Integrally cast excavator bucket and manufacturing method thereof

Abstract

The present invention provides an integrally cast excavator bucket and a manufacturing method thereof. The integrally cast excavator bucket comprises a lifting lug, a top plate, two side plates and a bottom plate connected with the two side plates. A method for manufacturing the integrally cast excavator bucket by adopting the cast steel comprises the following steps: putting cast steel components into a melting furnace, and carrying out modification treatment before furnace after melting is finished; manufacturing models and a template, coating, heating, vacuumizing, placing sandboxes, adding sand, molding, carrying out mold closing, casting, quenching, tempering and cooling to room temperature to finish casting of the excavator bucket. The integrally cast excavator bucket is formed by once casting from a low-alloy steel material by adopting a vacuum sealing technology, and is high in product strength, resistant to wear and corrosion, high in impact resistance and long in service life.

Claims

1. An integrally cast excavator bucket, comprising a lifting lug (1), a top plate, two side plates (3) and a bottom plate (4) connected with the two side plates (3), wherein the lifting lug (1), the top plate, the two side plates (3) and the bottom plate (4) are of an integral structure, wherein, cast steel for casting the excavator bucket consists of the following components in percentage by weight: 0.1% to 0.6% of C, 0.2% to 0.6% of Si, 0.5% to 1.8% of Mn, 0.5% to 1.6% of Cr, 0.2% to 0.75% of Ni, 0.1% to 0.6% of Mo, less than or equal to 0.035% of P, less than or equal to 0.035% of S, and the balance of Fe.

2. The integrally cast excavator bucket according to claim 1, wherein, cast steel for casting the excavator bucket consists of the following components in percentage by weight: 0.25% of C, 0.3% of Si, 1.2% of Mn, 0.8% of Cr, 0.25% of Ni, 0.4% of Mo, less than or equal to 0.035% of P, less than or equal to 0.035% of S, and the balance of Fe.

3. A method for manufacturing an integrally cast excavator bucket from cast steel, wherein, said method comprises the following steps: 1) putting cast steel components into a melting furnace and melting, such that a charging material is molten stably and uniformly to reach a casting requirement; 2) carrying out modification treatment before furnace on molten steel: adding rare earth to the melting furnace before casting and carrying out modification treatment on molten steel at 1600-1620 C., and then adding a grain refiner to further modify the molten steel to obtain modified molten steel; 3) manufacturing models and a template: manufacturing a bottom plate provided with an aspirating chamber, and an upper model and a lower model consistent with the excavator bucket, wherein air vents are formed in edges, dead angles, internal corners and deep grooves of the upper model and the lower model, the models are fixed on the bottom plate, and the air vents are directly communicated with the aspirating chamber of the bottom plate; 4) coating, heating and vacuumizing: heating an EVA plastic film having a size equal to that of the models of the excavator bucket to be softened to obtain a softened film, and starting a vacuumizing device, such that the softened film is tightly clung to the upper model and the lower model in the step 3) respectively, and a cast steel coating is spray-coated and dried to obtain a coated upper model and a coated lower model; 5) placing sandboxes, adding sand and molding: putting a sandbox equipped with a filtering and aspirating system onto the upper model coated in the step 4), filling the sandbox with dry quartz sand which does not contain an adhesive and additives, starting a vibration compacting table, compacting the quartz sand in the sandbox by vibration and flattening a sand surface, then covering a layer of plastic film and sealing, opening an aspirating valve, and molding the quartz in the sandbox at a negative pressure of 4 to 9 Kpa to form an upper box cavity; and putting the other sandbox equipped with a filtering and aspirating system onto the lower model coated in the step 4), and repeatedly operating said step to form a lower box cavity: 6) performing mold closing and casting: closing the upper box cavity and the lower box cavity in the step 5), placing a casting head, pouring the molten steel subjected to modification treatment in the step 2) into a cavity formed after the upper box cavity and the lower box cavity are closed and then casting, continuously vacuumizing for 2 to 2.5 h at a negative pressure of 4 to 9 Kpa after casting is finished, stopping vacuumizing at a negative pressure and hoisting the sandboxes, and breaking up the quartz sand to obtain a molded piece; 7) heating the molded piece in the step 6) in a heat treatment furnace to 890 to 910 C., preserving heat for 2.5 to 3 h and then quenching; 8) tempering the quenched molded piece, and naturally cooling the molded piece to room temperature after tempering is finished to obtain a tempered molded piece; and thus finishing casting of the excavator bucket.

