Composite Core Casting Process and Its Application

Abstract

The present invention provides a composite core casting process and its application. The composite core casting process comprises the following steps: (1) According to the manifestation of casting defects of the casting, the core of the part where mechanical penetration occurs is segmented to form a prefabricated core, which is made separately; (2) The prefabricated core is placed and fixed in the core box of the large core, and after sand shooting, the core sand is brought into contact with the prefabricated core to combine. After the core sand hardens and is demolded, an integrated overall core is obtained. This process can be applied to resin-coated sand casting, and the problem of mechanical penetration caused by the penetration of molten metal is solved by strengthening the density of the local core.

Description

Technical Field

[0001] The present invention belongs to the technical field of casting, and particularly relates to a composite sand core casting process and its application. Background Art

[0002] Casting is a forming method in which liquid metal is poured into a casting cavity adapted to the shape of the part. After it cools and solidifies, a metal part blank with a certain shape, size, and performance is obtained.

[0003] Generally speaking, the more complex the casting is, the more likely it is to produce casting defects such as sand adhesion, shrinkage porosity, etc. Therefore, castings with complex structures also pose higher requirements for the mold and casting process.

[0004] In casting production, a sand core is used to form the inner cavity of the casting or parts with complex shapes that are not easy to mold. When the sand core structure is complex, or the local cross-sectional dimension of the sand core is small, or the position is special, on the one hand, castings produced using a cold core will cause defects such as mechanical sand adhesion at the corresponding positions of the castings. On the other hand, during the sand shooting process of the sand mold, local non-compaction of the sand core will also occur, resulting in defects such as mechanical sand adhesion at the corresponding parts of the casting. Summary of the Invention

[0005] In view of the above technical problems, the present application proposes a composite sand core casting process and its application, and the specific technical solutions are as follows:

[0006] In the first aspect, the present invention provides a composite sand core casting process, including the following steps:

[0007] (1) According to the manifestation of casting defects of the casting, the sand core at the mechanically sand-adhered part is segmented to form a prefabricated sand core, which is made separately;

[0008] (2) The prefabricated sand core is placed and fixed in the core box of the large sand core. After sand shooting, the core sand is brought into contact and combined with the prefabricated sand core. After the core sand hardens and is demolded, an integrated whole sand core is obtained.

[0009] More specifically, the method for making the prefabricated sand core is as follows:

[0010] Put the molding sand into a muller, and then add a binder, a curing agent, and a lubricant, and mix the sand;

[0011] Put the mixed molding sand into the sand shooting cylinder of a core shooter. After heating the core box to the target temperature, shoot the core to make a sand sample. After hardening, demold it and take out the prefabricated sand core.

[0012] In some preferred embodiments, the molding sand in the prefabricated sand core is a mixed sand of chromite sand and silica sand, and the content of chromite sand is not less than 60%.

[0013] In some preferred embodiments, a thioester antioxidant is added simultaneously when making the prefabricated sand core.

[0014] In some preferred embodiments, the thioester antioxidant is dilauryl thiodipropionate (DLTDP), but is not limited to this substance, and may also be DSTDP, DTDTDP, DODTP, DHDTP, DMTDP, etc.

[0015] In some preferred embodiments, the addition amount of the thioester antioxidant is 0.01-0.07% of the binder.

[0016] In some preferred embodiments, the addition amount of the thioester antioxidant is 0.04% of the binder.

[0017] In a second aspect, the present invention provides an application of the above composite core casting process, and the composite core casting process is applied to coated sand casting.

[0018] The beneficial effects of the present invention are as follows: The sand core is separated, and the parts prone to mechanical penetration defects are separately made to form prefabricated sand cores, and then the overall sand core is made. The problem of mechanical penetration caused by the penetration of molten metal is solved by strengthening the density of the local sand core; at the same time, based on the composite structure of this sand core, the mixing ratio relationship of the molding sand can be changed, and the local cooling rate can be increased to avoid shrinkage porosity defects caused by the existence of hot spots. Description of the Drawings

[0019] Figure 1 Shows the state where the casting and the sand core are not separated;

[0020] Figure 2 Shows a structural schematic diagram of a torque converter housing casting;

[0021] Figure 3 Shows some of the sand cores applied to cast the torque converter housing casting;

[0022] Figure 4 Shows a structural schematic diagram of the prefabricated sand core formed by dividing the sand core. Detailed Embodiments

[0023] In the following description, certain specific details are set forth in order to provide a thorough understanding of the various embodiments. However, those skilled in the art should understand that the present invention may be practiced without these details. In other instances, well-known structures have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. Unless the context otherwise requires, throughout the specification and the appended claims, the word "comprising" shall be interpreted in an open, inclusive sense, i.e., as "including but not limited to".

