RU2778341C1 - Method for arc automatic surfacing with a consumable electrode in an inert gas - Google Patents

Abstract

FIELD: automatic arc surfacing.

SUBSTANCE: invention can be used in automatic arc surfacing of wear-resistant, heat-resistant, heat-resistant and corrosion-resistant metal layers on low-carbon and low-alloy steels with a consumable electrode with filler wire feed. Surfacing is carried out using an arc with bipolar current pulses with a frequency of at least 50 Hz with a given regulation of the ratio of the average current of direct polarity pulses to the average arc current (ϕ). As a consumable electrode, an electrode wire made of non-ferrous metal, which is an alloying element, is used. The seam is preliminarily welded without feeding the filler wire with an electrode wire from the same non-ferrous metal. The content of non-ferrous metal in the preliminary weld is determined by mass and the difference between the specified content of non-ferrous metal and its content in the preliminary weld is calculated. Depending on the result obtained, a filler wire is used, similar in composition to non-ferrous metal electrode wire or similar in composition to the welded part. The feed rate of the filler wire is calculated from the condition of obtaining a given content of the alloying element in the welding seam by choosing ϕ within the specified limits and taking into account the losses of the alloying element during welding.

EFFECT: method allows optimizing the content of non-ferrous metals in the weld during surfacing on steel, provides high productivity and stability of the surfacing process.

2 cl, 8 dwg, 5 tbl, 2 ex

Description

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

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 \u003d 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 formation of the 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 need for such variants of surfacing is great and will continue to grow. It can be noted that, for example, for conventional wear-resistant hardfacing, a large area of transverse penetration of the base metal is a disadvantage, while for the method under consideration this is a necessary feature. The proportion of the base metal in the weld metal by weight is required in the range of 60-80%.

The main technical problem of this method is the difficulty of ensuring the exact amount of aluminum content in the weld, at which the optimal performance characteristics of the deposited layer are achieved, which shows a wide range of allowable changes in the aluminum content in it. The problem is caused by the low stability of the melting rate of the filler metal, which is fed in the form of a wire into the arc column. The rate of melting of the filler wire is affected by the arc power, wire diameter, position along the length of the arc, its deformation and deviation from the required place of feeding into the arc, and other factors that are difficult to regulate and stabilize. 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 the arc. The power of the direct action arc affects the penetration of the base metal to a greater extent than the melting of the filler metal.

It has also been found that the addition of alloying elements to the wire, such as, for example, silicon, affect the hardness and wear resistance of the deposit. Studies of this method with silicon additives have shown that the optimal content of aluminum in the weld by weight in this case is already 20% (for the effect of silicon on hardness during surfacing, see the article A.I. alloys of the Fe-Al system. International scientific journal "Symbol of Science" No. 11-3/2016, P. 86-91, ISSN 2410-700X). The optimum hardness of the weld metal occurs at a certain aluminum content in the weld, which may depend on the content of alloying elements in the filler wire or in the base metal. Therefore, the content of the main alloying element in the weld (aluminum) must be maintained with a sufficiently high accuracy.

A serious 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 3-10 times less than when using a consumable electrode in an arc of reverse polarity. To melt the product, a straight polarity arc in argon with a tungsten electrode is used, which has a minimum melting ability compared to, for example, a reverse polarity arc with a consumable electrode. Calculations show that for the indicated range 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, i.e., to obtain a wear-resistant alloy in the weld, higher melting rate of aluminum wire. Therefore, with this method, it is difficult to obtain the required aluminum content in the weld, and this complexity increases with increasing aluminum content.

It is very difficult to ensure high accuracy of the aluminum content in the seam in this method. The consequence of both technical problems is that the selection of modes and conditions of surfacing for such a method is very laborious, and their maintenance during surfacing is unstable and fraught with difficulties.

A known method of restoring tread surfaces by surfacing, in which automatic surfacing with a consumable electrode is carried out, surfacing is performed in a shielding gas environment with a consumable austenitic electrode with the supply of an additional additive heated to a plastic state, which is introduced into the crystallizing part of the surfacing pool at a distance B from the consumable electrode, equal to ( 0.3 - 0.5)L, where L is the length of the surfacing pool, mm, while an additional additive is introduced in an amount of 20 - 40% by weight of the consumable electrode. (see, RF patent No. 2143962. Published on January 10, 2000, Bull. No. 1).

This method can be used for surfacing flat products, including aluminum wire on steel, as well as wires from other metals.

The technical problem of this method is the low technological flexibility of the surfacing process in relation to the consumable electrode, which manifests itself in a narrow range of possible regulation of the share of participation of the electrode metal in the weld metal. Low technological flexibility is due to the unidirectional influence of the mode parameters: arc current or surfacing speed on the cross-sectional area of penetration of the base metal and the cross-sectional area of the deposited metal. For example, with an increase in the welding speed, both the cross-sectional area of penetration of the base metal and the similar area of the deposited metal decrease. As a result, these main modes of surfacing have little effect on the share of the electrode metal in the weld metal, which makes it difficult to obtain a weld with a given content of the main alloying element. This leads to high labor intensity and cost of experimental selection of welding parameters, which provide an acceptable range of the content of the main alloying element in the weld. The low technological flexibility of the method is evidenced by the fact that in order to obtain the required chemical composition of the weld, a filler wire heated to a plastic state is used, the feed spread of which by weight is ±50% of the average value. Such a high spread confirms the low melting stability of the filler wire even when it is heated, which contributes to an increase in the melting stability.

