RU2798645C1 - Method of automatic build-up welding in inert gas by combination of arcs - Google Patents

Abstract

FIELD: build-up welding.

SUBSTANCE: method for automatic arc mechanized build-up welding in an inert gas by a combination of arcs of direct and indirect action is proposed. The invention can be used for automatic mechanized arc surfacing in an inert gas environment by a combination of arcs of direct and indirect action. To obtain a given non-ferrous metal content during build-up welding, the required indirect arc current between a non-consumable electrode and a consumable electrode made of non-ferrous metal, such as aluminium, or magnesium, or copper, or nickel, or molybdenum, or vanadium, is determined. The cross-sectional area of penetration of the base metal is measured without ignition of an indirect arc and without supply of a consumable electrode. The productivity of the base metal melting is calculated taking into account the density of the base metal and the rate of build-up welding. Then the consumable electrode build-up welding productivity is calculated taking into account the specified non-ferrous metal content in the weld metal and the indirect arc current between the non-consumable and consumable electrodes, which is necessary to obtain the non-ferrous metal content during build-up welding, taking into account the build-up welding coefficient.

EFFECT: simplified determination of the required indirect arc current to ensure the required content of non-ferrous metal in the built-up weld.

2 cl, 4 dwg, 2 ex

Description

The invention relates to the field of welding and can be used when applying wear-resistant, anti-friction, heat-resistant, heat-resistant and corrosion-resistant metal layers on low-carbon and low-alloy steels and other metals.

A known method of arc welding of wear-resistant coatings on the surface of parts made of low-carbon or low-alloy steels, including the use of aluminum wire or its alloys as a filler material, in which the welding process is carried out in an argon atmosphere under modes that provide a deposited layer with an aluminum content by weight in the range Ψ _E = 20-40% (see RF patent No. 2 327 551. Published on June 27, 2008. Bull. No. 18).

An important technical feature of this method of surfacing is that obtaining the desired properties of the weld in terms of wear resistance occurs directly in the process of forming a weld pool during the interaction of metals with very different physical properties: aluminum and steel. Two materials with low hardness, when interacting due to the formation of intermetallic phases, create a hard and wear-resistant weld metal. An important property of this method of obtaining a wear-resistant seam is the low cost and availability of filler material.

The main technical problem of this method is the low productivity of surfacing, which is due to the fact that no current is supplied to the wire, it is a filler wire and is heated only by heat transfer from the arc column. The productivity of surfacing with such a wire is at least 3 times less than when using a consumable electrode in an arc of reverse polarity. To melt the product, an arc of direct polarity in argon with a tungsten electrode is used, which has a minimum penetration ability compared to, for example, an arc of reverse polarity with a consumable electrode. Calculations show that at a given level of aluminum content, due to the low density of aluminum compared to steel in the deposited metal, the cross-sectional areas of penetration of the base metal and the deposited metal should be approximately equal, that is, to obtain a wear-resistant alloy in the weld, higher melting rates are required. aluminum wire.

Another technical problem is that the rate of melting of the filler wire is controlled only indirectly by the power of the direct arc and the place where the wire is fed into it. The power of the direct action arc affects the penetration of the base metal to a much greater extent than the melting of the filler metal. The range of possible changes in the melting rate of the filler wire is small. Thus, the method is not technologically flexible enough.

Also, the technical problem of this method is the difficulty of ensuring the exact amount of aluminum content in the weld, which ensures optimal performance of the deposited layer, which shows a wide range of allowable changes in the content of aluminum in it. The difficulty is due to the low stability of the melting rate of the filler wire. The rate of melting of the wire is affected by the power of the arc, the diameter of the wire, its deformation and deviation from the required place of filing into the arc, and other factors that are difficult to regulate and stabilize.

In most cases, the content of non-ferrous metal in the weld must be maintained with a fairly high accuracy.

It is very difficult to ensure high accuracy of the aluminum content in the weld in this method, as well as other non-ferrous metal additives. The consequence of these technical problems is that the selection of modes and conditions of surfacing for this method is very laborious, and during surfacing it is difficult to ensure the stability of the modes, a wide range of the required content of non-ferrous metal in the weld is not guaranteed.

A known method of automatic welding in an argon environment with a combination of arcs of direct and indirect action, through which the negative pole of the welding power source is connected to the non-consumable electrode, and its positive pole is connected to the product, a consumable electrode is used, connected to the positive pole of the power source, a compressed arc of direct action is ignited polarity between the non-consumable electrode and the product and the arc of indirect action between the non-consumable and consumable electrode through ballast resistance (see the article by I.E. Taver, M.Kh. Shorshorov. “Welding of steel with a double plasma jet”, Welding production, 1971, No. 10, S.26-28). This method is taken as a prototype. It can also be used for direct free arc welding.