[0024] The composite core casting process described in this application is described as follows:

[0025] (1)Fabricate a prefabricated sand core;

[0026] (2)Place and fix the prefabricated sand core in the core box of the large sand core. After sand shooting, make the core sand contact and combine with the prefabricated sand core. After the core sand hardens and demolds, an integrated whole sand core is obtained.

[0027] The fabrication method of the prefabricated sand core is as follows:

[0028] A. Sand mold preparation: Put the molding sand into a muller, and then add a binder, a curing agent, and a lubricant, and mull for 3 - 5 minutes;

[0029] B. Core shooting: Put the above - mixed molding sand into the sand - shooting cylinder of a core - shooting machine. When the heating temperature of the core box reaches 120 - 160 °C, conduct core shooting. The core - shooting pressure is 0.5 - 0.6 Mpa, and the core - shooting time is 2 - 3 s to make a sand sample. After hardening for 20 - 60 s, demold and take out the prefabricated sand core.

[0030] The fabrication method of the whole sand core is the same as that of the prefabricated sand core.

[0031] Exemplarily, this application combines Figure 2 with the casting structure to provide a more detailed description of the composite sand - core casting process of this application.

[0032] Figure 1 shows the state where the casting and the sand core are not separated. Figure 2 shows the structural schematic diagram of the torque - converter housing casting. Figure 3 shows a partial sand core corresponding to the casting of this torque - converter housing casting. Since Figure 2 the structure of the torque - converter housing casting in is complex, a combined sand core needs to be used to form the casting cavity. Figure 3 The sand core in is one of the combined sand cores.

[0033] Combined with this casting, during the actual casting process of obtaining the torque - converter housing casting, due to the complex structure of the torque - converter housing casting, after casting is completed Figure 3 mechanical sand adherence defects will occur at point A of the sand core in. Whether using a cold core or a hot core will cause mechanical sand adherence.

[0034] In the following examples and comparative examples, the description of the materials:

[0035] The phenolic resin is purchased from Suzhou Xingye Materials Technology Co., Ltd., CAS number 9003 - 35 - 4, product number PF0902.

[0036] The silica sand is purchased from Zhangwu Lianxin Foundry Silica Sand Co., Ltd., with a silicon dioxide content of 98.5%, a density of 2.66 (g / cm 3 ), and a mesh size of 50 - 100.

[0037] The chromite sand was purchased from Shanghai Shenyun Ferroalloy Co., Ltd., with a chromium content of 35-45%, item number JT044, and a mesh size of 70-140.

[0038] Dilauryl thiodipropionate was purchased from Panhua Chemical Co., Ltd., with a CAS number of 123-28-4 and a purity of 99%.

[0039] Hydroquinone was purchased from Panhua Chemical Co., Ltd., with a CAS number of 123-31-9 and a purity of 99%.

[0040] 2,6-Di-tert-butyl-4-methylphenol was purchased from Shanghai Gaoming Chemical Co., Ltd., with a CAS number of 34534-53-5.

[0041] Hexamethylenetetramine was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd., with a CAS number of 100-97-0.

[0042] Calcium stearate was purchased from Shanghai Macklin Biochemical Co., Ltd., with a CAS number of 1592-23-0 and item number C805417. Example 1

[0043] Separate the core sand in Figure 3 to form the precast core sand structure in Figure 4 , and the core sand in Figure 3 is made by the following method:

[0044] Put silica sand into a muller, then add phenolic resin, hexamethylenetetramine and calcium stearate, mull for 5 minutes, then put the prepared molding sand into the sand injection cylinder of a core shooter. When the core box heating temperature reaches 150 °C, carry out sand injection, the sand injection pressure is 0.5 Mpa, the sand injection time is 2-3 s, make a sand sample, demold after hardening for 50-60 s, and take out the precast core;

[0045] Put silica sand into a muller, then add phenolic resin, hexamethylenetetramine and calcium stearate, mull for 5 minutes, then put the prepared molding sand into the sand injection cylinder of a core shooter, place and fix the precast core in the core box of the large core, carry out sand injection, the sand injection pressure is 0.5 Mpa, the sand injection time is 5-10 s, make a sand sample, demold after hardening for 50-60 s, and take out the integral core.

