JPH05105938A - Manufacture of hearth roll - Google Patents

Abstract

PURPOSE:To prevent the development of welding crack at a joined part, to eliminate a welding repairing, to drastically reduce the manufacturing cost of a hearth roll and to prolong the service life of the hearth roll in three or more times compared with the conventional roll. CONSTITUTION:At the time of manufacturing the hearth roll by integratively weld-joining heat resistant steel-or heat resistant cast steel-made shafts 1, axles 2 and a barrel 3, the joining part between the shaft 1 and the axle 2 fits the axle 2 into the shaft 1 and the joining surfaces 5 of the shaft 1 and the axle 5 are mutually brought into contact with the inclined surfaces. The joining surfaces 4 of the axle 2 and the barrel 3 at the joining part between both are mutually brought into contact with the inclined surfaces. The joining surfaces 4, 5 are joined by an electron beam welding in the condition of closely contacting these joining surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hearth roll used in a heat treatment furnace for metals, and more specifically, joining the joints by high energy density welding such as electron beam welding or laser welding. , Reduce weld cracking,
The present invention relates to a method for manufacturing a hearth roll that reduces residual welding stress by applying a compressive force from both ends of the hearth roll in the axial direction of the hearth roll during welding.

[0002]

2. Description of the Related Art In a conventional hearth roll, as shown in FIG. 3, an axle 2 is fitted on a shaft 1, a barrel 3 is fitted on an axle 2, and a fitting portion between the shaft 1 and the axle 2 is fillet welded. At 13, the butt welding of the axle 2 and barrel 3 fitting part
It was joined by 14 and integrated. In addition, 17 is a keyway.

As shown in FIGS. 4 (a) to 4 (d), details of the respective joints are shown in FIG. 4 (a), in which a notch 11 is provided on the surface of the shaft 1 and the axle 2 is fitted to the notch 11. After tack welding,
This is an example of fillet welding 13. (b) is an example in which a projection 15 is provided on the surface of the shaft 1, the axle 2 is fitted to the projection 15, and butt welding 14 of the U groove is performed.

In (c), a notch 11 is provided on the inner surface of the axle 2 so that the axes of the axle 2 and the barrel 3 are completely aligned with each other, and the notch of the inner surface of the axle 2 is provided on the inner surface of the barrel 3. This is an example in which a protruding portion 12 shorter than the portion 11 is provided, the protruding portion 12 is fitted into the cutout portion 11, and butt welding 14 of the U groove is performed. The protrusion 12 also functions as a backing material. In order to make the wall thicknesses of the axle 2 and the barrel 3 uniform, a chamfer 16 is applied to the inner surface on the axle 2 side. (d) is
This is an example in which the butt welding 14 of the U groove of (c) is replaced with the electron beam welding 5 with the I groove.

[0005]

However, since the material of the hearth roll is heat-resistant steel or heat-resistant cast steel, the welds are hardened and cracks are likely to occur.
All had flaws. That is, the joint (a)
In many cases, there were many cracks in the fillet weld 13 and the cracks grew and spread early during use, and the shaft 1 often came out of the axle 2. In many cases, the joint part (b) became unusable due to cracking in the heat-affected zone of the axle 2. In addition, most of the joints (c) were also cracked, and welding repair was performed. In addition, the joint (d) is electron beam welded with a small heat affected zone,
It was difficult to obtain a joint without a gap at the tip of the groove, and this gap became a notch defect, and a crack was generated in the weld during use.

Further, since the hearth roll is made of heat-resistant steel or heat-resistant cast steel, after the welding, a heat treatment is performed after the welding to soften the heat-affected zone and remove the residual stress of the welding. This post-weld heat treatment was also one of the causes for increasing the manufacturing cost of the hearth roll.

The present invention has been made in order to solve these problems, and reduces welding cracks by making the joint surfaces of the joints mutually inclined surfaces and joining the joint surfaces by high energy density welding. In addition, a method for manufacturing a hearth roll that reduces welding defects, notch defects due to gaps in the joint, and welding residual stress by applying compressive force from both ends of the hearth roll during welding in the axial direction of the hearth roll The purpose is to provide.

[0008]

According to a first aspect of the present invention, when a heat-resistant steel or heat-resistant cast steel shaft, an axle and a barrel are welded and integrated to manufacture a hearth roll, the joint between the shaft and the axle is When the axle is fitted to the shaft, the joint surface of the shaft and the axle are in contact with each other on the inclined surface, and the joint portion of the axle and the barrel is in contact with the joint surface of the axle and the barrel with each other on the inclined surface, and these joint surfaces are in close contact with each other. A method for manufacturing a hearth roll in which the joining surfaces are joined by high energy density welding.

A second aspect of the present invention is a method for manufacturing a hearth roll, in which a compressive force is applied from both ends of a hearth roll temporarily assembled with a shaft, an axle and a barrel in the axial direction of the hearth roll to perform welding and joining.

