CN107745081B

CN107745081B - Differential pressure casting system and differential pressure casting method for U-shaped magnesium alloy piece

Info

Publication number: CN107745081B
Application number: CN201711170929.9A
Authority: CN
Inventors: 眭怀明; 卢艳丽; 王堃; 刘春霞
Original assignee: Yangzhou Fengming Photoelectric New Material Co ltd
Current assignee: Yangzhou Fengming Photoelectric New Material Co ltd
Priority date: 2017-11-22
Filing date: 2017-11-22
Publication date: 2023-05-12
Anticipated expiration: 2037-11-22
Also published as: CN107745081A

Abstract

The invention discloses a differential pressure casting system and a differential pressure casting method for a U-shaped magnesium alloy piece. The shell of the differential pressure pouring system comprises a U-shaped cavity with two arms extending forwards, an upper inner runner is arranged at the top of the U-shaped cavity, and the upper ends of the upper inner runners are respectively connected with an upper cross runner; the bottom of the U-shaped cavity is provided with lower ingates, the lower ends of the lower ingates are respectively connected with lower cross runners, transition straight runners respectively connected with the middle parts of the upper and lower cross runners are arranged between two arms of the U-shaped cavity, and the total sectional area of the lower ingates is larger than that of the upper ingates; the bottom center of the lower runner is connected with a pouring cup with a downward opening. The differential pressure pouring method sequentially comprises the steps of manufacturing an appearance mold and a core box mold, manufacturing a soluble core, closing a mold injection mold material, taking out a mold, dissolving the core, assembling the mold, degreasing, brushing, dewaxing, roasting, molding, filling, boosting, maintaining pressure and releasing pressure, and cooling to obtain the U-shaped magnesium alloy piece. The differential pressure pouring system and the differential pressure pouring method can realize sequential solidification and have high qualification rate.

Description

Differential pressure casting system and differential pressure casting method for U-shaped magnesium alloy piece

Technical Field

The invention relates to casting of a magnesium alloy piece, in particular to a differential pressure pouring system of a U-shaped magnesium alloy piece. The invention further relates to a differential pressure casting method of the U-shaped magnesium alloy piece, and belongs to the technical field of metal casting.

Background

The precision investment casting process is to make a model by using wax, wrap a plurality of layers of refractory materials such as clay, binder and the like on the outer surface of the model, heat the model to melt the wax and flow out, thereby obtaining an empty shell formed by the refractory materials, then pour the molten metal into the empty shell, knock the refractory materials into pieces after the metal is cooled, and the process for processing the metal is called precision investment casting or lost wax casting.

The common ends of the U-shaped magnesium alloy parts are connected, and the two arms extend downwards or upwards. Because the density of magnesium alloy is small, the heat capacity of the solution is small and the heat conductivity is large, the temperature of the alloy liquid is rapidly reduced in the flowing process, the oxidation and the air suction are extremely easy, the specific gravity of oxide is similar to that of light alloy liquid, the oxide mixed into the alloy liquid is difficult to skim, the volume shrinkage of the alloy liquid after solidification is large, defects such as shrinkage cavity, shrinkage cavity or slag inclusion are easy to occur, and the phenomenon of insufficient casting is easy to occur at the thin-wall parts of two arms of the U-shaped magnesium alloy piece.

Disclosure of Invention

The invention aims at solving the problems existing in the prior art and providing a differential pressure pouring system of a U-shaped magnesium alloy part, which can realize sequential solidification of castings and has high product quality.

In order to solve the technical problems, the differential pressure pouring system of the U-shaped magnesium alloy part comprises a sand box arranged above a sealing cover, wherein a liquid lifting pipe is arranged in the center of the sealing cover, the lower end of the liquid lifting pipe stretches into the lower part of a heat preservation furnace, a shell is arranged in the sand box, the shell comprises a U-shaped cavity with two arms stretching forwards, the top of the U-shaped cavity is provided with upper inner pouring channels respectively connected with two arms and a common end of the U-shaped cavity, and the upper ends of the upper inner pouring channels are respectively connected with upper transverse pouring channels; the bottom of the U-shaped cavity is provided with lower inner runners respectively connected with two arms and a common end of the U-shaped cavity, the lower end of each lower inner runner is respectively connected with a lower cross runner, a vertically extending transitional straight runner is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of each transitional straight runner are respectively connected with the middle parts of the upper cross runner and the lower cross runner; the total cross-sectional area of the lower ingate is larger than the total cross-sectional area of the upper ingate; and the bottom center of the lower cross runner is connected with a pouring cup with a downward opening.

Compared with the prior art, the invention has the following beneficial effects: the air inlet pipe on the sealing cover is used for air inlet, the metal liquid rises along the liquid lifting pipe under the air pressure in the heat preservation furnace, enters the lower horizontal pouring gate from the pouring cup, then enters the lower inner pouring gate, and then enters the U-shaped cavity from the lower inner pouring gate, and the air pressure in the heat preservation furnace is kept until the metal liquid in the cavity is completely solidified to form a casting. According to the principle that the pressure is equal to the pressure multiplied by the area, the upper ingate and the lower ingate form pressure difference in the pressurizing and pressure maintaining stages of pouring, and the castings can be sequentially solidified from top to bottom, so that the compactness of the products is ensured.

As an improvement of the invention, the lower port of the pouring cup is butted with the upper port of the lift tube; the top of the lift tube is provided with a lift tube flange which is turned outwards, and the center of the top of the lift tube flange is provided with an annular groove; the inner cavity of the lift tube is nested with a transfusion tube coaxial with the lift tube, the top of the transfusion tube is provided with a transfusion tube flange which is turned outwards, and the transfusion tube flange is embedded in an annular groove of the lift tube flange; the infusion tube is formed by sequentially screwing a first movable block to a fifth movable block from bottom to top, the first movable block to the fifth movable block are coaxially connected with each other in a smooth transition mode, the inner cavity of the first movable block is conical with the upper part being small and the lower part being large, the inner cavity of the second movable block is conical with the upper part being small, the inner cavity of the third movable block is cylindrical, the top of the third movable block is provided with an arc transition section with the upper part being small, the inner cavity of the fourth movable block is cylindrical, and the inner cavity of the fifth movable block is conical with the upper part being small and the lower part being large. Because the infusion tube is nested in the liquid lifting tube, the liquid lifting tube is convenient to replace or combine, so that the shape of the section in the liquid lifting tube can be changed at will, and the combination is strong; the flow speed of the alloy liquid is controlled by utilizing the change of the inner cavity structure of the infusion tube, so that turbulent flow is not generated, and skimming is realized; the molten metal is stable in filling, the defects of oxide slag inclusion and the like can be reduced, and the casting is solidified under pressure and has compact structure and high mechanical property. When the liquid lifting pipe is frozen, the whole replacement is not needed. Each movable block is connected through threads and can be replaced independently so as to adapt to the weight and the structure of castings, alloy liquid flows from bottom to top in the process, the first stage is a drainage stage, the splayed necking of an inner cavity of each movable block can control the alloy liquid to be free of turbulence, and skimming is performed by utilizing the splayed shape. The second stage is a transition stage, the alloy liquid sequentially flows through the second movable block and the third movable block, the section of the inner cavity is primarily enlarged, the flow speed is reduced, and the gas rolling of the alloy liquid at the position can be avoided by utilizing the arc transition of the opening of the third movable block. The third stage is the final casting stage, the alloy liquid sequentially flows through the movable block IV and the movable block V, the flow speed in the movable block IV is further reduced, the mouth of the movable block V is splayed, the effect of secondary skimming is formed, and the flow speed is controlled.

As a further improvement of the invention, the top of the upper cross runner is connected with a plurality of gas gathering grooves; the side walls of the lower ends of the lower ingates are respectively connected with buffer bags, and the free ends of the buffer bags are blind ends and respectively tilt upwards. A plurality of gas gathering grooves are arranged so as to facilitate the exhaust from the top; the buffer bag is positioned at the connecting part of the lower inner runner and the lower cross runner, can buffer the impact force of the magnesium liquid, can buffer the phenomenon of over-speed and over-current of the magnesium liquid caused by over-speed pouring speed due to unstable manual end bag in the pouring process, and reduces the secondary oxide slag of the magnesium liquid caused by unstable pouring.

