RU2557041C1 - Method of fusion welding of steel structures and device for its implementation - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to the machine building, and can be used during the fusion welding of the complex steel structures. Under the suggested method the welding is combined with heat treatment with use for this of the heating element in form of the ceramic pad-heated connected via the current switch to the welding power source. Besides, the device contains the electronic and bypass switches, programmable regulator, and thermoelectric converter located on the welded structures.

EFFECT: invention reduces power consumption during post-welding heat treatment, increases strength and reliability of the critical welded structures.

3 cl, 3 dwg

Description

The invention relates to mechanical engineering, mainly to fusion welding of steels and alloys, and can be used in the manufacture of complex structures.

At the moment, almost all technological processes for creating welded products share the operation of welding and heat treatment, the only exception is preheating, which is usually carried out by gas-oxygen burners with subjective control and maintaining the set temperature. This negatively affects the quality of the welded joints obtained (Heat treatment in mechanical engineering: a reference book / Edited by Yu.M. Lakhtin, A. G. Rakhstadt - M., "Mechanical Engineering", 1980, 422-423). In addition, welding often takes place in a canopy, without using a forming device, with poor formation of the root of the seam.

The known technology of heat treatment of welds, including welding, cooling the seam in air to ambient temperature, subsequent heating to Ac ₃ , holding, cooling at a controlled speed (RD 153-34.1-003-01. Welding, heat treatment and control of pipe systems of boilers and pipelines during installation and repair of power equipment, p. 17. Heat treatment of welded pipe joints.). But in this method, quick cooling occurs after welding, which leads to the appearance of a large temperature gradient over the section of the part, the appearance of thermal stresses of the first kind, to a decrease in mechanical properties (strength and ductility), and subsequent heat treatment does not guarantee the correction of surface micro- and submicrodefects. In addition, this technology is energy consuming and requires additional equipment.

It is known that holding the alloy at austenitizing temperature allows you to control the properties of the metal, including improving both the strength and ductility characteristics (Frolov A.V. Influence of phase transformations on the substructure and properties of medium alloyed steels. / Frolov A.V., Muraviev V.I. , Martynyuk AM, Kirikov A.V., Zhao Litao // Metallurgy of mechanical engineering No. 2. - 2012. - S. 6-10). But this technology involves cooling with reheating, which also has the disadvantages of the above method.

A method of preheating and subsequent heat treatment using flexible ceramic heating mats, in which temperature registration and regulation is carried out by placing a thermocouple on the surface of the connected part with connection to temperature recorders according to the feedback principle (RD 153-34.1-003-01. Welding, heat treatment and control of pipe systems of boilers and pipelines during installation and repair of power equipment, paragraph 17. Heat treatment of welded pipe joints.), has the following disadvantages:

1. Does not allow the formation of the root of the seam.

2. High economic costs during heat treatment, since a separate power source is used for heating.

The same disadvantages are the method of induction heating, in which the inductor is located on the surface of the connected products.

The use of forming devices (copper linings, copper-flux pillows, ceramic linings) allows you to form a return roll of a single-pass one-sided weld, but implies additional equipment for operations of preliminary, concurrent heating and subsequent heat treatment.

To eliminate the disadvantages, a welding method is proposed, combined with heat treatment, including welding, cooling the metal to an austenization temperature, holding it at this temperature until the polymorphic transformation begins, and subsequent cooling.

In the proposed method, the operations of welding, preheating and immediate cooling and the process of forming the root of the welded joint are combined. For this purpose, a power source for welding is used, in the circuit of which a proportional-integral-differentiated (PID) controller is integrated and a circuit that allows preheating and maintaining the set temperature during periods of inactivity of the welding arc (changing the coated electrode, scraping from slag, etc. .). This will increase the mobility of equipment, the efficiency and economic efficiency of heat treatment operations, as well as the quality of welded joints by forming them on a ceramic heater lining, which is located on the back of the seam.

A device for preliminary heat treatment of workpieces and final heat treatment of a weld (Fig. 1) contains: welding transformer (Tr), electronic switch (EC), bypass switch (BC), ceramic heater current switch (K), program controller (P) , control panel (PU), ceramic heater (KN), thermoelectric converter (TP). Structurally, BC and EC are located in the immediate vicinity of the welding transformer. Ceramic heater is placed directly on the welding workpieces. The thermoelectric converter is fixed on the welding workpieces in the immediate vicinity of the weld. The control panel, switch K and controller P are located in a separate housing near the welding station.

The welding process is as follows. After turning on the equipment, the control units of the control unit are transferred to the “TO” position (heat treatment). The control unit disconnects the bypass switch BC and connects the ceramic heaters KN through switch K. Controller P controls the operation of the EC switch according to the PID control algorithm, ensuring the workpieces are heated to the required temperature according to the required algorithm. Information about the temperature of the workpieces comes to the controller from the thermoelectric converter TP. After heating the workpieces to the required temperature, the program of the controller P stops, the control elements of the control unit are switched to mode “C” (welding). PU disconnects switch K and turns on the bypass switch BC. In this mode, welding is performed. At the end of welding, the control elements of the PU are transferred to the “TO” mode, and the regulator P is transferred to work according to program 2 — heat treatment of the weld. After that, the BC switch is turned off, and the switch K is turned on. The controller P controls the heating of the ceramic heater through the EC controller and controls the temperature of the metal using a thermoelectric converter.

