JPH11209865A - Formation of metal coating layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent recesses on the surface caused by the application of excessive electromagnetic stirring force on the molten zone at the time of remelting a primary coating layer formed on the surface of a base metal by thermal spraying or the like by induction heating. SOLUTION: At the time of subjecting a primary coating layer 11 on the surface of a base metal 10 to induction heating by an inductor 12, the penetrating depth δ of induced current is regulated to >=1.5 times the thickness (d) of the primary coating layer 11, by which the degree in which the induced current density reduces as it is deepen from the surface is made gentle, thus, the induced current density I0 in the surface of the primary coating layer is made low, and electromagnetic stirring force operating on the molten metal is made small to block the excessive flow of the molten metal, so that the generation of defects such as recesses on the surface can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal coating layer for imparting abrasion resistance, heat resistance, corrosion resistance, etc. on the surface of a base material such as a metal pipe or a metal strip. The present invention relates to a method of forming a primary coating layer by thermal spraying of a material, and then subjecting the primary coating layer to a melting treatment to form a dense metal coating layer (secondary coating layer).

[0002]

2. Description of the Related Art Conventionally, a thermal spray coating layer (primary coating layer) formed on the surface of a base material is re-melted to remove pores and gases contained in the thermal spray coating layer and to convert metal oxides into slag. Alternatively, a dense coating layer (secondary coating layer) is formed by floating on the surface of the fusion zone, and is securely bonded to the base material. As a heating method for performing the re-melting treatment of the thermal spray coating layer, there are heating with a gas flame, induction heating, heating with a furnace, and the like. Of these, heating with a gas flame can be easily carried out, so that it has been widely used.

Recently, as a method for re-melting a sprayed coating layer such as a boiler tube, a small region in the longitudinal direction of the sprayed coating layer is locally induction-heated by an annular inductor to melt the sprayed coating layer and to conduct the induction heating. A method in which the melted portion generated in the thermal spray coating layer is moved along the thermal spray coating layer, thereby re-melting the entire thermal spray coating layer. However, since the electromagnetic stirring force acts on the melted portion and a good coating layer with few pores can be formed, heating by a gas flame is being replaced.

[0004]

However, conventionally, the thickness of the sprayed coating layer is about 1 to 2 mm, and a good remelting treatment by induction heating is performed on the sprayed coating layer having such a thickness. However, it has been found that the following problem occurs when the thickness of the thermal spray coating layer is increased to 3 to 5 mm. That is, as shown in FIG. 11, the thermal spray coating layer 2 on the surface of the metal tube 1 is heated by an annular inductor 3 to form a fusion zone 4, and the inductor 3 is moved in the longitudinal direction of the metal tube 1. When the re-melting treatment was performed by using the re-melting treatment, the surface of the coating layer 5 after the re-melting treatment might have dents 6. Also, as shown in FIG.
In some cases, the re-melting process is performed by induction heating with the inductor 3 while rotating the metal tube 1. In this case, a spiral recess 7 is generated on the surface of the coating layer 5 after the re-melting process. In addition, the constriction 8 sometimes occurred at the end. The constriction 8 also occurs when the metal tube 1 is not rotated. Such depressions 6, 7 and constriction 8 lower the smoothness of the surface of the coating layer 5 and lower the product quality.
This was a serious defect and needed to be reduced as much as possible.

The present inventors have studied the causes of dents and constrictions on the surface of the coating layer and found the following items in order to solve the above-mentioned problems in the re-melting treatment by induction heating. That is, when the thickness of the coating layer is increased, and thus the thickness of the molten portion that melts the coating layer is increased, the molten metal is more likely to flow, so that the electromagnetic stirring force acts excessively to cause an undesirable flow in the molten metal. In addition, since the thickness of the coating layer is increased, the power required to melt the coating layer must be increased, and the electromagnetic stirring force itself is accordingly increased, which is preferable for the molten metal. As a result, a smooth flow on the surface of the coating layer was reduced. Therefore, these problems can be solved by suppressing the electromagnetic stirring force acting on the fusion zone so as not to be excessive according to the thickness of the fusion zone. On the other hand, the electromagnetic stirring force acting on the fusion zone depends on the magnitude of the density of the induction current flowing through the fusion zone (especially the induction current density on the surface layer) out of the total induction current applied. The current density may be reduced to a small value, and the induced current density is proportional to the power density per unit area of the coating layer supplied by the inductor.

However, simply lowering the power density takes time to heat and melt the coating layer, and the processing speed (the relative moving speed of the inductor with respect to the primary coating layer) must be reduced. There is a problem that the length of the child must be increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in view of the fact that the primary coating layer formed on the surface of the base material is re-melted by induction heating to form a dense metal coating layer. Metal coating capable of forming a metal coating layer having a high surface smoothness by preventing the occurrence of defects such as dents and constrictions on the surface, and capable of using a high-speed and / or short inductor. It is an object to provide a method for forming a layer.

