JPS61150761A - Carrying roller preventing heat loss from high temperature steel billet - Google Patents

Abstract

PURPOSE:To prolong the life of rollers and to reduce heat loss from high temperature steel billet during transportation of the billet by providing a heat resistant hard film having a heat transfer coefficient less than a specific value and a thickness in a specific range to the peripheral surface of metal rollers carrying high temperature billet through a backing layer. CONSTITUTION:The heat resistant hard film having <=0.015cal/cm.s. deg.C heat transfer coefficient and 2-20mm thickness is provided closely to the peripheral surface of rollers carrying high temperature billet through the backing layer being an Ni or Co base autogenous smelting alloy of about 0.05-2.0mm thickness. The film is recommended to be a ceramic or cermet film. Any treatment such as thermal spraying, plasma spraying, chemical deposition, or plating is allowable to form the film. The film reduces temperature decrease of the billet during transportation and prolongs the life of the rollers.

Description

[Detailed Description of the Invention] (Industrial Application Field) Slab support rolls, guide rolls, bending rolls, pinch rolls, etc. in continuous casting machines, table rollers in hot rolling mills, etc. that are in contact with high-temperature steel slabs. The metal rollers that operate during this period will be collectively referred to as conveyance rollers, and this specification will discuss the development and research on heat-insulating coatings for these rollers in order to prevent heat loss during the conveyance of high-temperature steel billets. We will propose the results of

(Prior Art) Regarding the technology of coating a heat-resistant material in order to prevent roll wear in a continuous casting machine, the following prior art can be found.

JP-A No. 57-130750 relates to a conveyor roller under a fusing machine for continuously casting four pieces, and in order to avoid the influence of the gas cutting flame on the strands, a thermal spray coating of metal, metal oxide, or metal carbide with a melting point of 1500° C. or higher is disclosed. However, it has nothing to do with the temperature drop that occurs in high-temperature steel pieces, and in fact, the thickness of the heat-resistant sprayed layer is 0.
．． It is only about 2111 and has almost no heat insulation effect.

On the other hand, JP-A-58-157563 discloses that in order to prevent a local temperature drop at both side edges of four continuously cast pieces, a heat insulating coating is applied to both end areas of the supporting rollers of the cast pieces, but the function is , since the edge portion is in direct contact with the metal roller base material and local cooling through that contact is prevented, heat removal from the slab cannot be avoided in most of the remaining contact area.

(Problems to be Solved by the Invention) The inventors have developed a method for preventing heat removal through full contact with conveying rollers of high-temperature steel pieces (including hot pieces) at 900 to 1200°C. Based on the results of our study of the heat-insulating coating necessary to maintain the temperature of the steel billet, its physical properties, and the relationship between coating thickness and roll surface temperature, we created a coating with a specified thermal conductivity around the body of the metal roller. It is an object of the present invention to effectively prevent a drop in temperature of a high-temperature steel billet during transportation by coating it with a predetermined thickness.

(Means for solving problems) The above objectives are advantageously achieved by the following considerations.

In other words, around the body of the metal roller, the thermal conductivity is 0.01.
M-thermal ceramic below 50ak/cm -s-D
This is a roller for transporting high-temperature steel billets to prevent heat loss, and is provided with a heat-insulating film closely coated with a coating thickness of 2 to 20 mm.

In practice, it is preferable that the heat insulating film has a surface coating made of a hard material, and that the metal roller has a base bonding layer between it and the heat insulating film.

In general, in continuous casting machine operation, the continuous casting strand surrounded by a solidified shell formed by the first cooling with a water-cooled mold passes through a cooling water injection in a second cooling zone, and then passes through a straightening zone. As an example, the surface temperature of the continuously cast strand drops to a temperature of 700-800''C when it is transferred to the roller table and reaches the cutting zone due to continued cooling.

In accordance with recent energy-saving trends, for so-called direct rolling or so-called hot-piece charging into the slab heating furnace, for example, water cooling after the straightening zone is discontinued.
Although the temperature can be maintained at about 00 to 1100° C., in this case, the durability of the conveying roller is significantly deteriorated.

Figure 1 shows that the surface temperature of the metal internal water-cooled roller of a continuous slab casting machine that reaches approximately 40°C when the circumference of the metal roller comes into contact with the slab.
At 0°C, the values of thermal conductivity on the surface of the roller are 0.004, o, oos and 0.0150aAl, respectively.
/cm, B, -c when each thermal insulation film is closely coated Ll,
The influence of the coating thickness on the roller surface peak temperature was determined by heat transfer analysis based on the side temperature results of a thermocouple buried just below the roller surface. The heat transfer coefficient of the heat insulating film depends on the selection of the coating material, which will be described later.

