CN112676536A - Lost foam ceramic cavity shell type casting and casting method thereof - Google Patents
Lost foam ceramic cavity shell type casting and casting method thereof Download PDFInfo
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- CN112676536A CN112676536A CN202011499408.XA CN202011499408A CN112676536A CN 112676536 A CN112676536 A CN 112676536A CN 202011499408 A CN202011499408 A CN 202011499408A CN 112676536 A CN112676536 A CN 112676536A
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Abstract
The invention relates to a lost foam ceramic cavity shell type casting and a casting method, comprising the following steps: carrying out simulation on a casting to be cast, and manufacturing a white mold according to a simulation result; the method comprises the following steps of (1) preparing a polystyrene foam white mold by using a white mold by using foamed polystyrene as a raw material; then coating a coating and drying to obtain a yellow mould; wherein the raw material components of the coating comprise aluminum oxide, silicon dioxide and wood fiber; carrying out heat treatment on the yellow mold, and then cleaning an inner cavity to obtain a cavity shell mold; and then boxing, pouring molten metal under negative pressure, cooling, solidifying and polishing to obtain the casting. According to the casting method provided by the invention, the white mold is coated with the special coating, the white mold influencing the recarburization of the casting is gasified, and the carbon remained on the surface of the shell is removed in advance, so that the obtained shell is not cracked and damaged; the method is suitable for producing high-end castings with the internal ultrasonic or ray inspection requirements, the surface magnetic powder or dye inspection requirements and the near surface special requirements; the method has no pollution discharge and is green and environment-friendly.
Description
Technical Field
The invention relates to the technical field of casting, in particular to a lost foam ceramic cavity shell type casting and a casting method thereof.
Background
Casting has been in the past for thousands of years, and with the development of modern technology, the appearance and inherent dimensional accuracy of castings are becoming more stringent. The existing casting method includes: sand casting, lost wax casting, lost foam casting, pressure casting, etc., and the casting technological methods have advantages and disadvantages.
The process of sand casting comprises the following steps: the method comprises the following steps of mould filling, sand filling, compaction, drawing, painting, core (with core) discharging, box closing, pouring, box opening, burr and riser removing, heat treatment, shot blasting, grinding and finishing and the like. The advantages are that: the size precision reaches CT10-13 grade, the iron-sand ratio is 1: and 4, the surface roughness is general. The disadvantages are as follows: the steel plate has flash and burr, is easy to produce air holes due to sand inclusion and slag inclusion, and has the serious consequence that the polishing workload is large in the later period of casting; further, since the iron-sand ratio is large, the total amount of the condensate and the harmful gas to be removed is large. The method is suitable for the production of castings with small batch size and heavy weight.
The process of lost wax casting comprises the following steps: mould-paint-dry-2 times expect-sand-dry-3 times paint-2 times sand-dry-4 times paint-3 times sand-dry (total 6-7 times paint, depending on the casting piece), high temperature steam dewaxing 900-930 degree to shell dry-pouring-cutting casting head (the process has no flash and burr), shot blasting-welding-polishing and trimming, etc. The advantages are that: the size precision reaches CT6-8 grades, and the iron-sand ratio is 1: 1.6-1.8, high surface roughness; the greatest advantage of this process is that no C (carbon) increase occurs. The disadvantages are as follows: the labor intensity of workers is high, and the discharge of cured substances is common. The method is suitable for the production of large-scale and light-weight castings.
The technological process of the lost foam casting process comprises the following steps: mould-white mould-1 coating-drying-2 coatings-drying-3 coatings-drying-4 coatings-drying (4-5 coatings in total, depending on the casting), boxing and pouring-cutting casting head (no flash and burr in the process), shot blasting-welding-polishing and trimming, etc. The advantages are that: the size precision reaches CT6-8 grades, and the iron-sand ratio is 1: 0.4-0.6, high surface roughness. The disadvantages are as follows: the biggest disadvantage is serious increase of C (carbon), especially low carbon steel and low alloy steel castings; c can be increased by 0.6 to the maximum extent, the probability of forming slag inclusion and air holes is high, and the discharge of a condensate is general; the labor intensity of workers is general. The method is suitable for the production of large-batch and common-weight castings; it is only suitable for cast iron and high-carbon steel castings, but low-carbon steel castings can hardly be used because of the problem of carburization.
The hollow shell pouring process adopts a lost foam mold, lost wax casting coating (shell making), white mold (white mold for lost foam) is burnt, and molten steel is poured. The process comprises the following steps: mould-white mould-1 coating-drying-2 coatings-drying-3 coatings-drying-4 coatings-drying (4-5 coatings in total, depending on the casting piece) -drying shell-baking shell-boxing and pouring-cutting casting head (the process has no flash and burr) -shot-blasting-welding-polishing and trimming, etc. The advantages are that: the size precision reaches CT6-8 grades, and the iron-sand ratio is 1: 0.3-0.4, high surface roughness; the process has the advantages that C (carbon) is not increased, the labor intensity of workers is low, and the emission of cured substances is very low; the process has the advantages of lost wax casting and lost foam casting, and avoids the disadvantages of the lost wax casting and the lost foam casting. The disadvantages are as follows: the cost is high. The method is suitable for the production of castings with large batch, high quality requirement and common weight.
