Casting process of lost film valve body

Abstract

The invention discloses a casting process of a lost membrane valve body, which comprises the following steps: S1, adopting expandable polystyrene particles, pre-foaming and curing, and molding under the conditions that the mold temperature is 90-105 DEG C and the steam pressure is 0.15-0.25 MPa to obtain a foam model consistent with the valve body in size; s2, the foam model split parts of the valve body are bonded and combined through a hot melt adhesive, and after bonding, a splicing seam is subjected to polishing treatment; and S3, preparing the special coating for the evanescent mode. The valve body produced through the technology is high in size precision and low in surface roughness, a large amount of subsequent machining is not needed, the production cost is reduced, a foam model does not deform, the foam model adopts special paint, the high temperature resistance and air permeability of a coating are improved, and the phenomena of air holes, burnt-on sand and the like are effectively reduced; and the mold filling capacity of molten metal is improved, the defects of shrinkage cavities, cold shut and the like are reduced, casting grains are refined, and casting stress is eliminated.

Description

Technical Field

[0001] This invention relates to the field of valve body casting technology, and in particular to a casting process for a disappearing film valve body. Background Technology

[0002] The valve body is the core component of a valve, and its casting quality directly affects the valve's sealing performance, pressure resistance, and service life. Lost foam casting is a near-net-shape casting technology with advantages such as high dimensional accuracy, good surface quality, and no need for parting or demolding, making it significantly advantageous in the production of complex castings. However, current lost foam casting of valve bodies still faces problems such as easy deformation of the foam model, poor coating permeability leading to porosity defects, and shrinkage cavities in thick sections, which limit its application in the mass production of valve bodies.

[0003] To address these issues, we propose a casting process for the body of a disappearing film valve. Summary of the Invention

[0004] The purpose of this invention is to provide a casting process for a vanishing film valve body to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A casting process for a vanishing film valve body includes the following steps: S1. Expandable polystyrene granules are pre-foamed and cured, and then molded under conditions of mold temperature of 90-105℃ and steam pressure of 0.15-0.25MPa to obtain a foam model with the same size as the valve body. S2. The foam model of the valve body is assembled by bonding the separate parts with hot melt adhesive. After bonding, the joints are sanded. S3. Prepare a special coating for lost foam casting; The coating is composed of the following raw materials in parts by weight: 60-70 parts quartz powder, 5-8 parts bentonite, 2-3 parts sodium carboxymethyl cellulose, and 25-30 parts water. S4. Immerse the foam model in the paint for 10-15 seconds. Remove it and drain off the excess paint. Let it air dry at room temperature for 1-2 hours, then put it in a drying room and dry it at 40-50℃ for 8-12 hours. S5. Lay dry quartz sand at the bottom of the sand box, put the dried foam model into the sand box, and use a vibrating table to perform three-dimensional vibration filling of sand. The vibration frequency is 30-50Hz and the amplitude is 0.5-1.0mm. Add quartz sand in batches during the filling process until the foam model is completely covered. The sand layer thickness is not less than 8cm. After the sand filling is completed, seal the sand box. S6. Pour the molten metal at a temperature of 1520-1560℃, and control the pouring speed at 0.8-1.2m / s. Use negative pressure pouring process during pouring, and control the negative pressure at 0.04-0.06MPa. Maintain the negative pressure until the casting solidifies. S7. After the casting cools to room temperature, it undergoes a sand removal process to remove surface sand. The casting is then shot-blasted at a speed of 50-60 m / s. Finally, it undergoes heat treatment: first, the temperature is raised to 650-700℃ and held for 2-3 hours, then raised to 900-950℃ and held for 3-4 hours. The casting is then cooled in the furnace to below 300℃ before being removed from the furnace to obtain the finished valve body.

[0006] Furthermore, in step S1, the density of the foam model is 18-22 kg / m³, and the surface roughness Ra ≤ 5 μm.

[0007] Furthermore, the expandable polystyrene particles have a particle size of 0.2-0.5 mm, a pre-foaming temperature of 80-85℃, a pre-foaming time of 15-20 min, and a curing time of 24-48 h.

[0008] Furthermore, in step S2, reinforcing ribs are attached to the easily deformable parts of the foam model. The reinforcing ribs are made of EPS and have a thickness of 3-5mm.

