A method for laminated jet forming of coated sand shell molds

Abstract

The present invention relates to a method for layered injection molding of a coated sand shell mold. This method uses an injection molding machine to sequentially inject coated sands of various different particle sizes onto the surface of a molding die to obtain a sand mold with a particle size gradient. The molding die is placed inside the molding machine housing, and a heating device is used to heat the molding die; then sandblasting is started, and the sandblasting process is carried out in sequence according to the process of increasing the particle size of the coated sand. After the sandblasting is completed, it is naturally cooled and solidified, and finally the sand mold is taken out. This method first sprays a layer of fine sand on the surface of the mold to form the innermost layer of the sand mold, improving the surface quality of the casting; the intermediate layer of the sand mold uses coated sand with a moderate particle size; the outer layer uses coarser sand grains to improve the gas permeability of the sand mold. It makes full use of the waste fine-grained quartz sand and coarse-grained quartz sand in the traditional sand mold process, reduces the consumption of ineffective quartz sand, reduces the production cost of the sand mold, and improves the quality level of the casting.

Description

Technical Field

[0001] The present invention belongs to the field of metal casting, and particularly relates to a method for manufacturing a coated quartz sand shell mold. Background Art

[0002] Sand casting is a casting method for producing metal castings by pouring molten metal into a sand mold. Steel, iron, and most non-ferrous alloy castings can be obtained by sand casting. Since the molding materials used in sand casting are inexpensive and easily available, and the sand mold is simple to manufacture, it is applicable to both single-piece production and batch production of castings. For a long time, it has been the basic process of casting production.

[0003] The sand mold manufacturing process is complex, usually manually manufactured, with low production efficiency and high costs. Therefore, the equipment for sand mold manufacturing has gradually developed towards automation. Currently, sand mold manufacturing equipment can generally be divided into three categories: jolt molding machines, jolt-squeeze molding machines, and injection-squeeze molding machines. Among them, injection-squeeze molding machines have the advantages of low noise, low labor intensity of workers, high production efficiency, and less environmental pollution. Therefore, injection-squeeze molding machines have become the key research and development direction of current sand mold manufacturing equipment.

[0004] An injection-squeeze molding machine uses compressed air to evenly spray molding sand onto the surface of the mold for pre-compaction, and then applies pressure for compaction. There are mainly vertical parting flaskless injection-squeeze molding machines and horizontal parting flaskless injection-squeeze molding machines. The vertical parting flaskless injection-squeeze molding machine does not require a sand box for molding. The molding sand is directly injected into the molding chamber with a template. The sand mold manufactured has high dimensional accuracy. Since there are cavities on both sides of the sand box, the production rate is very high, but it is more difficult to place cores and has strict requirements for the quality of molding sand. The horizontal parting flaskless injection-squeeze molding machine uses a sand box for molding. After the sand mold is manufactured, the mold is closed and the sand box is removed. It is more convenient to place cores and has a high production rate. The horizontal parting flaskless injection-squeeze molding machine is less used in China at present because it is more difficult to manufacture and the cost of the sand mold is relatively high.

[0005] The particle size of the coated sand has a great influence on the overall quality of the casting. Larger sand grains will lead to problems such as reduced surface finish, burrs, and voids, while smaller sand grains will result in low air permeability of the sand mold, causing defects such as porosity and misruns in the casting. Currently, to solve this problem, quartz sand of moderate particle size is mostly used for coating, and fine sand and coarse sand are not fully utilized, increasing the consumption of quartz sand and thus resulting in a relatively high production cost of the sand mold. Summary of the Invention

[0006] Aiming at the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for layered injection molding of a coated sand shell mold with reduced production costs.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for layered injection molding of coated sand shell type, which is carried out by using the following injection molding machine, and the structure of the injection molding machine is as follows:

[0008] It includes a molding machine housing and N storage sand boxes, N ≥ 2;

[0009] The N storage sand boxes are arranged above the molding machine housing, and the bottom of each storage sand box is connected to a transport pipe, each transport pipe passes through the top of the molding machine housing and enters the molding machine housing, and a sand shooting head is installed at the bottom of each transport pipe;

[0010] A molding die and a heating device are arranged in the molding machine housing, the molding die is placed on the heating device, and all the sand-shooting heads are located directly above the molding die;

