RU2263581C2 - Multilayer lightning-protection coating - Google Patents

Abstract

FIELD: protective coatings.

SUBSTANCE: invention relates to field of manufacturing composite materials for aircraft equipment and may be, in particular, used for protection of aircraft parts and units disposed on fuselage against lightning damage. Coating comprises dielectric and conducting layers. The former is made from cured polymeric epoxide or polyamide matrix and the latter, based on high-strength carbon fibers, is made from two or more single layers of carbon tissue arranged at an angle between -30 and +60° to each other, in interfibrillar space of which polymeric epoxide or polyamide binder with decomposition temperature ≥250°C is inserted. Binder contains uniformly distributed carbon particles of schungite (naturally occurring crystalline carbon substance with fulleroid structure and size 2-10 μm) in amount 5 to 40%.

EFFECT: enhanced lightning resistance and strength of coating, reduced manufacture expenses, and simplified manufacture process.

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Description

The invention relates to the field of materials for aircraft and can be used to protect against damage by lightning parts and assemblies of aircraft that go to the external circuit and are made of conductive layered polymer composite materials, in particular carbon fiber.

Carbon fiber reinforced plastics have found wide application in load-bearing structural elements of aircraft due to high rates of specific strength, rigidity, heat and electrical conductivity. During the flight, the orientation of the shifting lightning discharges to carbon fiber structures that come to the surface, similar to their orientation to metal structures, is observed. Since laminated carbon plastics are isotropically reinforced materials and have increased electrical resistance in the transverse direction, unprotected carbon fiber constructions of the external contour of the airframe (for example, thin-layer casing of bearing honeycomb panels) suffer damage that is unacceptable by operational and resource requirements: through breakdown with a diameter of 10 mm or more, splitting along the fibers by tens of centimeters from the lightning channel, delamination of the material and separation of its layers by air flow. Such damage is the result of thermal destruction of the polymer matrix, which is explosive in nature. To prevent thermal degradation of the matrix, it is necessary to increase the surface conductivity of carbon fiber. In existing systems of lightning protection (MOH), this is achieved by applying to the surface of carbon fiber structures that go to the external circuit, special coatings with increased indicators of electrical and thermal conductivity. In most technical solutions, these are solid or discrete metal layers separated from the structural support material by a dielectric layer with high dielectric strength. The metal layers take on the electrical energy of lightning, divert it from the central channel through its branches, convert it into heat and dissipate it. The dielectric layer performs an insulating function - it prevents the spread of an electric lightning discharge into the material of the supporting structure.

A known system of MOH and removal of static electricity from structures made of polymer composite materials, in which a knitted mesh of steel or copper filaments with a diameter of 0.03-0.08 mm is used as a current-collecting element. The use of knitted stainless steel mesh with a mass of 50 g / m ² in panels made of organoplastics reduced the drainage period of static electricity from 2000 to 10 seconds. The size of the through breakdown after a lightning strike did not exceed a diameter of 20 mm (Vishnyakov LR ANTK Antonov. Industry Reviews. Plastics, No. 12, p. 10, 2002).

The main disadvantage of lightning protection coatings using various metal structural elements is their large mass, which leads to a significant (from 500 to 1500 g / m ² ) weight gain of the protected structure.

Known technical solutions of MOH systems in which the reduction in the gain of the protected structure is achieved by replacing part of the metal elements with light conductive non-metallic ones: for example, a device for providing the MOH of the surface of vehicles using a combined (hybrid) mesh of metal wire and carbon fibers (EP patent No. 0318839) or MOH honeycomb structures using a wire mesh of aluminum and carbon fiber (US Patent No. 6432507).

Such solutions, although they provide a noticeable (30–50%) reduction in structural gain, leave corrosion issues problematic. In addition, the presence of metal elements on the surface of the outer contour of the glider deprives the aircraft of some additional advantages inherent to carbon fiber (radio absorption, shielding from electromagnetic radiation, x-ray transparency, etc.).

A multilayer MZ coating is known, consisting of a dielectric layer made of a polymer (e.g., epoxy) cured matrix, and a conductive layer consisting of high-strength carbon, boron, aramid or glass fibers with layers of nickel wire deposited on them. The coating is obtained by spiral winding at an angle of (-30) - (+ 60) ° to the axis of rotation of the protected part, with nickel-coated fibers placed on the outer surface of the structure and at least partially immersed in the surface of the impregnating resin (US Patent No. 5132168).