[0009] Furthermore, in step S5, the quartz sand has a particle size of 0.8-1.2 mm, a mud content of ≤0.5%, and a water content of ≤0.2%.

[0010] Furthermore, in step S6, the molten metal is carbon steel or stainless steel, and the sulfur content is controlled to be ≤0.03% and the phosphorus content to be ≤0.04% during the smelting process.

[0011] Furthermore, in step S7, after shot blasting, the surface defects of the casting are repaired using welding rods that match the material of the casting, and the surface is then ground smooth.

[0012] Compared with the prior art, the beneficial effects of the present invention are: The valve body produced by the process of this invention has high dimensional accuracy and low surface roughness, requiring no extensive subsequent machining, thus reducing production costs. The foam model does not deform, and the foam model uses a special coating that improves the high temperature resistance and air permeability of the coating, effectively reducing phenomena such as porosity and sand adhesion. Furthermore, this process improves the filling capacity of molten metal, reduces defects such as shrinkage cavities and cold shuts, refines the grain size of the casting, and eliminates casting stress. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the process flow in this invention. Detailed Implementation

[0014] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0015] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Please see Figure 1 A casting process for a disappearing film valve body includes steps such as foam model preparation, foam model assembly and reinforcement, coating and drying, molding and sand filling, casting and molding, and post-treatment. The details of each step are as follows: S1. Foam Model Preparation: Select expandable polystyrene (EPS) beads with a particle size of 0.2-0.5mm, pre-foam at 80-85℃ for 15-20 minutes, and cure for 24-48 hours to ensure that the beads are fully expanded and their performance is stable; fill the cured beads into the valve body mold, and heat and mold at 90-105℃ and 0.15-0.25MPa steam pressure to obtain a foam model with a density of 18-22kg / m³ and a smooth surface, ensuring that the mold size is consistent with the valve body design size.

[0018] S2. Foam Model Assembly and Reinforcement: For split valve body foam models, hot melt adhesive is used for bonding. After bonding, the joints are ground to avoid defects such as gaps during casting. 3-5mm thick EPS reinforcing ribs are pasted on easily deformable parts of the mold, such as flanges and areas with abrupt changes in wall thickness, to enhance the strength of the mold and prevent deformation during sand filling vibration.

[0019] S3. Coating Application and Drying: Prepare a special coating composed of quartz powder, bentonite, sodium carboxymethyl cellulose, and water. Quartz powder serves as a refractory aggregate to enhance the high-temperature resistance of the coating. Bentonite and sodium carboxymethyl cellulose act as binders and suspending agents to ensure the adhesion and stability of the coating. Immerse the foam model in the coating for 10-15 seconds to ensure that the coating evenly covers the surface of the mold. After draining off the excess coating, air dry at room temperature for 1-2 hours, and then place it in a drying room at 40-50℃ for 8-12 hours to dry the coating completely. The dry film thickness should be controlled at 0.8-1.2 mm to ensure both air permeability and prevent molten metal from penetrating and adhering to sand.

[0020] S4. Molding Sand Filling: Select quartz sand with a particle size of 0.8-1.2mm, a mud content of ≤0.5%, and a moisture content of ≤0.2%. The quartz sand has uniform particle size and good air permeability. Lay a 10-15cm thick layer of quartz sand at the bottom of the sand box as base sand, place the dried foam model in it, turn on the three-dimensional vibration table, and vibrate at a frequency of 30-50Hz and an amplitude of 0.5-1.0mm. Add quartz sand in batches until the sand layer completely covers the mold and the thickness is not less than 8cm. Vibration filling makes the molding sand dense and avoids the box collapsing during casting. After filling the sand, seal the sand box to prevent negative pressure leakage.

[0021] S5. Casting and Molding: Melt carbon steel or stainless steel liquid, control the sulfur and phosphorus content to ≤0.03% and ≤0.04% respectively to improve the mechanical properties of the casting; control the temperature of the molten metal at 1520-1560℃, and the pouring speed at 0.8-1.2m / s to avoid the foam model from decomposing incompletely and producing pores due to excessively high temperature, or the molten metal from having poor fluidity and producing cold shuts due to excessively low temperature; use negative pressure pouring, with a negative pressure of 0.04-0.06MPa. The negative pressure environment can accelerate the decomposition of the foam model and the discharge of gas, reduce the pore defects in the casting, and maintain the negative pressure until the casting is completely solidified.