The invention also aims to solve the problems in the prior art and provide a differential pressure casting method of the U-shaped magnesium alloy piece, which has the advantages of rapid and stable mold filling, good product precision and high qualification rate.

In order to solve the technical problems, the differential pressure casting method of the U-shaped magnesium alloy part comprises the following steps in sequence: the method comprises the steps that an appearance mould of a U-shaped workpiece model and a core box mould for manufacturing a core are manufactured respectively, wherein the appearance mould comprises an upper mould and a lower mould which are symmetrical, and mould cavities of the upper mould and the lower mould can be encircled to form the appearance of the U-shaped workpiece model; injecting the soluble material into a core box die under high pressure, cooling and shaping, and taking out the soluble material from the core box die to obtain a soluble core; positioning and placing the soluble core in a mold cavity of the appearance mold, and combining and locking an upper mold and a lower mold; fourthly, preparing a die material required for manufacturing the U-shaped workpiece model in a wax melting machine, and injecting the die material into a die cavity of a profile die; fifthly, cooling and shaping the die material to form a U-shaped workpiece integral model, separating the upper die from the lower die, and taking out the U-shaped workpiece integral model; sixth, immersing the whole model of the U-shaped workpiece in water, and dissolving the soluble core to obtain a wax model of the U-shaped workpiece; assembling the U-shaped workpiece wax mould and other parts of the pouring system to form a complete casting wax mould; the casting wax mould comprises a U-shaped cavity with two arms extending forwards, wherein the top of the U-shaped cavity is provided with upper inner runners respectively connected with the two arms and the common end of the U-shaped cavity, and the upper ends of the upper inner runners are respectively connected with upper cross runners; the bottom of the U-shaped cavity is provided with lower inner runners respectively connected with two arms and a common end of the U-shaped cavity, the lower end of each lower inner runner is respectively connected with a lower cross runner, a vertically extending transitional straight runner is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of each transitional straight runner are respectively connected with the middle parts of the upper cross runner and the lower cross runner; the total cross-sectional area of the lower ingate is larger than the total cross-sectional area of the upper ingate; the center of the bottom of the lower cross runner is connected with a pouring cup with a downward opening; soaking a casting wax mould in boric acid for 4-6 minutes to remove grease, then coating fire-resistant surface slurry on the surface of the casting wax mould, forming a fire-resistant surface layer after solidification, bonding a heat pipe extending horizontally outwards on the fire-resistant surface layer, bonding an inner end head of the heat pipe at a hot joint of the U-shaped workpiece wax mould, and mounting a copper block at an outer end head of the heat pipe; continuously brushing a fireproof coating on the periphery of a fireproof surface layer, sanding the fireproof coating to form a first fireproof coating, continuously brushing the fireproof coating, sanding to sequentially form a second fireproof coating to a sixth fireproof coating, and curing to form a shell wrapping the periphery of the casting wax mould; putting the shell into a dewaxing kettle, and dewaxing by adopting hot water; putting the dewaxed shell into a roasting furnace for roasting, cooling to the casting temperature and taking out; placing the mould shell in a sand box, filling resin sand between the mould shell and the sand box for moulding, and curing after the resin sand is filled and compacted; the mold shell and the sand box are placed above a sealing cover of a heat preservation furnace, a liquid lifting pipe is arranged in the center of the sealing cover, a pouring cup of the mold shell is in butt joint with the liquid lifting pipe downwards, magnesium metal liquid enters an inner cavity of the mold shell through the liquid lifting pipe to be filled, and after pressure boosting, pressure maintaining and pressure relief, the mold shell is cooled to obtain a U-shaped magnesium alloy piece.

Compared with the prior art, the invention has the following beneficial effects: the well-manufactured wax pattern is soaked in boric acid for degreasing, so that the adsorption of flame retardant on the surface of the wax pattern can be increased, and preparation is made for subsequent brushing; after the fireproof surface layer is coated, a heat pipe is adhered to a thick and large part (namely a hot joint) of the product, the heat pipe and the copper block are adopted as a cooling system, and the high heat transfer performance of the heat pipe and the high heat conductivity coefficient of the copper block can rapidly lead out and emit heat, so that the hot joint of the product can be well cooled, the bad defects of loosening, shrinkage porosity and hot cracking caused by overheating of the hot joint of the product are reduced, the product can be sequentially solidified, and the internal quality of the product is improved. Brushing the outer end of the heat pipe with a steel brush to strengthen the surface adsorption force, then smearing soldering paste, controlling the thickness of the soldering paste to be 0.5mm-1mm, inserting a copper block at the outer end of the heat pipe, adjusting the temperature of a hot air gun to 500 ℃, baking a welding position, and cooling and solidifying when the color changes from gray to silver and yellow transparent rosin flows out; therefore, good heat conductivity between the heat pipe and the copper block can be ensured, the heat pipe can be reused, and the cost is reduced. According to the principle that the pressure is equal to the pressure multiplied by the area, the upper ingate and the lower ingate form pressure difference in the pressurizing and pressure maintaining stages of pouring, and the castings can be sequentially solidified from top to bottom, so that the compactness of the products is ensured.

As an improvement of the invention, the preparation method of the soluble material in the step (a) is as follows: (1) the raw materials and the industrial urea are prepared according to the following components in parts by weight: 52 parts of nitrate: 23 parts of polyethylene glycol: 16 parts of purified water: 9 parts; (2) mixing industrial urea and purified water, heating to melt, uniformly stirring, adding nitrate and polyethylene glycol, and uniformly stirring. The water absorption and brittleness of the industrial urea are improved by adopting nitrate and polyethylene glycol in the soluble material, and the surface smoothness of the core can be improved after high-pressure injection molding; after the U-shaped workpiece integral model is put into water, the water dissolution speed of the mold core is high, and the production efficiency is improved.

As a further improvement of the invention, in the step of combining the upper die and the lower die, the positioning pins at the four corners of the upper die are respectively inserted into the positioning pin holes at the four corners of the lower die, and compression springs are respectively arranged between the lower end heads of the positioning pins and the bottoms of the corresponding positioning pin holes. After the pressure that the top surface of the upper die received is eliminated, compression spring's tension is upwards ejecting a little distance with the locating pin, solves the problem that upper die and lower mould are difficult to separate, and the prizing bad upper die even damages the model when avoiding getting the model.

As a further improvement of the present invention, the method for manufacturing the molding material in the step four is as follows: firstly, melting 20wt% of Sichuan wax, adding 5wt% of polyethylene and 5wt% of ethyl cellulose while stirring, adding 40wt% of rosin after the mixture is completely melted, and finally adding 30wt% of paraffin after the mixture is completely melted, and stirring uniformly. The surface finish of the wax mould made of the mould material is high, the roughness index can reach 1.6, the shrinkage rate of the wax mould can be reduced from 0.88% to 0.78%, and the size precision of the wax mould is higher.

As a further improvement of the invention, the refractory face slurry in the step is formed by uniformly mixing a refractory coating and a corundum powder, and the preparation method of the refractory coating comprises the following steps: (1) the raw materials and the silicon dioxide are prepared according to the following components by weight: 25 parts of water: 15 parts of absolute alcohol: 20 parts of magnesium oxide powder: 15 parts of boric acid: 20 parts of sulfur: 5 parts of the components are uniformly mixed and stirred to form a neutral binder, and the temperature is controlled at 30-40 ℃; (2) adding 1 weight part of magnesia powder, 1.05 weight parts of sulfur and 1.03 weight parts of corundum powder into the neutral binder, and continuously stirring for 1 hour; (3) adding 3 parts by weight of alkylphenol polyoxyethylene ether and stirring for 45-60 minutes. Compared with the traditional refractory coating formed by quartz powder and bauxite, the refractory coating provided by the invention has the advantages that the combination of magnesia powder, boric acid and sulfur is added, so that the oxidation resistance and flame retardance of the shell can be improved, and the oxidation of magnesium alloy liquid is avoided; finally, the added alkylphenol polyoxyethylene ether can improve the surface activity of the wax mould, so that the fireproof coating has better coating capability.