In addition to the shortcomings directly associated with the use of metal (weight gain, corrosion), the coating is distinguished by a great complexity and complex manufacturing technology. Due to the use of the spiral winding method, it can only be used to protect structures representing bodies of revolution. In addition, the nickel coating significantly reduces the absolute and specific elastic strength characteristics of light reinforcing fibers (carbon, aramid) and cannot be included in the design structure.

Known technical solutions for increasing the electrical conductivity of thermoplastic polymers without the use of metal elements: MOH for fairings based on layers of polyethylene vinyl acetate filled with soot (UK Patent No. 2295594); an electrically conductive polymer layer containing carbon black (Japan, application No. 3209394); an electrically conductive composition based on polyphenylene oxide and polyamide, containing 1.5-5% of conductive black carbon as electrically conductive particles (US Patent No. 6171523); conductive composition based on a mixture of polyurethane and polyacetal containing carbon black (Japan, application No. 3167297, class C 08 L 59/00, 1992).

The disadvantage of these technical solutions is the high (for carbon black more than 20 wt.%) Concentration threshold of percolation (filtration) of the electric charge through conductive particles dispersed in a polymer dielectric medium. Partial compensation for this drawback was achieved by replacing the fraction of carbon black with its organometallic compounds (polymer composition made of polyphenylene for a heat-resistant integrated circuit substrate with improved electrical conductivity - Japanese Application No. 3112519, class C 08 L 71/12, 1991). The use of large concentrations of known non-metallic conductive fillers leads to a decrease in the strength of polymers. Such technical solutions of the Ministry of Health are not able to perform combined load-bearing functions and cannot be included in the design scheme of an aircraft structure.

Closest to the claimed invention adopted as a prototype is a multilayer lightning protection coating consisting of a dielectric layer made of a polymer cured matrix and a conductive layer consisting of high-strength carbon fibers, in which the conductive layer is made of two or more layers of carbon twill fabric, satin and other types of weaving, located at an angle of (-30) - (+ 60) ° to each other, a polymer binder with a temperature of dest is introduced into the interfiber space of the carbon fabric uktsii ≥250 ° C, the carbon fabric layers are interconnected by multi-layer weaving or stitching a transversally reinforcing carbon fibers (EEPROM density is 5.1 to 1 cm ^2), providing an increase contact conductivity between the layers of carbon fabric. Also, to increase contact electrical conductivity, carbon nanomodifiers in an amount of 3-25% (wt.) Are introduced into the polymer binder of the conductive layer. The connection of the conductive and dielectric layers with a protected Uplastic construction can be performed both in a single technological cycle and by pressing the conductive layer onto the product using prepregs based on carbon fillers (RF Patent No. 2217320).

The disadvantages of the prototype are the great complexity, complex manufacturing technology associated with the flashing transversely reinforcing carbon fibers of specially oriented layers of carbon fabric. It is also possible that mechanical damage to the weaving of carbon fabric in the form of screeds, loops, and hooks is close, which causes a decrease in the elastic strength properties of the MZ coating and creates difficulties when it is included in the design structure.

The technical task of the invention is the creation of a lightweight, high-strength and technologically advanced lightning protection coating based on non-metallic conductive components with a high level of elastic strength properties, simplifying the manufacturing process and cheapening the coating, enabling it to be included in the design structure, preventing weight gain and corrosion of the product.

To solve the technical problem, a multilayer lightning protection coating is proposed, consisting of a dielectric layer made of a polymeric epoxy or polyamide cured matrix, and a conductive layer based on high-strength carbon fibers, in which the conductive layer is made of two or more monolayers of carbon fabric located at an angle ( -30) - (+ 60) ° to each other, into the interfiber space of which a polymeric epoxy or polyamide binder is introduced with a temperature of destruction ≥250 ° С, p and this in the binder particles are evenly distributed shungite -. natural crystalline carbon material 2-10 microns fulleroid structure in an amount of 5-40 wt%.

As the main material of the conductive layer of the MOH, twill, linen and other types of weaving are used from high-strength, high-modulus carbon bundles having high heat resistance (up to 1400 ° C) and electrical and thermal conductivity comparable with metals. The diameter of the bundles from 1K to 6K (from 1000 to 6000 filaments), the total thickness of one layer of fabric from 0.2 to 0.5 mm. Carbon tows take over and divert (scatter) through their fibers (filaments) the bulk of the energy of lightning. For greater efficiency, we propose stepwise orientation of carbon fabric monolayers in a conductive layer at angles of (-30) - (+ 60) ° to each other, creating a multi-directional direction of removal of electrical and thermal energy from the lightning channel.

