SU768756A1 - Method of preparing carbon articles - Google Patents

Description

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An additional difference is that a mixture of calcined petroleum coke with natural graphite is used as a carbon filler. Before pre-pressing, the composition is crushed to a fraction less than 0.8 mm and pre-pressing is carried out at a specific pressure of 350-450 KGS / CM2.

Repeated pressing of the workpieces in the perpendicular to the original direction leads to the movement of mass and rotation of the filler grains in the workpiece. Such displacement will be the greater, the higher the pressure of repeated pressing. As the pressure increases, the anisotropic properties (the difference in properties along the direction of the initial pressing and perpendicular to it) will decrease. With a re-pressure to initial ratio of 1.5, the properties of the material in mutually perpendicular directions become the same, i.e., the anisotropy disappears. A further increase in this ratio leads to the appearance of a new anisotropy of properties, which is the inverse of the initial one. Therefore, it is not advisable to increase the re-pressing pressure by more than 1.5 times.

A noticeable decrease in the initial anisotropy of the properties is observed at a re-pressing pressure that is at least 1.4 times higher than the initial pressure. Thus, the ratio of the re-compaction pressure to the initial pressure should be kept in the range 1.4-1.5.

The proposed method allows to eliminate the anisotropy of the properties of materials obtained by extrusion through a mouthpiece. For this, such materials are also subjected to repeated pressing in the matrix in the direction perpendicular to the direction of the first pressing.

Example. The proposed method was tested on an material of the type APB, which was a press, which is a press powder for cold pressing of articles in a mold. The composition contains 65 wt. % calcined petroleum coke (brand KPPS) in the form of particles with sizes less than 0.09 mm, 5 weight. % of natural graphite of the same size and 30% weight. medium temperature coal tar pitch (). A mixture of these components is prepared in a mixing machine with, cooled and crushed in a ball mill 11: e, then sieved through a sieve with a cell size of 0.8 mm. The resulting press powder contains fractions with a particle size of 0.8-0.5 mm 5-7%, 0.5-0.3 mm 12-16%, 0.3-0.09 mm 27-33%, mea 0 , 09 mm - about 50%.

Press powder is pre-pressed in a square section matrix of 20x20 mm at a specific pressure of 400 kg / cm. The pressed preparations of a cubic form under 768756

They extrude in the same matrix in the direction perpendicular to the direction of preliminary pressing at a specific pressure of 400, 440, 480, 520, 560, 600 and 640 kgf / cm2. Both preliminary and repeated pressing are performed at the same rate of pressure increase for all the blanks without exception. This speed was 20 kgf / cm per second.

Then these blanks are placed in a graphite crucible and burned in an industrial kiln to a temperature of 1300 ° C for 380 hours. The rate of temperature rise is: up to 104 hours; 400- 600 - 90; 600-800 - 70; 800-1000 - 50; 1000-1300 - 40; holding at 1300 ° С - 26. Total - 380 hours.

Calcined coke with a grain size of 0.15-0.5 mm is used as a charge for billets. Due to this, a reducing atmosphere was maintained during the firing in the crucible. In the kiln, during firing, a vacuum of 2–6 mm of water column is maintained.

The baked blanks are subjected to graphitization in the industrial electrical resistance. A graphite crucible with coke overfilling (grain size 0.15-0.5 mm) is placed in the graphitization furnace of the workpiece, therefore the graphitization of the samples also occurs under reducing atmosphere. The pressure in the graphitization furnace is atmospheric. The rate of temperature rise corresponds to the following schedule: up to 1000 ° C - 20 hours; 1000-1500 ° - 3; 1500-1800 ° - 3; 1800-2000 ° - 4; 2000-220 ° - 4; 2200-2500 ° - 6. Total - 40 hours. Upon reaching a temperature of 2500 ° C, the supply of electricity to the furnace is stopped, and the furnace is cooled for 4 days.

After graphitization, 2 samples are cut out from each blank No. 1–7 to measure the specific electrical resistance and the coefficient of thermal expansion of the material in two mutually perpendicular directions coinciding with the directions of the first and repeated pressing of the blanks.

Table 1 presents the physico-mechanical characteristics of the products. Obtained according to the proposed method (blanks 5-6), with a pressure reduction value during the preliminary pressing and re-pressing, going beyond the proposed limits (samples 1-4) and the prototype (form: 8).

In table 2, the results of anisotropy of the thermal expansion coefficient and specific electric power {) resistance for samples, yl asaHHbix in table 1. From the data in tables, it follows that irpH is the predicted ratio of specific pressures of side-perpendicular pressing (1.4-1.5) is reached

Table 1

Claims (2)

Claim 1. A method of producing carbon products, including preliminary press 5 pressing a composition based on carbon filler with pitch into billets, re-pressing the billets in a direction perpendicular to the pre-pressing direction with a specific pressure exceeding the pre-pressing pressure, and subsequent heat treatment of the billets, characterized in that, in order to reduce the anisotropy of the electrical resistance and coefficient thermal expansion of products, the specific pressure of the second pressing is 1.4-1.5 times higher than the pressure of preliminary pressing. 2. The method according to π. 1, characterized in that the mixture of calcined petroleum coke with natural graphite is used as a carbon filler, before preliminary pressing, the composition is crushed to a fraction of less than 0.8 mm and 25 preliminary pressing 'is carried out at a specific pressure of 350-450 kgf / cm ² .