JP7292670B2 - Dust exhaust gas blower runner and its repair method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a dust exhaust gas blower runner and a repair method thereof.

Exhaust gas generated in the steelmaking process is generally discharged by a blower in many cases. For example, in a sintering process for producing sintered ore using iron ore, carbonaceous material, and lime as sintering raw materials, the sintering raw materials are charged into a pallet of a sintering machine and then fired in an ignition furnace. Generally, the surface is ignited, the carbonaceous material is oxidized while the outside air is sucked from below the pallet, and the iron ore is sintered using the heat generated during oxidation. A wind box for air intake is installed below the pallet, and the lower end of the wind box is connected to a duct.
The sintering machine exhaust gas generated by burning the sintering raw materials on the pallet is sucked into the wind box by operating the sintering machine main exhaust gas blower installed in the middle of the duct, and is supplied with electricity through the duct. Introduced to the dust collector.

The life of the runner (impeller) of the main exhaust gas blower of the sintering machine is determined by wear due to dust collision (particularly, the tip of the blade plate is hit hard by dust) and thinning due to corrosion caused by the exhaust gas environment. be done.
Thinning of the runner of the exhaust gas blower used for exhaust gas containing such dust (dust-containing exhaust gas) is not limited to the main exhaust gas blower of the sintering machine, but also in the ironmaking process and steelmaking process, which are examples of the ironmaking process. Occur. Examples of the ironmaking process include an exhaust blower of a sintering machine ore discharge section of a blower, an exhaust gas blower of a drying furnace for coke coking coal, and the like. Examples of the steelmaking process include a blower for converter OG equipment, a blower for electric furnace dust collection equipment, and the like. Similar problems exist in coal boiler exhaust equipment and incinerator exhaust equipment, although they are not steelmaking processes.

In these facilities, the dust (soot) concentration in the exhaust gas is reduced so that it is below a predetermined regulation value before the exhaust gas is diffused into the atmosphere. However, the exhaust gas may contain dust of 0.7 mg/m ³ or more, although it is below the regulation value, and such dust-containing exhaust gas causes thinning of the runner of the blower.
Therefore, for wear parts such as runners of dust-containing exhaust gas blowers (hereinafter sometimes simply referred to as "runners"), improvements in wear resistance using metal build-up or the like have been conventionally studied.

For example, Patent Literature 1 discloses a water turbine in which a member having a build-up weld layer with higher erosion resistance and wear resistance than the base material is applied to a portion that receives an impact, and a manufacturing method thereof.
Further, in Patent Document 2, a first thermal spray coating containing a metal containing at least one of Ni, Cr, and Co and chromium carbide, and at least Ni, Cr, and Co on at least a part of the surface A water turbine runner coated with a second thermal spray coating comprising a metal comprising one and tungsten carbide is disclosed.

JP-A-2-230968 JP-A-9-303245

According to the technique described in Patent Document 1, a corresponding improvement in life can be expected, but the Vickers hardness is 300 to 700, so the wear resistance is insufficient. Also, the welding method is limited to plasma spraying, and it is desired that the blade can be repaired by a simpler method.
On the other hand, in the case of the technique described in Patent Document 2, the Vickers hardness of the second thermal spray coating is 1000 or more, and wear resistance is sufficiently ensured. The upper limit of the film thickness is about 1.0 mm, and there is a limit to extending the life. In addition, since preheating at a temperature of 400° C. or more and 650° C. or less for 1 hour or more and 30 hours or less is required, on-site repair is difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a runner having a longer life than conventional runners. Another object of the present invention is to provide a runner repair method capable of shortening the repair period compared to the conventional method.

