Process for preventing spheroidal graphite cast iron milling head body from being loose and porous

Abstract

The application discloses a process method for preventing spheroidal graphite cast iron milling head body from shrinkage and porosity, which comprises the following steps: setting a steel pipe core, filling sand in the steel pipe core to form an inner cavity core of the milling head body; arranging a plurality of external chillers on the inner wall of a cavity of the milling head body; and setting a feeding riser above the parting surface of the milling head body, wherein a riser neck is arranged between the feeding riser and the parting surface of the cavity of the milling head body. The process method can stably produce the milling head body castings without shrinkage and porosity by optimizing the structure of the castings and the feeding riser, reasonably arranging the external chillers and abandoning the resin sand core. The process method is characterized in that the setting of the steel pipe core and the fact that the outer periphery of the cavity is covered with the external chillers make the overall rigidity of the cavity very good, so that the expansion of the mold caused by the graphite balls separated out in the solidification process of the spheroidal graphite cast iron milling head body can be resisted, and the internal self-feeding of the milling head body castings in the solidification process is realized.

Description

Technical Field

[0001] This invention relates to the field of casting technology, specifically to a process method for preventing shrinkage and porosity in ductile iron milling head bodies. Background Technology

[0002] Milling heads are common machine tool accessories and one of the most core and technologically advanced functional components of a machine tool. General-purpose milling heads can greatly expand the machining capabilities of a machine tool, enabling milling, drilling, tapping, and other machining operations at any angle. Five-axis multi-axis milling heads can be used to process key components in aerospace, defense, nuclear energy, and other energy fields, such as aircraft engine blades, nuclear power pump blades, thermal power turbine blades, and nuclear submarine propellers.

[0003] The milling head body is made of QT600-3 material. While relatively small in size compared to the main machine tool structure, its internal wall thickness varies. The main blank wall thickness is approximately 40mm, but the wall thickness at hot spots may exceed 100mm. Furthermore, it contains numerous crisscrossing oil passages. Internal defects such as shrinkage cavities and porosity are not permitted; otherwise, oil leakage will occur, affecting the milling head's usability. Currently, the scrap rate for milling head bodies produced is high. Shrinkage cavities sometimes appear in the internal cavity during machining, and oil leakage sometimes occurs during hydraulic pressure testing, severely impacting the overall machine assembly. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the prior art by providing a process method to prevent shrinkage and porosity in ductile iron milling head bodies.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A process for preventing shrinkage and porosity in ductile iron milling head bodies includes setting a steel core, designing the steel core according to the inner cavity shape and size of the milling head body, and filling the steel core with sand to form the inner cavity core of the milling head body.

[0007] It also includes a plurality of external chills arranged on the inner wall of the cavity of the milling head body;

[0008] It also includes providing a feeding riser above the parting surface of the milling head body, and providing a riser neck between the feeding riser and the parting surface at the cavity of the milling head body.

[0009] This process optimizes the casting and feeding riser structure, rationally arranges the external chills, and abandons the use of resin sand cores. By taking these measures, it is possible to stably produce milling head castings without shrinkage porosity or looseness.

[0010] This process, through the use of the steel core and the outer periphery of the cavity being covered with external chills, results in excellent overall rigidity of the cavity (milling head casting mold). This rigidity can resist the expansion of the mold caused by graphite spheroids precipitated during the solidification of the ductile iron milling head, enabling self-compensation of the milling head casting during solidification. Furthermore, the steel core is in direct contact with the molten iron during the casting process, allowing it to absorb heat within the inner cavity of the milling head casting, accelerating circumferential cooling and reducing the tendency for shrinkage cavities and porosity on the circumferential surface of the inner cavity.

[0011] Filling the steel core with sand can improve its stability at high temperatures and resist excessive deformation. The steel core and the sand core formed by the filling sand also have a certain degree of yielding, which is beneficial to the solidification of the casting. However, excessive yielding will cause dimensional deviations. The combination of the steel core and the filling sand can control this yielding within a reasonable range.

[0012] Although existing technologies also use chills to accelerate cooling, these chills are mostly placed in thick parts of the casting. In this process, the external chills are not only placed in thick parts, but also form a comprehensive response with the steel core, providing favorable conditions for the milling head casting made of ductile iron to form self-feeding.

[0013] By adding a riser neck at the feeding riser and parting surface, the riser neck will close after liquid feeding is completed, making the entire milling head cavity a completely closed cavity. This facilitates the filling of the internal structure with graphite precipitated during the solidification and cooling process of the ductile iron milling head, resulting in a dense structure and preventing defects such as shrinkage porosity and looseness. This method of promoting self-feeding of ductile iron castings can also reduce the amount of molten iron poured, thus reducing molten iron waste.

