RU2707054C1 - Method for multiple drawing of articles with electric contact heating and article made by such method - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to metal forming and heat treatment, particularly, to production of articles from hard-to-strain, high-strength metals and alloys, including titanium and its alloys, nitinol. In method of multiple drawing of item with electric contact heating, which involves drawing of workpiece through serially arranged deforming devices with simultaneous passing through billet of electric current of specified parameters, deforming devices are rollers, which are electrically insulated from each other, supply of electric current to the workpiece is carried out through a current-feeding device located before the first in the direction of drawing roller cage, and through the last along the drawing process roller cage, note here that resistive shunts and / or additional current sources are connected between roller cages in parallel billet.

EFFECT: higher quality of articles due to reduced surface defects.

6 cl, 1 dwg, 4 ex

Description

The invention relates to the field of metal forming and heat treatment, in particular to the production of wire, rods, pipes from hardly deformable, high-strength metals and alloys, including titanium and its alloys, nitinol, for additive technology and other industrial objects.

 The prior art method for the manufacture of a continuously moving wire with heating in a flame stream while combining the processes of hot drawing and annealing (RU 2197543, IPC C21D 9/56, published on January 27, 2003). To heat the wire using a device containing a tubular muffle with a longitudinal groove and a torch.

 The disadvantages of this method are: low useful heat extraction for heating the material relative to the total heat release and the inability to quickly dispense the heating intensity due to difficulties in controlling the combustion process and the thermal inertia of the heater. In addition, heating of the material occurs from the surface, and it takes time to warm up the central part of the section, which limits the drawing performance. The disadvantage is the inability to concentrate the heat in the area adjacent to the drawing tool, due to its overheating and the additional cost of cooling it. As a result, when approaching the deformation zone, the material manages to cool, which does not allow the optimal drawing mode to be realized, especially on small workpiece sizes.

 A known method of manufacturing a wire from (α + β) -titanium alloy with induction heating before drawing or rolling (RU 2655482, IPC C22F 1/18, publ. 05.28.2018). The method includes heating and repeated deformation of the workpiece at a given heating temperature of the die or rollers. The declared values of the rated power and frequency of induction heating, as well as the strain rate of the workpiece, are selected depending on its diameter.

 Induction heating is used in most cases for large workpieces, which makes it impossible to place the inductor in the area of the inter-stand space for heating the material due to the dimensions of the inductor and heating of the drawing tool induced by induction, leading to overheating and additional costs for its cooling. With insufficient cooling of the drawing tool, the strength of the pulling portion of the processed material decreases, which leads to breaks. To install the inductor in the interstand space, an increase in the distance between the stands in the cassette is required, which leads to a loss of torsional rigidity of the material and rotation of the profile (twist), which ultimately makes it impossible to use this heating method for roller drawing. The disadvantages of the method should also include the presence of electromagnetic radiation.

 A known method of manufacturing a thin nickel-titanium wire with heating by a stream of infrared radiation before drawing (RU 2502823, IPC C22F 1/18, publ. 27.12.2013). Dosed heating is carried out by a set of semiconductor emitting diodes located around the die of the die.

 Infrared radiation is used in most cases for heating workpieces of small diameter with thin drawing of material due to the limited power of infrared emitters. In addition, there is the problem of placing them in the interstand space of the cartridge. The material is heated from the surface, and it takes time to heat the central part of the cross section, which limits the drawing performance.

 Closest to the claimed technical solution is a method of multiple wire drawing with electric contact heating, which includes sequential drawing of the workpiece through the dies with the simultaneous supply of electric current to the dies from a single source, in which the drawing is carried out with parallel connection of the dies to the current source. (SU 1731327, B21C 1/00, publ. 07.05.1992). As a result, there is an automatic distribution of current in the sections of the workpiece in all dies depending on the diameter, thereby achieving the same current density in these sections, which, in turn, ensures the preservation of the conditions of the electroplastic effect in all these sections.

