JPS5924919B2 - Non-consumable electrode for plasma arc welding and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for the plasma arc treatment of metals, more particularly for plasma arc welding of metals in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere. It concerns non-consumable electrodes.

The proposed non-consumable electrode for plasma arc welding in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere can be used with most success for plasma arc welding of low carbon and low alloy steels.

Plasma arc welding of steel in a carbon dioxide environment or in a carbon dioxide-based mixture atmosphere is compatible with other widely known welding methods, such as consumable electrode submerged arc welding, consumable electrode carbon dioxide shielded arc welding or consumable electrode In order to be comparable to formula carbon dioxide-based mixture shielded arc welding, non-consumable electrodes for plasma arc welding in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere must be used commercially with an arc current of 400 A or more. It is necessary to provide a suitable service life. For example, in the welding of ungrooved low carbon and low alloy steels, plasma arc welding speeds in a carbon dioxide atmosphere or carbon dioxide-based mixture atmosphere should be made equal to the welding speed with other known welding methods. Or to go even faster, use a non-consumable electrode for plasma arc welding with 400 to 1
It is necessary to provide a service life suitable for commercial use with arc currents in the range of 0.000A. A non-consumable electrode for plasma arc processing in an atmosphere of chemically reactive plasma-generating gases containing carbon dioxide, comprising a liquid-cooled metal holder made of copper and a zirconium insert metallurgically bonded to the holder. known to those skilled in the art (U.S. Pat. No. 319)
8932).

When using this non-consumable electrode in a carbon dioxide atmosphere, active inserts of zirconium (Activeins)
ert) reacts with the active components of the plasma generating gas, namely carbon and oxygen.

A coating of zirconium-carbon and zirconium-oxygen compounds is formed on the entire surface of the insert. Below, these compounds are mixed into a zirconium oxycarbide layer (ZirOOniumOxycar-Bidelaye).
r). Zirconium oxycarbide coatings have higher thermal stability and improved electron emission properties compared to metallic zirconium. The above non-consumable electrode is 300
It was used in equipment for plasma arc cutting or welding of metals with arc currents up to A. However, 3
In carbon dioxide shielded plasma arc processing with an arc current of 00 A or more, the service life of such an electrode is not suitable for commercial use.

This makes it impractical to use the electrode for plasma arc welding of low carbon and low alloy steels with a thickness of 6 mm or more in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere. Also known to those skilled in the art are non-consumable electrodes for plasma arc processing of metals in chemically reactive plasma generating atmospheres containing oxygen, nitrogen and/or carbon.

This non-consumable electrode comprises a copper or copper alloy holder and a hafnium insert (US Pat. No. 3,592,64).
(See No. 9).

When this non-consumable electrode is used in a carbon dioxide atmosphere, the hafnium insert chemically reacts with the active components of the plasma gas, namely carbon and oxygen.

A Hafnium Oxycarbide layer is formed on the entire working surface of the active insert, which layer has higher thermal stability and improved electron emission properties than the Zirconium Oxycarbide layer. With the service life of such a non-consumable electrode, it can be used for plasma arc treatment in a carbon dioxide atmosphere with an arc current of 400 A or less.

This service life is longer than that of electrodes with active inserts of zirconium. However, at higher arc currents, e.g. 400 A and above, the electrode becomes impractical due to its rapid erosion (wear) rate.Thus, non-consumable electrodes with active inserts of hafnium , cannot be used for plasma arc welding of low carbon steel and low alloy steel with a thickness of 61 Lm or more in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere.

Another prior art cathode (CathOd) for arc processing in chemically reactive atmospheres consists essentially of hafnium with a copper holder and alloying additives of various metals and/or their oxides. Contains an insert.

This cathode has a lower erosion rate compared to an electrode with an active insert of pure hafnium only when the arc is generated in an intermittent cycle.