From FIG. 1, it is clear that the roller surface temperature increases as the coating thickness of the heat insulating film increases, and the smaller the thermal conductivity of the heat insulating film, the higher the surface temperature becomes. When the coating thickness of Q150al/cIL-s-0 is less than 2 silk, the temperature rise compared to a metal roller without a coating is at most about 50°C or less, and therefore the thermal conductivity is 0.015 ( 3al/trowel, s
, it can be seen that if the coating thickness exceeds 0 or in that case is less than 2111, it is virtually impossible to provide the heat insulation effect necessary to prevent the desired temperature drop of the hot steel billet. Even if the temperature increases by more than 2 degrees, the rate of increase in the roller surface temperature is small, so it cannot be said to be a good idea from an economic standpoint.

On the other hand, when the coating thickness is 5 to 10 fl, even when the thermal conductivity k of the heat insulating film is 0.015 cal/cm, s1°C, the surface temperature increases by 75 to 100°C compared to the one without the film, especially k When the temperature is 0.0040al/an, s.degree. C., the temperature increases by 130 to 180"C.

From the above, the thermal conductivity k of the heat-insulating coating applied to the high-temperature steel billet conveying roller is 0.0150all:cm.
・Use material of S・"C or less, and the coating thickness is ft2
It should be ~20 xi+, more preferably 5-10xi+.

Examples of coating materials that meet this thermal conductivity condition are shown in Table 1! Suitable materials include one or more of 5K, Al2O8, Tie, ZrO2°Sin, MgO, Or, 08, and the like.

Table 1 The thermal conductivity changes somewhat depending on the porosity of the heat insulating film, but from the viewpoint of film strength, it is preferable that the porosity is 15 inches or less.

Next, FIG. 2 shows a cross section of the conveying roller according to the present invention, in which 1 is a heat insulating coating, 2 is a metal roller, and 3 is a surface coating or 4 is a base bonding layer. The surface coating 3 shown is a heat-resistant and abrasion-resistant material such as ceramic or cermet on the outer surface of the heat-insulating film 1 in order to improve the wear resistance of the conveying roller having the heat-insulating film 1.
The base bonding layer 4 shown in Figures (C) and (dl) is applied so that the surface of the metal roller is first coated with a material that helps improve the peeling resistance of the heat insulating film 1. .

The surface coating 3 is made of WO, Tie, (3rO, ZrO, N
Carbides such as bO, TaO and SiC, or these carbides with OO, Ni-Cr gold alloy QO-Qr gold alloy c
o-(3r-AJ
-AJ OCo-0r-W-Ni-Or, O, etc. 28 ~ Dispersion strengthened alloys are suitable, particularly preferred cases are shown in Table 2, and the surface hardness by thermal spraying is also shown.

Next, the base bonding layer 4 is made of Nior alloy, NlAjt alloy, N1 group self-pouring alloy, 00 group self-pouring alloy, ai (3oO
rAff tooorAjY: Alloy, NlorAJY alloy, Ni%NiP alloy, NiW alloy, etc. are suitable.
Regarding the base bonding layer 4, it is preferable to perform heat treatment after film formation in order to strengthen the bonding force.

The above solid coatings may be formed by any method such as flame spraying using WI acetylene as a heat source, plasma spraying using plasma as a heat source, water plasma spraying, other chemical vapor deposition methods, or plating methods. For the surface coating and base bonding layer, a coating thickness of about 0.05 to 2.0 nm is usually suitable.

Example In the continuous slab casting machine whose roll layout is shown in Fig. 3, all 15 rolls in sections ◎ to 0 are Or WO.
The present invention was applied to a conveyor roller made of steel and compared with conventional examples and comparative examples, and the results were obtained by comparing the effect of preventing the temperature drop that occurs in four continuously cast pieces and the fire resistance of the roller in Table 3.0 Heat Insulating Coating Conventional rollers that did not have a steel billet temperature drop of 75%
'C, but this invention can suppress the temperature to about 20°C. However, in Comparative Example 45, where the thickness of the heat insulating film is too thin, a sufficient heat insulating effect is not obtained at ΔT of 65°0.

(Effects of the Invention) According to the present invention, it is possible to effectively avoid a drop in temperature during transport of a high-temperature steel billet through a transport roller, without impairing the durability of the roller.

[Brief explanation of drawings]

Figure 1 is a graph showing the influence of the coating thickness of the heat insulating film on the surface peak temperature of the conveying roller, Figure 2 is a cross-sectional view of the roller, and Figure 3 is an example of the roll layout of a continuous casting machine. FIG.

Claims (1)

[Claims] 1. The circumferential surface of the metal roller has a thermal conductivity of 0.015.
A roller for transporting high-temperature steel billets to prevent heat loss, comprising a heat-insulating film closely coated with a heat-resistant ceramic having a coating thickness of 2 to 20 mm. 2. The roller according to claim 1, wherein the heat insulating coating has a surface coating of a hard material. 3. The roller according to claim 1 or 2, wherein the metal roller has a base bonding layer between it and the heat insulating coating.