A serious technical disadvantage of the method is also the low productivity of the melting of the electrode metal, which is inherent in the arc of reverse polarity used. In combination with the increased penetration capacity of such an arc, this makes it difficult to obtain the required range of aluminum content in the weld.

The technical disadvantages of this method are the possibility of ignition of the arc between the filler wire and the product, and the strong interaction of the magnetic fields of direct currents in the arc and the filler wire.

In the known method of automatic arc surfacing with a consumable electrode in an inert gas on steel with the supply of filler wire, the content of the alloying element in the weld is set by weight. Unlike the prototype, an arc with bipolar current pulses with a frequency of at least 50 Hz is used for surfacing by adjusting the ratio of the average current of direct polarity pulses per period to the average arc current per period within ϕ=0.1-0.9, using an electrode wire from non-ferrous metals, the filler wire is fed in the direction of the arc column or the weld pool, the filler wire is used in composition similar to the electrode wire or the base metal, first, at the arc current of reverse polarity recommended for welding for a given electrode diameter, the seam is welded without feeding the filler wire, measured the cross-sectional area of the weld and the deposited metal and determine the cross-sectional area of penetration of the base metal and the content of non-ferrous metal in the preliminary weld by weight, calculate the difference between the required and certain content of non-ferrous metal, in accordance with the sign of the difference, determine the type of filler wire and calculate the The speed of its supply, taking into account losses during surfacing, providing the required content of non-ferrous metal in the weld.

Aluminum, magnesium, zinc, copper, nickel, titanium or other non-ferrous metal wires can be used as electrode wire.

The technical result of the proposed method of surfacing or welding is to jointly provide the possibility of significantly expanding the range of the share of participation of the electrode metal in the weld metal ψ _E by changing the ratio of penetration of the base and electrode metals and creating the possibility of obtaining with high accuracy the required content of the alloying element from the non-ferrous metal in the weld weld at using as a heat source a high-performance, and at the same time flexible and stable arc with bipolar current pulses with a frequency of more than 50 Hz due to the proposed experimental-computational approach to determining the type and required feed rate of the filler wire based on one experiment. Accordingly, high performance characteristics of the deposited weld are ensured. This technical result is based on the joint use of the specific technological properties of a consumable electrode arc fed with bipolar current pulses, and on the effect of the absence of a significant effect of the melting rate of the filler wire on the cross-sectional area of the penetration of the base metal.

Another technical result is an increase in the productivity of melting the electrode metal, which leads to an increase in the productivity of surfacing. This technical result is based on the use of a direct-acting arc with bipolar current pulses, in the presence of current pulses of direct polarity, which provide a higher melting rate of the electrode wire at a stable melting rate and less penetration of the base metal, all other things being equal.

Another technical result is the absence of magnetic influence between the filler wire and the arc.

Figure 1 shows a diagram of the implementation of the method, in Fig. 2 cyclogram of impulses with the predominance of reverse polarity current; figure 3 - cyclogram of pulses with the predominance of current direct polarity; in fig. 4 - dependencies of the recommended current densities per consumable electrode, in Fig. 5 - dependence of the areas of the weld and surfacing on the current, fig.6 - dependence of the areas of the seam and surfacing on the welding speed, fig.7 - diagram of the melting coefficients for steel wires, fig. 8 is a chart of melting ratios for aluminum wires.

In FIG. Figure 1 shows a diagram of the surfacing process and a cross section of the weld after automatic arc surfacing on a plate with a consumable electrode in argon by the proposed method. Welding of weld 1 on plate 2 with thickness δ is carried out by direct action welding arc 3 with bipolar current pulses and electrode wire 4 containing the main alloying element from non-ferrous metal, for example, aluminum. The electrode wire may contain additives of other alloying elements in an amount not exceeding 2.5% by weight. Direct action arc 3 is powered by a welding power source of bipolar rectangular current pulses with a frequency of at least 50 Hz, which provides high-frequency ignition of pulse currents. Additionally, in the direction of the arc column or weld pool at a constant speed, filler wire 5 is fed in the composition of alloying elements similar to the electrode wire 4 or the base metal. Drops of molten filler wire 5 fall into the weld pool. The deposited weld 1, which is an alloy of the base metal with the electrode and filler, can be conditionally divided into the cross-sectional area of penetration of the base metal 6 and the cross-sectional area of the deposited metal 7. On the plate 1, they are separated by a dotted line passing along the front surface of the plate 1. The width of the deposited weld 1 E, penetration depth (penetration) H. The cross-sectional area of penetration of the base metal 6 is denoted by 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 deposited metal 7, equal to F _N

The areas F _W and F _H can be determined empirically on the plate from the macrosection of the weld cross section. The average melting performance of the electrode wire in g/s can be determined from its feed rate, and the average deposition performance from the difference in sample weights before and after welding and the deposition time.