[0008]

According to a first aspect of the present invention, when a primary coating layer formed on a surface of a base material by thermal spraying or the like is re-melted by induction heating, at least an induced current at the time of melting of the primary coating layer is reduced. The current penetration depth is set to be 1.5 times or more the thickness of the primary coating layer.
As described above, when the current penetration depth is 1.5 times or more the primary coating layer thickness, the current penetration depth is equal to or less than the primary coating layer thickness as conventionally performed. When the power density per unit area is constant, the induced current flowing through the base material (the amount of heat generated by the induced current is also transmitted to the primary coating layer and used for melting), and the primary coating layer is correspondingly increased. And the induced current density of the surface layer is reduced. As a result, the electromagnetic stirring force acting on the molten layer is reduced, and dents, constrictions, and the like of the coating layer, which have conventionally occurred when processing a thick coating layer, can be prevented.

Further, in the present invention in which the current penetration depth is 1.5 times or more the thickness of the primary coating layer, unlike the conventional case where the current penetration depth is small, the induced current density (maximum electromagnetic As long as the electromagnetic stirring force is suppressed to a certain level such that no dent or constriction occurs on the surface of the coating layer, no dent or the like occurs even if the power density is increased,
The effect that the processing speed can be increased by applying large electric power and the inductor can be shortened can be obtained.

In a second aspect of the present invention, an inductor for re-melting the primary coating layer by induction heating is electrically divided into a former inductor and a latter inductor in the moving direction, and the former inductor is provided. The power distribution to be applied to the object to be heated by the second-stage inductor is increased by the first-stage inductor to the melting point or near the melting point of the primary coating layer. It is set so that it can be melt-processed with an inductor, and further, the power density per unit surface area supplied to the object to be heated by the former-stage inductor is set high so as to enable rapid heating of the primary coating layer, The power density per unit surface area supplied to the object to be heated by the latter-stage inductor is set to be low so that the electromagnetic stirring force applied to the molten primary coating layer is not more than an allowable value. Here, in the case where the metal strip is an alloy, the melting point is defined as the temperature of the solid line that determines the presence or absence of the molten phase. In the second invention of the present application, with this configuration, the primary coating layer in the solid state, which is not adversely affected by the electromagnetic stirring force, can be quickly heated to the melting point or near the melting point by a short pre-stage inductor, and the melting point or Because the latter inductor heats and melts the primary coating layer, which has been heated to near the melting point, at a low power density, the induced current density in the melted area is small, and therefore the electromagnetic stirring force is also suppressed to a small extent. , And a desired melting process can be performed. In addition, since the amount of heat to be applied to the primary coating layer by the subsequent inductor may be small, even if the power density is low, the processing time is not required much, and the length of the inductor is not required much. For this reason, in the second invention as well, it is possible to perform prompt melting processing without causing dents, constrictions, and the like in the coating layer, and to obtain the effect of shortening the entire length of the inductor.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, a primary coating layer of a metal material is formed on a surface of a base material using a thermal spraying method or the like, and thereafter, a small region of the primary coating layer is locally locally heated with an inductor to perform induction heating. By melting the coating layer and moving the inductor relatively along the primary coating layer, the molten portion is moved along the primary coating layer, and the electromagnetic stirring force acting on the melting portion is used. Then, the present invention relates to a method for removing pores and oxides present in the primary coating layer to form a dense secondary coating layer.

The form, material, and the like of the base material used in the present invention are not particularly limited, and are arbitrary as long as a metal coating layer needs to be formed on the surface. For example, examples of the form of the base material include a tube, a rod, an H-shaped material, a strip having an arbitrary cross section such as an L-shaped material, a flat plate, and the like. Examples of the material include carbon steel, low alloy steel, and stainless steel. Steel, cast steel, cast iron, Ni-based alloy, Cu-based alloy and the like can be mentioned.
As a material of the coating layer formed on the surface of the base material, a Ni-based alloy, a Co-based alloy, or WC, Cr ₃ C ₂ ,
Examples of such materials include hard material particles such as TiB ₂ . In addition, it is desirable that a flux generating component such as B or Si is blended in the material of the coating layer so that re-melting can be smoothly performed so that the coating layer has self-solubility. As a method of forming a primary coating layer of a metal material on a base material, a thermal spraying method is generally used, but other methods such as a consolidation method, a centrifugal deposition method, and a slurry coating method may be employed. The thickness of the primary coating layer is determined so that a coating layer (secondary coating layer) having an intended thickness is finally obtained, and the present invention can be applied to coating layers of any thickness. It is of special significance to obtain the above-mentioned effect by applying to a thick film coating exceeding 2 mm, which has conventionally caused problems such as dents and constrictions.

