Cylindrical iron casting built-in iron core sand-coated core-making process method

Abstract

The invention discloses a sand-coated core manufacturing process method for a built-in iron core of a cylindrical iron casting, belongs to the technical field of sand core manufacturing, and adopts a precoated sand hot box core shooting process to produce the cylindrical iron casting. Shooting the core by adopting a hot core box core shooter; the built-in chilling block is arranged in the sand mold inner core; a layer of sand film is arranged on the periphery of the built-in chilling block; the built-in chilling block is of a hollow cylindrical sleeve structure, the upper end is closed, the lower end is open, and a vent hole is formed in the center of the upper end face. The appearance of the built-in chilling block is of a step-shaped structure, and the upper outer circle diameter is smaller than the lower outer circle diameter. The sand core is manufactured by adopting a built-in iron core and surface sand coating process, so that the cooling speed of the cast in a casting mold after casting is accelerated, the casting defects such as shrinkage porosity and shrinkage cavity can be prevented, the refining of cast iron tissues is facilitated, the mechanical property of the iron casting is improved, and the qualification rate of the cast is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sand core manufacturing, and particularly relates to a sand core manufacturing process for a cylindrical cast iron part with an embedded core. BACKGROUND

[0002] In the prior art, resin sand cores or coated sand cores are usually used in the production of cylindrical cast iron parts. However, the use of the whole sand core leads to slow cooling of the cast iron part, coarse cast iron structure, and shrinkage porosity in the last solidification part (thick wall inside) of the cast iron part due to the poor heat conduction and heat dissipation of the sand core, which results in poor quality and low qualified rate of the cast iron part.

[0003] Therefore, it is necessary to develop a sand core manufacturing process for a cylindrical cast iron part with an embedded core to solve the above problems. SUMMARY

[0004] The present application provides a sand core manufacturing process for a cylindrical cast iron part with an embedded core, which uses an embedded core and surface sanding process to manufacture the sand core, accelerates the cooling rate of the cast part in the mold after pouring, prevents shrinkage porosity and other casting defects, refines the cast iron structure, improves the mechanical properties of the cast iron part, and improves the qualified rate of the cast part.

[0005] To solve the above technical problems, the technical solution adopted by the present application is as follows:

[0006] A sand core manufacturing process for a cylindrical cast iron part with an embedded core, which uses a coated sand hot core box core shooting process to produce a cylindrical cast iron part; uses a hot core box core shooting machine to shoot the core; an embedded cold iron is arranged inside the inner core of the sand mold; a layer of sand film is arranged around the embedded cold iron; the embedded cold iron is a hollow cylindrical sleeve structure with a closed upper end and an open lower end, and a ventilation hole is formed in the center of the upper end face; the outer shape of the embedded cold iron adopts a stepped structure with a smaller upper outer diameter than a lower outer diameter.

[0007] Further improvement of the technical solution of the present application is that the material of the embedded cold iron is 45# steel or A3 carbon steel.

[0008] Further improvement of the technical solution of the present application is that the embedded cold iron sequentially includes an open section, an intermediate section, and a closed section from bottom to top; a ventilation hole is formed in the center of the upper end face of the closed section, and the ventilation hole is plugged with an internal hexagonal bolt during core shooting.

[0009] Further improvement of the technical scheme of the present application is that the inner diameter of the closed section is the same as that of the middle section, the outer diameter of the closed section is smaller than that of the middle section, and the included angle alpha between the outer diameter of the closed section and the outer diameter of the middle section is 135 degrees; the outer diameter of the open section is the same as that of the middle section, and the inner diameter of the open section is greater than that of the middle section.