The penetration area of the cross section of the base metal F _O can also be determined with the required accuracy using the formulas for heat propagation in the plate by measuring the dimensions of the weld without making a section of the cross section (see, for example, RF patent No. 2 704 676, Publ. 10.30.2019, Bulletin No. 31).

_The cross-sectional area of the deposited metal 7, in turn, conditionally includes two areas: metal deposited due to electrode wire 4 and deposited due to filler wire 5. determined from the results of a preliminary experiment on surfacing without the use of filler wire 5. This is possible due to the fact that the molten filler metal has a very small effect during the surfacing process on the value of the cross-sectional area of penetration of the base metal. The cross-sectional area of the weld metal obtained by melting the electrode wire dominates the cross-sectional area of the weld metal F _H due to its higher melting performance compared to the filler wire. Filler wire feed ensures the accuracy of the required content of non-ferrous alloying metal in the weld.

With known cross-sectional areas F _O and F _N , an important parameter of the weld can be determined - the proportion of additional metal in the weld metal ψ _E by weight, which is used to calculate the chemical composition of the weld from the known chemical compositions of the deposited and base metals. Since the density of the deposited weld over the entire volume is the same regardless of the densities of the main and additional metals, the ratio for the share of participation ψ _E by weight is valid

The use of an arc with bipolar current pulses for surfacing makes it possible to control the proportion of the electrode metal in the weld metal in a much wider range. With the predominance of current pulses of reverse polarity, the productivity of surfacing is lower and the productivity of melting the base metal is greater. With the predominance of current pulses of direct polarity, the productivity of surfacing is higher and the productivity of melting the base metal is lower. Thus, the ratio of average currents of pulses of opposite polarity in the arc is another additional parameter of the process, along with current, deposition rate, and electrode diameter. This significantly expands the technological capabilities of the arc in relation to the regulation of the chemical composition of the weld. The use of a frequency not lower than 50 Hz ensures high spatial stability of the arc and stability of the rate of melting of the electrode wire.

Despite the expansion of the range of regulation ψ _e by changing the ratio of the average current polarities of the arc with bipolar current pulses, such a change may not be enough to obtain the required ψ _e . One of the reasons for this is that arc welding power sources with bipolar current pulses have a control ratio of the pulse time ratio in relation to the period duration of at least 0.1, often 0.2. A more accurate value of the required ψ _E can be achieved using the supply of filler wire in composition close to the base metal or to the composition of the electrode wire. The type and speed of the filler wire feed are selected depending on the results of the experiment when surfacing a weld without feeding a filler wire. In this case, the effect of the weak influence of the melting rate of the filler wire on the penetration of the base metal is used.

When carrying out preliminary surfacing with aluminum electrode wire without feeding filler wire, a weld with a certain cross-sectional area F _SHO and cross-sectional area of the deposited metal F _BUT will be obtained. The difference between them gives the cross-sectional area of the base metal

In this case, the cross-sectional area of penetration of the base metal F _O will remain unchanged even when the filler wire is fed. This allows using formula (2) to determine the total cross-sectional area of the deposited metal required to provide the required value of ψ _E by weight.

where F _H is the cross-sectional area of the deposited metal during surfacing with the supply of filler wire according to the proposed method;

F _O is the cross-sectional area of the melting of the base metal in the preliminary experiment without feeding the filler wire.

Additional weld metal must be transferred to the weld metal by feeding the filler wire to ensure accurate non-ferrous alloy content is obtained.

When surfacing a dissimilar metal of the electrode wire, such as, for example, aluminum wire on steel, when determining the melting rate of the electrode wire, it is necessary to take into account the different densities of the base metal and the electrode one.

Let us assume that the required aluminum content in the deposited weld by weight is ψ _E =η. Then, when surfacing aluminum wire on a steel plate, taking into account the different densities of these metals, we can write

where ρ _Al is the density of aluminum wire, g/cm ³ ;

F _H1 - cross-sectional area of the deposited aluminum in the absence of its mixing with the base metal, cm ² ;

ρ _C - steel wire density, g/cm ³ ;

F _O - cross-sectional area of penetration of the base metal, cm ² , which can be determined from the section of the cross-section of the weld or by calculation using the formulas for the spread of heat during welding.

In formula (5), it is assumed that the weld metal has the density of aluminum, and the base metal has the density of low-carbon steel. We accept the density of steel ρ _С = 7.8 g/cm ³ , the density of aluminum is 2.7 g/cm ³ . Let us denote the ratio ρ _С / ρ _Al =β=2.89. Then, after transformations, we obtain from (5)

2.89(F _O / F _H1 ) +1 = 1/η.

At η = 0.3 (F _O / F _H1 ) = 0.81. Such a ratio is difficult to accurately obtain when using only electrode aluminum wire as an additional metal. It is necessary to determine such parameters of the surfacing process with filler wire feed, which would provide just such a ratio of areas in order to accurately obtain ψ _E = 0.3. This can be achieved using the proposed surfacing method.

Table 1 summarizes the calculation data for the ratio of the cross-sectional areas of penetration of the base metal and the deposited metal without mixing.

