A process for casting a ball joint for a sand conveying pipe corner connection

Abstract

The application relates to the technical field of connecting ball head casting, and discloses a sand conveying pipe corner connecting ball head casting process method, which comprises the following steps: designing an outer cavity mold and an inner cavity mold according to the casting appearance and the inner cavity structure of the ball head, and embedding a plurality of core bones in the outer cavity mold; placing the casting inner cavity mold in the casting outer cavity mold in sequence, so that an irregular forming cavity is formed between the inner cavity mold and the outer cavity mold, the forming cavity is in the shape of the outer contour of the ball head casting, and a casting mold blank is formed; fixing the core bones in the casting mold blank in connection, pouring molten steel into the forming cavity, and keeping the pouring temperature at 1540-1560 DEG C; taking out the ball head casting after the casting mold blank is kept for 3-4 hours; and cleaning the ball head casting and cutting off the riser for use. The ball head casting mold blank is constructed in the core assembling mode, common molten steel is directly poured, and the ball head does not need to be subjected to heat treatment, so that the strength and hardness of the casting are guaranteed, the service life of the ball head casting is effectively prolonged, and the manufacturing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of ball joint casting technology, and specifically to a casting process for a corner ball joint of a sand conveying pipe. Background Technology

[0002] Silica sand is one of the most commonly used raw materials in the foundry industry. In its use, silica sand needs to be transported to a sand mixer via a sand conveying pipe. The silica sand is propelled at high speed through the conveying pipe by compressed air. At pipe bends, to facilitate silica sand transport, a corner joint ball joint is usually used to change the direction of silica sand transport. Therefore, the part of the ball joint that is opposite to the pipe needs to withstand a large impact force. Furthermore, the main component of silica sand is SiO2, which has high hardness, causing significant wear to the impact area of ​​the ball joint, resulting in a short service life and frequent replacement.

[0003] To increase the service life of the ball heads, modern ball heads are hollow spheres with uniform wall thickness to reduce the impact of silica sand, and are made of high-hardness, wear-resistant high-manganese steel. However, because high-manganese steel is expensive, the replacement rate of the ball heads for sand conveying pipes is still around 40% annually under continuous production conditions, resulting in high production costs.

[0004] Therefore, in view of the problems of low service life and high cost of sand conveying pipe ball heads, there is an urgent need to provide a casting process for sand conveying pipe corner connection ball heads. Summary of the Invention

[0005] The present invention aims to provide a casting process for the corner connection ball head of a sand conveying pipe, thereby solving the problems of high cost and short service life of existing sand conveying pipe ball heads.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention relates to a low-cost, long-life sand conveying pipe corner connector ball head casting process, specifically a casting method for a sand conveying pipe corner connector ball head, comprising the following steps:

[0008] S1. Based on the external shape and structure of the ball head casting, design the outer cavity mold and pre-embed multiple core bones in the outer cavity mold;

[0009] S2, Design the inner cavity mold according to the inner cavity shape of the ball head casting;

[0010] S3, the inner cavity mold is placed in the outer cavity mold in sequence, so that an irregular forming cavity is formed between the inner cavity mold and the outer cavity mold. The forming cavity is the outer contour shape of the ball head casting. The outer surface of the forming cavity has through holes, so that the inner cavity mold and the outer cavity mold constitute the casting blank.

[0011] The molding cavity includes a thickened portion and a connecting portion connected in sequence, wherein the thickness of the thickened portion is 1.5-2 times the thickness of the connecting portion;

[0012] S4. Fix and connect the cores in the mold blank, and pour molten steel into the forming cavity through the through hole, keeping the pouring temperature at 1540-1560℃; so that the molten steel fills the entire forming cavity.

[0013] S5. After keeping the mold blank warm for 3-4 hours, take out the ball head casting formed in the molding cavity.

[0014] S6 is used after cleaning the ball head casting and removing the riser.

[0015] The principle and advantages of this scheme are as follows: This scheme constructs the ball head mold blank by core assembly and directly pours it using commonly used molten steel, without the need for heat treatment of the ball head. At the same time, thickened parts are reasonably set at the corresponding positions of the ball head to further improve the impact resistance of the ball head. After the ball head is shaped, the ball head casting can be directly removed, cleaned, and used.

