WO2011136692A1

WO2011136692A1 - Working electrode of an electro-hydraulic installation (variant embodiments)

Info

Publication number: WO2011136692A1
Application number: PCT/RU2011/000172
Authority: WO
Inventors: Юрий Васильевич ГРИГОРЬЕВ; Василий Юрьевич ГРИГОРЬЕВ
Original assignee: Grigoryev Jury Vasilyevich; Grigoryev Vassily Juryevich
Priority date: 2010-04-27
Filing date: 2011-03-18
Publication date: 2011-11-03
Also published as: RU2433865C1

Abstract

A working electrode of increased reliability is proposed for technological equipment using the phenomena which accompany a high-power electrical discharge in water in order to break up stone and concrete, to purify water and to cottonize fibrous materials. The electrode consists of a metal rod with a priming layer applied thereto, the rod being surrounded by a cast insulating shell made of polyurethane elastomer which has the following properties: - nominal tensile strength of a minimum of 30 MPa; - relative elongation at break of a minimum of 300%; - a shore A hardness of 70...90 nominal units. Furthermore, the surface of the rod has annular grooves or helical flutes for preventing the electrode from being knocked out of the shell by a shock wave which arises during the discharges. In order to improve the adhesion of the priming layer to the rod, microscopic unevennesses can be applied to the surface of the rod.

Description

OPERATING ELECTRODE HYDRAULIC INSTALLATION

(OPTIONS) The proposal relates to elements of equipment using phenomena that accompany a powerful spark electric discharge in water, that is, an electro-hydraulic (hereinafter - EG) effect, for the implementation of various technological processes, in particular for crushing stone, ores, concrete waste, water disinfection, cotonization of flax.

In the specified equipment (EG installations), the discharge occurs between the so-called working electrode connected to the positive high-voltage pole of the power source (pulse current generator) and usually grounded and connected to the negative pole of the power source by the structural element of the equipment.

Working electrodes (hereinafter referred to as electrodes) are metal rods (in the prior art they are sometimes called current conductors or current conductors), solid or hollow, solid or composite, surrounded along the entire length, except for the ends, by an insulating sheath. The terms “insulator”, “insulation”, “insulating shell”, “insulating shell”, which are used in the prior art, from the functional point of view mean the same thing, they are synonyms. But the term “insulator” in strict interpretation means an independent part, and the insulating shell, which will be discussed in the present description, is not a part, but a part of the electrode, which is an assembly unit, according to GOST 2.101 -68 or even a unit. In constructive terms, for brevity, the word “shell” will be used below without indicating its insulating properties. A power source is attached to one of the ends of the rod, the other end (hereinafter referred to as the working end), from which the discharge comes, is immersed in water.

For the occurrence of a spark discharge when a high-voltage pulse is applied to the electrode, it is crucial that the area of the non-insulated working end of the rod in contact with water is minimal. If this condition is not fulfilled, the storage capacitor of the power source is discharged through the water before the conductive channel for the spark is formed. If a spark nevertheless forms, then still a significant part of the source’s energy flows uselessly through the water, thereby reducing the energy efficiency of the process.

The shell portion adjacent to the working end of the electrode is destroyed by the combined action of a shock wave, an electric spark, and ultraviolet radiation accompanying the discharge. Water hammer, acting on the end part of the shell burnt by sparks, causes cracks. Repeating hydraulic shocks, deepening cracks, open the shell along the rod, thereby increasing the area of the surface of the rod in contact with water. Over time, the surface increases so much that the spark discharge no longer develops and the installation stops.

The electrode is removed from the installation and repaired by cutting off the damaged insulation, restoring the shape and integrity of the end part of the shell, and shortening the rod, and thereby the electrode. Replacement of rapidly shortening electrodes is the main cost item for the operation of EG installations. The electrode resource of a given initial length is determined by the loss of length for each repair and the duration of continuous operation from repair to repair. The most important indicator of the reliability of working electrodes is the time between failures (from repair to repair). It must be at least 20 thousand pulses in order for the industrial use of EG installations to be cost-effective. The time between failures of electrodes known from the prior art is lower than indicated by more than an order of magnitude.

Here and below, the contents of the terms related to the reliability of the electrodes are interpreted in accordance with GOST 27.002-89:

Resource - the total operating time of the object from the beginning of its operation to the transition to the limit state.

The ultimate state is the state of an object in which its further operation is unacceptable or inappropriate, or the restoration of its operational state is impossible or inappropriate.

Failure - an event consisting in the violation of the operational state of the object.

Failure criterion - a sign or a set of signs of violation of the object’s operational state, established in the regulatory and technical and (or) design (project) documentation.