However, for all applications, the service life of such a cathode is such that it can be used in plasma arc processing in a carbon dioxide atmosphere with arc currents not exceeding 400 A. Therefore, cathodes with active inserts of hafnium with alloying additives can be used in plasma applications of low carbon and low alloy steels with a thickness of 6 mm or more in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere. Cannot be used for arc welding.

The electrode disclosed in U.S. Pat. No. 3,198,932 involves placing a previously chemically treated zirconium active insert into a copper holder and simultaneously heating the holder and insert combination to metallurgically bond the active insert and copper holder. made by gluing.

Another of the electrodes described above involves cold stamping the active insert into a copper holder.
or by mechanical placement using other similar methods.

In all the electrodes mentioned above, an oxycarbide coating of the corresponding material of the active insert is obtained during arc combustion in a carbon dioxide atmosphere.

The principal object of the present invention is to provide a non-consumable electrode for plasma arc welding of metals and to develop a method of manufacturing this electrode, in which the active insert is suitable for commercial use at arc currents of 400 A and above. It is possible to use this non-consumable electrode with a suitable service life and to weld low carbon and low alloy steels without beveling at welding speeds equal to or higher than those obtained with conventional welding methods. formed and processed. For this primary purpose, a non-consumable electrode for plasma arc welding in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere with a holder of copper or copper alloy and an active insert of hafnium fitted into this holder has been proposed. A non-consumable electrode comprising an insert having a hafnium oxycarbide coating on its surface in a non-consumable electrode comprising an insert having a hafnium oxycarbide coating on its surface, characterized in that the active insert comprises a graphite layer applied on the hafnium oxycarbide layer. We propose a consumable electrode for arc welding.

The graphite layer applied on the hafnium oxycarbide and forming the surface of the active insert ensures a reduction in the heat flow to the non-consumable electrode and an improvement in the thermal stability and electron emission properties of the proposed non-consumable electrode. .

The amount of graphite in the graphite layer provided on the hafnium oxycarbide layer has the following relationship: h2 (0.25 to 0.75
)d where h is the height of the active insert, d is the diameter of the active insert, and is conveniently determined by the height and diameter of the active insert selected according to.

By forming a graphite layer on the main part or on the entire surface of the hafnium oxycarbide layer, and by applying the graphite layer thus formed to a working arc current (0 perating
In order to extend the service life of the electrode by continuously maintaining the non-consumable electrode during use at e1 electrical current, there is a need for stronger and more uniform cooling of the active insert. To meet these requirements, we recommend selecting the dimensions (ie height and diameter) of the active insert such that the height is smaller than the diameter.

It has been experimentally found that the non-consumable electrode does not work if the height of the active insert is less than 0.25 times its diameter, ie, the cooling of the insert is most intense.

This is due to the following facts. That is, cathode spot contraction occurs as the emitting surface material is supercooled, the arc becomes locally unstable and the non-consumable electrode is rapidly destroyed. When the height of the active insert exceeds 0.75 times its diameter, the minimum radial temperature gradient conditions of the hafnium oxycarbide layer are disturbed to such an extent that the formation and continued maintenance of the graphite layer is no longer possible; The electrode suddenly breaks down. To this main objective, the present invention provides a method for manufacturing a non-consumable electrode for plasma arc welding comprising joining a copper or copper alloy holder to an active insert. connecting to the cathode, placing a non-consumable electrode in a carbon dioxide atmosphere, and connecting an auxiliary electrode to the anode of the power source to form an arc between these electrodes;
Pre-forming a hafnium oxycarbide layer on the surface of the active insert at an arc current of less than 0.21 (I is the working current of the non-consumable electrode) and then increasing the arc current from 0.21 to A method of manufacturing a non-consumable electrode for plasma arc welding has been proposed, which is characterized in that a graphite layer is formed on the previously formed hafnium oxycarbide layer by increasing the speed to I at a rate of 40 amperes/second or less.

The time required to generate the arc and form the hafnium oxycarbide layer is 0.05 to 0.5 seconds.