4. The method according to claim 3, wherein, the melting temperature in step 1) is 1600 to 1650 C.; the molten steel casting temperature in step 6) is 1580 to 1660 C.; and the tempering conditions in the step 8) are: the tempering temperature is 540 to 560 C., and the heat preservation time is 3 to 4 h.

5. The method according to claim 3, wherein, the amount of rare earth added in the step 2) is 0.2% to 0.4% by weight of the molten steel, the rare earth element is lanthanum or cerium or yttrium or combinations thereof, and the modified molten steel stands for 10 to 15 minutes.

6. The method according to claim 3, wherein, the amount of the grain refiner added in the step 2) is 0.05% to 0.2% by weight of the molten steel, and the grain refiner is added to the molten steel under the protection of a protecting gas, wherein the grain refiner is TiN or YNi.sub.2Si.sub.2 or CeS or MnSi or TiaOb or BN or CrN or TiC or NbC or CeCo.sub.4B or combinations thereof, the grain refiner has a granularity of 10 to 500 nm, and the average grain size is 30 to 100 nm.

7. The method according to claim 3, wherein, a casting inoculator is added to a casting process in the step 6) in two batches, and the total addition amount of the inoculator is 0.05% to 0.07% by weight of the molten steel, to be specific: adding 20% to 30% by weight of casting inoculator when 1/13 molten steel is casted, adding molten steel in the second batch after first inoculation is performed for 1 to 2 minutes, then adding the remaining casting inoculator and performing second inoculation for 2 to 3 minutes, and finally adding the remaining molten steel, wherein the casting inoculator is conveyed in a helium atmosphere at a flow of 0.04 to 0.08 Kg/s; and the casting inoculator comprises the following components in parts by weight: 15 to 25 parts of W, 10 to 25 parts of Si, 10 to 30 parts of B, 1 to 5 parts of Ga and 15 to 18 parts of Ba, and the casting inoculator has a grain size of 250 to 400 m.

8. The method according to claim 3, wherein, a quenching solution composition adopted for quenching in the step 7) comprises the following components in parts by weight: 30 to 70 parts of polyvinylpyrrolidone, 0.2 to 5 parts of polyvinyl alcohol, 0.2 to 6 parts of triethanolamine, 2 to 4 parts of ethylene oxide and propylene oxide random copolymer, 0.6 to 0.7 part of sodium chloride, 0.6 to 1.2 parts of potassium chloride, 0.5 to 10 parts of anti-rust agent, 0.5 to 5 parts of sterilizing agent, 0.005 to 0.3 part of defoaming agent, 0.1 to 5 parts of scale inhibitor, 0.1 to 5 parts of cleaning dispersant, and 5 to 60 parts of water.

9. The method according to claim 3, wherein, in a process of preserving heat for 2.5 to 3 h after heating to 890 to 910 C., alcohol combusts in the heat treatment furnace to form a reducing atmosphere so as to prevent the molded piece from forming oxide skin.

10. The method according to claim 3, wherein, said method further comprises performing heating pretreatment on the molded piece obtained in the step 6) prior to operation in the step 7), said pretreatment method comprising: putting the molded piece in a heating furnace, heating to 800 to 850 C., preserving heat for 1.5 to 2.5 h, cooling in air to room temperature after discharged out of the furnace, and then performing treatment as described in the step 7).

11. The method according to claim 3, wherein, in a molded piece tempering process in the step 8), the vacuum degree in the furnace is 0. 025 to 0.05 MPa, methanol and NH.sub.3 are charged with methanol accounting for 60% and NH.sub.3 accounting for 40%, to form a nitrocarburized compound layer which is 9-10 m in depth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a structural schematic diagram of the excavator bucket of the present invention; and

(2) FIG. 2 is a structural schematic diagram of the excavator bucket of the present invention; wherein

(3) lifting lug 1, lifting lug reinforcing rib 2, side plate 3, bottom plate 4, wear-resistant block 5, wear-resistant sphere 6, front edge 7 of bucket, side toothed plate 8, longitudinal rib 9, and transverse rib 10 are marked.

DETAILED DESCRIPTION

(4) The present invention will be further illustrated below in combination with the following embodiments, however, the protection scope of the present invention is not limited to the scope described in embodiments.

(5) Embodiment 1

(6) An integrally cast excavator bucket, comprising a lifting lug (1), a top plate, two side plates (3) and a bottom plate (4) connected with the two side plates (3), wherein the lifting lug (1), the top plate, the two side plates (3) and the bottom plate (4) are of an integral structure.

(7) A side toothed plate (8) is provided on the side plate (3), and a lifting lug reinforcing rib (2) is provided at a position where the lifting lug (1) is connected with the top plate.

