Semi-true centrifugal casting method for large barrel-shaped casting product

Abstract

The invention discloses a semi-true centrifugal casting method for a large barrel-shaped casting product, which comprises the following steps: designing an outer mold and a sand core, designing a positioning structure, manufacturing a casting channel in the middle of the sand core, manufacturing an expanded blind riser at the bottom of the casting channel, and manufacturing the sand core by using a water glass and carbon dioxide blowing hardening process. The method comprises the following steps: profiling the interior of a sand core to manufacture a net-shaped steel framework, designing an exhaust rope for casting, brushing paint on the surface of the sand core and in an outer mold, positioning and closing a box, centrifuging according to the process, casting, collecting flow and slowly pouring when the calculated process weight is observed, stopping until molten steel reaches a pouring cup, naturally cooling, and cleaning the sand core to obtain a complete casting. Compared with the prior art, suspension type design of the sand core is achieved, the overall structural strength of the sand core is high, the sand core has good air permeability, shrinkage porosity or shrinkage cavity of the bottom of a product in the centrifugal process is avoided through the blind riser, and integrated centrifugal casting forming of a bottom plate and a barrel body of a casting product is achieved.

Description

Technical Field

[0001] The invention relates to the stainless steel casting industry, in particular to a semi-true centrifugal casting method for a large barrel-shaped casting product. Background Art

[0002] The current centrifugal casting process can only be used to cast tubular casting products. Some barrel-shaped casting products with bottoms cannot be centrifugally cast because during the centrifugal rotation of the mold, the molten steel at the bottom will spread to the surroundings due to centrifugal force, causing shrinkage or shrinkage holes at the bottom of the product, which will directly lead to product scrapping.

[0003] Therefore, the current production of barrel-shaped casting products is to cast the barrel wall and the bottom plate separately, and then weld the bottom plate around the barrel wall to the bottom. Due to the thick casting, it is difficult to achieve the designed strength of the product through welding. Therefore, it is urgent to design a new casting method that can cast the barrel wall and the bottom plate of the barrel-shaped casting product as a whole to meet the product design requirements. Summary of the invention

[0004] The purpose of the present invention is to design a new semi-true centrifugal casting method for large barrel-shaped casting products which solves the above-mentioned problems.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: a semi-true centrifugal casting method for large barrel-shaped casting products, the method flow is as follows:

[0006] Step 1: Design an outer mold according to the product parts drawing; design a sand core according to the inner cavity size of the product parts drawing;

[0007] Step 2: Design a flange on the top of the sand core and a positioning step on the top of the outer mold;

[0008] Step 3: Make a through hole in the middle of the sand core as a casting channel, calculate the shrinkage requirements of the product bottom plate thickness, and make an enlarged blind riser at the bottom of the casting channel with a height of 200-350mm. Use the blind riser to feed the shrinkage of molten steel during the centrifugal process;

[0009] Step 4: the sand core is made by using a water glass + carbon dioxide blowing hardening process, and a mesh steel skeleton is made inside the sand core;

[0010] Step 5: Design an exhaust rope for casting on the steel support and some empty spaces inside the sand core, wherein the exhaust rope extends all the way to the surface of the sand core and passes through the cover plate;

[0011] Step 6: Apply alcohol-based paint on the surface of the prepared sand core. After the paint is dry, put the sand core into an oven and bake it at 180°C for 4 hours. Then, take it out of the oven and cool it. After the sand core cools to below 60°C, bake the metal outer mold until the inner cavity temperature reaches 220°C. Then, start applying water-based paint for centrifugal casting and ensure that it is completely dry.

[0012] Step 7: hoist the sand core onto the positioning step of the outer mold for positioning and closing, then fix the cover plate to the outer mold with pins, place a pouring brick at the center hole of the cover plate, and then fix it with water glass sand;

[0013] Step 8: Hoist the assembled and checked mold onto the centrifuge and install it. After running the machine without load and verifying that it is correct, adjust the speed to 50-300RPM according to the process and run it at full speed.