As a further development of the invention, the sanding material of the fourth and fifth layers of the refractory coating in the step (A) is 50% by weight of precoated sand and 50% wt% of yellow sand, and the sanding material of the remaining refractory coatings is quartz sand. The fourth and fifth layers of refractory coating adopt precoated sand and yellow sand as sanding materials, so that the shell is convenient to clean, the increase of scrapped products caused by unclear shell cleaning (dead angle) is reduced, the collapsibility of the shell is increased, and the original air permeability of the shell is not influenced. And the sand spreading materials of the other layers adopt quartz sand, so that the strength of the shell is ensured.

As a further improvement of the invention, the roasting temperature of the middle-sized shell in the roasting furnace is 850 ℃ until no smoke exists, then the shell is taken out and put into the covering mixed solution for 5-8 minutes, then the shell is put into the roasting furnace again, the temperature is controlled to be 400-500 ℃ and kept for 0.5-1 hour, then the roasting furnace is closed, and the shell is taken out after the temperature is cooled to the casting temperature; the preparation method of the covering mixed solution comprises the following steps: 20 parts by weight of boric acid crystals are placed into 70 parts by weight of hot water, stirred to be completely dissolved, and 10 parts by weight of covering agent is added to be uniformly stirred. The method comprises the steps of roasting the shell at high temperature until no smoke exists, shaping the shell, setting the shell to have certain hardness, putting the shell into a covering mixed solution containing boric acid, covering the surface of the shell with a flame retardant, improving the flame retardant property of the shell, preserving the heat of the shell at 400-500 ℃ for 0.5-1 hour, cooling the shell to the casting temperature, eliminating the internal stress of the shell, and enabling the shape change to be very small during casting.

As a further improvement of the invention, the modeling in the step (A) is carried out in a modeling mechanism, the modeling mechanism comprises a sand box bottom plate for fixing a sand box, a mold shell is placed at the bottom center of an inner cavity of the sand box and a gate is downward, the sand box bottom plate is fixed on a swinging seat bottom plate, swinging seat vertical plates which are upwards erected are respectively arranged on the left side and the right side of the swinging seat bottom plate, swinging shafts which are outwards extended are respectively connected to the middle parts of the outer end surfaces of the two swinging seat vertical plates, the middle parts of the swinging shafts are respectively hinged to the upper ends of a fixed support, the outer ends of the swinging shafts are respectively connected with a driving disc, the outer end surfaces of the driving discs are respectively connected with a driving disc crank which is outwards extended, and the axis of the driving disc crank is parallel to the axis of the swinging shafts; the outer end of the driving disc crank is respectively connected with a rocker arm, the axis of the rocker arm is respectively perpendicular to the axis of the driving disc crank, the free end of the rocker arm is respectively connected with a rocker arm pin, the axis of the rocker arm pin is respectively parallel to the axis of the driving disc crank, the rocker arm pins are respectively inserted into waist-shaped long grooves at one end of a connecting rod and can slide along the waist-shaped long grooves, the free ends of the connecting rod are jointly hinged to a total driving rod, one end of the total driving rod is hinged to the free end of a cam, the fixed end of the cam is connected to a motor shaft of a motor, the motor is fixed on a motor seat, and the motor seat and the fixed support are respectively fixed on the ground. After the sand box inner cavity is filled with resin sand, the sand box inner cavity is fixed on a swinging seat bottom plate, a motor is started, the motor drives a cam to rotate, one end of a connecting rod is driven to do circular motion while a total driving rod rotates around the fixed end of the cam, the other end of the connecting rod drives a driving disc crank to swing through a rocker pin, the driving disc crank drives the driving disc to swing, the driving disc drives a swinging seat vertical plate and the swinging seat bottom plate to swing through a swinging shaft, the sand box swings back and forth on the swinging seat bottom plate, and the generated centrifugal force enables the resin sand to be gradually compact. Compared with manual pounding, the labor intensity is greatly reduced, and the modeling quality is ensured.

As a further improvement of the invention, in the step, the top of the lift tube is provided with a lift tube flange which is turned outwards, and the center of the top of the lift tube flange is provided with an annular groove; the inner cavity of the lift tube is nested with a transfusion tube coaxial with the lift tube, the top of the transfusion tube is provided with a transfusion tube flange which is turned outwards, and the transfusion tube flange is embedded in an annular groove of the lift tube flange; the infusion tube is formed by sequentially screwing a first movable block to a fifth movable block from bottom to top, the first movable block to the fifth movable block are coaxially connected with each other in a smooth transition mode, the inner cavity of the first movable block is conical with the upper part being small and the lower part being large, the inner cavity of the second movable block is conical with the upper part being small, the inner cavity of the third movable block is cylindrical, the top of the third movable block is provided with an arc transition section with the upper part being small, the inner cavity of the fourth movable block is cylindrical, and the inner cavity of the fifth movable block is conical with the upper part being small and the lower part being large. Because the infusion tube is nested in the liquid lifting tube, the liquid lifting tube is convenient to replace or combine, so that the shape of the section in the liquid lifting tube can be changed at will, and the combination is strong; the flow speed of the alloy liquid is controlled by utilizing the change of the inner cavity structure of the infusion tube, so that turbulent flow is not generated, and skimming is realized; the molten metal is stable in filling, the defects of oxide slag inclusion and the like can be reduced, and the casting is solidified under pressure and has compact structure and high mechanical property. When the liquid lifting pipe is frozen, the whole replacement is not needed. Each movable block is connected through threads and can be replaced independently so as to adapt to the weight and the structure of castings, alloy liquid flows from bottom to top in the process, the first stage is a drainage stage, the splayed necking of an inner cavity of each movable block can control the alloy liquid to be free of turbulence, and skimming is performed by utilizing the splayed shape. The second stage is a transition stage, the alloy liquid sequentially flows through the second movable block and the third movable block, the section of the inner cavity is primarily enlarged, the flow speed is reduced, and the gas rolling of the alloy liquid at the position can be avoided by utilizing the arc transition of the opening of the third movable block. The third stage is the final casting stage, the alloy liquid sequentially flows through the movable block IV and the movable block V, the flow speed in the movable block IV is further reduced, the mouth of the movable block V is splayed, the effect of secondary skimming is formed, and the flow speed is controlled.

As a further improvement of the invention, in the step of selecting, the lower port of the lift tube is closed, the circumference of the lower end of the lift tube is provided with a lift tube liquid inlet, the lift tube liquid inlet is provided with a pneumatic valve capable of closing or opening the lift tube liquid inlet, the circumference of the lift tube on one side of the lift tube liquid inlet is provided with a pneumatic valve cavity capable of accommodating the pneumatic valve, the upper end and the lower end of the lift tube liquid inlet and the pneumatic valve cavity are respectively provided with a door rail for sliding the pneumatic valve, the upper end and the lower end of the inner end of the pneumatic valve cavity are respectively fixedly connected with a tension spring, and the other end of the tension spring extends along the arc of the pneumatic valve cavity and is connected with the door frame of the pneumatic valve; the circumferential wall of the lift tube is also provided with an inert gas axial duct which is communicated in the axial direction, and the middle part of the inner end of the pneumatic valve cavity is communicated with the inert gas axial duct through a door closing pushing inlet. The liquid inlet of the liquid lifting pipe is arranged on the circumference of the lower end of the liquid lifting pipe, slag is not easy to be sucked into the bottom of the heat preservation furnace, the distance between the lower end of the liquid lifting pipe and the bottom of the furnace can be shortened, and the material waste of alloy liquid is reduced. After the alloy liquid is modified in the furnace, directly closing the box, sealing the box, then inputting high-pressure inert gas into an inert gas axial pore canal, wherein a part of inert gas enters a pneumatic valve cavity from a door closing push inlet, pushing a pneumatic valve to overcome the tension of a tension spring to advance so as to close a liquid inlet of a liquid lifting pipe, and the other part of inert gas leads to the bottom of the alloy liquid to refine and degas the alloy liquid, so that the alloy liquid is in limited contact with air, the refining and degassing effects are greatly improved, and the quality of the alloy liquid is improved; inert gas is adopted for degassing, so that the method is safe, pollution-free and high in efficiency. After refining, inert gas is stopped being input, the pneumatic valve is retracted into the pneumatic valve cavity under the action of the tension spring, the liquid inlet of the liquid lifting pipe is opened, the air inlet pipe on the sealing cover is used for air inlet, alloy liquid enters the inner cavity of the liquid lifting pipe, and the cavity of the shell is filled.