Table 1 ψ _E 0.15 0.20 0.30 0.40 R=F _O /F _H1 1.96 1.38 0.81 0.52

Thus, in order to provide an accurate value of ψ _E , it is first necessary to calculate the corresponding ratio R of the area F _O and the cross-sectional area of the deposited metal without mixing F _H1 . After that, it is required to perform surfacing with a consumable electrode without supplying a filler wire and make a macrosection of the weld cross section and measure the experimental values of the cross-sectional area of \u200b\u200bthe weld F _SHO and the deposited metal F _BUT , and then calculate the cross-sectional area of \u200b\u200bmelting the base metal F _O \u003d F _SHO - F _BUT . The experimental cross-section of the deposited metal _FHO can be accurately determined directly from the section after surfacing. That is, the required (calculated) cross-sectional area of the aluminum wire deposited without mixing should eventually be

On the other hand, it is possible to determine the real cross-sectional area of the deposited metal F _HО without mixing by the mass of the electrode metal deposited in the preliminary experiment М _Н in grams

where L is the length of the seam, see

After that, the sign of the difference between F _H1 and the experimental value of the cross-sectional area of the deposited metal F _BUT without mixing should be determined

If Δ is greater than zero, therefore, there is not enough aluminum in the designed weld and an additional aluminum filler wire should be fed into the weld.

If Δ is less than zero, then there is excess aluminum in the weld and additional steel filler wire should be fed into the weld.

Required melting and feed rate V _PAL aluminum filler wire

where V _C - welding speed, cm/s;

S - cross-sectional area of the aluminum filler wire, cm ² ;

ψ _PAL - loss factor of aluminum filler wire during surfacing on evaporation and spatter.

To determine the feed rate V _PFE steel filler wire, it is necessary to make an equation based on formula (2).

where P _E is the productivity of surfacing aluminum electrode wire with an arc, g/s;

ρ _С - density of steel, g/cm ³ ;

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

V _C - welding speed, cm/s;

V _NS - speed of transfer (surfacing) of steel filler wire into the seam, cm/s;

S _P - cross-sectional area of the steel filler wire, cm ² .

Formula (11) includes 3 terms in the numerator and denominator. The term in the denominator P _E takes into account the flow of aluminum into the seam by weight. The term ρ _С F _O V _C takes into account the entry of steel from the base metal into the weld and the term ρ _С V _PS S _П the entry of steel filler wire into the weld. Since we are only interested in the content of aluminum electrode metal in the weld by mass, then only one term PE is taken into account as the mass of the _deposited metal.

The performance of welding electrode wire P _E is determined by weighing the welding sample before and after welding and measuring the welding time in a preliminary experiment. By calculation, P _E can be determined by the formula, if the coefficient of loss of the electrode for evaporation and spraying ψ _P is known

where S _E - cross-sectional area of the electrode wire, cm ² ;

V _PE - melting rate of the electrode wire, cm/s;

ρ _AL is the density of aluminum, g/cm ³ .

In expression (11), the desired is the rate of deposition of steel filler wire V _NS . After transformations (11) we obtain

On the left side in square brackets we have a dimensionless value, and the dimension of the right side is in cm/s.

To obtain the required rate of melting (feed) of the steel filler wire, it is necessary to divide the value of V _HC by a coefficient that takes into account its losses due to evaporation and spatter

(1-ψ _PS ).

The loss factor of the filler wire during surfacing can be taken in the calculation based on the literature data and refined when performing surfacing according to the proposed method. In this case, the mass of the deposited metal is weighed and the mass of the spent wire is measured by its feed rate.

The fact that the melting of the filler wire does not have a significant effect on the penetration of the base metal is confirmed by the fact that, for example, even in experiments when welding with a current-carrying filler wire, there is no such effect, although drops of the electrode metal in this case are heated to a higher temperature (see article V.P. Sidorova, N.A. Borisova 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.

Also, a weak effect of the melting rate of the filler wire on the penetration of the base metal follows from the results of the article by A.I. Kovtunova et al. Determination of the parameters of a distributed heat source in the surfacing of alloys of the titanium-aluminum system. Metal technology. 2018. No. 12. C16-20. (see table on page 18). When the wire feed speed was changed by 6 times at a current of 270 A, the penetration of the base metal remained practically unchanged.

The inclusion of alloying elements other than the main one in the composition of the electrode wire up to 2.5% by weight changes the density of the electrode wire, but this can be easily taken into account by calculating the reduced density of the electrode wire. In addition, such a small content of alloying elements has little effect on the accuracy of the calculation and obtaining the required content of the main alloying element.

Table 2 lists the densities of base non-ferrous metals that can be used in hardfacing.

table 2 Metal Al mg Cu Zn Ni Ti Density, g / cm ³ 2.7 1.74 8.92 7.13 8.9 4.54

In Fig.2. the cyclogram of the arc current during surfacing or consumable electrode welding with bipolar rectangular current pulses is presented with the predominance of reverse polarity pulses in time. The currents during the pulses are the same. The time of pulses of direct polarity is indicated by t_EN, and reverse polarity t_EP. Total cycle time t_FROM. Average reverse polarity arc current I_EPC for the period

where I _EP is the average reverse polarity arc current per pulse, A

ϕ is the time fraction of the current of pulses of direct polarity per period.

