Casting method of conveying connecting pipe

Abstract

The invention relates to a casting method of a conveying connecting pipe. The conveying connecting pipe comprises the following components in percentage by weight: 3.2 to 3.4 percent of carbon, 1.8 to 2.2 percent of silicon, 0.5 to 0.7 percent of manganese, 0.15 to 0.2 percent of copper, 0.2 to 0.3 percent of nickel, 0.8 to 1.0 percent of chromium, 0.03 to 0.07 percent of magnesium (residual), 0.001 to 0.008 percent of nitrogen, less than or equal to 0.02 percent of phosphorus and less than or equal to 0.02 percent of sulfur. 0.02 to 0.08% of silicon carbide particles; and the balance of iron. The casting step comprises the processes of modeling, smelting, inoculation, spheroidizing, pouring, cleaning, heat treatment and the like, martensite is formed on a matrix, the matrix structure is high in strength and hardness, the matrix contains hard spots such as ferrochrome carbide, silicon carbide particles are embedded in the surface of the inner wall of the conveying connecting pipe, the abrasion resistance of the inner wall is further improved, and the service life of the conveying connecting pipe is prolonged. Therefore, the service life of the conveying connecting pipe is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of casting, and in particular relates to a casting method for a conveying connecting pipe. Background Art

[0002] Pipeline transportation is a common transportation method. In addition to transporting liquids and gases, it is also used for the transportation of solid-liquid mixtures such as crude oil and silt, or pneumatic transportation of powders. Pipeline transportation mainly includes equipment such as delivery pumps and delivery pipelines. In production, some transportation requires pressurization, that is, a delivery connecting pipe is set between the delivery pipelines, and the delivery connecting pipe is connected to the booster pump. The booster pump injects pressure into the delivery pipeline through the delivery connecting pipe to extend the delivery distance. Common delivery connecting pipes include connecting pipes, casings, and annular plugs; one end of the connecting pipe is used to connect to the delivery pipeline, and the other end is inserted into the casing. The annular plug is set on the connecting pipe to block one end of the casing; an input pipe or connecting hole for connecting to the booster pump is set on the annular plug, and the connecting hole can be obtained by machining later; the other end of the casing is reduced in diameter for connection with the delivery pipeline.

[0003] The common manufacturing methods for conveying connecting pipes are welding or integral casting; the welds of welded conveying connecting pipes are prone to cracking and have a short service life; the integral cast iron conveying connecting pipe is ductile iron, which has low strength, poor wear resistance and a short service life. Summary of the invention

