METHOD FOR REINFORCING WELDING TIP AND WELDING TIP

In order to extend a lifetime of a welding tip in a simple way, a surface reinforcing layer 2 is formed by ejecting a metal powder shot onto at least an inner peripheral surface of a welding tip 1 (1, 12) formed of any material of copper, a copper alloy or ceramic-dispersed copper at an ejection velocity of 100 m/sec or higher. The metal powder shot has an average particle diameter of 40 to 150 μm and hardness equal to or higher than the material of the welding tip 1 (11, 12). Then, a semiconductor film 3 is formed on the surface reinforcing layer 2 by further ejecting a tin powder with an average particle diameter of 10 μm to 100 μm having a tin oxide film formed thereon onto the surface reinforcing layer 2 at an ejection velocity of 200 m/sec or higher.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Outline of Manufacturing Method

A method for reinforcing the welding tip of the present invention includes: a step of forming a surface reinforcing layer2in the vicinity of an inner peripheral surface of a welding tip by ejecting a metal powder shot having hardness higher than that of a base material of the welding tip onto at least the inner peripheral surface of the welding tip; and a step of forming a semiconductor film3of tin oxide by further ejecting a tin powder shot having a tin oxide film formed thereon onto the surface reinforcing layer2.

Subject to be Processed

The welding tip to be processed in the present invention includes both of a contact tip11which is provided in a torch for arc welding described with reference toFIG. 2and forms a power distribution point with an electrode rod5, and a nozzle tip12which is provided in a torch for plasma welding as described with reference toFIG. 3and covers an outer periphery of an electrode rod6.

The contact tips for arc welding include various kinds of contact tips according to the difference of welding types, such as a contact tip for submerged arc welding, a contact tip for inert gas arc welding, and a nozzle tip for CO2gas arc welding, but the method of the present invention is applicable to any of these. Also, in the method of the present invention, both of a contact tip used for consumable welding with an electrode rod itself as a filler metal like MIG welding and a contact tip used for non-consumable welding with hardly consuming an electrode rod itself like TIG welding can be used as a subject to be processed.

Since the welding tip1(11,12) for both are welding and plasma welding is required to have high conductivity, copper, a copper alloy, and ceramic-dispersed copper are used as a material, and any of these can be processed in the present invention.

In addition, chromium copper, zirconium copper and the like are copper alloys generally used for the welding tip, and the present invention is applicable to any of these. Further, not limited to these, the present invention is also applicable to welding tips made of other copper alloys.

Processing Device

In both the step of forming the surface reinforcing layer and the step of forming the semiconductor film according to the present invention, a commercially available air type blasting device which is applied for known sandblasting and shot peening and the like can be used.

As an air type blasting device, various types of blasting devices have been provided, such as a gravity type (suction type) and a direct pressure type. In the processing method of the present invention, any blasting device may be used as long as an ejection powder can be ejected with a compressed gas at a certain ejection velocity, and the type of ejection is not particularly limited as long as an air type blasting device is used.

Step of Forming Surface Reinforcing Layer

The step of forming a surface reinforcing layer is carried out by first ejecting a metal powder shot having hardness equal to or higher than that of the base material of the welding tip onto at least the inner peripheral surface, preferably the inner peripheral surface and the outer peripheral surface of the above-mentioned welding tip, to form the surface reinforcing layer2in the vicinity of the surface of the welding tip at the ejection position.

Examples of the metal powder shot used for ejection may include high-speed steel and tungsten. Other than these, various kinds of metal powder shot can be used as long as the metal powder shot is formed of a metal material having hardness equal to or higher than that of the base material of the welding tip.

In addition, by ejecting the metal powder shot at high velocity to cause collision with the surface of the welding tip, part of a component of the metal powder shot can be diffused and penetrated in the vicinity of the surface of the welding tip. Therefore, for example, for the purpose of reinforcing and modifying copper or a copper alloy which is a base material of the welding tip, when other elements are diffused and penetrated thereto, components to be diffused and penetrated are included in the metal powder shot.

The metal powder shot used for ejection has an average particle diameter of 40 μm to 150 μm, and it is ejected at an ejection velocity of 100 m/sec or higher.

The reason for the shot diameter of 40 μm to 150 μm is that the shot diameter is required to be smaller in order to obtain a high ejection velocity, the surface roughness of the processed surface is made uniform and adjusted to give a contact surface which does not increase the electrical resistance. Further, the reason for the ejection velocity of 100 m/sec or higher is that it is a required condition in the above shot diameter to increase the temperature in the vicinity of the surface of the welding tip which is copper or a copper alloy with high heat dissipation to a required temperature, for example, the recrystallization temperature or higher.