Comprehensively analyzing the casting processes: (1) the sand casting is divided into two types of inorganic binder and organic binder; the inorganic binder can not increase carbon for low-carbon cast steel, but shakeout, cleaning and difficulty are caused, and the fash generated by the process problem can greatly increase the grinding amount of the subsequent process; the produced sand inclusion/air hole/slag inclusion can increase the brief repair and grinding amount; the organic binder solves the problem of sand falling, but brings the hazards of surface carburization and air holes, and simultaneously, the emission of a cured substance and harmful gases is high. (2) The lost wax casting is an inorganic binder, the production process is stable, the labor intensity of subsequent cleaning is low, but the emission of a cured product is still high, and only a small casting can be made. (3) Lost foam casting has been widely popularized in the production of cast iron and high carbon steel, but due to carburization, great difficulty and even great difficulty are encountered in the production of low carbon steel castings. How to combine the advantages of lost wax casting and lost foam casting to develop a novel casting process, which gasifies a white mold influencing the recarburization of a casting, removes C (carbon) remained on the surface of a shell in advance, and ensures that the shell is not cracked and damaged, thereby achieving the aim of producing a high-end steel casting and solving the problem.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a casting method of a lost foam ceramic cavity shell type casting, which gasifies a white mold influencing the recarburization of the casting, removes C (carbon) remained on the surface of a shell in advance and ensures that the shell is not cracked and damaged; basically no pollution is discharged, the labor intensity is reduced, and the cost is greatly reduced.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the invention provides a casting method of a lost foam ceramic cavity shell type casting, which comprises the following steps: the method comprises the following steps: carrying out simulation on a casting to be cast, and manufacturing a white mold according to a simulation result; step two: using Expanded Polystyrene (EPS) as a raw material, and manufacturing a polystyrene foam white mold by using a white mold; step three: coating a coating on the surface of a polystyrene foam white mold and drying to obtain a yellow mold; wherein, the raw material components of the coating comprise aluminum oxide, silicon dioxide and wood fiber; step four: carrying out heat treatment on the yellow mold, and then cleaning an inner cavity to obtain a cavity shell mold; wherein the heat treatment comprises the steps of heating, liquefying and charcoal burning for decarbonization; step five: and (4) boxing the cavity shell mold, pouring molten metal under negative pressure, cooling and solidifying, and polishing to obtain the lost foam ceramic cavity shell mold casting.
From the simulation result of the sand casting, when the simulation has defects, the actual casting result is definitely present; but when the simulation is not flawed, the result is not necessarily missing; for the combination of the lost wax casting process and the lost foam casting process, no ready reliable data exists in simulation software, so that larger deviation can be caused to simulation; according to the invention, a casting simulation numerical simulation system is adopted to carry out a large amount of correction and tests on data required by simulation, and after a preset result is obtained, the simulation result is datamation carried into the manufacture of the white mold, so that the development period can be greatly shortened, the casting process yield is improved, and the development cost is reduced.
In the second step of the invention, Expanded Polystyrene (EPS) is used as a raw material, and the type is preferably H-S. The method for manufacturing the polystyrene foam white mold by using the white mold comprises the following steps: (1) preheating: opening a lower drain valve of the steam-water distributor to drain water and closing the lower drain valve; opening the upper and lower model blow-down valves for steam heating, and closing the upper and lower blow-down valves when water is not available in the lower blow-down; when the pressure indicated by the pressure gauge reaches 0.06-0.12MPa, closing the steam inlet valve, and opening the upper and lower model blow-down valves until no steam overflows; opening the mold and blowing off the surface moisture of the lost foam mold; (2) feeding: feeding the material when the mould is in a closed state, and feeding the material into the cavity by using a material injection gun; (3) fusing and pressurizing: opening the upper and lower model blow-off valves, after supplying steam and water, lowering the upper die to coincide with the lower die, closing the upper and lower blow-off valves, closing the air supply valve when the pressure of the pressure gauge reaches the specified pressure of 0.4-0.5MPa, and opening the upper and lower model blow-off valves; (4) cooling and demolding: opening a water supply valve to supply water (room temperature water) in large flow, closing the water supply valve when the temperature of the die is reduced to the hand temperature, opening the die and introducing compressed air to lift the die, wherein the cooling time is 120-180 s.
In the third step of the invention, the raw material components of the coating comprise, by weight: 65-70 parts of aluminum oxide, 18-22 parts of silicon dioxide and 6.2-6.8 parts of wood fiber; wherein the length of the wood fiber is 0.8-1.5 mm; the raw material components of the coating preferably also comprise a preservative, and the preservative can be added according to the actual requirement. The coating adopted by the invention can be used as a coating for lost-wax cast alloy steel (comprising Al in percentage by mass)2O360-65％+SiO235-40 percent) of the aluminum-containing composite material, and wood fiber and high-alumina powder (Al) are added on the basis2O3Content up to 80%), and adding a preservative as required, wherein the weight ratio of the coating for the lost wax casting alloy steel, the wood fiber and the high-alumina powder is 100: 0.6: 60-70.
As a preferable scheme, in the fourth step of the present invention, the heat treatment specifically comprises the steps of: slowly heating the yellow mold at a heating rate of less than 2 ℃/min when the temperature is less than 90 ℃, heating the yellow mold to 280-320 ℃ along with the furnace after the temperature exceeds 90 ℃, and then preserving the heat for 20-30min to remove the liquefied polystyrene liquid; continuously heating to 650 ℃ to completely decompose and gasify the polystyrene liquid and other volatile matters permeated into the coating; then heating to 730 ℃, and preserving the heat for 30min to completely burn out the carbon residue. The invention adopts a resistance heat treatment furnace for heating, adds a spraying and UV photocatalytic oxidation device, realizes the removal of smoke dust and VOCs (calculated by non-methane total hydrocarbon), and achieves the emission reaching the standard. The heat treatment of the invention comprises three steps of slow temperature rise, liquefaction and charcoal burning decarburization, wherein in the liquefaction stage, after the yellow mold is completely liquefied, the resistance heat treatment furnace carriage is pulled out, and then the EPS liquid flowing out after liquefaction is collected; one is recycling, and the other is reducing harmful gas emission; in the carbon burning and decarbonizing stage, when the temperature in the furnace reaches 650 ℃, the yellow mold is completely gasified, but carbon residue still exists in the shell and on the inner wall; in order to remove carbon residues, the temperature is continuously heated to 730 ℃ and kept for 30min, all the carbon residues are burnt clean, and the obtained cavity shell mold is in an inorganic state.