[0016] This solution uses a pre-embedded core frame to fix the inner and outer mold cavities during casting, ensuring the connection stability of the mold blank and preventing the mold from lifting during casting, which could affect the forming quality of the ball head casting. Simultaneously, this solution directly maintains the casting temperature at 1540-1560℃, utilizing the original characteristics of the as-cast structure of the steel part, thus eliminating the need for heat treatment. This ensures the strength and hardness of the casting and effectively increases its service life. Furthermore, using commercially available molten steel for casting makes production more convenient and faster, facilitating internal factory production and significantly reducing production costs.

[0017] Secondly, the molten steel produced after production generally cannot be reused. It can be used to replace high-manganese steel, which is more expensive, thus reducing costs, reusing resources, and saving energy.

[0018] Preferably, as an improvement, the forming cavity includes a sand inlet and a sand outlet; the thickened portion includes an inlet thickened portion and an outlet thickened portion, the inlet thickened portion being located on the opposite side of the sand inlet, and the outlet thickened portion being located on the opposite side of the sand outlet; at least one core support is provided between the inner mold and the outer mold of the casting, and the core support is located within the outlet thickened portion. By rationally setting the position of the thickened portion according to the usage environment of the ball head, the local strength of the ball head can be specifically improved, and production costs can be saved. Simultaneously, the core support can stabilize the forming of the thickened portion, increase the wall thickness of specific parts of the ball head casting, thereby ensuring the wall thickness requirements of the ball head casting and improving the impact resistance of the ball head casting.

[0019] Preferably, as an improvement, the diameter of the thickened inlet is the same as the diameter of the sand inlet; the diameter of the thickened outlet is the same as the diameter of the sand outlet; and the core is positioned at the junction of the thickened outlet and the connecting part. Thickening the corresponding portions of the sand inlet and outlet specifically enhances the impact resistance of particular areas of the ball head, effectively improving the ball head's strength while reducing casting material usage and making rational use of resources.

[0020] Preferably, as an improvement, the outer cavity mold of the casting includes a No. 1 sand core and a No. 4 sand core that interlock with each other; each of the No. 1 sand core and the No. 4 sand core is provided with two core bones. The No. 1 sand core and the No. 4 sand core are fixedly connected by the core bones, thereby increasing the connection stability between the outer cavity mold and the inner cavity mold of the casting, preventing the mold from lifting during the pouring process, and ensuring the casting forming quality.

[0021] Preferably, as an improvement, a first hemispherical groove is provided at the center of the No. 1 sand core, and an annular countersunk hole is opened at the bottom of the first hemispherical groove to form the sand outlet of the ball head casting; a first semi-annular groove is provided on the upper side wall of the first hemispherical groove, and the annular countersunk hole is set at a certain angle with the first semi-annular groove, and the diameter of the annular countersunk hole is the same as the diameter of the first semi-annular groove.

[0022] Preferably, as an improvement, a second hemispherical groove is formed at the center of the fourth sand core, and a through hole is formed at the top of the second hemispherical groove, which is connected to the forming cavity; a second semi-annular groove is formed on the lower side wall of the second hemispherical groove, and the diameter of the second semi-annular groove is the same as that of the first semi-annular groove. The second semi-annular groove and the first semi-annular groove are arranged opposite to each other to form the sand inlet of the ball head casting. This ensures that the sand inlet and outlet of the ball head casting are arranged opposite to each other, and that the diameters of the sand inlet and outlet are the same, making the silica sand more stable during the transmission process, avoiding blockage and affecting the transmission efficiency. At the same time, it can ensure that the sand inlet and outlet speeds are comparable, reducing the impact force and effectively reducing the impact on the ball head casting.

[0023] Preferably, as an improvement, the inner cavity mold of the casting includes a second sand core and a third sand core that interlock; the second sand core and the third sand core have the same diameter, and the diameter of the second sand core is smaller than the diameter of the first hemispherical groove. This ensures that the second sand core and the third sand core can fit together completely, thereby guaranteeing the forming quality of the ball-head casting.

