SU887175A1 - Method of producing hollow thin-walled ceramic articles - Google Patents

Description

one

The invention relates to the field of powder metallurgy associated with the manufacture of parts made of refractory metals, oxides, cermets, carbides, nitrides, and similar compounds, and can be used in the manufacture of linings of high-temperature gas paths of power plants, multiscreen thermal insulations, thermocouple sheaths, and intermetallic superconducting solenoids, etc.

Tone: bone products from a series of refractory metals and compounds can be obtained by chemical vapor deposition method 1.

Thin-walled products are thereby obtained in a manner similar to coatings, with the only difference that the substrate on which the layer of the desired thickness is deposited is removed. In this way, for example, thin-walled products are made from pyrographite, pyrolytic boron nitride, from carbographite.

A significant drawback of the gas-phase deposition method is the impossibility of obtaining precipitation from complex alloys, solid solutions and other multi-element and multiphase compositions. The process is very complicated instrumental. Billets obtained by this method also have roughened surfaces and require

additional machining, such as grinding.

There is also known a method for producing multi-screen thermal insulations from carbides 5 and other refractory compounds. According to this method, insulation from powder-separator screens is made by casting plasticized ceramic screens and subsequent sintering. After

10 sintering screens are collected in packages and calibrated at 1700-2700 ° C under load 2.

The main difficulty with the implementation of the method is that in order to ensure the required exact dimensions and shape of the product after sintering, it is necessary to foil the screens assembled in a bag, to undergo special gage processing at a high temperature (usually 2000-2500 ° C).

20 This operation is difficult because it requires handling very thin, brittle foils. In addition, the hot calibration method does not allow for the production of whole cylindrical parts, and they have to be made of, for example, two semi-cylinders.

The closest to the technical essence and the achieved result of the invention is a method of producing hollow ceramic products, including the manufacture of a plasticized silicon-based tape, winding on a template, removing a template and then putting the semi-finished product on the steel cylinder, heating up to 200 ° C and high-temperature calcination at 1350-1450 ° C in nitrogen atmosphere 3. The disadvantage of this method is warping of the section) 1N. The purpose of the invented - the possibility of warping products. The goal is achieved by the manufacture of hollow, thin-walled ceramic products, including the production of plasticized masks with an alumina ceramic niolitelnym winding them on a template, removing the template and patronizing products, carbides of very low-melting metals, the template is made from graphite, before winding onto the template, successively apply a barrier layer of high-melting carbide carbide and a layer of paraffia or sucrose or Wood alloy, whose thickness is 1–10% less than The liners are linear shrinking of the tapes, the sintering is carried out in vacuum, after which the template is removed. In this case, the plasticized tapes are joined into closed rings by gluing with standard. The thickness of the product to be sintered according to the proposed method can be obtained within fairly wide limits - from 20 to 1000 microns in the case of single-layer products and up to 2-5 mm in the manufacture of a product from several layers of the same or dissimilar refractory materials. Thin plasticized metal or ceramic fi lms with a thickness of 20–1000 µm (and preferably 100– 300 µm) can be made, for example, by rolling strip – semi-finished products, rubber-modified rubber with epoxy resin, or by extruding a suspension of a refractory compound powder into an alcohol-ether polyvinylbutyral solution on a polyethylene terephthalate substrate. The thinnest leites with a minimum thickness of 15-20 microns are obtained by extruding the said suspensions. The dispersed filler of suspensions can be a powder of a fast-melting compound, for example, monocarbides NbC, TaC, TiC, etc., complex carbides NbC-ZrC, ZrC-TaC-, etc. Mostly: a single-layer cylindrical ring thickness from 20 to 200-300 microns. A film cast, for example, from a suspension with a carbide filler, is wrapped around a cylindrical substrate on which a layer of the substance to be removed is formed. And as a removable intermediate layer, it is most convenient to use paraffin, sucrose, or an alloy of them, paraffin is preferable. The thickness of the intermediate layer can not be very significant and is limited to 5-10 mm; with a large thickness, spontaneous corrugation of the tape may occur during sintering. Since the shrinkage of plasticized films is usually 15--20%, the maximum internal diameter of the sintered ring is respectively 113-80 mm. The film, tightly wrapped around the shablon with the intermediate layer, must be fixed, “squeezed. This crosslinking of the crts using films cast on polyvinyl butyral and a similarly high molecular weight organic bond is produced by gluing over the overlapped ends of the film moistened with ethanol. As the material of the template it is recommended to use ordinary graphite, which is easily machinable. In order to prevent carbidization, a barrier coating, for example, pyrolytic niobium carbide with a thickness of 20-100 µm, is applied to the graphite template with vapor deposition. Multi-layered tubes can be made in a similar way by applying a plasticized ribbon to the pattern of a multi-turn helix. The number of layers can reach 10-20. As the number of layers increases, it is difficult to obtain a tight ring after sintering, since the outer layers will sit down with an ever-increasing gap. An increase in the density of the ring can be achieved if the thickness of the intermediate layer to be removed is 1–10% smaller than the linear shrinkage of the plasticized tapes. This reduction in layer thickness is also useful in the manufacture of a single-layer ring, since it allows one to create a small tension of the ring on the substrate and thereby provide a smoother and more precise cylindrical shape. In the manufacture of a multilayer product from dissimilar materials with different beginning temperatures, the special layers must be laid on the template so that the inner layers have a sintering temperature lower than the outer ones and take care of the outer ones earlier. The proposed method is explained in the diagrams shown in FIG. 1-3. On the template 1 with the intermediate layer 2 put plasticized film 3 (Fig. 1, a). At the correctly chosen thickness of layer 2, the film after sintering (Fig. 1.6) fits the template tightly. Due to the stitching of the ends of the film, it does not diverge after the removal of the template; a thin-walled part is obtained (Fig. 1, c), the shape and dimensions of which exactly correspond to the external surface of the template.