As described above, in the present invention, in order to melt the primary coating layer, a small region of the primary coating layer is locally heated by induction using an inductor, and the inductor is heated along the primary coating layer. The entire length of the primary coating layer is melted by relatively moving the primary coating layer. The shape of the inductor used here is
It may be appropriately determined according to the shape of the primary coating layer and the base material,
For example, in the case where the base material is a strip such as a tubular body and the primary coating layer is formed on the outer peripheral surface thereof, an annular inductor (one or more turns) arranged so as to surround the strip.
In the case where the base material is a tubular body and the primary coating layer is formed on the inner peripheral surface thereof, an annular inductor disposed opposite to the inner peripheral surface is used in the tubular body, The primary coating layer formed on the inner and outer surfaces of the tube can be melted with an inductor placed inside and outside the tube.However, in the case of a tube or a rod, the tube or the rod is moved along its axis. Is preferably rotated around the center so that uniform processing is performed in the circumferential direction. When the base material is a plate material and a primary coating layer is formed on the plate surface, a linear, U-shaped or spiral guide disposed as an inductor in a plane substantially parallel to the plane. An inductor or an annular inductor surrounding a plate in the short side direction may be used.

Next, the size of the small region heated by the inductor, the power supplied by the inductor, the relative moving speed between the inductor and the primary coating layer, and the like are described by taking a tube as a typical example of the base material. This will be explained. FIG. 3 schematically shows a case where the primary coating layer 11 formed on the outer peripheral surface of the base material (metal tube) 10 is melted and heated, and an annular inductor 12 is provided around the base material 10.
(Length L). In order to melt-treat the primary coating layer 11 using the inductor 12, the inductor 12 is energized and a small area (area of length L) of the primary coating layer 11 facing the inductor 12 is induction-heated. While the inductor 12
Is moved relatively to the base material 10 (moving speed V). Here, the power density P supplied by the inductor 12 per unit area of the object to be heated (the primary coating layer and the base material thereunder)
_{If e} is uniform in both the circumferential direction and the longitudinal direction, the unit area portion 11a assumed on the primary coating layer 11
When passing under the, Yuki and raising the temperature continuously receives constant power density P _e, is no longer heated when it passes the inductor 12, the temperature slide into decline. A characteristic line 14 shown by a solid line in the graph of FIG. 4 is a graph of this temperature change that is simplified with respect to the time axis, and the unit area portion 1 at time t _0.
Heating for 1a is started, to reach the melting point T _m at time t _1, at time _{t 2 (= L / V)} , the unit area portion 11a is finished heat passes through the inductor 12 (temperature reached at that time _Te ). Therefore, the molten processed primary coating layer between the time t ₁ ~ time t _2, such as removal of pores is performed. Strictly speaking, the temperature rise characteristics during heating by the inductor (time t ₀ to time t ₂ ) are strictly necessarily linear due to a change in heat release due to temperature, a change in induction current density, a heat amount required for a phase change, and the like. However, the characteristic line 14 is simplified and shown as a straight line.

Here, when the power density _Pe is increased, as shown by a characteristic line 15, the heating rate is increased, and the power density Pe is increased.
_{When e} is reduced, the rate of temperature rise decreases as indicated by the characteristic line 16. Therefore, depending on the material properties of the primary coating layer 11, Toka setting the finally reached temperature T _e, if you set melt processing time (between t ₁ ~t ₂₎ to an appropriate value, the value of the power density P _e Accordingly, the length L and the processing speed V of the inductor 12 are determined, and conversely, if the processing speed V and the length L of the inductor 12 are determined, the required power density _Pe is determined accordingly. Becomes Power density P _e need not necessarily be constant in the longitudinal direction, dividing the inductor 12 in the longitudinal direction (moving direction), by changing the respective power density, the length of the inductor L and the processing speed V Can also be changed. On the other hand, the power density P applied to the primary coating layer 11
_e is restricted so that when the primary coating layer 11 is melted, an excessive electromagnetic stirring force does not act on the melted portion.

According to the first invention of the present application, when the primary coating layer is induction-heated while relatively moving the inductor along the primary coating layer as described above, at least the induction current at the time of melting of the primary coating layer is reduced. It is characterized in that the current penetration depth is 1.5 times or more the thickness of the primary coating layer. Here, the current penetration depth of the induced current means a distance (depth) from the surface at a position where the induced current density I ₁ is 1 / e of the induced current density I _{0 on} the surface. . That is, as shown in FIG. 2, when the material to be heated 20 is induction-heated by the inductor 21, the induced current density flowing through the material to be heated 20 is, as shown by the curve 22, the induced current density I on the surface. ₀ , the position where the induced current density I ₁ is 1 / e of the surface induced current density I ₀ ,
The distance (depth) δ from the surface is the current penetration depth of the induced current. Here, the specific resistance of the material to be heated 20 is ρ (Ω−c
m), the relative magnetic permeability is μ, and the frequency of the induction heating is f (Hz), the current penetration depth δ (cm) is expressed by Equation 1. However, about 90% of the absorbed power of the material to be heated 20 exists between the surface and the current penetration depth δ.

