Negative pressure molding method and lining plate production process

Abstract

The invention relates to the field of negative-pressure casting, and provides a negative-pressure molding method and a lining plate production process in order to solve the problem that the area of a sand box is small when a side face air exhaust sand box is used in an existing negative-pressure molding method, and the negative-pressure molding method comprises the steps that an upper mold and a lower mold are manufactured through a molding process, and the upper mold and the lower mold are oppositely combined to form a casting mold space through mold closing; molten metal is poured into the casting mold space, a casting is obtained after the molten metal is cooled, and the molding process comprises the steps that S100, a mold plate with an air exhaust hole is placed on an air exhaust box, so that the air exhaust hole communicates with the inner space of the air exhaust box; s200, the surface of the template is covered with a first plastic film, an air exhaust box is started, and the first plastic film is tightly attached to the surface of the template; s300, a sand box with the side face provided with a filtering exhaust pipe is placed on an exhaust box, then the sand box is filled with molding sand, and the surface of the molding sand is covered with a second plastic film; and S400, air in the molding sand is pumped out through a sand consolidation process, so that the molding sand is formed. According to the negative pressure molding method provided by the invention, the applicable area of the side air exhaust sand box can be increased.

Description

Technical Field

[0001] The invention relates to the field of negative pressure casting, and in particular to a negative pressure molding method and a lining plate production process. Background Art

[0002] Vacuum sealed molding is a physical molding method, which is called the third generation molding method among various molding methods of casting. It uses plastic film to seal the sand box and relies on a vacuum pump to extract the air in the mold, creating a pressure difference inside and outside the mold, making the dry sand compact to form the required cavity. Therefore, vacuum sealed molding is also known as "negative pressure molding method" or "decompression molding method". In foreign countries, it is abbreviated as V method, which is derived from the initials of the English word Vacuum.

[0003] Three types of sand boxes are commonly used in negative pressure molding, namely side suction type, tube suction type and metal hose suction type. Each suction method has its own advantages and disadvantages. For example, the side suction sand box has its suction point located around the molding sand. If the sand box is too large, the vacuum in the center of the sand mold formed by the molding sand is too small, which may lead to insufficient strength and collapse. Another example is the tube suction sand box, because its suction pipe extends into the middle of the sand mold, it can be used for large and medium-sized sand boxes, but under the obstruction of the suction pipe, the removal of castings and the setting of pouring and risers are restricted, and the versatility is weak. Another example is the metal hose suction sand box, which currently often uses a snake skin tube. When the air is pumped, the air between the sand particles is sucked through the gaps between the active nodes of the hose, while preventing fine sand and dust from being sucked in. The hose is hung on the inner wall of the sand box and fixed in the installation and fixing hole of the box belt. The distance between the hose and the cavity surface should be ≥50mm, otherwise the latent heat of metal solidification is too close to the cavity surface and the hose is easily damaged. This type of hose has a large gap and is easy to inhale sand and dust. Therefore, the vacuum pipeline system must be equipped with a sand filter and a water bath device to prevent sand and dust from entering the vacuum pump.

[0004] At present, there is an urgent need for a negative pressure molding method. Under the premise of using a side-exhaust sand box, the applicable sand box area can be larger than 1m 2 . Summary of the invention

[0005] The purpose of the present invention is to provide a negative pressure molding method to solve the problem that the area of ​​the sand box is small when the side suction sand box is used in the existing negative pressure molding method.

[0006] The present invention also aims to provide a lining production process, which can use a side-evacuated sand box to cast a lining with a larger casting area, and at the same time select a metal liquid with a specific component to improve the strength and wear resistance of the lining, thereby increasing the protective effect and applicability of the lining.

[0007] The embodiments of the present invention are implemented by the following technical solutions:

[0008] A negative pressure molding method, comprising: making an upper mold and a lower mold respectively through a molding process, closing the mold so that the upper mold and the lower mold are aligned to form a casting space, and finally pouring molten metal into the casting space, and obtaining a casting after the molten metal is cooled. The molding process includes:

[0009] S100, placing a template with exhaust holes on an exhaust box, so that the exhaust holes are connected to the inner space of the exhaust box;

[0010] S200, covering the surface of the template with a first plastic film, and starting the vacuum box so that the first plastic film is closely attached to the surface of the template;

[0011] S300, placing a sand box with a filter exhaust pipe on the side on the exhaust box, at which time the mold plate is located in the sand box, and then filling the sand box with molding sand and covering the surface of the molding sand with a second plastic film;

[0012] S400, extracting air from the molding sand through a sand consolidation process to form the molding sand;

[0013] The air extraction holes on the template include film-covered air holes and sand-fixing air holes, and a filter screen is provided in the sand-fixing air holes;

[0014] The sand consolidation process comprises:

[0015] D100, remove the air in the molding sand by filtering the suction pipe, so that the vacuum degree of the molding sand space is greater than the vacuum degree of the sand consolidation pores;

[0016] D200, generating through holes in the first plastic film at the openings of the sand consolidation pores through a film breaking process;

[0017] D300, secondary sand consolidation is performed through filtering the air suction pipe and / or the air suction box to obtain an upper mold or a lower mold.

[0018] Preferably, the D300 specifically includes the following operations: firstly, air is pumped out through the vacuum box to make the vacuum degree in the vacuum box equal to the vacuum degree in the molding sand space, and then the filtering vacuum pipe and the vacuum box are started simultaneously to solidify the molding sand, and finally an upper mold or a lower mold is obtained.

[0019] Preferably, the membrane breaking process includes one or more of an electrostatic punching process, a plasma punching process or a liquid solution pore process.

[0020] Preferably, the sand-fixing air hole includes a threaded section, and a filtering mechanism is provided in the sand-fixing air hole, and the filtering mechanism includes: a ring body, a rotating fan and a rotating shaft; the outer ring of the ring body is threadedly connected to the threaded section; the blades of the rotating fan are connected to the inner ring of the ring body, and when the air flow flows from the molding sand space to the vacuum box, the rotating fan rotates and drives the ring body to move away from the vacuum box; the bottom end of the rotating shaft is rotatably connected to the rotating fan, the top end of the rotating shaft is connected to the filter screen, and the side wall of the filter screen is slidably connected to the hole wall of the sand-fixing air hole.