In this way, when the metal powder shot is ejected at least onto the inner peripheral surface of the welding tip under the aforementioned conditions, heating and cooling are repeated by collision of the shot on the surface of the welding tip in collision with the shot, thereby miniaturize a structure in the vicinity of the surface of a collision part. At the same time, compressive stress is imparted to the collision part, which is then reinforced.

Part of the component in the metal powder shot is diffused and penetrated in the vicinity of the surface of the collision part to form the surface reinforcing layer2in the vicinity of the surface of the welding tip as shown in the enlarged drawing inFIG. 1.

The surface reinforcing layer2formed in this way obtains increased electrical conductivity attributed to a miniaturized structure as compared with the surface of an unprocessed inner peripheral surface of the welding tip.

Step of Forming Semiconductor Film

The step of forming a semiconductor film is performed by further ejecting a tin powder onto the surface reinforcing layer2formed by the above step to form the semiconductor film3of tin oxide.

As a tin powder to be ejected, one having a tin oxide film formed on the surface is used, and adhesion, diffusion, and penetration of this tin oxide to the inner peripheral surface of the welding tip causes formation of the semiconductor film3mentioned above.

The tin powder covered with such an oxide film can be obtained by manufacturing the tin powder with a water atomization method as an example. In this water atomization method, collision of molten tin with high-pressure water causes powderization and rapid solidification of molten tin in an instant, thereby obtaining a powder. In the tin powder obtained in this way, the surface thereof is oxidized by quenching in collision with water, providing the tin powder having the surface covered with an oxide film.

The tin powder to be used has an average particle diameter of 10 μm to 100 μm, preferably 20 μm to 50 μm. In order to form a film on the surface of a product to be processed by collision with the tin powder, it is necessary to increase the temperature of the tin powder by heating at collision, and this temperature increases in proportion to the collision velocity of the tin powder.

The tin powder having a particle diameter in the above range is easily carried by an air flow generated by a compressed gas used at ejection, and the ejection powder can be brought into collision with the surface of the product to be processed at a high velocity, thereby allowing suitable formation of the tin oxide film.

Each particle shape of the ejection powder to be used may be spherical, polygonal, or further a mixture of these and the shape thereof is not particularly limited.

The tin powder is ejected at an ejection velocity of 200 m/sec or higher. Increased temperature which is caused at a time of collision of the tin powder with the surface of the product to be processed is proportional to the velocity, and the tin powder is required to be ejected at a high velocity in order to suitably melt and adhere the tin powder to the surface of the product to be processed.

Particularly, the tin powder used in the method of the present invention has the oxide film formed on the surface thereof. Further, this oxide film (tin oxide) has a higher melting point than tin (unoxidized), and therefore the tin powder is required to be ejected at high ejection pressure and high ejection velocity as mentioned above.

As described above, the tin powder which has the oxide film formed on the surface and has an average particle diameter of 10 μm to 100 μm, preferably 20 μm to 50 μm is ejected at a relatively high velocity of 200 m/sec or higher and brought into collision with the inner peripheral surface of the welding tip. Then, the ejected tin powder comes into collision with the inner peripheral surface of the welding tip, and when the ejected tin powder is rebounded, part of the ejected tin powder melts and adheres to, or diffuses/penetrates into, and coats the inner peripheral surface to form the tin oxide film.

When tin powder is ejected at high velocity onto the inner peripheral surface of the welding tip at the ejection pressure or the ejection velocity mentioned above, a thermal energy is generated in the tin powder by the velocity change before and after collision against the surface of the product to be processed. Since this thermal energy is generated only in the deformed part with which the tin powder comes into collision, the temperature increases in the tin powder and locally in the vicinity of the inner peripheral surface of the welding tip, with which this tin powder comes into collision.

Since the temperature increases in proportion to the velocity of the tin powder before collision, a higher ejection velocity of tin powder ejection increases the temperature of the tin powder and the inner peripheral surface of the welding tip to high temperature. At this time, the tin powder is heated at the inner peripheral surface of the welding tip and accordingly this increased temperature causes oxidation of the temperature-increasing part of the tin powder. At the same time, it is considered that part of ejection powder which includes the oxide film formed on the surface of the tin powder is melted and adhered to, diffused and penetrated into, or coated on the surface reinforcing layer formed on the inner peripheral surface of the welding tip by the increased temperature, thereby forming the semiconductor film3.

