阅读说明：本技术 轻质结构砂芯模成型方法 (Light structure sand core mold forming method ) 是由 马娟 姚桂平 高李帅 刘朝晖 舒威 于 2020-11-17 设计创作，主要内容包括：本发明涉及固体火箭发动机壳体成型技术领域,公开了一种轻质结构砂芯模成型方法,包括如下步骤：分区并制作砂饼成型模具及缠绕芯轴；配制聚乙烯醇水溶液；制作共混砂料；将共混砂料填入砂饼成型模具中并捣实；加热固化；打磨后将砂饼连同所述轴套一起从砂饼成型模具中取出；将每个区域的砂饼依次套装在缠绕芯轴上,并用锁紧螺母压紧,然后将砂饼之间的对接缝填补平整；将组装好的砂芯模机加至所需的尺寸。本发明轻质结构砂芯模成型方法,其重量轻、强度高、制作工艺简单,能够替代复杂的石膏芯模,适用于大尺寸纤维缠绕壳体。(The invention relates to the technical field of solid rocket engine shell forming, and discloses a method for forming a sand core mold with a light structure, which comprises the following steps: partitioning and manufacturing a sand cake forming die and a winding mandrel; preparing a polyvinyl alcohol aqueous solution; preparing a blended sand material; filling the blended sand material into a sand cake forming die and tamping; heating and curing; after polishing, taking out the sand cake and the shaft sleeve from a sand cake forming die; sequentially sleeving the sand cakes in each area on a winding mandrel, tightly pressing the sand cakes by using a locking nut, and filling and flattening butt joints among the sand cakes; the assembled sand core molding machine is added to the desired dimensions. The method for molding the sand core mold with the light structure has light weight, high strength and simple manufacturing process, can replace a complex gypsum core mold, and is suitable for large-size fiber winding shells.)

1. A method for molding a sand core mold with a light structure is characterized by comprising the following steps: the method comprises the following steps:

A) partitioning the sand core mold according to the length size of an engine shell, and designing a corresponding sand cake forming mold and a winding mandrel (4) according to the size of each region, the diameter of the engine shell and the size of a front opening and a rear opening, wherein the sand cake forming mold comprises a female mold, a positioning disc arranged at the bottom of the female mold, a shaft sleeve sleeved on the positioning disc and a weight reducing disc arranged on the shaft sleeve;

B) preparing a polyvinyl alcohol aqueous solution, and mixing polyvinyl alcohol and water according to the weight ratio of 1: 3-5, heating to 90-100 ℃, and stirring with a stirrer until no sticky block exists in the polyvinyl alcohol aqueous solution;

C) drying quartz sand for 2-5 h at 100-150 ℃, then mixing the dried quartz sand with glass fiber and polyvinyl alcohol aqueous solution, and uniformly stirring by using a sand mixer to form a blended sand material;

D) coating a release agent on the sand cake forming die prepared in the step A) and drying the sand cake forming die, and filling the blended sand material prepared in the step C) into the sand cake forming die and tamping the sand cake forming die;

E) putting the blended sand material filled into the sand cake forming die into an oven for heating and curing;

F) after solidification, polishing and finishing the upper end face of each sand cake, leveling the upper end face of each sand cake to be flush with the edge of the female die, and taking out the sand cake together with the shaft sleeve from a sand cake forming die;

G) sequentially sleeving the sand cakes in each area on a winding mandrel (4), pressing the sand cakes by using a locking nut (5), and filling and flattening butt joints among the sand cakes;

H) the assembled sand core molding machine is added to the desired dimensions.

2. The method for molding a sand core mold with a light structure as claimed in claim 1, wherein: in the step A), the sand core mold is partitioned according to a front seal head sand cake (1), a rear seal head sand cake (2) and a barrel section sand cake (3) located between the front seal head sand cake (1) and the rear seal head sand cake (2), if the engine shell is long, a plurality of barrel section sand cakes (3) can be arranged, and the front seal head sand cake (1), the rear seal head sand cake (2) and the barrel section sand cake (3) correspond to a front seal head sand cake forming mold, a rear seal head sand cake forming mold and a barrel section sand cake forming mold.