[0021] Preferably, the molding sand is olivine sand, and the film breaking process includes: setting a jet nozzle in the sand consolidation pore, spraying any one of acid or organic solvent toward the first plastic film at the upper hole of the sand consolidation pore through the jet nozzle until the film breaking is completed; after the film breaking is completed, starting the vacuum box, and the upper surface of the filter screen rises to be flush with the upper surface of the first plastic film.

[0022] Preferably, the film breaking process adopts mixed acid solution to break the film; in parts by weight, the mixed acid solution includes 3-6 parts of formic acid and 2-4 parts of methanol; the first plastic film is an EVA film, the VA content of the EVA film is 22%-28%, and the thickness of the EVA film is 0.12-0.18mm.

[0023] Preferably, one side of the mold plate away from the vacuum box includes at least one bend, the upper opening of the coating air hole is aligned with the bend, and the distance between the upper opening of the sand consolidation air hole and the upper wall of the vacuum box is less than 1 / 3-1 / 2 of the height of the sand box.

[0024] Preferably, the side of the mold plate away from the vacuum box includes at least one horizontal section, the upper opening of the sand-fixing air hole is away from the end of the horizontal section, and the mold plate surface connected to the end gradually descends in the process of extending away from the end.

[0025] A lining plate production process adopts the negative pressure molding method to cast the lining plate; the molten metal includes, by mass percentage: C: 0.60%-0.70%, Si: 1.50%-1.80%, Mn: 0.92%-1.2%, Cr: 1.30%-2.00%, Mo: 0.01%-0.20%, Ni: 0.25%-0.60%, Al: 0.01%-0.05%, Cu: 0.05%-0.10%, V: 0.01%-0.20%, S≤0.03%, P: 0.01%~0.02%, and the rest is Fe and trace impurities, among which (Mo+V)≥0.08%.

[0026] Preferably, after the molten metal stays in the casting space for 5-10 hours, it is cooled to room temperature to obtain a preliminary plate; the preliminary plate is heated with the furnace and kept at 400-500°C for 2-3 hours, 650-750°C for 2-3 hours and 1000-1200°C for 4-5 hours, and the lining plate is obtained after water quenching, and the heating rate is 15-20°C / min.

[0027] The present invention has at least the following beneficial effects:

[0028] The present invention improves the existing mold plate and adds sand-fixing pores. When the first plastic film is covered on the surface of the mold plate, the first plastic film can be tightly attached to the surface of the mold plate through the combined effect of the film-covering pores and the sand-fixing pores; the process of vacuuming to fix the molding sand into an upper mold or a lower mold is improved, and vacuuming is no longer performed only around the molding sand. At the same time, the vacuum system of the vacuum box is used in conjunction with the film-breaking process and the sand-fixing pores, so that the vacuum position can be close to the middle of the molding sand, and then the sand mold is not easy to collapse when the area of ​​the sand box is increased, and the applicability of the side-vacuuming sand box is increased. At the same time, the load of subsequent operations, such as filtering of the vacuum pipeline system, taking out of castings, and selecting the location of the pouring and riser, will not be increased; by controlling the vacuum degree of the vacuum box and the molding sand space, the sand mold shape can be ensured to be stable during the film-breaking process; after adopting the negative pressure molding method provided by the present invention, the area of ​​the sand box can reach 2m 2 .

[0029] The present invention improves the proportion of molten metal components, so that the lining plate cast by the negative pressure molding method of the present invention has good strength and wear resistance, thereby improving the protective effect of the lining plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 It is the first schematic diagram of the negative pressure molding method;

[0032] Figure 2 is a second schematic diagram of the negative pressure molding method;

[0033] Figure 3 is a third schematic diagram of the negative pressure molding method;

[0034] Figure 4 It is a schematic diagram of the structure of a medium-sized plate of the negative pressure molding method of the present invention;

[0035] Figure 5 for Figure 4 Schematic diagram of the first state at A in the middle;

[0036] Figure 6 for Figure 4 Schematic diagram of the second state at A in the middle;

[0037] Figure 7 It is a schematic diagram of the connection between the rotating fan and the ring body;

[0038] Figure 8 This is a schematic diagram of the location of the sand consolidation pores;

[0039] Icons: 1-mold plate, 101-exhaust hole, 1011-film air hole, 1012-sand consolidation air hole, 2-exhaust box, 3-first plastic film, 4-sand box, 401-filter exhaust pipe, 5-second plastic film, 6-mold sand, 7-upper mold, 8-lower mold, 9-filter mechanism, 901-ring body, 902-rotating fan, 903-rotating shaft, 904-filter screen, 10-jet nozzle, 11-mold space, 12-pouring riser, 13-sand core. DETAILED DESCRIPTION

[0040] In order to make the purpose, method scheme and advantages of the embodiments of the present invention clearer, the method scheme in the embodiments of the present invention is clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0041] The negative pressure molding method in the prior art can refer to the following:

[0042] like Figure 1 As shown, after the vacuum box 2 and the template 1 are placed in place, the first plastic film 3 baked to a plastic state is covered on the template 1, and then the vacuum pump connected to the vacuum box 2 is used to evacuate air so that the film is closely attached to the surface of the template 1 for film forming. Figure 2 As shown, a sand box 4 with a filter exhaust pipe 401 is used to frame the mold plate 1 covered with a plastic film, and the sand box 4 is filled with molding sand 6 without adhesives and additives. The sand is compacted and flattened by micro-vibration, and a second plastic film 5 is placed on it to seal it. The valve is opened, and the air in the molding sand 6 is extracted through the filter exhaust pipe 401 on the side wall of the sand box 4, so that there is a pressure difference inside and outside the mold (about 300-400 mmHg). Due to the effect of the pressure difference, the mold is formed and has a higher hardness. The wet mold hardness meter reading can reach about 95. Finally, as shown in FIG. Figure 3 As shown, after the vacuum in the mold plate 1 is released, the mold is removed, the core is lowered, the box is closed and pouring is performed. After the molten metal solidifies, the mold is stopped from being evacuated. When the pressure in the mold approaches the atmospheric pressure, the mold collapses by itself.