In order to achieve the above object, the first invention includes two layers of weld overlay, an underlay and a top build, each having a thickness of 1.5 mm or more and 3.0 mm or less on at least a part of the surface. A runner for a dust flue gas blower,
The average value Hvm of the micro Vickers hardness of the base material to be subjected to the underlay is 100 to 400,
The average value Hvu of the micro Vickers hardness of the top layer is 1000 to 1400,
The average value Hvl of the micro Vickers hardness of the undercoat is 450 to 950, and the chromium content of the undercoat is 10 to 30% by mass,
The hardness gradient α defined by the formula (1) and the hardness gradient β defined by the formula (2) are each 18 or more and 320 or less.
α=(Hvu−Hvm)/[tu/2+tl] (1)
β=(Hvu−Hvl)/[(tu+tl)/2] (2)
However, tu: the layer thickness of the top layer (mm), tl: the layer thickness of the bottom layer (mm) ,
The micro Vickers hardness of the base material is the surface before welding, the micro Vickers hardness of the top layer is the surface of the top layer after welding, and the micro Vickers hardness of the bottom layer is the surface of the bottom layer after welding. , and 500 g load, 15 measurements at intervals of 0.5 mm, and the average value calculated as the average.

In the present invention, as shown in FIG. 1, the average value Hvu of the micro Vickers hardness of the upper layer is represented by half the layer thickness of the upper layer, and the average value Hvl of the micro Vickers hardness of the lower layer is lower. It is represented by 1/2 of the layer thickness of the pile. Also, the average value Hvm of the micro-Vickers hardness of the base material is represented by the surface of the base material. Based on this assumption, the hardness gradient α in the thickness direction between the overlying layer and the base material is expressed by Equation (1), and the hardness gradient β in the thickness direction between the overlying layer and the base material is represented by Equation (2).

In general, the wear resistance of a runner can be improved by welding overlay, thermal spraying, or the like. However, the inventors of the present invention have found that simply increasing the hardness of the outermost layer of the runner not only makes the surface layer more prone to cracking, but also promotes and grows the cracks.
The wear resistance of the runner is improved when the base metal is welded. However, if the hardness of the weld overlay is increased, the difference in hardness between the base material and the overlay layer increases, resulting in a large difference in mechanical properties such as thermal expansion coefficient between the base material and the overlay layer. As a result, when a tensile load acts on the runner or the runner thermally expands, cracks existing in the build-up layer progress and grow. When the crack progresses and the build-up layer peels off, the thickness of the base metal progresses from there, leading to breakage.

Thus, the present inventors discovered that not only mere wear but also wear due to peeling of the build-up layer due to the progress of cracks is a major factor that determines the life of the runner.
Therefore, in the present invention, the weld overlay of the runner is made of two layers, the upper and lower layers, and the hardness of the upper layer is increased to improve wear resistance, and the cracks that inevitably occur in the upper layer are prevented from progressing. By suppressing it, the overlying layer is prevented from being peeled off. Specifically, the hardness gradient α in the thickness direction between the top layer and the base material, and the hardness gradient β in the thickness direction between the top layer and the bottom layer are each set within a predetermined numerical range, so that the top layer and the Adjust the amount of change in hardness between the underlay and the base material, and the amount of change in the thermal expansion coefficient associated with this, to appropriate values.

A second invention is a method for repairing a runner of a dust-containing exhaust gas blower according to the first invention after use for a certain period of time, comprising:
It is characterized in that a top weld surfacing that satisfies the requirements of claim 1 is applied to the portion where the underlay is exposed.

In the runner of the dust-containing exhaust gas blower according to the present invention, the weld overlay is made up of two layers, the top layer and the bottom layer, and the hardness of the top layer is increased, and the hardness gradient α in the thickness direction between the top layer and the base material is , and the hardness gradient β in the thickness direction between the top layer and the bottom layer is set within a predetermined numerical range, thereby suppressing the progress of wear and the progress of cracks. As a result, it becomes possible to extend the life of the runner compared to the conventional one.

In addition, in the method for repairing the runner of the dust-containing exhaust gas blower according to the present invention, preheating and postheating are not performed, and the top welding is performed only at the place where the top layer is peeled off and the bottom layer is exposed. The repair process can be shortened in comparison.

FIG. 4 is a schematic diagram for explaining hardness gradients α and β; 1 is a perspective view of a runner of a main exhaust gas blower of a sintering machine according to one embodiment of the present invention; FIG. FIG. 4 is a cross-sectional view of the leading edge of the vane plate of the runner on which two layers of weld surfacing, a lower layer and an upper layer, are applied.

Next, an embodiment embodying the present invention will be described with reference to the attached drawings for understanding of the present invention.

