A mold structure for a cast iron piston with an inner cooling oil cavity and a piston manufacturing method

Abstract

The present invention relates to the field of piston casting technology, and specifically to a mold structure for a cast iron piston with an inner cooling oil cavity and a piston manufacturing method, comprising an outer mold and a core mold, wherein the core mold is hollow inside and has a through hole on the side wall, and the top of the core mold forms an inner cooling oil cavity sand core with an inner conformal hollow design, and the hollow inner cavity of the inner cooling oil cavity sand core is connected to the inner hollow of the core mold through a connecting column exhaust channel; the bottom wall of the outer mold inner cavity is directly opposite to the geometric center of the core mold, and a venting channel is provided, and a vertical runner is formed inside the side wall of one side of the outer mold inner cavity, and a plurality of horizontal runners connecting the vertical runner with the outer mold inner cavity are provided from bottom to top at intervals between the side wall between the vertical runner and the outer mold inner cavity, and a pouring cup is formed on the top of the vertical runner, and a closed riser is formed on the top wall of the outer mold inner cavity and is directly opposite to the venting channel, and the side wall of the closed riser is connected to the outside world through the inclined riser venting channel. The present invention is easy to operate, can be gravity cast sequentially solidified and self-shrinkage compensated, simplifies the production process, and improves production efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of piston casting, and in particular to a mold structure for a cast iron piston with an inner cooling oil cavity and a piston manufacturing method. Background Art

[0002] The piston is the core part of the internal combustion engine. With the improvement of emission standards, the power density of the internal combustion engine continues to increase, and the combustion temperature and mechanical load that the piston needs to withstand also increase accordingly. Especially for large-diameter marine or commercial engines, aluminum alloy pistons can no longer meet the use requirements. Cast iron pistons have the advantages of low cost and high strength and rigidity, and are increasingly used. In order to improve the reliability of cast iron pistons, it is necessary to cool the top of the piston that contacts the high-temperature combustion gas. Usually, an internal cooling oil cavity is set in the piston head. During operation, the piston head is cooled by spraying oil into the cooling oil cavity. In order to cast an internal cooling oil cavity in a cast iron piston, it is necessary to bond or assemble the internal cooling oil cavity sand core together when making the mold, and then cast it once when casting the piston, and then clean the sand mold to form a cast iron piston with a cooling oil cavity.

[0003] Patent 202211383436.4 introduces a mold structure for a ductile iron piston with an internal cooling oil chamber. The internal cooling oil chamber sand core needs to be bonded to the inner core of the mold. This bonding process requires manual operation and cannot fully guarantee the height position of the internal cooling oil chamber; Patent 202020204176.X introduces a ductile iron piston sand core structure, which requires adding cooling iron to the bottom and top molds, and is cast with the top facing down. The operation is complicated and cannot achieve sequential solidification.

[0004] In order to cast an inner cooling oil cavity, the inner cooling oil cavity sand core can only be made separately and then bonded to the mold due to the sand core manufacturing process. In addition, the sand core emits a large amount of gas when heated during the casting process. This bonding of the sand core affects the exhaust of the sand core, thereby causing the inner cooling oil cavity sand core to drift and break, resulting in a high casting scrap rate. In addition, the bonding of the sand core requires manual operation, which is inefficient and affects the positioning accuracy. Therefore, there is an urgent need for a mold structure and piston manufacturing process that can simplify the cast iron piston with an inner cooling oil cavity. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a mold structure for a cast iron piston with an inner cooling oil chamber and a piston manufacturing method. The inner cooling oil chamber sand core and the piston mold are manufactured together without bonding, thereby ensuring the position accuracy of the inner cooling oil chamber. The conformal hollow inner cooling oil chamber sand core solves the problems of inner cooling oil chamber sand core drift and breakage caused by large gas emission of the sand core. The casting is performed from bottom to top to improve the molding quality. The designed riser has the ability to compensate for shrinkage, does not require chiller, is easy to operate as a whole, and solidifies sequentially, thereby improving production efficiency and casting quality.

