RU2011700C1 - Device for application of high-melting coatings to fibrous materials - Google Patents

Abstract

FIELD: chemical engineering. SUBSTANCE: device comprises feeding unit, degassing reactor, reaction chambers, closing elements, accumulating unit. Reaction chambers have a channel of rectangular section formed by four graphite wall-boards wherein uniform temperature field is created. EFFECT: improved design. 3 cl, 4 dwg

Description

 The invention relates to chemical engineering, specifically to devices for high-temperature chemical deposition of refractory coatings from the gas phase onto carbon-graphite fibrous materials.

 Known devices for the deposition of coatings on fibrous materials. These devices have a reaction chamber, a receiving and loading device [1]. The chamber has water cooling and nozzles for input of the initial components and removal of pyrolysis products. When applying coatings in such devices, the electrically conductive fibrous material, which is a monofilament or yarn, is heated by passing current through it. The thread (yarn) is transported through the reaction chamber, into which the initial vapor-gas mixture is simultaneously fed.

 However, in such devices, the distribution of temperature fields along the length of the fibrous material is extremely uneven, which does not allow to achieve a sufficient uniformity of deposition of the coating on the material both in length and in depth when it is continuously transported through the reaction chamber.

 The patent [2] describes a method for applying silicon carbide coating on a thread in a two-chamber installation at atmospheric pressure with a vibration device to obtain a uniform coating along the depth of the fibrous material.

 However, the presence of a vibration device complicates the installation. In addition, this installation does not allow coating on tapes and fabrics. Due to the flow of gas components from chamber to chamber, it is impossible to control the composition of the coating and, therefore, to ensure the stability of the properties of the obtained fibrous material with a coating.

 A known device for the deposition of coatings on fibrous materials [3], adopted as a prototype, in which the camera in the form of cylindrical pipes are connected by channels with Teflon couplings. Each chamber has a longitudinal opening for fiber passage and a mercury seal that provides thermal insulation of adjacent chambers and a reliable electrical contact of the heated fiber with a power source. Each chamber has two nozzles for supplying reaction gases to the chamber and gas flowing from the chamber to the chamber along a parallel channel. There is also a device for pulling fibrous material.

 However, this device does not allow uniform deposition of the coating on the fibrous material if the fibrous material is a bundle or yarn (tape, fabric) due to local overheating or supercooling of such materials due to their polystructure. This applies, in particular, also to carbon-graphite materials (tape, tow), consisting of many elementary carbon fibers with a diameter of 3-10 microns. When transporting such materials, especially at elevated temperatures, tearing occurs (which is also facilitated by the presence of a vibration device), which additionally leads to the appearance of additional sections of material with zones of local overheating and, as a result, to more uneven deposition of the coating. The composition of the coating is not regulated.

 The need to obtain thin coatings uniform in thickness and continuous along their length based on various refractory materials or compounds obtained by gas vapor deposition is associated with the fact that later fibrous materials with these coatings are used independently as conductive elements in various electrical devices, and as reinforcing fillers for the manufacture of composite materials based on polymer, carbon, metal, ker nomic and other matrices. Coatings are a diffusion barrier that protects fibrous materials from interaction with a particular matrix and does not change their physical and mechanical characteristics, or perform protective functions in an oxidizing environment.

 The aim of the invention is to increase the uniformity and continuity of the deposited coating.

 This is achieved by the fact that a device for applying refractory coatings to fibrous materials, containing heated reaction insulated chambers with nozzles for supplying the initial reaction gases and exhaust gases, connected in series with each other by channels with shut-off elements, as well as equipped with fiber drawing means, a feed unit and a unit accumulation connected respectively to the first and last reaction chambers, equipped with a degassing reactor installed in front of the first reaction chamber, Each reaction chamber is provided with additional graphite walls made in the form of plates forming a through channel of rectangular cross section, while the locking elements are made in the form of two pairs of rollers clad with heat-resistant rubber, mounted in the channel hermetically with its walls for rotation, the feed and storage units are isolated from the atmosphere, the shell, respectively, is hermetically connected to the degassing reactor and the last reaction chamber, with each channel being equipped with a pipe connected to it in the vertical plane of the touch roller pairs.

