Composition for main-pump bearing bush and preparation method therefor

Abstract

The present application belongs to the the field of nuclear technology, and specifically relates to a composition for a main-pump bearing bush and a preparation method therefor. The composition comprises three phases, i.e., graphite, SiC and free Si, wherein the content of the graphite is greater than or equal to 40 wt%; the content of SiC is greater than or equal to 40 wt%; and the content of the free Si is less than or equal to 20 wt%. A siliconized graphite material comprising the formulation components can meet the basic operation requirements of a main pump with a relatively large axial load.

Description

The present application belongs to the field of nuclear technology and specifically relates to a composition for a main pump bearing shell and a preparation method thereof. Background of Art The nuclear main pump has characteristics such as safety, no leakage, smooth operation, low noise, self-lubrication, and compact structure. The bearing shell is a vulnerable component of the main pump, and its quality plays an important role in the stability, reliability, and service life of the pump. At present, there are three main types of materials used in thrust bearings of the main pumps of nuclear power units: metallic materials, polymers, and ceramic non-metallic materials. Among them, alloy bearings have high mechanical strength and corrosion resistance but low hardness and poor wear resistance, and require oil lubrication and thus are not suitable for the current high-temperature and high-speed operating environment. Polymer materials are good wear-resistant materials for bearings because they are lightweight, insulating, wear-resistant, and corrosion-resistant. For example, engineering plastics and polyetheretherketone (PEEK) have good wear resistance and mechanical properties, but their physical properties cannot meet the requirements for the use of high specific-pressure nuclear main pump thrust bearing shells. Bearings of ceramic non-metallic materials such as siliconized graphite and pure graphite have the characteristics of high thermal conductivity, wear resistance and chemical corrosion resistance, but their mechanical strength is relatively low and they are not suitable for main pumps with large axial loads. Summary of the Invention An object of the present application is to provide a composition for a main pump bearing shell and a preparation method thereof, so as to solve the problem in the prior art that the materials currently used in the thrust bearings of the main pumps of nuclear power units cannot meet the requirements. The following technical solutions are provided to achieve the object of the present application. One Example of the present application provides a composition for a main pump bearing shell, comprising graphite, SiC and free Si in three phases; wherein the graphite is included in an amount of greater than or equal to 40 wt%; the SiC is included in an amount ofgreater than or equal to 40 wt%; and the free Si is included in an amount of less than or equal to 20 wt%. Optionally, the graphite is in the form of particles with a diameter of 100 to 500 pm. Optionally, the graphite is included in an amount of 40 wt% to 45 wt%. Optionally, the SiC is included in an amount of 40 wt% to 50 wt%. Optionally, the free Si is included in an amount of 10 wt% to 20 wt%. Optionally, the composition has a material density of 2.5 to 2.8 g / cm3. Optionally, the composition has a friction coefficient of less than 0.03. Optionally, the composition has a compressive strength of greater than 500 MPa. The other Example of the present application provides a method for preparing any of the composition for a main pump bearing shell provided in the above Examples, including: preparing the composition by a vacuum reactive melt infiltration process. Optionally, the method further includes: controlling the content of graphite in raw materials so that the proportion of graphite in the composition is greater than 40 wt%; controlling the siliconization reaction time so that the proportion of SiC in the composition is greater than 40 wt%; and controlling the Si removal step at a high temperature so that the proportion of free Si in the composition is less than 20wt%. The beneficial technical effects of the present application are as follows. The Examples of the present application provides a composition for a main pump bearing shell and a preparation method thereof. It belongs to ceramic graphite-based composite materials and is used in the field of friction materials. The effect of the content of three phases of graphite, SiC, and free Si on the properties of siliconized graphite materials is determined by preparing a series of siliconized graphite materials with different compositional formulations via comprehensive performance testing and practical application verification. When the content of three phase components in the siliconized graphite satisfies the graphite proportion of greater than or equal to 40 wt%, the SiC proportion of greater than or equal to 40 wt% and the free Si proportion of less than or equal to 20 wt%, the siliconized graphite material satisfying the compositional formulations can reach a density of 2.5 to 2.8 g / cm3, a friction coefficient of less than 0.03, and a compressive strength of greater than 500 MPa. It has the properties of self-lubrication derived from graphite and high strength and chemical corrosion resistance derived from silicon carbide, and can meet the basic operation requirements of a main pump with a large axial load. Detailed Description of Embodiments In order to allow those skilled in the art to better understand the present application, the technical solutions in the Examples of the present application will be clearly and completely described below in conjunction with the drawings in the Examples of the present application. Obviously, the Examples described below are only part but not all of the Examples of the present application. Based on the Examples described in the present application, all other Examples obtained by those skilled in the art without any inventive work are within the scope of protection of the present application. In order to solve the existing technical problems, the present inventors discovered during research that the siliconized graphite material after siliconization has the properties of both self-lubrication derived from graphite and high strength and chemical corrosion resistance derived from silicon carbide, and is applicable in the operating environment of a main pump with a high axial load. At present, there is no mature siliconized graphite bearing product in China. Based on the above fact, in order to explain the above-mentioned advantages of the present application clearly and in detail, the specific embodiments of the present application will be described below in conjunction with the accompanying drawings. An Example of the present application provides a composition for a main pump bearing shell comprising three phases of graphite, SiC and free Si; wherein the graphite is included in an amount of greater than or equal to 40 wt%; the SiC is included in an amount of greater than or equal to 40 wt%; and the free Si is included in an amount of