RU2258032C1 - Method of manufacture of structural graphite - Google Patents

Abstract

FIELD: chemical industry and special-purpose technique; manufacture of large-sized blanks of shaped articles for chemical and heat-exchange apparatus.

SUBSTANCE: starting coke-filler is mixed with coal-tar pitch and is impregnated with it; then mixture is calcined at temperature of 1100°C and ground to size not exceeding 1.25 mm at content of particles of no more than 0.07 mm in the amount not exceeding 50%. For obtaining fine-grained materials, grinding is continued till particles of 0.5 mm have been obtained. Powder thus obtained is mixed with pitch and blanks are molded from hot coke-pitch mass by extrusion through tip or in mold, after which blanks are subjected to roasting and graphitization. After roasting and graphitization, blanks may be again impregnated with coal-tar pitch and subjected to repeated roasting. Density of material thus made ranges from 1.65 to 1.78 g/cm³, compressive strength ranges from 30.0 to 51.3 Mpa and bending strength ranges from 16 to 26.4 Mpa.

EFFECT: avoidance of rejects.

3 cl, 3 ex

Description

The invention relates to a technology for the production of artificial graphite materials and can be used in the manufacture of any calcined and graphitized materials with a matrix based on coal tar pitch with fine-grained and medium-grained filler according to the technology of pressing through the mouthpiece. In particular, the invention can be used in the manufacture of large-sized blanks for the manufacture of shaped products used in nuclear, electrothermal and thermal engineering, in chemical and heat-exchange equipment, as well as for the manufacture of various products of special equipment.

A common method for producing structural graphites with high density and strength by repeatedly impregnating the calcined billets with coal tar pitch or other impregnants. The basis for impregnation are preforms obtained by pressing hot coke-pitch mass or cold powder [1]. The main disadvantages of this method are high costs and a long production cycle. In addition, the mass for hot pressing must contain particles of filler with a particle size of several millimeters (grain), and the production of powder materials is accompanied by large losses on marriage during firing.

A known method of manufacturing powder materials with the processing of powder with oleic acid in an amount of 0.2-0.5% by weight of the filler to increase its ductility [2]. In another known method, it is proposed to modify the binder with a urea-formaldehyde oligomer in an amount of up to 20% [3]. These methods have not found application in practice due to the technical complexity of processing the powder with a small amount of plasticizer and changes in the chemical composition of the finished material [3].

The workpieces most uniform in material properties are obtained by pressing powders and coke pitch in isostats, which make it possible to apply volumetric compression of the pressed body with equal force [4]. In the Russian production of carbon products, the method has not yet been applied due to the high cost of hydrostats and the need to create special calcining equipment. The disadvantage of the isostatic pressing method is the limitation of the size of the pressed blanks. The known maximum length of the resulting workpieces is 1250 mm. The complexity of the technological process for producing structural graphites with a high level of properties at satisfactory yield on technological stages is largely due to differences in the formation of micro- and macrostructures of the material from filler coke and coke obtained by heating the binder [5].

The technology of hot pressing of coke pitch masses in connection with the above requires to obtain high strength and density of multiple impregnations.

A significant disadvantage of artificial graphites obtained by cold pressing of powders is their reduced thermal conductivity and high modulus of elasticity, which leads to a decrease in their heat resistance, estimated, for example, by the Kingeri criterion:

, где

where

σ is the strength;

λ is the thermal conductivity;

E is the modulus of elasticity;

α is the coefficient of thermal expansion.

Closest to the invention in technical essence is a known method for producing carbon-graphite materials, including calcining a mixture of coke filler with coal tar pitch, grinding the calcined material, mixing the resulting powder with pitch, pressing blanks from hot coke cake mass, firing and graphitization [6]. The disadvantage of this method is its complexity caused by multioperation. In particular, in this method, after obtaining a filler mixture with coal tar pitch, cakes are pressed from it, which are then burned in a tunnel oven, then crushed, crushed and mixed [6].

An object of the invention is to eliminate the disadvantages of the known methods of analogues and prototype, improving the quality of the obtained high-density heat-resistant fine-grained and medium-grained graphites and products from them, increasing the yield of billets, reducing production costs.

The solution to the technical problem is achieved by the fact that in the known method for producing carbon-graphite materials, including calcining a mixture of coke filler with coal tar pitch, grinding the calcined material, mixing the obtained powder with pitch, pressing the blanks from hot coke cake mass, firing and graphitizing them, before calcining the initial coke- the filler is impregnated with coal tar pitch, calcination is carried out at a temperature of 1100 ° C, and grinding to a fineness of not more than 1.25 mm with a particle content of not more than 0.07 mm is not less than e 50% and pressing is carried out by extrusion through the mouthpiece or in the mold.

The solution of this technical problem is also achieved by the fact that upon receipt of fine-grained carbon-graphite materials, the calcined material is crushed to a powder containing particles with a particle size of up to 0.5 mm.