FIG. Figure 2a shows a film in the form of a myogloam spiral 3, laid through intermediate layer 2 onto template 1. There is a barrier coating 4 on the template. After sintering, the spiral fits the template tightly (Fig. 2.6). Removing the spiral pattern from the template, shown in Fig. 2, c.

FIG. Figure 3 shows the layout of the myoglass layer and stripped off two films 3 and 5 of dissimilar materials.

Example 1. A single-layer niobium carbide liner with a diameter of 30 mm and a length of 60 mm is made. The blank billet is cast onto a polyethylene terephthalate tape from a suspension containing finely ground Niobium carbide powder (specific surface 3 m / g), and polyvinyl butyral plasticized with dibutyl sebacate in a complex organic solution is used as a binder. The molded polystyrene foam, another 120 µm, is dried and separated from the tape. Nz. Films cut strips 120X75 mm. The strip was attached to a cylindrical graphite template with a diameter of 30 mm and a wall thickness of 1.5 mm, on which a 3.5 mm thick paraffin layer was cast. Calcination is carried out in a vacuum oven with a vacuum not lower than I-IO mm Hg. Art. at a temperature of 1800 ° C (lifting speed of 350 degrees / h) and exposure to a final temperature of 30 MT. After firing, shrinkage of the liner was about 20%; as a result of shrinkage, the liner fits tightly to the graphite pattern, acquiring an even cylindrical shape. Zate.m with a graphite pattern carefully remove the carbide sleeve. The chemical composition of the liner is NbCo, 84.

Example 2. An eight-layer sleeve is made from a solid solution of ZrC - NbC with an inner diameter of 30 mm, a length of 60 mm and a wall thickness of about 1 mm. The film blank is cast on a half-ethylene terephthalate tape from a suspension containing finely ground fine compound Zro..g carbide (specific surface 3), and polyvinyl butyral plasticized with dibutyl sebacate in a complex organic solution is used as a binder. The cast pulp with a thickness of 120 µm is dried and then separated from the tape. From a film cut a strip 75 mm wide and 1000 mm long. This strip is wrapped with a graphite hollow cylindrical pattern with a diameter of 30 mm and a wall thickness of 1.5 mm, and there was a paraffin layer 3.5 mm thick. Calcination is carried out in a vacuum electric furnace with carbide-thiobium heaters at a temperature of 2500 ° C and a vacuum not lower than 1-19 mm Hg. Art. with a shutter speed at a final temperature of 30 min.

Example 3. A multilayer composite shell is made up of eight layers of tungsten and eight layers of ZrC-TaC solid solution under them. Film blanks are cast, similarly to the previous examples, of suspensions containing, respectively, fine ground (30 hours of breakage) tungsten powder, as well as other blanks, powder of composite carbide Zro.esTao.ssCo ,.

From the cast films, after drying and separation from the tape, blanks are cut out with a width of 75 mm and a length of 1 m each. Belt blanks are wound sequentially in a spiral on a graphite hollow pattern, similar to the previous examples. The template has a coating of niobium carbide deposited from the gas phase, with a thickness of about 50 MKm. The roasting is performed in a vacuum electric furnace with carbide-thiobium heaters at a temperature of 2400 ° C and a vacuum not lower than mm Hg. Art. with an exposure time of 2 hours. After calcination and removal of the graphite plate, a sleeve with an inner diameter of 30 mm, an outer diameter of 34 mm, a wall thickness of 2 mm and a length of 60 mm was obtained.

Claims (3)

1. A method for manufacturing hollow thin-walled ceramic products, including obtaining plasticized masses with powdered ceramic and filler, winding them onto a template, removing the template and sintering the products, characterized in that, to exclude the distortion of the products, high-melting caroids are used as the powder ceramic filler metals, template is made of graphite, before and on the template, a barrier layer of refractory metal carbide and a layer of paraffin or sucrose or Wood's alloy, whose thickness is 1 -10% less than the linear shrinkage of the tapes, sintering is carried out in vacuum, after which the template is removed. 2. A method according to claim 1, characterized in that the plasticized tapes are connected into closed rings by gluing with a standard. Sources of information taken into account in the examination 1. Avarbe RG. Chemical gas-phase sedimentation of refractory materials. L., 1976. 2. Authorship certificate of the USSR No. 586151, cl. C 04B 35/62, 1976. 3. The patent of England No. 1375223, cl. E 2P, pub. 1974.