[0046] In the above process, the prepared molding sand contains 5% phenolic resin, 3% calcium stearate, and the addition amount of hexamethylenetetramine is 10% of the phenolic resin, and the rest is silica sand.

[0047] Unless otherwise specified in this application, "%" are all mass percentages, that is, wt%.

[0048] Comparative Example 1

[0049] Put silica sand into a muller, then add phenolic resin, hexamethylenetetramine and calcium stearate, mull for 5 minutes, and then put the prepared molding sand into the sand injection cylinder of a core shooter. When the heating temperature of the core box reaches 150 °C, carry out core shooting. The core shooting pressure is 0.5 Mpa, and the core shooting time is 5 - 10 s to make a sand sample. After hardening for 60 s, demold and take out the integral core.

[0050] In the above process, the prepared molding sand contains 5% phenolic resin and 3% calcium stearate, and the addition amount of hexamethylenetetramine is 10% of the phenolic resin, and the rest is silica sand.

[0051] The cores obtained in Example 1 and the core obtained in Comparative Example 1 are respectively used for casting to obtain Figure 2 the castings shown in, and it is found that there are no obvious mechanical sand adhering defects at the corresponding positions of the precast sand cores of the castings in Example 1, while there are obvious mechanical sand adhering defects at the corresponding positions in Comparative Example 1; it shows that for the problem of local structure being prone to mechanical sand adhering defects caused by casting with one - piece - formed molding sand for complex - structure castings, this mechanical sand adhering defect can be solved by setting the part with mechanical sand adhering defect as a precast sand core and then making an integral core.

[0052] However, the mechanical sand adhering defect caused by making an integral core by one - piece forming covers the shrinkage porosity and shrinkage cavity defects that would originally appear at the same position, but the reasons for their formation are different. The mechanical sand adhering defect is caused by the insufficient density of the integral core made by one - piece forming at this place, resulting in the penetration of the molten metal and causing mechanical sand adhesion. The shrinkage porosity and shrinkage cavity defects are due to the formation of hot spots at this place, and the mechanical sand adhering defect directly covers this shrinkage porosity and shrinkage cavity defect. When the mechanical sand adhering defect is overcome, the shrinkage porosity and shrinkage cavity defects are exposed.

[0053] On the other hand, since the precast sand core is formed first and then the integral core is formed, the density of the sand core at the place where mechanical sand adhering defect occurs is ensured. However, the precast sand core is cured first, with lower surface activity, and a dense hardened layer may form on the surface after curing, hindering the bonding between new sand and old sand, resulting in a weak bonding ability between the precast sand core and the newly injected hot core sand, thereby affecting the bonding strength of the precast sand core. In the high - temperature environment of casting, interface separation occurs between the precast sand core and the integral core, and the precast sand core shifts, ultimately resulting in the deformation of the obtained casting. Example 2

[0054] The difference from Example 1 is that a mixed molding sand is used to replace silica sand to make the precast sand core.

[0055] The mixing ratio of the mixed molding sand is: 30 wt% chromite sand and 70 wt% silica sand. Example 3

[0056] The difference from Example 1 is that a mixed molding sand is used to replace silica sand to make the precast sand core.

[0057] The mixing ratio of the mixed sand is: 40 wt% chromite sand and 60 wt% silica sand. Example 4

[0058] It is different from Example 1 in that the precast sand core is made by replacing silica sand with the mixed sand.

[0059] The mixing ratio of the mixed sand is: 50 wt% chromite sand and 50 wt% silica sand. Example 5

[0060] It is different from Example 1 in that the precast sand core is made by replacing silica sand with the mixed sand.

[0061] The mixing ratio of the mixed sand is: 60 wt% chromite sand and 40 wt% silica sand. Example 6

[0062] It is different from Example 1 in that the precast sand core is made by replacing silica sand with the mixed sand.

[0063] The mixing ratio of the mixed sand is: 70 wt% chromite sand and 30 wt% silica sand.

[0064] The sand cores prepared in Examples 2 to 6 are used for casting to obtain Figure 2 the castings shown in, and the defects of mechanical adhering sand, shrinkage porosity and casting deformation are inspected respectively. The results are shown in Table 1.

