A method for forming a silicon carbide wear-resistant bushing blank

Abstract

The invention discloses a silicon carbide wear-resistant bushing blank forming method, which belongs to the field of silicon carbide technology and includes core design, mold making, grouting forming, demoulding, blank repair and inspection and other processes. In the grouting forming process, slurry is slowly injected into the mold cavity of an assembled mold along a pouring riser to facilitate the discharge of air holes in the mold cavity. The grouting is stopped when the slurry rises to the upper edge of the pouring riser. After the slurry intake at the lower part reaches the wall thickness, the unsolidified slurry is poured out through the pouring riser to complete a primary slurry return. Then, a certain amount of slurry is re-injected into the mold through the pouring riser, the pouring riser is blocked by a baffle plate equipped with a vent pipe, and then the mold is inverted so that one end of the vent pipe extending into the mold cavity passes through the slurry to balance the pressure inside and outside the mold cavity and prevent the blank from deforming. After a period of time, when the wall thickness reaches a specified size, the baffle plate is opened, and the unsolidified slurry is poured out through the pouring riser to complete a secondary slurry return.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide, and in particular to a method for forming a silicon carbide wear-resistant bushing blank. Background Art

[0002] Silicon carbide wear-resistant bushings, also known as silicon carbide plugs, are used in silicon carbide plug valves. Reaction-sintered silicon carbide has excellent properties such as high strength, high hardness, high wear resistance, oxidation resistance and chemical stability. It is an ideal material for making plug valves. However, Figure 1 The lower part of the blank 6 shown is spherical in shape, and the middle part is an arc cone. It has a large surface area, and the slurry absorption speed is fast during pouring, and the wall thickness quickly reaches the requirement. The upper flange part has more edges and corners, and the surface area is small, so the slurry absorption speed is slow and a longer slurry absorption time is required. In addition, the product requires a larger wall thickness at the sharp edges of the upper flange part. After pouring according to the conventional mold, the wall thickness near the flange position is difficult to meet the requirement. Therefore, silicon carbide emboli are often processed by splitting and then bonding and sintering. However, the bonding part has been deformed during the sintering process, which seriously affects the production efficiency and production cost. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a method for forming a silicon carbide wear-resistant bushing blank, which improves the processing technology. By feeding the slurry twice and adjusting the mold in the up and down directions, the effect of unequal wall thickness of the blank caused by high pressure and fast feeding of the slurry at the bottom and slow feeding of the slurry at the upper pressure is balanced. In particular, the feeding time of the positions with complex structure, slow feeding speed of the surface area and large wall thickness can be compensated separately to meet the processing requirements of products with different wall thicknesses.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for forming a silicon carbide wear-resistant bushing blank comprises the following steps:

[0006] 1) Core design: design the gypsum core mold according to the product shape;

[0007] 2) Mold production: a gypsum master mold is produced according to the gypsum core mold, and a mold is made by using the master mold, including an upper mold and a lower mold, wherein a cavity is provided in the lower mold, a pouring port connected to the cavity is provided on the upper mold, and a baffle for blocking the pouring port is provided on a side of the lower mold away from the upper mold, and a vent pipe extending into the cavity is inserted on the baffle;

[0008] 3) Slurry injection molding: Slowly inject the slurry into the mold cavity of the assembled mold along the pouring riser to facilitate the discharge of air from the mold cavity. Stop the slurry injection when the slurry rises to the upper edge of the pouring riser. After the slurry in the cavity solidifies to a certain thickness, use the baffle equipped with a vent pipe to block the pouring riser. Then invert the mold so that one end of the vent pipe extending into the cavity passes through the slurry to balance the pressure inside and outside the cavity and prevent the blank from deforming. After the blank is formed, open the baffle and pour out the unsolidified slurry through the pouring riser to complete the slurry return.

[0009] 4) Demolding: The product is cured for a period of time at room temperature. The curing temperature is set at 20 degrees Celsius to 30 degrees Celsius and the curing time is greater than 24 hours. After curing, the mold is opened, the blank is taken out, and the blank is sent to the drying room for drying. After the first stage of drying, the temperature is increased for the second stage of drying;

[0010] Repair and inspection of blanks: Repair and inspect the inner and outer surfaces of the dried blanks, remove the pouring and riser parts according to the drawings, and inspect the size and appearance of the blanks according to the drawings.

[0011] Preferably, in step 3), the slurry intake speed of the mold is carefully observed, and the slurry should be replenished in time during the slurry intake process to keep the slurry flush with the upper edge of the pouring and riser to prevent air holes from being generated due to untimely slurry replenishment.