[0004] In order to improve the service life of the conveying connecting pipe, the manufacturing method of the integrally cast conveying connecting pipe is improved to increase the strength and wear resistance; the present invention provides a casting method for the conveying connecting pipe; in order to achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for casting a conveying connecting pipe, characterized in that the composition of the conveying connecting pipe (by weight percentage) includes 3.2-3.4% carbon, 1.8-2.2% silicon, 0.5-0.7% manganese, 0.15-0.2% copper, 0.2-0.3% nickel, 0.8-1.0% chromium, 0.03-0.07% magnesium (residual), 0.001-0.008% nitrogen, ≤0.02% phosphorus, ≤0.02% sulfur; 0.02-0.08% silicon carbide particles; the rest is iron; the casting of the conveying connecting pipe comprises the following steps: Modeling: Rationally design the pouring system of the conveying connecting pipe, use resin sand to make the cavity and sand core; the cavity and sand core enclose the chamber and pouring system of the conveying connecting pipe, paint is applied on the inner surface of the cavity and the outer surface of the sand core, a cooling water pipe is buried in the sand core, and water is passed into the cooling water pipe after the molten iron is filled, so as to adjust the solidification order of the molten iron; the silicon carbide particles are diluted with the paint and then applied to the surface of the paint layer on the outer surface of the sand core; Melting: In the smelting furnace, pig iron, scrap steel, ferrosilicon, ferromanganese, ferrochrome, copper and nickel are added in proportion and the composition is adjusted to control the composition of molten iron to 3.2-3.4% carbon, 0.9-1.2% silicon, 0.5-0.7% manganese, 0.15-0.2% copper, 0.2-0.3% nickel, 0.8-0.9% chromium, ≤0.02% phosphorus, ≤0.02% sulfur; the rest is iron. After the composition of molten iron is qualified, the furnace temperature is controlled at 1400-1430℃; Inoculation and spheroidization treatment: a dam is set at the bottom of the ladle to separate it into a first area and a second area, rare earth magnesium-iron alloy particles are laid at the bottom of the first area, ferrosilicon alloy particles are covered on the surface of the rare earth magnesium-iron alloy particles, and iron filings are covered on the surface of the ferrosilicon alloy particles, and they are compacted and compacted; the amount of the rare earth magnesium-iron alloy particles added (percentage in molten iron) is 0.6-0.8%; the amount of the ferrosilicon alloy particles added (percentage in molten iron) is 1.2-1.4%; before the molten iron is taken out of the furnace and poured into the ladle, the molten iron rushes to the second area of ​​the ladle; Pouring and cleaning: When pouring the molten iron in the ladle into the mold cavity, add ferrochromium nitride particles along with the flow, the amount of ferrochromium nitride particles added is 0.1-0.2%, the nitrogen content of ferrochromium nitride is controlled at 0.3-0.5%, and the particle size of the ferrochromium nitride particles is 200-100 meshes; before pouring the molten iron, connect the cooling water pipe to the water source to let water flow, and the molten iron solidifies and forms. Before unpacking, close the cooling water pipe and disconnect it; after unpacking, cut off the pouring system of the conveying connecting pipe and grind it; Heat treatment: including quenching and tempering processes; Quenching process: heat the conveying connecting pipe to 880~900℃, keep warm for 1~3h; quench in hot water, the hot water temperature is ≥80℃; Tempering process: heat the conveying connecting pipe to 145~155℃, keep it warm for 4~6h, cool it to below 80℃ with the furnace, and take it out of the furnace.

[0005] The beneficial effects of the casting method of the conveying connecting pipe of the present invention are as follows: the composition and heat treatment of the conveying connecting pipe are reasonably designed to form ductile iron containing a small amount of carbide, which has high strength and wear resistance; The ratio of copper to nickel is designed to be between 1:1 and 1:2. During the solidification of molten iron, it is beneficial to the graphitization of carbon and improves and refines the matrix structure of the cast conveying connecting pipe. The total content is controlled below 0.5%. Copper and nickel are precious metals, which is beneficial to cost control. The chromium content is controlled at 0.8-1.0%. Chromium and carbon form chromium-iron carbides, forming hard points in the conveying connecting pipe, which is beneficial to provide hardness and wear resistance. At the same time, it provides condensation nuclei during the solidification of molten iron, which is beneficial to the refinement of the cast structure and the improvement of hardenability during heat treatment. Nitrogen and part of chromium are added in the form of ferrochromium nitride particles during the pouring process. The added ferrochromium nitride dissolves in the molten iron, which is conducive to the uniform distribution of nitrogen in the molten iron. Nitrogen is between 0.001 and 0.008%, to prevent excessive addition. During the solidification of the molten iron, nitrogen precipitates and forms pores; or too little addition will not play a role in expanding the austenite range; the addition of nitrogen is conducive to improving the stability of the residual austenite and the stability of the conveying connecting pipe after heat treatment. Adding 0.02 to 0.08% of silicon carbide particles to form hard points in the conveying connecting pipe is conducive to improving the wear resistance of the conveying connecting pipe.

[0006] A cooling water pipe is buried in the sand core. The cooling water pipe adjusts the solidification sequence of the molten iron so that the conveying connecting pipe can solidify in sequence. During the solidification process, the shrinkage caused by the liquid-solid transition is supplemented by the molten iron, thereby reducing the generation of shrinkage cavities or shrinkage. Silicon carbide particles are mixed with the coating and applied to the surface of the coating layer. The bonding strength between the silicon carbide particles and the coating is low. During the filling or solidification process, the silicon carbide particles are embedded in the inner wall surface of the conveying connecting pipe to provide wear resistance for the inner wall. Adding in this way is conducive to adhesion to the inner wall surface and reducing the dosage.