In the proposed method, the value of ϕ is proposed to be chosen within ϕ=0.1-0.9, and the pulse frequency is not less than 50 Hz. The proposed range of changes in ϕ allows you to maximize the range of possible values of ψ _E during surfacing or welding without the use of filler wire. Values of ϕ less than 0.1 should not be used, since the stability of re-ignition of the arc is possible, as well as the fact that industrial installations allow changing ϕ in increments of at least 0.1. Values of ϕ greater than 0.9 should not be used due to a possible violation of the stability of the melting rate of the electrode wire. The use of a pulse frequency of at least 50 Hz ensures high spatial stability of the arc and high stability of the rate of melting of the electrode wire.

Average straight polarity arc current I _ENC per period

where I _EP is the average current of the arc of direct polarity in the pulse, A.

Average arc current I _C per period

The average currents of the arc polarities per period I _ENC and I _EPC determine the melting performance of an electrode with that polarity per period.

Figure 3 shows the cyclogram of the arc current during welding with bipolar current pulses of a rectangular shape with the predominance of time pulses of direct polarity. The pulse currents are also the same. The designations in Fig. 3 are similar to those in Figs. 2. Formulas (14)-(16) are also valid in this case.

Figure 4 shows the dependence of current densities in welding with aluminum electrode wire in an arc of reverse polarity in argon on its diameter d. For each wire diameter, the current density can vary over a fairly large range. It decreases with increasing wire diameter. The top curve in Fig. 4 represents the maximum recommended current densities and the bottom one represents the minimum. The current density curves are calculated according to the data for currents given in the book by Melnichenko N.T. Assembly and welding of stainless steel and aluminum structures. L.: Mechanical engineering. 1968. 208 p. on page 96, in table 25. Similar data are quite widely given in the special literature.

The same table 25 shows data on the feed rate of the aluminum electrode wire. Based on these data, the melting coefficients of the electrode wire were calculated using the formula

where V _e - speed of melting (feed) of the electrode wire, cm / s,

ρ - wire metal density, g / cm ³ ,

j - current density in the cross section of the electrode, A/cm ² .

The dimension of α _R in this case is g/(A⋅s) and to convert to g/(A⋅h) it is necessary to multiply the value by 3600 s. The calculation results for α _P are shown in Table 3.

Table 3 d, mm 1.2 1.6 2.0 2.5 3.0 4.0 I, A Currents, A 100 250 150 300 200 350 250 400 280 450 400 500 α _P ,
g/(A⋅h) 7.4 10.2 8.8 12.0 10.3 10.2 13.0 12.0 8.3 10.3 10.4 12.5 Δ, % 17.3 15.4 0 4.0 11.0 8.8

The last line of Table 3 shows the relative deviation of the half-difference of the boundary values α _R for the range of currents to the average value (half-range of values from the average value).

Table 3 shows some slight trend towards an increase in the melting factor with increasing current density. This may be due to the different degree of heating of the electrode in the extension. The deposition coefficient α _H of a direct arc is easy to determine by weighing the difference in the masses of the deposited sample before and after deposition for a specific arc current and measuring the deposition current and time or using α _P , and the known loss coefficient for waste and spatter. Table 3 shows the low accuracy of determining the coefficient α _P and, consequently, the associated deposition coefficient α _N , which is necessary to calculate the melting capacity of the _PN electrode wire g/s.

The deposition factor in formula (18) should be used in g/(A⋅s).

Comparison of the melting coefficients of steel and aluminum electrode wires at the same currents shows that the melting coefficient of aluminum wire under the same conditions is approximately 1.5-1.7 times less than that of steel wire. The data were obtained according to the dependencies given in the book by V.A. Lenivkina and others. Technological properties of the welding arc in shielding gases (p. 112, Fig. 57 and 58). M.: Mashinostroenie, 1989, 264 p. The data refer to an arc of reversed polarity. This makes it difficult to obtain a sufficiently large amount of aluminum in the seam when surfacing aluminum on steel by a known method.

Figure 5 shows the dependence of the cross-sectional areas of penetration of the base metal and deposited metal and the proportion of the electrode metal in the weld metal when surfacing steel low-carbon welding wire on a plate of low-carbon steel welds in CO ₂ from the arc current. Dependencies are given in the book by E.N. Novozhilov. Fundamentals of metallurgy of arc welding in active shielding gases. M.: Mashinostroenie. - 1972.- 167 p. and are shown on page 102 in fig. 57 a. The coefficient ψ _E decreases with increasing current from 200 to 500 A from ψ _E =0.55 to ψ _E = 0.35, that is, by 40%. This is because at a certain current, the growth of the cross-sectional area of penetration of the base metal begins to significantly outpace the growth of the cross-sectional area of the deposited metal. The reason for this is the reflection of heat from the reverse plane of the plate when the current reaches a certain thickness. The areas are equal to each other at a current of 250 A, that is, for this current F _O / F _H =1. Dependences in figure 5 show that under these conditions, a change in current can, within certain limits, affect ψ _e and the content of the main alloying element in the weld when welding with a consumable electrode. However, this effect is not enough to ensure the required content of the main alloying element in the weld. Change ψ _e occurs approximately within 20% of the average value ψ _e =0.5, that is, in the range ψ _e =0.6-0.7.

