RU95665U1 - DEVICE FOR PLASMA HARDENING OF PRODUCTS FROM STEEL AND CAST IRON IN AUTOMATIC AND MANUAL MODES BY TWO-ARROW PLASMOTRON - Google Patents

Abstract

 A plasma hardening device containing a working gas supply system, an insulator, a cathode assembly, a nozzle with ferromagnetic jaws of a scanning device, structurally integrated into a small plasmatron, devices for fastening, turning and adjusting the plasma torch during operation, a cooling system for the nozzle and ferromagnetic jaws, a scanning device arcs, including a generator, an electromagnetic coil and ferromagnetic jaws, a control panel with a built-in oscillator and measuring instruments, a position indicator AC voltage on the coil, the regulator DC voltage on the coil, characterized in that the quenching is carried out by moving over the surface of articles with a small-sized twin-arc plasma torch simultaneously burning arcs of direct and indirect action, the electric power is controlled independently of each arc due to supply from a separate rectifier.

Description

The utility model relates to the field of metal and heat treatment, specifically, to plasma hardening of surfaces of steel and cast iron in automatic and manual mode.

A technical solution is known (RF Patent for the invention No. 2069131, publ. 11/20/1996), the essence of which is that the device for plasma processing of metals, contains a working gas supply system, an insulator and electrodes, one of which is an outlet and has an internal channel equipped with a working gas flow transducer connected to the output electrode and forming with it a common internal channel of variable cross section, the end surface of the working gas flow transducer being made conjugated to the processed surface awn products. The internal channel of this device ends with a slot. The device operates as follows: by known methods, an electric arc is excited between the electrodes. The working gas sequentially passes through the discharge gap, the output electrode and the flow transducer and produces heating of the surface of the product. Due to the relative movement of the plasma torch and the product, the surface of the latter is heated.

The disadvantages of the considered technical solutions include the low efficiency of heating the surface of the product. In plasmatrons generating an indirect arc burning between the electrodes (electrode and nozzle) of the plasma torch, heat transfer to the part is carried out by a gas-dynamic flow jet (plasma jet) through heat conduction, convection and radiation, therefore, the heating efficiency is lower than that of a direct-acting arc burning between the electrode and the surface of the workpiece. Thus, the effective efficiency of heating a surface with an argon-arc torch is 0.65 ... 0.75, a plasma arc is 0.60 ... 0.75, and a plasma jet is only 0.10 ... 0.50 (Korolev N.V. Calculations of thermal processes in welding , surfacing and thermal cutting: Textbook. - Yekaterinburg: USTU, 1996), which is associated with large losses of power in the plasma torch walls and the environment. For reliable operation of such plasmatrons, the use of water-cooled interelectrode inserts (insulators) with internal fins, which increase the size and weight, is required. In addition, the working distance between the plasma torch nozzle and the treated surface does not exceed a few millimeters, which complicates the monitoring of the process and does not allow to strengthen parts with a profiled working part. Power supply of plasmatrons with an indirect arc is carried out from specialized rectifiers with an open circuit voltage of at least 200 V. The device does not have technological universality, since the profile and dimensions of the treated surface are rigidly determined by the surface of the output electrode mated to it.

A technical solution is known (Utility Model Certificate of the Russian Federation No. 74922, published July 20, 2008) according to which a device for electric arc hardening of products containing a gas-electric torch, a refractory electrode, an arc power source, a brush device and a cooled torch is proposed, characterized in that the device further comprises an electromagnetic arc control in the form of a scanning device, and inert gas is supplied to the arc gap to protect the electrode and heated metal from oxidation. The water-cooled gas-electric burner of the device is designed to maintain an electric arc discharge between the surface of the part serving as the anode and the non-consumable tungsten electrode (cathode).

Thus, the gas-electric burner of the device generates a direct-acting electric arc burning between the electrode and the surface of the part, the heat transfer to the part is due to the heat conductivity, convection, radiation and kinetic energy of the charged particles stored in the electric field. The effective efficiency of a direct-acting arc is 10 ... 30% higher, respectively, higher electric and thermal power supplied to the surface of the product, all other things being equal.

The disadvantages of the considered technical solution include the relatively low temperature of the column of a freely burning electric arc, the low concentration of the heat flux on the workpiece surface, the possibility of uncontrolled movement of the anode spot of the arc on the surface of the product due to insufficient stabilization of its column by the gas-dynamic flow flowing from a large diameter nozzle.

A technical solution is known (RF Patent for Utility Model No. 78193, published on November 20, 2008), which is the closest in terms of essential features to the claimed one and adopted as a prototype, in accordance with which a device for surface hardening of products by moving a direct plasma arc over the surface of the product action, excited between the electrode and the product, containing a working gas supply system, an insulator, a cathode assembly, a nozzle, characterized in that the device includes one or two small plasma torches with direct action devices, for mounting, turning and adjusting the plasma torch during operation, a cooling system for the nozzle and ferromagnetic jaws of the plasma torch, an arc scanning device including a generator, an electromagnetic coil and ferromagnetic jaws, a rectifier with a falling external characteristic and an open-circuit voltage of 80-90 V, one or two control panels with a built-in oscillator and measuring instruments, an indicator of the position of the alternating voltage on the coil, a constant voltage regulator on the coil.

