A shell mold for a covered sand casting carbon steel and stainless steel gate valve body and its process

Abstract

The invention discloses a shell mold and a process for casting a carbon steel or stainless steel gate valve body by coated sand casting, comprising a shell mold as a whole composed of two coated sand shell molds, a sand core and a chiller component. The shell mold as a whole comprises a pouring cup, a riser, a top pouring port, a bottom pouring port, a valve body, a flange and a through diameter. The valve body is connected to the flange through the through diameter, a sealing ring is provided in the middle of the valve body, the flange and the through diameter, the sealing ring and the through diameter are thick-thin connecting parts, a chiller component is placed inside the coated sand shell mold, the chiller component is located at the thick-thin connecting part, a notch located between the chiller components is opened at the bottom of the coated sand shell mold, adding the chiller component can reduce the resistance of the coated sand shell to the shrinkage force, so that the sand shell can be easily collapsed when the casting is cooled, the chiller is more efficiently used, the amount of sand used is reduced, and the cost is reduced; the coated sand shell is grooved between two thick-thin connecting parts of any casting, while ensuring the casting performance, the resistance to the shrinkage stress is reduced, and the casting cost of the complex casting is lower.

Description

Technical Field

[0001] The present invention relates to the technical field of coated sand molds, and specifically to a shell mold for casting carbon steel and stainless steel gate valve bodies with coated sand and its process. Background Art

[0002] Currently, there is no technology that can mass-produce complex products with multiple thickness combinations without defects. The reason is that the heat dissipation, solidification time, and solidification shrinkage of cast parts with different thicknesses and lengths are different. Therefore, the shrinkage vector forces generated during the cooling of the casting are different. When the shrinkage vector force is greater than the casting structure force and less than the casting mold bearing pressure, defects (including cracks, hidden cracks, and deformations) will surely occur. And because the energy consumption and material loss of a single casting of metal castings are very large, the qualified rate and cost of mass-producing such products with coated sand are high, affecting production.

[0003] Based on this, the present invention designs a shell mold for casting carbon steel and stainless steel gate valve bodies with coated sand and its process to solve the above-mentioned problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a shell mold for casting carbon steel and stainless steel gate valve bodies with coated sand and its process to solve the problem of low qualified rate when mass-producing such products with coated sand.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A shell mold for casting carbon steel and stainless steel gate valve bodies with coated sand, including a whole shell mold composed of two split coated sand shell molds, a sand core, and a chill assembly. The two split coated sand shell molds are fixed by binding wires. The sand core and the whole shell mold are combined to form a complete valve body cavity. The whole shell mold includes a pouring cup, a riser, a top pouring port, a bottom pouring port, a valve body, a flange, and a bore diameter. The valve body is connected to the flange through the bore diameter. A sealing ring is provided in the middle of the valve body. The flange and the bore diameter, and the sealing ring and the bore diameter are thick-thin joints. A chill assembly is placed inside the coated sand shell mold. The chill assembly is located at the thick-thin joints. A notch is opened at the lower part of the coated sand shell mold between the chill assemblies. The pouring cup is connected to the top pouring port through a horizontal runner at the top. The pouring cup is connected to the bottom pouring port through a vertical runner and a horizontal runner at the bottom. The top pouring port and the bottom pouring port are communicated with the valve body.

[0006] Preferably, the chill assembly uses semi-circular conforming chills, and the chills are designed to be thinner at the top and thicker at the bottom.

[0007] Preferably, at least one notch is opened at each two thick-thin joints, and the depth of the notch is the same as the average thickness of the coated sand shell mold.

[0008] Preferably, the chill assembly includes multiple sections of chills, and the notches are opened between the multiple sections of chills.

[0009] Preferably, the coated sand shell mold is designed to be thick on the top and thin on the bottom.

[0010] Preferably, the lower inner wall of the shell-shaped integral body is provided with dot-shaped and strip-shaped protrusions, and the cold iron assembly is fixed by the dot-shaped and strip-shaped protrusions.