[0024] Preferably, as an improvement, the bottom of the second sand core is provided with a first protrusion, which is located within the annular countersunk hole to form a sand outlet; the upper sidewall of the second sand core is provided with a second protrusion, which is located within the first semi-annular groove. This ensures the formation effect of the sand outlet of the ball head casting.

[0025] Preferably, as an improvement, a first thickened layer is provided on the surface opposite to the second sand core and the second protrusion, forming the lower half of the thickened portion between the left side wall of the second sand core and the left side wall of the first hemispherical groove. This increases the wall thickness of the surface opposite to the sand inlet of the ball head casting, thereby increasing the impact resistance of the ball head casting to silica sand and thus improving the service life of the ball head casting.

[0026] Preferably, as an improvement, a third protrusion is provided on the lower sidewall of the No. 3 sand core, the third protrusion being located within the second semi-annular groove, and the diameter of the third protrusion being the same as the diameter of the second protrusion. This ensures the forming effect of the sand outlet of the ball-head casting.

[0027] Preferably, as an improvement, a second thickening layer is provided on the surface opposite to the third protrusion of the No. 3 sand core, forming the upper half of the thickened portion between the left side wall of the No. 3 sand core and the left side wall of the second hemispherical groove; a third thickening layer is provided on the top of the No. 3 sand core, forming an exit thickening portion between the top of the No. 3 sand core and the top of the second hemispherical groove. This increases the wall thickness of the surface opposite to the sand outlet of the ball head casting, thereby increasing the impact resistance of the ball head casting to silica sand and thus improving the service life of the ball head casting.

[0028] Conventional ball joints typically use high-manganese steel, which is harder and more wear-resistant, instead of molten steel commonly found in factories. This solution, however, employs a core-assembly method, constructing a mold blank into which molten steel can be directly poured. During pouring, the number and placement of thickened sections are carefully controlled, along with precise volume control, to ensure the ball joint's strength, effectively improve its impact resistance, and ultimately extend its service life. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the mold blank in an embodiment of the present invention;

[0031] Figure 3 This is a cross-sectional view of the molding cavity in an embodiment of the present invention;

[0032] Figure 4 As described in the embodiments of the present invention Figure 3 Schematic diagram of the cross-sectional structure of the middle AA section;

[0033] Figure 5 This is a right view of the molding cavity in an embodiment of the present invention. Detailed Implementation

[0034] The following detailed description illustrates the specific implementation method:

[0035] The reference numerals in the accompanying drawings include: No. 1 sand core, 101 first hemispherical groove, 102 annular countersunk hole, 103 first semi-annular groove, 2 first core skeleton, 3 No. 4 sand core, 301 second hemispherical groove, 302 second semi-annular groove, 303 through hole, 4 second core skeleton, 5 No. 2 sand core, 501 first protrusion, 502 second protrusion, 503 first thickened layer, 6 No. 3 sand core, 601 third protrusion, 602 second thickened layer, 603 third thickened layer, 7 tie rod, 8 mud core support, 9 sand inlet, 10 sand outlet, 11 thickened inlet, 12 thickened outlet, 13 connecting part, and 14 forming cavity.

[0036] The basic implementation examples are as follows: Figure 1 As shown:

[0037] A casting process for corner connectors of sand conveying pipes is disclosed, which involves casting the corner connectors of sand conveying pipes using molten steel without additional heat treatment, thereby reducing production costs while ensuring the service life of the connectors. The specific steps include:

[0038] Step 1: Based on the shape of the ball head casting, design sand core 1 (No. 1) and sand core 3 (No. 4); fasten sand core 1 and sand core 3 together to form the outer cavity mold of the ball head casting. Based on the shape of the inner cavity of the ball head casting, design sand core 5 (No. 2) and sand core 6 (No. 3) respectively; fasten sand core 5 and sand core 6 together to form the inner cavity mold of the ball head casting. In this embodiment, the sand cores are made of water glass sand or resin sand. Place the inner cavity mold into the outer cavity mold to form the overall mold blank for making the ball head casting. (See attached...) Figure 2 As shown, an irregular forming cavity 14 is formed between the inner cavity mold and the outer cavity mold. The forming cavity 14 is the outer contour shape of the ball head casting, and the outer surface of the forming cavity 14 has a through hole 303.