3. The method for molding a sand core mold with a light structure as claimed in claim 2, wherein: the front end enclosure sand cake forming die comprises a front end enclosure female die (11), the longitudinal section of the front end enclosure female die (11) is U-shaped, a front seal head positioning disc (12) is arranged at the center of the bottom of the front seal head female die (11), a vertical front seal head shaft sleeve (13) is sleeved on the front seal head positioning disc (12), a front seal head weight reducing disc (14) is arranged on the front seal head shaft sleeve (13), the longitudinal section of the front seal head weight reducing disc (14) is U-shaped, a front seal head locking screw (15) penetrates through the central bottom of the front seal head weight reducing disc (14), the front seal head locking screw (15) is fixed at the central position of the front seal head positioning disc (12), the front seal head female die (11), the front seal head positioning disc (12), the front seal head shaft sleeve (13) and the front seal head weight reducing disc (14) are coaxial, and the inner diameter of the front seal head weight reducing disc (14) is larger than that of the front seal head shaft sleeve (13).

4. The method for molding a sand core mold with a light structure as claimed in claim 2, wherein: the back end socket sand cake forming die comprises a back end socket female die (21), the longitudinal section of the back end socket female die (21) is U-shaped, a rear end socket positioning disc (22) is arranged at the center of the bottom of the rear end socket female die (21), a vertical rear end enclosure shaft sleeve (23) is sleeved on the rear end enclosure positioning disc (22), a rear end enclosure weight reducing disc (24) is arranged on the rear end enclosure shaft sleeve (23), the longitudinal section of the rear end enclosure weight reducing disc (24) is U-shaped, a rear end enclosure locking screw (25) penetrates through the central bottom of the rear end enclosure weight reducing disc (24), the rear end enclosure locking screw (25) is fixed at the central position of the rear end enclosure positioning disc (22), the rear end enclosure female die (21), the rear end enclosure positioning disc (22), the rear end enclosure shaft sleeve (23) and the rear end enclosure weight reducing disc (24) are coaxial, and the inner diameter of the rear seal head weight reducing disc (24) is larger than that of the rear seal head shaft sleeve (23).

5. The method for molding a sand core mold with a light structure as claimed in claim 2, wherein: the barrel section sand cake forming die comprises a barrel section female die (31), the longitudinal section of the barrel section female die (31) is rectangular and is provided with an upper opening and a lower opening, a barrel section female die base (36) is arranged below the barrel section female die (31), a barrel section positioning disc (32) is arranged at the central position of the barrel section female die base (36), a vertical barrel section shaft sleeve (33) is sleeved on the barrel section positioning disc (32), a barrel section weight reducing disc (34) is arranged on the barrel section shaft sleeve (33), the longitudinal section of the barrel section weight reducing disc (34) is U-shaped, a barrel section locking screw (35) is penetrated at the central bottom of the barrel section weight reducing disc (34), the barrel section locking screw (35) is fixed at the central position of the barrel section positioning disc (32), the barrel section female die (31), the barrel section positioning disc (32), the barrel section shaft sleeve (33) and the barrel section weight reducing disc (34) are coaxial, and the inner diameter of the barrel section weight reducing disc (34) is larger than the inner diameter of the barrel section shaft sleeve (33), the barrel section sand cake (3) is provided with a drawing inclination of 1-2 degrees, the barrel section positioning disc (32) is upwards concave to form a barrel section positioning disc weight reducing space (37), and the inner diameter of the barrel section positioning disc weight reducing space (37) is larger than that of the barrel section shaft sleeve (33).