Operating time between failures - the operating time of an object from the end of the restoration of its working state after a failure to the occurrence of the next failure.

Reliability - the property of an object to continuously maintain a healthy state for some time or time

Known technical solutions aimed at increasing the life of the electrodes, consisting in the use of composite rods consisting of a metal tube, rigidly fixed in an insulating shell, and a movable central part made of wire passed through it [L.A. Yutkin. Electro-hydraulic effect and its application in industry. L. ^ 'Engineering, 1986, p. 97] or steel rope [RF patent N ° 2013135 C1]. The end part of the tube is installed flush with the end part of the sheath. the central part behind the end part of the shell, thereby striving to distance the place of development of the discharge from the shell.

However, this solution does not increase the life of the electrodes. Due to insufficiently studied reasons, in such designs discharges very often develop from a tube in electrical contact with the central part. Such discharges quickly destroy the shell directly adjacent to the tube.

Also known are technical solutions aimed at increasing the life of the electrodes, consisting in the use of special metal tips that cover the end of the shell. Known, for example, are similar working electrodes for crushing and grinding various materials at voltages of the order of 300 ... 400 kV, containing a metal rod placed in an insulator made of high pressure polyethylene [patent SU Ν ° 1781892 A1, patent SU N ° 1790069 A1 ]. The working ends of the composite rods of known electrodes are provided with screwed tips having a recess in which the conical end part of the insulator is located. In an electrode similar in design [RF patent N ° 2013135 C1] with a composite rod, on the contrary, the tip mounted on the end of a flexible current lead passed through a steel tube rigidly fixed in the insulator is partially immersed in the recess at its end. In all three electrodes, the diameter of the tip exceeds the diameter of the end part of the insulator. Thus, the end face of the shell, as conceived by the authors of these inventions, is protected from destruction by discharges and shock wave.

But at voltages of the order of 50 kV characteristic of technological EG installations, such electrodes are very uneconomical, because of the large surface area in contact with water the tip of a significant part of the energy of the high-voltage pulse is spent on useless heating of water.

In addition, these solutions increase the resource of the electrodes very slightly. Water is a fairly dense medium and transmits a shock wave in all directions. Therefore, the insulator is exposed to the shock wave and from the sides, and not just from the end, where it is protected by a tip.

Also known is a working electrode of an electric discharge installation for the destruction of reinforced concrete waste, consisting of a steel rod surrounded along its entire length, with the exception of the ends, by an insulating sheath made of polyethylene. The end part of the shell on the side of the working end is made in the form of a conical funnel and, to prevent cracking, is equipped with a bandage covering it in the form of a metal tubular screen. The electrode was used in an installation with a voltage of 350 kV [patent SU N ° 1741900 A1]. Such an electrode is unsuitable for EG installations operating at voltages close to 50 kV. The presence of the screen increases the actual contact surface of the rod with water, since the electrical resistance of a narrow layer of water between it and the rod is small. The power source manages to discharge through the water before the spark discharge develops. The technical complexity of the electrode makes it difficult to recover from wear.

The insulating sheath made of polyethylene has a low resistance to abrasion and to the action of ultraviolet radiation from a spark discharge.

Also known is an electrode consisting of a metal rod with a smooth surface surrounded by an insulating sheath [RF patent N ° 2099142 C1]. An electrode of this design works better at voltages of the order of 50 kV, but its durability is low due to insufficient insulation resistance of the end part of the shell, exposed to the destruction of raw materials, shock waves, spark discharges. In addition, a rod without a tip, no matter how tight it is pressed into the shell, under the influence of repeated hydraulic shocks, is shifted in the shell. After he has moved, his connection with the shell is sharply weakened, and he quickly pushed into the shell. The protrusion of the rod beyond the shell decreases, the discharges approach the end part of the shell, accelerating its destruction. When the end of the rod is inside the shell, spark breakdowns become irregular or completely stop. Even a new electrode, not yet shortened by regrindings, in which the rod has moved, becomes unusable and cannot be restored.

In the known electrodes described above, high pressure polyethylene is usually used as the material for the sheath [SU JYO Patents 1741900 A1, 1781892 A1 and 1790069 A1]. According to the RF patent Ν ”60627 U1, the rod is either pressed into a heated insulator, or the insulator is pressed from molten granules directly onto the rod in a mold from which air is evacuated.