[0014] Step 9: After the quenched molten steel has reached the casting temperature, it is quickly cast. When the calculated process weight is observed, the flow is slowly reduced and poured until the molten steel reaches the pouring cup;

[0015] Step 10: The sand core is continuously operated on the centrifuge for 1-3 hours and then stopped. After natural cooling for 24 hours, the sand core is cleaned to obtain a complete casting.

[0016] Preferably, in step 2, the flange portion of the sand core has sufficient thickness, and the strength of the sand core is ≥1.5Mp.

[0017] Preferably, in step 2, a cover plate with many small holes is provided on the top of the sand core, the cover plate is fixed to the outer mold by pins, and the sand core to the flange is pressed tightly against the outer mold positioning step.

[0018] Preferably, in step 2, a center hole matching or slightly larger than the outer diameter of the lower end of the pouring brick is opened in the center of the cover plate.

[0019] Preferably, in step three, the method for calculating the size of the blind riser is based on a base plate with a thickness of 60 mm, wherein the diameter of the blind riser is 3.5 times the thickness of the base plate, and the height of the blind riser is 1.5-2 times the diameter of the blind riser.

[0020] Preferably, in step 4, the minimum distance between the skeleton and the outer wall of the sand core is not less than 40 mm, the grid distance is 250-300 mm, and the steel bar diameter is φ8-16 mm, so as to ensure that the sand core has good strength during centrifugal use and has a certain degree of yield after cooling.

[0021] Preferably, in step nine, the process weight is calculated based on the total amount of molten steel. When the molten steel is poured to the weight of the bottom of the blind riser, slow pouring must be performed to ensure good shrinkage compensation of the blind riser.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] 1. The present invention realizes the suspended design of the sand core by designing the installation structure of the sand core and the outer mold, and ensures that the sand core is always located at the center of the mold during the centrifugal rotation process.

[0024] 2. Through the structural design of the sand core, the overall structural strength of the sand core is improved, and it has good air permeability, so that it will not deform or crack during the centrifugal casting process.

[0025] 3. Through the design of the structure and size of the blind riser, the blind riser is used to continuously feed the shrinkage of molten steel during the centrifugal process to avoid shrinkage or shrinkage holes at the bottom of the product during the centrifugal process, thereby realizing the integrated centrifugal casting of the bottom plate and the barrel of the casting product. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a process flow chart of the present invention;

[0027] Figure 2 It is a structural schematic diagram of the mold of the present invention.

[0028] In the figure: 1. outer mold; 11. pin hole; 2. sand core; 21. mesh steel frame; 22. exhaust rope; 3. casting channel; 4. blind riser; 5. cover plate; 51. small hole; 6. product. DETAILED DESCRIPTION

[0029] The present invention will be further described below. The casting product to be processed has an upper diameter of about 1100mm, a lower diameter of about 1000mm, a height of 960mm, and a thickness of 60mm. It is large in size, heavy in weight, and thick in thickness. The connectivity between the barrel body and the bottom plate is very high. If the split type is used for separate processing, the connectivity between the bottom plate and the barrel body is poor. Even if welding is performed, the weld strength is difficult to meet the requirements. If it can be cast as one piece, the product performance requirements can be met. The conventional centrifugal casting method will inevitably cause the bottom plate to shrink or shrink during the centrifugal process. Therefore, there is no precedent in the art for centrifugal casting of large-volume, high-thickness barrel-shaped casting products.

[0030] Example: A semi-true centrifugal casting method for large barrel-shaped casting products, see Figure 1 , the method flow is as follows,

[0031] Step 1: Design an outer mold 1 according to the product part drawing. The design of the outer mold 1 must ensure that the outer dimensions of the part are shrunk after casting and meet the requirements of the part drawing for the outer dimensions after fine machining. Design a sand core 2 according to the inner cavity dimensions of the product part drawing. The design of the inner core must ensure that the inner dimensions and bottom of the part can be integrally formed with the cylindrical surface of the part, and meet the requirements of the part drawing for the bottom and inner cavity dimensions after shrinkage after casting and fine machining.