[0017]

(Equation 1)

As described above, in the first invention of the present application, the current penetration depth δ of the induced current when the primary coating layer of the base material surface is induction-heated and melted is set to one of the thickness d of the primary coating layer. .5 times or more (see FIG. 1). here,
As shown in Equation 1, the current penetration depth δ is a function of the specific resistance ρ, and the specific resistance ρ employs the specific resistance of the primary coating layer 11 in a molten state. Note that the specific resistance of the primary coating layer 11 in the molten state is larger than the specific resistance of the base material 10 in the solid state, and therefore, strictly speaking, the induced current density generated in the base material 10 is slightly The curve is shifted, but the difference is not so large,
In addition, since the magnitude of the induced current density (especially on the surface layer) in the primary coating layer 11 affects the occurrence of dents, constrictions, and the like in the coating layer, when the current density changes as shown by a curve 24 in FIG. There is no problem in assuming.

As is clear from Equation 1, the current penetration depth δ is a function of ρ and f, where ρ is a constant determined by the material of the primary coating layer. Therefore, in the practice of the present invention, the current penetration depth δ is set to 1.5 times the thickness d of the primary coating layer by setting the frequency f for performing induction heating low according to the thickness of the primary coating layer. It can be more than double. For example, the material of the primary coating layer 11 is SFNi4
(Self-fluxing alloy), the specific resistance ρ when molten is 110
Since the thickness of the primary coating layer 11 is 0.4 cm, the frequency f must be 7.7 kHz in order to make the current penetration depth δ 1.5 times or more the primary coating layer thickness. The following may be performed.

As shown by a curve 24 in FIG. 1, when a current distribution in which the current penetration depth δ is considerably larger than the thickness d of the primary coating layer 11 is employed, the surface portion of the base material 10 (the primary coating layer 11 A considerable amount of induced current also flows through the portion (contact portion), and this portion generates heat, which is also used for melting the primary coating layer 11. Therefore, it is not necessary to obtain the power required for melting the primary coating layer 11 only by the induced current flowing through the primary coating layer 11, and the induced current flowing through the primary coating layer 11 can be reduced accordingly. If the current penetration depth δ is small, for example, equal to the thickness of the primary coating layer 11, the inductor 12
In current density distribution when it is assumed that supplies the same power density P _e is as shown in curve 25 shown in FIG. 1 by the two-dot chain line,
The density of the current flowing through the primary coating layer is higher than in the case of the curve 24. In the curve 25, the surface induced current density I ₀ ′ is considerably larger than the surface induced current density I ₀ in the curve 24.

As described above, since the current penetration depth δ is conventionally set to be shallow and about the thickness of the primary coating layer 11, the induced current density I ₀ ′ on the surface is extremely large. Since a large electromagnetic stirring force according to the induced current density acts, dents and constrictions have occurred on the surface of the coating layer. However, in the first invention of the present application, when the same power density is used, the induced current density is curved. 24, the induced current density flowing through the primary coating layer 11 can be reduced, and particularly, the induced current density I ₀ in the surface layer can be reduced, so that the electromagnetic stirring force acting on that portion is reduced. The occurrence of dents and constrictions on the surface of the coating layer can be prevented. Conversely, the supply power density is set such that the induced current density I ₀ of the surface layer of the primary coating layer 11 becomes an allowable maximum value (a maximum value at which occurrence of dents and constrictions due to electromagnetic stirring force can be prevented). Then, in the case of the first invention of the present application, the supplied power density can be set to be larger than that in the case where the current penetration depth δ is made shallow, and therefore, the heating rate of the primary coating layer 11 (the characteristic line 14 Of the inductor 12 can be increased, the processing speed can be increased, and the length of the inductor 12 can be shortened.

[0022] As a result of the present inventor has confirmed, while a constant power density P _e, when began to increase the current penetration depth δ from a value equal to the thickness d of the primary coating layer 11, the primary coating layer Until the thickness d reaches about 1.5 times the thickness of the surface layer, the value of the induced current density in the surface layer sharply decreases. Therefore, the current penetration depth δ is reduced to 1.5 times the thickness d of the primary coating layer. By setting it to twice or more, the induced current density I ₀ in the surface layer can be effectively reduced, and the electromagnetic stirring force acting on that portion can be reduced. Therefore, in the first invention of the present application, the current penetration depth δ
Is 1.5 times or more the thickness d of the primary coating layer. It should be noted that the greater the current penetration depth δ, the smaller the induced current density I ₀ in the surface layer can be. However, if the current penetration depth δ is too large, the generated heat will be used for purposes other than melting of the primary coating layer 11 (base It is used for heating a deep part of the material 10), and the heating efficiency of the primary coating layer 11 is undesirably reduced. Considering this point, the current penetration depth δ is
It is preferable to keep the thickness of the primary coating layer 11 at about five times.