Tin as a metal is a soft metal with Vickers hardness of about 5 kg/mm2. Tin oxide which is oxide of tin, is a substance with high hardness such as Vickers hardness of about 1650 kg/mm2at the maximum. The hardness of the tin oxide film formed in this way is sufficient to form a film which is not easily worn out as compared with ceramics such as zirconia (about HV 1100 kg/mm2), alumina (about HV 1800 kg/mm2), silicon carbide (about HV 2200 kg/mm2), and aluminum nitride (about HV 1000 kg/mm2).

Further, the tin oxide film formed in this way does not easily cause peeling and the like by sliding of the electrode rod, etc.

Moreover, tin has a low melting point of 232° C. but tin oxide has a high melting point of 1630° C. Therefore, even in use for the welding tip, the welding tip has thermal characteristics sufficient to withstand to heating during welding.

Tin oxide without doping is a semiconductor having high electrical resistance, but the inner peripheral surface of the welding tip after the semiconductor film3of tin oxide is formed on the surface reinforcing layer2by the aforementioned method exhibited good conductivity although the principle and the like are unknown.

In addition, in the welding tip which is not processed according to the present invention, the electrical resistance increases as the temperature increases, and such increased electrical resistance causes shortage of power supply to the electrode rod or increased power consumption. At the same time, increased electrical resistance further causes generation of heat, and the sliding contact of the welding tip with the electrode rod in such a state results in higher abrasion speed and shorter lifetime. This also causes welding defect based on shortage of power supply or loose contact. In the inner peripheral surface of the welding tip, on which the semiconductor film is formed by surface reinforcement processing according to the method of the present invention, the electrical resistance of the semiconductor film3decreases as the temperature of the welding tip increases. Therefore, good electrical conductivity is maintained without shortage of power supply, increased power consumption, further increased temperature based on increased electrical resistance and the like even when the temperature of the welding tip is increased by heating during welding. As a result, the welding tip is also hardly worn out by contact with the electrode rod or plasma, and welding defect is hardly caused.

Effects and the Like

As described above, in the welding tip reinforced by the method of the present invention, the surface reinforcing layer2with high hardness is formed by ejection of the shot having hardness equal to or higher than the base material of the tip, and the semiconductor film3having thermal resistance and high hardness is further formed on the surface reinforcing layer2, whereby not only decreased conductivity anticipated by formation of the semiconductor film3is not observed, but also good conductivity is exhibited without increased electrical resistance even when the welding tip is heated to high temperature.

As a result, in the welding tip to which the surface reinforcement processing of the present invention is carried out, even combination of two kinds of processings mentioned above does not increase the surface hardness, but expression of electrical characteristics which could not be expected from two kinds of processings mentioned above increased the lifetime of the welding tip to 7 to 8 times longer than that of the unprocessed welding tip, and 2 to 3.5 times longer than that of the welding tip having only the surface reinforcing layer2formed thereon, and at the same time, drastically decreased generation of welding defect.

Examples of the reinforcement processing carried out to the welding tip are described below. The results for evaluating the characteristics of the welding tip to which each processing is performed are shown below.

The reinforcement method of the present invention was carried out to a contact tip for arc welding (made of chromium copper; φ1.2 mm) under the following conditions.

(1) Surface Reinforcement Processing

A metal powder was ejected to the inner peripheral surface and the outer surface of the contact tip under the following conditions, respectively.

(2) Step of Forming Semiconductor Film

A tin powder was ejected onto the inner peripheral surface and the outer surface of the contact tip under the following conditions, respectively, after the surface reinforcement processing was completed under the above conditions.

(3) Performance Evaluation

The results of performance evaluation are shown below in Table 3 for the contact tip of the present invention (Example 1) on which the surface reinforcing layer and the semiconductor film were formed under the above conditions, an unprocessed contact tip (Comparative Example 1), and a contact tip (Comparative Example 2) to which only the surface reinforcement processing was performed.

(4) Experimental Results

From the above results, the surface hardness was HV 139 kg/mm2in Comparative Example 1 (unprocessed), while it was HV 181 kg/mm2in Comparative Example 2 through the surface reinforcement step, showing that the diffusion effect of a metal component significantly improved hardness and stress, and increased the lifetime (durability) by 4 times.