[0010] Further improvement of the technical scheme of the present application is that the operation process of the coated sand hot core box core shooting process is as follows:

[0011] S1, complete safety inspection and production preparation before core production according to the operation file requirements;

[0012] S2, install and debug the core shooting mold and built-in chill in the core making equipment, ensure that the core shooting mold is accurately positioned, the mold opening and core taking are smooth, and the operation is convenient;

[0013] S3, power heating is performed on the core shooting mold, after the core shooting mold is heated to the preheating temperature, the release agent is sprayed on the surface of the core shooting mold cavity, the coating should be thin and uniform, and accumulation or omission is not allowed, and then the temperature is kept for a period of time;

[0014] S4, continue to heat the core shooting mold, when the temperature reaches the core shooting working temperature range required by the process, keep the temperature for a period of time, then start the core shooting operation, and after the core shooting is completed, the coated sand core is heated and solidified in the core shooting mold;

[0015] S5, after the sand core is solidified, the mold is opened and the core is taken out, the sand core is placed in the exhaust cabinet for cooling and the burrs and burrs on the sand core are thoroughly cleaned;

[0016] S6, perform the appearance quality inspection of the sand core, if there is a slight defect, use graphite paint for repair, after the inspection is qualified, transfer to the molding process for subsequent casting production.

[0017] Further improvement of the technical scheme of the present application is that in S3, the preheating temperature of the core shooting mold is 100-130 DEG C.

[0018] Further improvement of the technical scheme of the present application is that in S3, the release agent is methyl silicone oil, and the heat preservation time of the release agent is 10-15 min.

[0019] Further improvement of the technical scheme of the present application is that in S4, the core shooting working temperature range is 240±20 DEG C, and the heat preservation time is 10-15 min; when the core shooting operation is performed, the total pressure of the pipeline supplied by the air pressure station is greater than or equal to 0.60 Mpa, and the sand core shooting pressure is 0.35-0.50 Mpa.

[0020] Further improvement of the technical scheme of the present application is that in S4, after the core shooting is completed, the heating and solidification time of the coated sand core in the mold is 180±30s, and the thickness of the core sand layer of the iron core is 5-10mm.

[0021] Further improvement of the technical scheme of the present application is that before determining to produce the cylindrical cast iron piece by using the coated sand hot core box core shooting process, the raw materials, equipment and technical documents need to be prepared; the machining allowance and the inner cavity size of the cylindrical cast iron piece blank are determined; and after the coated sand hot core box core shooting process is completed, the subsequent operation of the cast iron piece blank production is still needed.

[0022] Due to the adoption of the above technical scheme, the present application has achieved the following technical progress:

[0023] 1. The present application adopts the built-in iron core sanding core process method, adjusts and controls the cooling speed of the castings in the mold after pouring, can more effectively control the cooling, solidification and crystallization process of the cast iron, improve the as-cast matrix structure of the castings, improve the solidification and shrinkage effect of the castings, eliminate the casting defects such as inner cavity shrinkage and shrinkage hole often occurred after machining of the castings, and improve the mechanical properties and quality of the castings.

[0024] 2. The present application fills the gap of the lack of built-in iron core sanding core process technology for cylindrical cast iron pieces in the prior art, solves the technical methods of design of built-in iron core (cold iron) of cylindrical cast iron pieces, design of hot core box core shooting mold, preparation process control of coated sand core and other technical methods, and solves the technical problems of process control of coated sand core.

[0025] 3. The present application realizes the design and production of built-in iron core (cold iron) of cylindrical cast iron pieces and hot core box core shooting mold, realizes effective control, smooth operation and stable control of the quality of the castings in the preparation process of the coated sand core, ensures the stable quality of the castings and improves the production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical scheme in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor;

[0027] Figure 1 is a structure diagram of the built-in cold iron provided in the embodiments of the present application;

[0028] Among them, 1 is an opening section, 2 is a middle section, 3 is a closed section, and 4 is a vent hole. DETAILED DESCRIPTION

[0029] It is to be understood that the terms "including", "comprising", "having" and their conjugates, as used throughout the specification and in the following Claims, shall not be construed restricted to encompassing only those steps or elements clearly listed, but shall include other non-listed or inherent steps or elements as well.