[0011] A process for casting a carbon steel or stainless steel gate valve body with coated sand, the casting process specifically comprising the following steps:

[0012] S1: Manufacture the chilled iron components according to the design requirements through the chilled iron mold;

[0013] S2: Mould manufacturing, designing a structure for reserving the cold iron position and notch position of the coated sand shell type in the mould, and reserving point-shaped and strip-shaped protrusion positions at the corresponding positions of the reserved cold iron position of the coated sand shell type;

[0014] S3: Install the mold on the sand shooting equipment, place the chiller in the designed mold chiller position, heat it through the electric heating tube on the mold, and after reaching the set temperature, shoot the coated sand into the mold cavity for curing. The curing time is determined according to the size of the sand shell. After the curing is completed, the sand shell can be taken out for standby use;

[0015] S4: Casting: When using the coated sand shell mold for casting, first load half of the sand core into half of the corresponding coated sand shell mold, then put the two halves of the coated sand shell mold together to form a completed cavity, and then bundle and fix them. After that, pour the molten steel through the pouring port from the bottom pouring port reserved at the bottom of the coated sand shell mold. When the molten steel reaches the top pouring port, the molten steel continues to pour from the top pouring port until the molten steel reaches the top of the cavity and the pouring is completed.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The use of this type of coated sand to cast the shell mold of carbon steel and stainless steel gate valve bodies greatly improves the pass rate of coated sand casting. Adding a chiller component can reduce the resistance of the coated sand shell to shrinkage forces, allowing the sand shell to easily collapse when the casting cools. Compared with other chiller processes, the chiller-forming process of the present invention is more precise, the chiller is more efficient, the amount of sand used is reduced, and the cost is reduced. By grooving the coated sand shell between two thick and thin connections of any casting, the coated sand shell can reduce resistance to shrinkage stress while ensuring the casting performance, making the casting cost of complex castings lower (low scrap rate, high pass rate). BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 It is a schematic axonometric structure diagram of the present invention;

[0020] Figure 2 For the present invention Figure 1 is a schematic top view structure diagram;

[0021] Figure 3 It is a schematic diagram of the overall connection structure of the core and the shell mold of the present invention;

[0022] Figure 4 It is a schematic core structure diagram of the present invention;

[0023] Figure 5 For the present invention Figure 1 is a schematic side view structure diagram;

[0024] Figure 6 It is a schematic notch structure diagram of the present invention;

[0025] Figure 7 It is a schematic diagram of the dot and strip protrusion structure of the present invention.

[0026] In the drawings, the list of components represented by each reference numeral is as follows:

[0027] 1. Overall shell mold; 2. Core; 3. Chilled iron assembly; 4. Sprue cup; 5. Riser; 6. Top gate; 7. Bottom gate; 8. Valve body; 9. Flange; 10. Bore diameter; 11. Sealing ring; 12. Thick-thin connection; 13. Notch; 14. Dot and strip protrusion; 15. Runner; 16. Sprue; 17. Chilled iron. Detailed implementation manners

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0029] Embodiment 1

[0030] Please refer to Figure 1-7, the present invention provides a technical solution: a shell mold for casting carbon steel and stainless steel gate valve bodies with coated sand, including a shell mold body 1 composed of two pieces of coated sand shell molds, a sand core 2, and a chill assembly 3. The two pieces of coated sand shell molds are fixed by binding wires, and an internal coated sand shell support is used to combine with the outer coated sand shell to form a complete cavity 8 of the valve body, which is the inner cavity of a sand shooting mold for batch preparation of coated sand shells.

[0031] The shell mold body 1 includes a pouring cup 4, a riser 5, a top gate 6, a bottom gate 7, a valve body 8, a flange 9, and a bore diameter 10. The valve body 8 is a casting set according to requirements, and the flange 9 is a pipe connection disc of the valve body 8 casting. On large pipeline valves, the flange 9 has the largest thickness. The sealing ring 11 is a thickened part in the middle of the valve body 8. The valve body 8 is connected to the flange 9 through the bore diameter 10. There is a sealing ring 11 in the middle of the valve body 8. The flange 9 and the bore diameter 10, and the sealing ring 11 and the bore diameter 10 are thick-thin joints 12, which are at the thickest place, while the bore diameter 10 is the thinnest structure of the valve body 8 casting and is prone to premature solidification and shrinkage. The chill assembly 3 is placed inside the coated sand shell mold, and the chill assembly 3 is located at the thick-thin joint 12. There is a notch 13 between the chill assemblies 3 at the lower part of the coated sand shell mold. The pouring cup 4 is connected to the top gate 6 through a horizontal runner 15 at the top. When the molten steel reaches the top gate 6, it automatically mainly uses top gating (the molten steel with a higher temperature is lighter). At this time, the cooled molten steel is at the lower part, and the continuously poured high-temperature molten steel is naturally at the upper part. This ensures that the upper half of the entire cavity solidifies last. The pouring cup 4 is connected to the bottom gate 7 through a vertical runner 16 and a horizontal runner 15 at the bottom. Due to the action of gravity, the molten steel will first enter the shell mold body 1 from the pouring cup 4 and the vertical runner 16 downward through the bottom gate 7. Using the bottom gate 7 for pouring first can prevent the molten steel from scouring the inside of the sand shell, and the cooling of the molten steel will start from the lower part first. The top gate 6 and the bottom gate 7 are connected to the valve body 8.