[0043] Embodiment 1: A negative pressure molding method, comprising: manufacturing an upper mold 7 and a lower mold 8 respectively through a molding process, closing the upper mold 7 and the lower mold 8 so that the upper mold 7 and the lower mold 8 are aligned to form a casting space 11, and Figure 3 As shown in the figure, a pouring riser 12 is provided, and finally, molten metal is poured from the pouring riser 12 into the casting space 11. After the molten metal is cooled, the riser part is cut off to obtain a casting. The molding process includes:

[0044] S100, placing the template 1 with the air extraction hole 101 on the air extraction box 2, so that the air extraction hole 101 is connected with the inner space of the air extraction box 2;

[0045] S200, covering the baked first plastic film 3 on the surface of the template 1, and starting the vacuum box 2, so that the first plastic film 3 is closely attached to the surface of the template 1;

[0046] S300, placing the sand box 4 with a filter exhaust pipe 401 on the side on the exhaust box 2, at which time the mold plate 1 is located in the sand box 4, and then filling the sand box 4 with molding sand 6, vibrating and flattening it, and then covering the surface of the molding sand 6 with a second plastic film 5;

[0047] S400, extracting air from the molding sand 6 through a sand consolidation process to shape the molding sand 6;

[0048] The air extraction holes 101 on the mold plate 1 include film-covered air holes 1011 and sand-fixing air holes 1012, and a filter screen 904 is provided in the sand-fixing air holes 1012;

[0049] The sand consolidation process comprises:

[0050] D100, remove the air in the molding sand 6 by filtering the exhaust pipe 401 to make the vacuum degree of the molding sand 6 space greater than the vacuum degree of the sand consolidation pores 1012;

[0051] D200, generating through holes in the first plastic film 3 at the openings of the sand-fixing pores 1012 by a film-breaking process;

[0052] D300, secondary sand consolidation is performed through filtering the air extraction pipe 401 and / or the air extraction box 2 to obtain an upper mold 7 or a lower mold 8.

[0053] In the specific implementation process, before closing the box, Figure 3As shown, a sand core 13 is placed. The first plastic film 3 can be baked by a plastic film baker. In order to make the plastic film evenly attached to the mold plate 1, the plastic film must be heated. There are many heating methods available, mainly electric heating, gas heating, water heating, etc. In Japan, gas heating is used, but because the electric heater is simple and easy to use, it is widely used in China. The electric heating equipment using far-infrared radiation panels, the entire heater is a rectangular cover, and a number of far-infrared radiation panels are installed under the cover. It can also be heated by far-infrared radiation quartz glass tubes. The heated film is placed 150 to 300 mm below the radiation panel group. Since the heat loss at the four corners and the periphery of the heater is large, but the heat in the center is more concentrated, such baking will cause uneven heating of the film. In order to make the baking temperature of the heater more uniform, the far-infrared radiation panels are generally divided into several groups. The voltage supplied by each group of far-infrared radiation panels is adjusted to make the heat emitted from the entire heater uniform, and the plastic film is heated to 60 to 80°C. The heating time can be determined by testing according to the type and thickness of the film. Generally, it is sufficient to heat until the film begins to sag after a mirror-like surface appears. The structural forms of plastic film baking machines mainly include hanging lifting type, mobile type and automatic film conveying type that matches the production line.

[0054] The mold plate 1 can be provided with a positioning pin sleeve that matches the sand box 4, and the mold plate 1 can be a wooden assembly type. In the V-method molding, the mold plate 1 does not contact the molding sand 6 and does not need to be specially vibrated, compacted or heated at high temperature, so the wear and deformation of the mold plate 1 is very small, and the service life is long. It is usually made of economical and easy-to-construct wooden molds. However, the special requirements of the V method should be considered in the wooden mold structure:

[0055] 1. The template 1 is made hollow to form a vacuum chamber. Reinforcing ribs are arranged inside the larger template 1 to ensure that the template 1 will not break or deform under the action of the vacuum negative pressure.

[0056] 2. Try to avoid sharp edges and corners on the template 1 to prevent the film from being sucked into place or being broken.

[0057] 3. The draft angle of the mold plate 1 can be very small, or even no draft angle is required. This is because the film and the mold plate 1 are relatively smooth during V-method molding, the friction is very small, and the required draft force is small.

[0058] 4. The surface of the template 1 needs to be provided with exhaust holes 101. The exhaust holes 101 are generally 1.5 to 2.5 mm in diameter. The location of the exhaust holes varies with the contour shape of the template 1. However, special attention must be paid to the locations of the template 1 such as convex and concave, folded edges, corners, etc. that are not easy to be flattened and covered with film. For templates 1 with tortuous lines and complex contours, the spacing of the exhaust holes 101 should be smaller; for templates 1 with simple shapes and straight lines, the spacing of the exhaust holes 101 should be larger. For the top surface and facade without concave parts, it is not necessary to drill the exhaust holes 101.

[0059] 5. The surface of the wooden mold should not be painted with dry paint solution, nor with other paints with a temperature resistance lower than 60-70°C, otherwise the mold will stick after the heated plastic film is covered, affecting the demolding. Generally, silver powder can be applied on the surface of the wooden mold to protect one side of the template.

[0060] In this embodiment, the four walls of the sand box 4 can be welded with steel plates to form a sealed interlayer, and a connected exhaust chamber is formed between the interlayers. A pipe joint is welded on the outer wall of the end of the sand box 4, and the pipe joint can be connected to the vacuum system using a rubber hose. There are exhaust holes 101 on the four inner walls of the sand box 4, and porous air filter plates are installed there. In order to prevent fine sand from being sucked into the vacuum pump, two layers of 110 mesh metal wire mesh can be sandwiched between the porous air filter plates.