[0014] In some embodiments, the steel core is a straight steel tube with a wall thickness of 10-15 mm, and the upper and lower ends of the steel core extend out of the cavity.

[0015] In some embodiments, the steel core is a T-shaped steel pipe, which is formed by welding together multiple straight steel pipes with a wall thickness of 10-15mm, and the three ends of the T-shaped steel pipe extend out of the cavity respectively.

[0016] Regardless of the type of steel core, its end protrudes from the cavity. The purpose of this is to use the protruding part as the core head for connecting and fixing the steel core, because the steel core must be stably held in the cavity before the molten iron is poured and molded, and its position remains unchanged when the molten iron enters.

[0017] Furthermore, the external chills are designed according to the wall thickness of the milling head body. The size of the external chills in the thicker wall areas is larger than that in the thinner wall areas. The external chills cover the inner wall of the cavity and are arranged row by row along the inner wall of the cavity. There are gaps between each row and between adjacent external chills. The staggered placement of the external chills between the upper and lower rows helps to form support and ensures the stability of the cavity surface where the chills are arranged, preventing sand collapse.

[0018] Furthermore, the external chill has a cuboid structure, the width of the external chill is selected between 60-120mm, the length of the external chill is 150mm or 75mm, and the gap between the external chills is 15-20mm.

[0019] Furthermore, one side of the external chill is provided with a shallow groove, the side of the external chill with the shallow groove is arranged away from the inner wall of the cavity, and the side of the external chill close to the inner wall of the cavity is provided with coated sand.

[0020] When the external chill is placed in the cavity, the shallow recess can accommodate resin sand. After hardening, the resin sand will be integrated with the entire cavity mold, which can limit and fix the external chill, ensuring the accuracy and stability of the external chill placement.

[0021] The side of the external chill with the coated sand should face the molten iron. Due to the coating sand, the molten iron can be prevented from sticking to the external chill, which helps to prevent the chill from sticking and improves the surface quality of the milling head casting.

[0022] Furthermore, the depth of the recessed shallow groove is 8-12mm, and the recessed shallow groove forms an arc-shaped enclosure around the outer chill, with the maximum cross-sectional dimension of the enclosure not exceeding 2mm; the thickness of the coated sand is 3-5mm.

[0023] Furthermore, the maximum cross-sectional dimension of the riser neck is smaller than the minimum cross-sectional dimension of the feeding riser, the inner diameter of the feeding riser is 1.2-1.5 times the hot spot dimension of the milling head body, the size of the riser neck is half the size of the feeding riser, and the height dimension is not less than 60mm.

[0024] Furthermore, the filling sand is self-hardening resin sand, and the cavity is obtained by molding the milling head body using sand box resin sand.

[0025] Furthermore, the cavity is provided with a process patch at the thin wall above the hot spot of the milling head body, and the riser neck is arranged on the process patch, which is equivalent to moving the position of the hot spot upward, so as to facilitate the molten iron in the feeding riser to enter the hot spot, achieve sequential solidification, and prevent shrinkage defects from occurring.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This process method improves the compactness of the sand mold, optimizes the structure of the casting and feeding riser, rationally arranges the external chills, and abandons the use of resin sand cores. By taking these measures, it can stably produce milling head castings without shrinkage porosity or looseness; 2. Through the setting of the steel tube core and the fact that the outer periphery of the cavity is covered with the external chills, the overall rigidity of the cavity (milling head casting mold) is very good, which can resist the mold expansion caused by the graphite spheres precipitated during the solidification of the ductile iron milling head, and can realize the self-feeding of the milling head casting during the solidification process; moreover, the steel tube core is in direct contact with the molten iron during the casting process, which can absorb heat in the inner cavity of the milling head casting, accelerate the circumferential cooling of the inner cavity, and reduce the tendency of shrinkage porosity on the circumferential surface of the inner cavity; 3. The steel tube core has higher strength and resistance to shrinkage. 4. The impact resistance is stronger, preventing defects such as sand adhesion from appearing in the inner cavity of the milling head body, and facilitating the cleaning of the inner cavity of the casting; 5. In this process, the arrangement of the external chill is not only in the thick parts, but also forms a comprehensive response with the steel tube core, providing favorable conditions for the self-feeding of the ductile iron milling head casting; 6. The riser neck is added at the feeding riser and the parting surface. After liquid feeding is completed, the riser neck will be closed, making the entire milling head cavity a completely closed cavity. This is conducive to the graphite precipitated during the solidification and cooling process of the ductile iron milling head body filling the internal structure, making the milling head body structure dense and preventing defects such as shrinkage porosity and looseness; 7. By adding the process supplement to the thin wall above the hot spot, it effectively moves the hot spot of the casting blank upward, making it easier for the molten iron in the feeding riser to enter the hot spot, achieving sequential solidification and preventing shrinkage porosity defects. Attached Figure Description

[0027] Figure 1 This is a casting process diagram (cross-section) for preventing shrinkage and porosity in ductile iron milling head bodies according to the present invention.

