A method of making large size isostatically pressed graphite articles

Abstract

The application discloses a method for preparing large-size isostatic pressing graphite products, and relates to the technical field of large-size graphite product preparation, and aims at solving the problem that the baking time of large-size isostatic pressing graphite products needs to be greatly prolonged in order to reduce cracking; the method comprises the following steps: crushing and grinding part of raw materials to obtain fine powder M, and crushing another part of the raw materials to obtain coarse particles N; the fine powder M is added into modified coal pitch to be kneaded into paste a; the fine powder M and the coarse particles N are respectively kneaded with modified coal pitch in two proportions to be kneaded into paste b and paste c; the paste a is ground into powder a; the paste b and the paste c are respectively ground into fine powder and coarse particles, and the fine powder and the coarse particles of the paste b and the paste c are mixed in proportion to be mixed into powder b and powder c; a core-shell structure is formed from the inside to the outside in a forming and charging area, the inner layer is filled with the powder c, the outer layer is filled with the powder a, and the transition layer is filled with a mixture of the powder a and the powder b, and then the mixture is pressed to be formed; and the production cycle of the large-size graphite products can be shortened under the premise of ensuring the qualified rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of large-scale graphite product preparation, in particular to a method for preparing large-scale isostatic pressing graphite product. BACKGROUND

[0002] The isostatic pressing graphite material has good electric conductivity and heat conductivity, and has good high-temperature strength, good corrosion resistance, self-lubrication, high bulk density, easy processing and a series of characteristics, and is closely connected with today's high-tech frontier technology, and has been widely used in various departments and industries of the national economy, especially in the photovoltaic and semiconductor fields. The hot field of single crystal silicon straight pulling is rapidly upgraded from the original 28 inches to 36 and 40 inches, and large-scale isostatic pressing graphite cylinders are needed for processing and manufacturing heat preservation barrels and heaters.

[0003] These requirements have high requirements on the size of the isostatic pressing graphite. The 40-inch single crystal hot field requires isostatic pressing graphite cylinders with a size of Ф1200*1000mm to improve its production efficiency. However, the larger the size of the isostatic pressing graphite product, the more difficult its preparation process, the higher the cost, and the lower the qualified rate of the finished product. In order to ensure that the baking process does not crack, the baking time of the large-scale green body with fine structure needs to be greatly extended to reduce the number of cracks. The baking time of the green body with a diameter of more than one meter is nearly two months, which greatly increases the production cost. Generally speaking, the finer the particles of the graphite product, the larger the size, and the longer the baking time required. Because of its large volume, there is a large temperature difference between the surface and the inside of the green body, resulting in inconsistent shrinkage inside and outside, and cracks are easily generated during baking.

[0004] Publication No. CN102502603A discloses a production process of large-scale fine-particle isotropic isostatic pressing high-purity graphite, which comprises the following steps: pre-preparation of powder; pre-preparation of sheet; pre-pressing of green body; pre-baking of broken sheet; pre-processing of broken coke powder; sheet processing; green body pressing; baking and impregnation. The graphitized product overcomes the shortcomings of the graphite product produced by the traditional production process, such as large particle size, low mechanical performance and physical and chemical indicators, poor isotropy, uneven and low bulk density, and small isostatic pressing graphite size. In order to reduce crack generation and improve the yield, the body is baked in a metal crucible to prevent temperature fluctuations from causing too large volume shrinkage difference. However, this method does not solve the problem of long baking time. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing large-scale isostatic pressing graphite product to solve the problem of long baking time of large-scale isostatic pressing graphite product to reduce cracking.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a method for preparing large-scale isostatic pressing graphite product, comprising the following steps:

[0007] Step S1: crushing and grinding a part of petroleum coke or pitch coke to obtain fine powder M, and crushing and grinding another part of petroleum coke or pitch coke to obtain coarse particles N;

[0008] Step S2: adding fine powder M into a kneader, adding modified coal pitch, and kneading to obtain paste a;

