RU2016844C1 - Method of reinforced graphite making - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: carbonaceous or carbon-containing fiber (diameter is 7-10 microns, length is 260-400 microns) is added at the mixing of coke with pitch at concentration 1.5-2.4% by mass. Carbon fiber must be impregnated with pitch preliminary. Properties of material prepared: values of bending, compression and expansion strength are 438, 900 and 275 kgs/cm², respectively. EFFECT: improved method of reinforced graphite making. 2 cl, 1 tbl

Description

 The invention relates to a technology for the production of structural carbon materials, in particular, the manufacture of graphite used as structural materials in high-temperature processes, antifriction, in semiconductor technology and other fields.

In terms of technical nature, the closest to the proposed method is [1], which involves mixing carbon fiber material with ground carbon filler and pitch, pressing from a mixture of preforms, and then firing and graphitizing them. Moreover, the carbon fiber material is coated before mixing anthracene coal tar fraction having a boiling point ^of 320-360 C and then graphitizing the preform is impregnated with pitch and optionally calcined and graphitizable.

 This method allows to increase the physicomechanical characteristics of the material only if four additional operations are introduced: two impregnations with pitch and two calcinations, which lengthens the production cycle of the final product by at least 800 hours. In addition, even if all the requirements are met, the physicomechanical characteristics do not reach world class for materials of this class.

 It should be noted that the value of the coke residue from the anthracene fraction of coal tar after firing is significantly inferior to the coke residue of the pitch. This significantly reduces the strength characteristics of the prototype compared with the proposed method.

 The aim of the invention is to improve the physico-mechanical properties and increase the isotropy of the material.

 The goal is achieved in that the method for producing reinforced graphite involves mixing crushed carbon filler with fibrous carbon material, pressing the resulting mass and heat treatment of the obtained preforms, and when mixing coke with pitch, a reinforcing fiber with a diameter of 7-10 microns and a length of 260-400 microns in amount of 1 5-2.4 wt.%.

As the reinforcing component is a mixture of wool waste (GOST 5679-85) with a high-temperature coal-tar pitch (TU 14-6-84-72) in 1: 1 ratio by weight, the pre-heat-treated at 500 ° ^C. The fiber diameter is 7-10 microns , length from 260 to 400 microns in an amount of from 1.5 to 2.4 wt.%. Then, after mixing at 115-120 ^{° C} for 25-30 minutes, the resulting paste was charged into the matrix at a temperature of walls 110-115 ^C and pressed at a specific pressure of 10-20 MPa / cm ² and held at a predetermined pressure for 1 min. The obtained preforms are loaded into metal containers with carbon filling from granules of calcined coke with a size of 1-5 mm and loaded into a chamber of a gas kiln. The duration of heat treatment is 200-400 hours, depending on the dimensions of workpieces, the maximum temperature of 920 ^{° C} and holding at this temperature for 10-20 hours. After cooling to 60 ° ^C and then the preform is discharged graphitizable Acheson type furnace in resistance to a temperature not lower than ^about 2600 C at a heating rate of 45-50 ^C / h. After switching off the furnace and cooling the core ^to 400 ^° C graphitized preform is discharged and sent for machining.

 The introduction of the reinforcing fiber into the coke pitch composition forms a material structure during heat treatment that is sufficiently resistant to compressive, tensile and bending forces. This is achieved by fiber reinforcement of microvolumes of the material. An important factor is the impregnation of the fibers with pitch, which provides strong coke bridges between the coke particles and the fibers, which increases the strength of graphite.

 The use of fibers with a diameter of less than 7 μm is impractical, since the surface of the filler increases sharply, for the wetting of which it is necessary to introduce an additional amount of binder into the composition, which causes cracks during heat treatment due to the intensification of the emission of volatiles.

 The use of fibers with a diameter of more than 10 μm increases the relaxation of the molded preforms and reduces the contact area of the mass of material with reinforcing elements, which leads to a decrease in properties. The relaxation of the workpieces causes the formation of microcracks and, as a result, a decrease in the strength characteristics of the final product.

 The use of fibers with a length of less than 260 microns is impractical, since their reinforcing effect is reduced, and more than 400 microns - causes the appearance of areas with a heterogeneous structure.

 The introduction of a fiber of less than 1.5 wt.% Does not give a significant improvement in physical and mechanical characteristics, and more than 2.4 wt.% - causes the formation of microcracks due to the increased elasticity of the fibers, which reduces the properties.

 Thus, the application of this method without the introduction of additional technological operations allows to obtain a reinforced material with higher and more stable properties compared to known analogues.