This method can be used for surfacing non-ferrous metals on other metals, it allows you to adjust the ratio of penetration of the base and deposited metals over a wide range.

The technical problem of the known method is the difficulty of determining the currents of arcs of direct and indirect action, providing the required content of non-ferrous metal in the seam by weight. When surfacing occurs, the joint release of power in the product of these two arcs, and most of the power absorbed by the electrode drops from the arc of indirect action, is transferred to the seam. There is an action of two different in properties and characteristics of heat sources on the product. It is difficult to determine the currents for the required ratio of the desired penetration of the product and the deposition of additional metal under the action of two such different heat sources. Therefore, it is necessary to perform several experimental surfacings to obtain the required ratio of the molten base and deposited metals.

In the known method of automatic surfacing in an inert gas medium by a combination of arcs of direct and indirect action, through which the negative pole of one welding power source is connected to the non-consumable electrode, and its positive pole is connected to the product, a consumable electrode connected to the positive pole of the second source is used in the indirect arc power, the negative pole of which is connected to a non-consumable electrode, a direct-action arc of direct polarity is ignited between the non-consumable electrode and the product and an indirect arc between the non-consumable and consumable electrode, the proportion of non-ferrous electrode metal in the weld metal Ψ _E by weight is set and surfacing is carried out at a given speed .

Unlike the prototype, in advance, at the current recommended for a given diameter of a non-consumable electrode, an arc of direct polarity melts the base metal without igniting an indirect arc and feeding an electrode wire, measure the cross-sectional area of the base metal penetration and calculate the productivity of its melting, according to a given Ψ _E , calculate the productivity surfacing of the electrode metal, providing the required content of non-ferrous metal in the weld, after which the diameter of the consumable electrode is selected and the dependence of its surfacing performance on the current in the reverse polarity arc and the required arc current of indirect action are determined.

As an electrode, for example, aluminum or magnesium or copper or nickel or molybdenum or vanadium wires can be used.

The technical result of the proposed surfacing method is to simplify the determination of the required indirect arc current to ensure the required mass content of non-ferrous metal in the weld weld due to the proposed experimental-computational approach to determining the required productivity of electrode wire surfacing. This technical result is based on the established fact of the absence of a significant effect of the productivity of surfacing of an indirect arc electrode wire on the cross-sectional area of penetration of the base metal.

Figure 1 shows a diagram of the implementation of the method, figure 2 - the dependence of the recommended current densities on the tungsten electrode, figure 3 - dependence of the base metal penetration area on the arc current, figure 4 - dependence of the deposition coefficient on the arc current.

Figure 1 shows a diagram of the proposed method of automatic surfacing in an inert gas environment with a combination of arcs of direct action on the plate. Argon or helium is used as an inert gas. Welding of a seam 1 on a plate 2 with a thickness δ is carried out jointly by a direct polarity welding arc 3 with a tungsten electrode 4 and an indirect arc 5 between the same tungsten electrode 4 and an electrode wire 6 made of non-ferrous or refractory metal, for example, aluminum. The electrode wire 6 is fed in the direction of the arc column 3 and the weld pool 7 at a speed V _e equal to the rate of its melting in the arc. The direct arc 3 of direct polarity is powered by a DC welding power source 8. The indirect arc 5 is powered by a DC welding power source 11. The tungsten electrode 4 and the electrode wire 6 are located in the same plane with the welding direction. Surfacing is carried out at a speed V _C . Drops of molten electrode wire 6 enter the weld pool 7. The deposited seam 1, which is an alloy of the base metal with the electrode, can be conventionally divided into the cross-sectional area of penetration of the base metal 9 and the cross-sectional area of the deposited metal 10. On the plate 2, they are separated by a dotted line passing along the front surface of the plate 2. The width of the weld 1 E, the depth of penetration (penetration) H. The cross-sectional area of penetration of the base metal 9 will be denoted F _O , it is determined as the difference between the cross-sectional area of the weld 1, equal to F _W and the cross-sectional area of the weld metal 10 equal to F _H .

During the preliminary experiment, the indirect arc 5 is turned off, and the electrode 6 does not participate in the surfacing process.

For the share of participation of the electrode metal in the weld metal by mass Ψ _E , the formula is valid

where P _N is the productivity of consumable electrode surfacing, g/s;

P _O - productivity of melting of the base metal, g/s.

From (1) it is possible to obtain a formula for the productivity of consumable electrode surfacing П _Н

The productivity of the melting of the base metal _PO is determined by the formula

where ρ _About - the density of the base metal, g/cm ³ ;

V _C - deposition rate, cm/s;

F _O - cross-sectional area of penetration of the base metal, cm ² .

The deposition rate of an indirect arc electrode has very little effect on the cross-sectional area of the base metal and the performance of the _PO . Therefore, these quantities can be determined independently of each other.