Resource of electrodes with such a shell, improved according to the patent

SU No 1741900 A1, does not exceed 1250 pulses [See: A.N. Baranov, N.T. Zinoviev, J.G. Tanbaev // Study of the tracking resistance of the insulation of high-voltage electrodes of electrical impulse plants for the destruction of substandard reinforced concrete // In: “Physics of pulsed discharges in condensed matter (abstract of the Vth All-Union School), September 1991, Institute of Pulse Processes and Technologies of the Academy of Sciences of the Ukrainian SSR, g . Nikolaev]. For industrial EG installations, such a resource is insufficient. There is also known a technical solution aimed at increasing the life of the electrodes, which differs from the above in that the radical the mechanical properties of the shell material change. In an electrode for electropulse fracture of solid materials containing a composite rod installed in an insulating sheath, in the form of a hollow conductor freely inserted into a metal sleeve, the sheath is made of an elastic, spongy material impregnated with a dielectric fluid [RF patent N ° 60627 U1]. Due to the technical complexity and low mechanical strength, such an electrode is unsuitable for use in rock crushing plants, where the electrode is immersed in a layer of destructible stones. The resource of such an electrode according to the data indicated in the description of the patent is about 300 pulses. For industrial EG installations, such a resource is absolutely insufficient.

The closest to the proposed technical essence and the achieved result is the working electrode of the electro-hydraulic crusher, consisting of a metal rod surrounded by an insulating sheath, the free ends of which protrude beyond the sheath for a short length [certificate for gas and condensate field of the Russian Federation 18360]. One end of the rod is used to connect to a high-voltage power source, and the other, immersed during work in water, is a working one. In the description of the utility model, it is noted that the shell material must have high resistance to the action of water, shock wave, ultraviolet radiation and the abrasive action of destructible raw materials.

A disadvantage of the known electrode is its low reliability. The known electrode has a small operating time between failures and a low resource due to the need for frequent and uneconomical regrinding due to degradation of the shell. In addition, for electrodes of known design, sudden failures caused by the displacement of the rod relative to the shell under the influence of hydraulic shocks are a frequent occurrence. The technical problem solved by this proposal is to increase the reliability of the working electrodes of technological EG installations.

It is solved by the fact that in the well-known working electrode of an electro-hydraulic installation containing a metal rod surrounded by an insulating sheath, a primer layer is applied to the rod, and the sheath is molded from polyurethane elastomer.

In addition, in the known working electrode of an electro-hydraulic installation containing a metal rod surrounded by an insulating sheath, a primer layer is applied to the rod, and the sheath is cast from a polyurethane elastomer having the following properties:

- conditional tensile strength not less than 30 MPa;

- elongation at break of at least 300%;

- shore hardness A 70 ... 90 conventional units.

In addition, in the well-known working electrode of an electro-hydraulic installation containing a metal rod surrounded by an insulating sheath, the rod has a variable cross-sectional area along its length and a primer layer is applied to it, and the sheath is made of polyurethane elastomer cast.

In addition, the surface of the rod is made wavy with a wave period equal to the length of the part of the rod protruding from the shell at the working end of the electrode.

In addition, the surface of the rod is made with annular grooves arranged in increments equal to the length of the portion of the rod protruding from the shell at the working end of the electrode.

In addition, in a known working electrode of an electro-hydraulic installation comprising a metal rod surrounded by an insulating sheath, the rod has at least one a helical groove or crest with a lifting angle of not more than 15 °, a primer layer is applied to it, and the shell is molded from polyurethane elastomer.

In addition, in the well-known working electrode of an electro-hydraulic installation containing a metal rod surrounded by an insulating sheath, the rod has microroughnesses, a primer layer is applied to the rod, and the shell is molded from polyurethane elastomer. The presence of a primer layer on the surface of the rod, many times increases the electrode life between failures and increases the reliability of the electrode due to the good adhesion of the rod to the insulating shell, eliminating the peeling of insulation from the rod and displacement of the rod in the shell under the action of a shock wave.

Thanks to the cast shell, the reliability of the electrode is increased by increasing its electric strength and improving the adhesion of the rod to the shell, and the manufacturing process of the electrode is cheaper.

Due to the use of cast polyurethane elastomer as a material for an insulating sheath covering the rod through an intermediate primer layer, the electrode life between failures and its life are many times increased.

Due to the indicated mechanical properties of the elastomer, the long-time operation of the electrode between failures is ensured due to the high resistance of the end part of the insulating shell to the pulse-periodic action of the shock wave.

Due to the use of cast polyurethane elastomer as the material for the insulating shell with a fixed hardness limit of 70 conventional units according to Shore A, the electrode life between failures and its life are many times increased. Due to the use of cast polyurethane elastomer as the material for the insulating shell with a set upper hardness limit of 90 conventional units according to Shore A, a high electrode life is ensured by increasing the long-term resistance of the shell to the pulse-periodic action of the shock wave.