[0011] The method for layered injection molding of coated sand shell molds using an injection molding machine comprises the following steps:

[0012] S1: Place N types of coated sands of different particle sizes into N storage sand boxes respectively;

[0013] S2: placing the molding die into the molding machine housing, and using a heating device to heat the molding die to 150-200°C;

[0014] S3: After adjusting the sandblasting pressure, time and the distance from the sandblasting port to the molding die, start sandblasting;

[0015] The sandblasting process is carried out in sequence according to the process from small to large particle size of the coated sand. When the coated sand with small particle size is fully spread on the molding mold, the coated sand with larger particle size is laid, and the process is carried out in sequence.

[0016] S4: After the spraying of coated sands of all particle sizes is completed, the heating is stopped, and the molding mold and the coated sand therein are cooled naturally and the sand mold is fixed, and then the sand mold is taken out.

[0017] As an improvement, each of the transport pipelines is connected to a plurality of sand distribution pipes, each of the sand distribution pipes is connected to M sand distribution branch pipes, M≥2, and a sand shooting head is installed at the bottom of each of the sand distribution branch pipes.

[0018] As an improvement, the M sand-shooting heads are distributed in a row.

[0019] As an improvement, the injection molding machine also includes a limit plate, the sand branch pipe is a telescopic tube, and the limit plate has a plurality of limiting holes. The bottoms of all the sand branch pipes pass through the limiting holes one by one, and each sand branch pipe is tightly fitted with the limiting hole.

[0020] As an improvement, the injection molding machine further includes a transmission device, which includes a motor and a lead screw. The output shaft of the motor is fixedly connected to the lead screw, and the lead screw passes through the limit disk and is threadedly connected to the limit disk.

[0021] As an improvement, the sandblasting pressure in S3 is controlled at 2 - 10 MPa.

[0022] As an improvement, the distance between the sand injection port and the mold in S3 is 20 - 50 cm.

[0023] As an improvement, the sandblasting time in S3 is controlled at 10 - 30 s.

[0024] Compared with the prior art, the present invention has at least the following advantages:

[0025] The invention method proposed by the present invention classifies the coated quartz sand by particle size, makes full use of the fine - grained quartz sand and coarse - grained quartz sand discarded in the traditional sand mold process, and uses layered injection to manufacture a sand mold with a multi - layer structure, improving the quality level of castings. First, a layer of fine sand is sprayed on the mold surface to form the innermost layer of the sand mold, improving the surface quality of the casting and avoiding problems such as burrs and voids on the casting surface; the middle layer of the sand mold uses coated sand with a moderate particle size; the outer layer uses coarser sand grains to improve the air permeability of the sand mold and avoid defects such as gas holes and misruns inside the casting. Make full use of the fine - grained quartz sand and coarse - grained quartz sand discarded in the traditional sand mold process, reduce the consumption of ineffective quartz sand, reduce the production cost of the sand mold, and improve the quality level of castings. Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of a molding machine.

[0027] Figure 2 It is a schematic diagram of the arrangement of sand injection heads.

[0028] In the figure, sand storage box - 1, transportation pipeline - 2, sand injection head - 3, sand mold - 4, heating device - 5, sand falling - 6, molding machine housing - 7, molding mold - 8, limit disk - 9, lead screw - 10, motor - 11. Detailed Embodiments

[0029] The present invention will be further described in detail below.

[0030] In the present invention, 'front', 'back', 'left', 'right', 'up' and 'down' all refer to the orientation in Figure 1 where 'front' refers to facing outwards relative to the paper surface in Figure 1 and 'back' refers to facing inwards relative to the paper surface in Figure 1 In

[0031] Embodiment, see Figure 1 and Figure 2, a method for layered injection molding of a coated sand shell mold, which is carried out by using the following injection molding machine. The structure of the injection molding machine is as follows:

[0032] It includes a molding machine housing 7 and N storage sand boxes 1, where N≥2; the N storage sand boxes 1 are arranged above the molding machine housing 7, and a transportation pipeline 2 is connected to the bottom of each storage sand box 1. Each transportation pipeline 2 passes through the top of the molding machine housing 7 and then enters the molding machine housing 7, and a sand injection head 3 is installed at the bottom of each transportation pipeline 2.