Preferably, in the third step of the present invention, the step of coating the surface of the polystyrene foam white mold with the coating and drying specifically comprises the steps of: coating a layer of coating on the surface of the polystyrene foam white mould, wherein the thickness of the coating is 0.6-0.9mm, and then drying for 5-6h at the temperature of 45 ℃ under the condition that the humidity is less than or equal to 16%; and repeating the coating and drying for 4-6 times. The total thickness of the coating according to the invention is preferably maintained between 3 and 5 mm. In the coating process, a polystyrene foam white mold is placed on a yellow mold base (made of Q235 steel material), the white mold is dried once in a drying chamber (the preset temperature of the drying chamber is 47 ℃ at the highest and 43 ℃ at the lowest) after 1 time of coating, the drying temperature is controlled to be 45 ℃, the humidity is less than or equal to 16 percent, the drying time is 5-6h, the initial drying time and the termination time are recorded (the initial drying time is timed from pushing the last drying trolley in), the thickness of the vertical surface of the coating of a pouring system after drying is measured by a vernier caliper each time, the coating thickness is 0.6-0.9mm after coating is dipped and brushed each time, and the total thickness of the coating is preferably maintained at 3-5 mm.
As a preferred scheme, the second step of the invention also comprises the step of pre-foaming and curing the expanded polystyrene, wherein the pre-foaming steam pressure is 0.3-0.4MPa, and the air pressure of compressed air is more than or equal to 0.3 MPa; the preset temperature is 100 ℃, the pre-foaming time is 11-20s, the heat preservation time is 11s, and the discharging time is 6-7s, so that the density of the foamed polystyrene particles is 30-32g/L, and the foamed polystyrene particles are naturally cured for not less than 6 h.
Preferably, in the third step of the present invention, before the coating is applied to the surface of the white polystyrene foam mold and the drying process is performed, a step of installing a gate and a riser on the white polystyrene foam mold is further included.
Preferably, in the fifth step of the invention, the negative pressure degree in the sand box is kept between-0.03 and-0.045 MPa in the negative pressure casting process, and the pressure maintaining time is more than or equal to 500s after the casting is finished.
As a preferred scheme, in the fifth step of the invention, in the boxing process, the height of the added bottom sand is 100-300mm, the bottom sand is uniformly filled inside and outside after being placed into the cavity shell mold, the part which is not easy to compact is tightly plugged, the filled sand is 45-55mm higher than the cavity shell mold, and the sand is scraped and compacted; and then sealed with a plastic film.
As a preferred scheme, in the fifth step of the invention, the polishing step comprises: the method comprises the following steps of (1) cleaning flash, burrs and dead head residues on the surface of a casting and in an inner cavity, wherein the non-machined surface is required to be smooth, and the machined surface is controlled to be not more than 2 mm; the casting is required to be smooth without obvious meat deficiency and bulge by cutting the flash, burr and residual root of the casting head.
The invention also protects the lost foam ceramic cavity shell type casting obtained by casting according to the method.
The technical scheme provided by the invention has the following beneficial effects:
(1) the casting method provided by the invention is very suitable for producing high-end castings which have ultrasonic or ray inspection requirements inside, magnetic powder or dye inspection requirements on the surface and special requirements on the near surface; in particular, the casting of the ultra-low carbon alloy steel (such as the duplex stainless steel with the C less than or equal to 0.03 percent) does not carburize, the nodulizing rate of the produced ductile iron casting is high, and the defects of slag inclusion (macroscopic and microscopic) and the like are few.
(2) The process casting and pouring process provided by the invention is flexible in design, and riser patching is matched with cold iron and local quick cooling negative pressure vibration pouring of chilling sand water wind to quickly release pressure and easily cut a heat preservation riser and other process measures, so that shrinkage cavity and shrinkage porosity defects are conveniently eliminated or crystal grains are refined, the requirements of internal flaw detection and pressure test (pressure test) of a casting are easily met, and the casting can be used as a high-end casting.
(3) The process shell provided by the invention is a high-temperature non-pulverization non-layering high-strength hard, high-refractoriness and high-permeability ceramic coating with the thickness of several millimeters, so that the surface and the near surface of a casting are free from defects such as sand holes, air holes and slag inclusion, the subsequent welding repair and polishing workload of the casting is greatly reduced, particularly the welding repair and polishing workload of high-alloy steel castings such as stainless steel and the like can be reduced by about 90%, the labor intensity is reduced, the appearance of the casting is ensured to be attractive, the cost is greatly reduced, and the environment is greatly improved.
(4) According to the process provided by the invention, more than 95% of foamed solid polystyrene plastic is changed into liquid polystyrene plastic in the process of manufacturing the shell, the liquid polystyrene plastic flows out of the shell and is recycled, and the conversion from the solid state to the liquid state is a physical change process, so that pollution to the environment is avoided, and waste can be utilized. A very small amount of decomposition products are intensively collected in the heating furnace and enter the smoke removing machine to be decomposed into CO2And H2And (4) discharging O.
(5) A small amount of flaky coating waste materials after the process casting is cleaned can be mixed with a back layer coating for utilization after being ground; powdery paint waste produced by lost foam casting is mixed into dry sand, and dust contamination is easily caused. Therefore, the process is basically pollution-free and emission-free, is the most environment-friendly process in various casting processes, and is the green casting with the real meaning.
In a word, the technical scheme provided by the invention is a new high-end casting process researched and developed by combining a lost foam casting method, a metal solidification theory, material science, casting technology and the like, is improvement and promotion of the lost foam casting method, and is characterized in that special coating is coated on the appearance of an EPS white mold to prepare a ceramic cavity thin-wall shell mold with high strength, high refractoriness, high air permeability, smooth inner wall and accurate size, and a high-quality casting is cast under the condition of negative pressure pouring. The fundamental difference between the process and the lost foam casting is as follows: the lost foam casting is to pour metal liquid into a foam plastic model coated with paint, and the process is to pour the metal liquid into a clean ceramic cavity shell mold; therefore, the application mode, the process measure and the quality grade of the casting of the two are essentially different. The process can produce high-end precision castings which are made of various alloy materials, have high internal and external quality and are heavy by dozens of kilograms to tons, can greatly improve the quality grades of various steel castings, ductile iron castings, gray iron castings and non-ferrous alloy castings, and is convenient to popularize and apply in the aspects of lost foam casting, wax mold precision casting and various sand mold casting.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The following examples are only for illustrating the technical solutions of the present invention more clearly, and therefore are only examples, and the protection scope of the present invention is not limited thereby.