PRI me R 1. Non-calcined petroleum coke brand KNPS (GOST 22898-78) crushed and dispersed into fractions. The preheated to 125 ^C. kneader with Z-shaped blades were charged medium temperature coal tar pitch (Brand A, GOST 10200-83) in an amount of 24.0 wt% and after its melting and heating to ¹²⁰ ° C poured filler -. Uncalcined petroleum coke and carbon fiber. The fiber used is obtained by crushing carbon fiber waste in a vibratory mill (GOST 28005-88) to the size of individual fibers with a diameter of mainly 8 μm (80%) and a length of about 300 μm (80%).

The mass was stirred for 20 min, a carbon fiber is added in an amount of 2 wt.% And stirred for another 10 min until the mass temperature of 120 ° ^C.

 The composition of the charge: coal tar pitch 24 wt.% Coke fraction with particle sizes: from 1000 to 500 microns 24%, from 500 to 100 microns 25%, from 100 to 10 microns 25%, carbon fiber 2%.

The finished weight at ¹²⁰ ° C was charged in a 150 mm diameter die, preheated to ¹¹⁰ ° C and pressed at a surface pressure of 15 MPa / cm ² exposure 1 minute under pressure. The thus-obtained billet diameter of 150 and 180 mm in an industrial gas fired furnaces in the carbon filling chamber at 920 ° ^C Exposure time at the maximum temperature was 20 hours, and the rate of temperature rise of 6 ° ^C / hr. Unloading of container blanks is carried out after they have cooled to 60 ° ^C.

Sintered blanks graphitizable in an industrial furnace at a maximum temperature ^of 2600 C in a chlorine environment, the average heating rate was 45 ^C / h.

 The remaining examples NN 2-5 are made in accordance with example N 1 and differ in diameter, fiber length, etc. (see table).

PRI me R 6. As a reinforcing element used a mixture of waste technical wool (GOST 5679-85) with high-temperature coal tar pitch (TU 14-6-84-72), pre-heat treated at 500 ^about C, in the form of particles with sizes mainly 350 μm (80%).

The particles of the reinforcing component was prepared in the following way: in a preheated 300 ^{° C} kneader capacity of 10 liters was charged with 1.5 kg of a pitch and after its melting and the temperature reached 280 ^{° C} was charged with 0.3 kg increments of every 5 min technical wool in a total amount 1.5 kg After loading the last part, mix it, cool and crush to a piece size of less than 5 mm. Then the crushed material is loaded into a VM-10 vibrating mill in an amount of 2 kg and dispersed for 5 minutes, unloaded and scattered to separate the fibers from 5 to 400 microns in length, mainly 350 microns (80%). The specified fraction is heat treated at 500 ^about C and then used as a reinforcing component.

The preheated to 125 ^C. kneader pitch pre-charged, and after its melting and heating to 120 ^{° C} was charged with the remaining components of the batch and stirred for 20 minutes to achieve a mass temperature of 120 ° ^C. The resulting mass is pressed and heat treated similarly to Example 1.

The composition of the charge: coal tar pitch 26 wt.%, Fraction with particle sizes from 1000 to 500 microns 23%
500 to 100 μm 23%
100 to 10 μm 23%
reinforcing component 5%.

The composition of the particles of the reinforcing fiber component is 40 wt.% After heat treatment at ⁵⁰⁰ ° C, e.g. the fiber content in the charge of 2 wt.%.

 Analyzing the results, we can conclude that the most acceptable way to obtain reinforced graphite is example 1, where compared with the prototype, the tensile strength of graphite in compression, tension, bending is higher by 62, 83, 41 %%, respectively, and the anisotropy coefficient is 5 times less. At the same time, the electrical resistance decreases by 25%. However, the density of graphite in the prototype, in comparison with the proposed method, is slightly higher, which is explained by the introduction of four additional operations into the technological process: 2 impregnations with pitch and 2 firing.

 The increase in the strength characteristics of graphite and their stabilization can lengthen the service life of products in the process of their work.

Claims (2)

 1. METHOD FOR PRODUCING REINFORCED GRAPHITE, including mixing crushed carbon filler with fibrous carbon material and pitch, compressing the resulting mass and subsequent firing and graphitization of the obtained blanks, characterized in that, in order to improve the physicomechanical properties of the material and increase its isotropy, as fibrous carbon material using carbon or carbon-containing fiber with a diameter of 7 to 10 microns and a length of 260 to 400 microns in an amount of 1.5 to 2.4 wt.%.  2. The method according to claim 1, characterized in that the carbon fiber is pre-impregnated with coal tar pitch.

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