FIG. 2 shows a runner 10 of a sintering machine main exhaust gas blower (an example of a dust-containing exhaust gas blower) according to one embodiment of the present invention.
The runner 10 includes a disk-shaped main plate 12 having a shaft hole 13 in the center, and a plurality of vanes 11 arranged at regular intervals along the direction of rotation. Each blade 11 is curved in an arc, and one curved end surface is fixed to the main plate 12 . A motor shaft (not shown) is inserted into the shaft hole 13 of the main plate 12 .

The runner 10 is housed in a casing (not shown), with a suction port for the sintering machine exhaust gas 14 on the front side of the runner 10 (on the side where the motor is not installed) and a blowing port for the sintering machine exhaust gas 14 on the side of the runner 10 . Each has an exit.

The dust (soot) in the main exhaust gas from the sintering machine, which is dust-containing exhaust gas, is 0.7 mg/ ^m3 or more, although it is below the regulation value, and has a relatively high concentration among the dust-containing exhaust gas (e.g., 8.0 mg/m3). m ³ or more, below the regulation value).

When the runner 10 is rotated by a motor (not shown), the sintering machine exhaust gas 14 is sucked into the casing through the suction port. The sintering machine exhaust gas 14 sucked into the casing flows into the runner 10 and flows out of the runner 10 through the gap between the blades 11 . The exhaust gas 14 from the sintering machine that has flowed out of the runner 10 moves in the rotation direction inside the casing and is discharged out of the casing from the outlet.

At least a portion of the surface of the runner 10 is provided with two layers of weld overlay, ie, an underlying layer and an upper layer, each having a thickness of 1.5 mm or more and 3.0 mm or less.
When the thickness of the weld overlay is less than 1.5 mm, the effect of extending the service life is reduced, while when it exceeds 3.0 mm, the temperature difference between the surface layer and the inside during welding increases crack generation.

The average value Hvm of the micro Vickers hardness of the base material to be underlaid is 100-400. If the average value Hvm of the micro Vickers hardness of the base material is less than 100, the strength of the base material itself may be insufficient.

The average value Hvu of the micro Vickers hardness of the overlay is 1000-1400. If the average micro Vickers hardness Hvu of the top layer is less than 1,000, the wear resistance is insufficient, while if it exceeds 1,400, the occurrence and propagation of cracks may not be suppressed.

The average micro Vickers hardness Hvl of the underlay is 450-950, and the chromium content of the underlay is 10-30% by mass. When the overlying layer is peeled off to expose the underlying layer, the average value Hvl of the micro Vickers hardness of the underlying layer is set to 450 or more in order to secure the wear resistance of the underlying layer. On the other hand, by setting the average value Hvl of the micro-Vickers hardness of the underlayer to 950 or less, it is possible to substantially suppress the generation of new cracks in the underlayer.

Since dust-containing exhaust gas such as sintering machine exhaust gas contains moisture, SOx, and NOx, acids derived from moisture, SOx, and NOx may adhere to the runner of the main exhaust gas blower of the sintering machine. When a crack occurs in the upper layer and progresses to reach the boundary between the upper layer and the underlayer, the acid may pass through the crack and corrode the boundary. Since different metals are in contact with each other at the boundary, corrosion tends to progress. Therefore, by adding chromium to the underlay and setting the content of chromium to maintain corrosion resistance to 10% by mass or more, the progress of corrosion at the boundary is suppressed. The upper limit of the chromium content is about 30% by mass, which is commercially available.

It should be noted that chromium may be contained in the top layer as well. However, since the exhaust gas from the sintering machine contains dust, the top layer is easily worn, and it is thought that wear resistance should be prioritized over corrosion resistance. Therefore, it is better to improve the wear resistance of the top layer by adding a small amount of chromium or not adding it, rather than lowering the wear resistance of the top layer by adding chromium to the top layer.