[0065]

[0066] Table 1

[0067] Combined with Table 1, from a qualitative perspective, it can be judged that the casting process of first forming the precast sand core and then forming the integral sand core can overcome the local mechanical adhering sand defect. At the same time, by carrying out special material mixing ratios for the precast sand core, although shrinkage porosity defects appear in Examples 2 to 4, there is an obvious improvement trend. And when the mixed sand contains at least 60% chromite sand, by using the excellent thermal conductivity and heat storage capacity of chromite sand, the cooling rate in the hot spot area is accelerated, and the shrinkage porosity defects are reduced, thereby overcoming the local shrinkage porosity defects.

[0068] Since the precast sand core is close to the casting cavity, when the precast sand core is displaced and causes casting deformation, the precast sand core will be displaced into the casting cavity, thereby causing the overall volume of the casting to become smaller. Therefore, the degree of casting size deformation defects can be quantitatively analyzed by measuring the volume of the casting.

[0069] The results of the casting deformation defects in Examples 2 to 6 are shown in Table 2.

[0070]

[0071] Table 2

[0072] The degree of dimensional deformation in Table 2 refers to the volume ratio of the actual obtained casting to the target casting. The smaller the value, the more severe the degree of dimensional deformation.

[0073] Combined with Table 2, it is found that as the addition amount of chromite sand in the mixed molding sand increases, the degree of casting dimensional deformation defects increases accordingly. Due to the relatively high content of chromite sand in the prefabricated sand core, the local heat conduction of the prefabricated sand core is accelerated, resulting in the premature separation of the interface between the prefabricated sand core and the overall sand core, and further making the casting dimensional deformation defects more significant. Example 7

[0074] The difference from Example 5 is that:

[0075] When making the prefabricated sand core, dilauryl thiodipropionate is added while adding the binder, and the addition amount of dilauryl thiodipropionate is 0.01% of the binder. Example 8

[0076] The difference from Example 5 is that:

[0077] When making the prefabricated sand core, dilauryl thiodipropionate is added while adding the binder, and the addition amount of dilauryl thiodipropionate is 0.02% of the binder. Example 9

[0078] The difference from Example 5 is that:

[0079] When making the prefabricated sand core, dilauryl thiodipropionate is added while adding the binder, and the addition amount of dilauryl thiodipropionate is 0.03% of the binder. Example 10

[0080] The difference from Example 5 is that:

[0081] When making the prefabricated sand core, dilauryl thiodipropionate is added while adding the binder, and the addition amount of dilauryl thiodipropionate is 0.04% of the binder. Example 11

[0082] The difference from Example 5 is that:

[0083] When making the prefabricated sand core, dilauryl thiodipropionate is added while adding the binder, and the addition amount of dilauryl thiodipropionate is 0.05% of the binder. Example 12

[0084] The difference from Example 5 is that:

[0085] When making the prefabricated sand core, dilauryl thiodipropionate is added while adding the binder, and the addition amount of dilauryl thiodipropionate is 0.06% of the binder. Example 13

[0086] The difference from Example 5 is that:

[0087] When making the precast sand core, dilauryl thiodipropionate is added simultaneously with the binder, and the addition amount of dilauryl thiodipropionate is 0.07% of the binder.

[0088] Comparative Example 2

[0089] The difference from Example 5 is that:

[0090] When making the precast sand core, dilauryl thiodipropionate is added simultaneously with the binder, and the addition amount of dilauryl thiodipropionate is 0.08% of the binder.

[0091] The sand cores prepared in Examples 7 to 13 and Comparative Example 2 are used for casting to obtain Figure 2 the castings shown in, and the defects of mechanical penetration, shrinkage porosity and casting deformation are inspected respectively. The results are shown in Table 3.

[0092]

[0093] Table 3

[0094] Combined with Table 3, it is found that adding dilauryl thiodipropionate simultaneously during the forming of the precast sand core can improve the dimensional deformation defects of the casting, and with the increase of the addition amount of dilauryl thiodipropionate, this improvement effect shows a trend of increasing first and then decreasing. And when the addition amount of dilauryl thiodipropionate increases to more than 0.08%, it instead has a negative effect. The optimal addition amount of dilauryl thiodipropionate is 0.04%.