6. The method for molding a sand core mold with a light structure as claimed in claim 1, wherein: in the step C), the mesh number of the quartz sand is 100-160, the length of the glass fiber is 2-6 mm, and the mass ratio of the quartz sand to the glass fiber to the polyvinyl alcohol aqueous solution is 10-5: 1-3: 1.

7. the method for molding a sand core mold with a light structure as claimed in claim 1, wherein: and in the step D), the release agent is coated on the female die, the positioning disc and the weight reducing disc of the sand cake forming die, and the shaft sleeve is not coated with the release agent.

8. The method for molding a sand core mold with a light structure as claimed in claim 1, wherein: in the step D), the release agent is a silicon rubber release agent, or polytetrafluoroethylene release cloth can be used for replacing the release agent.

9. The method for molding a sand core mold with a light structure as claimed in claim 1, wherein: in the step E), the curing system is kept at 90-110 ℃ for 5-8 h, then kept at 120-140 ℃ for 24-36 h, and finally cooled to below 50 ℃ along with the furnace and taken out of the furnace.

10. The method for molding a sand core mold with a light structure as claimed in claim 1, wherein: and G), filling the butt joint seams between the sand cakes by using putty, and curing at room temperature.

Technical Field

The invention relates to the technical field of solid rocket engine shell molding, in particular to a molding method of a light structure sand core mold.

Background

The fiber winding engine shell has great advantages in reducing the shell gravity and improving the mass ratio, and is the main development direction of the solid rocket engine shell in China. However, the winding shell must be formed on a core mold, which is commonly used as both a water-soluble sand core mold and a removable gypsum core mold.

The gypsum core mold is mainly used for large-size shells, the metal framework is contained in the core mold, the structure is quite complex, the tooling cost is high, the production process is complex, people are required to drill into the shells to disassemble the metal framework during demolding, then the gypsum is smashed and taken out, the operation difficulty is high, and the safety risk and the quality risk are high.

The water-soluble sand core mold is simple in structure, low in tooling cost and simple in manufacturing process, the sand core mold can be taken out after being dissolved only by flushing the sand core mold with warm water during demolding, but the sand core mold is large in dead weight and low in strength, is not suitable for large-size winding shells and is mainly used on small-size winding shells at present.

Disclosure of Invention

The invention aims to provide a method for forming a lightweight structural sand core mould, which has the advantages of light weight, high strength and simple manufacturing process, can replace a complex gypsum core mould and is suitable for large-size fiber winding shells.

In order to achieve the purpose, the method for molding the sand core mold with the light structure comprises the following steps:

the method for molding the sand core mold with the light structure is characterized by comprising the following steps of: the method comprises the following steps:

A) partitioning the sand core mold according to the length size of an engine shell, and designing a corresponding sand cake forming mold and a winding mandrel according to the size of each region, the diameter of the engine shell and the sizes of front and rear openings, wherein the sand cake forming mold comprises a female mold, a positioning disc arranged at the bottom of the female mold, a shaft sleeve sleeved on the positioning disc and a weight reducing disc arranged on the shaft sleeve;

B) preparing a polyvinyl alcohol aqueous solution, and mixing polyvinyl alcohol and water according to the weight ratio of 1: 3-5, heating to 90-100 ℃, and stirring with a stirrer until no sticky block exists in the polyvinyl alcohol aqueous solution;

C) drying quartz sand for 2-5 h at 100-150 ℃, then mixing the dried quartz sand with glass fiber and polyvinyl alcohol aqueous solution, and uniformly stirring by using a sand mixer to form a blended sand material;

D) coating a release agent on the sand cake forming die prepared in the step A) and drying the sand cake forming die, and filling the blended sand material prepared in the step C) into the sand cake forming die and tamping the sand cake forming die;

E) putting the blended sand material filled into the sand cake forming die into an oven for heating and curing;

F) after solidification, polishing and finishing the upper end face of each sand cake, leveling the upper end face of each sand cake to be flush with the edge of the female die, and taking out the sand cake together with the shaft sleeve from a sand cake forming die;

G) sequentially sleeving the sand cakes in each area on a winding mandrel, tightly pressing the sand cakes by using a locking nut, and filling and flattening butt joints among the sand cakes;

H) the assembled sand core molding machine is added to the desired dimensions.