The hardness gradient α in the thickness direction between the overlying layer and the base material and the hardness gradient β in the thickness direction between the overlying layer and the underlying layer are set to 18 or more and 320 or less, respectively. The hardness gradient α is calculated by the formula (3), and the hardness gradient β by the formula (4).
α=(Hvu−Hvm)/[tu/2+tl] (3)
β=(Hvu−Hvl)/[(tu+tl)/2] (4)
However, tu: upper layer thickness (mm), tl: lower layer thickness (mm)

It is considered that the propagation of cracks generated in the top layer is determined by the coefficient of thermal expansion of the base material and the bottom layer that restrains the top layer. However, since it is difficult to measure the coefficient of thermal expansion, in the present invention, the difference in coefficient of thermal expansion between materials was evaluated as a hardness gradient by substituting the micro Vickers hardness, which approximately matches the coefficient of thermal expansion. Since the degree of constraint is also affected by the build-up thickness, it is considered logical to use the hardness gradient to evaluate the degree of constraint.

According to the average values of the micro Vickers hardnesses of the base material, the top layer, and the bottom layer, and the layer thicknesses of the top layer and the bottom layer, the maximum values of the hardness gradients α and β are 633, but the hardness gradient If is too high, the coefficient of thermal expansion of the underlay and the base material will be too large compared to the overlay. As a result, when the runner of the main exhaust gas blower of the sintering machine thermally expands in a high-temperature environment (for example, about 120° C.), cracks tend to develop in the upper layer according to the expansion allowance of the lower layer and the base material.
According to the findings of the present inventors, by setting the hardness gradients α and β to 320 or less, it is possible to suppress the growth of cracks in the underlying layer or the upper layer due to the constraint of the base material.

On the other hand, according to the average value of the micro Vickers hardness of the base material, the top layer, and the bottom layer, and the layer thicknesses of the top layer and the bottom layer, the minimum values of the hardness gradients α and β are 16, If the hardness gradient is too low, for example, an underlay having approximately the same hardness as the overlay will be placed. This means that the thermal expansion coefficients of the upper and lower layers are approximately the same, and crack propagation in the upper layer due to restraint of the lower layer can be suppressed. However, although crack growth is suppressed from the perspective of thermal expansion, crack growth may occur due to the rotational vibration of the main exhaust gas blower of the sintering machine, so there is concern that cracks may reach the boundary between the upper and lower layers. remains. When a crack reaches the boundary between the upper layer and the underlayer, it is difficult to suppress the crack from propagating into the underlayer if the underlayer has the same hardness (toughness) as the upper layer.

Therefore, by lowering the hardness of the lower layer to some extent with respect to the upper layer, that is, by setting a lower limit for the hardness gradient, cracks penetrating the upper layer are suppressed from propagating into the inner layer. be able to. According to the findings of the present inventors, by setting the hardness gradients α and β to 18 or more, it is possible to suppress crack growth in the underlay or overlay due to the constraint of the base material.

FIG. 3 shows an example in which a bottom 16 and a top 17 are welded onto the tip of the vane plate 11 of the runner 10 . In this example, a plate 15 (base material) made of the same material as that of the blade 11 is processed into the same shape as the blade 11, and the plate 15 is provided with a lower lining 16 and a top lining 17 that satisfy the above-described requirements. It is fixed to the tip of 11.
The underlay 16 and the top build 17 may be applied directly to the vane plate 11 (base material).

The micro-Vickers hardness of the base material, underlay, and overlay is measured as follows.
The base material is the surface before welding, and the upper and lower layers are the surfaces after welding, respectively, and measured by a method according to JIS Z2244:2009 "Vickers hardness test - test method". The applied load (test force) is 500 g, 15 points are measured at intervals of 0.5 mm for each object, and the average is calculated to be the average value.

The thickness of the upper and lower layers is measured as follows.
A. When a plate (base material) with the same shape as the runner surface is created and the plate is attached to the runner surface after overlaying. Let the average value of three points be the build-up thickness. The plate is then attached to the runner surface.

B. There are two methods for measuring the thickness of the runner (base metal) when directly welding overlay on the surface.
(a) A method in which the relationship between welding conditions (current, voltage, welding speed, etc.) and overlay thickness is investigated in advance, and overlay welding is performed on the runner surface under welding conditions in which the overlay thickness is known. ) Method of measuring with an ultrasonic distance meter Since the top, bottom, and base materials are made of different materials, their boundaries can be detected by ultrasonic waves, and the build-up thickness can be calculated.