[0028] Figure 2 This is a cross-sectional diagram of another casting process for preventing shrinkage and porosity in ductile iron milling head bodies according to the present invention.

[0029] Figure 3 This is a schematic diagram of the cross-sectional structure of the external chill of the present invention;

[0030] Figure 4 This is a top view of the external chill structure of the present invention;

[0031] In the figure: 1. Milling head body (schematic casting); 2. Steel tube core; 3. External chill; 301. Shallow recessed groove; 302. Enclosure; 4. Riser neck; 5. Feeding riser; 6. Process subsidy. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely 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.

[0033] In the description of this invention, it should be noted that the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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. Therefore, they should not be construed as limitations on this invention.

[0034] like Figure 1 and Figure 2 As shown, a process method for preventing shrinkage and porosity of ductile iron milling head body includes setting a steel tube core 2, designing the steel tube core 2 according to the inner cavity shape and size of the milling head body 1, and filling the steel tube core 2 with sand to form the inner cavity core of the milling head body 1.

[0035] It also includes arranging several external chills 3 on the inner wall of the cavity of the milling head body 1; Figure 1 and Figure 2 The upper end face of the milling head body is the parting surface, and the outer perimeter of the entire shape is a sand mold. That is to say, removing the milling head body 1 is the cavity of the milling head body.

[0036] It also includes a feeding riser 5 provided above the parting surface of the milling head body 1, and a riser neck 4 provided between the feeding riser 5 and the parting surface at the cavity of the milling head body 1.

[0037] It also includes improving the compactness of the sand mold in the cavity by flowing sand layer by layer and compacting the resin sand layer by layer during the manufacturing process.

[0038] This process improves the compactness of the sand mold, optimizes the structure of the casting and feeding risers, rationally arranges the external chills, and abandons the use of resin sand cores. By taking these measures, it is possible to stably produce milling head castings without shrinkage porosity or looseness.

[0039] This process, through the installation of the steel core 2 and the outer periphery of the cavity being covered with external chills 3, makes the overall rigidity of the cavity (milling head casting mold) very good. It can resist the mold expansion caused by the graphite spheroids precipitated during the solidification of the ductile iron milling head, and can realize the self-compensating shrinkage inside the milling head casting during the solidification process. Moreover, the steel core is in direct contact with the molten iron during the casting process, and can absorb heat in the inner cavity of the milling head casting, accelerate the circumferential cooling of the inner cavity, and reduce the tendency of shrinkage cavities and porosity on the circumferential surface of the inner cavity.

[0040] Compared to the inner cavity sand core made of resin sand in the prior art, the steel tube core has higher strength and stronger impact resistance. In addition, the melting point of the steel tube core is higher than the temperature of molten iron (the pouring temperature of molten iron for milling head casting is 1360-1380°), so the steel tube core will not melt or stick together. Defects such as sand adhesion will not occur in the inner cavity of the milling head body 1, which facilitates the cleaning of the inner cavity of the casting.

[0041] Filling the steel core 2 with sand can improve its stability at high temperatures and resist excessive deformation. The steel core 2 and the sand core formed by the filling will also have a certain degree of yielding, which is beneficial to the solidification of the casting. However, excessive yielding will cause dimensional deviations. The combination of the steel core and the filling can control this yielding within a reasonable range.

[0042] Although existing technologies also use chills to accelerate cooling, these chills are mostly placed in thick parts of the casting. In this process, the external chill 3 is not only placed in thick parts, but also forms a comprehensive response with the steel tube core 2, providing favorable conditions for the self-compensating milling head casting made of ductile iron.

[0043] A riser neck 4 is added at the feeding riser 5 and the parting surface. After liquid feeding is completed, the riser neck 4 will close, making the entire milling head cavity a completely closed cavity. This facilitates the filling of the internal structure with graphite precipitated during the solidification and cooling process of the ductile iron milling head, making the milling head structure dense and preventing defects such as shrinkage porosity and looseness. This method of promoting self-feeding of ductile iron parts can also reduce the amount of molten iron poured, reducing molten iron waste.