[0033] A molding die 8 and a heating device 5 are provided inside the molding machine housing 7. The molding die 8 is placed on the heating device 5, and all the sand injection heads 3 are located directly above the molding die 8.

[0034] Preferably, multiple sand distribution pipes are respectively connected to each transportation pipeline 2, and M sand distribution branch pipes are connected to each sand distribution pipe, where M≥2. A sand injection head 3 is installed at the bottom of each sand distribution branch pipe. The M sand injection heads 3 are arranged in an integral array. Setting multiple sand injection heads 3 can, on the one hand, reduce the injection time and improve the production efficiency of the sand mold, and on the other hand, perform multi-point sand blasting on the molding die 11, so as to make the coated sand in the same layer as uniform as possible, that is, the error in the thickness of the coated sand at each place in the same layer is smaller. The integral array arrangement of the sand injection heads 3 can further improve the thickness consistency of the coated sand of the same particle size in one layer.

[0035] During specific implementation, for example, let N = 3 and M = 9. Three horizontally arranged multiple sand distribution pipes are respectively connected to each transportation pipeline 2, and three vertically arranged sand distribution branch pipes are further connected to each sand distribution pipe. Each storage sand box 1 stores a coated sand of a certain particle size. If three sand injection heads 3 that respectively inject three particle sizes are set as a group, then a 9*9 integral array is formed. As Figure 2 shown. Such a setting is mainly to ensure the thickness uniformity of the coated sand of the same particle size sprayed in one layer as much as possible.

[0036] Preferably, the sand distribution branch pipe is a telescopic pipe, and it further includes a limit disk 9. The limit disk 9 has multiple limiting holes. The bottoms of all the sand distribution branch pipes pass through the limiting holes in a one-to-one correspondence, and each sand branch pipe is in a tight fit with the limiting hole.

[0037] Preferably, the injection molding machine further includes a transmission device for controlling the distance between the sand injection port and the molding die 8. The transmission device includes a motor 11 and a lead screw 10. The output shaft of the motor 11 is fixedly connected to the lead screw 10. The lead screw 10 passes through the limit disk 9 and is threadedly connected to the limit disk 9. When the motor 11 rotates forward, the lead screw 10 also rotates forward, and then the limit disk 9 threadedly connected to the lead screw 10 moves downward, thereby driving the sand branch pipe connected to the limit disk 9 to move downward; when the motor 11 rotates in reverse, the lead screw 10 rotates in reverse, and the limit disk 9 threadedly connected to the lead screw 10 moves upward, thereby driving the sand branch pipe connected to the limit disk 9 to move upward. Thus, the distance between the sand injection port and the molding die 8 is adjusted.

[0038] Preferably, it further includes a PLC controller and a plurality of solenoid valves. A solenoid valve for controlling its on-off is provided on each transportation pipe 2, and all solenoid valves are connected to the PLC controller. The sandblasting time is preset in the PLC controller, and then the solenoid valves are controlled to act through the PLC controller, and finally the control of the sandblasting time is realized.

[0039] During specific implementation, a pressure regulating device can also be selected. For example, existing equipment such as an air compressor can be selected. The pressure regulating device is communicated with the transportation pipe 2, and the sandblasting pressure is realized by changing the compressed air pressure.

[0040] The method for performing stratified injection molding of a coated sand shell mold using an injection molding machine includes the following steps:

[0041] S1: Put N kinds of coated sands with different particle sizes into N storage sand boxes 1 respectively, that is, put one kind of coated sand with a certain particle size into each storage sand box 1.

[0042] S2: Place the molding die 8 into the molding machine housing 7, and use the heating device 5 to heat the molding die 8 to 150 - 200 °C.

[0043] S3: After adjusting the sandblasting pressure, time, and the distance from the sand injection port to the molding die 8, start sandblasting. The heating device 5 can adopt existing technologies such as heating resistance wires.

[0044] The sandblasting process is carried out in sequence according to the process of increasing the particle size of the coated sand. When a layer of the coated sand with a small particle size covers the molding die 8, then the coated sand with a larger particle size is laid, and so on; the falling sand 6 outside the molding die 8 ejected during the sandblasting process is stored at the bottom of the storage sand box 1.