Drawings

The invention will now be described in further detail with reference to the drawings and the detailed description, which are provided for reference and illustration only and are not intended to limit the invention.

Fig. 1 is a front view of a middle-sized case of the present invention.

Fig. 2 is a left side view of fig. 1.

Fig. 3 is a perspective view of fig. 1.

Fig. 4 is a diagram showing the operation of the molding mechanism used in the present invention.

Fig. 5 is a working state diagram of the first embodiment of the present invention during filling.

Fig. 6 is a schematic view of the lift tube of fig. 5.

Fig. 7 is a working state diagram of the second embodiment of the present invention in the mold filling process.

Fig. 8 is a front view of the lift tube of fig. 7.

Fig. 9 is a cross-sectional view of the inert gas ventilation state along A-A in fig. 8.

FIG. 10 is a cross-sectional view taken along A-A of the inert gas closed state of FIG. 8.

Fig. 11 is a perspective view of the lift tube inlet of fig. 8 in an open position.

Fig. 12 is a cross-sectional view of the inert gas ventilation state of fig. 11.

Fig. 13 is a cross-sectional view of the inert gas closed state of fig. 11.

In the figure: 1. a shell; a u-shaped cavity; 1b, pouring cup; 1c, upper ingate; 1d, upper cross gate; 1e, a lower ingate; 1f, a lower runner; 1g, transitional straight pouring gate; 1h, buffering the packet; 1j, a gas gathering groove; 2. a sand box; 3. a sand box bottom plate; 4. a swinging seat bottom plate; 5. a swinging seat riser; 6. a swing shaft; 7. a fixed bracket; 8. a drive plate; 9. driving a disk crank; 10. a rocker arm; 11. a rocker arm pin; 12. a connecting rod; 12a, a waist-shaped long groove; 13. a total drive rod; 14. a cam; 15. a motor; 16. a motor base; 17. a compression bar; 18. a heating unit; 19. a holding furnace; 20. sealing cover; 20a, an air inlet pipe; 21. a lift tube; 21a, a liquid inlet of a liquid lifting pipe; 21b. Inert gas axial duct; 21c, closing the door pushing inlet; 21d, pneumatic valve cavity; 21e, door rail; 21f, pneumatic valve; 21g, a tension spring; 22. an infusion tube; 22a, a movable block I; 22b, a second movable block; 22c, a movable block III; 22d, a movable block IV; 22e, a movable block five; 22f, a transfusion tube flange.

Detailed Description

In the following description of the present invention, the terms "front", "rear", "left", "right", etc. indicate an azimuth or a positional relationship based on the azimuth or the positional relationship shown in the drawings, and are merely for convenience of description of the present invention and for simplification of description, and do not mean that the apparatus must have a specific azimuth.

As shown in fig. 1 to 7, the differential pressure pouring system of the U-shaped magnesium alloy part of the present invention comprises a sand box 2 arranged above a sealing cover 20, a liquid lifting pipe 21 is arranged in the center of the sealing cover 20, the lower end of the liquid lifting pipe 21 stretches into the lower part of a heat preservation furnace 19, a mold shell 1 is arranged in the sand box 2, the mold shell 1 comprises a U-shaped cavity 1a with two arms stretching forwards, an upper ingate 1c respectively connected with the two arms and the common end of the U-shaped cavity 1a is arranged at the top of the U-shaped cavity 1a, and the upper end of each upper ingate 1c is respectively connected with an upper runner 1 d; the bottom of the U-shaped cavity 1a is provided with lower inner runners 1e which are respectively connected with two arms and a common end of the U-shaped cavity 1a, the lower end of each lower inner runner 1e is respectively connected with a lower cross runner 1f, a vertically extending transitional straight runner 1g is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of the transitional straight runner 1g are respectively connected with the middle parts of an upper cross runner 1d and a lower cross runner 1 f; the total sectional area of the lower ingate 1e connected with the U-shaped cavity 1a is larger than the total sectional area of the upper ingate 1c connected with the U-shaped cavity 1 a; the bottom center of the lower runner 1f is connected with a pouring cup 1b with a downward opening; the lower port of the pouring cup 1b is butted with the upper port of the liquid lifting pipe 21; the top of the lift tube 21 is provided with a lift tube flange which is turned outwards, and the center of the top of the lift tube flange is provided with an annular groove; the inner cavity of the lift tube 21 is nested with a transfusion tube 22 coaxial with the lift tube 21, the top of the transfusion tube 22 is provided with a transfusion tube flange which is turned outwards, and the transfusion tube flange is embedded in an annular groove of the lift tube flange.

The top of the upper runner 1d is connected with a plurality of gas gathering grooves 1j, so that the gas can be conveniently exhausted from the top. The side walls of the lower ends of the lower ingates 1e are respectively connected with buffer bags 1h, and the free ends of the buffer bags 1h are blind ends and respectively tilt upwards. The buffer bag 1h is positioned at the connecting part of the lower ingate 1e and the lower transverse pouring gate 1f, can buffer the impact force of the magnesium liquid, can buffer the phenomenon of over-fast and over-current of the magnesium liquid caused by over-fast pouring speed due to unstable manual end bag in the pouring process, and reduces the secondary oxide slag generated by unstable pouring of the magnesium liquid.

The air inlet pipe 20a on the sealing cover 20 is used for air inlet, the molten metal rises along the liquid lifting pipe 21 under the air pressure in the heat preservation furnace 19, enters the lower inner pouring gate 1e from the pouring gate, then enters the U-shaped cavity 1a from the lower inner pouring gate 1e, and the air pressure in the heat preservation furnace 19 is kept until the molten metal in the cavity is completely solidified to form a casting.

The total sectional area of the lower ingate 1e connected with the U-shaped cavity 1a is larger than the total sectional area of the upper ingate 1c connected with the U-shaped cavity 1 a. The number of the upper inner pouring gate 1c connected with the U-shaped cavity 1a is smaller than that of the lower inner pouring gate 1e connected with the U-shaped cavity 1a, and according to the principle that the pressure is equal to the pressure multiplied by the area, the upper inner pouring gate 1c and the lower inner pouring gate 1e form pressure differences in the pressurizing and pressure maintaining stages of pouring, and castings can be sequentially solidified from top to bottom, so that the compactness of products is ensured.

Because the infusion tube 22 is nested in the liquid lifting tube 21, the replacement or the combination are convenient, the shape of the section in the liquid lifting tube 21 can be changed at will, and the combination is strong; the flow rate of the alloy liquid is controlled by utilizing the inner cavity structure transformation of the infusion tube 22, so that turbulent flow is not generated, and skimming is realized; the molten metal is stable in filling, the defects of oxide slag inclusion and the like can be reduced, and the casting is solidified under pressure and has compact structure and high mechanical property. When the liquid lifting pipe 21 is frozen, the infusion pipe 22 can be replaced independently.

