JPH0352786A - Liner welding method for tube inside surface - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for overlaying the inner surface of a tube, in which powder of a non-ferrous alloy, etc. is overlay-welded to the inner surface of the tube in order to form a lining layer of a non-ferrous alloy, etc. on the tube. Regarding welding methods.

[Conventional technology]

In recent years, overlay welding methods using powder have attracted attention as automatic, highly efficient, and high quality overlay welding methods. Welding technology: Vof
fi34 (1986), N (1B), a plasma jet or a laser is used as the welding heat source. Also, as a powder supply method, powder is passed through a feeding nozzle together with a carrier gas to supply it to the heated melting part. Inclusion method and
A coating method in which powder is applied to the surface of a base material in advance is known, and the former has already reached a practical stage.

[Problem to be solved by the invention]

In such a powder overlay welding method, if the former blowing method is used as the powder supply method, the powder will be dispersed and injected from the feeding nozzle, and some of the powder will not reach the heated and molten part, resulting in It is unavoidable that there will be a drop in retention. Furthermore, when supplying powder using the latter coating method, it is necessary to mix the powder with a binder to form a paste in order to fix the powder to the base material surface, which requires time and effort to handle. Furthermore, variations in the paste coating thickness affect the strength of the overlay layer, so
Strict control of coating thickness is also required, further worsening workability.

The present invention was developed in view of the above circumstances, and is a welding method that can easily supply powder to the inner surface of a pipe with a high yield and uniform thickness using centrifugal force when the material to be overlaid is a pipe. The purpose is to provide a welding method.

[Means for Solving the Problems] In the overlay welding method of the present invention, powder to be overlaid is supplied to the inner surface of the tube while rotating the tube around its axis, and the powder is applied to the inner surface of the tube by centrifugal force. The powder layer is fixed in a layered state and then melted using a high energy density heat source.

FIGS. 1(a) and 1(b) show an embodiment of the overlay welding method of the present invention.

In this example, the pipe 1 to be overlaid is supported horizontally and rotates around its axis. When the powder 3 to be overlaid is supplied to the inner surface of the tube from the downward powder supply nozzle 2 while the tube 1 is rotating, the supplied powder 3 is fixed to the inner surface of the tube by the centrifugal force accompanying the rotation of the tube 1. . Therefore, if the powder supply nozzle 2 is moved at a constant speed in the axial direction of the tube 1 while supplying the powder 3 at a constant feed rate, a constant thickness of powder N4 is formed on the inner surface of the tube. I can go. Then, while forming a powder layer 4 on the inner surface of the tube, the powder layer 4 is irradiated with laser from a downward-facing torch 5, and the torch 5 is moved in the same direction as the powder supply nozzle 2 to melt the powder layer 4. As the process progresses, a built-up layer is formed on the entire inner surface of the tube.

[For production]

According to the overlay welding method of the present invention, the powder 3 supplied to the inner surface of the tube 1 is held in a layer on the inner surface of the tube by centrifugal force.
Almost all of the supplied powder 3 is overlaid. Therefore, overlay welding can be performed easily and with a high yield even on the inner surface of the tube, which is difficult to perform.

In the overlay welding method of the present invention, a powder layer 4 of a constant thickness is formed on the inner surface of the tube.
The moving speed of the powder supply nozzle 2 is determined according to the inner diameter of the tube 1 and the amount of powder fed by the powder supply nozzle 2 so that

The moving speed of the torch 5 is appropriately determined based on the laser output and the rotation speed of the tube 1 so that the powder layer 4 can be sufficiently melted without any breaks.

The rotation speed of the tube 1 is an important factor to prevent the powder 3 from falling from the inner surface of the tube, and when the tube 1 is horizontal, it is set as follows.

Tube inner diameter: D (mm) Weight of 1 powder: m Tube rotation speed: r (1'/sec) Tube angular velocity: w-2πf (radian/sec),
How to prevent powder 3 from falling from the inside of the tube? It is necessary that m・■・w2 ≧mg 2 . Therefore, .

Furthermore, as shown in FIGS. 2(a) and 2(b), when the powder layer 4 formed on the inner surface of the tube 1 is melted, the surface layer of the tube 1, which is the base material, also melts. The build-up layer 6 is diluted with the base material. The base material dilution rate i of this built-up layer 6 is calculated as follows.

Powder feeding amount: M (g/min) Powder feeding nozzle moving speed: u (m/min) Base metal penetration depth: d (ribs) If the specific gravity of the base metal is 2g, then the overlay layer The base material dilution rate i of 6 is as follows. Here, if the apparent specific gravity of the powder: p and the thickness of the powder layer: h (am), then πDup, so dg hp+ag. The calculated value of this base material dilution rate i becomes an index of yield.

That is, it means that the closer the actual base material dilution ratio i in the build-up layer is to the theoretically calculated base material dilution ratio i, the higher the yield. In the overlay welding method of the present invention, the base metal dilution rate is closer to its theoretical value than in the conventional blowing method, and an excellent yield is ensured.