The experimental procedures in the following examples are conventional unless otherwise specified. The test materials used in the following examples were purchased from a conventional reagent store unless otherwise specified. In the quantitative tests in the following examples, three replicates were set, and the data are the mean or the mean ± standard deviation of the three replicates.
The invention provides a casting method of a lost foam ceramic cavity shell type casting, which comprises the following steps.
1. Simulation of the casting: carrying out simulation on a casting to be cast, and manufacturing a white mold according to a simulation result; the invention carries out a large amount of correction and test on the data required by the simulation, and finally obtains ideal parameters, thereby greatly shortening the development period, improving the casting process yield and reducing the development cost.
2. Pre-foaming and curing: 1) the pre-foaming steam pressure reaches 0.3-0.4MPa, and the air pressure of compressed air is more than or equal to 0.3 MPa; 2) the EPS material adopts a model H-S; 3) starting up and preheating: the preset temperature is 100 ℃; 4) presetting during foaming: ensuring that the density of the EPS particles reaches 30-32g/L, the pre-foaming time is 11-20s, the heat preservation time is 11s, and the discharging time is 6-7 s; 5) after each pre-foaming, weighing by using an electronic scale, wherein the density of the granules is ensured to be within a control range; 6) delivering the mixture into a curing bin through a pipeline, and naturally curing for not less than 6 h.
3. White mold forming: 1) preheating: opening a lower drain valve of the steam-water distributor to drain water completely and closing the lower drain valve; opening the upper and lower model blow-down valves, and closing the upper and lower blow-down valves when the blow-down is heated by steam and no water is available; when the pressure of the pressure gauge reaches 0.06-0.12MPa, closing the steam inlet valve, opening the upper and lower model blow-down valves, and stopping until no steam overflows; opening the mold and blowing off the surface moisture of the lost foam mold; 2) feeding: feeding the material when the mould is in a closed state, and feeding the material into the cavity by using a material injection gun; 3) fusing and pressurizing: opening the upper and lower model blow-off valves, after supplying steam and water, lowering the upper die to coincide with the lower die, closing the upper and lower blow-off valves, closing the air supply valve when the pressure of the pressure gauge reaches the specified pressure of 0.4-0.5MPa, and opening the upper and lower model blow-off valves; 4) cooling and demolding: opening a water supply valve to supply water (room temperature water) in large flow, closing the water supply valve when the temperature of the die is reduced to the hand temperature, opening the die and introducing compressed air to lift the die, wherein the cooling time is 120-180 s.
4. Adding a pouring gate and a riser: according to the data obtained by the simulation, a sprue and a riser are additionally arranged on the white mold.
5. Coating: dipping and brushing the paint for 5 times to form a yellow mold, placing the yellow mold on a yellow mold base (made of Q235 steel material), drying the paint in a drying chamber for 1 time each time (the preset temperature of the drying chamber is 47 ℃ at the highest and 43 ℃ at the lowest), controlling the drying temperature to be 45 ℃, the humidity to be less than or equal to 16 percent, drying time to be 5-6h, recording the initial drying time and the termination time (the initial drying time is counted from pushing the last drying trolley in), measuring the vertical surface paint thickness of the pouring system after drying by using a vernier caliper every time each shift, dipping and brushing the paint for 5 times, wherein the paint thickness is 0.6-0.9mm, and the total paint thickness is 3-5 mm. And (3) filling the lost foam with sodium silicate sand after dipping and brushing 3 times of coating in 22 elliptical holes on the transmission end pressing ring and the transmission end pressing ring casting. In each 100kg of the coating material used in this step, Al is contained2O3The addition amount is 65-70kg, SiO218-22kg of wood fiber, 6.2-6.8kg of wood fiber (the length of the wood fiber is kept between 0.8 and 1.5mm), and the balance of preservative.
6. Drying the shell: the resistance heat treatment furnace is used for heating, and a spraying and UV photocatalytic oxidation device is added, so that smoke dust and VOCs (calculated by non-methane total hydrocarbons) are removed, and the emission reaching the standard is achieved. Comprises 3 stages of slow heating, liquefaction and charcoal burning decarburization: a slow heating stage (the temperature of the heat treatment furnace is less than 90 ℃), wherein the heating speed is less than 2 ℃/min; in the liquefaction stage, when the temperature is at 280-320 ℃, liquefying the white mold, keeping the temperature for 20-30min, pulling out the resistance heat treatment furnace car after the white mold is completely liquefied, and then collecting the EPS liquid flowing out after liquefaction; and in the carbon burning and decarbonizing stage, when the temperature in the furnace reaches 650 ℃, the white mold is completely gasified. But carbon residues still exist in the shell and on the inner wall, in order to remove the carbon residues, the shell is continuously heated to 730 ℃, the temperature is kept for 30min, all the carbon residues are completely burnt, and the shell is ensured to be in an inorganic state.
7. Cleaning an inner cavity: and (3) pulling the shell out of the heat treatment furnace along with a yellow mould frame (made of stainless steel materials), cooling to room temperature, and cleaning the inner cavity of the yellow mould after the shell is taken out of the furnace, so that the shell can be ready for boxing and pouring.
8. Boxing, vacuumizing and pouring: 1) checking whether the yellow mold is complete and white exposure exists. If the white area is found to be less than or equal to 2mm2The part of the paint is supplemented by alcohol-based paint; 2) preparing a saw blade, a sand scraping plate, a caliper of 0-600mm, alcohol-based paint, mould assembling glue, a connecting sand sleeve and the like; 3) pushing the sand box, clamping and jacking; adding bottom sand with the height of about 100 mm and 300mm, and strickling and compacting; 4) placing into a yellow mold, uniformly filling sand inside and outside, plugging the part which is not easy to compact by a hand, filling sand about 50mm higher than the yellow mold, scraping and compacting; 5) covering a plastic film, and additionally arranging a filter screen and a pouring cup; 6) filling sand, resetting the compaction table, loosening and clamping, and discharging; 7) vacuumizing, and connecting the sand box with a vacuum distributor by using a negative pressure rubber tube; adjusting a valve handle on the vacuum distributor to maintain the vacuum pressure of the valve handle at-0.035 to-0.045 MPa; 8) measuring the temperature by using a thermocouple temperature measuring gun, analyzing chemical components by using a spectrometer, and pouring after the components are qualified; 9) cooling and solidifying: the pressure stabilizing time is kept after pouring, and is determined according to the casting condition, and the pressure maintaining time is generally more than or equal to 500 s.