The disadvantage of the closest technical solution is the relatively low efficiency, because drawing through dies does not allow to achieve high values of single deformation. In the case of using roller stands as deforming devices instead of dies, with a similar parallel connection to a current source, there is no significant effect on the parameters of electric heating, and, therefore, on ensuring the electroplastic effect in all zones of deformation. This is due to the small contact surface of the roller stand with the workpiece. The regulation of the current parameters between the deforming devices in the known specified solution is not provided.

The disadvantage of this method is the risk of scoring and other surface defects associated with drawing through the dies.

The objective of the invention is to provide high performance drawing process to obtain high quality products.

The technical result is to achieve higher one-time deformations in the process of drawing with the provision of an electroplastic effect in all zones of deformation throughout the cross section of the workpiece. Improving the quality of manufactured products is achieved by reducing surface defects due to the elimination of the risk of scoring and other surface defects during drawing through roller stands.

The technical result is achieved by the fact that in the method of multiple drawing of the product with electric contact heating, which includes pulling the workpiece through successive deformation devices while simultaneously passing the specified parameters through the workpiece, roller stands made of electrically insulated from each other are used as deformation devices, supplying current to the workpiece is carried out through a current-supplying device located in front of the first roller the cage, and through the last along the drawing roller cage, while the roller cages are electrically connected to the workpiece, and between them parallel resistive shunts and / or additional current sources are connected

In contrast to the closest technical solution, the claimed method uses roller stands as deforming devices. Drawing on roller stands allows one-time deformation to be increased by replacing sliding friction with rolling friction.

Roller stands are made insulated from each other to ensure the flow of current through the workpiece. If you do not use the electrical insulation of the roller stands, then the current will flow not only through the workpiece, but also through the roller stands. This will not allow you to control the temperature on the workpiece between the roller stands during drawing.

The supply of electric current to the workpiece through the current-supplying device located in front of the first along the drawing roller cage, and through the last along the drawing roller cage, allows current to pass through the workpiece, and, therefore, the possibility of heating the workpiece and creating an electroplastic effect in all areas of its deformation .

The electrical connection of the roller stands and the workpiece, the connection between the roller stands parallel to the workpiece of resistive shunts and / or additional current sources makes it possible to maintain the specified parameters of the current passing through the workpiece both between the roller stands and in all deformation zones. Thus, in all zones of deformation, controlled heating of the workpiece and an electroplastic effect are ensured, which, in turn, allows controlling the mechanical properties of the material during drawing, significantly reducing the drawing force, and also increasing one-time deformations.

Thus, due to the drawing in the roller stands, ensuring the specified heating of the workpiece and the electroplastic effect in all zones of deformation, an increase in one-time deformation and, consequently, total deformation is achieved, which can significantly increase the productivity of the process. The productivity of the process also increases due to the reduction of cases of breakage of the workpiece due to the replacement of sliding friction by rolling friction during drawing on roller stands.

In the particular case of the method, the current-carrying device and roller stands are cooled.

Repeated drawing can be carried out in a protective atmosphere.

In the case of difficult to deform metals and alloys after repeated drawing, annealing can be carried out.

Optimally, in the case of difficult to deform metals and alloys, multiple drawing should be carried out in several stages with intermediate annealing.

The invention also relates to an article obtained by the claimed method.

The essence of the claimed method is illustrated by a schematic illustration of a device for its implementation, in which three roller stands are used for drawing.

The blank 1 (see Fig.) Is pulled through a current-supplying device 2, located in front of the first along the drawing stand at a distance necessary for pre-strain heating, and roller stands 3, 4, 5, assembled in a cassette and electrically insulated from each other by means of insulators 6. A current I _{5 of} predetermined parameters is supplied to the workpiece 1 from the main AC source 7 through a current-feeding device 2 and through the last roller stand 5. The AC parameters I _{5 are} set based on the conditions for the required heating of the workpiece for the first deformation zone (in the first along the rolling stand 3) and providing the electroplastic effect when drawing in this zone, taking into account the material, the geometrical parameters of the workpiece and the deformation parameters of the process according to well-known methods (For example, pp. 1711-1712 source: Troitsky O .A., Stashenko V.I. Technology of electroplastic rolling of titanium alloys and stainless steels.// Vestnik TSU, vol. 18, issue 4, 2013, pp. 1711-1712.). The workpiece 1 is deformed, sequentially passing through stands 3, 4, 5. In each zone of deformation, electrical contact occurs between the workpiece 1 and the rolls of the stand.