[0006] The present invention is achieved through the following technical solutions:

[0007] Provided is a mold for a cast iron piston with an inner cooling oil cavity, comprising an outer mold and a core mold arranged in the inner cavity of the outer mold, the core mold is hollow inside and a through hole connected to the inner cavity of the outer mold is opened on the side wall, an inner cooling oil cavity sand core is formed on the top of the core mold and is integrally formed with the core mold and has a hollow inner shape, the hollow inner cavity of the inner cooling oil cavity sand core is connected to the hollow inner cavity of the core mold through a vertically arranged connecting column exhaust channel; a bottom wall of the outer mold inner cavity is directly opposite to the geometric center of the core mold and is penetrated by a ventilation channel connected to the bottom of the core mold inner cavity, a vertical runner is formed inside one side wall of the outer mold inner cavity, a plurality of horizontal runners connecting the vertical runner with the outer mold inner cavity are spaced apart from bottom to top on the side wall between the vertical runner and the outer mold inner cavity, a pouring cup is formed on the top of the vertical runner, a closed riser is recessed on the top wall of the outer mold inner cavity and is directly opposite to the ventilation channel, and the side wall of the closed riser is connected to the outside through an inclined riser ventilation channel.

[0008] In this solution, the inner cooling oil cavity sand core and the piston mold are made together without bonding, thereby ensuring the position accuracy of the inner cooling oil cavity. At the same time, a conformal hollow inner cooling oil cavity sand core is designed to solve the problem of inner cooling oil cavity sand core drift and fracture caused by large gas emission of the sand core, thereby improving the molding quality. Multiple cross runners are designed to form a bottom-up casting molding method, making the pouring process more stable. At the same time, several cross runners from the bottom to the top will compensate for the shrinkage of the outer circle to avoid casting defects such as pores and slag inclusions, thereby improving the casting quality. By designing a thermal insulation riser, the riser can be insulated to increase the shrinkage compensation capacity and the air permeability of the riser can be increased to avoid pores.

[0009] Furthermore, the riser height is 25-35% of the piston height, the riser bottom diameter is 30-40% of the piston diameter, and the riser top diameter is 30%-60% of the riser bottom diameter.

[0010] Furthermore, the outer mold is a left-right split structure along the vertical runner direction, and the left outer mold and the right outer mold are connected by positioning pins after being spliced.

[0011] Only the outer mold is split left and right along the runner direction, and the core mold is not split to ensure that the core mold is complete and integrated.

[0012] Furthermore, the bottom wall surface of the left outer mold and the bottom wall surface of the right outer mold are respectively formed with positioning grooves for limiting cooperation with the bottom surface of the core mold.

[0013] A positioning groove is formed between the left outer mold and the right outer mold. The two positioning grooves are spliced ​​into a circular positioning groove for accommodating the core mold, which can facilitate the positioning of the core mold and ensure the stability of the core mold during casting.

[0014] Furthermore, the diameter of the vertical runner is 3-5 times the wall thickness of the piston, and the diameter of the horizontal runner is 20%-40% of the vertical runner.

[0015] Preferably, the total cross-sectional area of ​​the horizontal runner is larger than the cross-sectional area of ​​the vertical runner.

[0016] The total cross-sectional area of ​​the horizontal runner should be larger than that of the vertical runner in order to form a stable pouring speed and avoid air entrainment.

[0017] Furthermore, the height of the pouring cup is 30-60 mm higher than the riser, and the gate diameter at the top of the pouring cup is 2-4 times that of the vertical runner.

[0018] Furthermore, the wall thickness of the core mold is 15-30 mm, and the wall thickness of the conformal inner cooling oil cavity sand core is 5-10 mm.