(8) A plurality of wear-resistant blocks (5) and wear-resistant spheres (6) are provided in an area, close to a front edge (7) of the bucket, of the side plate (3), and the wear-resistant blocks (5) are close to a position where the side plate (3) is connected with the bottom plate (4);

(9) and two longitudinal ribs (9) are provided at positions, close to the two side plates (3), of the bottom plate (4), and a plurality of transverse ribs (10) are provided in the middle of the bottom plate (4).

(10) The integrally cast excavator bucket which is of an integral structure comprises a lifting lug (1), a lifting lug reinforcing rib (2), a top plate, two side plates (3), a bottom plate (4), wear-resistant blocks (5), wear-resistant spheres (6), longitudinal ribs (9) and transverse ribs (10).

(11) Embodiment 2

(12) Cast steel for casting the excavator bucket consists of the following components: 0.1% to 0.6% of C, 0.2% to 0.6% of Si, 0.5% to 1.8% of Mn, 0.5% to 1.6% of Cr, 0.2% to 0.75% of Ni, 0.1% to 0.6% of Mo, less than or equal to 0.035% of P, less than or equal to 0.035% of S, and the balance of Fe.

(13) Embodiment 3

(14) Cast steel for casting the excavator bucket consists of the following components: 0.3% of C, 0.3% of Si, 1.8% of Mn, 1.6% of Cr, 0.55% of Ni, 0.3% of Mo, 0.025% of P, 0.015% of S, and the balance of Fe.

(15) Embodiment 4

(16) Cast steel for casting the excavator bucket consists of the following components: 0.25% of C, 0.4% of Si, 1.2% of Mn, 0.8% of Cr, 0.75% of Ni, 0.4% of Mo, 0.035% of P, 0.035% of S, and the balance of Fe.

(17) Embodiment 5

(18) Cast steel for casting the excavator bucket consists of the following components: 0.1% of C, 0.2% of Si, 0.5% of Mn, 0.5% of Cr, 0.2% of Ni, 0.1% of Mo, 0.025% of P, 0.015% of S, and the balance of Fe.

(19) Embodiment 6

(20) Cast steel for casting the excavator bucket consists of the following components: 0.6% of C, 0.6% of Si, 1.6% of Mn, 0.6% of Cr, 0.45% of Ni, 0.6% of Mo, 0.025% of P, 0.015% of S, and the balance of Fe.

(21) Embodiment 7

(22) The method for casting the integral excavator bucket from the cast steel is characterized by comprising the following steps:

(23) 1) putting cast steel components into a melting furnace and melting at 1600 C., such that a charging material is molten stably and uniformly to reach a casting requirement;

(24) 2) carrying out modification treatment before furnace on molten steel: adding rare earth to the melting furnace before casting and carrying out modification treatment on molten steel at 1600 C., and then putting a grain refiner to further modify the molten steel to obtain modified molten steel;

(25) 3) manufacturing models and a template: manufacturing the bottom plate provided with an aspirating chamber, and an upper model and a lower model consistent with the excavator bucket, wherein air vents are formed in edges, dead angles, internal corners and deep grooves of the upper model and the lower model, the models are fixed on the bottom plate, and the air vents are directly communicated with the aspirating chamber of the bottom plate; the aspirating chamber of the bottom plate has a function of aspirating air from the models, such that the models are at a negative pressure state;

(26) 4) coating, heating and vacuumizing: heating an EVA plastic film having a size equal to that of the models of the excavator bucket to be softened to obtain a softened film, and starting a vacuumizing device, such that the softened film is tightly clung to the upper model and the lower model in the step 3) respectively, and a cast steel coating is spray-coated and dried to obtain a coated upper model and a coated lower model;

(27) 5) placing sandboxes, adding sand and molding: putting a sandbox equipped with a filtering and aspirating system onto the upper model coated in the step 4), filling the sandbox with dry quartz sand which does not contain an adhesive and additives, starting a vibration compacting table, compacting the quartz sand in the sandbox by vibration and flattening a sand surface, then covering a layer of plastic film and sealing, opening an aspirating valve, and molding the quartz in the sandbox at a negative pressure of 4 to 9 Kpa to form an upper box cavity; and putting the other sandbox equipped with a filtering and aspirating system onto the lower model coated in the step 4), and repeatedly operating said step to form a lower box cavity:

(28) 6) performing mold closing and casting: closing the upper box cavity and the lower box cavity in the step 5), placing a casting head, pouring the molten steel at 1580 C. subjected to modification treatment in the step 2) into a cavity formed after the upper box cavity and the lower box cavity are closed and then casting, continuously vacuumizing for 2 h at a negative pressure of 4 Kpa after casting is finished, releasing the negative pressure and hoisting the sandboxes, and breaking up the quartz sand to obtain a molded piece.