[0007] The inoculant is ferrosilicon and the spheroidizer is ferromagnesium alloy, and 1.2-1.4% and 0.6-0.8% are added respectively by the flushing method, which is beneficial to improving the graphitization level and spheroidization level during the solidification of molten iron. Through multiple tests and verifications, the nitrogen is added in the form of chromium nitride iron particles with a nitrogen content of 0.3-0.5% and a particle size of 200-100 meshes. The added chromium nitride iron is dissolved in the molten iron, which is beneficial to the uniform distribution of nitrogen in the molten iron. The nitrogen content is between 0.001-0.008%, which prevents excessive addition. During the solidification of molten iron, nitrogen elements precipitate to form pores; it replaces traditional nitrogen blowing and other methods of addition.

[0008] (4) Comparison of multiple test groups shows that controlling the quenching temperature at 880-900°C and holding time at 1-3h is conducive to the heat penetration of the transport connecting pipe, so that the matrix structure is completely transformed into austenite and the excessive growth of austenite is prevented. The quenching water temperature is controlled at ≥80°C. Under the premise of ensuring thorough quenching, it prevents the temperature from dropping too fast, which may cause microcracks in the transport connecting pipe. After quenching, the matrix structure of the transport connecting pipe is martensite.

[0009] Furthermore, the silicon carbide particles are nano-scale particles, and the particle size of the silicon carbide particles is ≤0.05 μm. After the silicon carbide particles are evenly mixed with the coating in a (weight ratio) of 1:1-3, they are evenly mixed with anhydrous alcohol in a (weight ratio) of 1:100-300, and then sprayed on the surface of the coating layer of the sand core.

[0010] Beneficial effects: After spraying on the surface of the coating layer of the sand core, the anhydrous alcohol evaporates and the silicon carbide particles adhere to the surface of the coating. During the molten iron filling process, since the particle size of the silicon carbide particles is controlled below 0.05μm, they are easy to diffuse or flush into the molten iron, providing condensation nuclei for the solidification of the molten iron, which is beneficial to the refinement of the grains. The inner surface of the conveying connecting pipe is inlaid with silicon carbide hard points, which is beneficial to improve the wear resistance of the inner surface of the conveying connecting pipe.

[0011] Furthermore, during the process of spraying the mixture of silicon carbide particles, coating and anhydrous alcohol on the coating layer surface of the sand core, the spraying pressure is 0.4~0.5MPa; the spraying direction is perpendicular to the coating surface of the sand core, and the distance between the nozzle and the coating surface of the sand core is controlled at 200mm~300mm.

[0012] Beneficial effects: The spraying pressure is controlled at 0.4~0.5MPa, the spraying direction is perpendicular to the coating surface of the sand core, and the distance is controlled at 200mm~300mm; while reducing the rebound of the mixture during the spraying process, it prevents the impact force of the mixture on the surface of the coating layer from being too low, thereby reducing the adhesion effect; it is conducive to the uniform adhesion of silicon carbide particles to the surface of the coating layer.

[0013] Furthermore, the cooling water pipe includes an inlet pipe, an outlet pipe and several branch pipes; along the axial direction of the sand core, the inlet pipe, the branch pipe and the outlet pipe are arranged in sequence, and the two ends of the branch pipe are respectively connected to the inlet pipe and the outlet pipe, and the several branch pipes are evenly spaced along the circumference of the sand core.

[0014] Beneficial effects: The cooling water pipe is arranged as an inlet pipe, an outlet pipe and several branch pipes; after the molten iron is filled into the mold, cooling water is introduced from the inlet pipe. The cooling water carries heat to adjust the solidification sequence of the conveying and connecting pipes, thereby realizing sequential solidification, which is beneficial to improving the density of the conveying and connecting pipe tissue; at the same time, the cooling water pipe forms a skeleton structure in the sand core, thereby reducing the breakage of the sand core during manufacturing, transportation or use.