9. Polishing: 8-10h after pouring, taking out of the box and entering a polishing and cleaning procedure: 1) shot blasting time of a casting of the shot blasting machine is set (generally set to be 6-8min), and a steel shot with a full CW1.5 (specification: phi 1.5 mm); 2) the casting is firmly and stably hoisted by using the cat head lifting hook, the conveyor starting button is pressed to convey the casting to the cleaning chamber, and the shot blasting chamber gate is closed; 3) pressing an automatic starting button, starting the shot blasting machine to work, opening a shot gate, starting sequential treatment, completing shot blasting work, closing the shot gate, opening a door of a shot blasting chamber, and pressing a conveyor starting button to output a casting to the outside of the shot blasting chamber; 4) the method comprises the following steps of (1) cleaning flash, burrs and dead head residues on the surface and in an inner cavity of a casting by using tools such as a hammer, a chisel and the like, wherein a non-processed surface is required to be smooth, and the control of a processed surface is not more than 2 mm; 5) grinding the flash, burr and dead root of a casting by using a grinding wheel grinder, wherein the casting is required to be smooth and has no obvious meat deficiency and bulge; 6) the inspector will inspect the cleaned castings and sort them by product category.
The casting method of the lost foam ceramic cavity shell type casting provided by the invention is further explained by combining specific embodiments.
The embodiment provides a casting method of a lost foam ceramic cavity shell type casting, which comprises the following steps.
1. Simulation of the casting: and (3) carrying out simulation on the casting to be cast, and manufacturing a white mold according to a simulation result.
2. Pre-foaming and curing: 1) the pre-expansion steam pressure reaches 0.35MPa, and the air pressure of compressed air is 0.3 MPa; 2) the EPS material adopts a model H-S; 3) starting up and preheating: the preset temperature is 100 ℃; 4) presetting during foaming: ensuring that the density of the EPS particles reaches about 31g/L, the pre-foaming time is 15s, the heat preservation time is 11s, and the discharging time is 6 s; 5) after each pre-foaming, weighing by using an electronic scale, wherein the density of the granules is ensured to be within a control range; 6) delivering the mixture into a curing bin through a pipeline, wherein the natural curing time is not less than 6 h.
3. White mold forming: 1) preheating: opening a lower drain valve of the steam-water distributor to drain water completely and closing the lower drain valve; opening the upper and lower model blow-down valves, and closing the upper and lower blow-down valves when the blow-down is heated by steam and no water is available; when the pressure of the pressure gauge reaches 0.1MPa, closing the steam inlet valve, opening the upper and lower model blow-down valves, and stopping until no steam overflows; opening the mold and blowing off the surface moisture of the lost foam mold; 2) feeding: feeding the material when the mould is in a closed state, and feeding the material into the cavity by using a material injection gun; 3) fusing and pressurizing: opening the upper and lower model blow-down valves, after supplying steam and water, lowering the upper die to coincide with the lower die, closing the upper and lower blow-down valves, closing the air supply valve when the pressure of the pressure gauge reaches the specified pressure of 0.4MPa, and opening the upper and lower model blow-down valves; 4) cooling and demolding: opening a water supply valve to supply water (room temperature water) in large flow, closing the water supply valve when the temperature of the die is reduced to the hand temperature, opening the die, introducing compressed air to lift the die, and cooling for 150 s.
4. Adding a pouring gate and a riser: according to the data obtained by the simulation, a sprue and a riser are additionally arranged on the white mold.
5. Coating: dipping and brushing the paint for 5 times to form a yellow mold, placing the yellow mold on a yellow mold base (made of Q235 steel material), drying the yellow mold once in a drying chamber (the preset temperature of the drying chamber is 45 ℃, the upward and downward floating possibility in the actual operation process is 2 ℃) after each paint is coated for 1 time, controlling the drying temperature to be 45 ℃, the humidity to be 16%, drying for 5.5h, recording the initial drying time and the termination time, wherein the thickness of the paint dipped and brushed every time is about 0.8mm, and the total paint thickness is 4mm after the paint is dipped and brushed for 5 times. And (3) filling the lost foam with sodium silicate sand after dipping and brushing 3 times of coating in 22 elliptical holes on the transmission end pressing ring and the transmission end pressing ring casting. In each 100kg of the coating material used in this step, Al is contained2O3The addition amount is 68kg, SiO2The addition amount is 20kg, the addition amount of wood fiber is 6.5kg (the length of the wood fiber is kept about 1 mm), and the balance is preservative.
6. Drying the shell: the resistance heat treatment furnace is used for heating, and a spraying and UV photocatalytic oxidation device is added, so that smoke dust and VOCs (in terms of non-methane total hydrocarbons) are removed, and the emission standard is reached. Comprises 3 stages of slow heating, liquefaction and charcoal burning decarburization: a slow heating stage (the temperature is less than 90 ℃) with the heating speed of less than 2 ℃/min; in the liquefaction stage, when the temperature reaches 300 ℃, liquefying the white mold, keeping the temperature for 25min, pulling out the heat treatment furnace car after the white mold is completely liquefied, and then collecting the EPS liquid flowing out after liquefaction; and in the carbon burning and decarbonizing stage, when the temperature in the furnace reaches 650 ℃, the white mold is completely gasified. But carbon residues still exist in the shell and on the inner wall, in order to remove the carbon residues, the shell is continuously heated to 730 ℃, the temperature is kept for 30min, all the carbon residues are completely burnt, and the shell is ensured to be in an inorganic state.
7. Cleaning an inner cavity: and (3) pulling the shell out of the heat treatment furnace along with a yellow mould frame (made of stainless steel materials), cooling to room temperature, and cleaning the inner cavity of the yellow mould after the shell is taken out of the furnace, so that the shell can be ready for boxing and pouring.