Compared to a conventional freely burning arc generated by a torch with a non-consumable electrode in an argon protective atmosphere, the temperature of which reaches 5000 ... 6000 K, a plasma arc with a comparable electric power has an increased (15000 ... 20,000 K) temperature and a more concentrated heat flux. This is achieved by reducing the conductive cross section of the arc, compressed in the nozzle channel by a plasma-forming gas stream, whose molecules, in turn, are ionized in the column of the arc discharge, thereby increasing the fraction of the ion current. In addition, the compression of the cross section of the arc also allows you to stabilize the position of the anode spot on the part, increase the density of the heat flux and the heating rate of the surface. The plasma-forming gas supplied to the nozzle channel provides thermal and electrical isolation of the arc column from the nozzle walls, providing its thermal and erosion resistance.

The disadvantages of the considered technical solution include the limited (0.8 ... 1.2 mm) depth of the hardened layer during processing without melting the surface. Quenching from the liquid phase (with melting the surface of the workpiece) allows you to increase the depth of the hardened layer, but, as a rule, requires subsequent mechanical surface treatment, which complicates the hardening process and reduces its technical and economic indicators.

Unlike the prototype, the claimed technical solution with the aim of increasing the depth of the hardened layer during processing without melting the surface of the product, expanding technological capabilities and improving the technical and economic indicators of the plasma hardening process provides for its implementation by a two-arc plasmatron with simultaneously burning arcs of direct and indirect action, moreover, electric ( and thermal) power of each arc is independently regulated. The block diagram of the device is presented in the figure, where:

1 - an arc of indirect action; 2 - arc of direct action; Ar is a plasma forming working gas (argon); And - the processed product; IP1 - indirect arc power source; IP2 - direct-acting arc power source; OSTs - pulse arc pathogen; P - double-arc plasmatron.

The device operates as follows: a high-voltage high-frequency discharge of a pulsed arc exciter pierces the gap between the tungsten electrode and the copper nozzle of the plasma torch P, which are under the voltage of the current source IP1. In the presence of a plasma-forming working gas Ar in the gap between the electrode and the nozzle, an indirect arc 1 is excited. Due to ionization in the burning arc of the atoms of the plasma-forming gas supplied to the plasma torch under pressure, a plasma jet is formed, which is blown out of the nozzle by a gas stream and, in the presence of a voltage of the current source IP2, applied to the electrode and the workpiece And, between them there is a direct-acting arc 2. The plasma torch nozzle is designed to compress and stabilize the column of the direct-acting arc, forming a plate mennoy jet arc indirect action, together forming a single gas-dynamic plasma flow. At the end of the nozzle of the plasma torch there are ferromagnetic jaws of the scanning device, which, when an electromagnetic flux is generated between them, which is formed by the inductance coil of the scanning device located in the tail of the plasma torch, deflects the plasma flow alternately left and right, acting on its own electromagnetic field. Due to the alternate deviation of the plasma flow (and the associated heating spot on the surface of the product) perpendicular to the translational displacement vector of the plasma torch, the width of the hardened zone on the surface of the workpiece significantly increases (from 5 ... 6 mm to 10 ... 20 mm), which increases the productivity of the surface hardening in the range of high currents.

For ease of setup, access to the hardened surface of complex configuration, the plasma torch is made in a compact design, which allows it to be used for hardening in manual operation.

The plasma hardening process is carried out by a plasma torch with two simultaneously independently controlled and independently controlled arcs of direct and indirect action (a plasma arc of direct polarity burning between the plasma torch electrode (cathode) and the surface of the workpiece (anode), as well as an arc burning between the cathode and nozzle (anode) of the plasma torch accordingly) allows:

1. Significantly expand the limits of regulation of heat input into the treated surface. The minimum heat input is ensured at the minimum currents of stable combustion of both arcs, and it is less than when using each arc separately, since when working together it is possible to provide lower minimum currents of stable combustion of each of the arcs due to thermal ionization of the arc gap by the action of the other arc. The maximum heat input is achieved at the maximum currents of each of the arcs, and it is naturally greater than with separate burning of the arcs, ceteris paribus. Within the range, the heat input is smoothly controlled by varying the power of each arc individually or both together, and, depending on the technological tasks of processing, the law of change in heat input can be different, since the thermal efficiency when heated by an arc of direct action and indirect action (by a plasma jet), as noted above vary significantly. The technical effect consists in expanding the technological capabilities of the process and improving its technical and economic indicators by increasing the thickness range of the workpieces - the minimum thickness (wall thickness) of the parts hardened without additional forced cooling is reduced. When processing massive parts in the range of maximum currents, it is possible to increase the productivity of the process by increasing the processing speed while maintaining the specific heat input per unit area.