Figure 6 shows the dependence of the cross-sectional areas of penetration of the base metal and the deposited metal and the proportion of the electrode metal in the weld metal when surfacing steel low-carbon welding wire on a plate of low-carbon steel welds in CO ₂ from the welding speed. Dependencies are given according to the same source as for Fig.5.

The dependence shows the absence of influence of the welding speed on ψ _e , which characterizes the low technological flexibility of the known surfacing method.

Figure 7 shows a diagram of the melting coefficients α _P for steel wires for direct and reverse polarity of the arc current when surfacing in argon with wire Sv-08G2S with a diameter of 2 mm. The diagram was built according to the data given in the monograph by V.A. Lenivkina et al. Technological properties of the welding arc in shielding gases. M.: Mashinostroenie, 1989. - 264 p. (Table 20 on page 115). The electrode overhang was 1.54 cm.

The experimental data of Fig. 7 indicate that at the same arc current of 340 A, the melting coefficient of the electrode wire at reverse polarity EP is α _P =13.0 g/(A⋅h), and at straight polarity EN α _P =22.1 (g/A⋅h ), i.e. on direct polarity α _P is 1.7 times greater. This is due to two reasons - to a greater extent, more power into the electrode from the cathode region of the arc than from the anode region and, to a lesser extent, lower heat content of the electrode metal droplets at direct polarity.

For various shielding gases, the ratio of melting coefficients for direct and reverse polarity is given in the reference book "Welding in mechanical engineering", Vol. 1, 1978 on page 238, table. 36. For an electrode wire diameter of 1.6 mm, the average value at a current of 350 A at direct polarity is 26.1 g / (A⋅h), and at the reverse 15.5 g / (A⋅h), that is, at direct polarity in 1.68 times more.

The surfacing coefficient α _H differs from the melting coefficient α _P only by a small percentage of losses due to waste and spatter, which do not affect the overall picture of the ratio of surfacing productivity at different polarities.

In FIG. 8 shows a similar diagram for surfacing aluminum electrode wire with a diameter of 1.2 mm on an aluminum plate at a current of 200 A with an arc in argon. The melting coefficient of the electrode wire at reverse polarity is 8.72 g/(A⋅h), and at straight polarity 19.33 (g/A⋅h), i.e. on direct polarity 2.16 times more. This result is described in the article by V.P. Sidorova et al. On the melting of an aluminum electrode by an argon arc of direct polarity. Vector of Science TSU, 2019. No. 4(50). pp.52-57.

However, in direct polarity, welding and surfacing with an arc in shielding gases with a consumable electrode is not carried out due to the low stability of the melting rate of the electrode wire and the low spatial stability of the arc. This is explained by the peculiarities of the behavior of the cathode spot on the rod electrode. To a greater extent, this is inherent in steel wires due to the presence of various oxides and impurities on the surface, which affect the cathodic arc voltage drop. To a lesser extent, this is inherent in aluminum electrode wire, in which only one Al ₂ O ₃ oxide of various thicknesses can be present on the surface.

The use of a bipolar arc with a current pulse frequency of at least 50 Hz for surfacing with a consumable electrode in shielding gases makes it possible to increase the stability of the process, both the rate of electrode melting and the spatial stability of the arc. At the same time, due to a significant difference in the intensity of penetration of the electrode and the product, this type of arc allows, by controlling the proportion of polarities in the period and the average polarity currents for the period, to control the ratio of the areas of penetration of the base and deposited metal and ψ _E in a very wide range.

The increase in stability is due to the fact that a change in polarity with a sufficiently high frequency suppresses the wandering of the cathode spot of the welding arc, both on the product and on the electrode. The stability of re-ignitions is ensured by the high current zero-crossing rate and the high-frequency arc exciters built into the welding machines.

For an arc with bipolar current pulses, we can write the formula for the deposition coefficient α

where α _EP is the deposition coefficient for a DC reverse polarity arc;

α _EN is the deposition factor for a DC direct polarity arc.

Denote the ratio (α _EN / α _EP ) = М>1. Then

α = (1-ϕ) α _EP + α _EP М⋅ϕ.

After transformations, we get

At ϕ = 0.1, reverse polarity prevails, at М=2 we get α =1.1 α _EP , and at ϕ = 0.9, direct polarity prevails, and at М=2 we get α =1.9 α _EP . That is, with an increase in the ratio of the duration of pulses of direct polarity to the duration of the period, according to the proposed method, it is possible to change the deposition coefficient by 73%. At the same time, a similar coefficient of penetration of the base metal will decrease, which can be denoted α _O . It will change to a lesser extent, however, in general, the range of possible changes in the proportion of the electrode metal in the weld will be much wider than that of the known method. The opposite direction of change in the areas of penetration of the base and deposited metals with a change in ϕ allows you to change ψ _e in a very wide range. The coefficient of penetration of the base metal, similar to the coefficient of welding for electrode wire, can be determined by the formula

where ρ _O is the density of the base metal, g/cm ³ ;

I - average arc current, A;

V _C - welding speed, cm / s.