(29) 7) argon protective heating the molded piece in the step 6) in a heat treatment furnace to 890 C., preserving heat for 2.5 h and then quenching; and

(30) 8) tempering the quenched molded piece at 540 C. in case of preserving heat for 3 h, and naturally cooling the molded piece to room temperature after tempering is finished, and thus finishing casting of the excavator bucket.

(31) The addition amount of rare earth in the step 2) is 0.2% by weight of molten steel, and the rare-earth element is a combination of lanthanum and yttrium according to a mass ratio of 1:2.

(32) The amount of the grain refiner added in the step 2) is 0.05% by weight of the molten steel, and the grain refiner is added to the molten steel under the protection of a protecting gas, wherein the grain refiner is TiN, and the grain refiner has a granularity of 10 to 500 nm, and the average grain size is 80 nm.

(33) The protecting gas is argon.

(34) Embodiment 8

(35) The method for manufacturing the integral excavator bucket from the cast steel is characterized by comprising the following steps:

(36) 1) putting cast steel components into a melting furnace and melting at 1650 C., such that a charging material is molten stably and uniformly to reach a casting requirement;

(37) 2) carrying out modification treatment before furnace on molten steel: adding rare earth to the melting furnace before casting and carrying out modification treatment on molten steel at 1620 C., and then putting a grain refiner to further modify the molten steel to obtain modified molten steel;

(38) 3) manufacturing models and a template: manufacturing the bottom plate provided with an aspirating chamber, and an upper model and a lower model consistent with the excavator bucket, wherein air vents are formed in major locations, such as edges, dead angles, internal corners and deep grooves of the models, the models are fixed on the bottom plate, and the air vents are directly communicated with the aspirating chamber of the bottom plate; the aspirating chamber of the bottom plate has a function of aspirating air from the models, such that the models are at a negative pressure state;

(39) 4) coating, heating and vacuumizing: heating an EVA plastic film having a size equal to that of models of the excavator bucket to be softened to obtain a softened film, and starting a vacuumizing device, such that the softened film is tightly clung to the upper model and the lower model in the step 3) respectively, and a cast steel coating is spray-coated and dried to obtain a coated upper model and a coated lower model;

(40) 5) placing sandboxes, adding sand and molding: putting a sandbox equipped with a filtering and aspirating system onto the upper model coated in the step 4), filling the sandbox with dry quartz sand which does not contain an adhesive and additives, starting a vibration compacting table, compacting the quartz sand in the sandbox by vibration and flattening a sand surface, then covering a layer of plastic film and sealing, opening an aspirating valve, and molding the quartz in the sandbox at a negative pressure of 4 Kpa to form an upper box cavity; and putting the other sandbox equipped with a filtering and aspirating system onto the lower model coated in the step 4), and repeatedly operating said step to form a lower box cavity;

(41) 6) performing mold closing and casting: closing the upper box cavity and the lower box cavity in the step 5), placing a casting head, pouring the molten steel at 1620 C. subjected to modification treatment in the step 2) into a cavity formed after the upper box cavity and the lower box cavity are closed and then casting, continuously vacuumizing for 2.5 h at a negative pressure of 9 Kpa after casting is finished, releasing the negative pressure and hoisting the sandboxes, and breaking up the quartz sand to obtain a molded piece.

(42) 7) alcohol combusts heating the molded piece to form a reducing atmosphere in the step 6) in a heat treatment furnace to 910 C., preserving heat for 3 h and then quenching; and

(43) 8) tempering the quenched molded piece at 560 C. in case of preserving heat for 4 h, and naturally cooling the molded piece to room temperature after tempering is finished, and thus finishing casting of the excavator bucket.

(44) The addition amount of rare earth in the step 2) is 0.4% by weight of molten steel, and the rare-earth element is a combination of lanthanum and yttrium according to a mass ratio of 1:2.

(45) The addition amount of the grain refiner in the step 2) is 0.2% by weight of molten steel, and the grain refiner is added to the molten steel under the protection of a protecting gas, and the grain refiner is a combination of YNi.sub.2Si.sub.2, CeS and MnSi according to a mass ratio of 1:2:3 and has a granularity being 10 to 200 nm and an average grain size being 50 nm.

(46) The protecting gas is argon.

(47) Preferably, in a molded piece tempering process in the step 8), the vacuum degree in the furnace is 0.025 MPa, methanol and NH3 are charged with methanol accounting for 60% and NH3 accounting for 40%, to form a nitrocarburized compound layer which is 9-10 m in depth.