[0030] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0031] The present application will be further described in detail below in conjunction with the drawings and examples:

[0032] A process for making a cylindrical cast iron part with a built-in core sand core, specifically comprising the following contents:

[0033] (1) Preparation of raw materials, equipment and technical documents

[0034] Prepare the core-making raw and auxiliary materials such as coated sand, release agent, paint, etc. required for the production of the core of the cast iron part; check the various equipment required for core-making, such as core shooter, core-making mold, tools, detection equipment, etc.; and prepare the various technical documents required for core-making operation, such as standard documents, process specifications, operation instruction books, core-making process monitoring record tables, etc.

[0035] 1) Coated sand: a molding and core-making material commonly used in the casting industry. It is mainly composed of raw sand (silica sand), binder and other additives. Compared with conventional casting sand, its unique feature is that it is coated with a thin film, which is made of special binder through special treatment. Coated sand has the advantages of high strength, good flowability and high temperature resistance, and is an important material for making sand cores and sand molds.

[0036] 2) Release agent: a kind of auxiliary material applied in the core-making process of coated sand core, which is coated on the inner surface of the core-making metal mold cavity to facilitate smooth demolding of the core when the core-making is completed, such as methyl silicone oil, etc.

[0037] 3) Paint: a kind of auxiliary material applied in the core-making process of coated sand core, which is coated on the surface of the prepared sand core to repair minor defects on the surface of the sand core and improve the surface quality of the sand core.

[0038] (2) Determine the machining allowance and inner cavity size of cylindrical iron castings

[0039] The method for determining the machining allowance and inner cavity size of cylindrical iron castings is usually determined by referring to the national standard GB / T6414 casting dimensional tolerance, geometric tolerance and machining allowance, combined with factors such as the casting shape and size, material grade, technical difficulty, and drawing on previous successful casting work practice experience.

[0040] Typically, the machining allowance for the inner diameter of cylindrical iron castings is 3-6mm (per side), the machining allowance for the two end faces is 2-5mm (per side), and the machining allowance for the outer diameter is 4-6mm (per side). For larger castings, the upper limit is used, and for smaller castings, the lower limit is used.

[0041] (3) Determine the core making process for cylindrical iron castings

[0042] The commonly used core making process methods for cylindrical iron castings can be divided into two categories: manual core making and machine core making. According to the different materials used in core making, they can be divided into clay sand cores, oil sand cores, resin sand cores and coated sand cores.

[0043] In order to ensure the quality of castings and improve production efficiency, the present invention adopts a coated sand hot core box core shooting process to produce cylindrical iron castings.

[0044] (4) Determine the material and size of the built-in chiller in cylindrical iron castings

[0045] According to the material, shape and size of the sand core of cylindrical iron castings, taking into account the material, shape and size of cylindrical iron castings, as well as the chemical composition of the castings and their casting performance characteristics, and conducting a casting process analysis on the iron castings, it is determined that the castings may have defects such as shrinkage cavities and shrinkage porosity and their characteristics, and then the chilling capacity required to eliminate casting defects is determined. After comprehensively considering the above factors, the material and structural size of the built-in chiller are determined.

[0046] Considerations for designing the material and dimensions of built-in chillers for cylindrical iron castings:

[0047] 1) If Figure 1 As shown, the built-in chiller adopts a hollow cylindrical sleeve structure with a closed upper end and an open lower end. From bottom to top, it includes an open section 1, a middle section 2, and a closed section 3. A vent hole 4 is opened at the center of the upper end surface of the closed section 3. During core shooting (it needs to be blocked before core shooting), the vent hole 4 is blocked with a hexagon socket bolt. It is not blocked during pouring to facilitate the exhaust of the sand core during the casting process.