Dimension α _О when using the indicated units of measurement g/(A⋅s).

Table 4 presents the calculated dependences of the ratio of the deposition coefficients α of the electrode for an arc with current pulses of different polarities on ϕ for various values of М according to formula (20). The values of M may vary depending on the diameter of the electrode and the arc current. The coefficient in the table shows how many times the deposition coefficient for given M and ϕ is greater than the similar coefficient for the reverse polarity of the arc.

Table 4 M ϕ 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.6 1.06 1.12 1.18 1.24 1.30 1.36 1.42 1.48 1.54 1.8 1.08 1.16 1.24 1.32 1.40 1.48 1.56 1.64 1.72 2.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

The area of penetration of the base metal in formula (21) changes with an increase in ϕ in the opposite way - it decreases. This is due to the fact that the power introduced into the product by the cathode region is significantly greater than by the anode region. The power transmitted to the product by the liquid electrode metal has little effect on the penetration of the base metal. Thus, the areas of penetration of the base metal F _O and the electrode metal F _H change in the opposite direction with a change in ϕ, which allows you to adjust ψ _E over a wide range. Accordingly, the chemical composition of the weld will be regulated within a very wide range.

To implement the method, you can also use installations that provide not only the regulation of ϕ, but also the pulse currents. In this case, formulas for average currents over a period will be valid and can be used.

The currents on the aluminum electrode wire can be selected on the basis of table 3.5 and the like for welding aluminum alloys with a consumable electrode on the reverse polarity of the arc in argon.

Table 5 δ, mm Number of layers d _E , mm Current, A U _D , V V _C , cm/s 3-5 1-2 1.6-2.0 180-200 28-30 0.56-0.61 6-8 1-2 2.0 250-300 28-30 0.50-0.61 8-12 2-3 2.0 250-300 28-30 0.44-0.56

Example 1. According to the proposed method, automatic surfacing of aluminum wire A0 with a diameter of d _e = 1.2 mm was carried out with a direct arc in argon on a plate 6 mm thick made of low-carbon steel 20 in order to ensure the optimal aluminum content in the seam ψ _e = 26% by weight . At the beginning, according to formula (6), it was obtained that for this the ratio of the cross-sectional area of penetration of the base metal to the cross-sectional area of the deposited metal (excluding mixing) should be R=F _O /F _H1 =0.985.

Then, preliminary surfacing was carried out with an arc with bipolar rectangular current pulses from a special power source - a DW-300 installation. The pulse frequency was 50 Hz. For automatic surfacing of aluminum electrode wire, a welding torch for mechanized welding from a FastMigMXF 65 unit was used, which was attached to an ADSV-6 automatic welding machine. The pulse currents were set the same for both polarities I _EN =I _EP =200 A. When surfacing with different polarity current pulses at ϕ=0.2, the average currents of direct polarity EN _C = 40 A for the period, reverse polarity EP _C = 160 A. Average current arc for the period was also 200 A. The feed rate of the electrode wire was V _E =13.3 cm/s.

The deposition rate in the preliminary experiment was V _C =0.25 cm/s. When surfacing on the plate, the length of the surfacing was provided L = 80 mm. The weld plates were weighed before and after surfacing with an accuracy of 0.1 g. The average value of the cross-sectional area of the deposited weld metal was determined from the mass of the deposited aluminum and the length of the weld in the experiment without mixing _FHO according to the formula (8).

For the deposited weld, by the mass of the deposited metal, the cross-sectional area of the deposited metal F _H =0.23 cm ^{2 of} the weld section F _W = 1.02 cm ² was obtained. Thus, it was obtained that the cross-sectional area of penetration of the base metal F _O = F _W - F _H =0.79 cm ² . Such a rather large area is obtained due to the small thickness of the plate due to the reflection of heat from the back plane.

The share of participation of the electrode metal in the weld metal in terms of cross-sectional area and mass in the preliminary surfacing ψ _E = 0.23/1.02=0.225. From the fact that the experimental value of ψ _E is less than the required ψ _E = 0.26, it follows that there is a lack of aluminum in the seam and aluminum wire should be used as a filler wire.

Using the previously obtained coefficient R =0.995 for ψ _E =0.26, we calculated the required cross-sectional area of the deposited aluminum without mixing 0.79/0.995 = 0.79 cm ² . The actual cross-sectional area of the welded aluminum without mixing is 0.76 / 1.24 = 0.61 cm ² . This means that there is a lack of weld aluminum without mixing Δ=0.79-0.61 = 0.18 cm ² . We take the diameter of the aluminum filler wire 1.2 mm. To determine its feed rate, we use formula (10). The wire loss factor was assumed to be 0.1.

V _PAL =Δ⋅V _C /S(1-ψ _AL ),

V _PAL \u003d (0.18 0.25) / (0.013 0.9) \u003d 3.84 cm / s.

The wire was fed into the arc column at an angle to the product surface from the side of the tail part of the weld pool. To obtain the melting of the filler wire at a given speed, its position relative to the arc column in height and the angle of inclination with respect to the surface of the product were adjusted.

