阅读说明：本技术 一种碳化硅陶瓷管制备方法 (Preparation method of silicon carbide ceramic tube ) 是由 邬国平 程雨浩 于明亮 程海林 沈赟 熊礼俊 谢方民 于 2019-11-29 设计创作，主要内容包括：本发明属于碳化硅陶瓷材料制备技术领域,具体为一种高致密性,高加工精度的碳化硅陶瓷管制备方法。所述碳化硅陶瓷管制品组织均匀、具有高致密性,高同轴度。制备方法步骤包括：(1)配置粉末(2)装置调整(3)粉末装填(4)冷等静压成型(5)抽芯截边整理(6)高温烧结。本发明解决了碳化硅陶瓷管的加工变形问题,所制碳化硅陶瓷管适用于核工业等高精度环境。(The invention belongs to the technical field of preparation of silicon carbide ceramic materials, and particularly relates to a preparation method of a silicon carbide ceramic tube with high compactness and high processing precision. The silicon carbide ceramic tube product has uniform structure, high compactness and high coaxiality. The preparation method comprises the following steps: (1) preparing powder (2), adjusting (3) powder filling, (4) cold isostatic pressing, (5) core-pulling edge-cutting finishing, (6) high-temperature sintering. The invention solves the problem of processing deformation of the silicon carbide ceramic tube, and the prepared silicon carbide ceramic tube is suitable for high-precision environments such as nuclear industry and the like.)

1. A preparation method of a silicon carbide ceramic tube is characterized by comprising the following steps: the method comprises the following steps:

(1) preparing ceramic raw material powder: preparing silicon carbide powder, a sintering aid, an adhesive, a plasticizer, a dispersant and a lubricant into filling powder;

(2) device adjustment: the rubber skin sleeve mold is arranged in a hanging basket, the centering sleeve is clamped into the rubber skin sleeve mold, the mandrel penetrates through the centering sleeve and is arranged in the rubber skin sleeve mold, the lower end cover is clamped into the mold and the mandrel is clamped by the clamp; the outer wall of the centering sleeve is provided with a spiral winding sheet;

(3) powder filling: the upper centering funnel is clamped into a leather sheath, a positioning cylinder is opened to fix a rubber sheath mold, a pull rod hole is fixed to a pulling plate, powder is added, the pulling plate is moved upwards to a specified distance firstly, quantitative powder is added, the centering sleeve is rotated, the added powder is extruded downwards by means of spiral reverse thrust of a spiral winding sheet to be uniformly distributed, the pulling plate is controlled to move upwards to a specified distance continuously, then feeding is continued, the centering sleeve is rotated again, the process is repeated until the centering sleeve completely takes out the rubber sheath mold, an upper end cover of the rubber sheath mold is sealed and clamped by a clamp;

(4) cold-static isostatic pressing: placing the hanging basket into isostatic pressing equipment by using a crane, adjusting the pressure to 110-115MPa, pressing the silicon carbide ceramic tube, keeping the pressure for 10 seconds after the pressure reaches the highest pressure, and opening the equipment to lift the hanging basket out after the pressure begins to be relieved to 0 MPa;

(5) core-pulling trimming finishing: taking out the upper end cover, firstly, drawing out the core rod in the pipe blank, taking out the lower end cover, slowly taking out the formed pipe from the rubber sleeve, and cutting off the part of the pipe with the length of 50mm which does not meet the requirement by using a lathe;

(6) and (3) high-temperature sintering: sintering the pressed and formed pipe blank in a high-temperature sintering furnace, wherein the sintering temperature is 1900-2300 ℃, the temperature is kept for 2-4 hours, the heating rate is 1-10 ℃/min, and the atmosphere is argon.

2. The method for preparing a silicon carbide ceramic tube according to claim 1, wherein: the outer side wall of the spiral winding sheet of the centering sleeve is in clearance fit with the inner wall of the rubber sleeve mold.

3. The method for preparing a silicon carbide ceramic tube according to claim 1, wherein: and (4) the spiral winding piece of the centering sleeve is arranged clockwise from bottom to top, and the rotating direction in the step (3) is anticlockwise.

4. The method for preparing a silicon carbide ceramic tube according to claim 3, wherein: and (4) the ceramic powder added in the step (3) falls down along the top surface of the spiral winding sheet of the centering sleeve.