Preferably, in the step a), the sand core mold is partitioned according to a front end socket sand cake, a rear end socket sand cake and a cylinder section sand cake located between the front end socket sand cake and the rear end socket sand cake, if the engine shell is longer, a plurality of cylinder section sand cakes can be arranged, and the front end socket sand cake, the rear end socket sand cake and the cylinder section sand cake correspond to a front end socket sand cake forming mold, a rear end socket sand cake forming mold and a cylinder section sand cake forming mold.

Preferably, the front seal head sand cake forming die comprises a front seal head female die, the longitudinal section of the front seal head female die is U-shaped, a front seal head positioning disc is arranged at the center of the bottom of the front seal head female die, a vertical front seal head shaft sleeve is sleeved on the front seal head positioning disc, a front seal head weight reducing disc is arranged on the front seal head shaft sleeve, the longitudinal section of the front seal head weight reducing disc is U-shaped, a front seal head locking screw is penetrated at the center bottom of the front seal head weight reducing disc, the front seal head locking screw is fixed at the center of the front seal head positioning disc, the front seal head female die, the front seal head positioning disc, the front seal head shaft sleeve and the front seal head weight reducing disc are coaxial, and the inner diameter of the front seal head weight reducing disc is larger than the inner diameter of the.

Preferably, back head sand cake forming die includes the back head die, the longitudinal section of back head die is the U type, back head die bottom central point puts and is equipped with the back head positioning disk, back head positioning disk upper cover has vertical back head axle sleeve, be equipped with back head weight reducing disk on the back head axle sleeve, the longitudinal section that back head weight reducing disk is the U type, back head locking screw has been worn to the central bottom of back head weight reducing disk, back head locking screw fixes the central point of back head positioning disk puts, back head die, back head positioning disk, back head axle sleeve, back head weight reducing disk are coaxial, just the internal diameter that back head weight reducing disk is greater than the internal diameter of back head axle sleeve.

Preferably, the cylinder section sand cake forming die comprises a cylinder section female die, the longitudinal section of the cylinder section female die is rectangular and is provided with an upper opening and a lower opening, a cylinder section female die base is arranged below the cylinder section female die, a cylinder section positioning disc is arranged at the center of the cylinder section female die base, a vertical cylinder section shaft sleeve is sleeved on the cylinder section positioning disc, a cylinder section weight reducing disc is arranged on the cylinder section shaft sleeve, the longitudinal section of the cylinder section weight reducing disc is U-shaped, a cylinder section locking screw is arranged at the center bottom of the cylinder section weight reducing disc in a penetrating mode, the cylinder section locking screw is fixed at the center of the cylinder section positioning disc, the cylinder section female die, the cylinder section positioning disc, the cylinder section shaft sleeve and the cylinder section weight reducing disc are coaxial, the inner diameter of the cylinder section weight reducing disc is larger than the inner diameter of the cylinder section shaft sleeve, the cylinder section sand cake is provided with a draft angle of 1-2 degrees, and the cylinder section positioning disc is upwards concave to form a cylinder section positioning disc, the inner diameter of the barrel section positioning plate weight reduction space is larger than that of the barrel section shaft sleeve.

Preferably, in the step C), the mesh number of the quartz sand is 100-160, the length of the glass fiber is 2-6 mm, and the mass ratio of the quartz sand to the glass fiber to the polyvinyl alcohol aqueous solution is 10-5: 1-3: 1.

preferably, in the step D), the release agent is coated on the female die, the positioning disc and the weight reducing disc of the sand cake forming die, and the shaft sleeve is not coated with the release agent.

Preferably, in the step D), the release agent is a silicone rubber release agent, or a polytetrafluoroethylene release cloth can be used instead of the release agent.

