A method for shaping VRH-CO2 and a vacuum sealing box

Abstract

This invention relates to a VRH-CO2 molding method and a vacuum sealing chamber, comprising: placing the sand mold into a vacuum chamber; first vacuuming: turning on the vacuum pump, achieving a vacuum degree ≥5 kPa in the sealed space, and then turning off the vacuum pump; the pressure inside the vacuum chamber is in a negative pressure state, with the change range not exceeding 0.5 kPa; blowing in CO2 gas; second vacuuming: after the CO2 blowing device is turned off, turning on the vacuum pump again to create a vacuum, and then turning off the vacuum pump; depressurizing the vacuum sealing chamber and removing the mold; this invention can produce thick sand molds, reduce the amount of carbon dioxide gas used, reduce the scrap rate, improve production efficiency, and improve the production environment.

Description

Technical Field

[0001] This invention belongs to the field of casting technology and relates to a VRH-CO2 (vacuity / vacuum replacement hardening-CO2) molding method and a vacuum sealing box. Background Technology

[0002] The main problem with the carbon dioxide hardening molding method used in the prior art is:

[0003] ① Excessive leakage of blown carbon dioxide results in a thin hardened layer in the sand mold / core, making it impossible to blow through to the inside and thus preventing the production of thick sand molds.

[0004] ②Since the maximum blowing pressure of carbon dioxide is 0.5 MPa, the pressure gradually decreases as the usage time increases. When the blowing pressure is insufficient to squeeze out the residual air inside the cavity, it will affect the hardening of the internal sand mold.

[0005] ③ Relying solely on carbon dioxide blowing to expel residual air from the mold cavity may result in uneven hardening in certain areas, even with sufficient pressure and smooth venting.

[0006] Patent document 1 (CN1061911C) discloses a method for molding (core), including sand mixing, molding, vacuuming, gas filling, and demolding steps. The method is characterized by: mixing 100 parts of casting sand with 0.5-10 parts of water glass and 0.05-1.5 parts of organic ester (by mass) until uniform, filling the sand box (core box) for molding; evacuating the air from the sand box to a vacuum degree of 0.01-0.09 MPa; filling the sand box with a mixture of methyl formate (5-100% by volume) and air or nitrogen to raise the pressure to 0.05-0.098 MPa, maintaining the pressure for 20-240 seconds; and finally releasing the pressure and demolding. Although this patent document, like this application, uses a vacuum followed by air blowing to achieve mold curing, it uses a water glass sand mold and blows in a liquid curing agent. It achieves aerosol curing by using compressed air or nitrogen as a carrier. The liquid curing material is an acid ester organic compound, which still causes environmental pollution.

[0007] Patent document 2 (CN1180002A) describes a carbon dioxide-cured resin sand, comprising quartz sand, sodium polyacrylate resin, etc. This resin sand exhibits the rapid CO2 curing effect of water glass sand in casting production, and its residual strength after casting is lower than that of ordinary resin sand, making it extremely easy to clean. The resin sand provided in this patent document does not produce any harmful gases or pollute the environment during the entire production process of core making and casting. However, the sodium polyacrylate resin used has a high organic content, and the VRH process is not involved, resulting in a relatively simple process and thus a higher CO2 consumption and carbon emissions.

[0008] Patent document 3 (CN103028703A) relates to a method for core-making of a cold box using sodium polyacrylate resin sand and carbon dioxide curing. The method includes: adding sodium polyacrylate resin and a hardening accelerator to raw sand and mixing them using a sand mixer; adding the resulting sand to a core-making sand hopper in a cold box; and blowing carbon dioxide into the core to harden the resin sand. The raw sand is a mixture of two types of molding sand with particle sizes of 40 / 70 mesh and 50 / 100 mesh. This method has advantages such as short hardening time, uniform hardening across the entire cross-section from the surface to the core, and resistance to deformation and cracking within a specified storage time. It is also environmentally friendly compared to other hardening methods. However, this patent document uses a two-component liquid material, with the second component being a hardening accelerator, and is further aided by carbon dioxide curing. Although this process has low carbon dioxide consumption, the presence of the hardening accelerator shortens the storage time of the resin sand. Furthermore, since it is a core-making process, it does not involve the VRH (Resin-Vacuum Heating) curing method.