[0015] Furthermore, the branch water pipe extends along the dragon profile of the sand core, and the diameter of the water pipe is 20-40 mm; the distance between the branch water pipe and the surface of the sand core is controlled to be 3-20 mm; and the circumferential angle between two adjacent branch water pipes is 25°-35°.

[0016] Beneficial effect: After many verifications, the water pipe diameter is selected to be 20~40mm; the distance between the water pipe and the sand core surface is controlled at 3~20mm. Under the premise that the cooling water in the water pipe carries heat to meet the requirements, the 3~20mm sand core layer blocks the direct contact between the molten iron and the water pipe, preventing the water pipe from being scalded. Direct contact between the molten iron and the cooling water poses a safety hazard.

[0017] Furthermore, during the sand core molding process, a chamber enclosed by the cooling water pipe is filled with light breathable materials such as straw rope, cotton wool or foam, and the light breathable material protrudes from the sand core near one end of the water inlet pipe.

[0018] Beneficial effects: Lightweight and breathable materials such as straw rope, cotton wool or foam can reduce the weight of the sand core, making it easier to transport and reducing the use of sand. During the process of filling the mold with molten iron, some of the lightweight and breathable materials are carbonized to form gaps, which can drain the gas in the cavity and the gas generated by the sand core, reducing the occurrence of casting defects such as choking and pores.

[0019] Furthermore, an exhaust hole is opened at the upper part of the groove of the sand core, and the diameter of the exhaust hole is ≤2mm; one end of the exhaust hole is in contact with and communicated with the lightweight breathable material.

[0020] Beneficial effect: The sand core generates gas after being heated. By setting the exhaust hole, the gas generated by the sand core can be further drained, thereby preventing or reducing the gas from penetrating into the molten iron and reducing the formation of pores in the conveying connecting pipe casting.

[0021] Furthermore, during the quenching process, the heating rate is controlled at 5-10°C / min; the temperatures are kept at 450°C and 700°C for 10-15 minutes respectively; and the time for the transport connecting pipe to fall from the heating furnace into the hot water is ≤20S.

[0022] Beneficial effects: Setting up stepped heating is conducive to burning through of the conveying connecting pipe, preventing thermal stress caused by excessive temperature difference between the inside and outside, and is conducive to hardening; the time between falling from the heating furnace into hot water is ≤20S, preventing the temperature from dropping too much during exposure to the air, which is not conducive to hardening and reduces the heat treatment effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the metallographic image of the uncorroded cast state during the trial production of the transport connecting pipe (magnified 100 times); Figure 2 This is the matrix structure diagram of the trial production process of the conveying connecting pipe after heat treatment (magnified 500 times). DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments: The embodiment of the casting method of the conveying connecting pipe of the present invention is as follows: 1. Composition control: The final composition of the conveying connecting pipe (by weight percentage) is controlled to be 3.2~3.4% carbon, 1.8~2.2% silicon, 0.5~0.7% manganese, 0.15~0.2% copper, 0.2~0.3% nickel, 0.8~1.0% chromium, 0.03~0.07% magnesium (residual), 0.001~0.008% nitrogen, ≤0.02% phosphorus, ≤0.02% sulfur; 0.02~0.08% silicon carbide particles; the rest is iron. During the trial process, the influence of composition segregation on composition detection during the solidification of molten iron was considered; the molten iron in the ladle before pouring was sampled and tested; considering the decline of inoculation and spheroidization, there is no need to wait for the results, and the sample was directly poured and molded. The specific composition of this trial is 3.34% carbon, 2.03% silicon, 0.57% manganese, 0.18% copper, 0.22% nickel, 0.82% chromium, 0.04% magnesium (residual), 0.005% phosphorus, and 0.006% sulfur.

[0025] 2. Casting process of conveying connecting pipe: a. Modeling: The size shrinks by 1% according to the line. The pouring system of the conveying connecting pipe is reasonably designed. The cavity and sand core are made of resin sand. The cavity and sand core enclose the chamber and pouring system of the conveying connecting pipe. The inner surface of the cavity and the outer surface of the sand core are painted. A cooling water pipe is buried in the sand core. After the molten iron is filled, water is passed into the cooling water pipe to adjust the solidification order of the molten iron.

