JPH01252762A - Method for coating inner surface of metallic cylinder - Google Patents

Abstract

PURPOSE:To form a dense coating film layer free of oxides and pores and having excellent adhesive and bonding properties by forming a thermally sprayed coating film layer of a low-melting-point metal on the inner surface of a metallic cylinder, and heating the layer while rotating the cylinder to melt the layer under vacuum. CONSTITUTION:The metallic cylinder 1 made of mild steel, etc., with the roughed surface is horizontally placed on a rotary supporting ring 4, and rotated by a rotating means 5 at a constant peripheral speed. A thermal spraying gas 2 supported by a gun moving jig 3 is simultaneously reciprocated to thermally spray a metal having a lower m.p. than the cylinder on the inner surface of the cylinder 1, and a coating film layer 6 is formed. An outflow interrupting plate 7 is set on both ends of the cylinder 1, and the cylinder is placed on the rotary ring 10 and rotated in a vacuum chamber 8. The cylinder 1 is heated by a heating source 11 consisting of a radiant heat reflecting plate 12 and a Kanthal wire 13, and held at a temp. higher than the m.p. of the thermal spraying metal by a thermocouple 14 to melt the coating film layer 6 on the inner surface. By this method, a good-quality coating film layer is formed on the inner surface of a metallic cylinder.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a method of applying a metal having excellent corrosion resistance and wear resistance, particularly a self-fusing alloy, etc. to the inner surface of a metal cylinder such as a steel pipe for oil drilling. The present invention relates to a method of coating the inner surface of a metal cylinder by thermal spraying to form a coating layer to improve the characteristics of the inner surface.

[Conventional technology]

The thermal spraying method, in which particles of metal or ceramics in a molten state are continuously sprayed onto the surface of a base material to form a coating layer having corrosion resistance, wear resistance, heat resistance, etc., is well known. This thermal spraying method is often used as a coating method for improving the surface properties of metal parts.

Examples of methods for forming a corrosion-resistant and wear-resistant coating layer on the inner surface of a metal cylinder using this thermal spraying method include:
There is one disclosed in Japanese Unexamined Patent Publication No. 186972/1983.

This prior art involves spraying metal powder such as Ni-Cr-3i-8 alloy, which has a lower melting point than that of the metal cylinder, on the inner surface of a metal cylinder such as CrMo alloy steel to form a coating layer, and then A metal cylinder is heated to a temperature above the melting point of the sprayed metal powder and below the melting point of the metal cylinder using an appropriate heating means such as high-frequency induction heating, and only the coating layer on the inner surface is melted from the inside. By heating and melting the corrosion-resistant and wear-resistant coating layer formed by thermal spraying, the countless pores formed in the coating layer during the thermal spraying process are removed, and the metal cylinder and Diffusion bonding is achieved at the interface of the coating layer, so that the coating layer on the inner surface of the metal cylinder is dense, has no pores, and is in a tightly bonded state.

Incidentally, in the above-mentioned conventional technology, Ni-Cr-3i-8 alloy used as an example of thermal spray metal and S
Ni-based and Go-based alloys containing i are particularly known as ``self-fusing alloys,'' and these self-fusing alloys are melted by heating and melting the coating layer after being thermally sprayed onto the surface of the metal base material. By performing the treatment, the oxides in the coating layer formed by thermal spraying are made to float to the surface of the coating layer as 8201, SiO It is well known that a coating layer can be made dense with pores, and that diffusion bonding with the base material can be promoted in the process, resulting in a coating layer that has excellent bonding properties with the base material.

[Problem to be solved by the invention]

As mentioned above, the surface of the metal base material has corrosion resistance, wear resistance,
By thermally spraying a metal such as a self-fusing alloy having heat resistance to form a coating layer, and then melting the coating layer,
It is possible to form a coating layer on the surface of the metal base material that contains few oxides, has no pores, is dense, and has excellent bonding properties with the base material.