The infusion tube 22 is formed by sequentially screwing a first movable block 22a to a fifth movable block 22e from bottom to top, the first movable block 22a and the fifth movable block 22e are coaxial and are in smooth transitional connection, the inner cavity of the first movable block 22a is conical with the upper part being small and the lower part being large, the inner cavity of a second movable block 22b is conical with the upper part being large and the lower part being small, the inner cavity of a third movable block 22c is cylindrical and the top is provided with an arc transitional section with the upper part being large and the lower part being small, the inner cavity of a fourth movable block 22d is cylindrical, and the inner cavity of the fifth movable block 22e is conical with the upper part being small and the lower part being large. Each movable block can be independently replaced through threaded connection so as to adapt to the weight and the structural requirement of the casting.

The flow rate of the alloy liquid can be well controlled and the skimming effect can be exerted by the wine pot-shaped flow passage in the inner cavity of the infusion tube 22. The alloy liquid flows from bottom to top, the first stage is a drainage stage, the splayed necking of the inner cavity of the movable block I22 a can control the alloy liquid not to be turbulent, and skimming is carried out by utilizing the splayed shape. The second stage is a transition stage, the alloy liquid sequentially flows through the second movable block 22b and the third movable block 22c, the cross section of the inner cavity is primarily enlarged, the flow speed is reduced, and the arc transition of the opening of the third movable block 22c can be utilized to avoid the alloy liquid from being curled up. The third stage is the final casting stage, the alloy liquid sequentially flows through the movable block IV 22d and the movable block V22 e, the flow speed in the movable block IV 22d is further reduced, the mouth of the movable block V22 e is splayed, the effect of secondary skimming is formed, and the flow speed is controlled.

Example 1

The invention relates to a differential pressure casting method of a U-shaped magnesium alloy part, which sequentially comprises the following steps: the method comprises the steps that an appearance mould of a U-shaped workpiece model and a core box mould for manufacturing a core are manufactured respectively, wherein the appearance mould comprises an upper mould and a lower mould which are symmetrical, and mould cavities of the upper mould and the lower mould can be encircled to form the appearance of the U-shaped workpiece model; injecting the soluble material into a core box die under high pressure, cooling and shaping, and taking out the soluble material from the core box die to obtain a soluble core; positioning and placing the soluble core in a mold cavity of the appearance mold, and combining and locking an upper mold and a lower mold; fourthly, preparing a die material required for manufacturing the U-shaped workpiece model in a wax melting machine, and injecting the die material into a die cavity of a profile die; fifthly, cooling and shaping the die material to form a U-shaped workpiece integral model, separating the upper die from the lower die, and taking out the U-shaped workpiece integral model; sixth, immersing the whole model of the U-shaped workpiece in water, and dissolving the soluble core to obtain a wax model of the U-shaped workpiece; assembling the U-shaped workpiece wax mould and other parts of the pouring system to form a complete casting wax mould; the casting wax mould comprises a U-shaped cavity with two arms extending forwards, wherein the top of the U-shaped cavity is provided with upper inner runners respectively connected with the two arms and the common end of the U-shaped cavity, and the upper ends of the upper inner runners are respectively connected with the upper cross runners; the bottom of the U-shaped cavity is provided with lower inner runners respectively connected with two arms and a common end of the U-shaped cavity, the lower end of each lower inner runner is respectively connected with a lower cross runner, a vertically extending transitional straight runner is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of the transitional straight runner are respectively connected with the middle parts of the upper cross runner and the lower cross runner; the total sectional area of the lower inner runner is larger than that of the upper inner runner; the center of the bottom of the lower horizontal pouring gate is connected with a pouring cup with a downward opening; soaking a casting wax mould in boric acid for 4-6 minutes to remove grease, then coating fire-resistant surface slurry on the surface of the casting wax mould, forming a fire-resistant surface layer after solidification, bonding a heat pipe extending horizontally outwards on the fire-resistant surface layer, bonding an inner end head of the heat pipe at a hot joint of the U-shaped workpiece wax mould, and mounting a copper block at an outer end head of the heat pipe; continuously brushing a fireproof coating on the periphery of a fireproof surface layer, sanding the fireproof coating to form a first fireproof coating, continuously brushing the fireproof coating, sanding to sequentially form a second fireproof coating to a sixth fireproof coating, and curing to form a shell wrapping the periphery of the casting wax mould; putting the shell into a dewaxing kettle, and dewaxing by adopting hot water; putting the dewaxed shell into a roasting furnace for roasting, cooling to the casting temperature and taking out; placing the molded shell 1 in a sand box 2, filling resin sand between the molded shell 1 and the sand box 2 for molding, and curing after the resin sand is filled and compacted; the mold shell 1 and the sand box 2 are placed above a sealing cover 20 of a heat preservation furnace 19, a liquid lifting pipe 21 is arranged in the center of the sealing cover 20, the lower end of the liquid lifting pipe 21 extends to the lower part of the heat preservation furnace 19, a pouring gate of the mold shell 1 is downward in butt joint with the liquid lifting pipe 21, magnesium metal liquid enters an inner cavity of the mold shell through the liquid lifting pipe 21 to be filled, and after pressure boosting, pressure maintaining and pressure relief, a U-shaped magnesium alloy piece is obtained through cooling.

The preparation method of the soluble material in the step (A) is as follows: (1) the raw materials and the industrial urea are prepared according to the following components in parts by weight: 52 parts of nitrate: 23 parts of polyethylene glycol: 16 parts of purified water: 9 parts; (2) mixing industrial urea and purified water, heating to melt, uniformly stirring, adding nitrate and polyethylene glycol, and uniformly stirring. The water absorption and brittleness of the industrial urea are improved by adopting nitrate and polyethylene glycol in the soluble material, and the surface smoothness of the core can be improved after high-pressure injection molding; after the U-shaped workpiece integral model is put into water, the water dissolution speed of the mold core is high, and the production efficiency is improved.

And step three, when the upper die and the lower die are combined, positioning pins at four corners of the upper die are respectively inserted into positioning pin holes at four corners of the lower die, and compression springs are respectively arranged between the lower end heads of the positioning pins and the bottoms of the corresponding positioning pin holes. After the pressure that the top surface of the upper die received is eliminated, compression spring's tension is upwards ejecting a little distance with the locating pin, solves the problem that upper die and lower mould are difficult to separate, and the prizing bad upper die even damages the model when avoiding getting the model.

The manufacturing method of the molding compound in the step four is as follows: firstly, melting 20wt% of Sichuan wax, adding 5wt% of polyethylene and 5wt% of ethyl cellulose while stirring, adding 40wt% of rosin after the mixture is completely melted, and finally adding 30wt% of paraffin after the mixture is completely melted, and stirring uniformly. The surface finish of the wax mould made of the mould material is high, the roughness index can reach 1.6, the shrinkage rate of the wax mould can be reduced from 0.88% to 0.78%, and the size precision of the wax mould is higher.

Brushing the outer end of the heat pipe with a steel brush to strengthen the surface adsorption force, then coating soldering paste, controlling the thickness of the soldering paste to be 0.5mm-1mm, inserting a copper block at the outer end of the heat pipe, adjusting the temperature of a hot air gun to 500 ℃, baking a welding position, and cooling and solidifying when the color of the heat pipe changes from gray to silver and yellow transparent rosin flows out; therefore, good heat conductivity between the heat pipe and the copper block can be ensured, the heat pipe can be reused, and the cost is reduced.

The fireproof surface slurry in the step F is formed by uniformly mixing fireproof paint and corundum powder, and the preparation method of the fireproof paint comprises the following steps: (1) the raw materials and the silicon dioxide are prepared according to the following components by weight: 25 parts of water: 15 parts of absolute alcohol: 20 parts of magnesium oxide powder: 15 parts of boric acid: 20 parts of sulfur: 5 parts of the components are uniformly mixed and stirred to form a neutral binder, and the temperature is controlled at 30-40 ℃; (2) adding 1 weight part of magnesia powder, 1.05 weight parts of sulfur and 1.03 weight parts of corundum powder into the neutral binder, and continuously stirring for 1 hour; (3) adding 3 parts by weight of alkylphenol polyoxyethylene ether and stirring for 45-60 minutes. Compared with the traditional refractory coating formed by quartz powder and bauxite, the refractory coating provided by the invention has the advantages that the combination of magnesia powder, boric acid and sulfur is added, so that the oxidation resistance and flame retardance of the shell can be improved, and the oxidation of magnesium alloy liquid is avoided; finally, the added alkylphenol polyoxyethylene ether can improve the surface activity of the wax mould, so that the fireproof coating has better coating capability.