[0032] Step 2: Design a flange on the top of the sand core 2 and a positioning step on the top of the outer mold 1. The positioning step and the flange are used to ensure that the core head of the sand core 2 can be accurately positioned. When designing the sand core 2, it is necessary to ensure that the sand core 2 has sufficient strength to withstand the centrifugal force after being positioned and assembled and rotated. Therefore, the flange of the sand core 2 should have sufficient thickness.

[0033] A cover plate 5 with many small holes 51 is provided on the top of the sand core 2. The small holes 51 on the cover plate 5 are used for ventilation of the sand core 2 and for the exhaust rope 22 to pass through so that the inside of the sand core 2 can be exhausted to the outside. The cover plate 5 is fixed to the outer mold 1 by pins, and the flange of the sand core 2 is pressed tightly against the positioning step of the outer mold 1. The cover plate 5 allows the sand core 2 to rotate safely and stably under centrifugal force. A center hole matching or slightly larger than the outer diameter of the lower end of the pouring brick is opened in the center of the cover plate 5 to place the pouring brick.

[0034] Step three, the casting of molten steel must be considered when manufacturing the sand core 2. A through hole is made in the middle of the sand core 2 as a casting channel to meet the needs of casting molten steel. At the same time, considering that the molten steel still needs to be compensated for shrinkage in the end, the compensation requirements of the bottom plate thickness of the product 6 are calculated, and an enlarged blind riser 4 is made at the bottom of the casting channel in the range of 200-350mm. The blind riser 4 is used to compensate for the shrinkage of the molten steel during the centrifugal process to avoid shrinkage or shrinkage holes at the bottom of the product 6 during the centrifugal process; the range height of the blind riser 4 is between 200-350mm, which can better compensate for the shrinkage of the bottom molten steel.

[0035] The size design of the blind riser 4 is one of the technical difficulties of the present invention. Through many experiments and combined with empirical formulas, the size calculation method of the blind riser 4 is as follows: taking the base plate with a thickness of 60 mm as the benchmark, the diameter of the blind riser 4 is 3.5 times the thickness of the base plate, and the height of the blind riser 4 is 1.5-2 times the diameter of the blind riser 4, which is specifically determined according to the diameter of the base plate. If the diameter of the base plate is greater than 1000 mm, the diameter of the blind riser 4 is increased, and if the diameter of the base plate is less than 1000 mm, the diameter of the blind riser 4 is reduced.

[0036] Step 4, the sand core 2 needs to rotate with the outer membrane, and the sand core 2 is suspended, so that the sand core 2 is not loose during the centrifugation process. The strength requirement of the sand core 2 is particularly important. For the design of the strength of the sand core 2, the sand core 2 described in the present invention is made using a water glass + carbon dioxide air blowing hardening process. In the existing air blowing hardening process, when the insertion depth of the air-blowing steel bar is 100mm, the sand core 2 has a certain strength and the blowing can be stopped to complete the curing. However, due to the high strength requirement of the present invention, the air-blowing steel bar needs to be inserted about 200mm until it is difficult to press down, proving that the strength of the sand core 2 meets the requirements. At this time, the blowing is stopped to complete the curing, and a mesh steel skeleton 21 is made inside the sand core 2 in the shape of a steel skeleton imitating the sand core 2 structure design, and is a mesh structure for enhancing the strength of the sand core 2. The grid distance of the steel skeleton is 250-300mm, and the steel bar diameter is φ8-16mm, so as to ensure that the sand core 2 has good strength during centrifugal use. The minimum distance between the skeleton and the outer wall of the sand core 2 is not less than 40mm, so that it has a certain degree of concession after cooling. By comparing the test blocks and performing strength comparison, it is found that the strength of the sand core 2 of the present invention needs to be ≥1.5Mp to meet the requirements of this process.

[0037] Step 5: During the working process, the sand core 2 will be heated by the high-temperature molten steel, and a large amount of gas will be discharged. Therefore, the exhaust problem of the sand core 2 needs to be considered. In terms of design, a casting exhaust rope 22 is designed in the steel support and some vacancies inside the sand core 2. The exhaust rope 22 is connected to the surface of the sand core 2 and passes through the cover plate 5, so that during the casting process, the gas can be quickly discharged from the sand core 2 to avoid the sand core 2 from bursting.