[0009] Patent document CN104439093A discloses a hardening process for water glass sand molds and a vacuum chamber used in the process. The process involves placing a sand mold made of water glass sand into a vacuum chamber and sealing the chamber. The temperature inside the vacuum chamber is maintained at 35℃~45℃, and the chamber is slowly and continuously evacuated, maintaining a pressure of 0.8~0.9 Pa for 1~2 minutes. To prevent the water glass sand from melting, a relatively high temperature and low pressure are maintained as much as possible, allowing water molecules on the surface of the sand mold to vaporize and escape from the vacuum chamber. To prevent deformation of the sand mold, the time is controlled to 1~2 minutes, allowing most of the water vapor to escape. The temperature of the vacuum chamber is reduced to 25℃, and the vacuum chamber is evacuated to 0.5 Pa. The evacuation is stopped and the vacuum chamber is sealed. CO2 is slowly introduced until the pressure in the vacuum chamber is 0.7 Pa, and this is maintained for 10-15 minutes. This step first reduces the temperature to maintain a good hardness of the sand mold, then removes air from the inside of the vacuum chamber to achieve a depressurization effect, and then introduces CO2 to maintain a low pressure inside the vacuum chamber. This ensures that the CO2 is in full contact with the water glass and achieves a better hardening effect.

[0010] The aforementioned patent documents are not highly relevant to this application. Summary of the Invention

[0011] The purpose of this invention is to improve the hardening speed, reduce the amount of carbon dioxide used, and ensure the uniformity of sand mold hardening during the process of using carbon dioxide gas to harden sand molds, thereby providing a VRH-CO2 molding method.

[0012] It should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0013] Moreover, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0014] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution:

[0015] A method for shaping VRH-CO2 includes the following:

[0016] Place the sand mold: Place the sand mold into the vacuum chamber;

[0017] First vacuuming: Turn on the vacuum pump, the vacuum level in the sealed space is ≥5KPa, then turn off the vacuum pump; the pressure inside the vacuum sealing box is in a negative pressure state, and the change range does not exceed 0.5Kpa;

[0018] Inject CO2 gas;

[0019] Second vacuuming: After the CO2 blowing device is turned off, the vacuum pump is turned on again to create a vacuum, and then the vacuum pump is turned off.

[0020] Depressurize and mold in a vacuum-sealed box.

[0021] Furthermore, the raw sand is selected from 50 / 100 or 70 / 140 scrubbed silica sand or recycled sand of the same type, and 2.5% of methyl phenolic resin is added. After mixing and grinding for 60 seconds, the sand is unloaded and shaped.

[0022] Furthermore, the sand mold is placed in a vacuum sealing box, using a two-layer sealing cover: an air blowing plate is placed on the upper surface of the sand mold, and a vacuum sealing box sealing plate ensures the vacuum sealing box is sealed. The two layers of seals are connected by a hose.

[0023] Furthermore, for the first vacuuming, the vacuum pump is turned on, and the pressure within the sealed space is ≤

[0024] -0.1MPa, vacuuming time ≥60s.

[0025] Furthermore, after the first vacuuming, the vacuuming is turned off, the pressure is maintained for ≥5 seconds, and then CO2 gas is introduced.

[0026] Furthermore, the CO2 blowing pressure is ≥0.2MPa, and the blowing time is 30-40 seconds.

[0027] Furthermore, after the CO2 blowing device is turned off, the vacuum pump is turned on again, and the vacuuming time is ≥60s.

[0028] Furthermore, the vacuum sealing box is 1800mm long, 1800mm wide, and 1000mm high. The wall thickness and upper sealing plate thickness of the vacuum sealing box are more than 100mm, and the bottom plate thickness is more than 150mm.

[0029] The vacuum pump has an exhaust capacity of over 7000 l / min and a vacuum degree of less than 133 Pa.

[0030] The air blowing plate is connected to the top sealing plate of the vacuum sealing box.

[0031] Furthermore, the sand mold is placed in a vacuum sealing box, using a double-layer sealing cover, with the two layers of seals connected by a flexible tube with an inner diameter of Φ10-Φ12mm.

[0032] Furthermore, the sand mold is made of methyl phenolic resin, which is a water-soluble alkaline material and contains about 70% inorganic components, and is hardened with CO2.

