CN109400162B

CN109400162B - Graphite for electric spark machining and preparation method thereof

Info

Publication number: CN109400162B
Application number: CN201811523024.XA
Authority: CN
Inventors: 何成林; 刘金平; 王新华
Original assignee: Hunan Changyu Science And Technology Development Co ltd
Current assignee: Hunan Changyu Science And Technology Development Co ltd
Priority date: 2018-12-13
Filing date: 2018-12-13
Publication date: 2021-08-03
Anticipated expiration: 2038-12-13
Also published as: CN109400162A

Abstract

The invention discloses graphite for electric spark machining, which is mainly prepared from the following raw materials in parts by mass: 45 to 55 percent of raw petroleum coke, 15 to 25 percent of graphite powder and 25 to 35 percent of modified asphalt. The invention also discloses a preparation method of the graphite for electric spark machining. The raw petroleum coke is used as the raw material of the graphite for electric spark machining for the first time, the cost of the raw petroleum coke is one third of that of calcined coke and one eighth of that of intermediate phase carbon microspheres, and the product prepared by blending the raw petroleum coke and the artificial graphite can meet the performance requirement of the graphite material for electric spark machining by only one-time roasting and one-time impregnation and one-time graphitization, thereby greatly shortening the production period and improving the productivity and the profit of enterprises.

Description

Graphite for electric spark machining and preparation method thereof

Technical Field

The invention belongs to the field of graphite material preparation, and particularly relates to graphite for electric spark machining and a preparation method thereof.

Background

In the process of electric spark machining, a tool electrode is a very important part, and at present, a copper electrode and a graphite electrode are frequently selected as tool electrodes in the field of electric spark machining. The melting point of graphite is as high as 3650 ℃, while the melting point of copper is 1083 ℃, so that the graphite electrode can bear a larger current setting condition, and when the scaling of the discharge area and the electrode size is larger, the superiority of high-efficiency rough machining of the graphite material is more remarkable. The heat conductivity coefficient of graphite is one third of that of copper, and the heat energy generated in the discharge process can effectively remove metal materials, so that the processing efficiency is higher than that of a copper electrode in medium and rough processing, and the discharge processing speed of the graphite electrode is 1.5-2 times faster than that of the whole copper electrode under the correct use condition according to the processing experience; therefore, graphite electrodes are widely used in electric discharge machining.

At present, most of raw materials used by domestic manufacturers for producing graphite materials for electric spark machining are calcined coke (calcined petroleum coke, calcined pitch coke or mixed coke of the calcined petroleum coke and the calcined pitch coke), mesocarbon microbeads are also used, but the cost of the mesocarbon microbeads is too high, so that the mesocarbon microbeads are not suitable for mass production, and the production cost is high for enterprises. The product made of calcined coke needs to be subjected to secondary impregnation and tertiary roasting, and the performance of the product subjected to primary graphitization treatment can meet the performance requirement of the graphite material for electric spark machining.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the defects and shortcomings in the background art and provide graphite for electric spark machining and a preparation method thereof.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

the graphite for electric spark machining is mainly prepared from the following raw materials in percentage by mass: 45 to 55 percent of raw petroleum coke, 15 to 25 percent of graphite powder and 25 to 35 percent of modified asphalt.

The graphite for electric discharge machining is preferably such that the particle size D50 of the raw petroleum coke is 10 to 12 μm; the particle size D50 of the graphite powder is 11-13 μm.

Preferably, the graphite for electric spark machining has the moisture content of less than or equal to 0.17 percent after being dried, the ash content of less than or equal to 0.22 percent, the volatile component of less than or equal to 11 percent and the sulfur content of less than or equal to 0.39 percent; the water content of the graphite powder is less than or equal to 0.11 percent, and the ash content is less than or equal to 0.12 percent; the softening point temperature of the modified asphalt is 118 ℃, and toluene insoluble matter (TI) is less than or equal to 29 percent. More preferably, the graphite powder is selected from graphite powders obtained by crushing graphite of the company.

According to the invention, raw petroleum coke is used as a raw material of graphite for electric spark machining for the first time, has high volatile content, has self-sintering shrinkage performance during roasting, and greatly improves the volume density and strength of the product; however, because the raw petroleum coke has high volatile content and large shrinkage during roasting, different internal stresses can be generated at each part of the product, and the product is easy to crack, therefore, the invention ensures the yield of the graphite for electric spark machining by introducing the graphite powder and mixing the graphite powder with the raw petroleum coke according to a certain proportion.

As a general inventive concept, the present invention also provides a method for preparing the graphite for electric discharge machining, comprising the steps of:

(1) drying raw petroleum coke, grinding the dried raw petroleum coke and graphite powder into powder by an airflow mill, dry-mixing according to the proportion, adding modified asphalt for wet mixing, taking paste out of a pot, and then rolling;

(2) carrying out secondary grinding on the sheet stock obtained in the step (1);

(3) and (3) sequentially carrying out isostatic pressing, roasting, dipping and graphitization on the powder obtained in the step (2) to obtain the graphite for electric spark machining.