[0010]

[Operation] High energy density welding is 10 to 100kW / cm ² energy density such as TIG welding and MIG welding.
Energy density of 000kW / cm ² or more. Therefore, by adopting high energy density welding at the joint, the joint surface is locally melted, and therefore the welding heat input is small, so that less energy is distributed to the base metal,
The heat-affected zone is extremely narrow, and the range of embrittlement and hardening is also extremely narrow. Moreover, deep cracking does not occur even if welding is performed without preheating. Although fine surface cracks may occur, this is a very shallow one that disappears completely during the roughing stage of finishing. Further, since the welding heat input is small, the residual stress and deformation of the welded portion are also small.

The joint portion between the shaft and the axle is fitted with the axle, and the joint surface is inclined at a right angle with respect to the axial center direction of the hearth roll, so that the joint portion is inclined, and the joint portion is used during use. The bending stress concentration applied to the portion can be relaxed.

By tilting the joint surface between the axle and the barrel by 2 to 3 in the same manner as described above, the joint portion between the axle and the barrel is not structured to fit the cutout portion and the protruding portion with each other. The axes of the barrels can be perfectly matched. For this reason, the backing material and the projecting portion corresponding to the backing material (see FIGS. 4 (c) and 4 (d)) are not necessary, and a weld portion having a large effective throat thickness can be obtained accordingly. Of course, by forming a protrusion corresponding to the backing material and inclining the joint surface, a more effective weld having a large throat can be obtained. In this case, it is convenient that the electron beam setting condition range becomes extremely wide and no scattering of spatters occurs.

Furthermore, since the joint surface between the axle and the barrel is inclined, when the axles on both sides are pressed against the central barrel, the joint surface end portion of the barrel and the joint surface end portion of the axle are inclined in the inclined direction of the joint surface. The component of the force acts toward, but the direction of action of this force is opposite to the direction of deformation that occurs during welding. Therefore, it is possible to manufacture a hearth roll with high dimensional accuracy and without weld cracking.

By applying a compressive force in the axial direction of the hearth roll from both ends of the hearth roll in which the shaft, the axle and the barrel are temporarily assembled, and welding them together, the shaft, the axle and the barrel are pressed and the joint surfaces are in close contact with each other. Gaps that cause welding defects and notch defects are eliminated, and good welded joints can be obtained. Further, by applying a compressive force during welding, it is possible to cancel the tensile residual stress generated in the direction perpendicular to the welding line after welding, and it is possible to manufacture a hearth roll in which the residual welding stress is significantly reduced.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 shows a hearth roll according to the first invention, which has a barrel outer diameter 91
A hearth roll of 8 mm, inner diameter 838 mm, wall thickness 40 mm, length 2000 mm is finished to an outer diameter of 900 mm and total weight of 1880 kg. In the figure, 1 is a shaft, 2 is an axle, 3 is a barrel, 4
Indicates the joint surfaces, respectively.

The shaft 1 was made of SUS-310S, the axle 2 was made of SCH-19, the barrel 3 was made of SCH-22, and the axle 2 and barrel 3 were made of centrifugally cast material. Axis 1 and axle 2
Shaft 1 and axle 2 with axle 2 fitted
And a joint surface 4 between the axle 2 and the barrel 3
The inclination angle is 2 °, the root gap is 0 mm, and no backing material is used. The inclination of the joint surface 4 between the axle 2 and the barrel 3 was set so that the tip of the joint surface of the barrel 3 was directed inward.

The joining of the joining surfaces 4 is performed by electron beam welding 5 in vacuum. The joining welding conditions of the axle 2 and the barrel 3 are as follows: beam current 120 mA, welding speed 500 mm / min, beam deflection 3 °, beam acceleration voltage. It is 70 kV. Also, the welding conditions for joining the shaft 1 and axle 2 are: beam current 150 mA, welding speed 40
0 mm / min, beam deflection 3 °, beam acceleration voltage 70 kV.

Ten hearth rolls were manufactured as described above, but the manufacturing time was about 1/50 of the conventional TIG welding and about 1/20 of the MIG welding. In addition, no weld cracking occurred at the joint of each hearth roll. After the post-welding heat treatment, 50 μm spraying (LCO-17) was performed on the surface of the hearth roll, and after fusing heat treatment at 900 ° C, Ra1.
Polished to a surface roughness of 5 μm or less, and put into practical use in a continuous annealing furnace of a chemical plating line. As a result, the hearth roll according to the present invention exhibited a life of about 3 times or more that of the conventional one.

Embodiment 2 FIG. 2 shows a hearth roll according to the second invention, which has a barrel outer diameter of 90.
4 mm, inner diameter 860 mm, wall thickness 22 mm, length 2000 mm finished as a hearth roll, 6 in the figure has a shaft with a through hole 2
Is an axle, 3 is a barrel, 7 is a through hole, 8 is a rod-shaped body, and 9 is a nut.

The material of the hearth roll is the same as in Example 1,
The shaft 6 was made of SUS-310S, the axle 2 was made of SCH-19, the barrel 3 was made of SCH-22, and the axle 2 and barrel 3 were made of centrifugally cast material. The shaft 6 has a through hole 7 having a diameter of 32 mm through which a rod-shaped body 8 such as a tie rod for applying a compressive force in the axial direction of the hearth roll passes during welding. Further, the shaft 2 is fitted with the axle 2. There is. Joint surface between shaft 6 and axle 2
The joint surface 10 between the axle 2 and the barrel 3 is perpendicular to the hearth roll axis direction.