Preferably, in the step E), the curing system is kept at 90-110 ℃ for 5-8 h, then kept at 120-140 ℃ for 24-36 h, and finally cooled to below 50 ℃ along with the furnace and taken out of the furnace.

Preferably, in the step G), the butt joint seam between the sand cakes is filled with putty, and is cured at room temperature.

Compared with the prior art, the invention has the following advantages:

1. the sand core mold is reinforced by adding a proper amount of glass fiber into the quartz sand, so that the problem that the sand core mold cannot be applied to a large-size winding shell due to insufficient strength is solved;

2. the sand cake is manufactured into a partially hollow structure through the weight reducing disc on the sand cake forming die, so that the weight of the sand core die is greatly reduced, and the problem that the large-size winding shell cannot be used due to the deformation of the winding core shaft caused by the overlarge dead weight of the sand core die is solved;

3. the invention is suitable for large-size winding shells, and compared with a gypsum core mould, the invention has the advantages of low tool cost, simple operation, short production period, high efficiency, higher safety of a water-soluble demoulding mode and small quality risk.

Drawings

FIG. 1 is a schematic structural view of a sand core mold in the method for molding a sand core mold of a lightweight structure according to the present invention;

FIG. 2 is a schematic structural view of a front head sand cake forming mold in the lightweight structure sand core mold forming method of the invention;

FIG. 3 is a schematic structural view of a back head sand cake forming die in the lightweight structure sand core die forming method of the invention;

FIG. 4 is a schematic structural view of a barrel segment sand cake forming mold in the lightweight structure sand core mold forming method of the invention;

the components in the figures are numbered as follows:

the device comprises a front seal head sand cake 1, a rear seal head sand cake 2, a barrel section sand cake 3, a winding mandrel 4, a locking nut 5, a front seal head female die 11, a front seal head positioning disc 12, a front seal head shaft sleeve 13, a front seal head weight reducing disc 14, a front seal head locking screw 15, a rear seal head female die 21, a rear seal head positioning disc 22, a rear seal head shaft sleeve 23, a rear seal head weight reducing disc 24, a rear seal head locking screw 25, a barrel section female die 31, a barrel section positioning disc 32, a barrel section shaft sleeve 33, a barrel section weight reducing disc 34, a barrel section locking screw 35, a barrel section female die base 36 and a barrel section positioning disc weight reducing space 37.

Detailed Description

The present invention will be described in further detail with reference to the following examples and the accompanying drawings.

When the method for molding the sand core mold with the light structure is implemented, the sand core mold is partitioned according to the length size of the engine shell, then designing a corresponding sand cake forming die and a winding mandrel 4 according to the size of each area, the diameter of the engine shell and the sizes of the front opening and the rear opening, the sand cake forming die comprises a female die, a positioning disc arranged at the bottom of the female die, a shaft sleeve sleeved on the positioning disc and a weight reducing disc arranged on the shaft sleeve, and particularly as shown in figure 1, a sand core die is divided into a front end socket sand cake 1, a rear end socket sand cake 2 and a barrel section sand cake 3 positioned between the front end socket sand cake 1 and the rear end socket sand cake 2, if an engine shell is longer, a plurality of cylinder section sand cakes 3 can be arranged, and a front seal head sand cake forming die, a rear seal head sand cake forming die and a cylinder section sand cake forming die which correspond to the front seal head sand cake 1, the rear seal head sand cake 2 and the cylinder section sand cake 3.

As shown in fig. 2, the front head sand cake forming die comprises a front head female die 11, the longitudinal section of the front head female die 11 is U-shaped, a front head positioning plate 12 is arranged at the center of the bottom of the front head female die 11, a vertical front head shaft sleeve 13 is sleeved on the front head positioning plate 12, a front head weight reducing plate 14 is arranged on the front head shaft sleeve 13, the longitudinal section of the front head weight reducing plate 14 is U-shaped, a front head locking screw 15 penetrates through the center bottom of the front head weight reducing plate 14, the front head locking screw 15 is fixed at the center of the front head positioning plate 12, the front head female die 11, the front head positioning plate 12, the front head shaft sleeve 13 and the front head weight reducing plate 14 are coaxial, and the inner diameter of the front head weight reducing plate 14 is larger than the inner diameter of the front head shaft sleeve 13.