[0019] A method for manufacturing a cast iron piston using a mold for a cast iron piston with an inner cooling oil cavity comprises the following steps:

[0020] S1. Design the blank casting according to the piston product and processing allowance;

[0021] S2. Design a sand core mold according to the casting, design a pouring cup, runner and riser on the mold, and divide the outer mold into a left outer mold, a right outer mold and a core mold;

[0022] S3, making the mold model after parting into a sand core mold;

[0023] S4, assemble the left outer mold, the right outer mold and the core mold, put the left outer mold first, then put the core mold into the left outer mold, assemble the right outer mold to the left outer mold and fix it with the positioning pin to form a complete piston casting mold;

[0024] S5, bury the assembled sand core mold into the sand box, and then cast the molten cast iron liquid with a temperature not less than 1300°C into the mold through the pouring cup until the riser and the vent hole are filled with molten iron, and the piston casting is completed;

[0025] S6. The sand core mold after cooling and forming is disassembled and cleaned, and then the runner and riser are cut to obtain a blank casting of the piston.

[0026] Preferably, the pouring speed is 120-180 kg / min, and the pouring time is 15-35 s.

[0027] Furthermore, when the mold is assembled, the fitting clearance between the core mold and the left outer mold and the right outer mold is 0.3-0.8 mm.

[0028] Preferably, the pouring cup includes a sizing portion and a reducing portion located below the sizing portion, the sizing portion being a hollow cylindrical structure, the top height of which is greater than the top height of the outer mold; the reducing portion being a hollow inverted frustum-shaped structure, the bottom inner diameter of the inverted frustum-shaped structure being the same as the inner diameter of the vertical runner.

[0029] Beneficial effects of the present invention:

[0030] In the present invention, the inner cooling oil cavity sand core and the piston mold are made together without bonding or assembly, which can simplify the production process and ensure the position of the inner cooling oil cavity and the position accuracy of the inner cooling oil cavity. At the same time, a conformal hollow inner cooling oil cavity sand core is designed to reduce the volume of the sand mold while ensuring the strength of the sand core, thereby reducing the gas emission of the sand core. The hollow inner cooling oil cavity sand core is connected with the hollow core mold to form an exhaust channel, so that the gas emitted by the inner cooling oil cavity sand core after being heated can be discharged in time, which solves the problem of drift and fracture of the inner cooling oil cavity sand core caused by large gas emission of the sand core, and improves the molding quality. At the same time, a casting system is provided, which forms a bottom-up casting molding method by designing multiple cross runners, so that the casting process is more stable. At the same time, several cross runners from the bottom to the top can compensate for the shrinkage of the outer circle to avoid casting defects such as pores and slag inclusions, thereby improving the casting quality. By designing a heat-insulating riser, the riser can be insulated to increase the shrinkage compensation capacity and the air permeability of the riser can be increased to avoid pores.

[0031] By designing several horizontal runners from bottom to top, the high-temperature molten iron can be turbulent, forming a bottom-up casting molding method. By designing the total cross-sectional area of ​​the horizontal runner to be larger than the vertical runner area, the pouring speed can be slowed down, thereby making the pouring process more stable and avoiding the entrainment of high-temperature molten iron. At the same time, the bottom-up design of the horizontal runner can compensate for the shrinkage of the outer circle of the piston during the solidification process.

[0032] The riser in the present invention is of a closed type, which can not only insulate the riser, but also cooperate with the riser exhaust channels on both sides to exhaust the mold, which can effectively eliminate casting defects such as pores and improve the casting quality.

[0033] The key point of the cast iron piston mold with inner cooling oil cavity and the piston manufacturing method of the present invention is that it also provides a production method of cast iron piston. Through the hollow design of the inner cooling oil cavity sand core and the hollow design of the core mold, as well as the design ratio between the various structures, the cooling speed from bottom to top can be made consistent during piston casting, thereby achieving sequential solidification and avoiding the generation of casting heat nodes and shrinkage. Through the connection of the inner cooling oil cavity sand core, the core mold and the outer mold vent hole, the overall ventilation effect of the mold can be ensured, and there is no need to place a chiller, simplifying the assembly and casting process. Through the design of the ratio of the riser height to the piston height, the shrinkage compensation effect of the riser can be guaranteed. Through the design of the vertical runner and the horizontal runner structure, the runner can compensate for the shrinkage of the piston while the piston solidifies sequentially. The above technical scheme can achieve the beneficial effects of gravity casting sequential solidification and self-shrinkage compensation, thereby simplifying the casting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a cross-sectional view of the mold structure in the present invention.

