RU2769190C1 - Welding flux granulation method - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention can be used in the production of granular fluxes for welding and surfacing of steels and alloys, in particular for welding carbon, alloy steels and alloys. The mixture of mineral raw materials for granulation can be both rocks and screenings of mining enterprises, as well as petrurgical raw materials, slags, ground to 0.25 mm. From the charge hopper 1, the ground raw material enters the charge flow control nozzle 2, which forms a stream of falling particles 4 in the granulation chamber 3, falling into a plasma arc 5 formed by a plasma torch 6, which operates from a power source 8 and a plasma gas 9 Granules in the molten state 12 fall on an inclined box for cooling and supplying granules and charge to the screening zone 11, where welding flux granules 16 are formed, entering the vibrating stand for screening granules and charge 10. Particles with a fractional composition of less than 0.25 mm come back into the batch hopper 1.EFFECT: improving the manufacturability and productivity of the method for granulation of the fused welding flux, which has a high alloying ability.1 cl, 1 tbl, 5 dwg

Description

The invention relates to methods for granulating welding consumables, namely for the manufacture of fluxes for welding carbon, alloy steels and alloys of various compositions, and can be applied in industry by enterprises producing welding consumables for welding steels and alloys of a wide range of compositions.

To improve the mechanical properties and quality of the weld metal, it is necessary to alloy the weld metal molten bath, and for this it is necessary to ensure the introduction of alloying, modifying, refining and deoxidizing components through the welding wire or flux.

Widely known technologies for the manufacture of welding fluxes: melting, sintering and agglomeration (patent US3413164A, Flux for arc welding and method for its manufacture). It is impossible to alloy the weld pool through flux during fused flux welding, since any ferroalloys and metal additives introduced into the flux charge during its melting during the manufacturing process oxidize and lose their metallurgical activity. Sintered fluxes make it possible to alloy the weld metal, but they are difficult to manufacture, and when they are obtained, the oxidation of metal components is also possible, because. the sintering process proceeds at high temperature heating (up to 1100°C). In addition, the low strength of the granules obtained by sintering leads to the loss of the welding and technological properties of the flux due to the formation of a dusty fraction. The technology for obtaining a granulated mass of agglomerated fluxes, which has ore-mineral components in its composition, makes it possible to introduce into the composition ferroalloys, single- and multi-component master alloys that alloy the weld pool during welding. However, agglomerated fluxes obtained by rolling, clumping or pressing in various versions also have, like sintered fluxes, a lower mechanical strength of the granules, and the hygroscopicity of alkali metal silicate as the main components makes the flux capable of absorbing moisture from the atmosphere, which entails the risk of porosity in the metal. weld.

A method of flux granulation is known, which consists in the fact that a layer of flux charge powder is applied to the surface of a metal plate with a reflectivity of at least 0.65, consisting of a mixture of non-metallic and metallic components with a fraction size of not more than 0.315 mm. Flux charge powder is exposed to light energy flow in the form of a light beam with a radiation wavelength of more than 0.56 μm and with a longitudinal velocity of the light beam relative to the processed powder of 0.01-20.0 cm/s. Melt droplets are cooled on the surface of a metal plate in a gaseous medium to form granules (RF patent No. 2387521 dated April 27, 2010).

The disadvantage of the known method is the low productivity due to the fact that only the surface of the mixture powder is processed in the pulsed mode, and not the entire volume.

A method is known for producing a self-protective granular flux, according to which a layer of powder of a flux charge containing oxides and carbides is applied to the surface of the plate, with a fraction size of not more than 0.5 mm. The charge is melted and melt drops are formed by exposing the charge layer to the flux with an electric short-circuit arc with a duration of not more than 1 s at a current of 50-200 A, depending on the bulk mass of the charge ignited between the plate made of conductive material and the electrode. The formed droplets are cooled in air to form granules. The technical result of the invention is to increase the efficiency of manufacturing strong welding flux granules (RF patent No. 2494847 C1, publ. 10.10.2013, MKI V23K 35/40).

The disadvantage of the known method is the low manufacturability and productivity due to the time-consuming operations of scattering the charge and collecting the flux from the metal plate, as well as the low coverage of the working area of the pointed graphite electrode, which required the ignition of the arc to granulate the flux a huge number of times, which is also a laborious operation. .

A known method for producing granular welding flux, including the melting of the mixture containing oxides and carbides, with a fraction size of 0.1-0.5 mm, the formation of melt drops under the influence of an electric arc and cooling drops with the formation of granules. The supply of the flux charge into the granulation zone is carried out through a dosing device located at a distance of 50-100 mm from the electric arc. The melting of the mixture and the formation of drops occurs when the particles of the mixture pass through a constant electric arc formed between two graphite electrodes with a diameter of 6-18 mm. A current of 100–300 A flows through the electrodes. The formed melt drops are cooled to form granules as they fall into a screening device installed below the electric arc (RF patent No. 2680031 C1, publ. 02.14.2019, MKI B01J 2/02; V23K 35/00).