As compared with the contact tips to which the surface reinforcement processing were thus performed, in the contact tip of the present invention to which the step of forming the semiconductor film was further carried out, improvement of hardness and stress was not observed relative to the contact tip to which only the surface reinforcement processing was carried out (Comparative Example 2), but increased lifetime (durability) was obtained such as 8 times longer than the unprocessed contact tip (Comparative Example 1) and also 2 times longer than the contact tip to which only the surface reinforcement processing was performed (Comparative Example 2).

The reason that the lifetime (durability) of the contact tip of the present invention was increased even though increased surface hardness or stress was not obtained relative to the contact tip to which only the surface reinforcement processing was carried out in this way (Comparative Example 2) is supposed to be the effect of high conductivity under the high temperature of the semiconductor film.

In addition, since the electrical conductivity was high under high temperature in this way, power consumption was able to be reduced, which was economical, and generation of welding defect caused by poor power supply was able to be drastically decreased at the same time. Further, the nozzle tip having the semiconductor film formed thereon gives good sliding of a wire. At the same time, since the semiconductor film of tin oxide has a high melting point and high hardness, it is hardly peeled even if in sliding contact with the electrode under high temperature, and the excellent electrical characteristics mentioned above can be continuously obtained for a long time.

Particularly, in this Example, the surface reinforcing layer and the semiconductor film of tin oxide were also formed on the outer surface of the contact tip. Accordingly, spatter was hardly adhered to any position of the contact tip during welding, and when adhered, it was able to be easily removed, thereby preventing the lifetime from being decreased by spatter adhesion.

The surface reinforcement processing of the present invention was performed on a nozzle tip (made of chromium copper, forged product: φ2.5 mm) for plasma welding under the following conditions, and the characteristics of the nozzle tip after processed were evaluated.

(1) Surface Reinforcement Processing

A metal powder was ejected onto the inner peripheral surface and the outer surface of the nozzle tip under the following conditions, respectively.

(2) Step of Forming Semiconductor Film

A tin powder was ejected onto the inner peripheral surface and the outer surface of the nozzle tip under the following conditions, respectively, after the surface reinforcement processing was completed under the above conditions.

(3) Performance Evaluation

The results of performance evaluation are shown below in Table 6 for the nozzle tip of the present invention on which the surface reinforcing layer and the semiconductor film were formed under the above conditions (Example 2), an unprocessed nozzle tip (Comparative Example 3), and a nozzle tip to which only the surface reinforcement processing was performed (Comparative Example 4).

(4) Experimental Results

Although the nozzle tip for plasma welding is not in direct contact with an electrode rod unlike the aforementioned contact tip for arc welding, it is to focus a plasma gas which is heated and expanded by arc heat between the outer periphery of the electrode rod and the inner periphery of the nozzle tip through a nozzle hole and eject it at high velocity. Therefore, the abrasion and the like of the nozzle tip for plasma welding directly influence the quality of welding.

The surface hardness was HV 174 kg/mm2in the nozzle tip (unprocessed product: Comparative Example 3) which was made of chromium copper and manufactured by forging, while the hardness was increased to HV 196 kg/mm2in the nozzle tip to which the surface reinforcement processing was carried out (Comparative Example 4). Increased stress was also observed at the same time, but the lifetime (durability) was increased only by 2 times.

On the other hand, in the nozzle tip of the present invention on which the semiconductor film was further formed after the surface reinforcement processing (Example 2), improvement of hardness and stress was not observed relative to the nozzle tip to which only the surface reinforcement processing was carried out (Comparative Example 4), but increased lifetime (durability) was observed such as 7 times longer than the unprocessed product (Comparative Example 3) and 3.5 times longer than the surface reinforced product.

Even when compared with the case of using either the unprocessed product (Comparative Example 3) or the surface reinforced product (Comparative Example 4), generation of welding defect was confirmed to be drastically decreased.

In this way, although neither hardness nor stress was changed before and after formation of the semiconductor film, increased lifetime and drastically decreased welding defect were caused in the nozzle tip. Therefore, it is supposed that both of these effects were obtained by the fact that formation of the semiconductor film of tin oxide prevented deterioration of electrical conductivity (rather improved electrical conductivity) even at high temperature.

Thus the broadest claims that follow are not directed to a machine that is configured in a specific way. Instead, said broadest claims are intended to protect the heart or essence of this breakthrough invention. This invention is clearly new and useful. Moreover, it was not obvious to those of ordinary skill in the art at the time it was made, in view of the prior art when considered as a whole.

Moreover, in view of the revolutionary nature of this invention, it is clearly a pioneering invention. As such, the claims that follow are entitled to very broad interpretation so as to protect the heart of this invention, as a matter of law.

Now that the invention has been described;