[0009] Step S3: adding fine powder M and coarse particles N into the kneader according to a first ratio, adding modified coal pitch, and kneading to obtain paste b; adding fine powder M and coarse particles N into the kneader according to a second ratio, adding modified coal pitch, and kneading to obtain paste c; the proportion of coarse particles N in the second ratio is higher than that in the first ratio;

[0010] Step S4: grinding paste a into powder a with a particle size larger than that of fine powder M; grinding paste b and paste c into fine powder and coarse particles respectively, mixing the fine powder and coarse particles obtained by grinding paste b according to a ratio to obtain powder b, and mixing the fine powder and coarse particles obtained by grinding paste c according to a ratio to obtain powder c;

[0011] Step S5: dividing the forming loading area into a core-shell structure of an inner layer, a transition layer and an outer layer from inside to outside, loading powder c in the inner layer, loading powder a in the outer layer, and loading a mixture of powder a and powder b in the transition layer; and then pressing to form.

[0012] Preferably, in step S1, the D50 of fine powder M is 6-20 μm, and the particle size of coarse particles N is 0.05-4 mm, and the D50 is 0.5-2.0 mm.

[0013] Preferably, in step S3, the first ratio is the mass ratio of fine powder M and coarse particles N being 1:0.5-10, and the second ratio is the ratio of fine powder M and coarse particles N being 1:1-20.

[0014] Preferably, in steps S2 and S3, the modified coal pitch is all medium temperature coal pitch, the softening temperature is 80-95 ℃, the kneading temperature is 140-220 ℃, and the kneading time is 80-140 min.

[0015] Preferably, in step S4, the particle size and D50 of powder a are 2-4 times those of fine powder M.

[0016] Preferably, in step S4, the fine powder and coarse particles obtained by grinding paste b are mixed according to a first ratio to obtain powder b, and the fine powder and coarse particles obtained by grinding paste c are mixed according to a second ratio to obtain powder c.

[0017] Preferably, in step S4, the particle size of the fine powder obtained by grinding paste b and c is the same as that of powder a, and the particle size and D50 of the coarse particles obtained by grinding paste b and c are the same as those of coarse particles N.

[0018] Preferably, in step S5, the mixing mass ratio of the powder a and the powder b of the transition layer is 1:0.1-5.

[0019] Preferably, in step S5, the volume ratio of the inner layer, the transition layer and the outer layer of the press-formed core-shell structure is 0.5-10:1:2-20.

[0020] Preferably, the above method comprises step S6: after forming, a graphite calcined product is obtained through primary calcination, and then a graphite product is obtained through impregnation, secondary calcination and graphitization.

[0021] Compared with the prior art, the method has the following beneficial effects:

[0022] The method for preparing the large-size isostatic pressing graphite product divides the large-size isostatic pressing graphite into an inner layer, a transition layer and an outer layer, and fills the inner layer with a coarse particle structure, the transition layer with a buffer structure of coarse and fine particles, and the outer layer with a superfine particle structure; the inner layer adopts the coarse particle structure, so that the thermal stress resistance is greatly improved, the heating rate during calcination and graphitization can be increased, and the production cycle can be effectively shortened; the transition layer is used to buffer the thermal stress caused by the different particles of the inner layer and the outer layer during calcination, so as to reduce the possibility of cracking, thereby solving the problem of low qualified rate of the large-size graphite product after the production cycle is shortened. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Fig. 1 is a schematic view of a main section of a forming structure according to the present application;

[0024] Figure 2 Fig. 2 is a schematic view of a top section of the forming structure shown in Fig. 1. Figure 1 DETAILED DESCRIPTION

[0025] A method for preparing a large-size isostatic pressing graphite product, comprising the following steps:

[0026] Step S1: a part of petroleum coke or pitch coke is crushed and ground to obtain fine powder M, which can be obtained by using an air jet mill or the like; for reference, the D50 of the fine powder M can be 6-20 μm; another part of the petroleum coke or the pitch coke is crushed and ground to obtain coarse particles N, which can be obtained by using a crusher or the like; for reference, the particle size of the coarse particles N can be 0.05-4 mm, and the D50 can be 0.5-2.0 mm;

