pipes, which is characterized by suppressing charcoal as much as possible and making the surface of the copper strip black.