However, in order to obtain the desired effect in this melting process, it is assumed that the metal of the coating layer must be heated to a temperature higher than the melting point to be in a molten state. The coating layer becomes fluid.

Therefore, the above-mentioned prior art (Japanese Patent Application Laid-open No. 186972/1983)
When forming a coating layer on the inner surface of a metal cylinder, as in
If the entire coating layer is melted in the melting process after thermal spraying, the coating layer that has obtained fluidity will flow downwards on the inner peripheral surface, making it impossible to maintain a stable coating layer. If the heating temperature is set low in order to suppress the flow, the effect of the melting process will be reduced, leading to the problem that the intended good coating layer will not be obtained.

However, the prior art (Japanese Patent Application Laid-open No. 186972/1983)
No mention is made of the flow of the coating layer on the inner surface of the cylinder during the melting process or how to deal with it.

On the other hand, the present inventors sprayed a self-fusing alloy onto the inner surface of a metal cylinder to form a coating layer, then partially heated and melted the coating layer with a burner, and sequentially applied this to the entire inner surface. We tried a method of melting treatment by suppressing the flow of the coating layer, but with this method, it was difficult to measure the temperature of the molten part on the inner surface of the cylinder, and the molten state could not be directly observed. It has been found that the problem arises that the melting process tends to be uneven and uncertain, and furthermore, when the melting process is performed in the atmosphere, the pores and oxides in the coating layer float to the surface of the coating. However, it was found that some of it remained in the coating and became a factor in deteriorating the properties of the coating layer.

In view of the above-mentioned problems, the present invention is capable of ensuring reliable melting treatment of a metal coating layer formed by thermal spraying on the inner surface, and has a structure that is dense with few oxides, free of pores, and has a high degree of compatibility with the base material. The object of the present invention is to provide a method for coating the inner surface of a metal cylinder, which makes it possible to form a coating layer with excellent adhesion and bonding properties.

[Means to solve the problem]

In order to achieve the above object, the present invention has the following gist. That is, in the method of coating the inner surface of a metal cylinder according to the present invention, a metal having a melting point lower than that of the metal cylinder is thermally sprayed onto the inner surface of the metal cylinder to form a coating layer, and then the metal cylinder is placed under vacuum. The coating layer on the inner surface of the sprayed metal is melted by heating it to a temperature higher than the melting point of the sprayed metal while rotating.

[Effect]

In the present invention, a coating layer is formed on the inner surface of a metal cylinder by spraying a metal having a melting point lower than that of the metal cylinder,
After that, the metal cylinder is heated to a temperature higher than the melting point of the sprayed metal, so it is possible to melt only the coating layer on the inner surface of the metal cylinder without melting the metal cylinder, and to melt the entire cylinder. By heating the inner surface, the coating layer on the inner surface can be uniformly heated and melted.

In addition, since the melting process is performed by heating the metal cylinder while rotating it under vacuum, the coating layer on the inner surface of the cylinder that has been heated and melted and has fluidity in the process of the melting process is
It is evenly pressed against the inner circumferential surface of the cylinder by the centrifugal force caused by the rotation of the cylinder, and the higher the fluidity, the more uniform the thickness becomes.

During this melting process, the pores and oxides in the coating layer, which are floated to the surface of the coating layer due to the difference in specific gravity, are encouraged to float by the addition of angular acceleration due to centrifugal force.
Furthermore, since this melting treatment is performed under vacuum, the floating separation of pores and oxides in the coating layer is further promoted, and gas components are also removed, resulting in a healthier coating layer.

In addition, during this melting process, the coating layer is pressed against the inner surface of the cylinder by centrifugal force, which further promotes diffusion bonding at the interface between the inner surface of the cylinder and the coating layer, resulting in tighter contact between the two.
The bonding becomes reliable.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, the outer diameter is 240Il11, the inner diameter is 200mm, and the length is 50mm.
A mild steel cylinder of No. 011!1 is prepared, and its inner surface is roughened by grid blasting, and then the inner surface is coated with a material that has corrosion and abrasion resistance and a melting point of 980 to 1040°C.
A Ni-based self-fluxing alloy containing B + Si + Cr was thermally sprayed.