[0027] Step S2: the fine powder M is added into a kneader, and modified coal pitch is added to obtain paste a through kneading;

[0028] ​Step S3: add fine powder M and coarse particles N into the kneader according to the first proportion, add modified coal pitch, and knead to obtain paste b; add fine powder M and coarse particles N into the kneader according to the second proportion, add modified coal pitch, and knead to obtain paste c; specifically, for example, the first proportion is that the mass ratio of fine powder M and coarse particles N is 1:0.5-10, and the second proportion is that the ratio of fine powder M and coarse particles N is 1:1-20, but it should be noted that the proportion of coarse particles N in the second proportion is higher than that in the first proportion;

[0029] In addition, in the above steps S2 and S3, the modified coal pitch can be medium-temperature coal pitch, and the softening temperature can be preferably 80-95℃, the kneading temperature is generally higher than the softening temperature, which can be further preferably 140-220℃, and the kneading time can be further preferably 80-140min.

[0030] Step S4: grind paste a into powder a with a particle size greater than fine powder M, and the particle size depends on the particle size of the raw material fine powder M used to make paste a, and in general, the particle size and D50 of powder a are preferably 2-4 times that of fine powder M; grind paste b and paste c into fine powder and coarse particles respectively, mix the fine powder and coarse particles obtained by grinding paste b to obtain powder b, and mix the fine powder and coarse particles obtained by grinding paste c to obtain powder c; wherein the particle size of the fine powder obtained by grinding paste b and paste c can be further the same as the particle size of powder a, and the particle size and D50 of the coarse particles obtained by grinding paste b and paste c can be further the same as those of coarse particles N; in addition, the mixing ratio of the fine powder and coarse particles of the two powders can be the same as the ratio used in step S3, that is, the fine powder and coarse particles obtained by grinding paste b are mixed according to the first proportion to obtain powder b, and the fine powder and coarse particles obtained by grinding paste c are mixed according to the second proportion to obtain powder c;

[0031] Step S5: refer to Figure 1 and 2 The forming loading area (generally cylindrical or cubic) is divided into an inner layer, a transition layer and an outer layer from the inside to the outside in a core-shell structure; the inner layer is loaded with powder c, the outer layer is loaded with powder a, and the transition layer is loaded with a mixture of powder a and powder b, and the mixing mass ratio of the two can be further set to 1:0.1-5; after loading, the core-shell structure is pressed and formed; further, the volume ratio of the inner layer, the transition layer and the outer layer of the pressed and formed core-shell structure is preferably 0.5-10:1:2-20.

[0032] The specific loading method of the forming loading area can be that a layer of powder a is first loaded at the bottom, a transition layer outer rubber sleeve is then placed in the middle, powder a is continuously loaded at the outer periphery of the outer rubber sleeve, a layer of mixed powder a and powder b is loaded at the bottom of the inner part, a transition layer inner rubber sleeve lower than the outer rubber sleeve is placed in the middle at the upper end of the mixed powder, the mixed powder is continuously loaded at the outer periphery of the inner rubber sleeve, the inner part is filled with powder c, the inner rubber sleeve is taken out, the mixed powder is continuously filled in the outer rubber sleeve, the outer rubber sleeve is taken out, and then powder a is continuously filled. Figure 1 and 2 The specific method does not affect the core scheme of the present application.

[0033] After forming, the subsequent processes in the prior art can be used for continuous processing, generally including baking, graphitization, etc., for example, after one baking, a graphitized baked product is obtained, and then after impregnation, two baking and graphitization, a graphite product is obtained. The subsequent processes are not the content required to be protected by the present application, and a large number of public documents in the field can be referred to, and thus will not be described in detail.

[0034] The technical scheme of the present application is further described below in combination with embodiments.

