A local chill mold and a local sequential forming method for a large cast

Abstract

The application discloses a local chilling mold for large castings and a local sequential forming method. A cooling cavity is arranged in a sand mold outer box and is matched with the shape of the sand mold outer box. A flowing cooling medium is filled in the cooling cavity. A plurality of expansion isolators are uniformly arranged on the inner side wall of the cooling cavity. The feeding end of the expansion isolators is communicated with the discharging end of a conveying device. The feeding end and the discharging end of the expansion isolators are communicated with a three-way electromagnetic valve. The local sequential forming method is used for casting the large castings by using the local chilling mold. S1, the mold is pre-installed with isolators; S2, a chilling time sequence is calibrated; S3, local chilling is performed in steps; and S4, a cooling mode is switched. The expansion and deflation states of the expansion isolators at different positions are independently controlled. The chilling start and end times of each hot spot area are independently controlled. The chilling is performed in steps according to the solidification requirement of the castings. The molten metal is guided to directional sequential solidification from a thin wall to a thick wall. The shrinkage hole, shrinkage porosity and hot crack defects are greatly eliminated. The internal structure uniformity of the castings is improved.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and in particular to a local chilling mold for large castings and a local sequential forming method. Background Technology

[0002] Large cast steel and cast iron gearbox housings and differential housings are generally characterized by large differences in wall thickness, dispersed heat points, and large casting dimensions. After pouring, the heat dissipation during the solidification process of the molten metal is extremely uneven. Relying solely on natural cooling of the sand mold can easily lead to casting defects such as shrinkage cavities, shrinkage porosity, hot cracks, coarse grains, and casting deformation, which seriously reduce the mechanical properties of the castings and the yield of finished products.

[0003] Existing casting chilling technologies are mainly divided into two categories: Integral water-cooled sand mold: A cooling chamber is set up throughout the sand mold and coolant is continuously circulated, with simultaneous forced cooling throughout the entire mold cavity. This method cannot distinguish the solidification sequence of different wall thicknesses and hot spots in the casting. The cooling rate of thick hot spots is not differentiated from that of thin-walled areas, and the molten metal cannot be guided to solidify in a predetermined path. Concentrated shrinkage defects still exist in thick-walled areas. At the same time, continuous cooling throughout the entire area will significantly increase the energy consumption of coolant, and excessive cooling in thin-walled areas is prone to cold shuts and cracks.

[0004] Fixed-insert localized quenching: Metal chills or fixed water-cooled inserts are pre-embedded at the hot spots of the mold, and the chills / inserts are in continuous contact with the cavity surface for heat dissipation from the time of pouring. This solution has obvious limitations: the position of the chills and water-cooled inserts and the cooling sequence cannot be flexibly adjusted. For large castings with multiple hot spots and complex variable wall thickness, it is impossible to achieve quenching in different areas and stages. In the early stage of pouring, the temperature of the molten metal is extremely high. The continuous contact of the chills with the cavity will cause rapid cooling and crusting on the surface of the casting, and the internal melt feeding channels will be closed prematurely, which will aggravate the internal shrinkage cavity problem. Moreover, the chills and inserts are fixed structures, and one set of molds can only adapt to a single specification of casting. The mold versatility is poor, and the amount of disassembly and modification work during modification and production change is large.

[0005] In addition, existing chilling molds lack media isolation and automatic compensation structures. For integral water-cooled sand molds, the cooling medium is always in contact with the mold cavity sidewalls, making it difficult to achieve multi-mode cooling switching between "air cooling - local chilling - full-area rapid cooling". For fixed-insert chilling sand molds, there is no buffer compensation structure after the inserts expand due to heat, and the internal pressure of the cooling cavity continues to rise, which can easily lead to leakage and sand mold cracking risks. Most importantly, existing chilling molds cannot realize the multi-heat-section step-by-step sequential solidification process for large castings.