At the joint between the axle 2 and the barrel 3, a notch 11 having a length of 7 mm is provided on the inner surface of the axle 2, and the inner surface of the barrel 3 has a length of 5 mm, a thickness of 5 mm and a tip radius of 2 mm.
The protrusion 12 is provided, and the protrusion 12 is fitted into the notch 11.

As described above, the shaft 6, the axle 2, and the barrel 3 are temporarily assembled in the shape of a hearth roll, and the through hole 7 of the shaft 6 is formed.
Through the rod-shaped body 8 and tightened with nuts 9 from both ends of the rod-shaped body 8 until a tensile force of 40 to 45 kgf / mm ² is applied to the rod-shaped body 8 and a compressive force is applied in the axial direction of the temporarily assembled hearth roll. .. The rod-shaped body 8 is made of SCM-445 and has a diameter of 30 mm.

The joining of each joining surface 10 is performed by electron beam welding 5 in vacuum. The joining welding conditions of the axle 2 and the barrel 3 are as follows: beam current 90 mA, welding speed 500 mm / min, beam deflection 3
The beam acceleration voltage is 70 kV. The welding conditions for joining the shaft 6 and axle 2 are as follows: beam current 150mA, welding speed 400m.
m / min, beam deflection 3 °, beam acceleration voltage 70 kV.

In the hearth roll manufactured as described above, the tensile residual stress generated in the direction perpendicular to the weld line after welding was 3-5 kgf / mm ² which was an extremely small value as it was welded. Note that the tensile residual stress generated in the direction perpendicular to the welding line after welding with a hearth roll by the conventional manufacturing method is 18 kgf / mm ² as-welded, 500 ° C, heat treatment after welding for 30 minutes, 17 kgf / mm after air cooling. ² , 500 ℃, 3 hours after welding heat treatment, after air cooling 15kgf / mm ² , 600 ℃, 1 hour after welding heat treatment, after air cooling 7
kgf / mm ² , 850 ℃, heat treatment after welding for 30 minutes, 4kgf / after air cooling
It was mm ² .

That is, in the method for manufacturing a hearth roll according to the present invention, the tensile residual stress generated in the direction perpendicular to the welding line after welding was extremely small, and the post-welding heat treatment could be omitted. This is a great advantage that significantly reduces the manufacturing cost of hearth rolls. In addition, no weld cracks occurred at the joints, and no weld repairs were made due to weld cracks, and the manufacturing cost could be greatly reduced. In the axial direction of the hearth roll, the compression force may be applied by compressing from both ends of the hearth roll with a hydraulic jack or the like without using the rod-shaped body.

[0026]

Industrial Applicability According to the present invention, the joining surfaces of the joining portions, where the joining surfaces are inclined surfaces, are joined by high energy density welding, and at the time of welding, both ends of the hearth roll are compressed in the axial direction of the hearth roll. A method for manufacturing a hearth roll that reduces welding defects, notch defects caused by a gap in a joint, and residual welding stress by applying force, and according to the method of the present invention, welding cracks are not generated in the joint. Therefore, there is no welding repair, heat treatment after welding is unnecessary, the manufacturing cost of the hearth roll can be greatly reduced, and the life of the hearth roll can be extended about 3 times or more compared with the conventional one. it can.

[Brief description of drawings]

FIG. 1 is an explanatory view of a hearth roll according to a first invention.

FIG. 2 is an explanatory view of a hearth roll according to a second invention.

FIG. 3 is an explanatory diagram of a hearth roll according to a conventional technique.

FIG. 4 is an explanatory diagram of a hearth roll according to a conventional technique.

[Explanation of symbols]

1 ... Axis, 2 ... Axle, 3 ... Barrel, 4 ... Bonding surface, 5 ...
Electron beam welding, 6 ... Shaft, 7 ... Through hole, 8 ... Rod-shaped body, 9
… Nuts, 10… Joint surfaces, 11… Notches, 12… Projections,
13 ... Fillet welding, 14 ... Butt welding, 15 ... Protrusion, 16 ...
Chamfer, 17 ... Keyway.

Claims (2)

[Claims] 1. When manufacturing a hearth roll by welding and joining a shaft, an axle and a barrel made of heat-resistant steel or heat-resistant cast steel, the joint between the shaft and the axle is such that the axle is fitted to the shaft and The joint surfaces of the axles contact each other with inclined surfaces, and the joint portions of the axle and barrel contact each other with the inclined surfaces of the joint surfaces of the axle and barrel, and the joint surfaces are in close contact with each other by high energy density welding. A method for manufacturing a hearth roll, which is characterized by joining. 2. A method for manufacturing a hearth roll, characterized in that a compressive force is applied from both ends of the hearth roll temporarily assembled with a shaft, an axle and a barrel in the axial direction of the hearth roll to perform welding and joining.