Particles of shungite carbon substance with a size of 2-10 microns impart conductivity and increased heat capacity to the polymer matrix, as well as transverse electrical and heat conductive contacts between the carbon fibers. This helps to maintain the health of the conductive layer after exposure to high thermal energies. As a result of the passage of the lightning current through the conductive layer, its density decreases by 3.5-5 times, and the specific energy release by 6-8 times. It provides not only protection for carbon-fiber bearing structures, but also the preservation of at least 85% of the strength of the conductive layer itself.

The introduction of a large (up to 40 wt.%) Amount of schungite crystalline carbon substance of a fulleroid structure into the polymer matrix, in contrast to amorphous forms of carbon (carbon black, carbon black), does not lead to a deterioration in the strength characteristics of the matrix. On the contrary, its morphology is improved, the supramolecular structure is improved, the free volume is selected, the "friability" is eliminated. The adhesion strength at the phase boundary “reinforcing fiber - polymer matrix” becomes greater than the cohesive strength of the material of the polymer matrix itself. The level of conductivity of the phase boundary increases by almost an order of magnitude.

Due to the guaranteed preservation of strength, the conductive layer can no longer be considered as a "sacrificial", but as a full-fledged element of the supporting structure. Its inclusion in the design scheme allows not only to completely avoid the structural gain, but even to facilitate it.

The connection of the conductive and dielectric layers with the protected working surface of the carbon fiber construction can be carried out both in a single technological cycle, and by pressing the conductive layer onto a previously formed working surface using semi-finished prepregs.

The advantages of the invention in this way are:

- the use of particles of schungite crystalline carbon substance of a fulleroid structure to impart conductivity to the polymer matrix, increased heat capacity, prevent thermal degradation, and also to increase the transverse conductivity of the conductive layer;

- the possibility of including the MZ coating in the design structure of the aircraft to prevent its weight gain due to the high initial level of elastic-strength characteristics of the conductive layer and its preservation of at least 85% residual strength after a lightning strike;

- the manufacturability of manufacturing the MZ coating by attaching the dielectric and conductive layers to the protected carbon-plastic supporting structure both in a single technological cycle and by the method of molding using semi-finished products of the MZ in the form of prepregs;

- the processability of combining particles of schungite crystalline carbon substance of a fulleroid structure with polymer binders, and also due to chemical affinity - with carbon fabric fillers, the absence of complex, labor-intensive technological operations of preparation and combination of components (stitching and weaving);

- the availability of natural raw materials of schungite filler of a fulleroid structure, low cost of raw materials, allowing to reduce the cost of 1 m ^{2 of} lightning protection coating by 7-12 times.

Examples of implementation

Example 1

Non-metallic lightning protection coating, including a dielectric layer made of a cured polymer matrix, for example, of a binder EDT-69N based on epoxy Dianova resin (TU 1-595-25-277-89), and a conductive layer consisting of three fabric monolayers with a thickness of 0, 23 mm plain weaving, located at an angle of ± 30 ° to each other, on the basis of high-strength carbon bundles with a diameter of 6K (6000 filaments), the BC-2526k binder based on chlorine-containing epoxy resin is introduced into the interfiber space (TU 1-595-25-261 -88) with temperature degradation 260 ° C, containing 5 wt.% of the particles shungite carbon substance III-1/1 (carbon content of 97.51%, the rate of conductivity σ = 1250 ohm / m) size of 2-10 microns. Conductive monolayers of MZ-coatings in the form of semi-finished prepregs are pressed to the surface of the protected carbon-plastic part by autoclave molding.

Example 2

Non-metallic lightning protection coating, including a dielectric layer made of a cured polymer matrix, for example, a binder SP-97C based on polyamide resin (TU 2224-415-00209349-2000), and a conductive layer made of two monolayers of twill fabric 0.5 mm, located at an angle of ± 45 ° to each other, on the basis of high-strength carbon bundles with a diameter of 1K, into the interfiber space of which a binder SP-97C based on a polyamide resin with a temperature of destruction of 390 ° C containing 20 wt.% particles of shung tovogo carbon substance III-1/1. The dielectric and conductive layers of the MZ coating are made in a single technological cycle of joint pressing with a protected carbon-plastic part.