[0035] The hot field of the Czochralski silicon single crystal in the photovoltaic industry is rapidly upgraded from the original 28 inches to 36 and 40 inches, and large-size isostatic pressing graphite cylinder materials are needed for processing and manufacturing heat preservation barrels, heaters, etc. Only the large-size ultra-fine structure crucible of the outer layer of the graphite product is needed, and the inner part of the graphite product can only be made into a small crucible with low added value. However, the preparation of such large-size ultra-fine structure isostatic pressing graphite product is particularly difficult (especially for a diameter of more than 1.2 m), the production cycle is long, at least more than half a year, and the qualified rate is low. Therefore, the method of the present application is used to improve this:

[0036] Embodiment 1

[0037] Raw material grinding: 1000 kg of pitch coke is broken and ground by air flow grinding, and the D50 of the fine powder M is 6 μm. A crusher is used to grind 400 kg of pitch coke into coarse particles N with a particle size D50 of 1.0 mm;

[0038] Mixing: the ground fine powder M is added to the mixing machine, and then the modified coal pitch with a softening point of 80℃ is added. The mixing temperature is 180℃, and after mixing for 120 min, the paste a with certain plasticity is prepared. The fine powder M and the coarse particles N are mixed with the modified coal pitch with a softening point of 80℃ at a ratio of 1:2 and 1:4 respectively, and the paste b and the paste c are obtained after mixing.

[0039] Secondary grinding: the paste a is ground by a rod pin crusher to a fine powder of paste a with D50 of 18 μm, the pastes b and c are ground to a fine powder of paste b with D50 of 18 μm and a coarse powder of paste c with D50 of 1.0 mm, respectively, and then each is mixed thoroughly, and the ratio of the fine powder to the coarse powder is 1:2 and 1:4, respectively.

[0040] Isostatic pressing: the cylindrical loading area is divided into an inner layer, an outer layer and an intermediate transition layer, the inner layer is loaded with the powder of paste c, and the outer layer is loaded with the powder of paste a; for the intermediate transition layer, a mixture of the fine powder of paste a and the powder of paste b is loaded, the ratio being 2:1, and the product diameter is 1.2 m,

[0041] Subsequent processes: after the loaded material is vacuumized, isostatic pressing is performed, and after the pressing, the volume ratio of the inner layer, the outer layer and the intermediate transition layer is 5:10:1. Primary baking is performed to obtain a graphite baked product, impregnation, secondary baking and graphitization are performed to obtain a graphite product.

[0042] Example 2

[0043] 1) Raw material grinding: 1000 kg of petroleum coke is ground by an air flow mill, and the fine powder M has a D50 of 12 μm; 600 kg of petroleum coke is ground by a crusher to a coarse particle N with a particle size D50 of 0.5 mm;

[0044] 2) Mixing: the ground fine powder M is added to a mixer, and then modified coal pitch with a softening point of 90 °C is added, the mixing temperature is 220 °C, and after mixing for 80 min, a paste a with certain plasticity is prepared; the fine powder M and the coarse particle N are mixed in a ratio of 1:10 and 1:20, respectively, and then modified coal pitch with a softening point of 90 °C is added, and pastes b and c are obtained after mixing.

[0045] 3) Secondary grinding: the paste a is ground by a rod pin crusher to a fine powder of paste a with D50 of 30 μm, the pastes b and c are ground to a fine powder of paste b with D50 of 30 μm and a coarse powder of paste c with D50 of 0.5 mm, respectively, and then each is mixed thoroughly, and the ratio of the fine powder to the coarse powder is 1:10 and 1:20, respectively.

[0046] 4) Isostatic pressing: the cylindrical loading area is divided into an inner layer, an outer layer and an intermediate transition layer, the inner layer is loaded with the powder of paste c, and the outer layer is loaded with the powder of paste a; for the intermediate transition layer, a mixture of the fine powder of paste a and the powder of paste b is loaded, the ratio being 1:5, and the product diameter is 1.5 m,

[0047] 5) Subsequent processes: after the loaded material is vacuumized, isostatic pressing is performed, and after the pressing, the volume ratio of the inner layer, the outer layer and the intermediate transition layer is 10:20:1. Primary baking is performed to obtain a graphite baked product, impregnation, secondary baking and graphitization are performed to obtain a graphite product.