[0033] A vacuum sealing box used in the molding method of VRH-CO2, the vacuum sealing box is 1800mm long, 1800mm wide, and 1000mm high, the wall thickness and upper sealing plate thickness of the vacuum sealing box are more than 100mm, and the bottom plate thickness is more than 150mm.

[0034] Equip a vacuum pump and a blowing plate. The vacuum pump has an exhaust capacity of over 7000 l / min and a vacuum degree of less than 133 Pa.

[0035] The air blowing plate is connected to the top sealing plate of the vacuum sealing box.

[0036] Furthermore, the vacuum sealing box adopts a two-layer sealing cover method. One layer of air blowing plate is sealed and fastened to the upper surface of the sand mold, and the other layer of vacuum sealing box sealing plate ensures the vacuum sealing box is sealed. The two layers of seals are connected by a hose.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] This invention can produce thick sand molds, reduce the amount of carbon dioxide gas used, reduce the scrap rate, improve production efficiency, and improve the production environment.

[0039] Because the methyl phenolic resin selected in this invention is a water-soluble alkaline material and contains 70%...

[0040] The inorganic components on the left and right sides are cured with CO2, which is more environmentally friendly than the original amine-cured phenol-urea alkyl resin. Attached Figure Description

[0041] The invention will now be further described with reference to the accompanying drawings:

[0042] Figure 1 This is a flowchart of a VRH-CO2 molding method according to the present invention;

[0043] Figure 2 This diagram illustrates the decrease in gas pressure as CO2 gas enters the sand mold after being dispersed through the blowing pipe and into the blowing plate. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be described in more detail below with reference to the accompanying drawings.

[0045] In the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0046] The described embodiments are some, but not all, of the embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0047] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The embodiments of this invention will now be described in detail with reference to the accompanying drawings.

[0048] In the description of this invention, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0049] The present invention will now be described in detail with reference to the accompanying drawings:

[0050] The resin selected in this invention needs to be hardened by CO2 gas. If the CO2 gas concentration is low or uneven, it will lead to uneven hardening of the sand mold, thereby affecting the quality and strength of the sand mold.

[0051] During the gas curing process, only by completely replacing the air in the mold cavity with CO2 gas and allowing it to fully react with the resin on the surface of the sand grains can the uniform curing and strength of the sand mold be guaranteed.

[0052] During the filling process, as the amount of CO2 gas increases, it continuously compresses the air in the cavity, causing the internal pressure of the cavity to rise. When the pressure rises to a certain level, the CO2 gas pressure becomes insufficient to extend further downward, resulting in the bottom sand mold failing to harden.

[0053] When the CO2 gas cannot continue to expel the air from the bottom of the cavity, the CO2 gas will diffuse in all directions, failing to meet the requirements for reduced production.

[0054] To address the above issues, this invention proposes a secondary VRH-CO2 gas vacuum-filling method to ensure uniform hardening of the sand mold and improve its strength.

[0055] See Figure 1 Preparations before operation:

[0056] 1) Select a vacuum-sealed box manufactured by a vacuum equipment factory. Length 1800mm, width...

[0057] For a vacuum chamber with a diameter of 1800mm and a height of 1000mm, the wall thickness and upper sealing plate thickness should be 100mm or more, and the bottom plate thickness should be 150mm or more.

[0058] 2) Select a vacuum pump with an exhaust capacity of 7000 l / min or higher and a vacuum degree of 133 Pa or lower.

[0059] 3) The air blowing plate is connected to the sealed top plate of the vacuum box.

[0060] Operating steps:

[0061] 1) Use 50 / 100 or 70 / 140 scrubbed silica sand or the same type of recycled sand as raw sand. Use methyl phenolic resin, add 2.5%, mix and grind for 60 seconds, then unload the sand and shape it.

[0062] 2) Placing the sand mold: Place the sand mold into the vacuum sealing chamber, attach the air blowing plate to the upper surface of the sand mold, and tighten it with calipers. Then attach the sealing plate of the vacuum sealing chamber and tighten it.

[0063] 3) Vacuuming: Turn on the vacuum pump, ensure the vacuum level in the sealed space is ≥5KPa, and the vacuuming time is ≥60s. Then turn off the vacuum pump.