[0022] S6. After the casting cools to room temperature, the sand is removed from the surface. The surface of the casting is cleaned by shot blasting at a speed of 50-60 m / s to improve the surface finish. The casting is then heat-treated by first low-temperature tempering to eliminate casting stress, and then high-temperature annealing to refine the grains. Specifically, the temperature is 650-700℃ for 2-3 hours and 900-950℃ for 3-4 hours. The casting is then cooled in the furnace to below 300℃ before being removed from the furnace, which effectively improves the strength and toughness of the casting. Finally, surface defects are repaired and polished to obtain a qualified valve body.

[0023] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0024] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A casting process for a vanishing film valve body, characterized in that: Includes the following steps: S1. Expandable polystyrene granules are pre-foamed and cured, and then molded under conditions of mold temperature of 90-105℃ and steam pressure of 0.15-0.25MPa to obtain a foam model with the same size as the valve body. S2. The foam model of the valve body is assembled by bonding the separate parts with hot melt adhesive. After bonding, the joints are sanded. S3. Prepare a special coating for lost foam casting; The coating is composed of the following raw materials in parts by weight: 60-70 parts quartz powder, 5-8 parts bentonite, 2-3 parts sodium carboxymethyl cellulose, and 25-30 parts water. S4. Immerse the foam model in the paint for 10-15 seconds. Remove it and drain off the excess paint. Let it air dry at room temperature for 1-2 hours, then put it in a drying room and dry it at 40-50℃ for 8-12 hours. S5. Lay dry quartz sand at the bottom of the sand box, put the dried foam model into the sand box, and use a vibrating table to perform three-dimensional vibration filling of sand. The vibration frequency is 30-50Hz and the amplitude is 0.5-1.0mm. Add quartz sand in batches during the filling process until the foam model is completely covered. The sand layer thickness is not less than 8cm. After the sand filling is completed, seal the sand box. S6. Pour the molten metal at a temperature of 1520-1560℃, and control the pouring speed at 0.8-1.2m / s. Use negative pressure pouring process during pouring, and control the negative pressure at 0.04-0.06MPa. Maintain the negative pressure until the casting solidifies. S7. After the casting cools to room temperature, it undergoes a sand removal process to remove surface sand. The casting is then shot-blasted at a speed of 50-60 m / s. Finally, it undergoes heat treatment: first, the temperature is raised to 650-700℃ and held for 2-3 hours, then raised to 900-950℃ and held for 3-4 hours. The casting is then cooled in the furnace to below 300℃ before being removed from the furnace to obtain the finished valve body.

2. The casting process of the vanishing film valve body according to claim 1, characterized in that: In step S1, the density of the foam model is 18-22 kg / m³, and the surface roughness Ra ≤ 5 μm.

3. The casting process of the vanishing film valve body according to claim 1, characterized in that: The expandable polystyrene particles have a particle size of 0.2-0.5 mm, a pre-foaming temperature of 80-85℃, a pre-foaming time of 15-20 min, and a curing time of 24-48 h.

4. The casting process of the vanishing film valve body according to claim 1, characterized in that: In step S2, reinforcing ribs are attached to the easily deformable parts of the foam model. The reinforcing ribs are made of EPS and have a thickness of 3-5mm.

5. The casting process of the vanishing film valve body according to claim 1, characterized in that: In step S5, the quartz sand has a particle size of 0.8-1.2 mm, a mud content of ≤0.5%, and a water content of ≤0.2%.

6. The casting process of the vanishing film valve body according to claim 1, characterized in that: In step S6, the molten metal is carbon steel or stainless steel, and the sulfur content is controlled to be ≤0.03% and the phosphorus content to be ≤0.04% during the smelting process.

7. The casting process of the vanishing film valve body according to claim 1, characterized in that: In step S7, after shot blasting, the surface defects of the casting are repaired. The repair is carried out using welding rods that match the material of the casting, and the surface is then ground smooth.

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