After surfacing in this mode with the supply of aluminum filler wire grade A0, after the manufacture of the macrosection, F _O = 0.78 cm ² , F _H = 0.27 cm ² , ψ _E = 0.256, that is, different from the required value by only 1, 5%. The results of the spectral analysis of the aluminum content in the weld confirmed the accuracy of the determination obtained by area. The cross-sectional area of penetration of the base metal changed by only 2%, and the cross-sectional area of the weld metal increased due to the supply of aluminum wire with a much lower density. As a result, the required aluminum content in the weld was ensured with high accuracy at a high deposition rate.

Example 2. With parameters similar to the parameters of example 1, surfacing was carried out, changing the proportion of pulses of direct polarity to ϕ = 0.8. The feed rate of the aluminum electrode wire was V _e = 21 cm/s.

For the deposited weld, we first obtained the average cross-sectional area of the deposited metal F _H =0.32 cm ² , the weld cross-section along the macrosection F _W = 0.95 cm ² . Thus, we got that F _O \u003d F _W - F _H \u003d 0.63 cm ² . The share of participation of the electrode metal in the weld metal in terms of cross-sectional area and mass in the preliminary surfacing ψ _E = 0.32/0.95= 0.34. From the fact that the experimental value ψ _E is greater than the required ψ _E = 0.26, it follows that there is an excess of aluminum in the weld and steel wire should be used as a filler wire. We accept the diameter of the steel filler wire 1.6 mm. Using formula (6), we calculate the ratio for the cross-sectional area of the deposited aluminum without mixing in the preliminary experiment

(F _O / F _H1 ) \u003d (1 / η-1) / 2.89 \u003d (1 / 0.34-1) / 2.89 \u003d 0.672.

Hence F _H1 \u003d 0.63 / 0.672 \u003d 0.94 cm ² .

Using formula (13), we calculated the transfer rate of the filler wire into the weld

V _NS \u003d [(1 / ψ _E -1) - (ρ _C F _O V _C / P _E )] [P _E / (ρ _C S _P )].

The productivity of welding electrode wire was determined by weighing according to the results of the preliminary experiment P _E = 0.63 g/s. Received the rate of transfer of the deposited metal to the seam

V _NS = [1/0.26-1) -7.8⋅0.63⋅0.25/0.63][0.63/7.8⋅0.02]= (2.85-1.95)4= 3.36 cm/s.

The melting rate (feed) of the steel filler wire was determined at a loss coefficient for evaporation and spattering ψ _P =0.05.

V _PS \u003d 3.36 / (1-0.05) \u003d 3.53 cm / s.

After surfacing in this mode with the supply of steel filler wire Sv-08A, after making a macrosection, F _O = 0.65 cm ² , F _H = 0.24 cm ² , ψ _E = 0.27, that is, different from the required value of the total by 3.8%. The cross-sectional area of the weld metal was slightly reduced due to the introduction of a filler wire with a much higher density into the weld. As a result, the required aluminum content in the weld was ensured with high accuracy at a high deposition rate. The wire was fed into the arc column at an angle to the product surface from the side of the tail part of the weld pool. To obtain the melting of the filler wire at a given speed, its position relative to the arc column in height and the angle of inclination with respect to the surface of the product were adjusted. The results of the spectral analysis of the aluminum content in the weld confirmed the accuracy of the determination obtained by area.

This method can be implemented through the use of modern equipment and accessories: installations for welding with bipolar current pulses, welding torches and automatic welding machines. Therefore, the method has industrial applicability.

Claims (2)

1. The method of automatic arc surfacing with a consumable electrode in an inert gas on a steel part with the supply of a filler wire, including obtaining a weld with a given content in it by weight of an alloying element, characterized in that surfacing is carried out using an arc with bipolar current pulses with a frequency of at least 50 Hz when adjusting the ratio of the average current of pulses of direct polarity to the average arc current for the welding period within ϕ = 0.1-0.9, while as a consumable electrode, an electrode wire made of non-ferrous metal, which is an alloying element, is used, and the seam is preliminarily deposited without feeding the filler wire with an electrode wire of the same non-ferrous metal at the current of the reverse polarity arc recommended for its diameter, then measure the cross-sectional area of the resulting weld and deposited metal and calculate the cross-sectional area of penetration of the base metal, after which the content in p preliminary seam of non-ferrous metal by weight and calculate the difference between the specified content of non-ferrous metal and its content in the preliminary seam, and if the content of the alloying element in the seam is less than that specified for surfacing, use a filler wire similar in composition to the mentioned non-ferrous metal electrode wire, and if it If the content in the weld is greater than the specified one, a steel filler wire is used that is similar in composition to the welded part, while the feed rate of the filler wire during surfacing is calculated from the condition for obtaining a given content of the alloying element in the weld by choosing ϕ within the specified limits and taking into account the losses of the alloying element during surfacing . 2. The method according to claim 1, characterized in that the surfacing is carried out with an electrode wire made on the basis of aluminum, or magnesium, or copper, or zinc, or nickel, or titanium.

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