JPS62103324A - Cooling method for steel bar or wire - Google Patents

Abstract

PURPOSE:To permit thorough draining and to make cooling with high accuracy by specifying the amt. of cooling water and a draining in the stage of subjecting the surface layer part of a wire or bar material by water spraying in succession of hot rolling and recuperating the surface layer part while conveying the wire or bar material in the atm. after draining. CONSTITUTION:The surface layer part of the bar or wire material M hot rolled with a finishing mill 1 is quickly cooled by the water spray cooling in a cooling box 7 array of a cooler 3 at the cooling pattern controlled from the Ar 1 transformation temp. or above down to the bainite transformation temp. or below in succession of the hot rolling. A large amt. of the cooling water is supplied to the front stage of the box 7 and a small amt. of the cooling water to the rear stage of the box 7. The material M enters a draining device 11 where the cooling water sticking to the material M is blown away by the back injection of the cooling water from a device 12 for back injection of the cooling water. The remaining water sticking to the material is successively blown off by the high-pressure air from an air blowing device 13. The marginal water wetting length of the wire or bat material to be introduced into the draining device is made extremely short by successively decreasing the cooling water according to the above-mentioned method, by which the thorough draining is made possible.

Description

[Detailed description of the invention] (1f: Field of use on the beam) The present invention relates to a method for cooling steel rods and wires.

(Prior art) Direct surface layer structure (surface quenching) of a steel bar or wire rod is achieved by hot rolling, followed by water jet cooling to heat the surface layer of the bar or wire rod to a temperature higher than the Arl change temperature. The cooling pattern is controlled (quick cooling) to below the bainite transformation temperature, preferably from above the Az transformation temperature to below the martensitic transformation temperature.In other words, the heat transfer coefficient on the surface of the rod and wire is increased to improve the radial heat conduction of the rod and wire. Cooling is done so that the rate is rate limiting.

Here, thermal conductivity rate-limiting refers to a situation in which when the heat transfer coefficient αkcal/+2h'c on the surface of the rod and wire increases, the heat conduction (thermal diffusion) in the radial direction of the rod and wire cannot keep up. Enter the thermal conductivity of the wire in kcal
/m2h'c, and the radius of the cup wire is r, and the state yE is such that input/r<α.

After quenching so that thermal conductivity is the limiting factor, the wire rods are blown with high-pressure air to drain water. Large diameter rods and wires are drained and subsequently cooled by water injection. It is known that the cooled rods and wires are transported in the atmosphere between a water cooling device and a cooling bed or a winder, and the surface layer is recuperated by heat conduction from the high temperature core.

(JP-A No. 4L134513, JP-A No. 51-90912
No., Japanese Patent Application Laid-Open No. 1-51-99819) The water cooling system consists of a plurality of cooling units arranged in a tanodem (
It consists of a cooling box). Each cooling box is equipped with an annular JV1 injection nozzle or a reverse injection nozzle, from which cooling water is injected at high pressure onto the wire rods. Further, the above-mentioned draining device is arranged in the middle of the cooling box row.

(Problems to be Solved by the Invention) Conventionally, cooling water was supplied to each cooling box so that the rods and wires were cooled at approximately the same large wood density. but,
In order to rapidly cool the rods and wires from the rolling temperature, a large amount of cooling water must be injected onto the rods and wires, so in order to completely drain the water during cooling, use a water drainer. 1! I had to install several in succession. Therefore, in order to aid heat recovery by draining water and cool the rod and wire according to the required cooling rate, there is a drawback that the waste zone becomes long. In addition, even if the surface temperature of the rod and wire rod decreased after quenching started, a large amount of cooling water was supplied to increase the heat transfer coefficient, but the radial thermal conductivity of the rod and wire rod was already rate-limiting. Even if kIA water barrier was supplied, there was a drawback that it was hardly used effectively.

(Means for Solving the Problems) The rod and wire cooling method of the present invention takes into consideration that the heat transfer coefficient increases as the rod and wire surface temperature decreases while maintaining the radial thermal conductivity of the rod and wire. Then, the rod and wire are cooled while decreasing the amount of cooling water as the rod and wire advances.

In order to reduce the amount of cooling water as the rods and wires advance, the amount of cooling water supplied is gradually reduced from the upstream cooling box. Next, cooling water is injected back onto the wire rod at the draining position, and air is then continuously blown to drain the rod and wire.

(Function) Since the amount of cooling water decreases as the rod and wire advances, the amount of cooling water adhering to the rod and wire at the entry side of the drainer is smaller than in the conventional method. In addition, by injecting the cooling water back onto the wire rod, the cooling water is directed toward the upstream side, and the cooling water is prevented from adhering to the wire rod and being carried into the position of the air blower. Therefore, only a small amount of cooling water is removed by air blowing, and the water is sufficiently drained. In addition, the heat transfer coefficient on the rod and wire surface is lower than before because the amount of cooling water is reduced, but the heat transfer coefficient is about 2XlO'kcal/m2h'c or more, which is necessary for cooling the rod and wire under the thermal conductivity rate-limiting condition in the radial direction. is ensured, so the number of structures in the surface layer of the rod and wire rod is hardly affected.