[0006] In summary, existing large casting cooling molds are unable to achieve localized rapid cooling that can be controlled by region and time sequence, and cannot accurately guide the molten metal to solidify in a directional and sequential manner. As a result, castings have many defects, poor mold adaptability, and a single cooling mode. There is an urgent need for a localized rapid cooling mold and forming process that can dynamically isolate the coolant, independently control the rapid cooling sequence in different regions, and is adaptable to large castings of various sizes. Summary of the Invention

[0007] The purpose of this invention is to provide a local quenching mold and a local sequential forming method for large castings, so as to solve the problems of existing large casting cooling molds that are difficult to achieve local quenching that is controlled by region and time sequence, cannot accurately guide the molten metal to solidify in a directional sequence, have many casting defects, poor mold adaptability, and a single cooling mode.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A large casting local chilling mold includes a sand mold outer box, a cooling cavity adapted to the shape of the sand mold outer box, a cooling medium filled in the cooling cavity, and a plurality of expansion isolators uniformly arranged on the inner side wall of the cooling cavity. The inlet end of the expansion isolator is connected to the outlet end of an external conveying device, and the inlet end and outlet end of the expansion isolator are connected to a three-way solenoid valve.

[0009] A further technical solution is as follows: the expansion isolator includes a hollow shaft, an expansion bladder, and a connecting pipe. Multiple hollow shafts are evenly arranged on the inner sidewalls of the cooling chamber and the mold cavity that are closest to each other. The expansion bladder is arranged on the hollow shaft. The connecting pipe, the three-way solenoid valve, the hollow shaft, and the expansion bladder are connected in sequence. The pressure relief end of the expansion bladder is connected to an external recovery device through the three-way solenoid valve.

[0010] A further technical solution is that a constraint disc adapted to the inflatable balloon is provided on the outer end of the hollow shaft.

[0011] A further technical solution is: the constraint disk is hollowed out.

[0012] A further technical solution is that the medium inside the inflatable balloon is gas.

[0013] A further technical solution is that the fluid cooling medium is a coolant.

[0014] A further technical solution is that an expansion compensation balloon is provided inside the cooling chamber.

[0015] A localized sequential forming method for large castings, where large castings are cast using a localized chilling mold, is described below: S1. First, design the sand mold outer box according to the shape and size of the casting and set the mold core inside the sand mold outer box to form the casting mold. Before casting, keep all expansion isolators in an expanded state to isolate the fluid cooling medium from the inner wall of the mold. S2. According to the wall thickness and flow channel direction of the casting, mark the sequence of chilling forming parts on the outer box of the sand mold or input the instruction of the sequence of chilling forming parts on the control system. S3. Based on S2, during or after casting, the external conveying equipment is started manually or automatically controlled by the control system, and the three-way solenoid valve is opened and closed. The expansion isolator on the corresponding rapid cooling forming part is in a collapsed state, the fluid cooling medium comes into contact with the inner wall of the mold forming, and rapid cooling begins according to the process cooling time, and so on. S4. After the quenching is completed, when air cooling is required, keep all expansion isolators in an expanded state; when rapid cooling is required, keep all expansion isolators in a collapsed state.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: This invention proposes a local quenching mold and a local sequential forming method for large castings, which can achieve precise local quenching in a time-sharing and zone-sharing manner: by independently controlling the expansion and contraction states of the expansion isolators at each location, the quenching start and end time of each hot spot area can be controlled individually, and quenching can be carried out step by step according to the solidification requirements of the casting, guiding the molten metal to solidify sequentially from thin wall to thick wall, greatly eliminating shrinkage cavities, porosity, and hot cracking defects, and improving the uniformity of the internal structure of the casting.

[0017] Multiple cooling modes can be switched freely: Relying on the isolation effect of the expansion spherical bladder, it can flexibly switch between three cooling modes: natural air cooling, single-area local quenching, and whole-area forced rapid cooling. In the early stage of pouring, the coolant can be isolated to prevent premature crusting on the surface of the casting and ensure smooth melt feeding channels. After quenching, the cooling rate can be selected as needed to adapt to the process requirements of large castings with different materials and wall thicknesses.

[0018] The mold is highly versatile and has low modification costs: the expansion isolators are modularly and evenly arranged on the side wall of the cooling chamber. For castings with different heat distribution, only the quenching sequence in the control system needs to be adjusted. There is no need to disassemble or replace chills or water-cooled inserts. One mold can be adapted to large castings of multiple specifications, reducing mold development and modification costs.