[0035] Figure 2It is a parameter comparison diagram of the QT500 cast iron piston casting of Example 1 of the present invention and the traditional process casting.

[0036] Figure 3 It is a parameter comparison diagram of the HT400 cast iron piston casting of Example 2 of the present invention and the conventional casting.

[0037] Figure 4 It is a parameter comparison diagram of the RuT420 cast iron piston casting of Example 3 of the present invention and the conventional casting.

[0038] As shown in the figure:

[0039] 1 is a pouring cup, 2 is a vertical pouring channel, 3 is a horizontal pouring channel, 4 is a venting channel, 5 is a riser, 6 is a riser venting channel, 7 is an inner cooling oil cavity sand core, 8 is a connecting column exhaust channel, 9 is an outer mold, 10 is a core mold, and 11 is a through port. DETAILED DESCRIPTION

[0040] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0041] A mold for a cast iron piston with an inner cooling oil cavity comprises an outer mold 9 and a core mold 10 arranged in the inner cavity of the outer mold 9, the core mold 10 is hollow inside and has a through hole 11 connected to the inner cavity of the outer mold 9 on the side wall, the top of the core mold 10 is formed with an inner cooling oil cavity sand core 7 which is integrally formed with the core mold 10 and has a hollow inner shape, the hollow inner cavity of the inner cooling oil cavity sand core 7 is connected to the hollow inner cavity of the core mold 10 through a vertically arranged connecting column exhaust channel 8; the bottom wall of the inner cavity of the outer mold 9 is directly opposite to the geometric center of the core mold 10 and is penetrated by a ventilation channel 4 connected to the bottom of the inner cavity of the core mold 10, a vertical runner 2 is formed inside the side wall of one side of the inner cavity of the outer mold 9, and a plurality of horizontal runners 3 connecting the vertical runner 2 with the inner cavity of the outer mold 9 are spaced apart from bottom to top on the side wall, such as Figure 1 As shown, in the present invention, six horizontal runners 3 are evenly spaced from bottom to top on the side of the vertical runner 2, and the total cross-sectional area of ​​the horizontal runners 3 is larger than the cross-sectional area of ​​the vertical runner 2 to form a stable pouring speed and avoid air entrainment.

[0042] A pouring cup 1 is formed at the top of the vertical runner 2, and a closed riser 5 facing the air vent 4 is formed on the top wall of the inner cavity of the outer mold 9, and the side wall of the closed riser 5 is connected to the outside through an inclined riser air vent 6.

[0043] The outer mold 9 is a left-right split structure along the vertical runner 2. The left outer mold and the right outer mold are connected by a positioning pin after being spliced. In order to ensure the stability of the assembly of the core mold 10 and the outer mold 9, the bottom wall surface of the left outer mold and the bottom wall surface of the right outer mold are respectively formed with positioning grooves for limiting the bottom surface of the core mold 10. The matching clearance between the core mold and the left and right outer molds is 0.5mm.

[0044] Example 1

[0045] A mold structure for a cast iron piston with an inner cooling oil cavity and a method for manufacturing a cast iron piston, comprising the following steps:

[0046] S1. Design the blank casting according to the piston product and processing allowance.

[0047] S2. Design the sand core mold according to the casting, design the runner and riser on the mold, and divide the mold into left outer mold, right outer mold and core mold. The piston height is 290mm, the diameter is 200mm and the wall thickness is 12mm. The upper mold height is 270mm, the riser height is 90mm, the riser bottom is 70mm, the riser top diameter is 130mm, the gate height is 40mm higher than the riser, the vertical runner diameter is 50mm, the gate diameter is 90mm, the conformal internal cooling oil cavity sand core wall thickness is 6mm, the connecting column wall thickness is 6mm, the lower mold height is 140mm, and the cross runner diameter is 15mm.

[0048] S3, making the mold model after parting into a sand core mold.

[0049] S4. Assemble the completed left outer mold, right outer mold and core mold, put the left outer mold first, then put the core mold into the lower left outer mold, and finally assemble the right outer mold onto the left outer mold to form a complete piston casting mold.