[0095] Comparative Example 3

[0096] The difference from Example 10 is that:

[0097] When making the precast sand core, hydroquinone is added to replace dilauryl thiodipropionate.

[0098] Comparative Example 4

[0099] The difference from Example 10 is that:

[0100] When making the precast sand core, 2,6 - di - tert - butyl - 4 - methylphenol is added to replace dilauryl thiodipropionate.

[0101] The sand cores prepared in Comparative Examples 3 and 4 are used for casting to obtain Figure 2 the castings shown in, and the defects of mechanical penetration, shrinkage porosity and casting deformation are inspected respectively. The results are shown in Table 4.

[0102]

[0103] Table 4

[0104] Combined with Table 4, it is found that when adding other substances with antioxidant effects during the forming of precast sand cores, although the dimensional deformation defects can be improved, the effect is not as good as that of dilauryl thiodipropionate.

[0105] While dilauryl thiodipropionate itself has antioxidant function, it has a relatively large molecular weight and belongs to a chain structure. After being added to the molding sand together with the binder, during the curing process of the sand mold, dilauryl thiodipropionate can capture the free radicals of the binder polymerization reaction, thereby delaying the polymerization and curing speed of the binder and reducing the degree of polymerization of the binder in the precast sand core. At the same time, due to the relatively large molecular weight of dilauryl thiodipropionate itself, it will hinder the cross-linking between binder molecules and reduce the cross-linking density of the binder in the precast sand core. When the precast sand core is placed in the core box of the large sand core to make the integral sand core, during the re-curing process, on the one hand, the binder injected into the core box of the large sand core by the core shooter can react and polymerize with the binder in the precast sand core with unsaturated degree of polymerization, improving the interfacial bonding strength between the precast sand core and the integral sand core. On the other hand, due to the reduction of the cross-linking density of the binder in the precast sand core, the binder and molding sand injected into the core box of the large sand core by the core shooter can also improve the permeability to the precast sand core, and can further improve the bonding strength between the precast sand core and the integral sand core. During the curing process of the precast sand core, dilauryl thiodipropionate will also break the chain to form substances with smaller molecular weights. Therefore, when preparing the integral sand core in the core box of the large sand core, the hindrance of cross-linking between binder molecules is reduced, so that both the integral sand core and the precast sand core can achieve better cross-linking polymerization and curing purposes. However, when the amount of dilauryl thiodipropionate added is excessive, it will affect the mechanical properties of the precast sand core after forming, making the precast sand core itself more likely to collapse and deform during the casting process. Therefore, the addition amount of dilauryl thiodipropionate should be controlled.

[0106] Hydroquinone and 2,6-di-tert-butyl-4-methylphenol are both phenolic antioxidants, which mainly rely on phenolic hydroxyl groups to provide hydrogen atoms to capture free radicals, and the structure changes little before and after the action. Therefore, although they can provide antioxidant function and affect the degree of polymerization of the binder in the precast sand core, the influence on the cross-linking density of the binder is not obvious. Therefore, during the process of making the integral sand core, the bonding strength between the precast sand core and the integral sand core cannot be further improved.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them.

Claims

1. Composite sand core casting process, characterized in that: The steps include: (1) According to the casting defects of the casting, the sand core at the location where mechanical sand sticking occurs is separated to form a prefabricated sand core, and the prefabricated sand core is made separately, wherein the medium-molded sand of the prefabricated sand core is a mixed sand of chromite sand and silica sand, and the content of chromite sand is not less than 60%; (2) The prefabricated sand core is placed and fixed in the core box of the large sand core. After sand shooting, the core sand is contacted and combined with the prefabricated sand core. After the core sand is hardened and demolded, an integrated whole sand core is obtained; The method for making the prefabricated sand core is as follows: Put the molding sand into the sand mixer, then add the binder and thioester antioxidant to mix the sand; Put the mixed molding sand into the sand shooting cylinder of the core shooting machine, heat the core box to the target temperature and shoot the core to make a sand sample. After hardening, demould and take out the prefabricated sand core; The thioester antioxidant is dilauryl thiodipropionate, and the added amount of the thioester antioxidant is 0.01-0.07% of the binder.

2. The composite sand core casting process according to claim 1, characterized in that: The added amount of the thioester antioxidant is 0.04% of the binder.

3. The composite sand core casting process according to any one of claims 1 or 2, characterized in that: The composite sand core casting process is applied to coated sand casting.

Images