JPS6057491B2 - Hearth roll in continuous annealing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hearth roll for a continuous annealing furnace for metal strips, and more specifically, for passing metal strips such as cold rolled steel strips at a constant speed without meandering in a continuous annealing furnace for metal strips. It concerns the hearth roll that can be done.

In recent years, the threading speed of continuous annealing furnaces has increased, and meandering of the strip inside the furnace has become a problem.

For example, the key point in the operation of a continuous annealing furnace is to control the temperature of the cold-rolled strip to be threaded according to a predefined heat cycle. It is necessary to control the sheet threading speed as specified. In this case, the temperature of the continuous annealing furnace can be controlled with sufficient precision using known technology, but the threading speed is problematic due to the meandering of the cold rolled strip inside the furnace, making it difficult to thread the strip as specified. speed cannot be achieved. That is,
Even with the same coil, the shape of the cold-rolled strip changes slightly,
Not adaptable to hearth rolls affected by heat, or
If the tension control for the cold-rolled strip, which expands and contracts due to heating and cooling, does not match the cold-rolled strip, the specified threading speed cannot be achieved, and as a result, it is difficult to prevent the cold-rolled strip from meandering in the furnace. is strongly desired. Generally, one of the methods to prevent meandering of cold-rolled strip is to
Efforts are being made to improve the shape of hearth rolls.

For example, FIGS. 1a, b, and c are front views of examples of conventional meandering prevention hearth rolls, in which each hearth roll 1 is tapered to provide a centering effect. Accordingly, the meandering of the strip is slightly improved. However, even with this shape of the hearth roll, the shape changes greatly due to heat, and therefore it is not possible to achieve a sufficient effect in preventing meandering. In particular, in the heating zone, the cold-rolled strip comes into contact with the hearth roll in a cold state, so the contact area of the cold-rolled strip in the center of the hearth roll is cooled, while the tapered parts at both ends expand due to the heat inside the furnace. The degree of taper becomes loose and the centering effect decreases, and therefore meandering prevention is not sufficiently improved. From this point of view, for example, as described in Japanese Patent Publication No. 54-7244, the hearth roll is tapered, and the uneven portion 2 is formed by shot blasting or the like at the central contact area of the cold rolled strip. (see Figure 2) has been proposed. According to this hearth roll, the friction coefficient of the cold-rolled strip during passing increases due to the uneven portion 2 at the center of the hearth roll, so the cold-rolled strip does not slip between the hearth roll and meandering is prevented. can. Furthermore, since the uneven portion 2 is provided only in the central portion of the hearth roll, centering force exceeding the allowable value does not occur on both ends of the cold-rolled strip due to the taper portion of the hearth roll, so that so-called heat buckling occurs. The occurrence of this is also prevented. In addition, here, the so-called heat buckle is caused by the strong centering force from the edge of the cold-rolled strip.
Wrinkles occur in the center of the cold-rolled strip during threading, and this wrinkling is indicated. However, even if the meandering of the cold-rolled I strip is considerably improved by the hearth roll having the above configuration, the following problem still remains.

First, since the hearth roll itself has low high-temperature hardness, the uneven portion at the central portion of the hearth roll wears out rapidly, and as the amount of cold rolled strip increases,
The uneven portion becomes smaller than the specified value.

For example, Figure 3 shows the relationship between the number of days of use and the meandering prevention effect when the hearth roll shown in Figure 2 is used.As is clear from this Figure, the meandering prevention effect of the strip increases with the number of days of use. It can be seen that the number of troubles is significantly reduced, and the trouble time is greatly increased. Therefore, as a measure to prevent this wear,
For example, it is possible to roughen the surface by sandblasting to form uneven parts, and then apply hard chrome plating to that surface to increase the surface hardness, but the normal operating temperature of hearth rolls can reach up to 900'C. Therefore, even hard chrome plating does not have sufficient high-temperature hardness, resulting in increased wear on the uneven parts. That is, if you closely observe this, you will see that the tops of the ridges of the uneven portion are worn away, and even if the ridge-forming member is made of hard chrome plating, it can be seen that the hardness at high temperatures does not hold high. Second, since the meandering amount of the cold-rolled strip varies depending on the strip passing speed, the degree of the unevenness of the uneven portion corresponding to the center of the hearth roll must be changed.

In other words, Tokko Akira? -7244 publication describes the surface roughness range as center line average roughness of 0.2 to 5.
．． Although it is set to 0μ, this depends on the threading speed.
It is necessary to distinguish the appropriate roughness. The present invention aims to solve the above-mentioned drawbacks, and specifically, even when used for a long time,
To propose a hearth roll whose meandering prevention effect is not impaired.

Hereinafter, the hearth roll according to the present invention will be explained in detail with reference to the drawings.

First, FIG. 4 shows a continuous annealing furnace equipped with a hearth roll 3 according to one embodiment of the present invention. In this continuous annealing furnace, the cold rolled strip 4 is passed through the hearth roll 3 into a heating zone 5, The strip 4 passes through each chamber such as a soaking zone 6, a rapid cooling zone 7, a slow cooling zone 8, and a final cooling zone 9.
is continuously annealed by heating, soaking, and cooling.

The hearth roll 3 that guides the cold rolled strip 4 in this way
is usually about 804 mm, and a plasma arc sprayed layer 10 is provided at the center of each hearth roll 3 as shown in FIG. Next, in the hearth roll 3 having this configuration, the plasma arc sprayed layer 10 (hereinafter simply referred to as the sprayed layer 10) is used.