(48) A casting inoculator is added to a casting process in the step 6) in two batches, and the total addition amount of the inoculator is 0.05% by weight of the molten steel, to be specific: adding 20% by weight of casting inoculator when molten steel is casted, adding molten steel in the second batch after first inoculation is performed for 2 minutes, then adding the remaining casting inoculator and performing second inoculation for 3 minutes, and finally adding the remaining molten steel, wherein the casting inoculator is conveyed in a helium atmosphere at a flow of 0.08 Kg/s; and

(49) the casting inoculator comprises the following components in parts by weight: 15 parts of W, 10 parts of Si, 10 parts of B, 15 parts of Ti and 15 parts of Ba, and the casting inoculator has a grain size of 120 m.

(50) Embodiment 9

(51) The method for manufacturing the integral excavator bucket from the cast steel is characterized by comprising the following steps:

(52) 1) putting cast steel components into a melting furnace and melting at 1630 C., such that a charging material is molten stably and uniformly to reach a casting requirement;

(53) 2) carrying out modification treatment before furnace on molten steel: adding rare earth to the melting furnace before casting and carrying out modification treatment on molten steel at 1610 C., and then putting a grain refiner to further modify the molten steel to obtain modified molten steel;

(54) 3) manufacturing models and a template: manufacturing the bottom plate provided with an aspirating chamber, and an upper model and a lower model consistent with the excavator bucket, wherein air vents are formed in major locations, such as edges, dead angles, internal corners and deep grooves of the models, the models are fixed on the bottom plate, and the air vents are directly communicated with the aspirating chamber of the bottom plate; the aspirating chamber of the bottom plate has a function of aspirating air from the models, such that the models are at a negative pressure state;

(55) 4) coating, heating and vacuumizing: heating an EVA plastic film having a size equal to that of models of the excavator bucket to be softened to obtain a softened film, and starting a vacuumizing device, such that the softened film is tightly clung to the upper model and the lower model in the step 3) respectively, and a cast steel coating is spray-coated and dried to obtain a coated upper model and a coated lower model;

(56) 5) placing sandboxes, adding sand and molding: putting a sandbox equipped with a filtering and aspirating system onto the upper model coated in the step 4), filling the sandbox with dry quartz sand which does not contain an adhesive and additives, starting a vibration compacting table, compacting the quartz sand in the sandbox by vibration and flattening a sand surface, then covering a layer of plastic film and sealing, opening an aspirating valve, and molding the quartz in the sandbox at a negative pressure of 4 Kpa to form an upper box cavity; and putting the other sandbox equipped with a filtering and aspirating system onto the lower model coated in the step 4), and repeatedly operating said step to form a lower box cavity;

(57) 6) performing mold closing and casting: closing the upper box cavity and the lower box cavity in the step 5), placing a casting head, pouring the molten steel at 1590 C. subjected to modification treatment in the step 2) into a cavity formed after the upper box cavity and the lower box cavity are closed and then casting, continuously vacuumizing for 2.4 h at a negative pressure of 7 Kpa after casting is finished, releasing the negative pressure and hoisting the sandboxes, and breaking up the quartz sand to obtain a molded piece.

(58) 7) vacuum protective beating the molded piece in the step 6) in a heat treatment furnace to 900 C., preserving heat for 2.8 h and then quenching; and

(59) 8) tempering the quenched molded piece at 550 C. in case of preserving heat for 3.5 h, and naturally cooling the molded piece to room temperature after tempering is finished, and thus finishing casting of the excavator bucket.

(60) The addition amount of rare earth in the step 2) is 0.3% by weight of molten steel, and the rare-earth element is a combination of lanthanum and cerium according to a mass ratio of 1:2.

(61) The addition amount of the grain refiner in the step 2) is 0.15% by weight of molten steel, and the grain refiner is added to the molten steel under the protection of a protecting gas, and the grain refiner is a combination of TiN, YNi.sub.2Si.sub.2, CeS, MnSi and CrN according to a mass ratio of 1:2:3:1 and has a granularity being 10 to 100 nm and an average grain size being 50 nm.

(62) The protecting gas is argon.

(63) In a molded piece tempering process in the step 8), the vacuum degree in the furnace is 0.05 MPa, methanol and NH3 are charged with methanol accounting for 60% and NH3 accounting for 40%, to form a nitrocarburized compound layer which is 9-10 m in depth.