[0039] For details, see attached. Figure 3 As shown, the molding cavity 14 includes a thickened portion and a connecting portion 13 connected in sequence. The thickness of the thickened portion is 1.5-2 times the thickness of the connecting portion 13. The molding cavity 14 includes a sand inlet 9 and a sand outlet 10 arranged at a 90° angle to each other. The diameter of the sand inlet 9 is the same as the diameter of the sand outlet 10. There are two thickened portions, namely an inlet thickened portion 11 and an outlet thickened portion 12. The inlet thickened portion 11 is arranged opposite to the sand inlet 9, and the outlet thickened portion 12 is arranged opposite to the sand outlet 10.

[0040] For details, see attached. Figure 4 and attached Figure 5As shown, the thickened inlet portion 11 and the thickened outlet portion 12 are generally circular, and the thickened outlet portion 12 has the same diameter as the thickened inlet portion 11. The diameter of the thickened outlet portion 12 is the same as the diameter of the sand inlet 9, i.e., both are R1. The thickness L1 of the thickened portion is greater than the thickness L2 of the connecting portion 13, and L1 is 1.5 times L2.

[0041] For details, see attached. Figure 2 As shown, a first hemispherical groove 101 is formed at the center of the No. 1 sand core 1. An annular countersunk hole 102 is formed at the bottom of the first hemispherical groove 101. The diameter of the annular countersunk hole 102 is smaller than the diameter of the sand conveying pipe, thus forming the sand outlet 10 of the spherical head. A first semi-annular groove 103 is formed on the upper side wall of the first hemispherical groove 101. The first semi-annular groove 103 is set at a 90° angle with the annular countersunk hole 102, and the diameter of the first semi-annular groove 103 is the same as the diameter of the annular countersunk hole 102. On both sides of the No. 1 sand core 1, a first core bone 2 is provided, which is respectively embedded on both sides of the first hemispherical groove 101.

[0042] Specifically, the fourth sand core 3 is positioned opposite to the first sand core 1. A second hemispherical groove 301 is formed at the center of the fourth sand core 3, and the diameter of the second hemispherical groove 301 is the same as the diameter of the first hemispherical groove 101. A through hole 303 is formed at the top of the second hemispherical groove 301 to facilitate the pouring of molten steel through the through hole 303. A second semi-annular groove 302 is formed on the lower side of the second hemispherical groove 301; the second semi-annular groove 302 is positioned opposite to the first semi-annular groove 103 and has the same diameter as the first semi-annular groove 103, thus forming the sand inlet 9 of the spherical head. A second core rib 4 is provided on each side of the fourth sand core, and the second core rib 4 is provided on each side of the second hemispherical groove 301.

[0043] Specifically, the second sand core 5 is hemispherical in shape, with a diameter smaller than that of the first hemispherical groove 101. It can be placed entirely within the first hemispherical groove 101 of the first sand core 1 and is flush with the top of the first sand core 1. The bottom of the second sand core 5 has a first protrusion 501, which can be embedded in the annular countersunk hole 102. The upper sidewall of the second sand core 5 has a second protrusion 502, which has the same diameter as the first protrusion 501 and can be embedded in the first semi-annular groove 103. A first thickening layer 503 is provided on the sidewall of the second sand core 5 opposite to the second protrusion 502, so that the lower half of the thickened portion 11 is formed between the left sidewall of the second sand core 5 and the left sidewall of the first hemispherical groove 101.

[0044] Specifically, the No. 3 sand core 6 is hemispherical in shape, positioned opposite to the No. 2 sand core 5, and has the same diameter as the No. 2 sand core 5. The No. 3 sand core 6 can be placed entirely within the second hemispherical groove 301 of the No. 4 sand core 3, and is flush with the bottom end of the No. 4 sand core 3. The through hole 303 connects to the top end of the No. 3 sand core 6. A third protrusion 601 is provided on the lower side wall of the No. 3 sand core 6. The third protrusion 601 is positioned opposite to the second protrusion 502, and the diameter of the third protrusion 601 is the same as that of the second protrusion 502. The third protrusion 601 can be embedded in the second semi-annular groove 302.