The sand spraying materials of the fourth and fifth layers of refractory coatings in the step of spraying are 50wt% of precoated sand and 50wt% of yellow sand, and the sand spraying materials of the rest refractory coatings are quartz sand. The fourth and fifth layers of refractory coating adopt precoated sand and yellow sand as sanding materials, so that the shell is convenient to clean, the increase of scrapped products caused by unclear shell cleaning (dead angle) is reduced, the collapsibility of the shell is increased, and the original air permeability of the shell is not influenced. And the sand spreading materials of the other layers adopt quartz sand, so that the strength of the shell is ensured.

In the step, the dewaxed shell 1 comprises a U-shaped cavity 1a with two arms extending forwards, wherein an upper ingate 1c connected with the two arms and the common end of the U-shaped cavity 1a is arranged at the top of the U-shaped cavity 1a, and the upper ends of the upper ingates 1c are connected with an upper cross runner 1d respectively; the bottom of the U-shaped cavity 1a is provided with lower inner runners 1e which are respectively connected with two arms and a common end of the U-shaped cavity 1a, the lower end of each lower inner runner 1e is respectively connected with a lower cross runner 1f, a vertically extending transitional straight runner 1g is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of the transitional straight runner 1g are respectively connected with the middle parts of an upper cross runner 1d and a lower cross runner 1 f; the total sectional area of the lower ingate 1e connected with the U-shaped cavity 1a is larger than the total sectional area of the upper ingate 1c connected with the U-shaped cavity 1 a; the pouring cup 1b with a downward opening is connected to the bottom center of the lower runner 1 f.

The top of the upper runner 1d is connected with a plurality of gas gathering grooves 1j, so that the gas can be conveniently exhausted from the top. The side walls of the lower ends of the lower ingates 1e are respectively connected with buffer bags 1h, and the free ends of the buffer bags 1h are blind ends and respectively tilt upwards.

Step two, the roasting temperature of the middle-sized shell in the roasting furnace is 850 ℃ until no smoke exists, then the shell is taken out and put into the covering mixed solution for 5-8 minutes, then the shell is put into the roasting furnace again, the temperature is controlled to be 400-500 ℃ and kept for 0.5-1 hour, then the roasting furnace is closed, and the shell is taken out after the temperature is cooled to the casting temperature; the preparation method of the covering mixed solution comprises the following steps: 20 parts by weight of boric acid crystals are placed into 70 parts by weight of hot water, stirred to be completely dissolved, and 10 parts by weight of covering agent is added to be uniformly stirred. The method comprises the steps of roasting the shell at high temperature until no smoke exists, shaping the shell, setting the shell to have certain hardness, putting the shell into a covering mixed solution containing boric acid, covering the surface of the shell with a flame retardant, improving the flame retardant property of the shell, preserving the heat of the shell at 400-500 ℃ for 0.5-1 hour, cooling the shell to the casting temperature, eliminating the internal stress of the shell, and enabling the shape change to be very small during casting.

As shown in fig. 4, the modeling in the step (2) is performed in a modeling mechanism, the modeling mechanism comprises a sand box bottom plate (3) for fixing a sand box (2), a mold shell (1) is arranged in the center of the bottom of an inner cavity of the sand box, a pouring gate of the mold shell (1) is downward, the sand box bottom plate (3) is fixed on a swing seat bottom plate (4), swing seat vertical plates (5) which are erected upwards are respectively arranged on the left side and the right side of the swing seat bottom plate (4), swing shafts (6) which extend outwards are respectively connected to the middle parts of the outer end surfaces of the two swing seat vertical plates (5), the middle parts of the swing shafts (6) are respectively hinged to the upper ends of a fixed support (7), driving discs (8) are respectively connected to the outer ends of the swing shafts (6), driving disc (9) which extend outwards are respectively connected to the outer end surfaces of the driving disc (8), and the axes of the driving disc cranks (9) are parallel to the axes of the swing shafts (6); the connection points of the driving disc crank 9 and the swinging shaft 6 and the driving disc 8 are respectively positioned at two ends of the diameter of the driving disc. The outer end of the driving disc crank 9 is respectively connected with a rocker arm 10, the axis of the rocker arm 10 is respectively perpendicular to the axis of the driving disc crank 9, the free end of the rocker arm 10 is respectively connected with a rocker arm pin 11, the axis of the rocker arm pin 11 is respectively parallel to the axis of the driving disc crank 9, the rocker arm pins 11 are respectively inserted into waist-shaped long grooves 12a at one end of a connecting rod 12 and can slide along the waist-shaped long grooves 12a, the free ends of the connecting rod 12 are jointly hinged on a total driving rod 13, one end of the total driving rod 13 is hinged on the free end of a cam 14, the fixed end of the cam 14 is connected on a motor shaft of a motor 15, the motor 15 is fixed on a motor seat 16, and the motor seat 16 and a fixed bracket 7 are respectively fixed on the ground.

After the inner cavity of the sand box 2 is filled with resin sand, the sand box is fixed on the swinging seat bottom plate 4, the motor 15 is started, the motor 15 drives the cam 14 to rotate, the total driving rod 13 rotates around the fixed end of the cam 14 and drives one end of the connecting rod 12 to do circular motion, the other end of the connecting rod 12 drives the driving disc crank 9 to swing through the rocker pin 11, the driving disc crank 9 drives the driving disc 8 to swing, the driving disc 8 drives the swinging seat vertical plate 5 and the swinging seat bottom plate 4 to swing through the swinging shaft 6, the sand box 2 swings back and forth on the swinging seat bottom plate 4, and the generated centrifugal force enables the resin sand to be gradually compact. Compared with manual pounding, the labor intensity is greatly reduced, and the modeling quality is ensured.

The sand box 2 is level with the tops of the swinging seat risers 5, a compression bar 17 is connected between the tops of the two swinging seat risers 5, and the middle part of the compression bar 17 is pressed at the top of the sand box 2. The sand box 2 can be fixed on the sand box bottom plate 3 by screwing the screws at the two ends of the compression bar 17, so that the sand box is very convenient and quick.

The center of the outer end surface of the swinging seat vertical plate 5 is respectively provided with a heating unit 18. The swinging seat vertical plate 5 is made of copper, and heat generated by the heating unit 18 is transferred to the sand box 2 through the swinging seat vertical plate 5, so that the curing time of resin sand is shortened, and the production efficiency is improved.

The sand box bottom plate 3 is provided with a sand box positioning groove and a mould shell positioning groove, the bottom of the sand box 2 is provided with a sand box positioning tenon which extends downwards, and the sand box positioning tenon is inserted into the sand box positioning groove; the bottom of the shell 1 is provided with a mould shell positioning tenon which extends downwards, and the mould shell positioning tenon is inserted into a mould shell positioning groove, so that the shell 1 and the sand box 2 can be positioned quickly and accurately.

In the step, a lift tube flange which is turned outwards is arranged at the top of the lift tube 21, and an annular groove is arranged in the center of the top of the lift tube flange; the inner cavity of the lift tube 21 is nested with a transfusion tube 22 coaxial with the lift tube 21, the top of the transfusion tube 22 is provided with a transfusion tube flange 22f which is turned outwards, and the transfusion tube flange 22f is embedded in an annular groove of the lift tube flange.

As shown in fig. 5 and 6, the air inlet pipe 20a on the sealing cover 20 is used for air inlet, the molten metal rises along the liquid lifting pipe 21 under the air pressure in the holding furnace 19 and enters the shell 1, and the air pressure in the holding furnace 19 is kept until the molten metal in the cavity is completely solidified to form a casting. Because the infusion tube 22 is nested in the liquid lifting tube 21, the replacement or the combination are convenient, the shape of the section in the liquid lifting tube 21 can be changed at will, and the combination is strong; the flow rate of the alloy liquid is controlled by utilizing the inner cavity structure transformation of the infusion tube 22, so that turbulent flow is not generated, and skimming is realized; the molten metal is stable in filling, the defects of oxide slag inclusion and the like can be reduced, and the casting is solidified under pressure and has compact structure and high mechanical property. When the liquid lifting pipe 21 is frozen, the infusion pipe 22 can be replaced independently.