The presence of a primer layer and microroughnesses on the surface of the rod, as well as the implementation of the rod with a variable transverse size or with a spiral groove / crest in length, increases the reliability of the electrode due to the good strengthening of the rod in the insulating shell, which prevents peeling of the insulation from the rod and the displacement of the rod in the cast polyurethane shell shock elastomer.

The implementation of the electrode rod with a wavy surface or annular grooves, the period of which is equal to the length of the protruding portion of the rod protruding from the shell at the working end of the electrode, simplifies electrode repair.

The implementation of the rod with a spiral groove or ridge simplifies its manufacture in large quantities and increases the reliability of the electrode, due to the constancy of the cross section of the rod along its entire length.

The essence of the proposal is illustrated by drawings.

Figure 1 shows the proposed electrode in section.

In FIG. 2 shows a larger scale section of the central part of the electrode.

In FIG. Figure 3 shows a section through an electrode with a spiral groove on the surface of a rod.

In FIG. 4 shows a section of an electrode with a spiral ridge on the surface of the rod. The proposed electrode consists of a metal rod 7, with a primer layer 2 deposited on it, surrounded by a cast insulating sheath 3 (hereinafter referred to as the sheath) of polyurethane elastomer. The rod can be made multilayer or composite, round or other cross-section. The purpose of the primer layer 2 is to strengthen the adhesion between the rod 1 and the sheath 3 in order to prevent the longitudinal displacement of the rod and the formation of a gap between the end part of the sheath and the rod due to repeated hydraulic shocks.

At high current loads, when the rod 1 is noticeably heated, the adhesion between the primed rod and the sheath becomes unreliable. To increase reliability, a round cross-section rod can be made with a variable cross-sectional area along its length. For example, its surface may be stepped or, as shown in FIG. 1, wavy. With a small need for electrodes, it is easier to use a stepped surface, which is created by shallow annular grooves (grooves). The pitch of the grooves or the wavelength may be equal to the length of the protruding part of the rod protruding from the shell at the working end of the electrode before operation. With an optimal combination of shell and rod resources, this length coincides with the length of the shell removed when the electrode is regrind. If the rod is not round, but, for example, oval or rectangular section, then one or more of its transverse dimensions can be variable.

The displacement of the rod can also be prevented by applying to the surface of the rod at least one helical groove (groove) 4 or at least one helical (spiral) ridge 5. It is possible to apply a larger number of grooves / ridges that form a multiple start on the surface of the rod thread. If the need for electrodes is great, then rods with a groove or comb are cheaper to manufacture than rods with a variable cross section. In addition, a constant cross section along the length of the rod with a groove / ridge eliminates its local overheating during operation. The groove depth / ridge height must be at least 0.07 rod diameter.

In order that even when the adhesion between the rod 1 and the primer 2 is lost, the rod does not slip (does not screw out) from the shell 3 under the action of shock waves, the angle β of the groove / ridge rise, measured by the angle between the helical line of the groove / ridge and the plane perpendicular to the axis of the rod (Fig. 1 and 2) should be no more than 15 °. This restriction on the angle β is tested experimentally for elastomers and primers of various compositions, copper and steel rods. At angles β greater than 15 °, a gradual unscrewing of the rod is possible under the influence of repeated shocks, especially when the rod is heated by the flowing current. At β = 0, the helical grooves turn into annular.

From the side of the working end b, the rod 1 is pointed and protrudes from the shell 3 to a small length. At the other end, there may be a thread 7 on the rod for connecting the wire from the power source.

To improve the adhesion of the rod 1 with the primer layer 2, its surface can be coated with microroughnesses 8, for example, from sandblasting or emery cloth. The characteristic size of microroughnesses is 1 ... 100 microns. The shape of microroughnesses is not standardized. Microroughness 8 increase the adhesion of the primer layer 2 with the rod. This prevents peeling of the shell from the rod at the end of the electrode, thereby increasing the time between failures and its life. As the primer layer 2, a polyurethane adhesive primer can be used, for example, type ADV-A-23 TU 2252-093- 22736960-04. During lengthy tests of electrodes with primers of the indicated and other types, the displacement of the primed rod relative to the shell was never observed regardless of the type of primer. Whereas the rods that were sandblasted but not primed were knocked out by the shock wave from the cast shell in the first two hours of operation. As the material of the insulating sheath 3, a polyurethane elastomer is used. The shell of this material is highly resistant to the abrasive action of the medium in which the electrode is immersed, to the action of an electric spark and ultraviolet radiation. Good strength characteristics of the shell are maintained over a wide range of temperatures, including negative ones.