[0048] 2) The outer shape of the built-in chiller adopts a stepped structure, usually the outer diameter of the upper closed section 3 is smaller, and the outer diameter of the lower part of the opening section 1 and the middle section 2 is larger. Specifically, the inner diameter of the closed section 3 is the same as that of the middle section 2, the outer diameter of the closed section 3 is smaller than that of the middle section 2, and the angle α at the transition from the outer diameter of the closed section 3 to the outer diameter of the middle section 2 is 135°; the outer diameter of the opening section 1 is the same as that of the middle section 2, and the inner diameter of the opening section 1 is larger than the inner diameter of the middle section 2.

[0049] The specific size of the built-in chiller needs to be adjusted according to the size of the cylindrical iron casting.

[0050] like Figure 1 As shown, it is beneficial to adjust the cooling and solidification sequence of the casting, ensure that the casting solidifies in a bottom-up order, and guide the casting defects into the riser by adding risers and other measures on the upper part of the casting, thereby eliminating defects such as shrinkage cavities and shrinkage porosity inside the casting.

[0051] 3) The built-in chiller material is usually 45# steel or A3 carbon steel.

[0052] 4) The built-in chiller needs to be used in conjunction with the hot core box core shooting mold. Therefore, the inner hole size of the built-in chiller opening section 1 should be closely coordinated with the positioning of the lower part of the mold and the core shooting machine worktable and the core ejecting device to ensure that the built-in chiller is accurately positioned, the core ejection is smooth, and the core making and core removal operations are relatively convenient.

[0053] (5) Determine the process parameters for sand coating of the core of cylindrical iron castings

[0054] The core making process of cylindrical iron castings with built-in iron core and sand coating usually adopts hot core box core shooting machine. The process parameter requirements are shown in Table 1 below.

[0055] Table 1 Process parameters for sand coating of built-in cores of cylindrical iron castings

[0056] Serial number Process parameter item Unit Process requirement Remark 1 Total pressure of pipeline MPa ≥0.60 Air supply of air compression station 2 Sand core shooting pressure MPa 0.35-0.50 Equipment instrument indication 3 Working temperature of core shooting mold ℃ 240±20 Temperature control instrument 4 Preheating temperature of core shooting mold ℃ 100-130 Temperature control instrument 5 Preheating time of core shooting mold Min 10-15 Time relay 6 Coated sand model - FS101 Certain brand 7 Recommended model of core shooter _ Z8612B Certain brand 8 Thickness of sand coating of core mm 5-10 Adjust according to need

[0057] (6) Processing and manufacturing of core molds and built-in chillers for cylindrical cast iron parts

[0058] According to product design requirements and process technology requirements, we design core shooting mold drawings for cylindrical iron castings and carry out mold manufacturing; we design built-in chiller component drawings for cylindrical iron castings and carry out built-in chiller manufacturing; at the same time, we design and manufacture casting patterns, templates, pouring system modules and other tooling molds that match the sand cores.

[0059] After the above mold and tooling are completed, the raw and auxiliary materials, production equipment and detection equipment required for casting production are prepared, appropriate operators are equipped and necessary technical safety training is carried out, so that the cylindrical cast iron part blank casting production can be carried out according to the standard file requirements. First, the built-in core sand core making operation is carried out.

[0060] (7) Core sand core making process of built-in core of cylindrical cast iron part

[0061] The operation process is as follows:

[0062] S1, safety inspection and production preparation before core making according to the operation file requirements;

[0063] S2, installation and debugging of the core shooting mold and built-in cold iron on the core making equipment to ensure that the core shooting mold is accurately positioned, the mold is smoothly opened and the core is easily taken;

[0064] S3, the core shooting mold is heated by power supply, and after the core shooting mold is heated to 100-130℃, the mold cavity surface is sprayed with release agent (methyl silicone oil), the coating should be thin and uniform, and there should be no accumulation or omission, and then it is kept for 10-15min;

