Low-alloy steel casting process for zero-tolerance fit of shell mold and shell core

Abstract

The invention relates to a low alloy steel casting process with zero tolerance fit of a shell mold and a shell core, which comprises the following steps: (1) precoated sand is manufactured before casting, the surface roughness of a casting is improved by adjusting the particle size ratio of various crude sand of the precoated sand, and the precoated sand comprises the crude sand of 50-70 meshes, the crude sand of 70-100 meshes, the crude sand of 100-140 meshes, the crude sand of 140-200 meshes and the crude sand of 200-280 meshes; (2) the same precoated sand is used when the shell mold and the shell core are cast, the temperature deviation of the mold is kept not higher than 5 DEG C in the shell making and core making processes, and the dimensional precision of the shell mold and the shell core is ensured; and (3) the shell mold shell cores of the hole casting and the shaft casting which are matched with each other are manufactured according to the step (1) and the step (2), the shell mold shell cores of the two castings are kept consistent, and in the casting process, the pouring molten steel components of the hole casting and the shaft casting are kept the same, and the pouring temperatures are kept the same. According to the invention, the production efficiency is greatly improved, and secondary waste products generated by machining are avoided, so that the production cost can be greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical manufacturing casting, and more specifically, to a low alloy steel casting process with zero tolerance matching of shell mold and shell core. Background Art

[0002] At present, in the process of making low-alloy steel castings using precision casting technology, the matching tolerance of the casting blank hole and the shaft can only be a9 (GB / T 1801-1999) at most. When the matching tolerance is higher than a9, mechanical processing is required to meet the requirements.

[0003] The reason why machining is required to meet the requirements when the matching tolerance is higher than a9 is that the current dimensional accuracy level of traditional precision casting low alloy steel castings can only reach CT5 level (GB / T 6414-2017), and the surface roughness of traditional precision casting low alloy steel castings can only reach Ra less than 12.5uM (GB / T6060), so subsequent machining is required after casting. However, the separate steps of casting and machining also affect the matching of the shell and core of low alloy steel, and the yield rate cannot be effectively improved. Therefore, it is necessary to propose a new casting process to achieve zero tolerance matching of the shell and core. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a low alloy steel casting process with zero tolerance matching of shell mold and shell core, which greatly improves the production efficiency and avoids secondary waste generated by mechanical processing, thereby greatly reducing production costs.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] A low alloy steel casting process with zero tolerance fit between shell mold and shell core is as follows:

[0007] (1) Preparing coated sand before casting, and improving the surface roughness of castings by adjusting the particle size ratio of various raw sands of coated sand, wherein the coated sand includes 50-70 mesh raw sand, 70-100 mesh raw sand, 100-140 mesh raw sand, 140-200 mesh raw sand and 200-280 mesh raw sand;

[0008] (2) The same coated sand is used when casting the shell mold and the shell core, and the mold temperature difference is kept within 5°C during the shell and core making process to ensure the dimensional accuracy of the shell mold and the shell core;

[0009] (3) The shell mold and shell core of the hole casting and the shaft casting are manufactured according to steps (1) and (2), and the shell mold and shell core of the two castings are kept consistent. During the casting process, the casting molten steel composition and the pouring temperature of the hole casting and the shaft casting are kept the same.

[0010] In one embodiment, in step (1), the coated sand includes, by mass percentage, 25-35% of 50-70 mesh raw sand, 15-25% of 70-100 mesh raw sand, 15-25% of 100-140 mesh raw sand, 10-20% of 140-200 mesh raw sand and 10-20% of 200-280 mesh raw sand.

[0011] In one of the embodiments, in step (3), a mark for pairing is prepared during the shell and core making process, and during the shell and core making process, it is ensured that each hole casting has a corresponding mark with the shaft casting that matches it. The mark is directly made on the sand shell or sand core, ensuring that the shell mold and shell core making process of the hole casting and the shaft casting are the same, thereby forming a permanent mark on the casting.

[0012] In one of the embodiments, in step (3), after the sand shells with matching markings are molded, during the process of placing and pouring, the hole casting and the sand shells with corresponding markings of the shaft casting that match it are placed in sequence and poured in sequence. During the pouring, the same pot of molten steel is used to complete the pouring of the hole casting and the shaft casting to ensure the consistency of the chemical composition and pouring temperature of the two castings, and to ensure the consistency of the solidification shrinkage of the castings.

[0013] In summary, the present invention has the following beneficial effects:

[0014] The present invention realizes one-piece casting without mechanical processing, ensures that the surface roughness Ra of the cast low-alloy steel casting is less than 6.3uM, can greatly improve production efficiency and avoid secondary waste generated by mechanical processing, thus greatly reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a process schematic diagram of the present invention. DETAILED DESCRIPTION

[0016] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0017] It is worth noting that the directional words such as "upper" and "lower" involved in this article are all relative to the viewing angle of the drawings and are only for the convenience of description and cannot be understood as limitations on the technical solution.