[0038] Step 6: Apply alcohol-based paint on the surface of the prepared sand core 2 with a thickness of 1.5-2mm to ensure smooth demoulding. After the paint is dry, put the sand core 2 into an oven and bake it at 180°C for 4 hours, then take it out of the oven for cooling. The cooling treatment of the sand core 2 is mainly beneficial to subsequent operations. If the sand core 2 has not cooled down, the mold temperature has reached a high temperature, which will cause the personnel to be unable to operate. Therefore, after the sand core 2 is cooled to below 60°C, the metal outer mold 1 is baked to make the inner cavity temperature uniformly reach 220°C, and then start to apply the water-based paint for special centrifugal casting and ensure complete drying;

[0039] Step 7: Use a crane to hoist the sand core 2 to the sand core 2 positioning step of the outer mold 1, position it, close the box, and then fix the cover plate 5 on the outer mold 1 with pins, and place a pouring brick at the center hole of the cover plate 5 and fix it with water glass sand;

[0040] Step 8: Hoist the assembled and checked mold onto the centrifuge and install it. After running the machine without load and verifying that it is correct, adjust the speed to 50-300RPM according to the process and run it at full speed.

[0041] Step 9: After the quenched molten steel has reached the casting temperature, it is quickly cast. When the calculated process weight is observed, the flow is slowly reduced and poured until the molten steel reaches the pouring cup;

[0042] In order to make the blind riser 4 well compensated during the casting process, the casting process is very important. The process weight needs to be calculated. The process weight is calculated based on the total amount of molten steel. When the weight of the molten steel cast to the bottom of the blind riser 4 is observed, slow pouring must be performed to ensure good compensation of the blind riser 4.

[0043] Step 10: The cooling capacity of the sand core 2 is weak. Depending on the structure of the product 6, the centrifuge is operated continuously for 1-3 hours and then stopped. The mold is unlocked and hoisted to the sand pit. After natural cooling for 24 hours, the box is opened and the workpiece with the sand core 2 is taken out. The sand is shaken out by a sand shaker, and the sand core 2 is cleaned to obtain a complete casting.

[0044] A semi-true centrifugal casting mold for a large barrel-shaped casting product 6, see Figure 2 , including an outer mold 1 and a sand core 2, wherein the lower end of the sand core 2 is suspended in the outer mold 1, and the upper end of the sand core 2 is fixedly connected to the upper end of the outer mold 1. A blind riser 4 is processed at the bottom of the sand core 2, and a casting channel 3 is opened at the center of the sand core 2, and the casting channel 3 is connected to the top of the blind riser 4. A mesh steel skeleton 21 for supporting is provided in the sand core 2, and a casting exhaust rope 22 is provided inside the sand core 2, and the exhaust rope 22 extends all the way to the upper surface of the sand core 2. A flange structure is provided at the upper end of the sand core 2, and a positioning step matching the diameter of the flange structure is provided at the upper end of the outer mold 1, and the upper end of the sand core 2 is positioned at the center of the outer mold 1 through the positioning step. It also includes a cover plate 5, which is arranged above the sand core 2, and pin holes 11 are provided around the outer mold 1, and the cover plate 5 is fixed in the outer mold 1 through pins matching the pin holes 11. The cover plate 5 is provided with a plurality of small holes 51 for pulling out the exhaust rope 22 , and a central hole for installing the casting brick is provided at the center.

[0045] The cover plate 5, the outer mold 1 and the sand core 2 are designed according to the shape of the product 6. The inner cavity formed between the outer mold 1 and the sand core 2 is the molten steel casting channel 3 of the product 6. After centrifugal forming, rough processing and fine processing are performed to obtain the product 6. The barrel body and the bottom plate of the product 6 are formed in one piece, which is convenient and quick. The sealing, safety and structural stability between the bottom plate and the whole body are much higher than those of the welding process. Moreover, the product 6 obtained by this process method has no shrinkage or shrinkage holes, and its thickness after fine processing can fully meet the thickness requirements of the product 6.