(64) A casting inoculator is added to a casting process in the step 6) in two batches, and the total addition amount of the inoculator is 0.07% by weight of the molten steel, to be specific: adding 20% by weight of casting inoculator when molten steel is casted, adding molten steel in the second batch after first inoculation is performed after 1 minute, then adding the remaining casting inoculator and performing second inoculation for 2 minutes, and finally adding the remaining molten steel, wherein the casting inoculator is conveyed in a helium atmosphere at a flow of 0.04 Kg/s; and

(65) the casting inoculator comprises the following components in parts by weight: 25 parts of W, 25 parts of Si, 30 parts of B, 20 parts of Ga and 18 parts of Ba, and the casting inoculator has a grain size of 250 to 350 m.

(66) Embodiment 10

(67) The method for manufacturing the integral excavator bucket from the cast steel is characterized by comprising the following steps:

(68) 1) putting cast steel components into a melting furnace and melting at 1640 C., such that a charging material is molten stably and uniformly to reach a casting requirement;

(69) 2) carrying out modification treatment before furnace on molten steel: adding rare earth to the melting furnace before casting and carrying out modification treatment on molten steel at 1610 C., and then putting a grain refiner to further modify the molten steel to obtain modified molten steel;

(70) 3) manufacturing models and a template: manufacturing the bottom plate provided with an aspirating chamber, and an upper model and a lower model consistent with the excavator bucket, wherein air vents are formed in major locations, such as edges, dead angles, internal corners and deep grooves of the models, the models are fixed on the bottom plate, and the air vents are directly communicated with the aspirating chamber of the bottom plate; the aspirating chamber of the bottom plate has a function of aspirating air from the models, such that the models are at a negative pressure state;

(71) 4) coating, beating and vacuumizing: heating an EVA plastic film having a size equal to that of models of the excavator bucket to be softened to obtain a softened film, and starting a vacuumizing device, such that the softened film is tightly clung to the upper model and the lower model in the step 3) respectively, and a cast steel coating is spray-coated and dried to obtain a coated upper model and a coated lower model;

(72) 5) placing sandboxes, adding sand and molding: putting a sandbox equipped with a filtering and aspirating system onto the upper model coated in the step 4), filling the sandbox with dry quartz sand which does not contain an adhesive and additives, starting a vibration compacting table, compacting the quartz sand in the sandbox by vibration and flattening a sand surface, then covering a layer of plastic film and sealing, opening an aspirating valve, and molding the quartz in the sandbox at a negative pressure of 4 Kpa to form an upper box cavity; and putting the other sandbox equipped with a filtering and aspirating system onto the lower model coated in the step 4), and repeatedly operating said step to form a lower box cavity;

(73) 6) performing mold closing and casting: closing the upper box cavity and the lower box cavity in the step 5), placing a casting head, pouring the molten steel at 1660 C. subjected to modification treatment in the step 2) into a cavity formed after the upper box cavity and the lower box cavity are closed and then casting, continuously vacuumizing for 2.3 h at a negative pressure of 6 Kpa after casting is finished, releasing the negative pressure and hoisting the sandboxes, and breaking up the quartz sand to obtain a molded piece.

(74) 7) heating the molded piece in the step 6) in a heat treatment furnace to 900 C., preserving heat for 2.8 h and then quenching; and

(75) during quenching, the molded piece is put into the quenching solution in a vacuum state or in an atmosphere of argon or helium, without contacting air, such that the pollutions of the workpiece from oxygen, hydrogen and the like in air are solved.

(76) 8) tempering the quenched molded piece at 550 C. in case of preserving heat for 3.5 h, and naturally cooling the molded piece to room temperature after tempering is finished, and thus finishing casting of the excavator bucket.

(77) The addition amount of rare earth in the step 2) is 0.35% by weight of molten steel, and the rare-earth element is a combination of lanthanum, cerium and yttrium according to a mass ratio of 1:1:3.

(78) The addition amount of the grain refiner in the step 2) is 0.15% by weight of molten steel, and the grain refiner is added to the molten steel under the protection of a protecting gas, and the grain refiner is a combination of YNi2Si2, TiaOb, CrN, TiC and NbC according to a mass ratio of 1:1:2:1:1 and has a granularity being 10 to 400 nm and an average grain size being 90 nm.

(79) The protecting gas is helium.

(80) In a molded piece tempering process in the step 8), the vacuum degree in the furnace is 0.03 MPa, methanol and NH3 are charged with methanol accounting for 600/0 and NH3 accounting for 40%, to form a nitrocarburized compound layer which is 9-10 m in depth.