[0065] S4, continue to heat the core shooting mold, and when the temperature reaches the core shooting working temperature of 240±20℃ required by the process, keep it for 10-15min before starting the core shooting operation. The core shooting pressure is generally 0.35-0.50MPa, and the film-coated sand core is generally heated and solidified in the mold for 180±30s after the core shooting is completed;

[0066] S5, after the sand core is solidified, the mold is opened and the core is taken out, the sand core is placed in the exhaust cabinet for cooling, and the flash and burrs on the sand core are thoroughly cleaned;

[0067] S6, the appearance quality of the sand core is inspected, and if there is slight porosity, material deficiency or other phenomena, graphite paint can be used for repair. After the inspection is qualified, it is transferred to the molding process for subsequent casting production.

[0068] (8) Subsequent operation of cylindrical cast iron part blank production

[0069] In addition to the core making process, other casting production and quality inspection processes such as molding, melting, pouring, cooling and sand removal, cleaning and inspection are basically the same as other ordinary cast iron part blank casting production processes, and there is no obvious change or special requirement. Under normal circumstances, process control can be done according to the requirements of the process file or the operation instruction book.

[0070] Embodiment

[0071] A cylindrical cast iron part

[0072] The cylindrical cast iron piece takes the gray cast iron piece No. 1 coupling sleeve as an example, and the built-in core sand core process method includes the following contents:

[0073] (1) Preparation of raw materials, equipment and technical documents α

[0074] 1.1 Production of castings and technical requirements

[0075] The casting material of No. 1 coupling sleeve is HT250, which belongs to cylindrical thick-walled gray cast iron piece, the main wall thickness is about 32mm, the outer shape size of the casting blank is about Φ191x270mm, and the weight of the casting is about 33Kg. The mechanical property requirement of the casting is that the tensile strength is not less than 250Mpa, and the Brinell hardness requirement is 180-240HB. The casting is not allowed to have casting defects affecting the strength and appearance quality of the casting.

[0076] 1.2 Selection and preparation of furnace charge and equipment

[0077] The melting equipment for producing No. 1 coupling sleeve is selected as a 0.5t medium frequency electric furnace. The cast iron melting furnace charge includes: Wu'an Z14 pig iron is selected, scrap steel is selected as low-carbon steel scrap from a rolling mill, and various iron alloys are purchased according to international standards. According to the technical requirements for acceptance of castings and combined with the actual production, the above-mentioned various casting production processes are prepared, and various casting molds are made. Furan resin self-hardening sand is mixed by using a resin sand special sand mixer, and the sand core is manually modeled and shot by using a hot core box core shooter (the sand core is pre-placed with a shaped cold iron). The core shooting equipment is usually selected as a Suzhou Z8612B hot core box core shooter.

[0078] (2) Determine the machining allowance of No. 1 coupling sleeve cast iron piece blank and the size of the inner cavity

[0079] Referring to the national standard GB / T6414 casting size tolerance, geometric tolerance and machining allowance, combined with the shape and size of the casting, the material grade, the technical difficulty and other factors, and referring to the successful casting working experience in the past, it is determined that the machining allowance of No. 1 coupling sleeve in the inner cavity diameter direction is 3mm (single side), the machining allowance of the blank on the two end faces of the cylinder is 4mm (single side), and the machining allowance of the blank in the outer diameter direction of the casting is 4mm (single side).

[0080] (3) Determine the core making process method of No. 1 coupling sleeve cast iron piece blank

[0081] In order to ensure the quality of the casting and improve the production efficiency, the hot core box core shooting process method is adopted for the production of the cast iron piece blank of No. 1 coupling sleeve.