[0026] After diluting the silicon carbide particles and the coating, brush them on the surface of the coating layer on the outer surface of the sand core. In this embodiment, the silicon carbide particles are nano-sized particles, and the particle size of the silicon carbide particles is ≤0.05μm. After the silicon carbide particles and the coating are evenly mixed in a (weight ratio) of 1:2, they are evenly mixed with anhydrous alcohol in a (weight ratio) of 1:200, and then sprayed on the surface of the coating layer of the sand core. After spraying on the surface of the coating layer of the sand core, the anhydrous alcohol evaporates, and the silicon carbide particles adhere to the surface of the coating. During the molten iron filling process, since the particle size of the silicon carbide particles is controlled below 0.05μm, it is easy to diffuse or flush into the molten iron, providing condensation nuclei for the solidification of the molten iron, which is beneficial to the refinement of the grains. The inner surface of the conveying connecting pipe is inlaid with silicon carbide hard points, which is beneficial to improve the wear resistance of the inner surface of the conveying connecting pipe. In other embodiments, under the premise that the adhesion of silicon carbide to the coating surface after spraying meets the requirements, the ratio of silicon carbide particles to the coating (by weight) can be 1:1 or 1:3 instead of 1:2; after uniform mixing, the ratio with anhydrous alcohol can be 1:100 or 1:300 instead of 1:200.

[0027] During the process of spraying the mixture of silicon carbide particles, coating and anhydrous alcohol on the coating layer surface of the sand core, the spraying pressure is 0.4~0.5MPa; the spraying direction is perpendicular to the coating surface of the sand core, and the distance between the nozzle and the coating surface of the sand core is controlled at 200mm~300mm. In this embodiment, the spraying pressure is 0.47 MPa; the distance between the nozzle and the coating surface of the sand core is 260mm; in the actual spraying process, the spraying distance fluctuates according to the shape of the conveying connecting pipe, and the overall control is between 200mm~300mm. Reasonable setting of the spraying pressure, spraying direction and spraying distance can reduce the rebound of the mixture during the spraying process, prevent the impact force of the mixture on the coating layer surface from being too low, and reduce the adhesion effect; it is conducive to the uniform adhesion of silicon carbide particles on the coating layer surface.

[0028] The cooling water pipe includes an inlet pipe, an outlet pipe and several branch pipes; along the axial direction of the sand core, the inlet pipe, the branch pipe and the outlet pipe are arranged in sequence, and the two ends of the branch pipe are connected to the inlet pipe and the outlet pipe respectively, and the branch pipes are evenly spaced along the circumference of the sand core. The cooling water pipe is configured as an inlet pipe, an outlet pipe and several branch pipes; after the molten iron is filled, the inlet pipe is passed with cooling water, and the cooling water carries heat to adjust the solidification sequence of the transport connecting pipe, realize sequential solidification, and is conducive to improving the density of the transport connecting pipe organization; at the same time, the cooling water pipe forms a skeleton structure in the sand core to reduce the breakage of the sand core during manufacturing, transportation or use.

[0029] The branch water pipe extends along the dragon outline of the sand core, and the diameter of the water pipe is 20~40mm; the distance between the branch water pipe and the surface of the sand core is controlled at 3~20mm; the circumferential angle between two adjacent branch water pipes is 25°~35°. Under the premise that the cooling water in the water pipe meets the requirements with heat, the 3~20mm sand core layer blocks the direct contact between the molten iron and the water pipe to prevent the water pipe from being scalded. The direct contact between the molten iron and the cooling water poses a safety hazard. In this embodiment, the diameter of the water pipe is specifically 30mm, and the distance between the branch water pipe and the surface of the sand core is controlled at 10mm.