(81) A casting inoculator is added to a casting process in the step 6) in two batches, and the total addition amount of the inoculator is 0.06% by weight of the molten steel, to be specific: adding 25% by weight of casting inoculator when molten steel is casted, adding molten steel in the second batch after first inoculation is performed for 1 to 2 minutes, then adding the remaining casting inoculator and performing second inoculation for 2.5 minutes, and finally adding the remaining molten steel, wherein the casting inoculator is conveyed in a helium atmosphere at a flow of 0.05 Kg/s; and

(82) the casting inoculator comprises the following components in parts by weight: 22 parts of W, 23 parts of Si, 25 parts of B, 18 parts of Ga and 17 parts of Ba, and the casting inoculator has a grain size of 250 to 300 m.

(83) Embodiment 11

(84) The addition amount of the grain refiner used in the method of the present invention is 0.1% by weight of molten steel, and the grain refiner is added to molten steel under the protection of a protecting gas; and the grain refiner is a combination of TiN, CeS, MnSi, TiaOb, BN, CrN, TiC, NbC and CeCo4B according to a mass ratio of 1:1:1:4:2:3:1:2:1 and has a granularity being 10 to 200 nm and an average grain size being 60 nm.

(85) Embodiment 12

(86) The addition amount of the grain refiner used in the method of the present invention is 0.19% by weight of molten steel, and the grain refiner is added to molten steel under the protection of a protecting gas, and the grain refiner is a combination of TiN, CeS, MnSi, TiaOb, BN, TiC and NbC according to a mass ratio of 1:2:3:2:1:3:4 and has a granularity being 10 to 400 nm and an average grain size being 90 nm.

(87) Embodiment 13

(88) The addition amount of the grain refiner used in the method of the present invention is 0.18% by weight of molten steel, and the grain refiner is added to molten steel under the protection of a protecting gas; and the grain refiner is a combination of TiN, YNi.sub.2Si.sub.2, CeS, MnSi and TiaOb according to a mass ratio of 1:2:1:2:3 and has a granularity being 10 to 180 nm and an average grain size being 95 nm.

(89) Embodiment 14

(90) The addition amount of the grain refiner used in the method of the present invention is 0.15% by weight of molten steel, and the grain refiner is added to molten steel under the protection of a protecting gas; and the grain refiner is a combination of TiN, CeS, MnSi, CrN and CeCo4B according to a mass ratio of 1:2:1:2:1 and has a granularity being 10 to 300 nm and an average grain size being 90 nm.

(91) Embodiment 15

(92) The addition amount of the grain refiner used in the method of the present invention is 0.050.2% by weight of molten steel, and the grain refiner is added to molten steel under the protection of a protecting gas; and the grain refiner is a combination of TiN, CeS, MnSi, TiaOb, BN and CeCo.sub.4B according to a mass ratio of 1:1:1:2:1:1 and has a granularity being 30 to 200 nm and an average grain size being 80 nm.

(93) Embodiment 16

(94) The quenching solution composition adopted for quenching in the method of the present invention comprises the following components in parts by weight: 30 to 70 parts of polyvinylpyrrolidone, 0.2 to 5 parts of polyvinyl alcohol, 0.2 to 6 parts of triethanolamine, 2 to 4 parts of ethylene oxide and propylene oxide random copolymer, 0.6 to 0.7 part of sodium chloride, 0.6 to 1.2 part of potassium chloride, 0.5 to 10 part of anti-rust agent, 0.5 to 5 part of sterilising agent, 0.005 to 0.3 part of defoaming agent, 0.1 to 5 part of scale inhibitor, 0.1 to 5 part of cleaning dispersant, and 5 to 60 parts of water.

(95) Embodiment 17

(96) The quenching solution composition adopted for quenching in the method of the present invention comprises the following components in parts by weight: 30 parts of polyvinylpyrrolidone, 4.5 parts of polyvinyl alcohol, 5.5 parts of triethanolamine, 3.5 parts of ethylene oxide and propylene oxide random copolymer, 0.6 part of sodium chloride, 0.7 part of potassium chloride, 0.5 part of anti-rust agent, 0.5 part of sterilising agent, 0.005 part of defoaming agent, 0.1 part of scale inhibitor, 0.1 part of cleaning dispersant, and 5 parts of water.

(97) The molecular weight of the polyvinylpyrrolidone is 200,000 to 500,000. The molecular weight of polyvinyl alcohol is 200,000 to 400,000. The molecular weight of the ethylene oxide and propylene oxide random copolymer is 200,000 to 400,000. The anti-rust agent is composed of 0.3 part of boric acid and 0.2 part of borate. The sterilising agent is composed of 0.3 part of triazine and 0.2 part of methylenedimorpholine. The defoaming agent is composed of 0.003 part of modified organosilicone and 0.002 part of polyether organosilicone. The scale inhibitor is hydroxyethylidene phosphonic acid. The cleaning dispersant is polyoxyethylene ether. The sterilising agent is of triazines.