In order to coat the entire surface of the active insert with a layer of hafnium oxycarbide, it is sufficient to maintain the arc current to be only 0.2 times the full working current of the non-consumable electrode. It is sufficient to maintain the current at 0.21 for the initial stages of hafnium oxycarbide layer formation, and also to increase the arc current from 0.2 I to completely for the formation of a graphite coating over the surface of the hafnium oxycarbide layer. It is necessary to gradually increase the arc current used at a rate of 1 to 40 amperes/second. If the gradual increase in arc current 1 starts from a value greater than 0.21 and has a rate greater than 40 amperes/second, the surface of the hafnium oxycarbide layer will be overheated and the radiant temperature distribution will be completely changed. disturbed, which prevents the formation of a graphite coating. The above objects, other objects, features and advantages of the present invention will become apparent from the more detailed description taken in conjunction with the accompanying drawings.

During use of a non-consumable electrode comprising a holder and an active insert, the active insert may erode and create a crater.
ter) is formed and the maximum service life is determined by the burnout of the active insert at the full depth of the crater.

It has been experimentally found that the erosion rate of the active insert tends to increase rapidly when non-consumable electrodes are used in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere at arc currents of 400 A and above. This rapid burnout of non-consumable electrodes in a carbon dioxide atmosphere or carbon dioxide-based mixture atmosphere is due to the following facts. That is, as the active insert erodes and the arc column enters the crater formed during use of the non-consumable electrode, heat flow tends to increase and catastrophic failure of the electrode occurs. However, some of the non-consumable electrodes (
Approximately 10% of the total number of electrodes tested) remained stable for several hours in a carbon dioxide atmosphere or carbon dioxide-based mixture atmosphere.

Analyzing the working surface structure of the active hafnium inserts of the investigated non-consumable electrodes, all of the stable non-consumable electrodes have a hafnium oxycarbide layer (on the surface of the active hafnium layer) covered with a graphite coating. On the other hand, it was found that the non-consumable electrode exhibiting a high erosion rate has no graphite film on its hafnium oxycarbide layer. Therefore,
The inventors have discovered the enhanced durability of the non-consumable electrode in a carbon dioxide atmosphere or carbon dioxide-based mixture atmosphere and the presence of a graphite layer on the working surface of a hafnium oxycarbide coating covering the active hafnium insert surface. It was found that there is a one-to-one relationship between

It has been experimentally found that the service life of the non-consumable electrode in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere is increased if a large part of the surface of the hafnium oxycarbide layer is covered with a graphite film.

Furthermore, it has been found that the graphite layer on the hafnium oxycarbide layer is always formed in the direction from the periphery to the center of the working surface, ie on the lowest operating temperature part of the hafnium oxycarbide layer. The inventors believe that the graphite layer on the surface of the hafnium oxycarbide film is the result of the interaction between the hafnium oxycarbide and carbon monoxide created by thermal dissociation of carbon dioxide in the cathode-proximal region of the arc column. be.

The main feature of the invention is that graphite is formed as a result of the interaction within a narrow temperature interval not exceeding 500°C.

This reality is responsible for the formation of a graphite layer on the peripheral part of the surface of the hafnium oxycarbide layer, which was observed experimentally, on the one hand, the operating temperature of the hafnium oxycarbide layer in this part is minimal, and on the other hand, this layer has a low radiant temperature gradient. Another noteworthy feature of the interaction between hafnium oxycarbide and carbon monoxide is the fact that this interaction occurs at high absolute temperatures, above 2500°C.

At such temperatures, the graphite layer causes most of the arcing current due to thermionic emission current, resulting in an extended service life of the non-consumable electrode.

This results from an increase in the active surface area of the oxycarbide layer coated with hafnium graphite. Experimental studies have shown that the service life of non-consumable electrodes depends on the surface area of the graphite-coated hafnium oxycarbide layer.