[0030] During the sand core molding process, the chamber enclosed by the cooling water pipe is filled with light breathable materials such as straw rope, cotton wool or foam, and the light breathable material protrudes from the sand core near one end of the water inlet pipe. During the molten iron filling process, part of the light breathable material is carbonized to form a gap, which has the function of draining the gas in the cavity and the gas generated by the sand core, reducing the occurrence of casting defects such as choking and pores. An exhaust hole is opened in the upper part of the groove of the sand core, and the diameter of the exhaust hole is ≤2mm; one end of the exhaust hole is in contact with and connected to the light breathable material. The sand core generates gas after being heated. By setting the exhaust hole, the gas generated by the sand core is further drained, preventing or reducing the gas from penetrating into the molten iron, and reducing the formation of pores in the conveying connecting pipe casting. In this embodiment, the diameter of the exhaust hole is set at 1mm.

[0031] b. Melting: Use an induction furnace to melt molten iron. First, add pig iron and scrap steel into the induction furnace for melting. According to a certain proportion, add alloys such as ferrosilicon, ferromanganese, ferrochrome, copper, and nickel into the induction furnace, and sample and analyze the molten iron in front of the furnace; control the composition of the molten iron to 3.2~3.4% carbon, 0.9~1.2% silicon, 0.5~0.7% manganese, 0.15~0.2% copper, 0.2~0.3% nickel, 0.8~0.9% chromium, phosphorus ≤0.02%, sulfur ≤0.02%; the rest is iron. In this embodiment, the composition of the molten iron is specifically 3.35% carbon, 1.02% silicon, 0.59% manganese, 0.19% copper, 0.223% nickel, 0.83% chromium, 0.005% phosphorus, 0.006% sulfur, and the rest is iron; considering the spectral analysis error and the later spheroidization and inoculation treatment, the molten iron can be controlled within the required range. After the molten iron composition is qualified, the furnace temperature is controlled at 1400~1430℃; during this trial process, the furnace temperature is 1415℃.

[0032] c. Inoculation and spheroidization treatment: A ladle with a dam at the inner bottom is selected, and the dam divides the inner bottom into a first area and a second area. During the molten iron smelting time, rare earth magnesium-iron alloy particles are laid at the bottom of the first area, and the amount of rare earth magnesium-iron alloy particles added (as a percentage of the molten iron discharged from the furnace) is 0.6-0.8%; the magnesium content of the selected rare earth magnesium-iron alloy particles is 10%-20%. After adding, the particles are leveled and compacted. The surface of the rare earth magnesium-iron alloy particles is covered with ferrosilicon alloy particles, and the amount of ferrosilicon alloy particles added (as a percentage of the molten iron discharged from the furnace) is 1.2-1.4%; the selected ferrosilicon is 75% ferrosilicon as an inoculant. The surface of the ferrosilicon alloy particles is covered with iron filings, and they are compacted again. In this embodiment, the amount of rare earth magnesium-iron alloy particles added is 0.65%, and the inoculant 75 ferrosilicon is 1.3%. Before the molten iron is poured into the ladle, adjust the position of the ladle so that the molten iron flowing out of the smelting furnace rushes to the second area of ​​the ladle; after the molten iron flows into the ladle, it quickly covers the inoculant and spheroidizer to prevent the molten iron from directly scouring the inoculant (75 ferrosilicon) and spheroidizer (rare earth magnesium-iron alloy particles) and reducing the effect of inoculation and spheroidizing treatment.

[0033] d. Pouring and cleaning: After the molten iron is spheroidized and inoculated in the ladle, the ladle is transferred to the pouring area. When the molten iron in the ladle is poured into the mold cavity, ferrochromium nitride particles are added along with the flow, and the amount of ferrochromium nitride particles added is 0.1~0.2%, and the nitrogen content of ferrochromium nitride is controlled at 0.3~0.5%. The particle size of the ferrochromium nitride particles is 200 mesh~100 mesh. Before pouring molten iron into the mold cavity, connect the cooling water pipe to the water source and let water flow. When the molten iron solidifies in the mold cavity, the cooling water pipe takes away part of the heat, adjusts the solidification order of the molten iron, and realizes the sequential solidification of the conveying connecting pipe. During the solidification process, the shrinkage of the liquid-solid transition is supplemented by the molten iron, reducing the generation of shrinkage cavities or shrinkage. After the molten iron solidifies, wait for 15 minutes to half an hour, turn off the cooling water pipe and disconnect it. After the conveying connecting pipe casting is cooled with the box to below 300℃, open the box for cleaning, remove the sand blocks on the surface or inside of the casting, cut off the pouring system of the conveying connecting pipe, and grind the flash or burrs.