(98) Embodiment 18

(99) The quenching solution composition adopted for quenching in the present invention comprises the following components in parts by weight: 70 parts of polyvinylpyrrolidone, 5 parts of polyvinyl alcohol, 6 parts of triethanolamine, 4 parts of ethylene oxide and propylene oxide random copolymer, 0.7 part of sodium chloride, 1.2 parts of potassium chloride, 10 parts of anti-rust agent, 5 parts of sterilising agent, 0.3 part of defoaming agent, 5 parts of scale inhibitor, 5 parts of cleaning dispersant, and 60 parts of water.

(100) The molecular weight of the polyvinylpyrrolidone is 300,000 to 400,000. The molecular weight of polyvinyl alcohol is 200,000 to 400,000. The molecular weight of the ethylene oxide and propylene oxide random copolymer is 200,000 to 400,000. The anti-rust agent is selected from ammonium carboxylate. The sterilising agent is composed of 3 parts of methylenedimorpholine or 2 parts of dimethyl oxazolidine. The defoaming agent is composed of 0.4 part of modified organosilicone and 0.1 part of polyether organosilicone. The scale inhibitor is organic phosphonic acid which is phosphoryl carboxylic acid. The cleaning dispersant is polyoxyethylene ether. The sterilising agent is of isothiazolinones.

(101) Embodiment 19

(102) The quenching solution composition adopted for quenching in the present invention comprises the following components in parts by weight: 40 parts of polyvinylpyrrolidone, 4 parts of polyvinyl alcohol, 5 parts of triethanolamine, 3 parts of ethylene oxide and propylene oxide random copolymer, 0.65 part of sodium chloride, 1.1 parts of potassium chloride, 6 parts of anti-rust agent, 3 part of sterilising agent, 0.2 part of defoaming agent, 3 parts of scale inhibitor, 3 parts of cleaning dispersant, and 35 parts of water.

(103) The molecular weight of the polyvinylpyrrolidone is 350,000 to 450,000. The molecular weight of polyvinyl alcohol is 200,000 to 400,000. The molecular weight of the ethylene oxide and propylene oxide random copolymer is 200,000 to 400,000. The anti-rust agent is composed of 2 parts of boric acid, 2 parts of borate and 2 parts of ammonium alcohol carboxylate. The sterilising agent is selected from methylenedimorpholine. The defoaming agent is selected from 0.005 part of modified organosilicone, 0.005 part of nanosilicon and 0.01 part of polyether. The scale inhibitor is phosphoryl carboxylic acid. The cleaning dispersant is polyoxyethylene ether. The sterilising agent is of isothiazolinones.

(104) Embodiment 20

(105) According to the method adopted in Embodiments 7-10, said method further comprises performing heating pretreatment on the molded piece obtained in the step 6) prior to operation in step 7), and said pretreatment method comprises the following steps: putting the molded piece in a heating furnace, heating to 800 to 850 C., preserving heat for 1.5 to 2.5 h, cooling to room temperature in air after discharged out of the furnace, and then performing treatment as described in step 7).

(106) TABLE-US-00001 TABLE 1 Comparison of Performances A Excavator Bucket Manufactured in The Present Invention with Excavator Bucket Manufactured With Other Technologies Elongation Yield Percentage Strength Tensile After Molding R.sub.p0.2 Strength Fracture Hardness Sand Object MP.sub.a R.sub.m MP.sub.a A% HRC Utilization Welded Excavator 345 470-660 21 20 Bucket Excavator Bucket 650 799 12 28-30 disposable Integrally Last from sand mold Excavator Bucket of 720 900 12 30-35 cyclically The Present utilized Invention

(107) As can be seen from Table 1, the excavator bucket manufactured by adopting the vacuum integral casting technology of the present invention can improve the yield strength, the tensile strength and the hardness of the excavator bucket, and molding sand for manufacturing can be repeatedly utilized.

(108) Above-mentioned embodiments are just preferred technical solutions of the present invention, should not be deemed as to the limitation of the present invention, and in case that embodiments in the present application do not conflict with features in the embodiments, may be combined to each other arbitrarily. The protection scope of the present invention should be the protection scope of the technical solutions recorded in claims, including equivalent alternatives of technical features in the technical solutions recorded in claims. That is, equivalent alternative improvements within this scope should fall into the protection scope of the present invention.