 In addition, in the device, the pulling means installed in the supply and accumulation units are provided with pairs of distribution rollers mounted fixed on the rotation axes, while the surfaces of both rollers of the pair are corrugated by annular grooves, and the annular grooves of one of the rollers of the pair are offset by the size of the distribution step of the corrugations relative to of another.

 Carrying out the technological process in such an isolated system makes it possible to ensure uniformity of the coating along the depth of the fibrous material, characterized by the ratio of the coating thickness of the fibers located in the center of the material to the coating thickness on the fibers located on the periphery of not less than 0.75. It must be emphasized that this is achieved without the use of various vibration devices or fiber spreaders, which, in addition, cannot be used in the case of coating a woven material, and which injure the fiber, leading to a decrease in its strength compared to the initial strength of the uncoated fibrous material.

 The introduction of a degassing reactor allows to increase the uniformity and continuity of the coating without significant damage to the fiber to 0.95-1.0, and in some cases, depending on the nature of the coating applied, leads to an increase in its strength due to the removal of adsorbed gases and other impurities from the fiber surface, thanks to the vacuum and temperature created in the degassing reactor. The uniformity of the coating can be improved by creating various technological conditions for the deposition of the coating in the chambers, as well as by varying the technological parameters (temperature, pressure, ratio of the starting components in the vapor-gas phase and the rate of transportation of fibrous material through the reaction chamber) in each of the chambers.

 The implementation of the walls of the reaction chambers and the degassing reactor from graphite plates forming a rectangular channel allows to increase the uniformity of the coating applied to the fibrous materials due to the fact that the rectangular heated working space ensures uniform heating across the entire surface of the fibrous material stretched through the chamber directed equidistant to these walls.

 In addition, the implementation of the heater from graphite allows for high temperatures in the working area and the absence of harmful impurities, since the heater material does not evaporate at high temperatures.

 The execution of the locking elements in the form of two pairs of rollers clad with heat-resistant rubber installed in the connecting channels is hermetic, and the connection of the channel for supplying inert gases to them also ensures uniformity and purity of the coating, since gas blowing through the locking element provides a pressure differential before and after this element and eliminates the reverse flow of the incoming reaction gas. In addition, such an arrangement and such a design of the locking elements provide transportation and processing in the reactors of fibrous material in the form of bundles and tapes.

 The supply of pulling means by pairs of distribution rollers with a corrugated surface ensures uniformity of winding and feeding of fibers, which also positively affects the uniformity of the coating, since the fibers are not intertwined, and thus they are not torn and broken.

 According to the information obtained as a result of the search, the indicated distinguishing features of the described device in another set and with the same properties are not found in technical solutions, which gives reason to consider the proposed device meets the criterion of "significant differences".

 In FIG. 1 is a schematic diagram of a device for applying refractory coatings to fibrous materials; in FIG. 2 - part of the reaction chamber with walls forming a heating element, limiting the reaction space of the chamber; in FIG. 3 - a device for ensuring uniform transportation through the chambers and stacking in the storage unit on the receiving coil, for example, carbon fiber material in the form of a navoi; in FIG. 4 - trap for capturing and neutralizing aggressive components of the exhaust gases.

 A device for applying refractory coatings to fibrous materials contains a degassing reactor 1, hermetically connected by channels with reaction heat-insulated chambers 2 and 3 by heating graphite walls 4 in the form of plates forming a cavity of a rectangular chamber section, a feed unit 5 and a fiber storage unit 6, two locking elements 7 , fiber broaching means, in which devices 8 are installed for uniform fiber transportation, nozzles 9 for blowing inert gas into the shut-off elements. The locking elements are made of two pairs of rollers clad with heat-resistant rubber, mounted in the channel hermetically with its walls for rotation. The nozzles 9 for inert gas blowing are connected to the shut-off elements on the outside in a vertical position of touching the pairs of rollers, there are nozzles 10 for supplying the starting components to the reaction chamber, nozzles 11 for pumping the installation and removing exhaust gases, installed before and after the trap system 12 for neutralizing and capture aggressive components of the exhaust gases and vacuum pumps (not shown in the diagram) to provide the required residual pressure in the reaction chambers connected to the nozzles 11.

 The degassing reactor is made similar to the reaction chambers, but has a different functionality.