[0032] Among them, the chill assembly 3 uses a semi-circular conforming chill 17. The chill 17 is designed to be thinner at the top and thicker at the bottom. The chill assembly 3 includes multiple segments of chill 17. The notch 13 is opened between the multiple segments of chill 17, which can facilitate grooving and at the same time is beneficial to the overall shrinkage of the casting and the sand shell.

[0033] By using the chill 17, the molten steel of the casting is rapidly cooled. Using the segmented semi-circular chill 17 can reduce the resistance of the coated sand shell to the shrinkage force, enabling the sand shell to easily collapse when the casting cools. Compared with other chill 17 processes, the conforming chill 17 process of the present invention is more precise and the utilization efficiency of the chill 17 is higher.

[0034] Among them, at least one notch 13 is opened at each two thick-thin joints 12, and the depth of the notch 13 is the same as the average thickness of the coated sand shell mold.

[0035] During use, through preliminary review of the coated sand casting products and review of the casting drawings, the relationship between the shrinkage of the casting and the stress of the coated sand shell is obtained. When the casting cools, it will shrink. This is a general physical phenomenon, but in the production of sand castings, there has never been a technology to do prestressing treatment. A part of the sand shell is made into a grooved form, which can ensure the overall structural strength of the sand shell and can also collapse from the weakest point when the casting cools and shrinks, thereby releasing the shrinkage force of the casting.

[0036] The coated sand shell mold is designed to be thick on the top and thin on the bottom, so that the molten steel can solidify from bottom to top (the thinner the area, the faster the heat dissipation and the faster the molten steel solidifies).

[0037] The lower inner wall of the shell mold 1 is provided with dot-shaped and strip-shaped protrusions 14, and the cold iron assembly 3 is fixed by the dot-shaped and strip-shaped protrusions 14, so that the cold iron 17 does not move during high-speed sand shooting.

[0038] Usage status:

[0039] design

[0040] 1. Carry out process review according to the drawings, examine the thick and thin joints of the castings 12, and determine the final structure of the product based on the review results.

[0041] 2. Process design: According to the structure in the drawing, design the conformable chill 17, design it at the weak link of the product structure (where cracks are prone to occur), and use the chill component 3 to accelerate the rapid solidification of this part.

[0042] Take valve body 8 as an example

[0043] Generally, the flange 9 of the coated sand valve body 8 casting product is thick and the diameter 10 is thin, which causes the cooling time of each part of the casting to be different, so the time of shrinkage during cooling and solidification is different. This difference in shrinkage speed will cause cracks at the root of the flange 9. The diameter 10 has a thin wall, a fast cooling speed, and a fast solidification time, while the solidification speed of the flange 9 is slow. Both will shrink towards themselves after solidification. Under this tensile force, cracks will be generated at the connection point between the two, that is, the root of the flange 9. At the same time, the hardness of the general sand shell is large, the shrinkage is very low, and the shrinkage rate of the metal is large, resulting in the shrinkage stress of the casting product cannot be released, and finally the stress of the casting product acts on the thick and thin connection 12 of the casting product, causing cracks. According to the places where crack defects are prone to occur in this valve body 8, the conformal cold iron 17 is designed.

[0044] According to the structural review of the valve body 8, at the thick-thin connection 12 (the vulnerable crack area), a semi-circular chill 17 with a shape following the R corner at the root of the flange 9 and the R corner at the connection between the sealing ring 11 and the through-diameter 10 is designed. The design standard of the chill 17 is thinner at the top and thicker at the bottom, so that the product solidifies in sequence from bottom to top. The semi-circular shape-following chill 17 can achieve the best state of molten steel utilization rate. An overly small shape-following chill 17 will make the riser 5 too large, wasting molten steel materials, while an overly large shape-following chill 17 will cause the casting product to have cold cracks due to too fast cooling speed, resulting in product defects or even scrapping.

[0045] The external chill 17 of the flange 9 will accelerate the cooling of the lower part of the flange 9, enabling the flange 9 to form a solidification process in sequence from bottom to top, reducing the erosion speed of the high-temperature molten steel on the sand shell, prolonging the heat resistance time of the shell mold, slowing down the disintegration speed of the sand shell, and reducing the sand consumption of the sand shell. The chill 17 is a recyclable product and can be reused.