[0019] The mold avoids the defects of traditional water-cooled molds, where the cooling medium is always in contact with the mold cavity sidewall, and fixed-insert type chilled sand molds, where the inserts have no buffer compensation structure after thermal expansion. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a large casting local chilling mold according to the present invention.

[0021] Figure 2 For the present invention Figure 1 A structural schematic diagram of the interior of the mold.

[0022] Figure 3 For the present invention Figure 2 A schematic diagram of the structure of the expansion isolator.

[0023] Figure 4 For the present invention Figure 3 A schematic diagram of the structure of the inflatable balloon.

[0024] Reference numerals: 1. Sand mold outer casing; 2. Cooling chamber; 3. Flowable cooling medium; 4. Expansion isolator; 5. Three-way solenoid valve; 6. Hollow shaft; 7. Expansion balloon; 8. Connecting pipe; 9. Constraint disc; 10. Expansion compensation balloon. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used 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, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Example

[0031] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, a large casting local chilling mold includes a sand mold outer box 1, a cooling chamber 2 arranged around the mold cavity inside the sand mold outer box 1, and a liquid coolant 3 filled inside the cooling chamber 2 as a fluid cooling medium; multiple sets of expansion isolators 4 are evenly arrayed on the inner side wall of the cooling chamber near the mold cavity.

[0032] The expansion isolator 4 consists of a connecting pipe 8, a three-way solenoid valve 5, a hollow shaft 6, and an expansion bladder 7. The hollow shaft 6 is vertically fixed to the inner wall of the cooling chamber 2, and the expansion bladder 7 is fitted on the outer side of the hollow shaft. A hollow constraint plate 9 is fixed to the outer end of the hollow shaft. One end of the connecting pipe 8 is connected to the three-way solenoid valve 5, and the other end is connected to the internal channel of the hollow shaft 6. The two sides of the three-way solenoid valve 5 are respectively connected to a compressed gas delivery device and a gas recovery device. An expansion compensation bladder 10 is built into the bottom of the cooling chamber 2 to buffer the internal pressure generated by the thermal expansion of the coolant.

[0033] The expansion bladder 7 is filled with compressed air. When the three-way solenoid valve 5 is connected to the conveying equipment for inflation, the expansion bladder 7 inflates and fits against the side wall of the cavity, completely separating the coolant 3 from the cavity sand wall, and the mold is only naturally air-cooled. After the solenoid valve is switched to the recovery end to depressurize, the air inside the expansion bladder 7 is discharged and collapses, and the coolant 3 directly contacts the side wall of the cavity, realizing local forced heat exchange.

[0034] It is worth noting that the constraint disk 9 can constrain the expansion balloon 7 to expand flat, so as to ensure that the expansion balloon 7 in the whole or in the region can form an effective isolation and completely displace the fluid cooling medium 3.

[0035] The expansion compensation balloon 10 is also connected to the external air supply equipment. When the casting is subjected to rapid cooling molding and rapid cooling molding, the expansion compensation balloon 10 is inflated to achieve full contact between the fluid cooling medium 3 and the mold cooling wall. Example

[0036] Using the local sequential forming method for large castings with the mold described in Example 1, taking a large cast steel box casting with large differences in wall thickness as an example, the steps are as follows: S1. Mold pre-assembly and isolation: Sand mold outer box 1 is processed according to the shape of the box casting, and corresponding mold core is assembled inside to form the casting cavity; before casting, the compressed gas delivery equipment is started, all three-way solenoid valves 5 are opened to open the inflation passage, all expansion balloons 7 are inflated, and the coolant 3 is isolated from the inner wall of the cavity. During the casting stage, the sand mold is used for natural heat dissipation to avoid the surface of the casting from solidifying quickly and sealing the feeding channel.

[0037] S2. Quenching sequence calibration: The bottom flange, side wall boss, and top reinforcing rib of the casting are three concentrated heat points. The quenching sequence is entered into the control system in the order of "bottom flange → side wall boss → top reinforcing rib".

[0038] S3. Step-by-step local quenching: 2 minutes after the molten metal is poured, the control system automatically controls the three-way solenoid valve at the corresponding position of the bottom flange to release pressure. The expansion balloon 7 in this area collapses, and the coolant contacts the cavity to quench the hot spot of the bottom flange for 8 minutes. After completion, the system automatically switches to the next set of solenoid valves to perform local quenching on the side wall boss for 6 minutes. Finally, the top reinforcing rib is quenched for 5 minutes, and all hot spots are solidified sequentially in sequence, guiding the molten metal to directionally feed from the top to the bottom flange.