5. The method for preparing a silicon carbide ceramic tube according to claim 1, wherein: and (3) a vibrator is arranged at the bottom of the rubber leather sleeve die, the vibrator is started before the material is fed for the second time in the step (3) or when the centering sleeve rotates, and the vibration emitted by the vibrator is transmitted to the rubber leather sleeve die, so that the fed material is uniformly vibrated.

6. The method for preparing a silicon carbide ceramic tube according to claim 2, wherein: the top end of the centering sleeve is connected with a ball screw, the ball screw is in threaded connection with a screw nut, the screw nut is rotatably connected to the support, the screw nut is connected with a servo motor through a coupler, and the servo motor rotates forwards or reversely and drives the ball screw to ascend or descend spirally through the screw nut.

Technical Field

The invention relates to the technical field of engineering ceramic materials, in particular to a preparation method of a silicon carbide ceramic tube.

Background

The silicon carbide ceramic has the characteristics of high thermal conductivity, small expansion coefficient, small volume density, high hardness, good wear resistance, high temperature resistance, good chemical stability, high strength and the like, so that the silicon carbide ceramic is suitable for high-temperature, corrosive and oxidative environments. The heat exchange tube of the heat exchanger in the nuclear industry has extremely high requirements on high temperature resistance, corrosion resistance and corrosion resistance of the tube in the working process, and the silicon carbide can work in the environments of oxidation, corrosive atmosphere and radiation for a long time at high temperature due to the excellent characteristics of the silicon carbide, so the silicon carbide is commonly used for manufacturing the heat exchange tube of the heat exchanger in the nuclear industry.

The engineering reliability of silicon carbide ceramics depends to a large extent on the size and the number of defects therein, the existence of which is directly related to the structural nonuniformity of the formed green body, which leads to more serious nonuniformity of the structure of the sintered product. Therefore, it is desirable that the forming method and the sintering method should minimize the number and size of defects in the material and eliminate or reduce the density gradient. According to the existing preparation method of the silicon carbide ceramic tube, the product has the defects of low coaxiality, low machining precision and the like, and the high-precision requirement in the nuclear industry is difficult to completely meet.

The silicon carbide ceramic forming industry mainly comprises the following methods:

(1) dry pressure forming: the method of press-molding powder filled in a mold by using mechanical pressure or oil pressure is a good molding method for a product having a large yield and a low requirement for shape, but it is very important and difficult to prepare and select raw materials, and it has been difficult to obtain a uniform density, flowability and releasability of the raw materials, and design of the mold have been the focus of research.

(2) Slurry casting and forming: in general, the powder is dispersed in water to form a slurry, and the slurry is poured into a porous mold made of gypsum or the like, and the mold is molded after absorbing water. The method has the advantages of capability of forming and processing products with complex shapes compared with the traditional method, high mould cost, easy cracking after drying after forming, low efficiency and high cost.

(3) Casting reaction sintering: the mixed blank of silicon carbide and carbon is heated, the carbon in the blank reacts with gaseous silicon or liquid silicon to generate porous and pure silicon carbide or silicon carbide with pores filled with excessive silicon, but the reaction sintering process is difficult to control, the phenomenon of sintering impermeability of dead skin exists, the correct selection of the proportional relationship between silicon carbide and carbon in the mixture is important, and the form and the property of the carbon are also key factors influencing the sintering impermeability, and further improvement is needed. Furthermore, pressureless sintering is adopted, submicron silicon carbide powder is used as a raw material, sintering is carried out under the condition of no pressure, carbon and boron are generally added as sintering aids, rare earth elements are also added as sintering aids, sintering is carried out under the protection of inert gas or in vacuum at the temperature of not less than 2000 ℃, during the sintering process, polytype conversion and grain growth of silicon carbide can occur, the process is difficult to control reasonable sintering temperature, and the selection of the sintering aids is very critical.

(4) Extrusion molding and sintering: the silicon carbide powder is added with water, methyl fiber and other organic binding agent to make it have certain plasticity, and then forced by piston screw to make it pass through die under the action of certain force, so that it is a forming method for protecting die form. Since the cross-sectional shape is the same, a product having the same shape and an arbitrary length can be molded, but the molding density is low and large pores are likely to remain.