That is, the service life of a non-consumable electrode is longest when the entire surface of the hafnium oxycarbide layer is coated with graphite, while the graphite layer covers at least 0% of the total working surface of the hafnium oxycarbide layer during use of the non-consumable electrode. .4 if formed over an area of 25 times and maintained continuously
A service life that is satisfactory for commercial use as a non-consumable electrode for plasma arc welding in a carbon dioxide atmosphere with an arc current of 00 A or more (with the proposed dimensions of the active insert)
can get. Based on these, a carbon dioxide atmosphere or a carbon dioxide base comprising a holder 1 made of copper or a copper alloy (FIG. 1) and an active insert 2 of hafnium fitted in contact with this holder is proposed. A non-consumable electrode for plasma arc welding in a mixed atmosphere was proposed.

A hafnium oxycarbide layer 3 is provided on the outer surface of the insert 2. A hafnium oxycarbide layer 3 is coated with a graphite layer 4 .

The precoating of the hafnium oxycarbide layer 3 with a graphite layer 4 ensures a high resistance of the non-consumable electrode when the non-consumable electrode is used in a carbon dioxide atmosphere or in a carbon dioxide-based mixture atmosphere. .

Note that the proposed non-consumable electrode in this case works as a cathode arc plasma torch. The combination of the hafnium oxycarbide layer 3 and the graphite layer 4 on the emissive surface of the active insert 2 provides a work function (WOr
This has the advantageous effect of minimizing kfunctionOn). The minimum work function for electron emission allows lower operating temperatures to be obtained on the emitting surface of the non-consumable electrode at a given arc current, thereby reducing the heat flow to the non-consumable electrode. decreases. As a result, thermal erosion of the active insert 2 is reduced, which increases the service life of the non-consumable electrode. In FIG. 2, which shows the non-consumable electrode from the side of the working surface, a graphite layer 4 partially covers the hafnium oxycarbide layer 3.

Graphite layer 4 overlays layer 3 with hafnium oxycarbide layer 3
and holder 1 in the direction towards the axis of the non-consumable electrode. It has been experimentally found that it is sufficient for the graphite layer 4 to cover 0.25 times the total surface of the hafnium oxycarbide layer 3 to give the non-consumable electrode satisfactory performance at arc currents of 400 A and above.

The reduction in heat flow improves the thermal stability of the non-consumable electrode, ie minimizes erosion of the active insert 2.

In the embodiment of FIG. 3, the graphite layer 4 completely covers the hafnium oxycarbide 3. In the embodiment of FIG.

In this case, the highest usability of non-consumable electrodes is achieved, which makes it possible to carry out plasma arc welding in a carbon dioxide atmosphere or in a carbon dioxide-based mixture atmosphere with an arc current of less than 1000 A. Specific embodiments of the proposed non-consumable electrode and examples tested using the non-consumable electrode for plasma arc welding of low-carbon and low-alloy steels in a carbon dioxide atmosphere or in a carbon dioxide-based mixture atmosphere. is described below.

Example 1 A copper holder with a diameter of 20 mm and a diameter of 3.6 mw! In a non-consumable electrode comprising a hafnium active insert, a hafnium oxycarbide layer was formed on the surface of the active insert, and a graphite layer was formed on the entire working surface of the hafnium oxycarbide layer.

The active insert had a height (thickness) of 0.9 mm.

Diameter 11m77! The non-consumable electrode was tested in plasma arc welding under the following conditions in a plasma torch with a nozzle.

The plates were welded in a downward position without groove processing at a speed of 30 m/h with complete penetration per pass.

The service life of the non-consumable electrode, which is the total time of arc combustion in the welding process, reached 1 hour. Example 2 Copper holder with a diameter of 20mm and a diameter of 3T! T7! In a non-consumable electrode comprising a hafnium active insert of L, a hafnium oxycarbide layer was formed on the surface of the active insert.

A graphite layer was formed on a surface 0.75 times larger than the surface of this hafnium oxycarbide layer. The height of the active insert is 1
．． It was 5mm. The non-consumable electrode was tested in plasma arc welding under the following conditions in a plasma torch having a nozzle with a diameter of 8 mm.