Example two

The other steps are the same as those in the first embodiment, and the adopted lift tube 21 has a different structure, as shown in fig. 7-13, in the step, the lower port of the lift tube 21 is closed, the circumference of the lower end of the lift tube 21 is provided with a lift tube liquid inlet 21a, the lift tube liquid inlet 21a is provided with a pneumatic valve 21f capable of closing or opening the lift tube liquid inlet, the circumference of the lift tube on one side of the lift tube liquid inlet 21a is provided with a pneumatic valve cavity 21d capable of accommodating the pneumatic valve 21f, the upper end and the lower end of the lift tube liquid inlet 21a and the pneumatic valve cavity 21d are respectively provided with a door rail 21e for sliding the pneumatic valve 21f, the upper end and the lower end of the inner end of the pneumatic valve cavity 21d are respectively fixedly connected with a tension spring 21g, and the other end of the tension spring 21g respectively extends along the circular arc of the pneumatic valve cavity 21d and is connected with a door frame of the pneumatic valve 21 f; the circumferential wall of the lift tube 21 is also provided with an inert gas axial duct 21b which is communicated in the axial direction, and the middle part of the inner end of the pneumatic valve cavity is communicated with the inert gas axial duct 21b through a door closing pushing inlet 21 c.

The liquid inlet 21a of the liquid lifting pipe is arranged on the circumference of the lower end of the liquid lifting pipe 21, slag is not easy to be sucked into the bottom of the holding furnace 19, the distance between the lower end of the liquid lifting pipe 21 and the bottom of the furnace can be shortened, and the material waste of alloy liquid is reduced. After the alloy liquid is modified in the furnace, the box closing and box sealing operation are directly carried out, then high-pressure inert gas is input into an inert gas axial pore canal 21b, one part of inert gas enters a pneumatic valve cavity 21d from a door closing push inlet 21c, a pneumatic valve 21f is pushed to overcome the tension of a tension spring 21g to advance so as to close a liquid inlet 21a of a liquid lifting pipe, and the other part of inert gas is led to the bottom of the alloy liquid to refine and degas the alloy liquid, so that the degassing is carried out in a closed environment, the contact space between the alloy liquid and air is limited, the refining and degassing effect is greatly improved, and the quality of the alloy liquid is improved; inert gas is adopted for degassing, so that the method is safe, pollution-free and high in efficiency. After refining, inert gas is stopped being input, the pneumatic valve 21f is retracted into the pneumatic valve cavity 21d under the action of the tension spring 21g, the liquid inlet 21a of the liquid lifting pipe is opened, the air inlet pipe 20a on the sealing cover 20 is used for air inlet, alloy liquid enters the inner cavity of the liquid lifting pipe, and the cavity of the shell 1 is filled.

The foregoing description is only of a preferred embodiment of the invention and is not intended to limit the scope of the invention. In addition to the embodiments described above, other embodiments of the invention are possible. All technical schemes formed by equivalent substitution or equivalent transformation fall within the protection scope of the invention.

Claims

1. The utility model provides a differential pressure casting system of U-shaped magnesium alloy spare, includes the sand box of arranging in sealed lid top, the center of sealed lid is equipped with the stalk, the lower part of holding furnace is stretched into to the lower extreme of stalk, be equipped with the shell in the sand box, the shell includes the U-shaped die cavity that both arms stretched out forward, characterized by: the top of the U-shaped cavity is provided with upper inner runners respectively connected with two arms and a common end of the U-shaped cavity, and the upper ends of the upper inner runners are respectively connected with upper cross runners; the bottom of the U-shaped cavity is provided with lower inner runners respectively connected with two arms and a common end of the U-shaped cavity, the lower end of each lower inner runner is respectively connected with a lower cross runner, a vertically extending transitional straight runner is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of each transitional straight runner are respectively connected with the middle parts of the upper cross runner and the lower cross runner; the total cross-sectional area of the lower ingate is larger than the total cross-sectional area of the upper ingate; the center of the bottom of the lower cross runner is connected with a pouring cup with a downward opening; the top of the upper cross runner is connected with a plurality of gas gathering grooves; the side walls of the lower ends of the lower ingates are respectively connected with buffer bags, and the free ends of the buffer bags are blind ends and respectively tilt upwards.

2. The differential pressure casting system of U-shaped magnesium alloy parts according to claim 1, wherein the lower port of the tundish is in abutment with the upper port of the lift tube; the top of the lift tube is provided with a lift tube flange which is turned outwards, and the center of the top of the lift tube flange is provided with an annular groove; the inner cavity of the lift tube is nested with a transfusion tube coaxial with the lift tube, the top of the transfusion tube is provided with a transfusion tube flange which is turned outwards, and the transfusion tube flange is embedded in an annular groove of the lift tube flange; the infusion tube is formed by sequentially screwing a first movable block to a fifth movable block from bottom to top, the first movable block to the fifth movable block are coaxially connected with each other in a smooth transition mode, the inner cavity of the first movable block is conical with the upper part being small and the lower part being large, the inner cavity of the second movable block is conical with the upper part being small, the inner cavity of the third movable block is cylindrical, the top of the third movable block is provided with an arc transition section with the upper part being small, the inner cavity of the fourth movable block is cylindrical, and the inner cavity of the fifth movable block is conical with the upper part being small and the lower part being large.

3. The differential pressure casting method of the U-shaped magnesium alloy piece is characterized by comprising the following steps in sequence: the method comprises the steps that an appearance mould of a U-shaped workpiece model and a core box mould for manufacturing a core are manufactured respectively, wherein the appearance mould comprises an upper mould and a lower mould which are symmetrical, and mould cavities of the upper mould and the lower mould can be encircled to form the appearance of the U-shaped workpiece model; injecting the soluble material into a core box die under high pressure, cooling and shaping, and taking out the soluble material from the core box die to obtain a soluble core; positioning and placing the soluble core in a mold cavity of the appearance mold, and combining and locking an upper mold and a lower mold; fourthly, preparing a die material required for manufacturing the U-shaped workpiece model in a wax melting machine, and injecting the die material into a die cavity of a profile die; fifthly, cooling and shaping the die material to form a U-shaped workpiece integral model, separating the upper die from the lower die, and taking out the U-shaped workpiece integral model; sixth, immersing the whole model of the U-shaped workpiece in water, and dissolving the soluble core to obtain a wax model of the U-shaped workpiece; assembling the U-shaped workpiece wax mould and other parts of the pouring system to form a complete casting wax mould; the casting wax mould comprises a U-shaped cavity with two arms extending forwards, wherein the top of the U-shaped cavity is provided with upper inner runners respectively connected with the two arms and the common end of the U-shaped cavity, and the upper ends of the upper inner runners are respectively connected with upper cross runners; the bottom of the U-shaped cavity is provided with lower inner runners respectively connected with two arms and a common end of the U-shaped cavity, the lower end of each lower inner runner is respectively connected with a lower cross runner, a vertically extending transitional straight runner is arranged between the two arms of the U-shaped cavity, and the upper end and the lower end of each transitional straight runner are respectively connected with the middle parts of the upper cross runner and the lower cross runner; the total cross-sectional area of the lower ingate is larger than the total cross-sectional area of the upper ingate; the center of the bottom of the lower cross runner is connected with a pouring cup with a downward opening; soaking a casting wax mould in boric acid for 4-6 minutes to remove grease, then coating fire-resistant surface slurry on the surface of the casting wax mould, forming a fire-resistant surface layer after solidification, bonding a heat pipe extending horizontally outwards on the fire-resistant surface layer, bonding an inner end head of the heat pipe at a hot joint of the U-shaped workpiece wax mould, and mounting a copper block at an outer end head of the heat pipe; continuously brushing a fireproof coating on the periphery of a fireproof surface layer, sanding the fireproof coating to form a first fireproof coating, continuously brushing the fireproof coating, sanding to sequentially form a second fireproof coating to a sixth fireproof coating, and curing to form a shell wrapping the periphery of the casting wax mould; putting the shell into a dewaxing kettle, and dewaxing by adopting hot water; putting the dewaxed shell into a roasting furnace for roasting, cooling to the casting temperature and taking out; placing the mould shell in a sand box, filling resin sand between the mould shell and the sand box for moulding, and curing after the resin sand is filled and compacted; the mold shell and the sand box are placed above a sealing cover of a heat preservation furnace, a liquid lifting pipe is arranged in the center of the sealing cover, a pouring cup of the mold shell is in butt joint with the liquid lifting pipe downwards, magnesium metal liquid enters an inner cavity of the mold shell through the liquid lifting pipe to be filled, and after pressure boosting, pressure maintaining and pressure relief, the mold shell is cooled to obtain a U-shaped magnesium alloy piece.