[0082] (4) Determine the material and size of the built-in cold iron of No. 1 coupling sleeve cast iron piece

[0083] The material of the built-in cold iron of No. 1 coupling sleeve cast iron piece is preferably 45# steel, and the size of the built-in cold iron is as follows:

[0084] The inner diameter of the opening section 1 is 91 mm, the height of the opening section 1 is 51 mm, the outer diameter of the opening section 1 and the intermediate section 2 is 107 mm, the height of the opening section 1 and the intermediate section 2 is 180 mm, the inner diameter of the intermediate section 2 and the closed section 3 is 84 mm, the outer diameter of the closed section 3 is 94 mm, the thickness of the upper end surface of the closed section 3 is 10 mm, and the shape of the vent hole 4 is also stepped, and the total height of the built-in chill is 286 mm.

[0085] (5) Determine the process parameters of the sand core covering process for the built-in iron core of the No. 1 coupling sleeve cast iron part

[0086] Table 2 Process parameters of the sand core covering process for the built-in iron core of the No. 1 coupling sleeve cast iron part

[0087]

[0088]

[0089] (6) Manufacture of the sand core mold and built-in chill for the No. 1 coupling sleeve cast iron part

[0090] According to the product design requirements and process technical requirements, the core shooting mold drawing of the cylindrical cast iron part is designed, and the mold is made; the built-in chill part drawing of the cylindrical cast iron part is designed, and the built-in chill is made; at the same time, the tooling mold such as casting mold, mold plate, pouring system module matched with the sand core is designed and manufactured.

[0091] After the above-mentioned mold and tooling are completed, the raw and auxiliary materials, production equipment and detection equipment required for casting production are prepared, appropriate operators are equipped and necessary technical safety training is carried out, so that the casting production of the cylindrical cast iron part blank can be carried out according to the standard file requirements, and the sand core covering process for the built-in iron core is carried out first.

[0092] (7) Process flow of sand core covering process for built-in iron core of No. 1 coupling sleeve cast iron part

[0093] The operation process is as follows:

[0094] S1, safety inspection and production preparation before sand core production according to the operation file requirements;

[0095] S2, installation and debugging of the core shooting mold and built-in chill on the sand core equipment, to ensure that the core shooting mold is accurately positioned, the mold is smoothly opened and the core is taken, and the operation is convenient;

[0096] S3, the core shooting mold is heated, and after the core shooting mold is heated to 100-130℃, the release agent (methyl silicone oil) is sprayed on the surface of the core cavity of the core shooting mold, the coating should be thin and uniform, and there should be no accumulation, dripping or omission, and then it is kept for 10-15 min;

[0097] S4, the core shooting mold continues to heat up, and when the temperature reaches the core shooting working temperature 240±20℃ required by the process, the core shooting operation is started after 10-15 min of heat preservation, the core shooting pressure is generally 0.35-0.50 MPa, and after the core shooting is completed, the film-coated sand core is heated and solidified in the core shooting mold for generally 180±30 s;

[0098] S5, after the sand core is solidified, the mold is opened and the core is taken out, the sand core is placed in the air exhaust cabinet for cooling and temperature reduction, and the flash and burrs on the sand core are thoroughly cleaned;

[0099] S6, the appearance quality of the sand core is inspected, if there is slight porosity, material shortage or the like, graphite paint can be used for repair, and after the inspection is qualified, the sand core is transferred to the molding process for subsequent casting production.

[0100] (8) Perform subsequent operations for No. 1 coupling sleeve cast iron blank production

[0101] After the core making process is completed, other subsequent casting production and quality inspection processes, such as molding, melting, pouring, cooling and sanding, cleaning, and inspection, are basically the same as other ordinary cast iron blank casting production processes, and there is no obvious change or special requirement. Under normal circumstances, process control is required according to the process documents or operation instruction book.

[0102] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for making a core by sand coating with an internal iron core of a cylindrical iron casting, characterized by: Cylindrical iron castings are produced using the coated sand hot core box core shooting process; the cores are shot using a hot core box core shooting machine; the built-in chiller is arranged inside the inner core of the sand mold; a layer of sand film is provided on the periphery of the built-in chiller; the built-in chiller is a hollow cylindrical sleeve structure with a closed upper end and an open lower end, and a ventilation hole is provided in the center of the upper end face; the built-in chiller has a stepped outer shape, with the upper outer diameter being smaller than the lower outer diameter.