8. Boxing, vacuumizing and pouring: 1) checking whether the yellow mould is complete and has no white spots; 2) preparing a saw blade, a sand scraping plate, a caliper of 0-600mm, alcohol-based paint, mould assembling glue, a connecting sand sleeve and the like; 3) pushing the sand box, clamping and jacking; adding bottom sand with the height of about 200mm, and scraping and compacting; 4) placing into a yellow mold, uniformly filling sand inside and outside, plugging the part which is not easy to compact by a hand, filling sand about 50mm higher than the yellow mold, scraping and compacting; 5) covering a plastic film, and additionally arranging a filter screen and a pouring cup; 6) filling sand, resetting the compaction table, loosening and clamping, and discharging; 7) vacuumizing, and connecting the sand box with a vacuum distributor by using a negative pressure rubber tube; adjusting a valve handle on the vacuum distributor to maintain the vacuum pressure of the valve handle at-0.04 MPa; 8) measuring the temperature by using a thermocouple temperature measuring gun, analyzing chemical components by using a spectrometer, and pouring after the components are qualified; 9) cooling and solidifying: keeping the pressure stabilizing time for 600s after pouring.
9. Polishing: 9h after pouring, taking out of the box and entering a polishing and cleaning procedure: 1) setting shot blasting time of a shot blasting machine casting for 7min, and preparing enough CW1.5 steel shots (specification: phi 1.5 mm); 2) the casting is firmly and stably hoisted by using the cat head lifting hook, the conveyor starting button is pressed to convey the casting to the cleaning chamber, and the shot blasting chamber gate is closed; 3) pressing an automatic starting button, starting the shot blasting machine to work, opening a shot gate, starting sequential treatment, completing shot blasting work, closing the shot gate, opening a door of a shot blasting chamber, and pressing a conveyor starting button to output a casting to the outside of the shot blasting chamber; 4) the method comprises the following steps of (1) cleaning flash, burrs and dead head residues on the surface and in an inner cavity of a casting by using tools such as a hammer, a chisel and the like, wherein a non-processed surface is required to be smooth, and the control of a processed surface is not more than 2 mm; 5) the casting is ground by a grinding wheel grinder to form flash, burr and sprue stub, and the casting is required to be smooth and have no obvious meat deficiency and bulge.
The casting prepared by the embodiment can completely meet the requirements of two types of clamping ring steel castings of a non-transmission end clamping ring and a transmission end clamping ring of a permanent magnet motor of a subway. The Zhongche group Tanzhou electric locomotive research institute Limited company is used for Shenzhen subway No. 10 line permanent magnet motor, saves energy by 30% compared with the traditional asynchronous alternating current motor, and is designed in a use environment according to low temperature (minus 40 ℃), wherein two pressing rings of a non-transmission end pressing ring and a transmission end pressing ring are steel castings.
Material designation: g20Mn5, performance criteria were: Q/XD116-2019 Purchase Specification for Steel castings for traction motors, wherein the chemical composition requirements are as follows in Table 1: wherein C (%): 0.17-0.23, less than or equal to 0.020% of S (%), and less than or equal to 0.020% of p (%).
TABLE 1 chemical composition requirements
| Number plate | C(％) | Si(％) | Mn(％) | Cr(％) | Mo(9％) |
| G20Mn5 | 0.17-0.23 | ≤0.6 | 1.00-1.60 | ≤0.30 | ≤0.12 |
| ZG230-450 | 0.20-0.30 | 0.20-0.50 | 0.50-0.90 | ≤0.35 | ≤0.20 |
| Number plate | Ni(％) | Cu(％) | P(％) | S(％) | - |
| G20Mn5 | ≤0.80 | ≤0.30 | ≤0.020 | ≤0.020 | - |
| ZG230-450 | ≤0.30 | ≤0.30 | ≤0.040 | ≤0.040 | - |
The mechanical properties required are shown in table 2 below: wherein the low-temperature (minus 40 ℃) impact absorption work Akv (J) is more than or equal to 27J.
TABLE 2 mechanical Property requirements
Internal quality requirements: the internal quality inspection of the casting adopts an X-ray flaw detection method. Class B products do not require radiographic inspection unless otherwise specified.
The inside of the casting is not allowed to have crack defects, and other defects meet the following regulations: 1) the internal quality of the important areas marked in the drawing is required to meet the quality grade requirement of DIN 1690-V2; 2) the internal quality of the other non-critical areas should comply with the quality class requirements of DIN 1690-V3.
The casting process originally designed in China is a water glass casting process, and has the problems that the surface quality of a casting is poor, and the casting can hardly be formed in 22 oval holes; by adopting the resin sand casting process, the problems of recarburization on the surface of a casting and high casting rejection rate exist; the main problems of the lost foam casting process are that carbon defects, lost foam are not completely burnt out, residues formed by residual lost foam particles are remained, and the rejection rate is still high.
The three casting processes of sand casting, lost wax casting and lost foam casting are difficult to meet the requirement of X-ray flaw detection for internal quality inspection of castings, and even if flaw detection is passed, the yield is very low, and the requirement of customers cannot be met.
The invention adopts a lost foam hollow shell casting process, namely, a lost foam white mold adopts 5 times of coating to dip-coat, dry, and the yellow mold with the technical indexes of coating thickness, strength, air permeability and the like meeting the requirements is put into a heat treatment furnace, heated to the specified temperature according to the determined heat treatment process, kept warm, the EPS material in the yellow mold is burnt out, and the inner cavity of the yellow mold is cleaned after the yellow mold is taken out of the furnace; filling the casting with sodium silicate sand in 22 elliptical holes on the lost foam, and putting the casting into a heat treatment furnace along with a yellow mold for subsequent processes; then boxing and vacuum negative pressure pouring are carried out according to a normal lost foam process; controlling the quality of molten iron in the electric furnace, including the temperature and chemical composition of the molten iron; and controlling the tapping temperature, the pouring time and the pouring speed of the molten iron, namely adopting a flow reducing measure to slowly pour, and ensuring stable pouring. Through the technological design innovation, 300 produced pressing ring orders completely pass the flaw detection of a checking mechanism.