Next, in the second invention of the present application, in the method of induction heating the primary coating layer while relatively moving the inductor along the primary coating layer as described above, as shown in FIG. The inductor 12 is connected to the former inductor 12a with respect to the moving direction.
And the latter-stage inductor 12b, and the former-stage inductor 12a and the latter-stage inductor 12b are heated (the primary coating layer 11).
The power distribution to be applied to the base material 10) is increased by raising the temperature of the primary coating layer 11 to its melting point or near its melting point by the former inductor 12a, and then increasing the temperature of the primary coating layer 11 to its melting point or near its melting point by the subsequent induction. And the power density P _ea per unit surface area supplied by the former-stage inductor 12a to the object to be heated is set to be high so that the primary coating layer can be quickly heated. The power density P _eb per unit surface area supplied by the latter-stage inductor 12b to the object to be heated is set low so that the electromagnetic stirring force applied to the molten primary coating layer 11 is equal to or less than an allowable value. With such a setting, a temperature change when an arbitrary unit area portion 11a assumed on the primary coating layer 11 passes below the inductor 12 becomes, for example, a characteristic line 30 shown in the cluff of FIG. . That is, heating is started at time t ₀ , and the heating is performed under the pre-stage inductor 12 a (time t ₁
= L _a / V), rapid heating is performed, and the former inductor 1
At the outlet of 2a, the temperature reaches the temperature T _i close to the melting point T _m , and then the temperature is slowly increased by the latter-stage inductor 12b, reaches the melting point T _m at the time t ₂ , and reaches the time t ₃ (= L /
The heating is completed at V) (the final temperature is _Te ). Therefore, the molten processed primary coating layer between the time t ₂ ~ time t _3, etc. removal of pores is performed.

Here, during the melting treatment of the primary coating layer 11 by the latter-stage inductor 12b, the power density P _eb is kept low so that the electromagnetic stirring force applied to the molten portion is less than the allowable value. Processing can be performed without causing dents or constrictions on the surface, and the primary coating layer 1
When 1 is not subjected to electromagnetic stirring force in the solid state, a large power density _Pea is applied, so that the temperature can be quickly raised by the short former-stage inductor 12a. Can be performed. If the power density
If it is not divided into the latter stage, the whole must be treated with the latter power density P _eb , and in this case, since the heating rate is low, the length of the inductor 12 is increased or the treating speed V is decreased. There must be. In the second invention of this application, this problem can be solved.

In order to effectively implement the second invention of the present application,
Temperature T _{i of} primary coating layer 11 at the exit of pre-stage inductor 12a
May be the melting point T _m , but it is better that the melting does not proceed at this stage.
_i the 90-95% of the value of the melting point T _m (absolute temperature ratio)
It is good to set. The Atsushi Nobori from the temperature to the melting point T _m is not required to Sashitaru time by subsequent inductor.

As described above, the power density P _eb of the latter-stage inductor 12b is set so that the electromagnetic stirring force applied to the molten portion is equal to or less than the allowable value, and therefore, the induced current density in the surface layer is equal to or less than the allowable value. In this case, the current penetration depth δ is not particularly limited. However, as described with reference to FIG. 1, the induced current density at the surface layer changes when the current penetration depth δ is different even for the same power density _Peb . In other words, the induced current density at the surface layer is different. When the density is the same, the power density P _eb can be set large by increasing the current penetration depth δ. Therefore, even in the implementation of the second invention of the present application, it is preferable that the current penetration depth δ by the latter-stage inductor 12b be 1.5 times or more the thickness of the primary coating layer 11.
On the other hand, in the former-stage inductor 12a, there is no adverse effect due to the electromagnetic stirring force, so it is not necessary to keep the induced current density in the surface layer small. Therefore, the current penetration depth δ is determined by taking the heating efficiency of the primary coating layer 11 into consideration. The thickness may be set substantially equal to the thickness of the coating layer 11. However, when the front-stage inductor 12a and the rear-stage inductor 12b are connected to a common power supply, the applied frequency is the same and the current penetration depth δ is the same. The penetration depth (that is, the applied frequency) may be selected such that

In FIG. 5, the front-stage inductor 12a and the rear-stage inductor 12b are close to each other, but they need not always be arranged close to each other, and may be arranged at an appropriate interval. . The case in which there is an interval is preferable because the interference between the two inductors 12a and 12b is avoided.

The former inductor 12a and the latter inductor 12b can be operated by a common power supply, so that the cost of the power supply can be reduced. On the other hand, if they are operated by separate power supplies, respectively. In each case, a desired application frequency (current penetration depth) and a desired power density can be set, and the production speed can be easily improved. In many cases,
Since the common power supply can sufficiently cope with the situation, the power distribution and the setting of the power density when the common power supply is used will be described below.