less than or equal to 20 wt%, which fills up the remaining space of the composition. At this time, the material has a density of 2.5 to 2.8 g / cm3, a friction coefficient of less than 0.03, and a compressive strength of greater than 500 MPa. The bearing shell made of this composition can meet the basic operating requirements of a nuclear main pump. It should be noted that this composition is siliconized graphite material. As a composite material, it mainly contains three phases of SiC, graphite and free Si. The final performance is closely related to the proportion of the three components. Graphite has the functions of heat conduction and lubrication. If the content thereof is too low, the friction coefficient of the material will increase and the self-lubricating effect cannot be produced, and if the content thereof is too high, the mechanical properties of the material will decrease. SiC has high hardness and high strength, and plays a role in structural support and wear reduction, but if the content thereof is too high, the friction coefficient will increase. Free Si is a residual phase during the preparation and needs to be controlled to a low level, otherwise the material wear will increase and the corrosion resistance will decrease. When the graphite proportion is controlled to greater than or equal to 40 wt%, the SiC proportion is controlled to greater than or equal to 40 wt%, and the content of free Si is controlled to less than or equal to 20 wt%, the material has a density of 2.5 to 2.8 g / cm3, a friction coefficient of less than 0.03, and a compressive strength of greater than 500 MPa, and the bearing shell made of this composition can meet the basic operating requirements of a nuclear main pump. Example 1 The content of graphite was 40 wt%, the content of SiC phase was 45 wt%, and the content of free Si was 15 wt%. The sample had a density of 2.63g / cm3, a friction coefficient of 0.025, and a compressive strength of 560 MPa. Example 2 The content of three phases was adjusted on the basis of Example 1, so that the content of graphite was 42 wt%, the content of SiC phase was 47 wt%, and the content of free Si was 11 wt%. The resultant siliconized graphite had a density of 2.62 g / cm3, a friction coefficient of 0.029, and a compressive strength of 600 MPa. Example 3 The content of three phases was adjusted on the basis of Example 1, so that the content of graphite was 45 wt%, the content of SiC phase was 45 wt%, and the content of free Si was 10 wt%. The resultant siliconized graphite had a density of 2.60 g / cm3, a friction coefficient of 0.020, and a compressive strength of 530 MPa. Example 4 The content of three phases was adjusted on the basis of Example 1, so that the content of graphite was 45 wt%, the content of SiC phase was 40 wt%, and the content of free Si was 15 wt%. The resultant siliconized graphite had a density of 2.59 g / cm3, a friction coefficient of 0.03, a porosity of 0.1, and a compressive strength of 505 MPa. Example 5 The content of three phases was adjusted on the basis of Example 1, so that the content of graphite was 40 wt%, the content of SiC phase was 40 wt%, and the content of free Si was 20 wt%. The resultant siliconized graphite had a density of 2.54 g / cm3, a friction coefficient of 0.028, a porosity of 0.05, and a compressive strength of 515 MPa. Example 6 The particle size of graphite particles was screened and the graphite particles having a particle size of 105 pm was selected, so that the content of graphite was 40 wt%, the content of SiC phase was 45 wt%, and the content of free Si was 15 wt% on the basis of Example 1. The siliconized graphite had a density of 2.58 g / cm3, a friction coefficient of 0.03, a porosity of 0.1, and a compressive strength of 510 MPa. Example 7 The particle size of graphite particles was screened and the graphite particles having a particle size of 495 pm was selected, so that the content of graphite was 40 wt%, the content of SiC phase was 45 wt%, and the content of free Si was 15 wt%on the basis of Example 1. The siliconized graphite had a density of 2.60 g / cm3, a friction coefficient of 0.029, a porosity of 0.9, and a compressive strength of 520 MPa. Based on the composition for a main pump bearing shell provided in the Examples above, the Examples of the present application further provide a method for preparing any of the composition for a main pump bearing shell provided in the Examples. The method for preparing the composition for a main pump bearing shell provided in the Examples of the present application includes: preparing the composition by a vacuum reactive melt infiltration process. It should be noted that large-size siliconized graphite materials are prone to crack for two main reasons: cracking of the porous graphite green body and cracking during the siliconization process. Therefore, it is necessary to study the green body forming mechanism to avoid the cracking of the green body caused by rapid volume changes during pyrolysis and shrinkage of carbon raw materials, and at the same time, to study the melt infiltration mechanism to determine the reaction sites and reaction rates of C and Si during the siliconization process to avoid the collapse and cracking of the green body caused by excessive reaction of the skeleton of the porous carbon green body. In addition, the study on the infiltration mechanism will also help control the proportion and distribution uniformity of each phase in the siliconized graphite material, which is a guarantee for the material performance and the stability of the preparation process. (I) Mixing process In order to ensure that the raw materials for preparing a full-size siliconized graphite material bearing shell are evenly mixed, it is necessary to optimize the material formula, extend the mixing time, and adjust the mixer rotation rate to ensure that the components are fully and evenly mixed. (II) Molding process The granulated material is molded to obtain a green body with a certain strength. (III) Debonding process The green body obtained by molding is debonded to obtain a porous green body with uniform pore distribution. (IV) Siliconization process In order to ensure the infiltration of the components into the green body during the siliconization process, the silicon particle disposal method and the siliconization time need to be gradually adjusted. In some possible implementations of the Examples of the present application, the method further includes: controlling the content of graphite in raw materials so that the proportion of graphite in the composition is greater than 40 wt%; controlling the siliconization reaction time so that the proportion of SiC in the composition is greater than 40 wt%; controlling the Si removal step at high temperature so that the proportion of free Si in the composition is less than 20wt%. The present application has been described in detail above in conjunction with the accompanying drawings and the Examples. However, the present application is not limited to the Examples. Various modifications can be made without departing from the gist of the present application within the scope of knowledge of those of ordinary skill in the art. Contents not elaborated in detail in the present application can be implemented by combining with the prior art.