Both the casting reaction sintering and the extrusion molding sintering have uncontrollable deformation in the sintering process due to uneven material distribution of the blank, and the final silicon carbide ceramic tube finished product has low coaxiality precision. The invention adopts the method of spiral packing densification and isostatic pressing sintering molding, the final silicon carbide ceramic tube finished product has higher compactness and more stable property, and can meet the high precision requirement in the application of the nuclear industry.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of a silicon carbide ceramic tube, which has the advantages of high compactness and high precision and is suitable for the environment with high precision requirement in the nuclear industry.

The technical scheme of the invention is to provide a preparation method of a silicon carbide ceramic tube, which comprises the following steps:

(1) preparing ceramic raw material powder: preparing silicon carbide powder, a sintering aid, an adhesive, a plasticizer, a dispersant and a lubricant into filling powder;

(2) device adjustment: the rubber skin sleeve mold is arranged in a hanging basket, the centering sleeve is clamped into the rubber skin sleeve mold, the mandrel penetrates through the centering sleeve and is arranged in the rubber skin sleeve mold, the lower end cover is clamped into the mold and the mandrel is clamped by the clamp; the outer wall of the centering sleeve is provided with a spiral winding sheet;

(3) powder filling: the upper centering funnel is clamped into a leather sheath, a positioning cylinder is opened to fix a rubber sheath mold, a pull rod hole is fixed to a pulling plate, powder is added, the pulling plate is moved upwards to a specified distance firstly, quantitative powder is added, the centering sleeve is rotated, the added powder is extruded downwards by means of spiral reverse thrust of a spiral winding sheet, the powder is uniformly distributed, the pulling plate is controlled to move upwards to a specified distance continuously, then the material is added continuously, the centering sleeve is rotated again, the process is repeated until the centering sleeve completely takes out the rubber sheath mold, an upper end cover of the rubber sheath mold is sealed and clamped by a clamp;

(4) cold-static isostatic pressing: placing the hanging basket into isostatic pressing equipment by using a crane, adjusting the pressure to 110-115MPa, pressing the silicon carbide ceramic tube, keeping the pressure for 10 seconds after the pressure reaches the highest pressure, and opening the equipment to lift the hanging basket out after the pressure begins to be relieved to 0 MPa;

(5) core-pulling trimming finishing: taking out the upper end cover, firstly, drawing out the core rod in the pipe blank, taking out the lower end cover, slowly taking out the formed pipe from the rubber sleeve, and cutting off the part of the pipe with the length of 50mm which does not meet the requirement by using a lathe;

(6) and (3) high-temperature sintering: sintering the pressed and formed pipe blank in a high-temperature sintering furnace, wherein the sintering temperature is 1900-2300 ℃, the temperature is kept for 2-4 hours, the heating rate is 1-10 ℃/min, and the atmosphere is argon.

Specifically, the outer side wall of the spiral winding sheet of the centering sleeve is in clearance fit with the inner wall of the rubber sleeve mold.

Specifically, the spiral winding piece of the centering sleeve is arranged clockwise from bottom to top, and the rotating direction in the step (3) is anticlockwise.

Specifically, the ceramic powder added in the step (3) falls down along the top surface of the spiral wound sheet of the centering sleeve.

Specifically, the bottom of the rubber leather sheath mold is provided with a vibrator, the vibrator is started before the material is fed for the second time in the step (3) or when the centering sleeve rotates, and the vibration emitted by the vibrator is transmitted to the rubber leather sheath mold, so that the fed material is uniformly vibrated.

Specifically, the top end of the centering sleeve is connected with a ball screw, the ball screw is in threaded connection with a screw nut, the screw nut is rotatably connected to the support, the screw nut is connected with a servo motor through a coupler, and the servo motor rotates forwards or reversely and drives the ball screw to ascend or descend spirally through the screw nut.

After adopting the structure, the invention has the following advantages: the invention adopts the centering sleeve, which not only can uniformly disperse the blanking, but also can play a role of uniformly stirring when the rubber sleeve is reversely rotated, and simultaneously can continuously press the powder in the rubber sleeve die, so that the powder of the rubber sleeve die is more uniform, the material is uniform, the forming size precision is high, and the centering sleeve can be widely applied to key parts with high precision requirements, such as key heat exchange parts, in petrochemical industry, nuclear industry and the like.

Drawings

FIG. 1 is a schematic view of an isostatic mold for a silicon carbide ceramic tube according to the invention.