The above two methods can be adopted when welding overlay is applied directly to the runner surface. However, since the overlay material may contain substances such as carbides that hinder the transmission of ultrasonic waves, method (a) is preferable. .

When repairing the runner of the main exhaust gas blower of the sintering machine that has been used for a certain period of time, the portion where the underlay is exposed should be welded with a top weld surfacing that satisfies the above requirements.

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment. Other possible embodiments and modifications are also included.

Verification tests conducted to verify the effects of the present invention will be described.
Tables 1 and 2 show a list of test results. The test conditions are as follows.
(a) Test piece A test piece was a base material of length x width x thickness = 200 mm x 50 mm x 6 mm. The reason why the thickness of the test piece was set to 6 mm is that the thickness of the portion of the runner of the main exhaust gas blower of the sintering machine that is most damaged due to wear and cracking is 6 mm.
A two-layer overlay was applied to the surface of the test piece by arc welding under the conditions described in Tables 1 and 2 to prepare a test piece A. Also, a test piece B was produced under the same conditions as the test piece A.
The test piece A was used for the verification test, and the test piece B was not subjected to the test and was used for comparison in the evaluation.

(b) Tensile test A tensile test was performed on test piece A with a maximum load of 90 kN (300 MPa).
Observe the cross section of the test piece (thickness direction x length direction about 10 mm), and confirm the average crack length L (mm), which is the average value of the top 10 crack lengths, and the microscope field of view (20 times). The crack densities N (lines/mm ² ) were measured for test piece A and test piece B, respectively, and were _defined as LA, _NA , _LB , and _NB .
For each test piece, the evaluation value of the average crack length L was calculated as (L _A −L _B )/L _A and the evaluation value of the crack density N was calculated as (N _A −N _B )/N _A , and the average crack length If both the evaluation value of L and the evaluation value of crack density N were 0.5 or less, it was judged to be acceptable, and otherwise, it was judged to be unsatisfactory.

(c) Thermal expansion test A process of placing the test piece A in a furnace set at 120°C (actual machine operating environment) for 2 hours and then naturally cooling for 1 hour was repeated 10 times.
The thermal expansion test was evaluated in the same manner as the tensile test.

(d) Final evaluation When both the tensile test and the thermal expansion test were passed, it was evaluated as ◯ (acceptable), and in other cases, it was evaluated as x (impossible).

It can be seen from Table 1 that all of the examples were evaluated as ◯, while from Table 2, all of the comparative examples were evaluated as x.

10: runner, 11: vane plate, 12: main plate, 13: shaft hole, 14: sintering machine exhaust gas, 15: plate (base material), 16: underlay, 17: overlay

Claims (2)

A runner for a dust-containing exhaust gas blower, wherein at least a part of the surface is provided with two layers of weld overlay, a base layer and a top layer, each having a thickness of 1.5 mm or more and 3.0 mm or less,
The average value Hvm of the micro Vickers hardness of the base material to be subjected to the underlay is 100 to 400,
The average value Hvu of the micro Vickers hardness of the top layer is 1000 to 1400,
The average value Hvl of the micro Vickers hardness of the undercoat is 450 to 950, and the chromium content of the undercoat is 10 to 30% by mass,
A runner for a dust-containing exhaust gas blower, characterized in that the hardness gradient α defined by formula (1) and the hardness gradient β defined by formula (2) are 18 or more and 320 or less, respectively.
α=(Hvu−Hvm)/[tu/2+tl] (1)
β=(Hvu−Hvl)/[(tu+tl)/2] (2)
However, tu: the layer thickness of the top layer (mm), tl: the layer thickness of the bottom layer (mm) ,
The micro Vickers hardness of the base material is the surface before welding, the micro Vickers hardness of the top layer is the surface of the top layer after welding, and the micro Vickers hardness of the bottom layer is the surface of the bottom layer after welding. , and 500 g load, 15 measurements at intervals of 0.5 mm, and the average value calculated as the average. A method for repairing a runner of a dust-containing exhaust gas blower according to claim 1 after use for a certain period of time,
A method for repairing a runner of a dust-containing exhaust gas blower, characterized in that an upper weld surfacing that satisfies the requirements of claim 1 is applied to the portion where the underlay is exposed.

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