The productivity of surfacing a consumable electrode made of non-ferrous metal _ПН in an indirect arc should be determined by the formula

where α _H is the deposition coefficient g/(A⋅s), which should be determined as for an arc with a direct consumable electrode of reverse polarity, since the electrode in the indirect arc is the anode, and the polarity of the product in the direct arc does not matter for the speed melting of the electrode and the productivity of its surfacing;

I - indirect arc current, A.

_PN in formula (4) can often be determined from the given reference data on the deposition coefficients in the DC arc of reverse polarity, on which, in most cases, consumable electrode welding is carried out in inert gases. Also, the deposition coefficient can be determined from the electrode wire feed rates, usually given in the tables of welding modes. In this case, known electrode loss factors for evaporation and spatter are used.

Substituting _PO from (3) into (2) and _PN from (4) into (2), we obtained a formula from which it is possible to determine the required indirect arc current I

Thus, having the dependence of P _N on the current in the arc of reverse polarity with a consumable electrode P _N = f (I), it is possible to determine the required value of the arc current of indirect action. Dependence P _N =f(I) can be easily obtained by surfacing with an arc of reverse polarity on the plate at several values of current and weighing the plate before and after surfacing.

Usually, in the literature, graphical dependences of the melting coefficient α _P of electrodes from different metals on current are often given. Using them, it is easy to obtain the dependence of the melting performance on the current. Then the deposition rate

where Ψ _P is the coefficient of evaporation and splashing losses. Its value for welding in shielding gases usually varies within narrow limits.

The performance of melting and surfacing of the electrode wire for a given electrode diameter depends on the overhang. Therefore, the value of surfacing productivity should be obtained at a constant overhang, which will be similar when performing the proposed surfacing method.

The fact that the melting of the electrode wire of an indirect arc does not have a significant effect on the penetration of the base metal is confirmed by the fact that no such effect was found in experiments on surfacing with such a wire, although drops of the electrode metal in this case are heated to a high temperature (see article V. Sidorova P., Borisova N.A. The process of surfacing with a combination of arcs of direct and indirect action. Welding and Diagnostics. - 2020. No. 6. P. 39-43). This is also confirmed by the fact that it is difficult to carry out the process of surfacing with an indirect arc with two steel consumable electrodes on steel without taking special measures to ensure the melting of the base metal.

Figure 2 shows the dependence of the allowable current density on the tungsten electrode in an arc of direct polarity on the diameter of the electrode. This dependence has the form of a hyperbola. The dependence is given in the article by V.P. Sidorova et al. On allowable currents on a tungsten arc electrode with bipolar current pulses. Bulletin of the Perm National Research Polytechnic University. Mechanical engineering, materials science. -2020. -T.22, No. 4. -С.5-12.DOI:10.15593/2224-9877/2020.4.01

Figure 3 shows a General view of the dependence of the area of penetration of the base metal on the effective power of the arc in argon of direct polarity with a tungsten electrode when exposed to the plate. Up to a certain current, the area grows almost linearly with increasing power. Starting from a certain current power, the intensity of the area growth increases due to the increase in heat reflection from the reverse surface of the plate. The effective power of the arc is proportional to its current.

Figure 4 shows the dependence of the coefficient of melting of aluminum wires on the arc current of reverse polarity. Curve A takes place for a wire diameter of 1.6 mm, and curve B for a wire with a diameter of 2 mm. The melting performance is equal to the product of the melting factor and the arc current. Dependencies are given in the book by V.A. Lenivkina et al. Technological properties of the welding arc in shielding gases. M .: Mashinostroenie, 1989. - 264 p. on p. 112, fig. 58. When using such dependences, it is necessary to use the coefficient of losses for evaporation and spraying Ψ _P .

For magnesium wire, the dependence of the melting factor on the arc current is shown on page 242, fig.

For wires made of other non-ferrous metals, the deposition productivity dependence can be easily determined directly in experiments with an arc of reverse polarity or in experiments with an indirect arc.

Example 1. According to the proposed method, automatic surfacing of SVA5 aluminum wire according to GOST 7871-75 with a diameter of d _E = 1.25 mm was carried out with a direct arc with a tungsten electrode in argon on a plate 6 mm thick from low-carbon steel 20 in order to ensure the optimal aluminum content in seam Ψ _E \u003d 25% by weight. The aluminum content in this wire is not less than 99.5% by weight. Diameter of a tungsten electrode of the EVCh brand is 3 mm. The angle of sharpening of the end of the electrode was 60°. For this electrode, a straight polarity arc current of 150 A was chosen.

At this current, without turning on _the arc of indirect action, preliminary surfacing was performed on the plate at a speed of Vc=0.3 cm/s. mm ² .