[0044] In some embodiments, the steel core 2 is a straight steel tube with a wall thickness of 10-15 mm, and the upper and lower ends of the steel core 2 extend out of the cavity.

[0045] In some embodiments, the steel core 2 is a three-way steel pipe, which is formed by welding together multiple straight steel pipes with a wall thickness of 10-15mm, and the three ends of the three-way steel pipe extend out of the cavity respectively.

[0046] Based on the model of the milling head, it can be divided into a straight milling head structure and a three-way milling head structure. These two types of milling head structures use straight steel pipes and three-way steel pipes as steel cores, respectively, which can form the inner cavity sand core in full size. Regardless of the type of steel core, the end of the steel core extends out of the cavity. The purpose of this is to use the extended part as the core head to connect and fix the steel core. This is because before the molten iron is poured and formed, the steel core must be stably held in the cavity and maintain its position when the molten iron enters.

[0047] Furthermore, the external chill 3 is designed according to the wall thickness of the milling head body. The size of the external chill 3 set at the thicker wall is larger than the size of the external chill 3 set at the thinner wall. The external chills cover the inner wall of the cavity. The external chills 3 are arranged row by row along the inner wall of the cavity, with gaps between each row and gaps between adjacent external chills 3. The external chills between the upper and lower rows are staggered.

[0048] The external chills 3, through their regular arrangement, can better exert their chilling effect; the staggered placement of the external chills between the upper and lower layers helps to form support, ensuring the stability of the cavity surface where the chills are arranged and preventing sand collapse.

[0049] For milling head castings, which have an internal hole structure and an uneven external shape, the inconsistent wall thickness may be on the circumference or on the plane. The size and number of external chills distributed in different locations will affect their solidification properties.

[0050] The external chill 3 used in this process is a cuboid structure, combined with... Figure 3 and Figure 4 As shown, the width of the external chill is selected between 60-120mm, such as 35mm, 55mm, 70mm and 110mm; the length of the external chill is 150mm or 75mm (half the length); and the gap between the external chills is 15-20mm.

[0051] The circumferential surface uses 60mm wide external chills, while other planes generally use 120mm wide external chills. However, considering the size of the plane, the width can be selected from 60mm, 75mm, 90mm and 120mm.

[0052] Furthermore, one side of the external chill 3 is provided with a shallow groove 301, and the side of the external chill 3 with the shallow groove 301 is arranged away from the inner wall of the cavity, while the side of the external chill 3 close to the inner wall of the cavity is provided with coated sand.

[0053] When the external chill is placed in the cavity, the shallow recess can accommodate resin sand. After hardening, the resin sand will be integrated with the entire cavity mold, which can limit and fix the external chill, ensuring the accuracy and stability of the external chill placement.

[0054] The side of the external chill 3 with the coated sand should face the molten iron. Due to the coating sand, the molten iron can be prevented from sticking to the external chill, which helps to prevent the chill from sticking and improves the surface quality of the milling head casting.

[0055] Furthermore, the depth of the recessed shallow groove 301 is 8-12mm, and the recessed shallow groove 301 forms an arc-shaped enclosure 302 around the outer chill, the maximum cross-sectional dimension of the enclosure 302 not exceeding 2mm; the thickness of the coated sand is 3-5mm.

[0056] For example, when the total thickness of the outer chill is 35mm, the thickness of the recessed portion in the middle is about 10mm. The same logic applies to other thicknesses; for example, if the thickness is 55mm, the inner dimension is 45mm, and if the thickness is 70mm, the inner dimension is 60mm, a difference of 10mm. The resulting enclosure has rounded corners on both the inner and outer sides. The dimensions of the outer chill are shown in Table 1 below, where B is the width of the outer chill and B1 is the width of the shallow recessed groove.

[0057] Table 1: Dimensions and weight of external chills with a length of 150mm

[0058] 1 60 58 1.9 2 75 73 2.2 3 90 88 2.8 4 120 118 3.8

[0059] Furthermore, the maximum cross-sectional dimension of the riser neck 4 is smaller than the minimum cross-sectional dimension of the feeding riser 5, and the inner diameter of the feeding riser is 1.2-1.5 times the hot spot size of the milling head body. Preferably, the size of the riser neck is about half the diameter of the feeding riser, and the size of the riser neck is about 60mm.

[0060] Furthermore, the filling sand is self-hardening resin sand, and the cavity is obtained by molding the milling head body using sand box resin sand.

