JPH0436787B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of overlay welding to a predetermined workpiece (base material), and particularly to a method of overlay welding a powder material to the workpiece using a plasma arc. Processed parts (base material) such as valves, pipes, rolls, etc.
Overlay welding is conventionally known in which a predetermined overlay (filler metal) is welded to improve the wear resistance, heat resistance, corrosion resistance, etc. of the surface of a workpiece. And one of them is the so-called PRW
There is a plasma powder welding method called (Plasma Arc Powder Welding) method. This plasma powder overlay welding method converts an arc (pilot arc) generated at the tip of an electrode in the torch inner cylinder of a plasma arc torch into a plasma arc by plasma gas supplied to a passage in the torch inner cylinder. On the other hand, the plasma arc is transferred between the electrode and the workpiece by a welding current flowing between the electrode and the workpiece, and a carrier gas is used in the plasma arc to perform the work. A welding method in which a powder material to be overlaid on a member is supplied, the powder material is welded and transferred to the surface of the workpiece, and a predetermined overlay is performed, as described above. Since a powder material is used as the overlay material, the material for the overlay material can be easily selected from a wide range and melted easily, and the amount of penetration into the base material is small, so the dilution rate is low. In addition, compared to the case of using bar materials, it has excellent characteristics such as faster melting speed and shorter welding time.
Moreover, it has been attracting attention in recent years because it is easy to fully automate the device. By the way, in this plasma powder build-up welding method, if the flow rate of the plasma gas is too high, the molten build-up material at the center of the build-up part of the workpiece will be blown toward the periphery by the force of the plasma gas, and the build-up part will be damaged. This can lead to problems such as poor bead shape, but conventionally, when such problems occur, simply reducing the flow rate causes the plasma arc to retract, and the plasma is transferred to the workpiece. This has the disadvantage that the conditions under which an arc can be stably supplied are severely limited, making it impossible to use it particularly with high-voltage type torches. Here, the present invention has been made in view of such circumstances, and its purpose is to
Plasma powder overlay that can stably supply plasma arc to the workpiece without restricting the usage conditions of the plasma arc torch, and evenly distribute the overlay material to obtain a good bead shape. The purpose is to provide a welding method. In order to achieve this object, in the plasma powder overlay welding method according to the present invention, the inside of the torch and the outer cylinder of the torch each having a nozzle portion at the tip are arranged, and the electrode is arranged in the center of the inner cylinder of the torch. In this state, plasma gas of a predetermined pressure is supplied to the passage in the torch inner cylinder, while a predetermined pressure is supplied to the passage between the torch inner cylinder and the torch outer cylinder. A plasma arc that is supplied with a carrier gas containing a powder material and is provided with a shield gas blowing means that blows out shield gas in a substantially cylindrical shape in the axial direction around the tip nozzle part of the torch outer cylinder. In the above-mentioned plasma powder welding method (PPW method) using a torch, the current-voltage characteristics of the power source for flowing welding current between the electrode and the workpiece are rectangular and fixed within the working current range. The idea was to convert it into a voltage. In this way, even if the amount of plasma gas is reduced, the amount of regression of the plasma arc due to the reduction will be compensated by the voltage of the power supply, so the regression of the plasma arc will be eliminated and the plasma will not reach the workpiece. The arc is maintained stably, the bead shape in the built-up portion of the workpiece is also formed in a good condition, and the usage conditions of the torch are not restricted. In other words, in the past, the current-voltage characteristic of the power source for supplying welding current was such that the voltage decreased approximately in proportion to the increase in current. When the arc retracts, the range in which the retraction can be compensated for by boosting the voltage is limited to a narrow range where the amount of current is small, but according to the present invention, even in a range where the amount of current is large, the torch can be compensated for by increasing the voltage. Since a large voltage can be applied, even if the plasma arc retracts due to a decrease in the amount of plasma gas as mentioned above, or even if the torch used is of a high voltage type, the retraction can be compensated for by the voltage. This can be sufficiently compensated for by boosting the pressure. Note that the voltage maintained by the power supply here is
The voltage is large enough to maintain a stable plasma arc between the electrode and workpiece even when the amount of plasma gas decreases, but this voltage depends on the capacity and shape of the torch, the distance between the electrode and workpiece, and the welding current. Since it differs depending on the operating current range, etc., it must be set appropriately each time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clarify the present invention more specifically, one embodiment of overlay welding on an automobile valve will be described in detail below with reference to the drawings. First, FIG. 1 is an explanatory diagram of a plasma overlay welding apparatus in which the present invention is suitably implemented, and 10 is the tip of a plasma arc torch (hereinafter simply referred to as a torch). The torch 10 includes a tungsten electrode 12 at its center, and a torch inner tube 14 and a torch outer tube 16 are coaxially arranged outside the electrode 12 at a predetermined distance from each other. Between the electrodes 12 and the torch inner cylinder 14, and between the torch inner cylinder 14 and the torch outer cylinder 16,
Annular passages 18 and 20 are formed, respectively. The passage 18 is connected to a plasma gas supply device 24 via a pipe 22, and plasma gas at a predetermined pressure is supplied at a predetermined flow rate. The plasma gas supplied to this passage 18 is ejected to the outside from a nozzle 30 provided at the tip of the torch inner cylinder 14. In addition, this plasma gas is
An inert gas such as argon gas or helium gas is used. Further, the passage 20 is connected to a carrier gas supply device 34 via a pipe 32, and the pipe 32 is further connected to a carrier gas supply device 34.