[0064] 4) The pressure inside the vacuum sealing chamber should be negative, with the range of change not exceeding 0.5 kPa, and the pressure holding time ≥ 5 seconds; otherwise, check the surrounding seal. Blow in CO2 gas, with a CO2 blowing pressure ≥ 0.2 MPa and a blowing time of 30-40 seconds.

[0065] 5) After the CO2 blowing device is turned off, repeat the operation process of steps 3 and 4.

[0066] 6) After shutting off the blowing device, turn on the vacuum pump to extract the residual gas. The vacuuming time should be ≥60s. Then, turn off the vacuum pump and depressurize the vacuum sealing box to remove the mold.

[0067] Explanation of the reasons for using a two-stage reciprocating vacuum blowing hardening method and related experiments:

[0068] In a vacuum-sealed chamber, the sand mold and its surrounding environment are already in a vacuum state. Theoretically, during the external inflation process, the sand mold should easily be filled. However, in practice, it has been found that using only a single vacuum curing method results in localized areas of poor curing.

[0069] Analysis of the reasons:

[0070] After the sand mold is sealed by the air-blowing sealing plate, because the sand mold is sealed by both the sand box and the air-blowing plate, the gas in the sand mold cannot be effectively discharged during the vacuuming process. Moreover, CO2 gas enters the air-blowing plate through the air-blowing pipe, and after being dispersed, the gas pressure entering the sand mold decreases (see...). Figure 2 ).

[0071] Increasing the number of air intake pipes and gas cylinders is necessary to ensure the gas pressure entering the sand mold; however, increasing the number of air intake pipes will affect the sealing of the vacuum chamber and the factory floor space.

[0072] When using a two-stage reciprocating VRH-CO2 gas vacuum-filling method, the strength of the bottom sand mold can be increased by more than 80%, and no problem of poor hardening occurs. Further increasing the number of vacuum-filling cycles results in only a slight increase in strength; in fact, after more than three cycles, the strength tends to decrease (see Table 1).

[0073] Table 1 shows the relationship between the number of vacuum pumping cycles and the vacuum intensity.

[0074] Table 1

[0075] Number of vacuum pumps 1 time 2 times 3 times 4 times Tensile strength (MPa) 0.29 0.52 0.54 0.48

[0076] Explanation of why a flexible hose with an inner diameter of Φ8-Φ12mm is used for the connection of two layers of seals:

[0077] Since the hose connected to the pressure reducing valve is only Φ12mm, if the hose connection between the sealing plates is too high or too low, it will cause uneven air volume in the upper and lower parts of the sand mold, as shown in Table 2.

[0078] Table 2 shows the relationship between the inner diameter of the connection and its strength (secondary vacuuming-air blowing).

[0079] Table 2

[0080]

[0081] Explanation of the reason for the two-layer sealing cover:

[0082] Air is blown through the sealing plate of the vacuum chamber, and diffused around the vacuum chamber. Without sufficient pressure to fill the sand mold, the sand mold cannot harden.

[0083] Determining the vacuuming time and blowing time:

[0084] ① Connect a sealed bag to the air inlet of the vacuum chamber and disconnect the connecting pipes between the two sealing plates. Turn on the vacuum device. After the air inside the sealed bag is completely evacuated, record the time. This time is the minimum evacuation time before filling with CO2 gas. Through experiments, when the vacuum chamber is 3.24m... 3 When the sand mold occupies 50% of the space, the vacuuming time must be ≥60s to ensure that the sealed bag is in a vacuum state.

[0085] ② The determination of the blowing time is similar to the method for determining the number of blowing times. The optimal blowing time is determined by comparing the strength of the sand mold at the top and bottom ends and finding the highest value. Table 3 shows the strength changes at different blowing times based on experimental comparisons.

[0086] Table 3 shows the relationship between vacuuming time and air blowing volume.

[0087] The tensile strength at the top and bottom of the sand mold is ≥0.5MPa.

[0088] Table 3

[0089]

[0090] Set a vacuum holding time; when the negative pressure intensity of the connected pressure gauge remains stable for more than 5 seconds, the value will no longer change.

[0091] This invention employs a secondary vacuum blowing method to ensure uniform hardening and improve the strength of the sand mold.

[0092] The sand mold is placed in the vacuum chamber and sealed with two layers of covers. One layer is a blower plate that seals the upper surface of the sand mold, and the other layer is a vacuum chamber sealing plate that ensures the vacuum chamber is sealed. The two seals are connected by a flexible hose with an inner diameter of Φ10-Φ12mm.