[0048] Example 3

[0049] 1) Raw material grinding: 1000 kg of pitch coke is broken and ground by air flow mill, the D50 of the fine powder M is 20 μm, 200 kg of pitch coke is ground into coarse particles N with a particle size D50 of 2.0 mm by a crusher;

[0050] 2) Mixing: the ground fine powder M is added to the mixing machine, and then the modified coal pitch with a softening point of 95℃ is added, the mixing temperature is 220℃, after mixing for 140 min, the paste a with certain plasticity is prepared; the fine powder M and the coarse particles N are mixed according to the ratio of 1:0.5 and 1:2 respectively, and then the modified coal pitch with a softening point of 95℃ is added, and the paste b and the paste c are obtained after mixing;

[0051] 3) Secondary grinding: the paste a is ground into the paste a fine powder with a D50 of 45 μm by a rod pin crusher, the pastes b and c are ground into the fine paste powder with a D50 of 45 μm and the coarse particle paste with a D50 of 2.0 mm respectively, and then they are fully mixed, the ratio of the fine powder to the coarse particle is 1:0.5 and 1:2 respectively.

[0052] 4) Isostatic pressing: the cylindrical loading area is divided into inner layer, outer layer and intermediate transition layer, the paste c powder is loaded in the inner layer area, and the paste a powder is loaded in the outer layer area; for the intermediate transition layer, the mixture of the paste a fine powder and the paste b powder is loaded, the ratio is 1:1, the product diameter is 0.8 m,

[0053] 5) Subsequent process: the loaded material is vacuumized and then isostatic pressing is carried out, the volume ratio of the inner layer, the outer layer and the intermediate transition layer after forming is 1:10:1. The graphite calcined product is obtained by primary calcination, impregnation and secondary calcination, and the graphite product is obtained by graphitization.

[0054] Example 4

[0055] 1) Raw material grinding: 1000 kg of pitch coke is broken and ground by air flow mill, the D50 of the fine powder M is 16 μm, 300 kg of pitch coke is ground into coarse particles N with a particle size D50 of 1.5 mm by a crusher;

[0056] 2) Mixing: the ground fine powder M is added to the mixing machine, and then the modified coal pitch with a softening point of 85℃ is added, the mixing temperature is 140℃, after mixing for 100 min, the paste a with certain plasticity is prepared; the fine powder M and the coarse particles N are mixed according to the ratio of 1:5 and 1:15 respectively, and then the modified coal pitch with a softening point of 85℃ is added, and the paste b and the paste c are obtained after mixing;

[0057] 3) Secondary grinding: the paste a is ground into the paste a fine powder with a D50 of 40 μm by a rod pin crusher, the pastes b and c are ground into the fine paste powder with a D50 of 40 μm and the coarse particle paste with a D50 of 1.5 mm respectively, and then they are fully mixed, the ratio of the fine powder to the coarse particle is 1:5 and 1:15 respectively.

[0058] 4) isostatic pressing loading: the cylindrical loading area is divided into inner layer, outer layer and intermediate transition layer, the inner layer area is loaded with paste c powder, the outer layer area is loaded with paste a powder; for the intermediate transition layer, the mixed material of paste a fine powder and paste b powder is loaded, the ratio is 1:0.2, the product diameter is 1.2m,

[0059] 5) subsequent process: after the loaded material is vacuumized, isostatic pressing is carried out, the volume ratio of the inner layer, the outer layer and the intermediate transition layer after forming is 2:8:1. After primary roasting, impregnation, secondary roasting and graphitization, the graphite product is obtained.

[0060] Comparative Example 1

[0061] The paste a prepared in Example 1 is filled in the inner layer, the outer layer and the intermediate transition layer, and other conditions remain unchanged, and the product diameter is still 1.2m.