[0045] Specifically, a second thickening layer 602 is provided on the side wall of the No. 3 sand core 6 opposite to the third protrusion 601. The second thickening layer 602 is disposed opposite to the first thickening layer 503, and forms the upper half of the thickened portion 11 between the left side wall of the No. 3 sand core 6 and the left side wall of the second hemispherical groove 301. A third thickening layer 603 is provided on the top of the No. 3 sand core 6, so that the top of the No. 3 sand core 6 and the top of the second hemispherical groove 301 form a thickened portion.

[0046] Step two: Place sand core 5 and sand core 6 sequentially into sand core 1, so that the first protrusion 501 is embedded in the annular countersunk hole 102 and the second protrusion 502 is embedded in the first semi-annular groove 103, so that sand core 6 is placed flush with sand core 5. Then, place an annular clay core support 8 at the edge of the third thickened layer 603 on top of sand core 6, and then lower sand core 3, so that the clay core support 8 separates sand core 6 and sand core 3, forming a thickened part 12. The clay core support 8 is placed at the junction of the thickened part 12 and the connecting part 13, and the mold blank is assembled in this way to complete the box assembly.

[0047] Step 3: Remove the outer sand molds of sand core 1 and sand core 3 on both sides to expose the first core rib 2 and the second core rib 4 pre-embedded on both sides; at the same time, use four tie rods 7 to weld their ends to the first core rib 2 and the second core rib 4 respectively, so that the first core rib 2 and the second core rib 4 are connected, thereby fixing sand core 1 and sand core 3 together through tie rods 7.

[0048] Step four: Pour molten steel into the through hole 303, maintaining the pouring temperature at 1540-1560℃, so that the molten steel flows into the forming cavity through the through hole 303 and fills the entire forming cavity, thereby forming the ball head casting.

[0049] Step 5: After keeping the mold blank warm for 3-4 hours, open the box and take out the ball head casting from the molding cavity. After cleaning the casting to remove sand, perform shot blasting.

[0050] Step six: Use gas cutting to remove the riser formed on the casting, perform magnetic particle inspection on the cut surface, and repair any cracks or defects to obtain the ball head casting.

[0051] In this embodiment, the connecting ball head is cast using a core-assembly molding method and directly poured from molten steel. This eliminates the need for heat treatment of the casting; instead, the casting can be used directly after surface cleaning, saving on manufacturing processes. Furthermore, the high hardness of the original as-cast structure of the solidified steel product directly meets the hardness requirements of the casting, improving its impact resistance to silica sand and thus extending its service life.

[0052] Meanwhile, during casting, the first core rib 2 and the second core rib 4, after assembly, are fixedly connected by tie rods 7, ensuring a stable connection between the No. 1 sand core 1 and the No. 4 sand core 3. This prevents the casting box from lifting during casting, thus ensuring stability and the quality of the casting. Furthermore, by adding a thickened layer and a mud core support 8, the wall thickness is increased on the opposite sides of the sand inlet and outlet after casting, thereby increasing the impact resistance of the ball head and effectively improving its service life. This method is simpler and more reliable than the conventional method of adding a pressure iron to the top of the upper core.

[0053] Furthermore, in this embodiment, molten steel or residual water used in conventional production can be used for casting, which is more suitable for internal manufacturing in foundries. Molten steel is easier to obtain and the cost is lower. In addition, the residual water formed after production cannot be reused in production, so the residual water can be effectively recycled and reused, reducing resource waste and effectively reducing production costs.