 The channel of a rectangular cross section of the reaction chamber, which is a heating element, formed by four graphite boards - walls 13 and 14, allows you to create a uniform temperature field in the chambers, which ensures uniform coating on the fibrous materials across their width. Boards 13 and 14 are tightly pressed against each other using wedge-shaped crackers 15 made of graphite. Current leads 16 have water-cooled shirts and are made with landing nests for crackers 15.

 The fiber broaching means is equipped with a device for uniform transportation through the reaction chambers and stacking the fiber in the form of Navoi on the receiving coil (Fig. 3), are a pair of distribution ebonite rollers 17, the surface of which is corrugated by annular grooves 18 for bundles. The sharp edges of the grooves are blunted. The rollers are mounted on the axes 19, mounted on a T-shaped bracket 20, and are offset relative to each other by the size of the distribution step of the corrugations (the size of the step is determined by the textile parameters of the bundle - the number and diameter of elementary fibers). The bracket is mounted in the nodes of the supply and accumulation (Fig. 1). With this design, the fiber is uniformly fed into the reactor, then into the reaction chambers, and then tightly and evenly placed on the receiving coil.

 The system for capturing and neutralizing aggressive constituents and solid particles in the exhaust gases consists of three series-connected traps of the same type (Fig. 4). The trap has a steel body 21 with a conical bottom, an inlet L-shaped 22 and an outlet 23 nozzles with flanges for connection, a cover 24 for pouring reagents and cleaning the trap, a drain hatch 25 for unloading waste, a chimney 26, located in the trap body 21 at the inlet nozzle 22, and a metering nozzle 27 (also on the inlet pipe 22) to create a predetermined velocity of the gas flow in the trap. Each of the traps has its own technological function of cleaning, - the first trap along the gas flow from the furnace to the vacuum pump is used to trap large solid particles, the second is used to neutralize the aggressive components of the exhaust gases through an aqueous solution of alkali 23, poured into the conical part of the body 21.

 The process of coating fibrous materials in the installation is as follows.

 The fibrous material on the spool in the form of a navoi is placed in the feed unit 5, and the fiber, using a special device, is sequentially through the pulling means, degassing reactor 1, reaction chambers 2 and 3, the shut-off elements 7 are pulled into the accumulation unit 6, where it is then pulled through the pulling means with device 8 for uniform transportation and is mounted on the receiving coil of the accumulation unit. Fiber supply and accumulation units are sheathed from the atmosphere and hermetically connected to the degassing reactor and the last reaction chamber, respectively. The installation is evacuated, water is supplied to cool the reaction chambers.

 The transport device carries out broaching with a given speed of fibrous material, depending on its chemical composition. The reaction chambers are turned on and according to the program for each chamber, depending on the composition of the deposited coating, it is displayed at the corresponding temperature.

 To obtain a two-layer coating, for example, of silicon and titanium carbides with a thickness of the order of 50 mm, each coating is applied to a VMN-4 carbon fiber. In the degassing reactor 1, the temperature should be in the range 1273-1473 K to remove the sizing and degassing the fiber, and in chambers 2 and 3 1623 + 10 K. When reaching the set temperatures in the reaction chambers, the carbon fiber transportation speed was adjusted gradually, simultaneously to the shut-off elements 7 hydrogen was supplied. The initial vapor-gas mixture was fed into the reaction chamber 2 (composition: silicon tetrachloride, methane, hydrogen in a molar ratio of 1: 2: 10) and the necessary pressure was set in the chamber. Then, the initial vapor-gas mixture of a different composition was fed into the reaction chamber 3, in which the pressure set for this chamber was set.

 In the process of coating deposition, continuous monitoring of process parameters is carried out: temperature, pressure, feed rate of the fibrous material, flow rate of the starting components. The process ends after coating the starting carbon fiber. Then, the transportation mechanism, heating of the reaction chambers is sequentially turned off, reagents are supplied and the reaction chambers are cooled to room temperature, the vacuum valves are closed in series, the vacuum pumps and water cooling are turned off, the installation is depressurized and rebooted.

 After that, quality control of the obtained coated fibrous material is carried out and coating continuity is assessed: chemical analysis of the coated fiber, estimation of the coating thickness by the calculation method and using an electronic scanning microscope both at the periphery of the fibrous material and in the center of the material, determination of the specific surface, etc.