(Example) FIG. 1 shows an outline of a cooling device used in the method of the present invention. As shown in the drawings, a cooling device 3 and a winding machine 21 are disposed following the finishing mill 1.

The cooling device 1 is divided into a quenching zone 4 and a quenching and recuperation zone 5, including a plurality of cooling boxes 7 arranged in a tough row.
It's getting better. Each cooling box 7 is equipped with an annular forward injection nozzle or reverse injection nozzle (none of which is shown). The rods and wires M running through the cooling box 7 are cooled by jetting cooling water from around them through nozzles.

A drainer is disposed approximately in the center of the seven rows of cooling boxes, that is, between the quenching zone 4 and the quenching and recuperation zone 5. The draining device 11 includes a cooling water reverse injection device 12,
The air blower adjacent to the outlet side of this consists of a device ff113. The wire rod M, which has been cooled in the quenching zone 4 and entered the draining device 11, is first sent to the cooling water reverse injection device 12, where the cooling water adhering to the rod or wire M is blown off by reverse injection of cooling water. Subsequently, the air blowing device 13 blows off the residual adhering water with high-pressure air.

Note that a quenching end temperature detector 15 and a recuperation temperature detector 17 are disposed on the outlet side of the drainer 11 and the inlet side of the winder 21, respectively. Both temperature detectors15.17
Based on the measurement results, the amount of cooling water supplied to each cooling box 7 is adjusted, and the rods and wires M are cooled at a required cooling rate.

When cooling water is injected onto the rod or wire, the rod or wire is cooled by heat transfer from the rod or wire to the cooling water, but the cooling due to heat transfer in this case is rate-limited by radial thermal conductivity. therefore,
As shown in Figure 2, the surface temperature was carefully kept at a low F from the start of cooling.
do. In the example shown in Fig. 2, approximately 0.7 se is elapsed from the start of cooling.
After c elapses, the temperature becomes 250°C or less. Furthermore, the heat transfer coefficient on the rod and wire surface is a function of the rod and wire surface temperature, and increases as the temperature decreases. This is because the rod and wire rods are cooled by the upward heat transfer of the cooling water, and during cooling the heat transfer changes from film boiling to hidden nucleate boiling heat transfer. Equation (1) shows an example of the influence coefficient of the heat transfer coefficient depending on the rod and wire surface temperature Ts.

Influence fik=exp(3,28-0,00494s)
...-(+) As is clear from equation (1), the heat transfer coefficient increases exponentially as the rod and wire surface temperature Ts decreases.

Therefore, as the rod and wire temperature decreases, i.e., the equation (
Even if the amount of cooling water is reduced in inverse proportion to the influence coefficient ak obtained in 1), the heat transfer coefficient required for surface direct quenching cooling is approximately 2.
0,0OOkca! /ll2h'c can be obtained. FIG. 3 shows an example in which the amount of cooling water is reduced as the rod and wire surface temperature Ts decreases based on equation (1). According to FIG. 3, the amount of cooling water when the rod surface temperature is 500° C. may be 80 (approximately 175 of the amount of cooling water when the temperature is 1'c).

From the above, the front stage of the cooling device supplies a large amount of cooling water to the cooling box, and as the surface temperature decreases.

That is, a small amount of cooling water is supplied to the downstream cooling box along the straight line in FIG. Cooling water is supplied to the cooling box in which the surface temperature of the rod and wire is approximately 250° C. or less in an amount sufficient to suppress surface recuperation due to heat conduction from the center of the rod and wire.

When the amount of cooling water is gradually reduced as described above, the length of the water-wetted edge of the #5 wire introduced into the draining device becomes extremely short. As a result, the load on the draining device is small and water can be drained sufficiently.

Note that when the amount of cooling water (water density) decreases.

Since it becomes difficult to supply cooling water uniformly in the circumferential direction of the rod and wire rod, a method in which water is directly jetted against the rod and wire rod is not preferable. Therefore, it is preferable that the cooling box in the latter stage uses a cooling method having a swirling flow in the inner tube, an immersion cooling method, or a mist cooling method.

(Effects of the Invention) Since water can be sufficiently drained during cooling, the rod and wire rod can be cooled with high precision according to the required cooling rate, and the amount of cooling water can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a cooling device implementing the method of the present invention;
FIG. 2 is a diagram showing an example of a cooling curve of a wire rod, and FIG. 3 is a diagram showing a relationship between the surface temperature of the wire rod and the 1π reduction ratio of cooling water. l... Finishing rolling mill, 3... Cooling device, 7... Cooling box, 11... Draining device, 12... Cooling water reverse injection device, 13... Air blowing device, 21... ... Winding machine.

Claims (1)

[Claims] Following hot rolling, the surface layer of the rod and wire rod is cooled by water jet cooling to control the cooling pattern from above the Ar_1 transformation temperature to below the bainite transformation temperature, and while being conveyed in the atmosphere, the surface layer is cooled by heat conduction from the high temperature center. In this method, the rod and wire are cooled while reducing the amount of cooling water as the rod and wire advances, and cooling water is injected back onto the rod and wire, and air is continuously blown to drain the rod and wire. A method for cooling steel rods and wires.