2. The method for making a core with sand coating inside a cylindrical iron casting according to claim 1, characterized in that: The built-in chiller is made of 45# steel or A3 carbon steel.

3. The method for making a core with sand coating inside a cylindrical iron casting according to claim 1, characterized in that: The built-in cold iron comprises an opening section (1), a middle section (2) and a closed section (3) in order from bottom to top; a vent hole (4) is provided at the center of the upper end surface of the closed section (3); and the vent hole (4) is sealed with a hexagonal bolt during core shooting.

4. The method for making a core with sand coating inside a cylindrical iron casting according to claim 3, characterized in that: The inner diameter of the closed section (3) is the same as that of the middle section (2); the outer diameter of the closed section (3) is smaller than that of the middle section (2); and the angle α at which the outer diameter of the closed section (3) transitions to the outer diameter of the middle section (2) is 135°; the outer diameter of the opening section (1) is the same as that of the middle section (2); and the inner diameter of the opening section (1) is larger than the inner diameter of the middle section (2).

5. The method for making a core with sand coating inside a cylindrical iron casting according to claim 1, characterized in that: The operating procedures of the coated sand hot core box core shooting process are as follows: S1. Carry out safety inspection and production preparation before core production according to the requirements of the operation documents; S2. Install and debug the core shooting mold and built-in chiller on the core making equipment to ensure that the core shooting mold is accurately positioned, the mold opening and core removal are smooth, and the operation is convenient; S3. Power the core shooting mold for heating. After the core shooting mold is heated to the preheating temperature, spray a release agent on the surface of the core shooting mold cavity. The coating should be thin and even, and no accumulation or omission is allowed. Then keep the mold warm for a period of time. S4, the core shooting mold continues to heat up. When the temperature reaches the core shooting working temperature range required by the process, it is kept warm for a period of time before starting the core shooting operation. After the core shooting is completed, the coated sand core is heated and solidified in the core shooting mold; S5. After the sand core is cured, the mold is opened and the core is removed. The sand core is placed in a fume hood to cool down, and the flash and burrs on the sand core are thoroughly cleaned; S6. Check the appearance quality of the sand core. If there are minor defects, use graphite paint to repair them. After passing the inspection, transfer them to the molding process for subsequent casting production.

6. The method for making a core with sand coating inside a cylindrical iron casting according to claim 5, characterized in that: In S3, the core shooting mold is heated to a preheating temperature of 100-130°C.

7. The method for making a core with sand coating inside a cylindrical iron casting according to claim 5, characterized in that: In S3, the release agent is methyl silicone oil, and the insulation time of the release agent is 10-15 minutes.

8. The method for making a core with sand coating inside a cylindrical iron casting according to claim 5, characterized in that: In S4, the core shooting operating temperature range is 240±20℃, and the holding time is 10-15min. During the core shooting operation, the total pressure of the air supply pipeline of the air compressor station is ≥0.60Mpa, and the sand core shooting pressure is 0.35-0.50Mpa.

9. The method for making a core with sand coating inside a cylindrical iron casting according to claim 5, characterized in that: In S4, after the core shooting is completed, the coated sand core is heated and cured in the mold for 180±30s, and the thickness of the core coating sand layer is 5-10mm.

10. The method for making a core with sand coating inside a cylindrical iron casting according to claim 1, characterized in that: Before deciding to use the coated sand hot core box core shooting process to produce cylindrical iron castings, it is necessary to prepare raw materials, equipment and technical documents; determine the machining allowance and inner cavity size of the cylindrical iron casting blank; after completing the coated sand hot core box core shooting process, subsequent operations for casting blank production are required.

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