As shown in fig. 3, the back head sand cake forming die comprises a back head female die 21, the longitudinal section of the back head female die 21 is U-shaped, a back head positioning disc 22 is arranged at the center of the bottom of the back head female die 21, a vertical back head shaft sleeve 23 is sleeved on the back head positioning disc 22, a back head weight reducing disc 24 is arranged on the back head shaft sleeve 23, the longitudinal section of the back head weight reducing disc 24 is U-shaped, a back head locking screw 25 penetrates through the center bottom of the back head weight reducing disc 24, the back head locking screw 25 is fixed at the center of the back head positioning disc 22, the back head female die 21, the back head positioning disc 22, the back head shaft sleeve 23 and the back head weight reducing disc 24 are coaxial, and the inner diameter of the back head weight reducing disc 24 is larger than the inner diameter of the back head shaft sleeve 23.

As shown in fig. 4, the cylinder section sand cake forming mold comprises a cylinder section female mold 31, the longitudinal section of the cylinder section female mold 31 is rectangular and is opened up and down, a cylinder section female mold base 36 is arranged below the cylinder section female mold 31, a cylinder section positioning disk 32 is arranged at the center of the cylinder section female mold base 36, a vertical cylinder section shaft sleeve 33 is sleeved on the cylinder section positioning disk 32, a cylinder section weight reducing disk 34 is arranged on the cylinder section shaft sleeve 33, the longitudinal section of the cylinder section weight reducing disk 34 is U-shaped, a cylinder section locking screw 35 is penetrated at the center bottom of the cylinder section weight reducing disk 34, the cylinder section locking screw 35 is fixed at the center of the cylinder section positioning disk 32, the cylinder section female mold 31, the cylinder section positioning disk 32, the cylinder section shaft sleeve 33 and the cylinder section weight reducing disk 34 are coaxial, the inner diameter of the cylinder section weight reducing disk 34 is larger than the inner diameter of the cylinder section shaft sleeve 33, the cylinder section sand cake 3 is provided with a mold draft of 1-2 degree, the cylinder section positioning disc 32 is upwards concave to form a cylinder section positioning disc weight reducing space 37, and the inner diameter of the cylinder section positioning disc weight reducing space 37 is larger than that of the cylinder section shaft sleeve 33.

When the sand cake forming die is used, the positioning disc is fixed on the female die, the shaft sleeve is arranged on the positioning disc, the weight reducing disc is arranged on the shaft sleeve, and the mixed sand material is poured into a space between the female die and the weight reducing disc.

Example 1:

table 1 example 1 core mold size

Serial number	Item	Size of
			1	Sand core mould diameter/mm	850
2	Sand core mould length/m	1200

A method for molding a sand core mold with a light structure comprises the following steps:

A) the sand core mold is partitioned according to the length size of an engine shell, and then a corresponding sand cake forming mold and a winding mandrel 4 are designed according to the size of each area, the diameter of the engine shell and the size of a front opening and a rear opening, wherein the sand cake forming mold comprises a female mold, a positioning disc arranged at the bottom of the female mold, a shaft sleeve sleeved on the positioning disc and a weight reducing disc arranged on the shaft sleeve;

B) preparing a polyvinyl alcohol aqueous solution, and mixing polyvinyl alcohol and water according to the weight ratio of 1: 3, heating to 90 ℃, and stirring by using a stirrer until no sticky block exists in the polyvinyl alcohol aqueous solution;