FIG. 1a is a partially cutaway front view showing an overview of the thermal spraying apparatus used in this example, and FIG. 1a is a sectional view taken along the line AA in FIG. 1a.

In Fig. 1a and Fig. 1, (1) is a cylinder, and the cylinder (1) is made of the above-mentioned roughened mild steel, and here it is shown set in a thermal spraying device. show.

(2) is a plasma spray gun;
is held in a gun moving jig (3) and is movable in the longitudinal direction of the inner diameter of a cylinder (1) set in the device.

(4) is a rotation support wheel, and the rotation support wheel (4) is
A plurality of cylinders are arranged in pairs in two rows to support the cylinder (1) horizontally, and are driven by a rotating means (5) to rotate the cylinder (1) supported on the upper part. .

Thermal spraying is performed by rotating the cylinder (1) at a constant circumferential speed via a rotary wheel (4) and reciprocating the thermal spraying gun (2) between both ends of the cylinder (1) at a constant speed. Ji
The thickness of (6) was approximately 111II11.

Next, the coating N (6) formed on the entire inner surface of the cylinder (1) by the above thermal spraying was subjected to a melting treatment.

FIG. 2a is a front sectional view showing the main parts of the melt processing apparatus used in this example, and FIG. 2A is a sectional view taken along the line AA in FIG. 2a.

In Fig. 2a and Fig. 2, (1) is a cylinder, and the cylinder (1) is the one described above with a coating layer (6) formed on its entire inner surface, and here the melting treatment Indicates the state set in the device.

(7) is an outflow blocking plate, and the outflow blocking plate (7) is a ring-shaped member with an inner diameter smaller than that of the cylinder (1), and is attached concentrically to both end faces of the cylinder (1). It is rare.

(8) is a vacuum chamber, the vacuum chamber (8)
A plurality of rotating wheels 0 are disposed in pairs in two rows on the inner bottom to horizontally support the cylinder (1), and are driven by a rotating means (9) to rotate the cylinder (1) at high speed. A heating a! is installed in the upper part of the cylinder (1), which is hung from the earthen wall at a freely adjustable height, and covers the entire length of the upper part of the cylinder (1) in an arc shape, which is supported by the rotating wheel 00). a+). The heating source θ0 has an arc-shaped radiant heat reflecting plate 02) disposed on its upper part, and a Kanthal wire side which is controllably energized by a power supply means (not shown) is disposed on its lower surface.

04 is a temperature measuring thermocouple, and the temperature measuring thermocouple is arranged to measure the temperature inside the cylinder (1) set in the vacuum chamber (8).

During the melting process, the degree of vacuum in the vacuum chamber (8) is reduced to 1O-3.
The cylinder (1) was heated under the following conditions:
Constantly 0.6M/sec in the process of heating, holding, and cooling
, and for cooling, Ar gas was introduced into the vacuum chamber (8), and the cooling rate was 600'C at a cooling rate of 50'C/Hr under an inert atmosphere of the Ar gas. After that, the vacuum chamber (8) was opened to allow cooling in the atmosphere.

Coating layer (6) on the inner surface of the cylinder (1) obtained after the above treatment
exhibits a smooth surface, and when the cylinder was fractured and investigated, the thickness of the coating layer (6) was almost uniform on each fractured surface, and each cross-sectional structure was porous and free of residual oxides. It exhibited a dense and good structure with very few particles, and the bonding state at the interface with the inner surface of the mild steel cylinder was also very good.

FIG. 3 is a photograph of the metallographic structure showing the cross-sectional structure of the coating layer (6) on the inner surface of the cylinder (1) obtained in this example, and the range indicated by A in the figure shows the coating layer (6). , B indicate the cross-sectional structure of the base material, the mild steel cylinder (1).