2. To increase the depth of the hardening zone without melting the surface of the workpiece (up to 2 ... 2.5 mm in the implemented range of modes) at the maximum arc current of indirect action. The depth of the hardened zone increases due to a decrease in the average heating rate to pre-quenching temperature due to lower heating efficiency and the heat flux density of the indirect arc. When its contribution to the total heat flux introduced into the product increases, it is possible to reduce the speed of the main translational movement of the heating spot, at which surface melting begins. The combination of these factors extends the range of heat treatment modes, providing a change in the structure and properties in the heat-affected zone, due to more complete homogenization of austenite with an extended heating time. The use of one indirect arc to achieve a similar depth of the hardening zone, ceteris paribus, requires a significant increase in its current, which is accompanied by overheating and destruction of the plasma torch of comparable dimensions and mass, since more than 50% of the thermal power of such an arc is spent on heating the plasma torch, and therefore worsen technical and economic indicators of the process.

Given the above, the use of a plasma torch for plasma hardening with two simultaneously burning independently adjustable arcs of direct and indirect action provides a synergistic effect of increasing the depth of the hardened layer during processing without melting the surface of the product, expanding technological capabilities and improving technical and economic parameters of the process.

Thus, a technical solution is proposed for surface hardening of products by moving a plasma torch above the product surface with two independently controlled arcs of direct and indirect action simultaneously burning. At the same time, the nozzle of the plasma torch and the ferromagnetic jaws of the scanning device are forcedly cooled with water, using the scanning device they control the shape of the plasma flow, providing a targeted deflection of the heating spot for processing hard-to-reach surface areas of hardened products of complex configuration, with relative movement of the plasma torch and the product, a hardened zone is obtained on its surface, whose width is regulated. It is possible to control the width of the zone by changing the distance from the end of the plasma torch to the product and / or the voltage on the electromagnetic coil of the scanning device, as well as changing the flow rate of the plasma-forming gas. The mode of deviation of the plasma flow from the axis of the plasma torch is provided, which allows for the regulation of the width and angle of deviation of the plasma flow from the center of the nozzle with the plasma axis unchanged.

An example implementation of the proposed technical solution.

The device comprises a working gas supply system, an insulator, a cathode assembly, a nozzle with ferromagnetic jaws of a scanning device structurally integrated into a small twin-arc plasmatron; devices for mounting, turning and adjusting the plasma torch during operation; plasmatron nozzle cooling system; a scanning device including a generator, an electromagnetic coil and ferromagnetic jaws; two rectifiers with a falling external characteristic and an open circuit voltage of 80 ... 90 V; control panel with a built-in pulse exciter of the arc, an indicator of the position of the alternating voltage on the coil, a constant voltage regulator on the coil and measuring instruments - ammeters and voltmeters.

The table shows the parameters of the regime and the results of plasma hardening of the surface of the rolling roll of steel type 60XH produced using the inventive device. The processing process provides for obtaining a surface hardened from a solid state (without fusion) with a fine-grained martensitic-austenitic structure, high microhardness (8000 ... 10000 MPa), wear and crack resistance. By increasing the depth of the hardened layer, the wear resistance of the working surface and the service life of the rolls increase, and the cost of their acquisition is reduced.

Table Indicator Single arc plasmatron with direct arc Single arc plasmatron with indirect arc The inventive device is a plasma torch in dual-arc mode, including Direct arc Indirect Arc The minimum current of steady burning of an arch, And 100 ... 120 110 ... 120 5 ... 10 fifty Maximum arc current, A 350 250 150 200 The average value of the arc current, A 170 150 70 150 The speed of the plasma torch, cm / s 3 ... 4 0.3 ... 0.5 1 ... 3 Depth of hardened layer, mm 0.8 ... 1.2 1.5 ... 1.8 1.6 ... 2.5 Hardness of the surface of the hardened layer, HRC 55 ... 60 45 ... 50 50 ... 55

Claims (1)

A plasma hardening device containing a working gas supply system, an insulator, a cathode assembly, a nozzle with ferromagnetic jaws of a scanning device, structurally integrated into a small plasmatron, devices for fastening, turning and adjusting the plasma torch during operation, a cooling system for the nozzle and ferromagnetic jaws, a scanning device arcs, including a generator, an electromagnetic coil and ferromagnetic jaws, a control panel with a built-in oscillator and measuring instruments, a position indicator AC voltage on the coil, the regulator DC voltage on the coil, characterized in that the quenching is carried out by moving over the surface of articles with a small-sized twin-arc plasma torch simultaneously burning arcs of direct and indirect action, the electric power is controlled independently of each arc due to supply from a separate rectifier.