[0093] Turn on the vacuum pump, ensure the pressure in the sealed space is ≤-0.1MPa, and maintain the vacuum for at least 60 seconds.

[0094] Turn off the vacuum pump, maintain the pressure for ≥5 seconds, and then fill with CO2 gas.

[0095] CO2 blowing pressure ≥ 0.2 MPa, blowing time 30-40 seconds.

[0096] After the CO2 blowing device is turned off, the vacuum pump is turned on again, and the vacuuming time is ≥60s.

[0097] The present invention provides another embodiment of a vacuum sealing box used in the above-mentioned VRH-CO2 molding method. The vacuum sealing box is 1800mm long, 1800mm wide, and 1000mm high. The wall thickness and the thickness of the upper sealing plate of the vacuum sealing box are more than 100mm, and the thickness of the lower bottom plate is more than 150mm.

[0098] The vacuum pump has an exhaust capacity of over 7000 l / min and a vacuum degree of less than 133 Pa.

[0099] The air blowing plate is connected to the top sealing plate of the vacuum sealing box.

[0100] The vacuum sealing box uses a two-layer sealing cover. One layer of air blowing plate is sealed on the upper surface of the sand mold, and the other layer of vacuum sealing box sealing plate ensures the vacuum sealing box is sealed. The two layers of seals are connected by a flexible hose with an inner diameter of Φ8-Φ12mm.

[0101] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A method for shaping VRH-CO2, characterized in that, Includes the following: Place the sand mold: Place the sand mold into a vacuum-sealed box; First vacuuming: Turn on the vacuum pump, the vacuum level in the sealed space is ≥5KPa, then turn off the vacuum pump; the pressure inside the vacuum sealing box is in a negative pressure state, and the change range does not exceed 0.5Kpa; Inject CO2 gas; Second vacuuming: After the CO2 blowing device is turned off, the vacuum pump is turned on again to create a vacuum, and then the vacuum pump is turned off. Depressurize and mold in a vacuum-sealed box; The raw sand is selected from 50 / 100 or 70 / 140 scrubbed silica sand or recycled sand of the same type. The amount of methyl phenolic resin added is 2.5%. After mixing and grinding for 60 seconds, the sand is discharged and shaped. For the first vacuuming, turn on the vacuum pump, ensure the pressure in the sealed space is ≤-0.1MPa, and the vacuuming time is ≥60s; After the first vacuuming, turn off the vacuuming and maintain the pressure for ≥5 seconds before filling with CO2 gas.

2. The VRH-CO2 molding method according to claim 1, characterized in that: CO2 blowing pressure ≥ 0.2 MPa, blowing time 30-40 seconds.

3. The VRH-CO2 molding method according to claim 1, characterized in that: After the CO2 blowing device is turned off, the vacuum pump is turned on again, and the vacuuming time is ≥60s.

4. The VRH-CO2 molding method according to claim 3, characterized in that: The sand mold is placed in a vacuum sealing box and sealed with two layers of covers. The two layers of seals are connected by a flexible tube with an inner diameter of Φ10-Φ12mm.

5. The VRH-CO2 molding method according to claim 1, characterized in that: The sand mold is made of methyl phenolic resin, which is a water-soluble alkaline material and contains about 70% inorganic components. It is hardened with CO2.

6. A vacuum-sealed box used in the molding method of VRH-CO2 according to any one of claims 1 to 5, characterized in that: The vacuum sealing box is 1800mm long, 1800mm wide, and 1000mm high. The wall thickness and upper sealing plate thickness of the vacuum sealing box are more than 100mm, and the bottom plate thickness is more than 150mm. Equip a vacuum pump and a blowing plate. The vacuum pump has an exhaust capacity of over 7000 l / min and a vacuum degree of less than 133 Pa. The air blowing plate is connected to the sealing top plate of the vacuum sealing box; The vacuum sealing box uses a two-layer sealing cover. One layer of air blowing plate is sealed on the upper surface of the sand mold, and the other layer of vacuum sealing box sealing plate ensures the vacuum sealing box is sealed. The two layers of seals are connected by a flexible hose with an inner diameter of Φ8-Φ12mm.

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