[0039] S4. Cooling mode switching: After the step-by-step quenching of all hot sections is completed, the internal melt of the casting is fed back. If the casting requires high dimensional accuracy, control the depressurization of all expansion bladders 7, and the coolant will contact the cavity in the entire area for rapid cooling and demolding. If the casting requires low internal stress, inflate all expansion bladders 7 to expand and isolate the coolant, and the casting will be air-cooled to room temperature in the sand mold.

[0040] This invention relies on the inflation / deflation of an expansion balloon to isolate the coolant from the cavity wall, and uses a three-way solenoid valve to achieve independent control of a single area. During the initial pouring stage, the coolant is isolated to prevent premature crusting on the casting surface. Then, according to the thermal distribution sequence of the casting, the gas inside the corresponding balloon is released sequentially, allowing the coolant to contact the cavity in stages for localized rapid cooling, forcing the casting to solidify along a preset path. An expansion compensation balloon in the cooling cavity counteracts the thermal expansion pressure of the coolant, ensuring stable mold operation. In the later stages of molding, it allows for free switching between full-area rapid cooling and natural air cooling, balancing casting quality and production efficiency.

[0041] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A local chilling mold for large castings, comprising a sand mold outer box, characterized in that: The outer casing (1) of the sand mold is provided with a cooling chamber (2) adapted to its shape. The cooling chamber (2) is filled with a fluid cooling medium (3). Multiple expansion isolators (4) are evenly arranged on the inner side wall of the cooling chamber (2). The feed end of the expansion isolator (4) is connected to the discharge end of the external conveying equipment. The feed end and discharge end of the expansion isolator (4) are connected to a three-way solenoid valve (5).

2. The large casting local chilling mold according to claim 1, characterized in that: The expansion isolator (4) includes a hollow shaft (6), an expansion balloon (7), and a connecting pipe (8). Multiple hollow shafts (6) are evenly arranged on the inner sidewall of the cooling chamber (2) closest to the mold cavity. The expansion balloon (7) is arranged on the hollow shaft (6). The connecting pipe (8), the three-way solenoid valve (5), the hollow shaft (6), and the expansion balloon (7) are connected in sequence. The pressure relief end of the expansion balloon (7) is connected to the external recovery equipment through the three-way solenoid valve (5).

3. The large casting local chilling mold according to claim 1, characterized in that: The hollow shaft (6) is provided with a constraint disc (9) adapted to the inflatable balloon (7) at its outer end.

4. The large casting local chilling mold according to claim 1, characterized in that: The constraint disk (9) is hollowed out.

5. The large casting local chilling mold according to claim 1, characterized in that: The medium inside the inflatable balloon (7) is gas.

6. The large casting local chilling mold according to claim 1, characterized in that: The fluid cooling medium (3) is a coolant.

7. The large casting local chilling mold according to claim 1, characterized in that: An expansion compensation balloon (10) is provided inside the cooling chamber (2).

8. A method for localized sequential forming of large castings, characterized in that, Large castings are cast using a local chilling mold as described in any one of claims 1-7, with the local sequential forming method as follows: S1. First, design the sand mold outer box according to the shape and size of the casting and set the mold core inside the sand mold outer box to form the casting mold. Before casting, keep all expansion isolators in an expanded state to isolate the fluid cooling medium from the inner wall of the mold. S2. According to the wall thickness and flow channel direction of the casting, mark the sequence of chilling forming parts on the outer box of the sand mold or input the instruction of the sequence of chilling forming parts on the control system. S3. Based on S2, during or after casting, the external conveying equipment is started manually or automatically controlled by the control system, and the three-way solenoid valve is opened and closed. The expansion isolator on the corresponding rapid cooling forming part is in a collapsed state, the fluid cooling medium comes into contact with the inner wall of the mold forming, and rapid cooling begins according to the process cooling time, and so on. S4. After the quenching is completed, when air cooling is required, keep all expansion isolators in an expanded state; when rapid cooling is required, keep all expansion isolators in a collapsed state.

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