In the preparation method, preferably, in the step (1), the dry mixing time is 55-70min, and the temperature of the dry mixed powder is not lower than 150 ℃; the temperature of the paste taken out of the pot is not lower than 180 ℃.

In the preparation method, preferably, in the step (2), the content of the secondarily milled material passing through a 200-mesh screen is over 85%.

In the above production method, the pressure for isostatic pressing in the step (3) is preferably 100 to 120 MPa. The volume density of the green compact obtained after isostatic compaction was 1.31g/cm³～1.40g/cm³(ii) a The bulk density of the green compact should not be too high, because the green petroleum coke has self-sintering property, and the volume of the product is greatly shrunk during roasting, which easily causes cracking of the product.

In the preparation method, preferably, in the step (3), the roasting process includes a temperature raising stage, a temperature keeping stage and a cooling stage.

Preferably, in the step (3), the impregnation process includes preheating the roasted product at 220-250 ℃ for 6-8 h, vacuumizing the preheated product in an impregnation tank with a vacuum degree of 0.098-0.1 MPa and a vacuum maintaining time of 80-100 min, and adding impregnant asphalt to perform high-pressure impregnation at a pressure of 1.5-1.8 MPa and a pressure maintaining time of 6.5-8.5 h.

In the above preparation method, preferably, in the step (3), the graphitization process is that the impregnated product is directly heated to 2800-3000 ℃ by an acheson furnace, and then cooled by power failure.

Compared with the prior art, the invention has the advantages that:

(1) the raw petroleum coke is used as the raw material of the graphite for electric spark machining for the first time, the cost of the raw petroleum coke is one third of that of calcined coke and one eighth of that of intermediate phase carbon microspheres, and the product prepared by blending the raw petroleum coke and the artificial graphite can meet the performance requirement of the graphite material for electric spark machining by only one-time roasting and one-time impregnation and one-time graphitization, thereby greatly shortening the production period and improving the productivity and the profit of enterprises.

(2) The raw petroleum coke is selected as the raw material, the raw petroleum coke has the self-sintering characteristic, the uniform shrinkage characteristic can be always kept in the heat treatment process, the graphite powder can play a role of a skeleton, the performance is stable, the graphite prepared by mixing the raw petroleum coke powder with the raw petroleum coke powder can keep the structure stable, the product is not easy to crack in the heat treatment process, and the finished product rate of the product is improved to be more than 85%.

(3) The performance of the graphite material prepared by the invention meets the requirements of the graphite electrode for electric spark machining, and compared with the conventional process, the process at least reduces one-time impregnation and two-time roasting when the same performance is achieved, shortens the production period of the product, saves the production cost for a company, and improves the economic benefit.

Drawings

FIG. 1 is a flowchart of a process for producing graphite for electric discharge machining in example 1 of the present invention.

Detailed Description

In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

Example 1:

the graphite for electric spark machining is mainly prepared from the following raw materials in percentage by mass: 50% of Hongkong raw petroleum coke, 20% of graphite powder and 30% of modified asphalt.

The preparation method of graphite for electric discharge machining according to the embodiment is shown in fig. 1, and comprises the following steps:

(1) drying raw petroleum coke, and performing jet milling on the dried raw petroleum coke to obtain raw petroleum coke powder with the particle size D50 of 10-12 mu m, wherein the raw petroleum coke powder contains 0.17 percent of water, 0.22 percent of ash, 11 percent of volatile matter and 0.39 percent of sulfur;

the graphite crushed processing material of the company is aerated into graphite powder, the moisture content of the graphite powder is 0.11 percent, and the ash content is less than or equal to 0.12 percent;

(2) putting the raw petroleum coke powder and the graphite powder into a double-stirring-blade mixing and kneading pot for dry mixing (the shape of the stirring blade is a Z-shaped stirring blade) for 60min, wherein the temperature of the mixed material after dry mixing is not lower than 150 ℃; adding binder modified asphalt (the softening point temperature is 118 ℃, and the toluene is not contained by 29%) for wet mixing, and wet mixing for 70min (the pot-out temperature of the paste after wet mixing is 170-190 ℃;

(3) and (3) carrying out double-roller sheet rolling treatment on the paste taken out of the pot, wherein the thickness of the sheet stock is required to be as follows: the thickness of the primary sheet material is 2 mm-3 mm, the thickness of the secondary sheet material is less than or equal to 2mm, and the size (length and width) of the sheet material is less than or equal to 30mm and 30 mm;

(4) secondarily grinding the sheet materials to make the content of the ground materials passing through a 200-mesh screen exceed 85%;

(5) and (3) carrying out isostatic compaction (with the pressure of 110MPa) on the material obtained in the step (4) to obtain a green body, wherein the green body has the weight of 115kg and the size of: 623mm 562mm 244mm, green bulk density: 1.35g/cm³；