The current parameters in the workpiece 1 in the sections between the roller stands 3 and 4, 4 and 5 are regulated by resistive shunts 8 connected in parallel with the resistance values R ₁ and R ₂ (as shown in Fig. The currents I ₃ , I respectively flow through the workpiece between these stands _1. ) And / or additional current sources. At the same time, the values of the current strength between the roller stands are also set based on the conditions of the required heating of the workpiece in each deformation zone and ensuring the electroplastic effect in this zone, taking into account the material, geometric parameters of the workpiece and deformation parameters of the process according to the known methods specified for I ₅ .

Connection in the claimed manner of resistive shunts 8 (Fig.) With resistance R ₁ and R ₂ (Fig.) Is used to eliminate overheating of the workpiece, which can occur due to a decrease in its cross section during drawing and, as a result, an increase in current density. Overheating of the workpiece, in turn, can lead to its breakage.

In this case, the current balance looks like this:

I ₅ = I ₁ + I ₂ = I ₃ + I ₄ , (1)

where I ₅ is the current supplied to the workpiece from the current source;

I ₁ is the strength of the current passing through the workpiece between stand 4 and stand 5;

I ₂ is the strength of the current passing through the shunt resistive resistance R ₁ ;

I ₃ - current strength passing through the workpiece between stand 3 and stand 4;

I ₄ - the strength of the current passing through the shunt resistive resistance R ₂ .

From the formula (1) it follows:

I ₁ = I ₅ -I ₂ (2)

I ₃ = I ₅ –I ₄ (3)

Thus, according to formulas (2) and (3), the established values of I ₁ and I _{3 are} achieved by changing the values of I ₂ and I _4, respectively, which, in turn, are determined and regulated by the value of the resistances R ₁ and R _{2 of the} resistive shunts 8.

Connection parallel to the workpiece in the areas between the roller stands of additional current sources is used if the value of the current strength from the main source is not enough to warm the workpiece to the required temperature. In this case, the established values of the current strength between the stands are achieved by changing the values of the current strength of additional sources.

Connecting parallel to the workpiece in the sections between the roller stands and resistive shunts, and additional current sources are used when additional heating of the workpiece is necessary under non-stationary modes, for example, when starting drawing and entering stationary mode.

To illustrate the regulation of the current between the stands for this case, when dragging, for example, through three roller stands, you can use the example of the simultaneous use of an additional current source connected parallel to the workpiece in the area between the first and second roller stands, and resistive shunts connected in parallel to the workpiece in the areas between the first-second and second-third roller stands. Moreover, the ratio is true:

I ₅ = I ₁ + I ₂ (4)

where I ₅ is the current supplied to the workpiece from the main current source;

I ₁ - current strength passing through the workpiece between the second and third along the drawing stand;

I ₂ is the strength of the current passing through a resistive shunt between the second and third stands with resistance R ₁ .

From the formula (4) it follows:

I ₁ = I ₅ -I ₂ (5)

The following relation is also valid:

I ₃ = I ₅ -I ₄ + I _add. (6)

where I _add - current strength of an additional current source,

Thus, according to formula (5), the set current value I_onebetween the second and third along the drawing stand reach by changing the current I₂passing through a resistive shunt between the second and third stand, which, in turn, is determined by the resistance value of the specified resistive shunt. Set current value I₃ between the first and second along the drawing stand according to the formula (6) reach: firstly, by changing the current I₄passing through a resistive shunt between the first and second stand by adjusting the value of its resistance R₂; secondly, by the addition of current I_additional necessary value.

Similarly, parallel connection of additional current sources and resistive shunts in other combinations is used. The required values of the current strength between the stands are also regulated by the known dependencies, by analogy with the above.

The number of roller stands in the cartridge and the heating temperature of the workpiece inside the cartridge are selected based on the deformation route and the margin of safety and ductility of the material during drawing.