Claims

1. A composition for a main pump bearing shell, comprising graphite, SiC and free Si in three phases;wherein the graphite is included in an amount of greater than or equal to 40 wt%; the SiC is included in an amount of greater than or equal to 40 wt%; and the free Si is included in an amount of less than or equal to 20 wt%.

2. The composition for a main pump bearing shell according to claim 1, wherein the graphite is in the form of particles with a diameter of 100 to 500 pm.

3. The composition for a main pump bearing shell according to claim 1, wherein the graphite is included in an amount of 40 wt% to 45 wt%.

4. The composition for a main pump bearing shell according to claim 1, wherein the SiC is included in an amount of 40 wt% to 50 wt%.

5. The composition for a main pump bearing shell according to claim 1, wherein the free Si is included in an amount of 10 wt% to 20 wt%.

6. The composition for a main pump bearing shell according to any of claims 1 to 5, wherein the composition has a material density of 2.5 to 2.8 g / cm3.

7. The composition for a main pump bearing shell according to any of claims 1 to 5, wherein the composition has a friction coefficient of less than 0.03.

8. The composition for a main pump bearing shell according to any of claims 1 to 5, wherein the composition has a compressive strength of greater than 500 MPa.

9. A method for preparing the composition for a main pump bearing shell according to any of claims 1 to 8, including:preparing the composition by a vacuum reactive melt infiltration process.5 10. The method for preparing the composition for a main pump bearing shellaccording to claim 9, further including:controlling the content of graphite in raw materials so that the proportion of graphite in the composition is greater than 40 wt%;controlling the siliconization reaction time so that the proportion of SiC in the 10 composition is greater than 40 wt%; andcontrolling the Si removal step at a high temperature so thatthe proportion of free Si in the composition is less than 20wt%.