A powder supply device 36 is connected to the middle part of 2,
A predetermined powder material (overlay material) is supplied from the powder supply device 36. In other words,
A carrier gas containing a predetermined amount of powder material is supplied to the passage 20, and the carrier gas is ejected to the outside from a nozzle 38 provided at the tip of the torch outer cylinder 16. As the powder material, it is possible to use various filler metal powders such as Co-based, Ni-based, and Fe-based, and it is possible to select the appropriate one depending on the purpose of overlay welding or the material of the workpiece. It will be selected. In addition, as the carrier gas, argon gas, similar to the above plasma gas,
An inert gas such as helium gas is used. On the other hand, cooling water passages 40 and 42 are provided in the nozzles 30 and 38 of the torch inner cylinder 14 and the torch outer cylinder 16, respectively.
0 and 38. Furthermore, a shielding gas such as argon gas or helium gas is supplied to the tip of the torch outer cylinder 16 from a shielding gas supply device 44 through a pipe 46, and the shielding gas is supplied to the torch 1.
The welded portion is shielded by being blown out in a substantially cylindrical shape in the axial direction of 0. Further, between the electrode 12 of the torch 10 and the torch inner cylinder 14, a predetermined pilot current is supplied from a pilot power source 48, and the electrode 12 and the workpiece to be overlay welded ( A predetermined main current (welding current) is supplied from a main power source 50 to an automobile valve 54 (base material). Further, a high frequency oscillator 52 is inserted between the electrode 12 and the torch inner cylinder 14 in parallel with the pilot power source 48. The valve 54 is fixed to a backing 56 that rotates around one axis at a predetermined speed, and as the valve 54 rotates, a predetermined surface hardening is applied to the welded part (built-up part) 58 of the cap part of the valve 54. Welding is now being done. In order to perform overlay welding in the apparatus configured as described above, first, a pilot current is supplied from the pilot power source 48 to generate a pilot arc between the tip of the electrode 12 and the nozzle 30 of the torch inner cylinder 14. At the same time, the plasma gas supply device 24
Plasma gas is supplied into the annular passage 18 from the annular passage 18 .
As a result, a plasma arc is formed at the tip of the electrode 12. Note that this plasma arc can be generated at a predetermined period determined by the high frequency oscillator 52. After that, main current (welding current) is supplied from the main power supply 50 between the electrode 12 and the valve 54,
The plasma arc formed at the tip of the electrode 12 is moved to the bulb 54. In this state, a carrier gas containing a predetermined powder material is supplied into the passage 20 from the carrier gas supply device 34 and the powder supply device 36, and is ejected from the nozzle 38.
This ejected powder material is melted by a plasma arc and overlay welded to the cap weld portion 58 of the valve 54, as shown by the broken line in FIG. At this time, shielding gas is blown out from the tip of the torch 10 so that the molten powder material and the welded portion 58 are not affected by oxygen in the air. In the apparatus for overlay welding as described above, in this embodiment, the flow rate of the plasma gas ejected from the nozzles 30 and 38 is, for example, 0.6 to
Approximately 1.2/min (gas pressure is ^{approximately} 1.5Kg/mm2)
is set relatively low, and the electrode 12
The current-voltage characteristics of the main power supply 50 for passing a melting current between the valve 54 and the valve 54 as a processing member are approximately rectangular, as shown by the solid line in FIG. In the following, the output voltage is maintained at approximately 60V, and by setting the plasma gas flow rate and the current-voltage characteristics of the main power source 50 as described above, the automotive valve 54 Overlay welding of the molten part 58 is performed over a wide range of voltage type torches 10 without the plasma arc becoming unstable during welding, and a good bead shape can be obtained. It is. Note that the main power supply 50 having the current-voltage characteristics as described above can be obtained, for example, by adopting a thyristor-controlled rectification method.