The plates were welded in a downward position without groove processing at a speed of 50 m/h with complete penetration per pass.

The service life of the non-consumable electrode, which is the total time of arc combustion in the welding process, reached 1.7 hours. Example 3 In a non-consumable electrode comprising a 16 mu diameter copper holder and a 2.6 mm diameter hafnium active insert,
A hafnium oxycarbide layer was formed on the surface of the active insert.

A graphite layer was formed on a surface 0.25 times the surface of this hafnium oxycarbide layer. The height of the active insert is 1.9m77! It was hot. The non-consumable electrode was tested in plasma arc welding under the following conditions in a plasma torch having a nozzle with a diameter of 8 mm.

The plates were welded in a downward position without groove processing at a speed of 50 m/h with complete penetration per pass.

The service life of the non-consumable electrode, which is the total time of arc combustion in the welding process, reached 7 hours. Example 4 Copper holder with a diameter of 20mm and a diameter of 3m77! In a non-consumable electrode comprising an active insert of hafnium, a hafnium oxycarbide layer was formed on the surface of the active insert.

A graphite layer was formed on a surface 0.85 times larger than the surface of this hafnium oxycarbide layer. The height of the active insert is 1
．． It was 2mm. The non-consumable electrode was tested in plasma welding under the following conditions in a plasma torch with a 9 mm diameter nozzle.

The plates were welded in a downward position without grooves at a speed of 80 m/h with complete penetration per pass.

The service life of the non-consumable electrode, which is the total time of arc combustion in the welding process, reached 2.1 hours. To obtain a graphite layer on a hafnium oxycarbide layer and constant maintenance of the graphite coating when the non-consumable electrode is used for plasma arc welding in an atmosphere of carbon dioxide or a mixture based on carbon dioxide. For this reason, it is preferred to apply a graphite layer onto the hafnium oxycarbide layer beforehand, ie before use of the non-consumable electrode for plasma arc welding. If the non-consumable electrode is treated by arc combustion in a carbon dioxide atmosphere, then the non-consumable electrode to be treated serves as a cathode, i.e. the electrode is connected to the cathode of an arc current source; It has been experimentally found by the inventors that favorable effects of a graphite layer applied on a hafnium oxycarbide layer can be obtained.

This has been demonstrated by experiments by the inventors in which a non-consumable electrode treated with an arc acts as an anode, ie the electrode is connected to the anode of an arc current source. In all these experiments, without exception, rapid destruction of the non-consumable electrode occurred unless a graphite layer was formed on the working surface of the active insert. We have shown that when a non-consumable electrode (as a cathode) is treated by arc combustion in a carbon dioxide atmosphere, a hafnium oxycarbide layer is actually formed on the surface of the active insert immediately after arcing. I found it.

Conditions for hafnium oxycarbide layer formation (i.e.
Even though the arc current and arc burning period) are varied widely, the conditions for forming the graphite layer on the hafnium oxycarbide layer are strictly specified as experiments have shown.

This results from the need to maintain a defined temperature and a defined temperature gradient on the working surface of the hafnium oxycarbide with graphite layer formation.

From experimental results and by comparing the thermal properties of the hafnium oxycarbide layer, the hafnium active insert, and the copper holder, the inventors have reached the following conclusions. Thus, in order to meet the aforementioned conditions for providing a graphite coating, it is necessary to observe a limited rate of increase in the arc current as well as a limited connection scheme of the non-consumable electrode to the power supply circuit. The apparatus for carrying out the method for manufacturing non-consumable electrodes comprises a DC power supply 5 (FIG. 4), the cathode of which is connected to the holder 1 of the non-consumable electrode, while the anode is connected to an additional electrode 6. has been done. Hafnium active insert 2
The holder 1 into which the carbon dioxide introduction means 8 is fitted
and a compartment 7 provided with carbon dioxide evacuation means 9. A non-consumable electrode comprising a copper holder 1 with an active insert 2 of hafnium pre-fitted in contact with the copper holder 1 is placed in the compartment 7 and connected to the DC power supply 5. Carbon dioxide is supplied into the compartment 7. Next, an arc 10 is generated between the additional electrode 6 previously connected to the anode of the DC power source 5 and the active insert 2 of hafnium. Curve 11 shown in Figure 5
represents the arc current value as a function of time. The ordinate shows the current value of the arc 10, and the abscissa shows the time required to manufacture the non-consumable electrode. Considering the curve 11, after the arc 10 is generated for a period τ≦0.5 s with an arc current below 0.21, a hafnium oxycarbide layer 3 is formed on the emitting surface of the hafnium active insert 2; A hafnium oxycarbide layer covers the entire emissive surface of the active hafnium insert 2.