[0061] The vibration of the molding sand 6 can adopt the existing vibration table. The packing density of the molding sand 6 has a great influence on the casting. In order to improve the compressive strength and hardness of the molding sand 6, the packing density must be increased, and for this reason, it is necessary to vibrate when filling the sand. In addition, the vibration is also conducive to the filling of some local positions that are difficult to reach when filling the sand due to the influence of the natural stacking angle. When the film is partially bridged or the wrinkles are perpendicular to the sand filling direction, it will also affect the sand filling below it. After the decompression molding, the folded film will be pulled open in the direction where it is not filled, so that the casting surface forms an open state. When the compactness is not enough, it will also cause the danger of increasing the wall thickness of the casting due to the expansion of the sand, and it will also increase the seam of the parting surface. Therefore, it is very important to perform necessary vibrations during sand filling so that the dry sand with high fluidity can obtain sufficient compactness. The main parameters that affect compactness are the magnitude and direction of the exciting force. In the transverse convex and concave parts of the parts and the local bridges or wrinkles of the film perpendicular to the sand filling direction, the unidirectional exciting force in the vertical direction alone often cannot meet the requirements of local filling and compactness. The most ideal is to apply three-dimensional vibration to the molding sand 6 to make it flow in an irregular three-dimensional manner, to achieve the best filling and compacting effect, and to improve the filling and compacting efficiency. For castings with simple shapes and no transverse concave and convex parts, ordinary vibration tables can be used; but when the castings are more complex, with horizontal holes or transverse concave and convex changes, it is best to use a three-dimensional vibration table, which can meet the different vibration forms and exciting force modeling requirements of various castings, effectively avoid poor sand filling and improve filling and compacting efficiency.

[0062] like Figure 4As shown, in this embodiment, additional sand-fixing pores 1012 are provided on the mold plate 1. The aperture and number of the sand-fixing pores 1012 are not limited in this embodiment, and can be set according to the shape of the mold plate 1 and the specifications of the sand box 4. The filter screen 904 in the sand-fixing pores 1012 can be 120 meshes, and the air flow can be ensured to pass through while the molding sand 6 does not pass through. The vacuum box 2 needs to be provided with openings corresponding to the sand-fixing pores 1012, so that the vacuum system of the vacuum box 2 can be directly used to realize the sand-fixing pores 1012 to evacuate the sand mold. In this embodiment, the sand box 4 is first used to evacuate the sand mold so that the shape has a certain degree of stability, and then the first plastic film 3 is made to have a through hole through which the air flow can pass through by a film breaking process. Before the film is broken, the sand box 4 is used to evacuate the sand 6 once, so as to prevent the sand 6 from falling from the through hole, and the vacuum degree of the space of the molding sand 6 is controlled to be greater than the vacuum degree of the sand-fixing pores 1012, so as to further prevent the sand 6 from falling. The molding sand 6 space refers to the gap space formed by the stacking of molding sand 6.

[0063] Example 2: In order to make the vacuum degree of each part of the sand mold as consistent as possible, improvements were made on the basis of Example 1. The D300 specifically includes the following operations: first, air is pumped through the vacuum box 2 to make the vacuum degree in the vacuum box 2 equal to the vacuum degree in the space of the molding sand 6, and then the filtering vacuum pipe 401 and the vacuum box 2 are started at the same time to realize the solidification of the molding sand 6, and finally the upper mold 7 or the lower mold 8 is obtained.

[0064] During the specific implementation process, since the vacuum degree of the molding sand 6 space is greater than the sand-fixing pores 1012 before the film is broken, the air in the vacuum box 2 has a movement tendency to enter the molding sand 6 from the through hole after the film is broken, thereby balancing the vacuum degree of the two spaces. Since the sand-fixing pores 1012 in this embodiment are opened near the middle of the sand box 4, and the vacuum degree of the middle of the sand box 4 is relatively low due to the distance from the filter exhaust pipe 401 of the sand box 4, if the air in the exhaust box 2 enters the sand mold again, it will affect the morphological stability of the sand mold. Therefore, after the film is broken, the vacuum degree in the two spaces is first made consistent by the vacuum system of the exhaust box 2, and then the vacuum system of the sand box 4 and the vacuum system of the exhaust box 2 are used at the same time to make the vacuum degree of each part of the molding sand 6 as consistent as possible. The vacuum degree can be detected by a pressure gauge, and a pressure gauge can be set in the exhaust box 2 and in the side wall interlayer of the sand box 4 respectively. Through the existing control system, such as the PLC control system, the pressure gauge is electrically connected to the control system, and the opening and closing of the vacuum system and the exhaust rate are controlled by the value comparison of the pressure gauge.

[0065] Embodiment 3: The membrane breaking process includes one or more of an electrostatic punching process, a plasma punching process or a liquid pore-inducing process.

[0066] In the specific implementation process, both the electrostatic punching machine and the plasma punching machine are existing technologies. The punching end can be placed on the sand-fixing pore 1012 and aligned with the upper hole to achieve the punching of the first plastic film 3. There are two types of punching operations. One is that the first plastic film 3 at the upper hole of the sand-fixing pore 1012 is broken and dropped as a whole to form a through hole; the other is to punch a number of small through holes in the first plastic film 3 at the upper hole of the sand-fixing pore 1012. Liquid-induced pores refer to the damage of the first plastic film 3 by the corrosion of the solution.

[0067] A water bath filter tank can be set in the vacuum system, which can not only prevent the fine sand or dust sucked from the sand box 4 from entering the pump and affecting the normal operation of the pump, but also prevent the fine sand or dust from entering the pump and wearing the parts. A dust cover, a filter screen 904, a liquid level indicator and a dust exhaust valve are set in the water bath filter tank. The fine yarn and dust sucked from the sand box 4 are blocked by the dust cover, filtered by the water bath and the filter screen 904, and sink by their own weight to the bottom of the tank body. The dust exhaust valve is opened regularly to remove the fine yarn and dust that have fallen. In order to improve the filtering effect, it is necessary to consider increasing the filtering area and reducing the filtering speed, and to increase the cross-sectional area of ​​the filter tank as much as possible. In addition, since the solution used in the membrane breaking process is under negative pressure, it can also be removed by a water bath. Vacuum pumps are divided into dry and wet types. Dry vacuum pumps can obtain high vacuum, but the structure is complex and prone to failure, and maintenance is inconvenient, especially the low air extraction volume. The wet vacuum pump has a low vacuum degree, but a large air extraction volume, reliable use and low failure rate. When V-method molding, it is not necessary to have too high a vacuum degree, which is generally within the range of -0.04 to -0.06 MPa. Generally, a wet vacuum pump can meet the vacuum degree required for V-method molding, especially its large air extraction capacity is suitable for the needs of V-method molding. Generally, a water ring vacuum pump is selected. When selecting, attention should be paid to the relationship between the air extraction capacity and the vacuum degree. Generally speaking, the greater the vacuum degree formed, the smaller the air extraction capacity. The air extraction capacity of the vacuum pump can be determined according to the size of the sand box 4, the number of sand boxes 4 that are vacuumed at the same time, the air leakage caused by the film burning during casting, and the air leakage of the vacuum system except the sand box 4.