FIG. 7 shows an inductor 1 for melting a primary coating layer 11 formed on the outer peripheral surface of a base material 10 made of a tubular body.
2 is divided into a front-stage inductor 12a and a rear-stage inductor 12b,
Also, an example is shown in which they are used by connecting them to a common power supply device 35. In this embodiment, the former inductor 1
Both 2a and the latter-stage inductor 12b are annular and are arranged so as to surround the base material 10, and are connected in parallel to the power supply device 35. Here, the front stage inductor 12a, the number of coil turns of the subsequent inductor 12b N _a, N _b, the coil width F
_a , F _b , β is the impedance ratio of the heating target facing the front and rear inductors (details will be described later), and P ₀ is the heating power. Power P _a distributed to the front and rear inductors 12a and 12b , _Pb and their ratio λ ₁ are given by Equations 2, 3 and 4.

[0030]

(Equation 2)

[0031]

(Equation 3)

[0032]

(Equation 4)

The first-stage inductor 12a and the second-stage inductor 12
The power densities P _ea , P _eb per unit surface area of the primary coating layer 11 facing b, and the ratio λ ₂ thereof are represented by Expressions 5, 6, and 7.

[0034]

(Equation 5)

[0035]

(Equation 6)

[0036]

(Equation 7)

By adjusting the number of coil turns and coil width of each of the front and rear inductors and the impedance ratio of the object to be heated facing the front and rear inductors based on the above formulas 2 to 7, Desired power distribution (P _a
/ P ₀ , P _b / P ₀ ), power density P _ea , P _eb, etc. For example, when obtaining the temperature rising characteristic indicated by the line 30 in the graph shown in FIG. 6, in order to make the outlet temperature of the former-stage inductor 12a to be an appropriate value (T _i ), the temperature rising temperature must be equal to the electric power P
_The number of coil turns N _a and N _b and the impedance ratio β may be set using Equation 2 as being proportional to _a and P _b . That is, the outlet temperature T _i of the previous inductor 12a, approximately 95% of the melting point T _m, when set to about 90% of the final temperature T _e, as a P _a / P ₀ = 0.90 From equation (2), the number of coil turns N ₁ and N ₂ and the impedance ratio β may be set. It should be noted that what is obtained from Equation 2 is a guide, and more precisely, a numerical calculation (FEM)
Etc.) or an actual load test.

Further, in the latter-stage inductor 12b, it is necessary to keep the power density _Peb small, to raise the temperature slowly, and to give a necessary stirring time so that an excessive electromagnetic stirring force does not act. Therefore, it is preferable to accurately set the power density P _eb . The setting of the power density P _eb can be performed using Expression 6.

[0039] Here, the coil turns N _b of the impedance ratio β and subsequent inductor 12b is, when shown graphically the effect on power density P _eb by the outlet temperature and subsequent inductor 12b of the preceding inductors 12a, FIG. 8 FIG.
8 and 9, u shown on the vertical axis is the ratio of the outlet temperature T _i to the final temperature T _e , that is, u = T _i / T _e , and P _eb ′ is the total power P ₀ . The ratio of the power density P _eb by the latter-stage inductor 12b to the power density when supplied by a single-turn coil, that is, P _eb ′ = P _eb / (P ₀ / πDF). Figure 8 is a number of coil turns N _a of the front inductors 12a 1, 9 is one in the case of the 2 number of coil turns N _a.

[0040] Figure 8, as seen from FIG. 9, to reduce the number of coil turns N _a of the preceding inductors 12a, subsequent inductor 12b
By increasing the number of coil turns N _b, front inductor 12
by increasing the power distribution of a can increase the outlet temperature T _i of the previous inductor, also, it is possible to lower the power density P _eb by subsequent inductor 12b. A similar tendency can be obtained by increasing the impedance ratio β. Therefore, it is possible to coil turns N _a, by adjusting the N _b and the impedance ratio β obtain the desired heating characteristics. In particular, the power density P _eb becomes small when increasing the number of coil turns N _b, and since the change is small, the power density P _eb
Can be set finely, which is preferable.

The impedance ratio β used in the above formulas 2 to 7 is β = (impedance Z _b per coil of the rear inductor) / (impedance Z _a per coil of the previous inductor). .