[0054] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A casting process for a ball-shaped joint of a sand conveying pipe corner connection, characterized in that... This includes the following steps: S1. Based on the casting shape and structure of the ball head, design an outer cavity mold and pre-embed multiple core bones in the outer cavity mold; the outer cavity mold includes a No. 1 sand core and a No. 4 sand core that interlock with each other; each of the No. 1 sand core and the No. 4 sand core has two core bones; on both sides of the No. 1 sand core, there is a first core bone; on both sides of the No. 4 sand core, there is a second core bone. S2, Design the inner cavity mold according to the inner cavity shape of the ball head casting; S3, the inner cavity mold is placed in the outer cavity mold in sequence, so that an irregular forming cavity is formed between the inner cavity mold and the outer cavity mold. The forming cavity is the outer contour shape of the ball head casting. The outer surface of the forming cavity has through holes, so that the inner cavity mold and the outer cavity mold constitute the casting blank. The forming cavity includes a thickened portion and a connecting portion connected in sequence. The forming cavity includes a sand inlet and a sand outlet arranged at a 90° angle to each other. The thickness L1 of the thickened portion is greater than the thickness L2 of the connecting portion, and L1 is 1.5 times L2. There are two thickened portions, including an inlet thickened portion and an outlet thickened portion. The inlet thickened portion is located on the opposite side of the sand inlet, and the outlet thickened portion is located on the opposite side of the sand outlet. At least one core support is provided between the inner mold and the outer mold of the casting, and the core support is located within the outlet thickened portion. S4. Fix and connect the cores in the mold blank, and pour molten steel into the forming cavity through the through hole, keeping the pouring temperature at 1540-1560℃; so that the molten steel fills the entire forming cavity. S5. After keeping the mold blank warm for 3-4 hours, take out the ball head casting formed in the molding cavity. S6 is used after cleaning the ball head casting and removing the riser.

2. The casting process for a corner connection ball head of a sand conveying pipe according to claim 1, characterized in that: The diameter of the thickened inlet is the same as the diameter of the sand inlet; the diameter of the thickened outlet is the same as the diameter of the sand outlet; the mud core is provided at the junction of the thickened outlet and the connecting part.

3. The casting process for a ball-shaped connector of a sand conveying pipe according to claim 1, characterized in that: The first hemispherical groove is provided at the center of the No. 1 sand core. An annular countersunk hole is opened at the bottom of the first hemispherical groove to form the sand outlet of the ball head casting. A first semi-annular groove is provided on the upper side wall of the first hemispherical groove. The annular countersunk hole is set at a certain angle with the first semi-annular groove. The diameter of the annular countersunk hole is the same as the diameter of the first semi-annular groove.

4. The casting process for a corner connection ball head of a sand conveying pipe according to claim 3, characterized in that: A second hemispherical groove is formed at the center of the No. 4 sand core. A through hole is formed at the top of the second hemispherical groove, and the through hole is connected to the forming cavity. A second semi-annular groove is formed on the lower side wall of the second hemispherical groove. The diameter of the second semi-annular groove is the same as that of the first semi-annular groove. The second semi-annular groove is arranged opposite to the first semi-annular groove to form the sand inlet of the ball head casting.

5. The casting process for a corner connection ball head of a sand conveying pipe according to claim 4, characterized in that: The inner cavity mold of the casting includes a No. 2 sand core and a No. 3 sand core that interlock with each other; the No. 2 sand core and the No. 3 sand core have the same diameter, and the diameter of the No. 2 sand core is smaller than the diameter of the first hemispherical groove.

6. The casting process for a corner connection ball head of a sand conveying pipe according to claim 5, characterized in that: The bottom of the No. 2 sand core is provided with a first protrusion, which is located in the annular countersunk hole to form a sand outlet; the upper side wall of the No. 2 sand core is provided with a second protrusion, which is located in the first semi-annular groove.

7. The casting process for a corner connection ball head of a sand conveying pipe according to claim 6, characterized in that: A first thickening layer is provided on the surface opposite to the second protrusion of the No. 2 sand core, so that the lower half of the thickening part is formed between the left side wall of the No. 2 sand core and the left side wall of the first hemispherical groove.

8. The casting process for a corner connection ball head of a sand conveying pipe according to claim 7, characterized in that: The lower sidewall of the No. 3 sand core is provided with a third protrusion, which is located in the second semi-annular groove. The diameter of the third protrusion is the same as that of the second protrusion.

9. The casting process for a corner connection ball head of a sand conveying pipe according to claim 8, characterized in that: A second thickening layer is provided on the surface opposite to the third protrusion of the No. 3 sand core, so that the upper half of the thickened part is formed between the left side wall of the No. 3 sand core and the left side wall of the second hemispherical groove; a third thickening layer is provided on the top of the No. 3 sand core, so that the top of the No. 3 sand core and the top of the second hemispherical groove form a thickened part.

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