4. The differential pressure casting method of the U-shaped magnesium alloy part according to claim 3, wherein the preparation method of the soluble material in the step (c) is as follows: (1) the raw materials and the industrial urea are prepared according to the following components in parts by weight: 52 parts of nitrate: 23 parts of polyethylene glycol: 16 parts of purified water: 9 parts; (2) mixing industrial urea and purified water, heating to melt, uniformly stirring, adding nitrate and polyethylene glycol, and uniformly stirring.

5. The differential pressure casting method of the U-shaped magnesium alloy part according to claim 3, wherein in the step of combining the upper die and the lower die, positioning pins at four corners of the upper die are respectively inserted into positioning pin holes at four corners of the lower die, and compression springs are respectively arranged between the lower end heads of the positioning pins and the bottoms of the corresponding positioning pin holes.

6. The method for differential pressure casting of U-shaped magnesium alloy parts according to claim 3, wherein the method for manufacturing the mold material in step ii is as follows: firstly, melting 20wt% of Sichuan wax, adding 5wt% of polyethylene and 5wt% of ethyl cellulose while stirring, adding 40wt% of rosin after the mixture is completely melted, and finally adding 30wt% of paraffin after the mixture is completely melted, and stirring uniformly.

7. The differential pressure casting method of the U-shaped magnesium alloy part according to claim 3, wherein the refractory surface slurry in the step of forming is formed by uniformly mixing refractory paint and corundum powder, and the preparation method of the refractory paint is as follows: (1) the raw materials and the silicon dioxide are prepared according to the following components by weight: 25 parts of water: 15 parts of absolute alcohol: 20 parts of magnesium oxide powder: 15 parts of boric acid: 20 parts of sulfur: 5 parts of the components are uniformly mixed and stirred to form a neutral binder, and the temperature is controlled at 30-40 ℃; (2) adding 1 weight part of magnesia powder, 1.05 weight parts of sulfur and 1.03 weight parts of corundum powder into the neutral binder, and continuously stirring for 1 hour; (3) adding 3 parts by weight of alkylphenol polyoxyethylene ether and stirring for 45-60 minutes.

8. A method of differential pressure casting of U-shaped magnesium alloy parts according to claim 3, wherein the fourth and fifth refractory coatings in step c h a r a c t e r i z e d in that the sand material of the fourth and fifth refractory coatings is 50wt% precoated sand and 50wt% yellow sand, and the sand material of the remaining refractory coatings is quartz sand.

9. The method for casting U-shaped magnesium alloy part by differential pressure according to claim 3, wherein the baking temperature of the middle-sized shell in the baking furnace is 850 ℃ until no smoke exists, then the shell is taken out and put into the covering mixed solution for 5-8 minutes, then the shell is put into the baking furnace again, the temperature is controlled to be 400-500 ℃ and kept for 0.5-1 hour, then the baking furnace is closed, and the shell is taken out after the temperature is cooled to the casting temperature; the preparation method of the covering mixed solution comprises the following steps: 20 parts by weight of boric acid crystals are placed into 70 parts by weight of hot water, stirred to be completely dissolved, and 10 parts by weight of covering agent is added to be uniformly stirred.

10. The differential pressure pouring method of the U-shaped magnesium alloy part according to claim 3, wherein the modeling in the self-curing step is performed in a modeling mechanism, the modeling mechanism comprises a sand box bottom plate for fixing a sand box, a mold shell is placed at the bottom center of an inner cavity of the sand box and a gate is downward, the sand box bottom plate is fixed on a swinging seat bottom plate, swinging seat vertical plates which are upwards erected are respectively arranged on the left side and the right side of the swinging seat bottom plate, swinging shafts which are outwards extended are respectively connected to the middle parts of the outer end surfaces of the two swinging seat vertical plates, the middle parts of the swinging shafts are respectively hinged to the upper ends of a fixed support, the outer end heads of the swinging shafts are respectively connected with driving discs, the outer end surfaces of the driving discs are respectively connected with driving disc swinging handles which are outwards extended, and the axes of the driving disc swinging handles are parallel to the axes of the swinging shafts; the outer end of the driving disc crank is respectively connected with a rocker arm, the axis of the rocker arm is respectively perpendicular to the axis of the driving disc crank, the free end of the rocker arm is respectively connected with a rocker arm pin, the axis of the rocker arm pin is respectively parallel to the axis of the driving disc crank, the rocker arm pins are respectively inserted into waist-shaped long grooves at one end of a connecting rod and can slide along the waist-shaped long grooves, the free ends of the connecting rod are jointly hinged to a total driving rod, one end of the total driving rod is hinged to the free end of a cam, the fixed end of the cam is connected to a motor shaft of a motor, the motor is fixed on a motor seat, and the motor seat and the fixed support are respectively fixed on the ground.

11. The method for casting U-shaped magnesium alloy pieces by differential pressure according to claim 3, wherein in the step, a lift tube flange turned outwards is arranged at the top of the lift tube, and an annular groove is arranged at the center of the top of the lift tube flange; the inner cavity of the lift tube is nested with a transfusion tube coaxial with the lift tube, the top of the transfusion tube is provided with a transfusion tube flange which is turned outwards, and the transfusion tube flange is embedded in an annular groove of the lift tube flange; the infusion tube is formed by sequentially screwing a first movable block to a fifth movable block from bottom to top, the first movable block to the fifth movable block are coaxially connected with each other in a smooth transition mode, the inner cavity of the first movable block is conical with the upper part being small and the lower part being large, the inner cavity of the second movable block is conical with the upper part being small, the inner cavity of the third movable block is cylindrical, the top of the third movable block is provided with an arc transition section with the upper part being small, the inner cavity of the fourth movable block is cylindrical, and the inner cavity of the fifth movable block is conical with the upper part being small and the lower part being large.

12. The differential pressure pouring method of the U-shaped magnesium alloy part according to claim 3, wherein in the step of selection, the lower port of the lift tube is closed, the circumference of the lower end of the lift tube is provided with a lift tube liquid inlet, the lift tube liquid inlet is provided with a pneumatic valve capable of closing or opening the lift tube liquid inlet, the circumference of the lift tube on one side of the lift tube liquid inlet is provided with a pneumatic valve cavity capable of accommodating the pneumatic valve, the upper end and the lower end of the lift tube liquid inlet and the upper end and the lower end of the pneumatic valve cavity are respectively provided with a door rail for sliding the pneumatic valve, the upper end and the lower end of the inner end of the pneumatic valve cavity are respectively fixedly connected with a tension spring, and the other end of the tension spring extends along the circular arc of the pneumatic valve cavity and is connected with a door frame of the pneumatic valve; the circumferential wall of the lift tube is also provided with an inert gas axial duct which is communicated in the axial direction, and the middle part of the inner end of the pneumatic valve cavity is communicated with the inert gas axial duct through a door closing pushing inlet.