[0012] Preferably, in step 3), before slurry injection, the weight of the mold cavity slurry needs to be calculated according to the product volume and slurry density, and the prepared slurry is 1-3 times greater than the specified cavity slurry weight;

[0013] Before grouting, test the slurry feeding time T of the product wall thickness according to the slurry parameters of this batch;

[0014] According to the slurry feeding time Tslurry feeding tested before pouring, the slurry stops being injected into the mold cavity at time T1, the spherical arc cone part reaches the wall thickness of the blank, the pouring riser is blocked, the mold is inverted, the flange part of the product is at the bottom, and the bottom continues to feed the slurry, and the slurry is returned after the tested slurry feeding time T2, where T2﹤T1≤Tslurry feeding, T2+T1≥Tslurry feeding;

[0015] After pouring, the solidification time of the blank is more than 24 hours.

[0016] Preferably, in step 4), the temperature of the drying chamber in the first stage of drying is 30-40°C, and after drying for 30-40 hours, the temperature is raised to perform the second stage of drying, and the drying temperature of the second stage of drying is 80-100°C, and the drying time is 24-30 hours.

[0017] Preferably, in step 4), the curing temperature is set to 20 degrees Celsius to 30 degrees Celsius and the curing time is greater than 24 hours.

[0018] Preferably, the ventilation pipe is configured as a plastic pipe.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention improves the processing technology, and through two feedings, the mold is adjusted in the up and down directions to balance the influence of unequal wall thickness of the blank caused by high pressure at the bottom of the slurry and fast feeding, and slow feeding at the upper pressure. In particular, the feeding time of the position with complex structure, slow feeding speed of surface area and large wall thickness is compensated separately, so as to meet the processing requirements of products with different wall thicknesses.

[0021] The design of the vent pipe in the present invention can balance the pressure inside and outside the cavity, and can avoid deformation of the solidified slurry caused by the reduction of the pressure inside the cavity due to the downward movement of the slurry after the mold is turned over, which is beneficial to improving the forming effect of the blank. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of an existing silicon carbide wear-resistant bushing blank;

[0023] Figure 2 The present invention is a schematic diagram of the overall structure of a silicon carbide wear-resistant bushing blank forming die.

[0024] In the figure: 1-upper die, 2-lower die, 3-baffle, 4-gating riser, 5-vent pipe, 6-blank. DETAILED DESCRIPTION

[0025] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0026] like Figure 2 A method for forming a silicon carbide wear-resistant bushing blank is shown, comprising the following steps:

[0027] 1) Core design: design the gypsum core mold according to the product shape;

[0028] 2) Mold production: a gypsum master mold is produced according to the gypsum core mold, and a mold is made by using the master mold, including an upper mold 1 and a lower mold 2, wherein a cavity is provided in the lower mold 2, a pouring spout 4 connected to the cavity is provided on the upper mold 1, and a baffle 3 for blocking the pouring spout 4 is provided on a side of the lower mold 2 away from the upper mold 1, and a vent pipe 5 extending into the cavity is inserted on the baffle 3;

[0029] 3) Slurry injection molding: slowly inject the slurry into the mold cavity of the assembled mold along the pouring riser 4 to facilitate the discharge of air from the mold cavity. Stop the slurry injection when the slurry rises to the upper edge of the pouring riser 4. After the slurry in the cavity solidifies to a certain thickness, use the baffle 3 equipped with a vent pipe 5 to block the pouring riser 4. Then, invert the mold so that one end of the vent pipe 5 extending into the cavity passes through the slurry. The vent pipe 5 balances the pressure inside and outside the cavity to prevent the pressure difference inside and outside the mold from causing deformation of the blank. After the blank is formed, open the baffle 3 and pour out the unsolidified slurry through the pouring riser 4 to complete the slurry return. Pay attention to the slurry intake speed of the mold. During the slurry intake process, timely replenish the slurry to keep the slurry flush with the upper edge of the pouring riser 4 to prevent air holes from being generated due to untimely replenishment.