[0046] If the built-in chill 17 is not designed, it is necessary to increase the thickness of the sand shell to ensure the heat resistance time of the sand shell. However, the thickened sand shell will also slow down the cooling of the flange 9 and increase the resistance to the shrinkage stress of the casting product, resulting in cracks.

[0047] Adopting the shell mold of the present invention, since the design of the built-in chill 17 will reduce the sand usage ratio according to the traditional process. The original process is to design the sand shell in a 1:1 ratio. The mass ratio of the molding sand to the casting product is the same. After the chill 17 is designed, the sand-iron (i.e., molding sand to casting product) ratio is (0.6 - 0.8):1, greatly reducing the sand consumption and lowering the cost. At the same time, the original sand shell without the rapid cooling effect of the chill 17 needs to be thick to meet the requirements of sand mold matching for pouring.

[0048] The slotting of the resin-coated sand shell should be in the lower half. Due to the shrinkage of the casting during cooling, when there is no slotting, the sand shell will prevent the casting from shrinking, resulting in tensile cracks at the thick-thin connection 12 of the casting. After using the slotting process, the shrinkage resistance of the sand shell to the casting during shrinkage is solved, avoiding the generation of cracks. During shrinkage, the slotting position of the sand shell will disintegrate first to form a shrinkage joint, providing space for the shrinkage of the casting. Opening a slot at the middle position of the lower half of each casting can, to a certain extent, avoid tensile cracks during the shrinkage of the casting, but cracks may still occur. The most preferred solution is to open at least one slot at every two thick-thin connections 12 of the casting.

[0049] Example 2

[0050] It also includes a process for casting a resin-coated sand carbon steel and stainless steel gate valve body 8, and the casting process specifically includes the following steps:

[0051] S1: Manufacture the chill assembly 3 according to the design requirements through the chill 17 mold;

[0052] S2: Die manufacturing. Design and reserve the structure of the chill 17 positions and notch 13 positions of the pre-coated sand shell mold in the die. Directly manufacture the grooved positions, and reserve dot-shaped and strip-shaped protrusions 14 positions at the corresponding positions of the reserved chill 17 positions of the pre-coated sand shell mold; enable the chill 17 to be limited to the designed position (entirely wrapped inside the sand shell) to ensure that it will not move during sand injection.

[0053] S3: Install the die on the sand injection equipment. First, place the chill 17 at the designed chill 17 position of the die, and then heat it through the electric heating tubes on the die itself. After reaching the set temperature (190 - 230 degrees Celsius), inject the pre-coated sand into the die cavity for curing. The curing time is determined according to the size of the sand shell (existing process). After curing is completed, the sand shell can be taken out for use; the manufacturing process of the sand core 2 is the same as that of the sand shell.

[0054] S4: Casting: When using the pre-coated sand shell mold for casting, first install half of the sand core 2 into half of the corresponding pre-coated sand shell mold, then combine the two assembled pre-coated sand shell molds together to form a complete cavity, and then tie and fix them. After that, pour the molten steel through the pouring gate from the bottom injection port 7 reserved at the bottom of the pre-coated sand shell mold. When the molten steel reaches the top injection port 6, the molten steel starts to be poured continuously from the top injection port 6 until the molten steel reaches the top of the cavity, and the pouring is completed.

[0055] The process adopts the method of bottom injection first and then top injection to ensure that the molten steel is poured more smoothly and reduce the erosion of the molten steel on the cavity. When the molten steel reaches the top injection port 6, it automatically mainly uses top injection (the hot molten steel is lighter in weight). At this time, the cooled molten steel is at the bottom, and the continuously poured high-temperature molten steel is naturally at the upper part. This ensures that the upper half of the entire cavity solidifies last. When the casting starts to solidify, due to the action of the chill 17, the bottom starts to solidify first, and solidification occurs in sequence from bottom to top. The shrinkage space generated during the cooling and shrinkage of the casting is continuously filled by the high-temperature molten steel above, so that the intercrystalline structure inside the casting is more compact. During the cooling and solidification process of the casting, due to the action of the chill 17, the thick-thin connection parts 12 between the flange 9 and the through-hole diameter 10, and the sealing ring 11 and the through-hole diameter 10 will solidify first. After that, the shrinkage stress generated after the through-hole diameter 10, the flange 9, and the sealing ring 11 solidify will not cause tensile cracking effects on the connection parts (the shrinkage force is less than the mechanical damage force of the steel body at the connection parts). During solidification, due to the thin thickness of the sand wall at the grooved part, it will collapse first, forming a shrinkage space, thereby buffering the stress during shrinkage and also avoiding the generation of cracks. When the casting cools, the sand shell naturally collapses, and then the casting can be subjected to post-treatment, and one sand casting is completed. The chill 17 can be recycled and reused.