[0034] e. Heat treatment: including quenching and tempering process; Quenching process: heat the conveying connecting pipe to 880~900℃, keep warm for 1~3h; quench into hot water, the hot water temperature is ≥80℃. In this embodiment, the quenching process adopts step-by-step heating, and the heating rate is controlled at 5~10℃ / min; keep warm for 10~15min when heated to 450℃ and 700℃ respectively; setting up step-by-step heating is conducive to burning through the conveying connecting pipe, preventing the excessive temperature difference between the inside and outside from forming thermal stress, and is conducive to quenching. During the trial process, the heating rate was set to 7℃ / min; keep warm for 15min when heated to 450℃ and 700℃ respectively; finally heated to 890℃, keep warm for 2.5h; the temperature of the hot water is not lower than 80℃. After heating is completed, the time for the conveying connecting pipe to fall from the heating furnace into the hot water is controlled within 20S; prevent the temperature from dropping too much during exposure to the air, which is not conducive to quenching and reduces the heat treatment effect.

[0035] Tempering process: heat the transport connecting pipe to 145-155°C, keep it warm for 4-6 hours, cool it to below 80°C with the furnace, and take it out of the furnace. In this embodiment, the maximum tempering heating temperature is 150°C and the holding time is 5 hours; it is mainly to eliminate the thermal stress in the transport connecting pipe.

[0036] In the trial production of the conveying connecting pipe, the graphite is not corroded in the cast state, and the graphite is spherical, with a small amount of agglomerates, the spheroidization rate is ≥95%, and the spheroidization level is level 1. Figure 2 As shown; after heat treatment, the matrix structure is tempered martensite + fine carbides, such as Figure 2As shown; the hardness is 58HRC, and the tensile strength is 605MPa. During use, the matrix structure of the conveying connecting pipe is high in strength and hardness. The matrix contains hard points such as chromium iron carbide. Silicon carbide particles are embedded on the inner wall surface of the conveying connecting pipe to further improve the wear resistance of the inner wall, thereby increasing the service life of the conveying connecting pipe.

[0037] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A method for casting a conveying connecting pipe, characterized in that: The components of the conveying connecting pipe (by weight percentage) include 3.2-3.4% carbon, 1.8-2.2% silicon, 0.5-0.7% manganese, 0.15-0.2% copper, 0.2-0.3% nickel, 0.8-1.0% chromium, 0.03-0.07% magnesium (residual), 0.001-0.008% nitrogen, ≤0.02% phosphorus, ≤0.02% sulfur; 0.02-0.08% silicon carbide particles; the rest is iron; the casting of the conveying connecting pipe includes the following steps: Modeling: Rationally design the pouring system of the conveying connecting pipe, use resin sand to make the cavity and sand core; the cavity and sand core enclose the chamber and pouring system of the conveying connecting pipe, paint is applied on the inner surface of the cavity and the outer surface of the sand core, a cooling water pipe is buried in the sand core, and water is passed into the cooling water pipe after the molten iron is filled, so as to adjust the solidification order of the molten iron; the silicon carbide particles are diluted with the paint and then applied to the surface of the paint layer on the outer surface of the sand core; Melting: In the smelting furnace, pig iron, scrap steel, ferrosilicon, ferromanganese, ferrochrome, copper and nickel are added in proportion and the composition is adjusted to control the composition of molten iron to 3.2-3.4% carbon, 0.9-1.2% silicon, 0.5-0.7% manganese, 0.15-0.2% copper, 0.2-0.3% nickel, 0.8-0.9% chromium, ≤0.02% phosphorus, ≤0.02% sulfur; the rest is iron. After the composition of molten iron is qualified, the furnace temperature is controlled at 1400-1430℃; Inoculation and spheroidization treatment: a dam is set at the bottom of the ladle to separate it into a first area and a second area, rare earth magnesium-iron alloy particles are laid at the bottom of the first area, ferrosilicon alloy particles are covered on the surface of the rare earth magnesium-iron alloy particles, and iron filings are covered on the surface of the ferrosilicon alloy particles, and they are compacted and compacted; the amount of the rare earth magnesium-iron alloy particles added (percentage in molten iron) is 0.6-0.8%; the amount of the ferrosilicon alloy particles added (percentage in molten iron) is 1.2-1.4%; before the molten iron is taken out of the furnace and poured into the ladle, the molten iron rushes to the second area of ​​the ladle; Pouring and cleaning: When pouring the molten iron in the ladle into the mold cavity, add ferrochromium nitride particles along with the flow, the amount of ferrochromium nitride particles added is 0.1-0.2%, the nitrogen content of ferrochromium nitride is controlled at 0.3-0.5%, and the particle size of the ferrochromium nitride particles is 200-100 meshes; before pouring the molten iron, connect the cooling water pipe to the water source to let water flow, and the molten iron solidifies and forms. Before unpacking, close the cooling water pipe and disconnect it; after unpacking, cut off the pouring system of the conveying connecting pipe and grind it; Heat treatment: including quenching and tempering processes; Quenching process: heat the conveying connecting pipe to 880~900℃, keep warm for 1~3h; quench in hot water, the hot water temperature is ≥80℃; Tempering process: heat the conveying connecting pipe to 145~155℃, keep it warm for 4~6h, cool it to below 80℃ with the furnace, and take it out of the furnace.