[0068] Embodiment 3: In order to prevent the first plastic film 3 from being damaged and the molding sand 6 from entering the damaged gap during the subsequent exhaust process, resulting in defects in the mold space 11 formed after the mold is closed, improvements are made on the basis of Embodiment 1, such as Figure 4-7As shown, the sand-fixing air hole 1012 includes a threaded section, and a filtering mechanism 9 is arranged inside the sand-fixing air hole 1012, and the filtering mechanism 9 includes: a ring body 901, a rotating fan 902 and a rotating shaft 903; the outer ring of the ring body 901 is threadedly connected to the threaded section; the blades of the rotating fan 902 are connected to the inner ring of the ring body 901, and when the air flow flows from the molding sand 6 space to the vacuum box 2, the rotating fan 902 rotates and drives the ring body 901 to move away from the vacuum box 2; the bottom end of the rotating shaft 903 is rotatably connected to the rotating fan 902, and the top end of the rotating shaft 903 is connected to the filter screen 904, and the side wall of the filter screen 904 is slidably connected to the hole wall of the sand-fixing air hole 1012.

[0069] During the specific implementation process, the ring body 901 and the rotating fan 902 can be made of lightweight plastic materials to facilitate the airflow to drive the two to move. The shape of the blades of the rotating fan 902 can refer to the existing technology, and this embodiment is not limited. The moving airflow can drive it to rotate. If the film breaking process adopts the method of removing the complete first plastic film 3 at the upper opening of the sand-fixing pore 1012, a complete through hole is formed. After the film breaking is completed, there is a certain gap between the sand mold and the filter screen 904, and the sand mold has no support. After the vacuum system of the vacuum box 2 is turned on, the molding sand 6 may enter the gap space, resulting in morphological defects in the upper mold 7 or the lower mold 8. Therefore, this embodiment is arranged as follows Figure 5 The rotating fan 902 shown in the figure, after the membrane is broken, cooperates with the air flow movement of the vacuum box 2 when the air is exhausted, and the rotating fan 902 rotates, driving the ring body 901 to move upward, and then driving the filter screen 904 to move upward until it is as shown in FIG. Figure 6 As shown, the upper surface of the filter screen 904 is flush with the upper surface of the first plastic film 3, thereby ensuring the morphological standard of the sand mold. Since the first plastic film 3 will be hot-melted and decomposed by the molten metal during the pouring stage, the through holes on the first plastic film 3 will not cause defects in the shape of the casting. The length of the threaded section can be set according to the height to which the filter screen 904 needs to rise, so as to prevent the filter screen 904 from squeezing the sand mold when the vacuum box 2 is evacuating air. Since the mesh number of the filter screen 904 is large, almost no grid pattern will be left on the sand mold. If there is a requirement for the smoothness of the casting surface, it will also be polished in the subsequent process, so the existence of the filter screen 904 will not affect the final molding quality of the casting.

[0070] Example 5: In order to prevent the molding sand 6 from clumping, affecting the exhaust process or reducing the sand mold performance, such as strength and heat resistance, after chemical reaction, improvements are made on the basis of Example 4. The molding sand 6 is made of olivine sand, and the film breaking process includes: a jet nozzle 10 is set at the sand consolidation pore 1012, and any one of acid or organic solvent is sprayed toward the first plastic film 3 at the upper hole of the sand consolidation pore 1012 through the jet nozzle 10 until the film breaking is completed; after the film breaking is completed, the vacuum box 2 is started, and the upper surface of the filter screen 904 rises to be flush with the upper surface of the first plastic film 3.

[0071] In the specific implementation process, although there are many ways to break the film, in order to reduce the economic cost of industrial implementation, this embodiment selects the liquid dissolution process. If an electrostatic puncher or plasma puncher is selected, most of the existing devices can only be used for one casting station, but in the industrial manufacturing process, there are often a large number of stations that perform frequent casting operations simultaneously, and thus a large number of punching equipment is required, which has a high economic cost. However, the price of liquid dissolution-related equipment is low, and the spraying of multiple stations can be simply achieved by laying out branch pipes, and it will not occupy too much plant area, further reducing production costs.

[0072] Olivine sand has good acid resistance and may react only under strong acid, while organic solvents have almost no corrosive effect on the molding sand 6. The use of a jet nozzle 10 can ensure the spraying height and range of the acid or organic solvent. In addition, reasonable control of the jet flow rate and flow path can reduce the impact of the jet on the sand mold. In the selection of materials for devices that may contact acid or organic solvents, such as the mold plate 1, the vacuum box 2, and the rotating fan 902, some acid-resistant or organic solvent-resistant materials, such as stainless steel, glass, and PTFE, need to be selected. The mold plate 1 can be made of PTFE, which is resistant to high pressure while facilitating the production of the vacuum hole 101, so as to avoid damage to the mold plate 1 when the vacuum is high.

[0073] Example 6: In order to quickly break the film without affecting the molding sand 6, an improvement was made on the basis of Example 5, and the film breaking process adopted a mixed acid solution; in parts by weight, the mixed acid solution included 3-6 parts of formic acid and 2-4 parts of methanol; the first plastic film 3 was an EVA film, the VA content of the EVA film was 22%-28%, and the thickness of the EVA film was 0.12-0.18mm.