The casting method provided by the invention not only thoroughly overcomes various special defects of lost foam casting castings, but also greatly improves the quality grade of various steel castings, ductile iron castings, gray iron castings and non-ferrous alloy castings. (1) The density of the white mold can be higher, so that the size of the casting is more accurate; the foam beads on the surface of the white mold are more compact, micro gaps can be modified, the coating has high strength and cannot be broken by high-temperature pulverization of molten metal, the surface of a casting is smoother, the near surface (within 0-5mm of the surface or a blind area of ultrasonic flaw detection) does not have the defects of slag inclusion, air holes, sand inclusion, sand holes and the like, and the white mold is more convenient to polish and machine and has better appearance quality. (2) The method is very suitable for high-end castings with the internal ultrasonic or ray inspection requirements, the surface magnetic powder or dye inspection requirements and the near surface special requirements. In particular, the casting of the ultra-low carbon alloy steel (such as the duplex stainless steel with the C less than or equal to 0.03 percent) does not carburize, and the produced ductile iron casting has high nodularity and less slag inclusion (macroscopic and microscopic) and other defects. (3) Because the coating is not cracked and deformed when being quickly dried by high temperature and strong wind, the production efficiency is not reduced but improved compared with lost foam casting, and the coating can be poured within 2 days from the coating. (4) The white mould and the coating are easy to correct and strengthen, and the casting deformation is prevented. (5) The coating is not easy to deliquesce and soften, the damage rate of the shell can be reduced to 1%, and the yield of the casting can reach more than 98%. (6) Because the foamed plastic white mold is liquefied and recovered by more than 95 percent, a small amount of volatile gas is easy to be intensively subjected to smoke removal treatment, and the environment-friendly and energy-saving effects are achieved. (7) The process has the defects that a shell making procedure is added compared with lost foam casting, and the casting forming cost is also improved.
Compared with precision casting of a fired mold (wax pattern), the casting method provided by the invention has the advantages that the quality of the cast method is close to that of the precision casting of the fired mold (wax pattern), the casting cost is lower, the cast method can be used for manufacturing large and medium-sized workpieces, and the casting process measures are flexible: (1) can cast precision castings with single weight of dozens of kilograms to several tons. (2) The production efficiency is high, and the method is generally from the beginning of coating to pouring for 2 days. (3) The production cost is reduced (especially the high alloy steel parts are most obvious). (4) The process only dips in the coating without sanding, and the shell is not easy to deform, crack, delaminate and peel; the method is more advantageous when being made into complicated large pieces; the energy is saved. (5) The hot pouring is not needed, the working condition is improved, and the technological measures such as iron chill and the like can be implemented to eliminate the defects of shrinkage cavity and shrinkage porosity of the casting. (6) The shell is thin and light, is only 1/2-1/3 of the wax mould precision casting shell, is convenient to operate and saves materials. (7) The shell making process has no acid, alkali and odor emission, and is more environment-friendly. (8) The coating has excellent coating property on the wax mould, no discharge during shell making and high production efficiency, the original precision casting mould can be partially utilized, and the negative pressure pouring facility is added, so that the coating can be popularized to the precision casting of the wax mould to prepare larger castings.
Compared with various sand casting methods, the casting method provided by the invention has the advantages that the cost is close to that of the sand casting method, the internal and external quality is improved by a plurality of levels, and the process has the main advantages that: (1) the dimensional accuracy of the casting is improved from CT12-14 to CT 5-8; the surface roughness is improved from Ra50-100 μm to Ra12.5-25 μm. (2) The production efficiency is improved by 1-2 times compared with the casting of sodium silicate sand and various resin sands. (3) The sand core is not needed, the draft of the drawing die is negligible, the wall thickness of the casting is uniform, no parting surface and no flash batch seam exist, the size precision of the casting is high, and the cutting and polishing workload is small. (4) The advantages are more prominent when the casting with complex structure is made. (5) The casting and pouring process is flexible in design, and riser patching is matched with technological measures such as chilling blocks, local quick-cooling negative-pressure vibration pouring of chilling sand water air, quick pressure relief and easy cutting of heat preservation risers, so that shrinkage cavity and shrinkage porosity defects are eliminated conveniently or crystal grains are refined, the requirements of internal flaw detection and pressure testing of castings are easily met, and the casting and pouring process can be used as high-end castings. (6) The coating used in various sand casting, lost foam casting, V method casting and the like is easy to be pulverized at high temperature and washed and damaged when metal liquid is poured. The process shell is a high-temperature non-pulverization non-layering high-strength hard, high-refractoriness and high-permeability ceramic coating with the thickness of several millimeters, so that the surface and the near surface of a casting are free from defects such as sand holes, air holes and slag inclusion, the subsequent welding repair and polishing workload of the casting is greatly reduced, the welding repair and polishing workload of the high-alloy steel casting such as stainless steel can be reduced by about 90%, the labor intensity is reduced, the appearance of the casting is attractive, the cost is greatly reduced, and the environment is greatly improved. (7) The quality of the high-end casting with the magnetic powder inspection requirement on the surface is easier to ensure. (8) The coating can be used for reinforcing large pieces weighing several tons. (9) The negative pressure pouring facility and the foam plastic model are added, so that the method can be popularized in sand casting production. The process is not suitable for being popularized in the production of small and medium cast iron parts, non-ferrous alloy die casting and the like in an automatic flow line.
The casting method provided by the invention is convenient for removing the dead head of the wear-resistant part: wear-resistant castings such as wear-resistant alloy steel, high manganese steel, high-chromium cast iron and the like all require large riser feeding, and because the castings are difficult to remove due to high hardness and easy to break due to flame hot cutting, the casting can be easily knocked by utilizing the characteristic that the casting is brittle in an as-cast state, the process can be matched with a heat-insulating riser, so that the labor intensity is reduced, and the cost is reduced.