2. The casting method of the conveying connecting pipe according to claim 1, characterized in that: The silicon carbide particles are nano-scale particles, and the particle size of the silicon carbide particles is ≤0.05 μm. The silicon carbide particles are mixed evenly with the coating in a (weight ratio) of 1:1-3, and then mixed evenly with anhydrous alcohol in a (weight ratio) of 1:100-300, and then sprayed on the surface of the coating layer of the sand core.

3. The casting method of the conveying connecting pipe according to claim 2, characterized in that: During the process of spraying the mixture of silicon carbide particles, coating and anhydrous alcohol on the coating layer surface of the sand core, the spraying pressure is 0.4-0.5MPa; the spraying direction is perpendicular to the coating surface of the sand core, and the distance between the nozzle and the coating surface of the sand core is controlled at 200mm-300mm.

4. The casting method of the conveying connecting pipe according to claim 1, characterized in that: The cooling water pipe includes an inlet pipe, an outlet pipe and several branch pipes; the inlet pipe, the branch pipe and the outlet pipe are arranged in sequence along the axial direction of the sand core, the two ends of the branch pipe are respectively connected to the inlet pipe and the outlet pipe, and the several branch pipes are evenly spaced along the circumference of the sand core.

5. The casting method of the conveying connecting pipe according to claim 4, characterized in that: The branch water pipe extends along the dragon outline of the sand core, and the diameter of the water pipe is 20-40 mm; the distance between the branch water pipe and the surface of the sand core is controlled to be 3-20 mm; the circumferential angle between two adjacent branch water pipes is 25°-35°.

6. The casting method of the conveying connecting pipe according to claim 5, characterized in that: During the sand core molding process, a chamber enclosed by the cooling water pipe is filled with light breathable materials such as straw rope, cotton wool or foam, and the light breathable material protrudes from the sand core near one end of the water inlet pipe.

7. The casting method of the conveying connecting pipe according to claim 6, characterized in that: An exhaust hole is opened at the upper part of the groove of the sand core, and the diameter of the exhaust hole is ≤2mm; one end of the exhaust hole is in contact with and communicated with the light air-permeable material.

8. The casting method of the conveying connecting pipe according to claim 1, characterized in that: During the quenching process, the heating rate is controlled at 5~10℃ / min; when heated to 450℃ and 700℃, the temperature is kept warm for 10~15min respectively; the time between the transport connecting pipe falling from the heating furnace into the hot water is ≤20S.

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