[0046] The above is a detailed introduction to the semi-true centrifugal casting method for a large barrel-shaped casting product provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope, and changes and improvements to the present invention will be possible without exceeding the concept and scope specified in the attached claims. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A semi-true centrifugal casting method for large barrel-shaped casting products, characterized in that: The method flow is as follows: Step 1: Design an outer mold according to the product parts drawing; design a sand core according to the inner cavity size of the product parts drawing; Step 2: Design a flange on the top of the sand core and a positioning step on the top of the outer mold; Step 3: Make a through hole in the middle of the sand core as a casting channel, calculate the shrinkage requirements of the product bottom plate thickness, and make an enlarged blind riser at the bottom of the casting channel with a height of 200-350mm. Use the blind riser to feed the shrinkage of molten steel during the centrifugal process; Step 4: the sand core is made by using a water glass + carbon dioxide blowing hardening process, and a mesh steel skeleton is made inside the sand core; Step 5: Design an exhaust rope for casting on the steel support and some empty spaces inside the sand core, wherein the exhaust rope extends all the way to the surface of the sand core and passes through the cover plate; Step 6: Apply alcohol-based paint on the surface of the prepared sand core. After the paint is dry, put the sand core into an oven and bake it at 180°C for 4 hours. Then, take it out of the oven and cool it. After the sand core cools to below 60°C, bake the metal outer mold until the inner cavity temperature reaches 220°C. Then, start applying water-based paint for centrifugal casting and ensure that it is completely dry. Step 7: hoist the sand core onto the positioning step of the outer mold for positioning and closing, then fix the cover plate to the outer mold with pins, place a pouring brick at the center hole of the cover plate, and then fix it with water glass sand; Step 8: Hoist the assembled and checked mold onto the centrifuge and install it. After running the machine without load and verifying that it is correct, adjust the speed to 50-300RPM according to the process and run it at full speed. Step 9: After the quenched molten steel has reached the casting temperature, it is quickly cast. When the calculated process weight is observed, the flow is slowly reduced and poured until the molten steel reaches the pouring cup; Step 10: The sand core is continuously operated on the centrifuge for 1-3 hours and then stopped. After natural cooling for 24 hours, the sand core is cleaned to obtain a complete casting.

2. A semi-true centrifugal casting method for a large barrel-shaped casting product according to claim 1, characterized in that: In step 2, the flange portion of the sand core has sufficient thickness, and the strength of the sand core is ≥1.5Mp.

3. The semi-true centrifugal casting method for a large barrel-shaped casting product according to claim 1, characterized in that: In step 2, a cover plate with many small holes is provided on the top of the sand core, and the cover plate is fixed to the outer mold by pins, and the sand core to the flange is pressed tightly against the outer mold positioning step.

4. A semi-true centrifugal casting method for a large barrel-shaped casting product according to claim 3, characterized in that: In step 2, a center hole matching the outer diameter of the lower end of the pouring brick is opened in the center of the cover plate.

5. The semi-true centrifugal casting method for a large barrel-shaped casting product according to claim 1, characterized in that: In step three, the method for calculating the size of the blind riser is based on a base plate with a thickness of 60 mm. The diameter of the blind riser is 3.5 times the thickness of the base plate, and the height of the blind riser is 1.5-2 times the diameter of the blind riser.

6. A semi-true centrifugal casting method for a large barrel-shaped casting product according to claim 1, characterized in that: In step 4, the minimum distance between the skeleton and the outer wall of the sand core is not less than 40 mm, the grid distance is 250-300 mm, and the steel bar diameter is φ8-16 mm.

7. A semi-true centrifugal casting method for a large barrel-shaped casting product according to claim 1, characterized in that: In step nine, the process weight is calculated based on the total amount of molten steel, and slow pouring is performed when the molten steel reaches the weight of the bottom of the blind riser.

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