) is composed of a metal welding layer 10b and a metal compound 10a, the metal compound 10a is embedded and supported in the metal welding layer 10b, and a part of the metal compound 10a is made to protrude from the metal welding layer 10b and is thermally sprayed. The surface of the layer 10 is structured in an uneven manner. At this time, the metal compound has excellent wear resistance at high temperatures, and from this point of view, tungsten carbide (hereinafter referred to as WC) or the like, which has high high temperature hardness, is preferable. In addition, when it is desired to embed WC, cobalt is used as the weld metal and WC is applied to the surface of the hearth roll.
It can be formed by plasma arc spraying so that a portion of C protrudes from the surface.

That is, when particles 10a of a hard metal compound such as WC are supported on the sprayed layer 10 by a metal welding layer 10b made of CO, the surface roughness of the sprayed layer 10 is equal to the size of the particles 10a of the metal compound such as WC. In addition, metal compound particles with high high temperature hardness such as WC particles 1
0a (3000 Hv or more at high temperature for WC particles), the surface can be easily formed into an uneven shape.

Therefore, even if the cold-rolled strip is annealed for a long time, the metal compound particles 10a are hardly worn away during the annealing, and the cold-rolled strip always maintains a sufficient coefficient of friction with the sprayed layer. The plate can be threaded with this method, and meandering can be sufficiently prevented.
Even when adjusting the surface roughness of the sprayed layer to the following appropriate conditions, it can be adjusted by adjusting the size of the metal compound particles 10a, and the surface roughness can be adjusted to suit the passing speed of the cold-rolled strip. Furthermore, the sprayed layer 10 has an effective width L(7) of the hearth roll 3.
It is sufficient to form about 115 to 213L. The surface roughness of the sprayed layer 10 is the centerline average roughness (Ha), which is determined as follows in relation to the thickness (t) of the cold-rolled strip.

(a) If the plate thickness (t) is 0.6Tm or more, 11100S
≦Se≦71300XS+2 (b) Plate thickness (t) 0.6T1r! ! If less than t, 11
200S≦Excitation≦1160S+2 where S is the threading speed (m/m) of the metal strip.

If the surface roughness is determined in relation to the plate thickness, plate threading speed, etc. as described above, meandering of the metal strip can be sufficiently prevented and the metal strip can be passed at a constant speed.

Next, examples will be described.

Example 1 First, the dimensions shown in Fig. 5 (L = 1500 m, .D1 = 5
The center line average roughness (
A plasma arc sprayed layer 10 having a thickness of 4 μm was formed using the following materials.

This thermal sprayed layer 10 is made by spraying WC particles in a CO solvent using a plasma arc.For comparison, a hearth roll of the same size is subjected to shot peening under the same conditions to create unevenness. The surface was plated with hard chrome, and this was used as a comparative example. When these two hearth rolls were continuously used at 700 to 800°C and the usage period until the surface roughness of the sprayed layer and the uneven portion reached 0.8 μm, the one according to the present invention was 546.
14 days for the comparative example.

Example 2 For the hearth roll according to the present invention in Example 1, the thickness (t) of the cold-rolled strip and the passing speed (m/min) were varied, and the appropriate surface roughness of these and the thermal sprayed layer was determined. However, the results shown in Figure 7 were obtained (in addition, when the operating temperature is 400 to 800°C, and t≧0.6m,
In Figure 5, Mr. = 790 顛φ, DENI 794T1gRφ, L
= 1500m hearth roll o) 0 Also, the 7th
In the figure, the dashed line range is t≧0.6m, and the solid line range is t<
In the optimum range of this test result, the upper limit of the surface roughness is the limit of heat buckling caused by an increase in the restraining force of the strip, and the lower limit is the limit of the occurrence of meandering of the strip. I was asked.

From FIG. 7, it can be seen that the relationship between the threading speed and the surface roughness is such that the faster the threading speed, the greater the amount of meandering of the strip, and the more likely slippage occurs between the roll and the strip. As explained in detail above, since the present invention is provided with a plasma arc sprayed layer in which metal compound particles are supported by a welding layer in the central portion, when applied to a continuous annealing furnace, The life of the roll can be greatly extended.

In addition, product yield is improved due to fewer troubles caused by meandering. That is, in the conventional example, the yield was reduced by about 0.12% due to problems caused by meandering of the strip.
According to the present invention, this amount is approximately 0.04%. ) Brief description of the drawings Figures 1A, b and c are front views of conventional hearth rolls, Figure 2 is a front view of an improved hearth roll from the conventional example, and Figure 3 is shown in Figure 2. A graph showing the relationship between the number of days the hearth roll is used and the number of line stops due to meandering of the cold-rolled strip. FIG. 4 is a layout diagram of an example of a continuous annealing furnace. FIG. A front view, FIG. 6 is an enlarged cross-sectional view of the plasma arc sprayed layer,
FIG. 7 is a graph showing the relationship between maximum sheet passing speed and surface roughness in the hearth roll of the present invention.

Claims (1)

[Claims] 1. A hearth roll equipped with a plasma arc sprayed layer in the center, which is installed in a continuous annealing furnace that heats, soaks, and then cools a metal strip to continuously anneal it. The metal compound particles are embedded in the metal welding layer so that a portion thereof protrudes from the surface, and the surface is uneven, and the centerline average roughness (Ha) of the surface particle size of the sprayed layer is (a) When the metal strip thickness is 0.6 mm or more, 1/100S≦Ha≦7/3
00×S+2 (b) When the metal strip thickness is 0.6 mm or less, 1/200S≦Ha≦1/60S+2 However,
A hearth roll in a continuous annealing furnace for metal strip, characterized in that S is the threading speed (m/m) of the metal strip.