The solution to the technical problem is also achieved by the fact that after firing the preforms are impregnated with coal tar pitch and re-fired.

The invention consists in the following. The initial coke-filler is impregnated with pitch and calcined in this form in order to stabilize its properties, which allows to completely eliminate or reduce its ability to shrink during firing in the composition of the fired preforms, which leads to their destruction. To provide the possibility of obtaining long billets, the coke-filler compacted by impregnation is ground after calcination to a powder containing grains up to 0.5 mm or 1.25 mm in size, which allows long billets to be pressed by extrusion of a hot mass through the mouthpiece. The material obtained in this way has a combination of the best properties of materials obtained by hot and cold pressing, which ensures its higher heat resistance.

The invention is illustrated by the following examples.

Example 1. High-density fine-grained carbon-graphite blanks with a length of 1200 mm and a cross section of 280 * 280 mm were made by preparing a press mass from crushed (fineness less than 0.5 mm) impregnated and calcined petroleum coke and coal tar pitch. The pitch content in the press was 21%. A press mass heated to 80 ° C was pressed through the mouthpiece and, at the exit from the mouthpiece, billets 1200 mm long were cut. The blanks were calcined and graphitized using conventional technology. The resulting preforms had a density of 1.78 g / cm ³ , compressive strength - 51.3 MPa, bending strength - 26.4 MPa. When machining blanks to obtain shaped products marriage was not detected.

Example 2. High-density medium-grain carbon-graphite blanks with a length of 1200 mm and a cross section of 280 * 280 mm were made by preparing a press mass from crushed (fineness less than 1.25 mm) impregnated and calcined petroleum coke and coal tar pitch. The pitch content in the press was 18%. A press mass heated to 85 ° С was pressed through the mouthpiece and, at the exit from the mouthpiece, billets 1200 mm long were cut. The blanks were calcined and graphitized using conventional technology. The resulting preforms had a density of 1.76 g / cm ³ , compressive strength of 47.6 MPa, and bending strength of 21.2 MPa. When machining blanks to obtain shaped products marriage was not detected.

Example 3. High-density fine-grained carbon-graphite blanks with a length of 1200 mm and a cross section of 280 * 280 mm were made by preparing a press mass from crushed (fineness less than 0.5 mm) impregnated and calcined petroleum coke and coal tar pitch. The pitch content in the press was 21%. A press mass heated to 80 ° C was pressed through the mouthpiece and, at the exit from the mouthpiece, billets 1200 mm long were cut. The billets were fired, impregnated with coal tar pitch, again fired, impregnated a second time with pitch and fired for the third time, after which they were graphitized by conventional technology. The resulting preforms had a density of 1.80 g / cm ³ , compressive strength of 70.4 MPa, bending strength of 32.6 MPa. When machining blanks to obtain shaped products marriage was not detected. The characteristics of the products obtained by the prototype method were: density - 1.65 g / cm ³ , compressive strength - 30.0 MPa, bending strength - 16 MPa. When machining products, the yield of marriage was 14%.

Thus, the manufacture of high-density fine-grained and medium-grained carbon-graphite products in accordance with the invention provides an increase in their quality, minimizes the yield of rejects and the cost of products.

Sources of information

1. B.C. Veselovsky. Coal and carbon-graphite structural materials. M. "Science". 1966, p. 106-112, 136-140, 184-196.

2. A.S. USSR No. 1189806, class C 01 B 31/04, 1985

3. RF patent No. 2145584, class C 04 B 35/66, 2000

4. Balshin M.Yu. The scientific basis of powder metallurgy and fiber metallurgy. M. "Metallurgy", 1972, 365 pp.

5. Lobastov N.A., Deev A.N., Bagrov G.N., Mokhova N.S. About the reasons for the different strengths of graphites based on non-calcined and calcined cokes. Sat Graphite-based structural materials. M. Metallurgy, 1972, No. 7, pp. 41-46.

6. A.S. USSR No. 1130928 (Cl. H 01 R 43/12), 1982

Claims (3)

1. A method of producing carbon-graphite materials, including calcining a mixture of coke-filler with coal tar pitch, grinding the calcined material, mixing the resulting powder with pitch, pressing the blanks from hot coke pitch, firing and graphitizing, characterized in that before calcining the initial coke- the filler is impregnated with coal tar pitch, calcination is carried out at a temperature of 1100 ° C, and grinding is done to a particle size of not more than 1.25 mm with a particle content of not more than 0.07 mm not less than 50% and pressing is carried out by extrusion AI through the mouthpiece or in the mold. 2. The method according to claim 1, characterized in that upon receipt of fine-grained carbon-graphite materials, the calcined material is ground to a powder containing particles with a particle size of up to 0.5 mm 3. The method according to claim 1 or 2, characterized in that after firing the preforms are impregnated with coal tar pitch and fired again.