[0050] S5. Bury the assembled sand core mold into the sand box, then heat the smelted QT500 to 1450℃ and cast it into the mold through the pouring cup. The pouring speed is 130kg / min and the pouring time is 30s. Until the riser and the air vent are filled with the molten metal, the piston casting is completed.

[0051] S6. The sand core mold after cooling and forming is disassembled and cleaned, and then the runner and the riser are cut to obtain a blank casting of the piston.

[0052] The piston casting produced by Example 1 was compared with the QT500 cast iron piston casting produced by the traditional process. The results are as follows: Figure 2 The performance of the casting obtained by the piston manufacturing method of the present invention is obviously better than that of the casting obtained by the traditional method.

[0053] Example 2

[0054] A mold structure for a cast iron piston with an inner cooling oil cavity and a method for manufacturing a cast iron piston, comprising the following steps:

[0055] S1. Design the blank casting according to the piston product and processing allowance.

[0056] S2. Design the sand core mold according to the casting, design the runner and riser on the mold, and divide the mold into left outer mold, right outer mold and core mold. The piston height is 330mm, the diameter is 230mm and the wall thickness is 15mm. The upper mold height is 300mm, of which the riser height is 100mm, the riser bottom diameter is 90mm, the riser top diameter is 150mm, the gate height is 50mm higher than the riser, the vertical runner diameter is 60mm, the gate diameter is 150mm, the wall thickness of the sand core of the conformal internal cooling oil cavity is 7mm, the wall thickness of the connecting column is 7mm, the lower mold height is 150mm, and the cross runner diameter is 20mm.

[0057] S3, making the mold model after parting into a sand core mold.

[0058] S4. Assemble the completed left outer mold, right outer mold and core mold, put the left outer mold first, then put the core mold into the lower left outer mold, and finally assemble the right outer mold onto the left outer mold to form a complete piston casting mold.

[0059] S5. Bury the assembled sand core mold into the sand box, then heat the smelted HT400 to 1500℃ and cast it into the mold through the pouring cup. The pouring speed is 150kg / min and the pouring time is 20s. When the riser and the air vent are filled with the molten metal, the piston casting is completed.

[0060] S6. The sand core mold after cooling and forming is disassembled and cleaned, and then the runner and the riser are cut to obtain a blank casting of the piston.

[0061] The piston casting produced by Example 1 was compared with the HT400 cast iron piston casting produced by the conventional process. The results are as follows: Figure 3 shown.

[0062] Example 3

[0063] A mold structure for a cast iron piston with an inner cooling oil cavity and a method for manufacturing a cast iron piston, comprising the following steps:

[0064] S1. Design the blank casting according to the piston product and processing allowance;

[0065] S2. Design the sand core mold according to the casting, design the runner and riser on the mold, and divide the mold into left outer mold, right outer mold and core mold. The piston height is 250mm, diameter is 170mm, and wall thickness is 8mm. The upper mold height is 230mm, of which the riser height is 80mm, the riser bottom diameter is 60mm, the riser top diameter is 120mm, the gate height is 30mm higher than the riser, the vertical runner diameter is 35mm, the gate diameter is 110mm, the wall thickness of the sand core of the conformal internal cooling oil cavity is 5mm, the wall thickness of the connecting column is 5mm, the lower mold height is 110mm, and the cross runner diameter is 10mm.

[0066] S3, making the mold model after parting into a sand core mold.

[0067] S4. Assemble the completed left outer mold, right outer mold and core mold, put the left outer mold first, then put the core mold into the lower left outer mold, and finally assemble the right outer mold onto the left outer mold to form a complete piston casting mold.

[0068] S5. Bury the assembled sand core mold into the sand box, then heat the smelted RuT420 to 1520℃ and cast it into the mold through the pouring cup. The pouring speed is 100kg / min and the pouring time is 25s. When the riser and the air vent are filled with the molten metal, the piston casting is completed.

[0069] S6. The sand core mold after cooling and forming is disassembled and cleaned, and then the runner and the riser are cut to obtain a blank casting of the piston.