The disadvantage of the known method is the insufficient concentration of the heat source and the specific power of the carbon arc due to which the granulation process has a low productivity.

The closest in technical essence is a method for producing granular welding flux, including melting in a heating source of a flux charge containing oxides with a fraction size of 0.1-0.5 mm and cooling the formed droplets to form granules. The flux charge is fed into the heating source in the form of a monolithic plate formed using sodium liquid glass as a binder. As a heating source, a direct-acting plasma arc is used, formed by the flow of a current of 30-200 A between the plasma torch and the conductive electrode, and the formed melt drops are cooled in water (RF patent No. 2716344 C1, publ. 11.03.2020, MKI B23K 35 /40; B23K 35/362). This method is adopted as a prototype.

Signs of the prototype, coinciding with the essential features of the claimed invention: the supply of the charge flux containing oxides in the granulation zone; melting the mixture and forming drops of the melt under the influence of a plasma arc formed when a current of 50-200A flows between the plasma torch and a conductive non-consumable electrode; cooling the formed droplets with the formation of granules.

The disadvantages of the known method, taken as a prototype, are the use of binders for the manufacture of raw materials for granulation in the form of plates, as well as the need for additional operations in the form of granulation in water, followed by drying. These shortcomings lead to a decrease in manufacturability and productivity in general.

The objective of the invention is to increase the productivity of the method of granulating fused welding flux with a plasma arc for the manufacture of strong spherical welding flux granules containing non-metallic components and additives with increased alloying ability.

The problem was solved due to the fact that in the known method of welding flux granulation, including the supply of a flux charge containing oxides to the granulation zone, the charge melting and the formation of melt drops under the influence of a plasma arc formed when a current of 50-200A flows between the plasma torch and the conductive with a non-consumable electrode, cooling the formed droplets with the formation of granules, according to the invention, the charge is fed into the granulation zone in the form of a powder with a fraction size of up to 0.25 mm, in a volume of 12-24 kg / h, from a height of 20-60 mm, the formed drops are cooled in air followed by sifting the obtained granules.

The features of the proposed technical solution, which are different from the prototype, are that the mixture is fed into the granulation zone in the form of a powder with a fraction size of up to 0.25 mm, in a volume of 12-24 kg/hour, from a height of 20-60 mm; the formed droplets are cooled in air, followed by sifting the resulting granules.

The proposed method does not require the preparation of raw materials with mixing with binders and the manufacture of a monolithic plate, and the operation of drying the finished flux granules is not required due to the fact that dry cooling in air is used, rather than wet cooling in a pool of water. This leads to a significant increase in the performance of the plasma granulation method in comparison with the prototype.

The proposed method is illustrated by the drawings shown in Fig. 1-5.

Figure 1 shows a schematic diagram of the method of plasma granulation.

The diagram shows: 1- bunker for the charge; 2-nozzle for charge flow control; 3- chamber for granulation; 4- charge; 5- plasma arc; 6- plasma torch; 7- hose for argon supply; 8- power supply; 9- cylinder with plasma-forming gas (argon); 10 - vibrating stand for sifting granules and charge; 11 - inclined box for cooling and supplying granules and charge to the screening zone; 12 - granules in the molten state; 13- electrode holder; 14 - copper plate; 15 - non-consumable conductive electrode; 16 - welding flux granules.

Figure 2 - mixture of hornblendite after crushing and screening before plasma granulation: General view, x100.

Figure 3 - mixture of hornblendite after crushing and sieving before plasma granulation: splintered particles, x1000.

Figure 4 - granules of the welding flux obtained by plasma granulation of the hornblendite charge: a general view of the morphology of the granules, x75.

Figure 5 - granules of the welding flux obtained by plasma granulation of the hornblendite charge: a spherical particle with micropores on the surface, x150.

The method of plasma granulation of the welding flux is carried out as follows.

As a raw material for granulation, a mixture containing oxides is used in the form of a powder. The mixture of mineral raw materials for granulation can be both rocks and screenings of mining enterprises, as well as petrurgical raw materials, slags, ground to 0.25 mm. The mixture is fed into the granulation zone in the amount of 12-24 kg/hour, from a height of 20-60 mm. The granulation process (figure 1) consists in the fact that from the hopper for the charge 1, the ground raw material enters the nozzle 2 to control the charge flow, which form in the chamber for granulation 3 a stream of incident particles 4 falling into the plasma arc 5 formed by the flow of current 50-200A between the plasma torch 6 and a conductive non-consumable electrode 15 installed in the holder 13 for the electrode. The plasma torch 6 operates from a power source 8 and a plasma-forming gas 9. Due to the high thermal effect, one of the walls of the chamber 3 is made in the form of a copper plate 14.