 Below we consider for comparison examples of technological processes for coating a fibrous material using the example of silicon carbide coating on a carbon fiber of VMN-4 grade from the vapor-gas phase of the composition monosilane - methane - hydrogen - argon and the composition of silicon tetrachloride - methane - hydrogen.

 PRI me R 1. A carbon tow is pre-degassed at 1573 K, a residual pressure of 50 Pa and a transport speed of 20 m / h.

 A silicon carbide coating is deposited from the vapor-gas phase of the composition monosilane - methane - hydrogen - argon taken in a molar ratio of 1: 15: 95: 9, sequentially in two stages, first at a temperature of 1573 K, then by reversing the carbon tow at a temperature of 1673 K, in both cases, with a residual pressure of 100 Pa and a carbon fiber transport speed of 10 m / h in a single-chamber installation with a tubular graphite heater.

 With an increase in the strength of the coated carbon fiber by ≈20% compared with the strength of the initial carbon fiber and the average coating thickness of ≈75 nm, the ratio of coating thicknesses on elementary fibers is ≈1.00.

 PRI me R 2. The carbon tow is pre-degassed at 1573 K, a residual pressure of 50 Pa and a transport speed of 20 m / h.

 A silicon carbide coating is deposited from the vapor-gas phase of the composition silicon tetrachloride - methane - hydrogen, taken in the ratio 1: 2: 18, sequentially in two stages, first at a temperature of 1573 K, then by reversing the carbon tow at a temperature of 1653 K, in both cases a residual pressure of 10-14 kPa and a carbon fiber transport speed of 30 m / h in a single-chamber installation with a tubular graphite heater.

 With an increase in the strength of the coated carbon fiber by ≈20% compared with the strength of the initial carbon fiber and the average coating thickness of ≈75 nm, the ratio of coating thicknesses on elementary fibers is ≈1.00, i.e., the same effect is achieved as in the example 1.

 The implementation of carbon fibers with a silicon carbide coating, for example, in a composite material based on a metal matrix (alloy 1911) showed that the tensile strength of such a composite material is 20-30% higher than the strength of the composite material obtained by reinforcing alloy 1911 with carbon fiber with uneven coated.

 Thus, the present invention allows to increase the uniformity and continuity of the deposited coating, as well as to create the possibility of varying the composition of the coating and as a result to obtain composite materials based on these fibrous materials with refractory coatings with high performance characteristics. (56) 1. Patent of England N 1122645, cl. C 1 A K 4, announced 12.08.65.

 2. The patent of Germany N 3423166, class. D 01 F 11.10; 9/08, claimed 30.06.86.

 3. England patent N 1266481, cl. C 7 F, claimed Jan 23, 1970.

Claims (3)

 1. DEVICE FOR APPLICATION OF REFRIGERATING COATINGS ON FIBROUS MATERIALS, containing heated reaction heat-insulated chambers with nozzles for supplying the initial reaction gases and exhaust gases, connected in series with each other by channels with shut-off elements, as well as a fiber feed unit and fiber storage unit equipped with fiber drawing means, connected respectively, to the first and last reaction chambers, characterized in that it further comprises a degassing reactor installed in front of the first the reaction chamber, while the locking elements are made in the form of two pairs of rollers clad with heat-resistant rubber mounted in the channel hermetically with its walls with the possibility of rotation and equidistant transportation of fibrous material through the reaction chambers, each reaction chamber is additionally equipped with graphite walls made in the form of plates forming a through channel of rectangular cross section, while the graphite walls of the chambers are equidistant to the horizontal plane of contact of the pairs of rollers, and the feed nodes and akopleniya are sealed and are respectively connected to the reactor and degassing the last reaction chamber.  2. The device according to p. 1, characterized in that each channel is equipped with a pipe connected to it from the outside in a vertical plane of contact of the pairs of rollers.  3. The device according to paragraphs. 1 and 2, characterized in that the broaching means are provided with pairs of distribution rollers mounted fixed on the axis of rotation, while the surfaces of both rollers have annular grooves, which are displaced on one of the rollers relative to the annular grooves of the other roller by the size of the distribution groove pitch.

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