The main factor determining the life of the electrodes is the wear of the end part of the shell, which manifests itself in the form of cracks starting from the end of the working end 6 of the electrode and propagating along the electrode. The criterion for the failure of the end part of the shell along the length of the cracks is the state when the length of the cracks reaches 15 mm. Starting from this length, the crack growth rate begins to significantly exceed the rod wear rate. Losses in the length of the electrode during its repair increase, the full resource of the electrode is reduced, operating costs are growing.

Polyurethane elastomers are usually obtained by mixing, followed by curing of at least two components. It was experimentally established that for the insulating shell, it is important not the chemical composition and ratio of the components, not the temperature regime of curing - they can vary, but the mechanical properties of the obtained elastomer. Limit values mechanical properties were determined experimentally during pilot tests of a ten-electrode EG crusher for stone. The material was considered suitable for the manufacture of shell 3 if, in a mode with a discharge repetition rate of 2 Hz at a discharge energy of 4 kJ, the time between failures caused by degradation of the end part of the shell exceeded 3 hours. This time approximately corresponded to the time of rod wear and was acceptable for industrial applications of EG installations.

It has been established experimentally that the material of the insulating shell meets this criterion if its conditional tensile strength, determined according to GOST 270-75, exceeds at least 30 MPa. A limit on the upper limit was not established, at least up to 50 MPa: the resource of the end part gradually but slightly increased with the growth of this indicator.

It was also established experimentally that the shell material meets the above criteria of suitability, if its elongation at break, determined according to GOST 270-75, exceeds at least 300%. There were no restrictions on the upper limit, at least up to 550%: the end-face resource monotonously increased with the growth of this indicator.

It was also established experimentally that the Shore A hardness of the shell material, determined according to GOST 263-75, should be within 70 ... 90 conventional units. With a hardness less than 70 and greater than 90 conventional units, cracks in the end part of the shell grow faster than the rod wears out. At lower hardness, in addition to cracks, the abrasive wear of the shell and those of its sections that are located at a distance from the end of the electrode and are exposed to the abrasive action of the destructible material for a long time becomes significant. In addition, electrodes typically subjected to bending by processed raw materials, with a hardness of less than 70 conventional units poorly resist bending. With greater hardness, cracks appear later, but, having arisen, grow faster, separate pieces are chipped from the shell. The crack growth rate in excessively hard insulation increases with an increase in the discharge pulse repetition rate, which indicates the fatigue nature of wear. The shell also undergoes abrasive wear, but if the polyurethane elastomer has good resistance to cracking, then abrasive wear is also relatively small.

The thickness of the sheath of polyurethane elastomer is determined from the conditions for obtaining a sufficiently rigid mechanically electrode. It always automatically turns out to be sufficient to ensure the electric strength of the shell at voltages up to 1 00 kV.

The proposed electrodes are made by pouring a polyurethane, usually two-component, injection system placed in the form of a primed rod. A small amount of gas bubbles remaining in the shell does not cause a noticeable decrease in its electric strength, and therefore, pouring is performed without evacuation at atmospheric pressure.

Claims

CLAIM

1. The working electrode of an electro-hydraulic installation, comprising a metal rod surrounded by an insulating sheath, characterized in that a primer is applied to the rod and the sheath is cast from polyurethane elastomer

2. The working electrode of the electro-hydraulic installation, containing a metal rod surrounded by an insulating sheath, characterized in that a primer is applied to the rod and the sheath is cast from a polyurethane elastomer having the following properties:

- conditional tensile strength not less than 30 MPa;

- elongation at break of at least 300%;

- shore hardness A 70 ... 90 conventional units.

3. The working electrode of the electro-hydraulic installation, containing a metal rod surrounded by an insulating sheath, characterized in that the rod has a variable cross-sectional area along its length and a primer layer is applied to it, and the shell is molded from polyurethane elastomer.

4. The working electrode according to claim 3, characterized in that the surface of the rod is made wavy with a wave period equal to the length of the part of the rod protruding from the shell at the working end of the electrode.

5. The working electrode according to claim 3, characterized in that the surface of the rod is made with annular grooves arranged in increments equal to the length of the portion of the rod protruding from the shell at the working end of the electrode.

6. A working electrode of an electro-hydraulic installation, comprising a metal rod surrounded by an insulating sheath, characterized in that the rod has at least a length along its length at least one helical groove or crest with a lifting angle of not more than 15 °, a primer layer is applied to it, and the shell is molded from polyurethane elastomer.

7. The working electrode of the electro-hydraulic installation, containing a metal rod surrounded by an insulating shell, characterized in that the rod has microroughnesses, a primer layer is applied to the rod, and the shell is molded from polyurethane elastomer.