C) drying quartz sand for 2 hours at 100 ℃, then mixing the dried quartz sand with glass fiber and polyvinyl alcohol aqueous solution, and uniformly stirring by using a sand mixer to form a blended sand material, wherein the mesh number of the quartz sand is 100, the length of the glass fiber is 2mm, and the mass ratio of the quartz sand to the glass fiber and the polyvinyl alcohol aqueous solution is 10: 1: 1;

D) coating a release agent on the sand cake forming die prepared in the step A) and drying the sand cake forming die, then filling the blended sand material prepared in the step C) into the sand cake forming die and tamping the sand cake forming die, wherein the release agent is coated on a female die, a positioning disc and a weight reducing disc of the sand cake forming die, the release agent is not coated on a shaft sleeve, and the release agent is a silicon rubber release agent;

E) putting the blended sand material filled into the sand cake forming mold into an oven for heating and curing, wherein the curing system is that the temperature is kept at 90 ℃ for 5 hours, then the temperature is kept at 120 ℃ for 24 hours, and finally the temperature is reduced to below 50 ℃ along with the oven and the mixture is taken out of the oven;

F) after solidification, polishing and finishing the upper end face of each sand cake, leveling the upper end face of each sand cake to be flush with the edge of the female die, and taking out the sand cake together with the shaft sleeve from a sand cake forming die;

G) sequentially sleeving a formed front end socket sand cake 1, a formed barrel section sand cake 3 and a formed rear end socket sand cake 2 on a winding mandrel 4, pressing the sand cakes by using a locking nut 5, filling and flattening butt joints among the sand cakes, filling the butt joints among the sand cakes by using putty, and curing at room temperature;

H) the assembled sand core molding machine is added to the desired dimensions.

Example 2:

table 2 example 21 core mold dimensions

Serial number	Item	Size of
			1	Sand core mould diameter/mm	1000
2	Sand core mould length/m	2000

A method for molding a sand core mold with a light structure comprises the following steps:

A) the sand core mold is partitioned according to the length size of an engine shell, and then a corresponding sand cake forming mold and a winding mandrel 4 are designed according to the size of each area, the diameter of the engine shell and the size of a front opening and a rear opening, wherein the sand cake forming mold comprises a female mold, a positioning plate arranged at the bottom of the female mold, a shaft sleeve sleeved on the positioning plate and a weight reducing plate arranged on the shaft sleeve;

B) preparing a polyvinyl alcohol aqueous solution, and mixing polyvinyl alcohol and water according to the weight ratio of 1: 5, heating to 100 ℃, and stirring by using a stirrer until no sticky block exists in the polyvinyl alcohol aqueous solution;

C) drying quartz sand at 150 ℃ for 5h, then mixing the dried quartz sand with glass fiber and polyvinyl alcohol aqueous solution, and uniformly stirring by using a sand mixer to form a blended sand material, wherein the mesh number of the quartz sand is 160, the length of the glass fiber is 6mm, and the mass ratio of the quartz sand to the glass fiber and the polyvinyl alcohol aqueous solution is 5: 3: 1;

D) paving polytetrafluoroethylene demolding cloth on the sand cake forming die prepared in the step A) and drying the sand cake forming die, and then filling the blended sand material prepared in the step C) into the sand cake forming die and tamping the sand cake forming die, wherein the polytetrafluoroethylene demolding cloth is paved on a female die, a positioning disc and a weight reducing disc of the sand cake forming die, and the shaft sleeve is not paved with the polytetrafluoroethylene demolding cloth;

E) putting the blended sand material filled into the sand cake forming mold into an oven for heating and curing, wherein the curing system is to keep the temperature at 110 ℃ for 8h, then keep the temperature at 140 ℃ for 36h, and finally, cooling to below 50 ℃ along with the oven and discharging;

F) after solidification, polishing and finishing the upper end face of each sand cake, leveling the upper end face of each sand cake to be flush with the edge of the female die, and taking out the sand cake together with the shaft sleeve from a sand cake forming die;

G) sequentially sleeving a formed front end socket sand cake 1, 2 barrel section sand cakes 3 and a formed rear end socket sand cake 2 on a winding mandrel 4, pressing the barrel section sand cakes and the rear end socket sand cake by using a locking nut 5, filling and flattening butt joints among the sand cakes, filling the butt joints among the sand cakes by using putty, and curing at room temperature;

H) the assembled sand core molding machine is added to the desired dimensions.