According to the formula (3), the productivity of melting the base metal was calculated

P _O = 7.8⋅0.3⋅0.3=0.702 g/s.

According to formula (2), the required productivity of electrode metal deposition was calculated.

P _N \u003d (0.25 ⋅ 0.702) / 0.75 \u003d 0.234 g / s.

Then, by weighing experiments, it was established for an arc of reverse polarity in argon with a consumable electrode from the same welding wire that the current to ensure such a deposition rate is 110 A.

Then surfacing was performed according to the proposed method in the established modes: direct arc current 150 A, indirect arc current 110 A. A weld was obtained with cross sections F _O =31 mm ² , F _W =42 mm ² . Then F _H \u003d 11 mm ² . As a result, Ψ _E = 0.262 = 26.2% was obtained. This is close to the required Ψ _{E =} 0.25.

Example 2. According to the proposed method, automatic surfacing of nickel wire NP2 according to GOST 2179-75 with a diameter of d _E = 1.25 mm was carried out with a direct arc with a tungsten electrode in argon on a plate 6 mm thick from low-carbon steel 20 in order to ensure the optimal nickel content in seam Ψ _E \u003d 20% by weight. The nickel content in this wire is not less than 99.5% by weight. Diameter of a tungsten electrode of the EVCh brand is 3 mm. The angle of sharpening of the end of the electrode was 60°. A current of 150 A was chosen for this electrode.

At this current, preliminary surfacing was performed at a speed of Vc=0.3 cm/s. Then, a section of the cross-section of the preliminary surfacing was made and it was determined from it that the cross-sectional area of penetration of the base metal was F _O =30 mm ² .

According to the formula (3), the productivity of melting the base metal was calculated

P _O = 7.8⋅0.3⋅0.3=0.702 g/s.

According to formula (2), we calculated the required productivity of surfacing electrode metal from nickel

P _N \u003d (0.2 ⋅ 0.702) / 0.8 \u003d 0.193 g / s.

Then, by weighing experiments, it was established for an arc of reverse polarity in argon with a consumable electrode from the same welding wire that the current to ensure such a deposition rate is 80 A.

Then, surfacing was performed according to the proposed method in the established modes: direct arc current 150 A, indirect arc current 80 A. A weld was obtained with cross sections F _O =31 mm ₂ , F _W =42 mm ² . F _H \u003d 11 mm ² . Then we get Ψ _E \u003d 0.262 \u003d 26.2%. This is close to the required Ψ _{E =} 0.25.

The method can be used not only for surfacing aluminum on steel, but also for other wires: copper, chromium, nickel, titanium. Also, as the base metal, not only steel, but other metals with a predominance of one chemical element can be used. This method can be implemented through the use of modern equipment and accessories: installations for welding with bipolar current pulses, welding torches and feeders, automatic welding machines. Therefore, the method has industrial applicability.

Claims (2)

1. A method for automatic arc mechanized surfacing in an inert gas environment using a combination of direct and indirect arcs, including connecting a non-consumable electrode to the negative pole of one welding power source, the positive pole of which is connected to the product, while a non-ferrous metal consumable electrode is used in the indirect arc, connected to the positive pole of the second power source, the negative pole of which is connected to a non-consumable electrode, at the same time, a direct-action arc of direct polarity is ignited between the non-consumable electrode and the product and an indirect arc between the non-consumable and consumable electrode, surfacing is carried out to obtain a given content of non-ferrous metal in the deposited metal Ψ _e , % by weight, characterized in that in order to obtain a given non-ferrous metal content during surfacing, the required indirect arc current between a non-consumable electrode and a consumable non-ferrous metal electrode is determined, while the base metal of the product is preliminarily melted with a non-consumable electrode with an arc of direct polarity at the recommended for a given diameter of the current electrode without ignition of an indirect arc and without supply of a consumable electrode, the obtained cross-sectional area of penetration of the base metal is measured, taking into account which the productivity of melting of the base metal P _o , g / s, is calculated by the expression P _o \u003d ρ _o ⋅ V _s ⋅F ₀ , where ρ _o is the density of the base metal, g/cm ³ , V _s is the deposition rate, cm/s, F ₀ is the cross-sectional area of penetration of the base metal, cm ² , then taking into account the given content of non-ferrous metal in the weld metal calculate the performance of welding consumable electrode P _n , g / s, according to the expression P _n \u003d Ψ _e ⋅ P _about / (1-Ψ _e ), and the arc current of indirect action I, A, between non-consumable and consumable electrodes, necessary to obtain during surfacing a given content of non-ferrous metal, is determined from the expression P _n \u003d α _n I, where α _n is the deposition coefficient, g / A⋅s. 2. The method according to p. 1, characterized in that aluminum, or magnesium, or copper, or nickel, or molybdenum, or vanadium wire is used as a consumable electrode.

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