[0074] During the specific implementation process, a reasonable acid concentration can ensure the dissolution of the first plastic film 3 without affecting the molding sand 6. The VA content of the EVA film used in the negative pressure molding method in the prior art is generally less than 20%, because under a vacuum state, the EVA film is easy to harden, and the air permeability and flexibility deteriorate, affecting the quality of the casting, such as the appearance of defects such as pores inside the casting. However, the VA content in the EVA film affects its performance. The higher the VA content, the higher the solubility and elongation. Therefore, when the VA content is increased, the film breaking process is easier to achieve the purpose. At the same time, when the elongation of the EVA film is increased, the thickness can be appropriately reduced, which further helps the realization of the film breaking. In addition, although the VA content of the EVA film in this embodiment is increased, the air permeability of the EVA film is guaranteed due to the existence of the film breaking process. According to the applicant's experiment, the optimal content of VA is 25% and the optimal thickness of EVA is 0.14mm.

[0075] By combining formic acid and methanol and making a reasonable ratio, the mixed acid solution can dissolve the EVA film quickly without affecting the olivine sand. At the same time, the mixed solution infiltrating the molding sand 6 can be pyrolyzed into reducing gas after the metal liquid is injected, which prevents the metal liquid from being oxidized and forming pressure in the gaps of the sand mold, reduces or prevents the infiltration of the metal liquid, and does not increase the ash content of the molding sand 6, which is beneficial to the reuse of the molding sand 6. Since the first plastic film 3 will decompose under the heat of the metal liquid, the decomposed gas needs to be taken out, and methanol is also a good carrier, which is beneficial to the removal of the gas after the decomposition of the first plastic film 3.

[0076] Embodiment 7: In order to better achieve the close contact between the first plastic film 3 and the template 1 and to increase the available area of ​​the sand box 4, improvements are made on the basis of Embodiments 1-6, such as Figure 4 As shown, one side of the mold plate 1 away from the vacuum box 2 includes at least one bend, the upper opening of the coating air hole 1011 is aligned with the bend, and the distance between the upper opening of the sand consolidation air hole 1012 and the upper wall of the vacuum box 2 is less than 1 / 3-1 / 2 of the height of the sand box 4.

[0077] During the specific implementation process, when the first plastic film 3 is covered on the surface of the template 1, the bending part of the surface of the template 1 is where the deformation of the first plastic film 3 is large. In order to prevent the first plastic film 3 from wrinkling and smoothly cover the bending part of the template 1, the upper hole of the coating pore 1011 is aligned with the bending part in this embodiment. Figure 4 Only one sand-fixing air hole 1012 is shown in the figure, and the number and arrangement of the sand-fixing air holes 1012 can be set according to actual conditions. Since the purpose of the sand-fixing air holes 1012 is to increase the vacuum degree in the middle of the sand mold, making the middle part more compact and preventing the mold from collapsing, the arrangement positions of the sand-fixing air holes 1012 are mainly concentrated in the middle of the sand box 4. Figure 2 It can be seen that with respect to the movement of the air flow in the middle of the sand box 4 toward the filter exhaust pipe 401, the upper part moves first rather than the lower part. Therefore, the thicker the middle sand mold is, the greater the difference between the vacuum degree of the gap between the sand mold below it and the vacuum degree around the sand mold. Therefore, the setting positions of the coating air holes 1011 are mainly concentrated in the part with thicker sand mold. For the part with thinner sand mold thickness, even if it is located in the middle of the sand box 4, it can be selected whether to set the sand-fixing air holes 1012 according to the actual situation.

[0078] Embodiment 8: In order to prevent the mixed liquid from affecting the first plastic film 3 around the sand-fixing pores 1012, an improvement is made on the basis of Embodiment 7, such as Figure 8 As shown, the side of the mold plate 1 away from the vacuum box 2 includes at least one horizontal section, the upper opening of the sand consolidation hole 1012 is away from the end of the horizontal section, and the surface of the mold plate 1 connected to the end gradually descends during the process of extending away from the end.

[0079] In the specific implementation process, if the sand consolidation pores 1012 are Figure 8 As shown in the figure, the mixed liquid is more likely to move toward the two sides of the sand-fixing air hole 1012, thereby possibly damaging the first plastic film 3 around the sand-fixing air hole 1012. The sand-fixing air hole 1012 can be as shown in the figure. Figure 4 The vertical arrangement shown in the figure, and the jet direction of the jet nozzle 10 is vertically upward to reduce the diffusion of the mixed liquid to the surroundings. In addition, since the vacuum degree of the molding sand 6 space is greater than the vacuum degree of the sand-fixing pores 1012 during the film breaking process, the vacuum degree difference is controlled so that the movement trend of the mixed liquid can remain upward even under its own action, thereby preventing it from falling on the first plastic film 3 around the sand-fixing pores 1012.

[0080] Embodiment 9: This embodiment provides a lining plate production process, adopts the negative pressure molding method to cast the lining plate; in terms of mass percentage, the molten metal includes: C: 0.60%-0.70%, Si: 1.50%-1.80%, Mn: 0.92%-1.2%, Cr: 1.30%-2.00%, Mo: 0.01%-0.20%, Ni: 0.25%-0.60%, Al: 0.01%-0.05%, Cu: 0.05%-0.10%, V: 0.01%-0.20%, S≤0.03%, P: 0.01%~0.02%, and the rest is Fe and trace impurities, among which (Mo+V)≥0.08%.

[0081] During the specific implementation process, the applicant applied for a patent with publication number CN110846586A on December 16, 2019, and the patent name is a high-strength and high-wear-resistant steel ball steel and its preparation method. The applicant hopes to use the molten metal components in the aforementioned patent for lining plate manufacturing, and make full use of the synergistic coordination of the components in the molten metal to improve the strength and wear resistance of the lining plate. The preparation method of the molten metal can refer to the aforementioned patent, and this embodiment will not be repeated.

[0082] Example 10: In order to further improve the performance of the lining plate, improvements were made based on Example 9. After the molten metal stayed in the casting space for 5-10 hours, it was cooled to room temperature to obtain a preliminary plate. The preliminary plate was heated with the furnace and kept at 400-500°C for 2-3 hours, 650-750°C for 2-3 hours and 1000-1200°C for 4-5 hours, and the lining plate was obtained after water quenching. The heating rate was 15-20°C / min.

[0083] In the specific implementation process, in the patent with publication number CN110846586A, the preparation of the steel ball blank is forging, while this embodiment is casting. Therefore, how to achieve or approach the product performance of the forging process through the casting process under the same molten metal composition is one of the research focuses of the applicant. This embodiment defines the heat treatment process of the primary plate.