Example 3:

table 3 example 3 core mold size

Serial number	Item	Size of
			1	Sand core mould diameter/mm	1200
2	Sand core mould length/m	2400

A method for molding a sand core mold with a light structure comprises the following steps:

A) the sand core mold is partitioned according to the length size of an engine shell, and then a corresponding sand cake forming mold and a winding mandrel 4 are designed according to the size of each area, the diameter of the engine shell and the size of a front opening and a rear opening, wherein the sand cake forming mold comprises a female mold, a positioning disk arranged at the bottom of the female mold, a shaft sleeve sleeved on the positioning disk and a weight reducing disk arranged on the shaft sleeve;

B) preparing a polyvinyl alcohol aqueous solution, and mixing polyvinyl alcohol and water according to the weight ratio of 1: 4, heating to 95 ℃, and stirring by using a stirrer until no sticky block exists in the polyvinyl alcohol aqueous solution;

C) drying quartz sand for 3.5h at 130 ℃, then mixing the dried quartz sand with glass fiber and polyvinyl alcohol aqueous solution, and uniformly stirring by using a sand mixer to form a blended sand material, wherein the mesh number of the quartz sand is 140, the length of the glass fiber is 4mm, and the mass ratio of the quartz sand to the glass fiber and the polyvinyl alcohol aqueous solution is 7: 2: 1;

D) coating a release agent on the sand cake forming die prepared in the step A) and drying the sand cake forming die, then filling the blended sand material prepared in the step C) into the sand cake forming die and tamping the sand cake forming die, wherein the release agent is coated on a female die, a positioning disc and a weight reducing disc of the sand cake forming die, the release agent is not coated on a shaft sleeve, and the release agent is a silicon rubber release agent;

E) putting the blended sand material filled into the sand cake forming mold into an oven for heating and curing, wherein the curing system is that the temperature is kept at 100 ℃ for 6h, then the temperature is kept at 130 ℃ for 30h, and finally the temperature is reduced to below 50 ℃ along with the oven and the mixture is taken out of the oven;

F) after solidification, polishing and finishing the upper end face of each sand cake, leveling the upper end face of each sand cake to be flush with the edge of the female die, and taking out the sand cake together with the shaft sleeve from a sand cake forming die;

G) sequentially sleeving a formed front end socket sand cake 1, 4 barrel section sand cakes 3 and a formed rear end socket sand cake 2 on a winding mandrel 4, pressing the barrel section sand cakes and the rear end socket sand cake by using a locking nut 5, filling and flattening butt joints among the sand cakes, filling the butt joints among the sand cakes by using putty, and curing at room temperature;

H) the assembled sand core molding machine is added to the desired dimensions.

The sand core mold with the light structure prepared by the embodiment 1-3 is large in size and high in strength, and meets the use requirement of a fiber winding engine shell.

According to the method for molding the sand core mold with the light structure, the sand core mold is reinforced by adding a proper amount of glass fiber into quartz sand, so that the problem that the sand core mold cannot be applied to a large-size winding shell due to insufficient strength is solved; the sand cake is manufactured into a partially hollow structure through the weight reducing disc on the sand cake forming die, so that the weight of the sand core die is greatly reduced, and the problem that the large-size winding shell cannot be used due to the deformation of the winding core shaft 4 caused by the overlarge dead weight of the sand core die is solved; the invention is suitable for large-size winding shells, and compared with a gypsum core mould, the invention has the advantages of low tool cost, simple operation, short production period, high efficiency, higher safety of a water-soluble demoulding mode and small quality risk.