Here, the equivalent circuit of the coil including the object to be heated can be represented as shown in FIG. 10. Therefore, the impedances Z _a and Z _b are the impedances (R _c , X _c ) of the coil itself, The impedance (R,
X), and the impedance (X _g ) of the gap between the coil and the object to be heated. Among them, the impedance (R, X) of the object to be heated is proportional to the square root (√ρ) of the resistivity of the object to be heated, and the resistivity ρ is
Since towards the case of the liquid phase than in the case of heating the object (the primary coating layer 11) is solid phase quite large, if the other factors the same, the impedance impedance Z _b in the subsequent stage inductor 12b is in front inductors 12a much larger than Z _a, therefore, the impedance ratio beta, a slightly larger than 1. Air gap impedance (X _g )
Is proportional to the area of the gap, and the area of the gap can be appropriately changed. Therefore, the impedance ratio β can be freely changed by changing the area of the gap. For example, as shown in FIG.
By increasing the gap 2b, the impedance ratio β can be increased, for example, to 4 to 6. However, when the area of the gap is increased, the heating efficiency is reduced, so that the width of the gap is determined in consideration of the efficiency. Furthermore, coil width F _A, (A small coil width, the impedance becomes large) be changed F _B impedance varying so, may adjust the impedance ratio β by varying coil width F _A, the F _B . Therefore, as mentioned above,
At the time of setting the number of turns, coil width, and the like of the front inductor 12a and the rear inductor 12b, the impedance ratio β can be adjusted to an appropriate value to obtain a desired temperature rising characteristic. .

[0043]

As shown in FIG. 7, an inductor 12 for a base material 10 consisting of a tube is divided into a front inductor 12a and a rear inductor 12b and connected in parallel to a common power supply unit 35. Thing, the size of the base material 10, the outer diameter 52m
m, the thickness was 6 mm, and the design was made based on Formulas 2 to 7, and the following specifications were obtained. Front inductor 12a: coil turns N _a = 2 coil width F _a = 10 mm coils and tube and spacing = 10 mm later stage inductor 12b: coil turns N _b = 6 coil width F _b = 10 mm distance between the coil and the tube = 20mm Distance between center inductor 12a and rear inductor 12b (center-to-center distance) = 45mm

In the inductor 12 of this specification, the impedance ratio β = 6. Therefore, in FIG. 9, u (= T _i / T ₀ ) and P _eb ′ [= P _eb /
(P ₀ / πDF)] are values indicated by points P and Q, respectively.

The material of the primary coating layer is SFNi4 (JIS H8303) to be subjected to the melting treatment by the inductor 12A.
Specified Ni-based self-fluxing alloy. Melting point: 1000 ± 20 °
C) and the thickness d is 1, 2, 3, 4, 5 m, respectively.
Samples 1, 2, 3, 4, and 5 were prepared. And
Melting treatment was performed on each sample using the inductor 12A, at a processing speed (movement speed of the sample with respect to the inductor 12A) of 5 mm / s, and under the processing conditions shown in Table 1. In addition, since the specific resistance ρ of the coating layer 11 is 110 μΩ-cm, the current penetration depth δ is calculated from Expression 1, when the frequency is 9.8 kHz, δ = 5.33 mm, and the frequency is 4.5.
At kHz, δ = 7.86 mm. From this value, the magnification (δ / d) with respect to the coating thickness d was determined, and the value is also shown in Table 1.

Each temperature during each melting process was measured, and the power density P _eb per unit surface area of the sample facing the latter-stage inductor 12b was calculated. The results are also shown in Table 1. Further, the surface quality of the coating layer after each melting treatment was visually inspected, and the results are also shown in Table 1. "O" in the quality column of Table 1 indicates that the surface was smooth and had a good appearance,
“X” indicates a case where a dent or constriction has occurred on the surface.

[0047]

[Table 1]

As can be clearly understood from Table 1, in any of the melting processes for the samples, the pre-stage inductor outlet temperature T _{i is used.}
Is very close to the melting point. Therefore, the primary coating layer 11 can be quickly heated and heated by the former inductor 12a having a short number of turns of two coils, and the lower power The coating layer is heated at a density and melted. For this reason, the electromagnetic stirring force acting on the fusion zone is reduced, and good processing is performed (tests 1 to 3, 6 to 8). However, test 4,
In No. 5, although the coating layer is heated at a low power density and subjected to the melting treatment, the surface quality is deteriorated. This is presumably because the current penetration depth is small in magnification with respect to the thickness of the coating layer (1.33 and 1.07), the current density in the surface layer is high, and a large electromagnetic stirring force is acting.
Thus, it can be seen that increasing the magnification of the current penetration depth with respect to the coating layer thickness (for example, 1.5 times or more) can reduce the electromagnetic stirring force and prevent the surface quality from deteriorating.

[0049]

As described above, in the first invention of the present application, at least when the primary coating layer is induction-heated and melted, the current penetration depth of the induced current is set at 1.10 times the thickness of the primary coating layer.
By making it 5 times or more, the induced current density of the primary coating layer, especially the surface layer, can be reduced, thereby reducing the electromagnetic stirring force acting on the molten layer and causing dents, constrictions, etc. in the coating layer. This has the effect of preventing the formation of a metal coating layer of good quality.