[0084] test:

[0085] Liner production process of Example 1-11: Scrap steel, pig iron, ferrochrome, ferromolybdenum and nickel blocks are loaded into an induction melting furnace, and when the molten steel is dissolved, ferrosilicon, ferromanganese, aluminum blocks, copper blocks and ferrovanadium are added in sequence through a secondary feeding device for vacuum melting, and the maximum temperature of the molten steel is raised to 1600°C, and casting is performed after the temperature is reduced to 1450°C. The results of the molten metal composition test are in mass percentage, and the molten metal includes: C: 0.64%, Si: 1.61%, Mn: 0.97%, Cr: 1.42%, Mo: 0.13%, Ni: 0.31%, Al: 0.01%, Cu: 0.07%, V: 0.15%, S: 0.003%, P: 0.012%, and the rest is Fe and trace impurities.

[0086] The liner is cast by a negative pressure molding method. The negative pressure molding method includes making an upper mold and a lower mold respectively through a molding process, closing the box so that the upper mold and the lower mold are aligned to form a casting space, and finally pouring molten metal into the casting space. After the molten metal is cooled, a casting is obtained. The molding process includes:

[0087] S100, placing a template with exhaust holes on an exhaust box, so that the exhaust holes are connected to the inner space of the exhaust box;

[0088] S200, covering the surface of the template with a first plastic film, and starting the vacuum box so that the first plastic film is closely attached to the surface of the template;

[0089] S300, placing a sand box with a filter exhaust pipe on the side on the exhaust box, at which time the mold plate is located in the sand box, and then filling the sand box with molding sand and covering the surface of the molding sand with a second plastic film;

[0090] S400, extracting air from the molding sand through a sand consolidation process to form the molding sand;

[0091] The air extraction holes on the template include film-covered air holes and sand-fixing air holes, and a filter screen is provided in the sand-fixing air holes;

[0092] The sand consolidation process comprises:

[0093] D100, remove the air in the molding sand by filtering the suction pipe, so that the vacuum degree of the molding sand space is greater than the vacuum degree of the sand consolidation pores;

[0094] D200, generating through holes in the first plastic film at the openings of the sand consolidation pores through a film breaking process;

[0095] D300, secondary sand consolidation is performed through filtering the air suction pipe and / or the air suction box to obtain an upper mold or a lower mold.

[0096] The sand-fixing pore includes a threaded section, and a filter mechanism is arranged inside the sand-fixing pore. The filter mechanism includes: a ring body, a rotating fan and a rotating shaft. The outer ring of the ring body is threadedly connected to the threaded section; the blades of the rotating fan are connected to the inner ring of the ring body. When the airflow flows from the molding sand space to the vacuum box, the rotating fan rotates and drives the ring body to move away from the vacuum box; the bottom end of the rotating shaft is rotationally connected to the rotating fan, and the top end of the rotating shaft is connected to the filter screen, and the side wall of the filter screen is slidably connected to the hole wall of the sand-fixing pore. The molding sand adopts olivine sand, and the film breaking process includes: a jet nozzle is arranged in the sand-fixing pore, and any one of acid or organic solvent is sprayed toward the first plastic film at the upper opening of the sand-fixing pore through the jet nozzle until the film breaking is completed; after the film breaking is completed, the vacuum box is started, and the upper surface of the filter screen rises to be flush with the upper surface of the first plastic film. The film breaking process adopts mixed acid solution to break the film; in terms of weight, the mixed acid solution includes 3-6 parts of formic acid and 2-4 parts of methanol; the first plastic film is an EVA film, the VA content of the EVA film is 22%-28%, and the thickness of the EVA film is 0.12-0.18mm. The side of the mold plate away from the vacuum box includes at least one bend, the upper opening of the film-coating pore is aligned with the bend, and the distance between the upper opening of the sand-fixing pore and the upper wall of the vacuum box is less than 1 / 2 of the height of the sand box. The side of the mold plate away from the vacuum box includes at least one horizontal section, the upper opening of the sand-fixing pore is away from the end of the horizontal section, and the mold plate surface connected to the end gradually descends in the process of extending away from the end.

[0097] After the molten metal stays in the casting space for 8 hours, it is cooled to room temperature to obtain a preliminary plate; the preliminary plate is heated with the furnace and kept at 400-500℃ for 2 hours, 650-750℃ for 3 hours and 1000-1200℃ for 4.5 hours, and then the lining plate is obtained after water quenching, and the heating rate is 15-20℃ / min.

[0098] Comparative Example 1:

[0099] The relevant parameters of the embodiment and the comparative example are shown in Table 1. Temperature 1 refers to the temperature of the first insulation when the primary plate is heated with the furnace. Temperature 2 refers to the temperature of the second insulation when the primary plate is heated with the furnace. Temperature 3 refers to the temperature of the third insulation when the primary plate is heated with the furnace.

[0100] Table 1

[0101]

[0102]

[0103]

[0104] The mixed acid solution ratio of Comparative Example 2 is 5 parts of formic acid and 3 parts of water, and the remaining process steps are consistent with Example 15.

[0105] In comparative example 3, the distance between the upper hole of the sand-consolidating pore and the upper wall of the vacuum box is greater than 1 / 2 of the height of the sand box, and there is a wall on the upper surface of the model whose distance from the upper wall of the vacuum box is less than 1 / 2 of the height of the sand box. The remaining process steps are the same as those in Example 15.

[0106] In comparative example 4, the upper opening of the sand-consolidating pore is located at the end of the horizontal section, and the remaining process steps are the same as those in example 15.

[0107] Comparative Example 5: The molten metal adopts the proportions shown in Table 2, and the remaining process steps are consistent with those of Example 15.

[0108] Table 2

[0109]

[0110] Comparative Example 6: The molten metal adopts the proportions shown in Table 3, and the remaining process steps are consistent with those of Example 15.

[0111] Table 3

[0112]

[0113]

[0114] The performance and appearance of the liner plates prepared according to the processes of Examples 1-15 and Comparative Examples 1-4 were tested. The results are shown in Table 4.