[0018] like Figure 1 As shown, the present invention proposes a low alloy steel casting process with zero tolerance matching of shell mold and shell core, as follows:

[0019] (1) preparing coated sand before casting, and improving the surface roughness of the casting by adjusting the particle size ratio of various raw sands of the coated sand. Specifically, the coated sand includes 25-35% of 50-70 mesh raw sand, 15-25% of 70-100 mesh raw sand, 15-25% of 100-140 mesh raw sand, 10-20% of 140-200 mesh raw sand and 10-20% of 200-280 mesh raw sand in terms of mass percentage;

[0020] (2) The same coated sand is used when casting the shell mold and the shell core, and the mold temperature difference is kept within 5°C during the shell and core making process to ensure the dimensional accuracy of the shell mold and the shell core;

[0021] (3) The shell mold and shell core of the hole casting and the shaft casting are manufactured according to steps (1) and (2), and the shell mold and shell core of the two castings are kept consistent. During the casting process, the pouring molten steel composition and pouring temperature of the hole casting and the shaft casting are kept the same.

[0022] In step (1), in order to ensure that the surface roughness Ra of the low alloy steel casting is less than 6.3uM, the present invention produces specific coated sand. Under the premise of not affecting the tensile strength, high temperature resistance and gas evolution of the coated sand, the original sand particle size ratio of the coated sand is adjusted, and 140-200 mesh original sand and 200-280 mesh original sand are added, instead of conventionally using coating to improve the surface roughness of the casting. The reason is that it is difficult to control the thickness of the coating during the coating process on the sand shell and the sand core, which will directly affect the dimensional accuracy of the casting.

[0023] In the prior art, the conventional coated sand composition is 34-45% of 50-70 mesh raw sand, 25-35% of 70-100 mesh raw sand and 25-35% of 100-140 mesh raw sand, and coating is required to improve the surface roughness of the casting. The present invention proposes a new coated sand composition, and no coating is needed, which solves the problem that uneven coating thickness affects the dimensional accuracy of the casting.

[0024] In step (2), the temperature difference between shell making and core making is small, and the large temperature difference will not lead to different degrees of thermal expansion and contraction of the sand shell and the sand core.

[0025] In step (3), the specific control method is as follows:

[0026] During the shell and core making process, the matching mark is prepared. During the shell and core making process, each hole casting is guaranteed to have a corresponding mark with the shaft casting that matches it. The mark is made directly on the sand shell or sand core to ensure that the shell mold and core making process of the hole casting and the shaft casting are the same, thereby forming a permanent mark on the casting for matching use;

[0027] After the two castings (two low-alloy steel castings, the hole and the shaft) are molded together, during the placement and pouring process, the sand shells with corresponding markings on the hole casting and the matching shaft casting are paired and placed in sequence and poured in order, so as to ensure the consistency of the molten steel pouring temperature of the hole casting and the matching shaft casting.

[0028] The sand shell with matching marks (after mold closing) must be poured with the same pot of molten steel to ensure the consistency of the chemical composition and pouring temperature of the two castings, and the consistency of the solidification shrinkage of the castings, so that the two castings cast from the same furnace can be used in pairs, thereby ensuring the consistency of the casting dimensions and achieving zero tolerance matching of the two low-alloy steel castings of the hole and the shaft.

[0029] The present invention realizes one-piece casting without mechanical processing, ensures that the surface roughness Ra of the cast low-alloy steel casting is less than 6.3uM, can greatly improve production efficiency and avoid secondary waste generated by mechanical processing, thus greatly reducing production costs.

[0030] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A low alloy steel casting process with zero tolerance fit between shell mold and shell core, characterized in that: as follows: (1) Preparing coated sand before casting, and improving the surface roughness of castings by adjusting the particle size ratio of various raw sands of coated sand, wherein the coated sand includes 50-70 mesh raw sand, 70-100 mesh raw sand, 100-140 mesh raw sand, 140-200 mesh raw sand and 200-280 mesh raw sand; (2) The same coated sand is used when casting the shell mold and the shell core, and the mold temperature deviation is kept within 5°C during the shell and core making process to ensure the dimensional accuracy of the shell mold and the shell core; (3) The shell mold and shell core of the hole casting and the shaft casting are manufactured according to steps (1) and (2), and the shell mold and shell core of the two castings are kept consistent. During the casting process, the casting molten steel composition and the pouring temperature of the hole casting and the shaft casting are kept the same.

2. The low alloy steel casting process with zero tolerance fit between shell mold and shell core as claimed in claim 1, characterized in that: In step (1), the coated sand includes, by mass percentage, 25-35% of 50-70 mesh raw sand, 15-25% of 70-100 mesh raw sand, 15-25% of 100-140 mesh raw sand, 10-20% of 140-200 mesh raw sand and 10-20% of 200-280 mesh raw sand.

3. The low alloy steel casting process with zero tolerance fit between shell mold and shell core as claimed in claim 1, characterized in that: In step (3), during the shell and core making process, a mark for pairing is prepared to ensure that each hole casting has a corresponding mark with the shaft casting that matches it. The mark is directly made on the sand shell or sand core to ensure that the shell mold and shell core manufacturing processes of the hole casting and the shaft casting are the same, thereby forming a permanent mark on the casting.

4. The low alloy steel casting process with zero tolerance fit between shell mold and shell core as claimed in claim 1, characterized in that: In step (3), after the sand shell with matching marks is molded, the same pot of molten steel is used to cast the hole casting and the shaft casting to ensure the consistency of the chemical composition and pouring temperature of the two castings and to ensure the consistency of the solidification shrinkage of the castings.

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