In the second invention of the present application, an inductor for re-melting the primary coating layer by induction heating is electrically divided into a former-stage inductor and a later-stage inductor with respect to the moving direction.
By making the first stage inductor a high power density and the second stage inductor a low power density, the primary coating layer is quickly heated to the melting point or near the melting point by the first stage inductor. The melt processing can be performed with the stirring power kept small, and the metal coating layer of good quality can be formed using a relatively short inductor or at a high processing speed.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a state in which a primary coating layer of a base material surface is induction-heated by an inductor, and a graph showing an induced current density distribution in the primary coating layer and the base material.

FIG. 2 is a schematic cross-sectional view illustrating a state in which a general material to be heated is induction-heated by an inductor, and a graph showing an induced current density distribution in the material to be heated.

FIG. 3 is a schematic cross-sectional view illustrating a state in which a primary coating layer of a base material formed of a tubular body is heated by an inductor.

FIG. 4 is a graph showing a temperature rise characteristic when the primary coating layer is heated in the state shown in FIG. 3;

FIG. 5 is a schematic cross-sectional view illustrating a state in which a primary coating layer formed of a tubular body is heated by using an inductor and applying the second invention of the present application.

FIG. 6 is a graph showing a temperature rise characteristic when the primary coating layer is heated in the state shown in FIG.

FIG. 7 is a schematic cross-sectional view illustrating a state in which a primary coating layer made of a tubular body is heated by a front inductor and a rear inductor connected to a common power supply device.

FIG. 8 shows a case where the former inductor and the latter inductor having the configuration shown in FIG. 7 are used, and when the number of turns of the former inductor is one;
U for the number of turns N _b in the subsequent stage inductor, a graph showing the relationship between P _eb '

FIG. 9 shows a case where the former inductor and the latter inductor having the configuration shown in FIG. 7 are used, and when the number of turns of the former inductor is two.
U for the number of turns N _b in the subsequent stage inductor, a graph showing the relationship between P _eb '

FIG. 10 is a circuit diagram illustrating impedances of a first-stage inductor and a second-stage inductor having the configuration shown in FIG. 7;

FIG. 11 is a schematic side view showing a state in which a coating layer on the outer periphery of a tube is treated by a conventional method.

FIG. 12 is a schematic side view showing a state in which the coating layer on the outer periphery of the tube is treated by a conventional method different from that in FIG. 11;

[Explanation of symbols]

 Reference Signs List 10 base material (tube) 11 primary coating layer 12 inductor 12a front-stage inductor 12b rear-stage inductor 35 power supply device

Claims (5)

[Claims] 1. A primary coating layer of a metal material is formed on a surface of a base material by a thermal spraying method or the like, and thereafter, a small area of the primary coating layer is locally induction-heated using an inductor, and By melting the primary coating layer and moving the inductor relatively along the primary coating layer, the molten portion is moved along the primary coating layer, and the electromagnetic stirring force acting on the molten portion is increased. Utilizing, removing pores and oxides that were present in the primary coating layer, in a method of forming a dense secondary coating layer, at least the current penetration depth of the induced current at the time of melting of the primary coating layer. A method for forming a metal coating layer, wherein the thickness is 1.5 times or more the thickness of the primary coating layer. 2. A primary coating layer of a metal material is formed on a surface of a base material by using a thermal spraying method or the like, and thereafter, a small region of the primary coating layer is locally subjected to induction heating using an inductor, and By melting the primary coating layer and moving the inductor relatively along the primary coating layer, the molten portion is moved along the primary coating layer, and the electromagnetic stirring force acting on the molten portion is increased. Utilizing the method to remove pores and oxides present in the primary coating layer and to form a dense secondary coating layer, wherein the inductor is formed into a former inductor and a latter inductor in the moving direction. It is electrically divided, and the power distribution to be given to the heating target by the former inductor and the latter inductor is increased by heating the primary coating layer to the melting point or near the melting point with the former inductor, and the melting point or the melting point is near. The primary coating layer heated to It is set so that it can be melt-processed with an inductor, and further, the power density per unit surface area supplied to the object to be heated by the former-stage inductor is set high so as to enable rapid heating of the primary coating layer, A method for forming a metal coating layer, wherein the power density per unit surface area supplied to the object to be heated by the second-stage inductor is set low so that the electromagnetic stirring force applied to the molten primary coating layer is below an allowable value. 3. The method for forming a metal coating layer according to claim 2, wherein a current penetration depth of the induced current by the latter-stage inductor is 1.5 times or more the thickness of the primary coating layer. 4. The former-stage inductor and the latter-stage inductor are connected in parallel to a common power supply, and the number of turns of each coil is
The desired power distribution and power density for the front and rear inductors are obtained by adjusting a coil width, an impedance ratio of a heating target facing the front and rear inductors, and the like. A method for forming a metal coating layer. 5. The metal tube according to claim 1, wherein the base material is a metal tube, and a primary coating layer is formed on an outer peripheral surface of the metal tube.
The method for forming a metal coating layer according to any one of the above.