[0062] Comparative Example 2

[0063] The paste b in Example 1 is removed, only the inner layer and the outer layer are present, and the intermediate transition layer is not present, and other conditions remain unchanged, and the product diameter is still 1.2m.

[0064] Table 1 Production cycle and qualified rate of examples and comparative examples

[0065] Production cycle / day Yield / % Example 1 114 93.6 Example 2 136 92.1 Example 3 79 98.6 Example 4 87 95.7 Comparative Example 1 162 71.2 Comparative Example 2 114 82.4

[0066] Generally speaking, the finer the particle size of the formula of the graphite product, the larger the specification, the longer the production cycle, the lower the qualified rate, and the easier the product to crack and crack.

[0067] It can be seen from the combination of Example 1 and Comparative Example 1 that the production cycle of Example 1 is greatly reduced, and the qualified rate is effectively improved. It can be seen from the combination of Example 1 and Comparative Example 2 that the addition of the intermediate transition layer according to the method of the application can effectively improve the qualified rate of the product.

[0068] The above is only a preferred embodiment of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements easily thought of by those skilled in the art within the technical range disclosed by the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be limited by the protection scope defined by the claims.

[0069] The details not described in the present application are the known technology of those skilled in the art.

Claims

1. A method for preparing large-format isostatically pressed graphite products, characterized in that, Includes the following steps: Step S1: Crush and grind a portion of petroleum coke or pitch coke to obtain fine powder M, and crush and grind another portion of petroleum coke or pitch coke to obtain coarse particles N. Step S2: Add fine powder M to a kneader, add modified coal tar pitch, and knead to obtain paste a; Step S3: Add fine powder M and coarse particles N to a mixer in the first ratio, add modified coal tar pitch, and mix to obtain paste b; add fine powder M and coarse particles N to a mixer in the second ratio, add modified coal tar pitch, and mix to obtain paste c; the proportion of coarse particles N in the second ratio is higher than that in the first ratio. Step S4: Grind paste a into powder a with a particle size larger than fine powder M; grind paste b and paste c into fine powder and coarse particles respectively; mix the fine powder and coarse particles of paste b in a certain proportion to obtain powder b; mix the fine powder and coarse particles of paste c in a certain proportion to obtain powder c. Step S5: Divide the molding and filling area into a core-shell structure from the inside out, consisting of an inner layer, a transition layer, and an outer layer. The inner layer is filled with powder c, the outer layer with powder a, and the transition layer with a mixture of powder a and powder b. After filling, press and shape the material. In step S1, the fine powder M has a D50 of 6–20 µm, and the coarse particles N have a particle size of 0.05–4 mm and a D50 of 0.5–2.0 mm. In step S3, the first ratio is the mass ratio of fine powder M to coarse particles N of 1:0.5 to 10, and the second ratio is the mass ratio of fine powder M to coarse particles N of 1:1 to 20. In step S4, the particle size and D50 of powder a are 2 to 4 times that of fine powder M; In step S4, the fine powder and coarse particles of paste b are mixed in the first ratio to obtain powder b; the fine powder and coarse particles of paste c are mixed in the second ratio to obtain powder c. In step S4, the fine powder particles ground from pastes b and c have the same particle size as powder a, and the coarse particles ground from pastes b and c have the same particle size and D50 as coarse particles N. In step S5, the mixing mass ratio of powder a and powder b in the transition layer is 1:0.1 to 5. In step S5, the volume ratio of the inner layer, transition layer, and outer layer of the pressed core-shell structure is 0.5–10:1:2–20.

2. The method for preparing large-format isostatically pressed graphite products according to claim 1, characterized in that: In steps S2 and S3, the modified coal tar pitch is medium-temperature coal tar pitch with a softening temperature of 80–95°C, a kneading temperature of 140–220°C, and a kneading time of 80–140 min.

3. The method for preparing large-format isostatically pressed graphite products according to claim 1, characterized in that, It also includes step S6: after molding, the graphite is first fired to obtain a graphite product, and then impregnated, fired a second time, and graphitized to obtain a graphite product.

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