The charge lingers on the surface of the non-consumable electrode 15 and copper plate 14, and under the thermal action of the plasma arc 5, the charge particles are fused into drops and molten granules 12 are formed.

The granules in the molten state 12 fall on the inclined box 11 for cooling and feeding the granules and charge into the sifting zone, where welding flux granules 16 are formed, entering the vibrating stand 10 for sifting the granules and charge, where the fractional composition of particles less than 0.25 mm is returned to batch bin 1.

Feeding the charge into the plasma granulation zone in the amount of 12-24 kg/hour ensures high productivity of the plasma granulation process, which is at least 30% of the total mass of the charge that has passed the granulation process, while ensuring the stability of the plasma granulation process.

Feeding the charge into the zone of plasma granulation in a volume of less than 12 kg/h does not provide the required performance.

Feeding the charge into the zone of plasma granulation in a volume of more than 24 kg/hour leads to instability of the process, since the excess volume of the charge extinguishes the plasma arc.

Feeding the charge into the plasma granulation zone from a height of 20-60 mm ensures high productivity of the plasma granulation process with a stable process and a high percentage of charge entering the granulation zone.

When the charge is supplied from a height of less than 20 mm, the charge supply nozzle is clogged due to the fact that the charge is melted directly at the nozzle exit.

Feeding the charge from a height of more than 60 mm is impractical, due to the fact that the charge scatters and a low percentage enters the granulation zone, which does not provide the required performance.

The use of a plasma arc leads to an increased concentration of the heat source and an increased specific power of the plasma arc, which leads to greater productivity, since the plasma arc is directed directly into the granulation zone, and to a lower power consumption per product volume.

The plasma arc current during granulation is 50-200 A. At low currents up to 50 A, the thermal power of the plasma arc is not enough to melt the charge into granules, which ensures productivity at the level of analogues. At currents of more than 200 A, due to a violation of the stability of the process, significant evaporation of the charge and rapid burnout of the electrodes, the duration of the granulation process cannot be ensured.

During the experiments, non-consumable electrodes with a diameter of 3 to 22 mm and a direct-acting plasma torch were used. The power source of the plasma arc used in the development of the granulation method is a welding inverter that ensures continuous operation of the granulation process at currents up to 200 A.

It has been experimentally established that the maximum fraction of the charge used should not exceed 0.25 mm to ensure a stable process of remelting the charge into welding flux granules under the thermal action of the plasma arc, and to ensure that the plasma arc power is sufficient to convert the required volume of the supplied charge into granules. .

For granulation, petrurgical raw materials of the gabbroid group of the Ural region were used, the slag base of these rocks contains all the necessary elements for welding fused fluxes. At the same time, the chemical composition does not change significantly during granulation (table).

According to the results of the morphological analysis of the prepared mixture for granulation, it was found that the fractional composition of the main mass is composed of particles of a splintered (angular) shape within 5–250 μm (Fig.2-3). This form of particles is due to crushing in cam and ball mills of rock to the desired fraction.

The share of the required fractional composition of the welding flux from the total mass of the charge that has passed the granulation process is provided at least 30%.

The morphology of the particles after granulation and screening is shown in Fig.4-5. The granules have a spherical shape of particles ranging in size from 0.5 to 2.8 mm. The surface of the granules is different variations: 1) smooth without relief; 2) with particles of a finely dispersed charge, which melted and roughened the surface; 3) granules fused with particles of a smaller size, forming agglomerates of a complex spherical shape; 4) granules, on the surface of which micropores may be present.

According to the results of elemental chemical analysis before and after granulation of the charge of rocks using a plasma arc, the changes are not significant (table).

Based on the results of strength tests obtained using the proposed method, the granules revealed that they have a strength that, according to the requirements of GOST 21560.2-82, corresponds to the strength of fused flux granules, and is 18-19 N/mm ² .

When testing for welding and technological properties of granular welding flux obtained using the proposed method, it was found that the resulting welding flux has satisfactory properties of seam formation, separability of the slag crust after welding, and arc stability.

The advantages of the claimed method in comparison with the prototype:

- charge in the form of powder, used in the claimed volume, provides greater productivity, no need for initial preparation of raw materials in mixing with binder components;

- cooling in air provides better manufacturability compared to cooling the granules in water, due to the absence of drying operations for the resulting granules.

Claims (1)

A method for granulating a welding flux, which includes supplying a flux charge containing oxides to the granulation zone, melting the charge and forming melt drops under the influence of a plasma arc formed when a current of 50-200A flows between the plasma torch and a conductive non-consumable electrode, cooling the formed drops with the formation of granules, which differs by feeding the charge into the granulation zone in the form of a powder with a fraction size of up to 0.25 mm in a volume of 12-24 kg/h from a height of 20-60 mm, the formed droplets are cooled in air, followed by sifting the resulting granules.

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