The casting method provided by the invention is energy-saving and environment-friendly, the realization of the real green casting lost foam casting is known as the '21 st century green casting', and the production process of the process is more environment-friendly than the lost foam casting: (1) except that the common sand of the two is recycled, the smoke is discharged, the polystyrene foam plastic white mould in the lost foam casting is heated by molten metal for 100% combustion or gasification in the pouring process, part of the smoke is directly discharged into the atmosphere, and the other part of the smoke is simply treated by a vacuum pump system and discharged into the atmosphere, so that the environment is polluted to some extent. In the process, more than 95% of foamed solid polystyrene plastic is changed into liquid polystyrene plastic in the process of manufacturing the shell, the liquid polystyrene plastic flows out of the shell and is recycled, and the solid-liquid conversion is a physical change process, so that the pollution to the environment is avoided, and the waste can be utilized. A very small amount of decomposition products are intensively collected in the heating furnace and enter the smoke removing machine to be decomposed into CO2And H2And (4) discharging O. (2) A small amount of flaky coating waste materials after the casting is cleaned by the process can be mixed with the back layer coating for utilization after being ground. Powdery paint waste produced by lost foam casting is mixed into dry sand, and dust contamination is easily caused. Therefore, the process is basically pollution-free and emission-free, is the most environment-friendly process in various casting processes, and is the green casting with the real meaning.
The casting method provided by the invention has the unique advantages of quickly manufacturing the casting sample or producing single casting in small batches: (1) A3D carved foam plastic block white mold or a 3D additive printing hollow plastic mold is adopted, surface modification, coating shell manufacturing and negative pressure pouring are carried out, a sample piece can be manufactured within a week, the quality of the sample piece is similar to that of the white mold manufactured by the mold, and the construction period, the quality and the cost are superior to those of the 3D printed sample piece. (2) The single-piece or small-batch single-order production is realized, the number of factors is small, the construction period is short, the mold is not suitable to be opened, and the manual production and the production of the white mold by using the foamed plastic plate by a multi-dimensional engraving machine can be realized. (3) The unique advantages of the process can be utilized to realize intelligent and flexible production, and the customized production and service can be implemented by combining with the Internet.
It is to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the invention pertains. Unless specifically stated otherwise, the relative steps, numerical expressions, and values of the components and steps set forth in these embodiments do not limit the scope of the present invention. In all examples shown and described herein, unless otherwise specified, any particular value should be construed as merely illustrative, and not restrictive, and thus other examples of example embodiments may have different values.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention, and all of the technical solutions are covered in the protective scope of the present invention.
Claims (10)
1. A casting method of a lost foam ceramic cavity shell type casting is characterized by comprising the following steps: the method comprises the following steps: carrying out simulation on a casting to be cast, and manufacturing a white mold according to a simulation result; step two: using foamed polystyrene as a raw material, and manufacturing a polystyrene foam white mold by using the white mold; step three: coating a coating on the surface of the polystyrene foam white mold and drying to obtain a yellow mold; wherein the raw material components of the coating comprise aluminum oxide, silicon dioxide and wood fiber; step four: carrying out heat treatment on the yellow mold, and then cleaning an inner cavity to obtain a cavity shell mold; wherein the heat treatment comprises the steps of heating, liquefying and carbon burning for decarbonization; step five: and boxing the cavity shell mold, pouring molten metal under negative pressure, cooling and solidifying, and polishing to obtain the lost foam ceramic cavity shell mold casting.
2. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: in the third step, the raw material components of the coating comprise, by weight: 65-70 parts of aluminum oxide, 18-22 parts of silicon dioxide and 6.2-6.8 parts of wood fiber; wherein the length of the wood fiber is 0.8-1.5 mm; the raw material components of the coating preferably further comprise a preservative.
3. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: in the fourth step, the heat treatment specifically comprises the steps of: heating the yellow mold to 90 ℃ at a heating rate of less than 2 ℃/min, then heating the yellow mold to 320 ℃ along with the furnace, and preserving the heat for 20-30min to remove the liquefied polystyrene liquid; continuously heating to 650 ℃ to completely decompose and gasify the polystyrene liquid and other volatile matters permeated into the coating; then heating to 730 ℃, and preserving the heat for 30min to completely burn out the carbon residue.
4. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: in the third step, the step of coating the polystyrene foam white mold surface with the coating and drying the polystyrene foam white mold surface specifically comprises the following steps: coating a layer of coating on the surface of the polystyrene foam white mould, wherein the thickness of the coating is 0.6-0.9mm, and then drying for 5-6h at the temperature of 45 ℃ under the condition that the humidity is less than or equal to 16%; and repeating the coating and drying for 4-6 times.
5. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: in the second step, the method also comprises the step of pre-foaming and curing the expanded polystyrene, wherein the pre-foaming steam pressure is 0.3-0.4MPa, and the air pressure of compressed air is more than or equal to 0.3 MPa; the preset temperature is 100 ℃, the pre-foaming time is 11-20s, the heat preservation time is 11s, and the discharging time is 6-7s, so that the density of the foamed polystyrene particles is 30-32g/L, and the foamed polystyrene particles are naturally cured for not less than 6 h.
6. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: in the third step, before the coating is coated on the surface of the white polystyrene foam mold and the white polystyrene foam mold is dried, a step of adding a pouring gate and a riser on the white polystyrene foam mold is further included.
7. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: and fifthly, keeping the negative pressure degree in the sand box to be-0.03-0.045 MPa in the negative pressure pouring process, and keeping the pressure for more than or equal to 500s after pouring is finished.
8. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: step five, in the boxing process, the height of bottom sand is 100-300mm, the bottom sand is uniformly filled inside and outside after being placed into the cavity shell mold, the part which is not easy to compact is tightly plugged, the filled sand is 45-55mm higher than the cavity shell mold, and the bottom sand is scraped and compacted; and then sealed with a plastic film.
9. The method of casting a lost foam ceramic cavity shell casting according to claim 1, wherein: in the fifth step, the polishing step comprises: the method comprises the following steps of (1) cleaning flash, burrs and dead head residues on the surface of a casting and in an inner cavity, wherein the non-machined surface is required to be smooth, and the machined surface is controlled to be not more than 2 mm; the casting is required to be smooth without obvious meat deficiency and bulge by cutting the flash, burr and residual root of the casting head.
10. A lost foam ceramic cavity shell casting cast according to the method of any one of claims 1 to 9.
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