(6) Roasting the green body according to the roasting curve of table 1, wherein the weight of the roasted product is as follows: 100.9kg, actual size: 555 x 502 x 220, the bulk density of the monolith measured as: 1.65g/cm³Compared with green compact, the volume shrinkage of the product after roasting is 39.4%, the volume density is improved by 22.2%, and the self-burning of the green petroleum coke product during roasting is reflectedA junction shrinkage property;

attached table 1 firing curve

This period of time	Set temperature (. degree. C.)	℃/h
			0	30	-
34	200	5
			20	250	2.5
50	300	1
			80	350	0.625
300	500	0.5
			80	550	0.625
60	600	0.833333
			100	700	1
66	800	1.51515
			50	900	2
48	900	0
			24	900	0
50	800	－2
			50	700	－2
50	600	－2
			50	500	－2
50	400	－2
			50	300	－2
50	200	－2
			50	100	－2
200	50	－0.25

(7) Preheating the roasted product at 235 ℃ for 7h, vacuumizing the preheated product in an impregnation tank at the vacuum degree of 0.098-0.1 MPa for 90min, introducing impregnant asphalt for high-pressure impregnation at the pressure of 1.7MPa for 7h, and measuring the impregnation weight gain of the product to be 12.9 percent after high-pressure impregnation;

(8) feeding the dipped product into an Acheson graphitizing furnace, heating to 2800 ℃, and finally cooling along with the furnace to obtain graphite for electric spark machining; the yield of the graphite reaches 90 percent.

The weight of the product after graphitization is as follows: 100.7kg, actual size: 538 × 490 × 210, the bulk density of the monolith measured is: 1.82g/cm³The volume shrinkage of the graphitized article was 9.7%, and the bulk density was increased as compared with the one-shot article10.3 percent, and shows that the raw petroleum coke product also has great self-sintering shrinkage performance during graphitization.

The graphitized product obtained by the preparation is machined into a sample (5 groups), and the basic physicochemical indexes (average value) of the graphitized product are detected according to industry related standards (GB/T2457-2009, GB/T1431-2009, GB/T3074.1-2008, JB/T8133.4-1999, GB/T242530-2009, GB/T3074.4-2003 and GB/T245729-2009) respectively, wherein the volume density is 1.81g/cm³The compressive strength is as follows: 112MPa, breaking strength: 58MPa, Shore hardness: 57, resistivity: 13.5. mu. omega. m, coefficient of thermal expansion (room temperature-600 ℃): 5.1X 10^-6/° c, porosity: 13.8 percent.

Claims

1. The preparation method of the graphite for electric spark machining is characterized in that the graphite for electric spark machining is mainly prepared from the following raw materials in percentage by mass: 45 to 55 percent of raw petroleum coke, 15 to 25 percent of graphite powder and 25 to 35 percent of modified asphalt, and the preparation method comprises the following steps:

(3) and (3) sequentially carrying out isostatic pressing, primary roasting, primary dipping and primary graphitization on the powder obtained in the step (2) to obtain the graphite for electric spark machining.

2. The preparation method according to claim 1, wherein in the step (1), the dry mixing time is 55-70min, and the temperature of the powder after dry mixing is not lower than 150 ℃; the temperature of the paste taken out of the pot is not lower than 180 ℃.

3. The method of claim 1, wherein in step (2), the content of the secondarily milled material passing through a 200-mesh screen is more than 85%.

4. The production method according to claim 1, wherein in the step (3), the isostatic compaction pressure is 100 to 120 MPa.

5. The method according to claim 1, wherein in the step (3), the roasting process comprises a temperature raising stage, a temperature holding stage and a cooling stage.

6. The preparation method according to claim 1, wherein in the step (3), the impregnation process comprises preheating the roasted product at a temperature of 220 ℃ to 250 ℃ for 6h to 8h, vacuumizing the preheated product in an impregnation tank at a vacuum degree of 0.098MPa to 0.1MPa for a vacuum maintaining time of 80min to 100min, and adding impregnant pitch for high-pressure impregnation at a pressure of 1.5MPa to 1.8MPa for 6.5h to 8.5 h.

7. The method according to claim 1, wherein in the step (3), the graphitization is performed by heating the impregnated product directly through an Acheson furnace to 2800 ℃ to 3000 ℃ and then cooling the product without power.

8. The method of claim 1, wherein the green petroleum coke has a particle size D50 of 10 to 12 μ ι η; the particle size D50 of the graphite powder is 11-13 μm.

9. The method of claim 1, wherein the green petroleum coke has a post-bake moisture content of 0.17% or less, an ash content of 0.22% or less, a volatiles content of 11% or less, and a sulfur content of 0.39% or less; the water content of the graphite powder is less than or equal to 0.11 percent, and the ash content is less than or equal to 0.12 percent; the softening point temperature of the modified asphalt is 118 ℃, and toluene insoluble matter (TI) is less than or equal to 29 percent.