Further, the variation in the actual base material dilution rate i is an index of the uniformity of the overlay. The overlay welding method of the present invention has less variation in the welding method than the conventional binder application method, and has excellent uniformity in overlay distribution.

The material of the pipe 1 is not particularly limited, and examples thereof include low alloy steel, alloy steel, and the like.

Regarding the powder 3, the material and particle size that can be subjected to powder overlay can be selected as appropriate.

In the embodiment shown in FIG. 1, the torch 5 is moved from behind the powder feeding nozzle 2 at the same time;
It is also possible to melt the powder layer 4 after forming the powder layer 4 on the entire inner surface. Moreover, instead of moving the powder feeding nozzle 2 and the torch 5, the tube 1 may be moved in the axial direction. Furthermore, the tube l may be inclined. As for the heat source, a laser is used, but an arc, plasma jet, etc. may also be used.

〔Example〕

The following is a diagram illustrating an embodiment of the overlay welding method of the present invention.
The overlay welding method of the present invention was carried out in the modes shown in a) and (b). The material to be overlaid is STB42 carbon steel pipe for boilers and heat exchangers (C content = 0.28%, specific gravity q = 7.
9) was used. Pipe dimensions are outer diameter 127m and wall thickness 5I.
III1, with a total length of 1000 temples. As the powder to be overlaid, a Ni-50% Cr alloy (particle size 10 to 44 μm) was used. The apparent specific gravity of this alloy powder is 3.4. The laser was a CO2 laser, and the light was focused on the inner surface of the tube using a lens.

Other overlay welding conditions are as follows.

Tube rotation speed f: 4 (1/sec) = 240 (rpm) Powder feeding amount M: 50 (g/min) Powder feeding nozzle movement speed u: 1 0 0 (+mn
/min) Powder layer thickness h: 0.4 (am) Laser output: 1700 (W) Laser torch movement speed: 100 (IIn/sh
in) After overlay welding on the inner surface of the tube under the above conditions, the amount of C in the overlay layer was investigated over the entire length of the tube, and the distribution of the actual value of the base metal dilution ratio i in the tube axis direction was investigated. The actual value of the base material dilution rate i is the amount of C in the powder (CP) = 0. 0 5%, C content CCb of base material = 0. 28%, and the amount of carbon in the built-up layer was determined by the following formula as CH. The survey results are shown in Figure 3.

C. -C, 0.23 For comparison, overlay welding was also carried out using the conventional blowing method and coating method.

In the blowing method, a carrier gas (Ar3 1!./l) is injected from the front of the laser torch under the same laser conditions and powder amount.
The powder was blown directly into the laser-heated melting zone using the following method. In the coating method, the powder was applied to the inner surface of the tube using water glass as a binder. Since the apparent specific gravity of powder containing a binder is reduced to 2.7, the coating thickness was set to 5 mm to ensure the same amount of powder as when no binder was used. The laser conditions were the same as those for the above two methods.

The distribution of the base material dilution ratio i in the tube axis direction in the blowing method and coating method is shown in FIGS. 4 and 5, respectively. Further, Table 1 shows the dilution rate average value, standard deviation, and yield based on the actual value of the base material dilution rate i in the above three methods.

The yield was determined by the target value/average value, using the theoretically calculated value (23%) of the base material dilution rate i as the target value.

As is clear from Table 1, Figures 3 to 5, and Table 1, the yield of the method of the present invention is much superior to that of the conventional blowing method, and comparable to the coating method. Regarding the standard deviation, the method of the present invention is superior not only to the coating method but also to the blowing method. Therefore, in the method of the present invention, the uniformity of the build-up layer is extremely good.

〔Effect of the invention〕

The overlay welding method of the present invention can retain almost the entire amount of the fed powder on the inner surface of the tube by using centrifugal force due to the rotation of the tube. Therefore, the yield is extremely high despite the direct feeding of the powder.

In addition, by directly feeding the powder and using centrifugal force, it is possible to easily build up the inner surface of the tube, which is difficult to weld, and the build-up layer has excellent uniformity. Therefore, the method of the present invention can be said to be industrially extremely significant as a means of forming a lining layer on the inner surface of a tube.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are schematic diagrams showing one embodiment of the present invention, FIGS. 2(a) and (b) are schematic diagrams showing the form and process of the built-up layer, and FIGS. 3 to 5. is a graph showing the distribution of the base material dilution rate in the tube axis direction. In the figure, l: tube, 2: powder supply nozzle, 3: powder, 4: powder layer, 5: torch, 6: overlay layer. l1 Figure 2 Figure 3 Method of the present invention Figure 4 Blowing method 0 500 1000 Axial position W (mm) 5 Coating method Figure Axial position (mm)

Claims (1)

[Claims] (1) While rotating the tube around its axis, supply the powder to be overlaid onto the inner surface of the tube, fix the powder in a layer on the inner surface of the tube by centrifugal force, and create a powder layer with high energy density. A welding method for overlaying the inner surface of a tube, which is characterized by melting using a heat source.