The current of the arc 10 is then increased to the full working current value of the non-consumable electrode at a rate of 40 A/s or less without interrupting the arc combustion, with the result that the graphite layer 4 is deposited on the hafnium oxycarbide layer 3. It is formed. Then extinguish the arc. In this case, if the total combustion time is τ1 × τ × τ2, then the graphite layer 4 partially covers the hafnium oxycarbide layer 3 by 0.00% of the hafnium oxycarbide layer 3.
Cover more than 25 times.

If τ≧τ2=40A/8 (where I is the full working current value of the non-consumable electrode), the graphite layer 4 covers the entire hafnium oxycarbide layer 3. The proposed manufacturing method of non-consumable electrodes for welding in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere allows the formation of a hafnium oxycarbide layer on the active insert during one cycle of arc combustion, and Allows the formation of a graphite layer on top of it. The specific embodiments of the invention described above are not intended to limit the invention.

Various modifications and changes may be made to the invention without departing from the scope and spirit of the claims.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a non-consumable electrode according to the invention, FIG. 2 is a view indicated by arrow A in FIG. 1, and FIG. 4 is a schematic diagram illustrating a method for manufacturing a non-consumable electrode according to the present invention, and FIG. FIG. 5 is a graph of a curve showing the arc current as a function of time when a non-consumable electrode is manufactured by the method according to the invention. 1... Copper or copper alloy holder, 2...
hafnium active insert, 3... hafnium oxycarbide layer, 4... graphite layer, 5...
...DC power supply, 6...Additional electrode, 10.
·····arc.

Claims (1)

[Scope of Claims] 1. A holder comprising: (a) a holder of copper or a copper alloy; and (b) an active insert of hafnium fitted within the holder, on the surface of which a layer of hafnium oxycarbide is disposed. In a non-consumable electrode for plasma arc welding in a carbon dioxide atmosphere or a carbon dioxide-based mixture atmosphere, the active insert 2
A non-consumable electrode for plasma arc welding, characterized in that the electrode comprises a graphite layer 4 applied on said hafnium oxycarbide layer 3. 2 The amount of graphite layer 4 applied on the hafnium oxycarbide layer 3 satisfies the following relationship: h=(0.25 to 0.7
5) d where h is the height of the active insert, d is the diameter of the active insert, and is limited by the height and diameter of the active insert 2 selected according to A non-consumable electrode for plasma arc welding according to scope 1. 3. A method for manufacturing a non-consumable electrode for plasma arc welding, comprising joining a holder of copper or copper alloy to an active insert of hafnium, wherein said holder 1 is connected to the cathode of a power source 5, and said non-consumable electrode is Placed in a carbon atmosphere, an additional electrode 6 is connected to the anode of said power source 5 to generate an arc 10 between these electrodes, and a layer of hafnium oxycarbide 3 is deposited on the surface of said active insert 2 by 0.2I.
(I is the operating current of the non-consumable electrode), and then the arc current was increased from 0.2I to I at a rate of 40 amperes/second or less to deposit the graphite layer 4 first. A method for manufacturing a non-consumable electrode for plasma arc welding, characterized in that the electrode is formed on the hafnium oxycarbide layer 3 formed in .