Shown in the figure:

1. the device comprises a vibrator, 2, a lower end cover, 3, a hanging basket, 4, a centering sleeve, 5, a pull rod, 6, a centering funnel, 7, a positioning cylinder, 9, a pull plate, 10, a ball screw, 11, a guide rail, 12, a servo motor, 13 and a rubber sleeve die.

Detailed Description

The invention will be further explained with reference to the drawings.

As shown in fig. 1, the preparation method of the silicon carbide ceramic tube of the present invention comprises the following steps:

(1) preparing powder

Preparing silicon carbide powder, a sintering aid, an adhesive, a plasticizer, a dispersant and a lubricant into filling powder;

(2) device adjustment

A rubber sheath mould is arranged in a hanging basket 3, a centering sleeve 4 is clamped into the rubber sheath mould 13, a mandrel passes through the centering sleeve 4 and is arranged in the mould, a lower end cover 2 is clamped into the rubber sheath mould 13 and is clamped by a clamp;

(3) powder filling

Go up centering funnel 6 card and go into the leather sheath, open positioning cylinder 7 and fix rubber leather sheath mould 13, fix 5 holes of pull rod to arm-tie 9 on, begin to add the powder, move up arm-tie 9 earlier to the assigned distance, add quantitative powder, the outside lateral wall of the spiral winding piece of centering cover 4 and the inner wall clearance fit of rubber leather sheath mould. The spiral winding sheet of the centering sleeve 4 is arranged clockwise from bottom to top, and the rotation direction is anticlockwise. The ceramic powder falls down along the top surface of the spiral winding sheet of the centering sleeve. The added powder is uniformly distributed by the spiral reverse thrust of the spiral winding sheet during rotation, the pulling plate 9 is continuously controlled to move upwards for a specified distance and then the material is continuously added, the process is repeated until the centering sleeve 4 is completely pulled out of the die, the upper end cover of the die is sealed and clamped by a clamp; the servo motor 12 is connected to the lead screw nut through a connector and drives the lead screw nut to rotate, the lead screw nut rotates forward to drive the ball screw 10 to spirally ascend, and the lead screw nut rotates backward to drive the roller screw 10 to spirally descend. A guide rail 11 for the ball screw 10 to ascend and descend is arranged below the servo motor 12, and the axial linear ascending and descending of the ball screw 10 are ensured.

(4) Cold static equal pressure forming

Placing the hanging basket 3 into isostatic pressing equipment by using a crane, adjusting the pressure to 110-115MPa, pressing the silicon carbide ceramic tube, keeping the pressure for 10 seconds after the pressure reaches the highest pressure, and opening the equipment to hang the hanging basket 3 out after the pressure begins to be relieved to 0 MPa;

(5) core-pulling trimming

Taking out the upper end cover, firstly drawing out the core rod in the pipe blank, taking out the lower end cover 2, slowly taking out the formed pipe from the rubber leather sheath mold 13, and cutting off the part of the pipe with the two ends of 50mm which does not meet the requirement by using a lathe;

(6) high temperature sintering

Sintering the pressed and formed pipe blank in a high-temperature sintering furnace, wherein the sintering temperature is 1900-2300 ℃, the temperature is kept for 2-4 hours, the heating rate is 1-10 ℃/min, and the atmosphere is argon.

Furthermore, the two ends of the rubber leather sheath are fixed at the two ends of the hanging basket 3 in the step (2), and the middle part of the rubber leather sheath is positioned by a limiting ring, so that the rubber leather sheath mold 13 is prevented from being distorted due to self weight. The centering sleeve 4 is a screw rod with a spiral structure.

Further, the centering funnel 6 and the centering sleeve 4 in the step (3) are tightly connected, and after the powder is added through the centering funnel 6, the added powder can be tightly filled in a gap between the rubber leather sleeve and the core rod due to the reverse thrust of the spiral structure of the centering sleeve.

The bottom of the rubber leather sheath mold 3 is provided with the vibrator 1, the vibrator 1 is started before the material is fed for the second time in the step (3) or when the centering sleeve 4 rotates, and the vibration emitted by the vibrator 1 is transmitted to the rubber leather sheath mold 13, so that the fed material is uniformly vibrated.

The present invention is not limited to the above-described embodiments, and those skilled in the art can make equivalent modifications or substitutions without departing from the spirit of the present invention, and such equivalent modifications or substitutions are included in the scope defined by the claims of the present application.