There is no problem even if a rectification method other than that is adopted. Conventionally, when performing overlay welding similar to the above, the plasma gas flow rate was 2.5/
There was an inconvenience that the bead shape exhibited a lack of thickness in the central part of the welding part 58.When trying to solve this inconvenience by reducing the plasma gas flow rate, the main power supply 50 was turned off as shown in FIG. Since the current-voltage characteristics were as shown by the broken line, the plasma arc became unstable in the range where the voltage was low and the amount of current was large, making it impossible to perform good overlay welding. . Incidentally, in the method of this embodiment in which the characteristics of the main power supply 50 are made constant voltage within the operating current range, and in the conventional method having the characteristics shown by the broken line in FIG. Amount (0.6~
1.2/min).
Table 1 shows the results of investigating the plasma arc generation situation and bead shape. The automobile valve 54 as a processed part is made of 21-4N material, and the diameter of the umbrella part is 36 mm (the width of the welded part 58 is about 4 mm).
The welding speed was 4.5 mm/s and 6.0 mm/s. Furthermore, regarding the voltage types of the torch 10, those of 30, 40, and 45V were targeted.

[Table] As is clear from Table 1, in the conventional method in which the current-voltage characteristics of the main power source 50 are not regulated at a constant voltage within the operating current range (approximately 300 A or less in this example), the welding current is high. The plasma arc was not stable in the range where the voltage decreased, and therefore overlay welding could not be performed satisfactorily, but if the characteristics were made rectangular and the voltage was made constant as in this example, Even in such a range, and even if the torch 10 is of a high voltage type, a plasma arc can be stably generated during overlay welding, and as a result, a good bead shape can be obtained. . Note that the range indicated by the diagonal line slanting to the right in FIG. This is the range in which the plasma arc in the method can be stably generated. Although one embodiment of the present invention has been described above, the present invention should not be interpreted as being limited to this embodiment. For example, in the above embodiment, the processed part (base material) is a valve 54 for an automobile whose umbrella part has a diameter of 36 mm, but the processed part is a valve 54 whose cap part has a diameter other than 36 mm. In addition, there is no problem in using pipes, rolls, etc. as processing members. Further, in the embodiment described above, the voltage of the main power supply 50 was maintained at approximately 60V, but the maintained voltage may be changed depending on the situation. Furthermore, the operating current range is not limited to about 300A or less as in the above embodiment,
Of course, it can be changed depending on the situation. Although not listed in detail, it goes without saying that the present invention can be implemented with various modifications and improvements without departing from the spirit thereof.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a plasma overlay welding apparatus that can suitably carry out the present invention, and FIG. 2 shows the current-voltage characteristics of the main power source shown in FIG. 1 together with those of a conventional power source. It is a diagram. 10: Plasma arc torch, 12: Electrode, 2
4: Plasma supply device, 50: Main power supply, 5
4: Valve (processed member).

Claims (1)

[Claims] 1. A torch inner cylinder and a torch outer cylinder, each having a nozzle at its tip, are installed coaxially with an electrode disposed at the center of the torch inner cylinder, and a predetermined pressure is applied to the passage inside the torch inner cylinder. plasma gas is supplied to the torch, and a carrier gas containing a predetermined powder material is supplied to the passage between the torch inner cylinder and the torch outer cylinder. A plasma arc torch is provided with a shield gas blowing means for blowing shield gas in a substantially cylindrical shape in the axial direction around the tip nozzle portion of the plasma arc torch. While the arc is made into a plasma arc by the plasma gas supplied to the passage in the inner cylinder of the torch, the plasma arc is
The welding current passed between the electrode and a predetermined workpiece causes a transition between the electrode and the workpiece, and also causes a welding current between the torch inner cylinder and the torch outer cylinder to flow into the plasma arc. In the welding method, the powder material to be overlaid on the workpiece is supplied through a passage, the powder material is melted and transferred to the surface of the workpiece, and a predetermined overlay is performed. 1. A plasma powder overlay welding method, characterized in that the current-voltage characteristics of a power source for passing a welding current between an electrode and a workpiece are made rectangular so that the voltage is constant within the working current range.