This ensures that the controlled current flows through the workpiece in front of the first deformation zone and between the stands, which makes it possible to heat the workpiece in a controlled manner and provide an electroplastic effect in all the workpiece deformation zones.

Example 1

A wire was drawn from VT6 titanium alloy from a diameter of 7.0 mm to a diameter of 6.0 mm. Drawing was carried out on dies connected to a current source (by the closest method). The drawing speed was 5 m / min. To achieve a total degree of deformation of 26.53%, drawing was carried out in two passes of 7 mm in 6.5 mm and 6.5 mm in 6 mm with intermediate annealing. The productivity of the drawing process was 2.16 m / min.

Example 2

A wire was drawn from VT6 titanium alloy from a diameter of 7.0 mm to a diameter of 6.0 mm. The drawing was carried out on a cassette consisting of two roller stands electrically isolated from each other. A resistive shunt was connected between the roller stands parallel to the workpiece. To heat and obtain an electroplastic effect, an alternating current with a pulse density of 200 A / mm ² and a frequency of 400 Hz was passed through the billet. The current source was connected to a current-supplying device — a tribal apparatus — and a second roller stand. Drawing speed 5m / min. The total degree of deformation was 26.53%. The productivity of the drawing process was 5m / min.

Example 3

Bars were made from titanium alloy VT20 with a diameter of 5.5 mm from a workpiece with a diameter of 7.0 mm. The drawing was carried out using three roller stands, electrically isolated from each other. For additional heating, an additional current source was connected between the first and second along the drawing by roller stands. A resistive shunt was connected between the second and third along the drawing stand with a roller stand parallel to the workpiece. To heat and obtain an electroplastic effect, a pulse current density of 200 A / mm ² and a frequency of 400 Hz was passed through the preform. The roller stands were cooled with water-cooled hold down refrigerators. To eliminate oxidation of the workpiece, the treatment was carried out in a protective atmosphere. The main current source was connected to a current-supplying device — a tribe apparatus — and a third roller stand along the way. Drawing speed - 5 m / min. The total degree of deformation was 38.27%. The productivity of the drawing process is 5.95m / min.

Example 4

The wire was drawn in several stages from a PT-3V titanium alloy from a diameter of 7.0 mm to a diameter of 5.3 mm. The drawing was carried out alternately on two cassettes. Each cassette consisted of two roller stands electrically isolated from each other. Between the electrically insulated roller stands in the cassettes, resistive shunts were connected parallel to the workpiece. To heat and obtain an electroplastic effect, a pulse current density of 200 A / mm ² and a frequency of 400 Hz was passed through the preform. For each cassette, the current source was connected to a current-supplying device — a tribe apparatus — and to the last along the drawing stand of the roller cassette. After drawing on the first cassette, the preform was annealed. Drawing speed - 5 m / min. The degree of total deformation was 42.67%. The productivity of the drawing process was 3.2 m / min.

The above examples do not limit all possible cases of using the method. Similarly, wire and rods can be made from other hardly deformable, high-strength metals and alloys, as well as pipes from these materials.

Claims (6)

1. The method of multiple drawing of the product with electric contact heating, including pulling the workpiece through sequentially located deforming devices while simultaneously supplying the specified parameters to the workpiece, characterized in that roller stands made of electrically insulated from each other use current supply to the workpiece as deforming devices carried out through a current-carrying device located in front of the first along the drawing roller stand, and through the last at drawing at a roller stand, wherein between the roller stands parallel connected resistive shunts the workpiece and / or additional power sources. 2. The method according to p. 1, characterized in that the current-carrying device and roller stands are cooled. 3. The method according to p. 1 or 2, characterized in that the drawing is carried out in a protective atmosphere. 4. The method according to one of paragraphs. 1-3, characterized in that after drawing carry out annealing. 5. The method according to one of paragraphs. 1-4, characterized in that the drawing is carried out in several stages with intermediate annealing. 6. The product, characterized in that it is made by the method according to any one of paragraphs. 1-5.

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