[0030] Before grouting, it is necessary to calculate the weight of the cavity slurry according to the product volume and slurry density, and prepare slurry that is 1-3 times larger than the specified cavity slurry weight. According to the size of the mold, the prepared slurry can fill the mold cavity; before grouting, test the slurry consumption time Tslurry consumption to reach the product wall thickness according to the parameters of this batch of slurry; according to the slurry consumption time Tslurry consumption tested before pouring, stop injecting the slurry into the mold cavity for T1, the spherical arc cone part reaches the wall thickness of the blank, block the pouring riser 4, invert the mold, the flange part of the product is at the bottom, and the bottom continues to consume slurry, and continues to return slurry according to the tested slurry consumption time T2, where T2﹤T1≤Tslurry consumption, T2+T1≥Tslurry consumption; the solidification time of the blank after pouring is more than 24 hours;

[0031] 4) Demolding: The product is cured for a period of time at room temperature. After curing, the mold is opened, the blank is taken out, and the blank is sent to the drying room for drying. After the first stage of drying, the temperature is increased for the second stage of drying. The temperature of the drying room for the first stage is 30-40°C. After drying for 30-40 hours, the temperature is increased again for the second stage of drying. The second stage of drying is 80-100°C and the drying time is 24-30 hours.

[0032] 5) Repair and inspection of blanks: Repair and inspect the inner and outer surfaces of the dried blanks, and remove the 4 parts of the pouring and riser according to the drawings, and inspect the size and appearance of the blanks according to the drawings.

[0033] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for forming a silicon carbide wear-resistant bushing blank, characterized in that: The steps include: 1) Mold core design: design the gypsum core mold according to the product shape; 2) Mold making: a gypsum master mold is made according to the gypsum core mold, and a mold is made by using the master mold, including an upper mold and a lower mold, wherein the lower mold is provided with a cavity, the upper mold is provided with a pouring port connected to the cavity, and a baffle plate for blocking the pouring port is provided on a side of the lower mold away from the upper mold, and a vent pipe extending into the cavity is inserted on the baffle plate; 3) Slurry injection molding: Slowly inject the slurry into the mold cavity of the assembled mold along the pouring riser to facilitate the discharge of air from the mold cavity. Stop the slurry injection when the slurry rises to the upper edge of the pouring riser. After the slurry in the cavity solidifies to a certain thickness, use the baffle equipped with a vent pipe to block the pouring riser. Then, invert the mold so that one end of the vent pipe extending into the cavity passes through the slurry to balance the pressure inside and outside the cavity and prevent the blank from deforming. After the blank is formed, open the baffle and pour out the unsolidified slurry through the pouring riser to complete the slurry return. Among them, before grouting, the slurry feeding time T of the product wall thickness is tested according to the parameters of this batch of slurry. 吃浆 ; According to the slurry eating time T tested before pouring 吃浆 , the slurry stops being injected into the mold cavity for T1, the spherical arc cone part reaches the wall thickness of the blank, the pouring riser is blocked, the mold is inverted, the flange part of the product is at the bottom, and the bottom continues to absorb the slurry. Continue to return the slurry after the tested slurry absorption time T2, where T2﹤T1≤T 吃浆 , T2+T1≥T 吃浆 ; The solidification time of the blank after pouring is more than 24 hours; 4) Demolding: The product is cured for a period of time at room temperature. The curing temperature is set at 20 degrees Celsius to 30 degrees Celsius and the curing time is greater than 24 hours. After curing, the mold is opened, the blank is taken out, and the blank is sent to the drying room for drying. After the first stage of drying, the temperature is increased for the second stage of drying; 5) Repair and inspection of blanks: Repair and inspect the inner and outer surfaces of the dried blanks, remove the pouring and riser parts according to the drawings, and inspect the size and appearance of the blanks according to the drawings.

2. A method for forming a silicon carbide wear-resistant bushing blank according to claim 1, characterized in that: In step 3), pay attention to the slurry absorption speed of the mold. During the slurry absorption process, add slurry in time to keep the slurry flush with the upper edge of the pouring and riser to prevent air holes from being generated due to untimely slurry addition.

3. The method for forming a silicon carbide wear-resistant bushing blank according to claim 2, characterized in that: In step 3), before grouting, the cavity slurry weight needs to be calculated based on the product volume and slurry density, and the prepared slurry should be 1-3 times larger than the specified cavity slurry weight.

4. The method for forming a silicon carbide wear-resistant bushing blank according to claim 1, characterized in that: In step 4), the temperature of the drying chamber in the first stage of drying is 30-40°C. After drying for 30-40 hours, the temperature is raised to carry out the second stage of drying. The drying temperature of the second stage of drying is 80-100°C and the drying time is 24-30 hours.

5. The method for forming a silicon carbide wear-resistant bushing blank according to claim 4, characterized in that: In step 4), the curing temperature is set to 20 degrees Celsius to 30 degrees Celsius and the curing time is greater than 24 hours.

6. The method for forming a silicon carbide wear-resistant bushing blank according to claim 1, characterized in that: The ventilation tube is configured as a plastic tube.

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