FIG. 4 and FIG. 5 are metallographic photographs showing the cross-sectional structure of the coating layer portion of the comparative example of this example, and these are
This is a coating layer formed by thermally spraying a self-fusing alloy with the same composition under the same conditions on the same mild steel plate surface as in this example, and the only difference from this example is the melting treatment conditions after thermal spraying. .

Figure 4 shows the cross-sectional structure of an example melted in the atmosphere without rotation, and Figure 5 shows the cross-sectional structure of an example melted without rotation in an Ar atmosphere.The range indicated by A in each figure is The portion of the coating layer portion indicated by B indicates the cross-sectional structure of the mild steel plate portion that is the base material.

Compared to the comparative examples shown in FIGS. 4 and 5, the example shown in FIG. 3 has extremely little residual oxide in the coating layer, and has a dense and good structure. It can be seen that the diffusion bonding state with the base metal, mild steel, is also very good.

In this example, the metal to be thermally sprayed is B +
Although a Ni-based self-fluxing alloy containing S 11 Cr was used,
This is just an example; metals with other compositions or self-fusing alloys may be used depending on the required characteristics of the inner surface of the cylinder, as long as they have a lower melting point than the metal material of the cylinder to be sprayed. Can be done.

In addition, for these applications, cylindrical metal materials and
Depending on the selection and combination of metals to be sprayed, there may be large differences in thermal expansion and cooling contraction between the two.
The characteristics of the metal material of the target cylinder and the sprayed metal are thoroughly studied in advance, and a graded thermal spraying is applied in which thermal expansion coefficient adjustment metal such as Mo, WSWC, or Tic is interposed between the two. In addition, it is desirable that consideration be given to applying constant temperature treatment or slow cooling treatment during cooling after thermal spraying and melting treatment.

Furthermore, as the melting treatment equipment, a vacuum heat treatment furnace can be used as long as it does not deviate from the gist of the present invention, which heats and cools the cylindrical object while rotating it. It is also a preferable example to arrange it along the entire length of the inner diameter side and heat it from the inner surface side.

〔Effect of the invention〕

As described above, according to the method for coating the inner surface of a metal cylinder according to the present invention, the metal coating layer formed by thermal spraying on the inner surface can be made to have a uniform thickness with a relatively smooth surface. The internal structure can be made porous and dense with extremely little residual oxide, and can have excellent adhesion and bonding properties with the base material, forming a coating layer with excellent properties on the inner surface of the metal cylinder. can be done.

[Brief explanation of the drawing]

Fig. 1a is a partially cutaway front view showing an outline of a thermal spraying apparatus according to an embodiment of the present invention, Fig. 1 is a sectional view taken along line A-A in Fig. A front cross-sectional view showing the main parts of the melt processing apparatus according to the embodiment, a cross-sectional view taken along the line AA in FIG. 2 or FIG. 2a, and FIG. Metal Structure Photographs FIGS. 4 and 5 are metal structure photographs showing the cross-sectional structure of the coating layer portion of the comparative example. (1)-Cylinder, (2)-Thermal spray gun, [3)-
Gun moving jig, (4) one rotation support ring, (5) one rotation means, (6) - coating layer, (7) - outflow blocking plate,
(8) - Vacuum chamber, (9) Single rotation means, 00
) - Rotating wheel, (ID - Heating source. Patent applicant Kobe Steel Co., Ltd. Agent Patent attorney Akira Yomitsu - Figure 1a Figure 1S Figure 2α Figure 2b

Claims (1)

[Claims] A coating layer is formed by spraying a metal with a melting point lower than the melting point of the metal cylinder on the inner surface of the metal cylinder, and then the metal cylinder is heated under vacuum to a temperature higher than the melting point of the sprayed metal while rotating. A method for coating the inner surface of a metal cylinder, characterized in that the coating layer on the inner surface is melt-treated.