[0056] The use of this coated sand to cast the shell mold of carbon steel and stainless steel gate valve body 8 greatly improves the qualified rate of coated sand casting. Through the early stage of the evaluation method of castings, the mold opening manufacturing cost of the coated sand mold can be greatly reduced, and a large amount of mold development cost can be saved. Due to the reasonable design idea, the mold opening accuracy is greatly improved, which will greatly reduce the mold opening cost. From design to actual use of the mold, it takes several times of trimming. The mold that cannot be trimmed can only be scrapped, and the mold opening cost will be directly doubled. The conforming efficiency of the cold iron 17 is higher. By slotting the coated sand shell between the two thick and thin joints 12 of any casting, the coated sand shell can reduce the resistance to shrinkage stress while ensuring the pouring performance, so that the casting cost of complex castings is lower (low scrap rate, high qualified rate).

[0057] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0058] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A shell mold for a covered sand casting carbon steel and stainless steel gate valve body, characterized in that: It includes an integral shell mold composed of two split shell molds made of coated sand, a sand core, and a chill assembly. The two split shell molds made of coated sand are fixed by binding wires. The sand core and the integral shell mold are combined to form a complete valve body cavity. The integral shell mold includes a pouring cup, a riser, a top gate, a bottom gate, a valve body, a flange, and a bore diameter. The valve body is connected to the flange through the bore diameter. A sealing ring is provided in the middle of the valve body. The flange and the bore diameter, and the sealing ring and the bore diameter are thick-thin joints. The chill assembly is placed inside the shell mold made of coated sand. The chill assembly is located at the thick-thin joints. A notch is opened at the lower part of the shell mold made of coated sand between the chill assemblies. The pouring cup is connected to the top gate through a horizontal runner at the top. The pouring cup is connected to the bottom gate through a vertical runner and a horizontal runner at the bottom. The top gate and the bottom gate communicate with the valve body. The chill assembly adopts a semi-circular conforming chill. The chill is designed to be thinner at the top and thicker at the bottom. At least one notch is opened at each of the two thick-thin joints. The depth of the notch is the same as the average thickness of the shell mold made of coated sand. The chill assembly includes multiple sections of chills. The notch is opened between the multiple sections of chills.

2. The shell mold for a covered sand casting carbon steel and stainless steel gate valve body according to claim 1, characterized in that: The shell mold made of coated sand is designed to be thicker at the top and thinner at the bottom.

3. The shell mold for a covered sand casting carbon steel and stainless steel gate valve body according to claim 1, characterized in that: Dot-shaped and strip-shaped protrusions are provided on the inner wall of the lower part of the integral shell mold. The chill assembly is fixed by the dot-shaped and strip-shaped protrusions.

4. Based on the casting process of the shell mold of the coated sand casting carbon steel and stainless steel gate valve body as described in any one of claims 1-3, it is characterized in that: The casting process specifically includes the following steps: S1: Manufacture the chill assembly according to the design requirements through a chill mold. S2: Mold manufacturing. Design and reserve the structure of the chill position and notch position of the shell mold made of coated sand in the mold, and reserve the dot-shaped and strip-shaped protrusion positions at the corresponding positions of the reserved chill position of the shell mold made of coated sand. S3: Install the mold on the sand shooting equipment. First, place the chill in the designed chill position of the mold, and then heat it through the electric heating tubes on the mold itself. After reaching the set temperature, inject the coated sand into the mold cavity for curing. The curing time is determined according to the size of the sand shell. After curing is completed, the sand shell can be taken out for use. S4: Casting: When using the shell mold made of coated sand for casting, first install half of the sand core into half of the corresponding shell mold made of coated sand, then combine the two assembled shell molds made of coated sand to form a complete mold cavity, and then bind and fix them. After that, pour the molten steel through the pouring port from the bottom gate reserved at the bottom of the shell mold made of coated sand. When the molten steel reaches the top gate, the molten steel starts to be poured from the top gate until the molten steel reaches the top of the mold cavity, and the pouring is completed.

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