Example 3

Non-metallic lightning protection coating, comprising a dielectric layer made of a cured polymer matrix, for example, a BC-2526k binder based on chlorine-containing epoxy resin, and a conductive layer made of two monolayers of twill weaving 0.2 mm thick, located at an angle of ± 60 ° each to a friend, based on high-strength carbon tows with a diameter of 2.5K, in the interfiber space of which a binder BC-2526k based on a chlorine-containing epoxy resin with a temperature of destruction of 260 ° C, containing 40 ac.% of the particles shungite carbon substance III-1/1. The dielectric and conductive layers of the MZ coating are made in a single technological cycle of joint autoclave molding with a protected carbon-plastic part.

The prototype is a multilayer MZ coating consisting of a dielectric layer made of a cured polymer matrix, for example, an VS-2526k epoxy binder, and a conductive layer made of three layers of carbon twill fabric based on high-strength carbon fibers with a diameter of 2.5 K and a thickness of 0 , 23 mm each layer, located at an angle of ± 60 ° to each other, a VS-2526k polymer binder with a degradation temperature of 260 ° C is introduced into the interfiber space, the layers of carbon fabric being interconnected by firmware non-reinforcing carbon fibers (firmware density is 5 per 1 cm ² ). Between the individual layers of carbon fabric, a carbon nanomodifier — fullerene C60 in the amount of 15 wt% is introduced into the polymer binder of the conductive layer.

The results of bench tests of samples of carbon fiber structures with various options for MZ coating under conditions simulating the effect of displacing lightning electrical discharges are presented in Tables 1 and 2. Lightning resistance tests were carried out in the Test Center for Electromagnetic and Mechanical Impacts of SIC 26 Central Research Institute in accordance with the methods adopted in RF, and international FAR regulations. Each sample was exposed to a single lightning current pulse with the following parameters:

Component A:

- maximum current value, kA 200; - front duration, μs fifty; - pulse duration, μs 185.

Component C:

- maximum current value. A 750; - pulse duration (t), ms 60; - charge, kL 10.3.

Table 1
The nature and level of damage to the conductive layer after a lightning strike Type of damage to the conductive layer in the lightning strike zone Damage Diameter, mm Prototype Example 1 Example 2 Example 3 Fluffing of bundles into individual carbon fibers thirty 17 12 8 Carbon fiber tearing eighteen 12 8 6 Destruction of the upper monolayer fifteen 8 6 4 table 2
The residual strength of the conductive layer after a lightning strike The distance from the center of the lightning strike, mm Saving the strength of the conductive layer,% Prototype Example 1 Example 2 Example 3 0 76 79 80 87 twenty 79 81 87 96 40 89 95 95 100 60 100 100 100 100 80 100 100 100 100

The test results showed that the proposed non-metallic lightning protection coating is able to effectively protect the carbon fiber structures of the external circuit of aircraft from the effects of shifting lightning discharges with current values of I = 200 kA and electric charge Q = 10 kL. Only partial destruction of the surface of the conductive layer is observed with the phenomena of rupture of individual fibers of the upper layer of carbon fabric and the fluffing of carbon bundles. The underlying monolayers of carbon fabric in the conductive coating are maintained unchanged. The insignificance of lightning protection damage is evidenced by the results of determining the residual strength of the material of the conductive layer depending on the distance from the center of the lightning channel: in the center of the shock, the residual strength is about 80% of the original, and when the distance from the center of the lightning strike is 60 mm and further, the material strength is fully restored 100%. High characteristics of lightning resistance and strength make it possible to include conductive layers of the MZ coating in the design structure, the introduction of conductive particles directly into the polymer binder can reduce the complexity of the manufacturing process, and the use of affordable and inexpensive raw materials can reduce its cost.

Claims (1)

A multilayer lightning protection coating comprising a dielectric layer made of a cured polymer epoxy or polyamide matrix and a conductive layer based on high-strength carbon fibers made of two or more monolayers of carbon fabric located at an angle of (-30) - (+ 60) ° to friend, in the interfiber space of which a polymeric epoxy or polyamide binder is introduced with a temperature of destruction ≥250 ° С with carbon particles evenly distributed in it, characterized in that as carbon native particles use particles of shungite - a natural crystalline carbon substance of a fulleroid structure in the size of 2-10 microns in an amount of 5-40 wt.%.