[0070] The piston casting produced by Example 1 was compared with the RuT420 cast iron piston casting produced by the conventional process. Figure 4 Compared with the traditional process, the casting obtained by the casting method of this embodiment has better performance in tensile strength, hardness and elongation.

[0071] Of course, the above description is not limited to the above examples. Technical features not described in the present invention can be achieved by or by using existing technologies, which will not be described here. The above embodiments and drawings are only used to illustrate the technical scheme of the present invention and are not limitations of the present invention. The present invention is described in detail with reference to the preferred implementation methods. Ordinary technicians in this field should understand that changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention do not depart from the purpose of the present invention, and should also fall within the scope of protection of the claims of the present invention.

Claims

1. A mold for a cast iron piston with an inner cooling oil cavity, comprising an outer mold and a core mold arranged in the inner cavity of the outer mold, characterized in that: The core mold is hollow inside and has a through hole connected to the outer mold cavity on its side wall. An inner cooling oil cavity sand core is formed on the top of the core mold, which is integrally formed with the core mold and has a hollow interior. The hollow inner cavity of the inner cooling oil cavity sand core is connected to the hollow inside of the core mold through an exhaust duct of a vertically arranged connecting column; a ventilation duct connected to the bottom of the core mold cavity is penetrated through the bottom wall of the outer mold cavity facing the geometric center of the core mold, a vertical runner is formed inside the side wall of one side of the outer mold cavity, and a plurality of horizontal runners connecting the vertical runner with the outer mold cavity are spaced apart from bottom to top on the side wall between the vertical runner and the outer mold cavity, a pouring cup is formed on the top of the vertical runner, and a closed riser is recessed on the top wall of the outer mold cavity facing the ventilation duct, and the side wall of the closed riser is connected to the outside world through an inclined riser ventilation duct.

2. The mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The riser height is 25-35% of the piston height, the riser bottom diameter is 30-40% of the piston diameter, and the riser top diameter is 30%-60% of the riser bottom diameter.

3. The mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The outer mold is a left-right split structure along the vertical runner direction, and the left outer mold and the right outer mold are connected by positioning pins after being spliced.

4. The mold structure for a cast iron piston with an inner cooling oil cavity according to claim 3 is characterized in that: The bottom wall surface of the left outer mold and the bottom wall surface of the right outer mold are respectively formed with positioning grooves for limiting cooperation with the bottom surface of the core mold.

5. The mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The diameter of the vertical runner is 3-5 times the thickness of the piston wall, and the diameter of the horizontal runner is 20%-40% of the vertical runner.

6. The mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The total cross-sectional area of ​​the horizontal runner should be larger than the cross-sectional area of ​​the vertical runner.

7. The mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The height of the pouring cup is 30-60mm higher than the riser, and the gate diameter at the top of the pouring cup is 2-4 times that of the vertical runner.

8. The mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The wall thickness of the core mold is 15-30mm, and the wall thickness of the conformal internal cooling oil cavity sand core is 5-10mm.

9. A method for manufacturing a cast iron piston using the mold for a cast iron piston with an inner cooling oil cavity according to claim 1, characterized in that: The following steps are involved: S1. Design the blank casting according to the piston product and processing allowance; S2. Design a sand core mold according to the casting, design a pouring cup, runner and riser on the mold, and divide the outer mold into a left outer mold, a right outer mold and a core mold; S3, making the mold model after parting into a sand core mold; S4, assemble the left outer mold, the right outer mold and the core mold, put the left outer mold first, then put the core mold into the left outer mold, assemble the right outer mold to the left outer mold and fix it with the positioning pin to form a complete piston casting mold; S5, bury the assembled sand core mold into the sand box, and then cast the molten cast iron liquid with a temperature not less than 1300°C into the mold through the pouring cup until the riser and the vent hole are filled with molten iron, and the piston casting is completed; S6. The sand core mold after cooling and forming is disassembled and cleaned, and then the runner and riser are cut to obtain a blank casting of the piston.

10. The method for manufacturing a cast iron piston with a mold for a cast iron piston with an inner cooling oil cavity according to claim 9, characterized in that: The pouring speed is 120-180kg / min and the pouring time is 15-35s.

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