[0061] Furthermore, the cavity is provided with a process subsidy 6 on the thin wall above the hot spot of the milling head body, and the riser neck 4 is arranged on the process subsidy 6.

[0062] For hot spots surrounded by thin walls on the top and bottom, it is usually difficult for molten iron to enter the hot spot. By adding the process supplement 6 to the thin wall above the hot spot, it is actually effective to move the hot spot of the casting blank upward, so that the molten iron in the feeding riser 5 can enter the hot spot, achieve sequential solidification, and prevent shrinkage defects from occurring.

[0063] exist Figure 1 In the production process of the straight-through milling head shown, a steel pipe with a wall thickness of 12mm and an outer diameter of about 152mm is used as the inner core of the inner cavity. Depending on the wall thickness, different thicknesses of external chills are selected on the outside of the milling head body, so that the entire milling head body solidifies in a high-rigidity cavity. A riser neck is added below the riser used for feeding. The size of the riser neck is half the size of the feeding riser. After the molten iron in the riser replenishes the liquid contraction in the milling head body, the riser neck is closed, so that the graphite precipitated in the later solidification of the milling head body self-feeds in the closed high-rigidity cavity, forming a dense structure.

[0064] exist Figure 2In the production process of the tee milling head shown, a steel pipe with an inner wall thickness of 12mm and an outer diameter of about 170mm is first made by welding to serve as the inner core. Then, corresponding external chills are placed according to the wall thickness of different parts of the milling head body to obtain a high-rigidity milling head body cavity. In addition, in order to facilitate the feeding of the thick hot section of the milling head body, a process supplement is designed to facilitate the feeding of the hot section of the milling head body by the molten iron in the feeding riser through the riser neck. Similarly, after the liquid shrinkage of the feeding hot section is completed, the riser neck is sealed in time, so that the graphite precipitated in the later solidification of the milling head body self-feeds in the sealed high-rigidity cavity to form a dense structure.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preventing shrinkage and porosity in ductile iron milling head bodies, characterized in that, This includes setting a steel core, designing the steel core according to the inner cavity shape and size of the milling head body, and filling the steel core with sand to form the inner cavity core of the milling head body; It also includes arranging a plurality of external chills on the inner wall of the cavity of the milling head body; the external chills are designed according to the wall thickness of the milling head body, and the size of the external chills arranged in the thicker wall area is larger than the size of the external chills arranged in the thinner wall area; the external chills cover the inner wall of the cavity, and the external chills are arranged row by row along the inner wall of the cavity, with gaps between each row and gaps between adjacent external chills, and the external chills in the upper and lower rows are staggered; It also includes a feeding riser provided above the parting surface of the milling head body, and a riser neck provided between the feeding riser and the parting surface at the cavity of the milling head body; the maximum cross-sectional dimension of the riser neck is smaller than the minimum cross-sectional dimension of the feeding riser, the inner diameter of the feeding riser is 1.2-1.5 times the hot spot dimension of the milling head body, and the height dimension of the riser neck is not less than 60mm; The steel core has a melting point higher than that of molten iron, so it will not melt or stick together.

2. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 1, characterized in that, The steel core is a straight steel tube with a wall thickness of 10-15 mm, and the upper and lower ends of the steel core extend out of the cavity.

3. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 1, characterized in that, The steel core is a three-way steel pipe, which is welded together from multiple straight steel pipes with a wall thickness of 10-15mm, and the three ends of the three-way steel pipe extend out of the cavity.

4. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 1, characterized in that, The external chill has a cuboid structure, the width of the external chill is selected between 60-120mm, the length of the external chill is 150mm or 75mm, and the gap between the external chills is 15-20mm.

5. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 1, characterized in that, One side of the external chill is provided with a shallow groove, and the side of the external chill with the shallow groove is arranged away from the inner wall of the cavity. The side of the external chill close to the inner wall of the cavity is provided with coated sand.

6. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 5, characterized in that, The depth of the recessed shallow groove is 8-12mm, and the recessed shallow groove forms an arc-shaped enclosure around the outer chill, with the maximum cross-sectional dimension of the enclosure not exceeding 2mm; the thickness of the coated sand is 3-5mm.

7. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 1, characterized in that, The filling sand is self-hardening resin sand, and the cavity is obtained by molding the milling head body using sand box resin sand.

8. The process method for preventing shrinkage and porosity of ductile iron milling head bodies according to claim 1, characterized in that, The cavity is provided with a process patch on the thin wall above the hot spot of the milling head body, and the riser neck is arranged on the process patch.

Images