A circuit diagram of the installation is shown in FIG. 2. The electronic switch is made according to the scheme of a triac power regulator on the elements R1-R3, C1-C2, VS1-VS2, Pr1-Pr2. Variable resistor R1 controls the maximum heating power. The filter chain R3-C2 prevents the breakdown of the triac VS2 from surges of the mains voltage. The thermal fuse Pr located on the heatsink of the VS2 simistor protects the triac from overheating.

The contactor K1 is used as a bypass switch.

The PID controller Aries TPM251 was used as a program controller.

The control panel is made on the contactor K2 and buttons Kn1-Kn2 according to the scheme with self-retention. Indicator lights HL1-HL2 indicate the operating mode of the device.

When implementing the device, the following elements were used in the circuit:

- capacitors: C1 = MBM-0.1 μF - 150 V; C2 = MBM-0.1 μF - 500 V;

- fuse Pr1 = PR2-60;

- thermal fuse Pr2 = TZD-084;

- resistors: R1 = СП3-4вМ - 0.5-220 кОм; R2 = MLT - 0.125-6.8 kOhm; R3 = MLT - 1-68 Ohms;

- dinistor VS1 = DB3;

- triac VS2 = BTA40-600;

- transformer Tr;

- contactors: K1; K2;

- buttons Kn1, Kn2;

- indicator lamps HL1, HL2;

- ceramic heater KN;

- program controller: P = ARIES TPM251.

Welding on a ceramic lining - heater is carried out as follows: on the reverse side of the root of the seam with a minimum gap there is a ceramic lining heater, consisting of flat ceramic elements in series connected to each other via nichrome wire with through holes (Fig. 3). In the central part of the rug thus assembled, there are ceramic elements with a groove, the dimensions of which are determined by the necessary geometric parameters of the root of the weld joint and installed directly below it in the joint line with the aim of shaping the back side of the weld. At a distance of 20-25 mm from one of the welded edges, a thermocouple is installed between the ceramic mat and the part to control the temperature. The surface of the front side and the root of the seam is insulated with thermal insulation material. By electrical contact heating of a nichrome thread located inside ceramic elements, the metal of the parts to be joined is heated to the required temperature. When the desired value is reached, welding is performed. During the period of inactivity of the welding arc, the heating temperature control device analyzes the correspondence of the set temperature to the real value and, if necessary, the abutting edges are heated. Having finished the welding process, the welder immediately puts the heating device into heat treatment mode and, if necessary, provides additional thermal insulation.

When welding extended butt joints of sheet structures, it is necessary to use several power sources equipped with a temperature control device. In this case, the joints are divided into several sections, the number of which depends on the length of the joint and welding is carried out simultaneously by several welders according to the scheme of the inverse-step method. The beginning and end of the preheating, welding and heat treatment process should be carried out synchronously.

During the heat treatment, the temperature control device (URT) controls and stabilizes the speed of heating and cooling of the welded joint, as well as the temperature and holding time. After the operation is completed, the URT is switched off automatically. A weld can be transferred for quality control.

The proposed method was tested when welding samples from 30KhGSA alloy. The mechanical properties of welded joints are presented in the Table.

The method can be carried out both in workshop conditions and at assembly sites, both during welding of steels and alloys, as well as non-ferrous metals, both butt joints of sheet structures and pipe blanks, both straight and curved structures. It can be used both in auto, ship, aircraft, rocket engineering, in the production of oil refining complex facilities, in construction, and in railway transport, both in the aggregate of technological operations, and for exclusively heating and heat treatment.

Claims (3)

1. The method of fusion welding of steel structures, including preparing the edges for welding, heating the welded edges, fusion welding with the formation of the root of the seam and heat treatment of the weld, while the above-mentioned heating and heat treatment is carried out using ceramic heating elements that are installed on the welded structures, characterized in that as ceramic heating elements use ceramic lining-heaters made with the possibility of speed control heating using at least one welding power source in the absence of welding arc and are arranged at the back side of the weld root. 2. The method according to p. 1, characterized in that, depending on the length of the butt joints of the structures, the butt joints are divided into sections, the welding of which is carried out simultaneously according to the inverse method using welding power sources equipped with a temperature control device, the beginning and end of welding processes and heat treatment of each site for a given mode is carried out synchronously. 3. A device for fusion welding of steel structures, comprising at least one welding power source with a welding transformer, electronic and bypass switches, ceramic heating elements, a current switch of said elements, a program controller and a thermoelectric converter configured to be placed on the structures to be welded, characterized the fact that ceramic heating elements are made in the form of ceramic lining-heaters with the possibility of regulation soon their heating by means of a welding power source during the absence of a welding arc and installation on welding structures from the back side of the weld root, and the program controller is made in the form of a proportional-integral-differential controller.

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