[0115] Table 4

[0116]

[0117]

[0118] From the comparison between the embodiment and comparative examples 5-6, it can be seen that the liner produced by the production process of the present invention has improved mechanical properties. The optimal process parameters can refer to Example 15. In addition, when the present invention uses low-manganese molten metal, the impact toughness of the liner produced is much higher than that of comparative example 5, and even higher than that of the alloyed high-manganese steel in comparative example 6. Although the liner produced by the liner production process provided by the present invention does not fully reach the high-strength, toughness and wear-resistant steel ball steel in the patent with publication number CN110846586A in terms of performance, it is much higher than the liner in the prior art. It can be seen that the combination of the molten metal component and the heating process of the primary plate in the present invention can effectively improve the performance of the liner.

[0119] It can be seen from Example 15 and Comparative Examples 1-2 that the mixed acid solution ratio provided by the present invention is beneficial to improving the performance of the lining.

[0120] It can be seen from Example 15 and Comparative Examples 3-4 that the sand consolidation pore setting positions provided by the present invention are beneficial to improving the liner performance.

[0121] After testing, the linings produced according to the processes of Examples 1-15 had no appearance defects, and the linings produced according to the process of Comparative Example 4 had excellent performance but slight appearance defects.

[0122] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A negative pressure molding method, comprising: After the upper mold and the lower mold are made respectively by the molding process, the upper mold and the lower mold are assembled so as to form a casting space, and finally molten metal is poured into the casting space, and a casting is obtained after the molten metal is cooled. The molding process includes: S100, placing a template with exhaust holes on an exhaust box, so that the exhaust holes are connected to the inner space of the exhaust box; S200, covering the surface of the template with a first plastic film, and starting the vacuum box so that the first plastic film is closely attached to the surface of the template; S300, placing a sand box with a filter exhaust pipe on the side on the exhaust box, at which time the mold plate is located in the sand box, and then filling the sand box with molding sand and covering the surface of the molding sand with a second plastic film; S400, extracting air from the molding sand through a sand consolidation process to form the molding sand; The air extraction holes on the template include film-covered air holes and sand-fixing air holes, and a filter screen is provided in the sand-fixing air holes; The sand consolidation process comprises: D100, remove the air in the molding sand by filtering the suction pipe, so that the vacuum degree of the molding sand space is greater than the vacuum degree of the sand consolidation pores; D200, generating through holes in the first plastic film at the openings of the sand consolidation pores through a film breaking process; D300, secondary sand consolidation is performed through filtering the air suction pipe and / or the air suction box to obtain an upper mold or a lower mold.

2. The negative pressure molding method according to claim 1, characterized in that: The D300 specifically includes the following operations: firstly, air is pumped out through the vacuum box to make the vacuum degree in the vacuum box equal to the vacuum degree in the molding sand space, and then the filtering vacuum pipe and the vacuum box are started at the same time to solidify the molding sand, and finally an upper mold or a lower mold is obtained.

3. The negative pressure molding method according to claim 1, characterized in that: The membrane breaking process includes one or more of an electrostatic punching process, a plasma punching process or a liquid solution pore-inducing process.

4. The negative pressure molding method according to claim 1, characterized in that: The sand consolidation pore includes a threaded section, and a filtering mechanism is provided in the sand consolidation pore, and the filtering mechanism includes: A ring body, wherein the outer ring of the ring body is threadedly connected to the threaded segment; A rotating fan, wherein the blades of the rotating fan are connected to the inner ring of the ring body, and when the air flows from the molding sand space to the air extraction box, the rotating fan rotates and drives the ring body to move away from the air extraction box; A rotating shaft, the bottom end of which is rotatably connected to the rotating fan, the top end of which is connected to the filter screen, and the side wall of the filter screen is slidably connected to the hole wall of the sand consolidation pore.

5. The negative pressure molding method according to claim 4, characterized in that: The molding sand is olivine sand, and the film breaking process includes: a jet nozzle is arranged in the sand consolidation pore, and any one of acid or organic solvent is sprayed toward the first plastic film at the upper hole of the sand consolidation pore through the jet nozzle until the film breaking is completed; after the film breaking is completed, the vacuum box is started, and the upper surface of the filter screen rises to be flush with the upper surface of the first plastic film.

6. The negative pressure molding method according to claim 5, characterized in that: The film breaking process adopts mixed acid solution to break the film; in parts by weight, the mixed acid solution includes 3-6 parts of formic acid and 2-4 parts of methanol; the first plastic film is an EVA film, the VA content of the EVA film is 22%-28%, and the thickness of the EVA film is 0.12-0.18mm.

7. The negative pressure molding method according to any one of claims 1 to 6, characterized in that: The side of the mold plate away from the vacuum box includes at least one bend, the upper opening of the coating air hole is aligned with the bend, and the distance between the upper opening of the sand consolidation air hole and the upper wall of the vacuum box is less than 1 / 3-1 / 2 of the height of the sand box.

8. The negative pressure molding method according to claim 7, characterized in that: The side of the template away from the vacuum box includes at least one horizontal section, the upper opening of the sand consolidation air hole is away from the end of the horizontal section, and the template surface connected to the end gradually descends during the process of extending away from the end.

9. A lining board production process, characterized in that: The liner is cast by the negative pressure molding method described in any one of claims 1 to 7; In terms of mass percentage, the molten metal includes: C: 0.60%-0.70%, Si: 1.50%-1.80%, Mn: 0.92%-1.2%, Cr: 1.30%-2.00%, Mo: 0.01%-0.20%, Ni: 0.25%-0.60%, Al: 0.01%-0.05%, Cu: 0.05%-0.10%, V: 0.01%-0.20%, S≤0.03%, P: 0.01%~0.02%, the rest are Fe and trace impurities, among which (Mo+V)≥0.08%.

10. The lining board production process according to claim 9, characterized in that: After the molten metal stays in the casting space for 5-10 hours, it is cooled to room temperature to obtain a preliminary plate; the preliminary plate is heated with the furnace and kept at 400-500℃ for 2-3 hours, 650-750℃ for 2-3 hours and 1000-1200℃ for 4-5 hours, and then the lining plate is obtained after water quenching, and the heating rate is 15-20℃ / min.

Images