[0045] S4: After all the coated sands of all particle sizes are sprayed, stop heating. After the molding die 8 and the coated sand inside it are naturally cooled and the sand mold is fixed, take out the sand mold 4 to obtain a sand mold 4 with the same shape as the molding die 8.

[0046] Preferably, the sandblasting pressure in S3 is controlled at 2-10 MPa. The sandblasting pressure is achieved by changing the compressed air pressure. When the pressure is less than 2 MPa, the coated sand shell layer formed on the surface of the molding die by the sprayed coated sand is loose and not compact, with low strength, and it is not convenient for subsequent demolding operations. When the sandblasting pressure is greater than 10 MPa, when the coated sand reaches the surface of the molding die, the kinetic energy is too large, which is easy to cause splashing and cannot effectively form a coated sand shell layer.

[0047] Preferably, the sandblasting time in S3 is controlled at 10-30 s. When the sandblasting time is less than 10 s, the thickness of the coated sand layer with different particle sizes formed is too thin to meet the quality requirement standards such as the strength of the sand mold. When the sandblasting time is longer than 30 s, the thickness of the formed coated sand layer is too thick. In addition to causing ineffective consumption of the coated sand and increasing production costs, it will also affect the quality of the casting. For example, if the thickness of the surface fine particle coated sand layer is too thick, it will affect the gas permeability of the casting and cause defects such as porosity and insufficient pouring in the casting.

[0048] Preferably, the distance from the sand injection port to the molding die 8 in S3 is 20-50 cm. When the distance is less than 20 cm, due to the too close distance between the sand injection head and the molding die, the sand injection ranges of each nozzle cannot effectively cover the surface of the molding die, resulting in a too thin local coated sand shell layer or even defects, affecting the subsequent surface quality of the casting. When the distance is greater than 50 cm, the overlapping area of the sand injection ranges of each nozzle increases, and the local coated sand layer thickness increases, resulting in a poor uniformity of the coated sand shell layer.

[0049] The quartz sand raw material is screened and then subjected to coating treatment. It is classified according to its particle size range and is respectively loaded into different sand storage boxes in the molding machine. The sand storage boxes are connected to sand injection heads that can spray coated sand with different particle sizes. A plurality of sand injection heads are arranged above the mold to spray coated sand of one particle size at the same time to make it evenly distributed on the mold. At the same time, a plurality of sand injection heads that can spray coated sand with different particle sizes are arranged above the mold to reduce the spraying time and improve the production efficiency of the sand mold.

[0050] The method of the present invention uses a spray forming machine to sequentially spray coated sands with various different particle sizes on the surface of the molding die to obtain a sand mold with a particle size gradient.

[0051] 1. In the present invention, fine particle coated quartz sand is used on the outermost layer of the sand mold, i.e., the side in contact with the molding die. While reducing burrs and improving the surface finish of the casting, the fine particle quartz sand removed by screening in the traditional sand mold process is fully utilized, reducing the ineffective consumption of quartz sand and the production cost.

[0052] 2. In the outermost layer of the sand mold, the present invention uses coarse-grained coated quartz sand. While enhancing the air permeability of the sand mold and avoiding defects such as porosity and misruns caused by poor air permeability in the casting, it makes full use of the large-grained quartz sand that is sieved out and causes rough casting surfaces in the traditional sand mold process, reducing the ineffective consumption of quartz sand and lowering production costs.

[0053] 3. For the intermediate layer involved in the present invention, medium-grained coated sand in the conventional sand mold process can be used, or the particle size composition can be optimized through a numerical simulation model and further decomposed into different particle size layers.

[0054] The present invention adopts the layered injection molding of a coated sand shell mold. While improving the utilization efficiency of coated sand with different particle sizes, it obtains a sand mold with a particle size gradient. Due to its high surface flatness, the existence of a particle size gradient inside, and excellent air permeability performance, it plays an important role in reducing surface burrs, avoiding defects such as porosity and misruns, improving the quality level of castings, and reducing production costs.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for laminated injection molding of a coated sand shell mold, characterized in that: It is carried out by using the following injection molding machine, and the structure of the injection molding machine is as follows: It includes a molding machine housing (7) and N storage sand boxes (1), where N≥2; The N storage sand boxes (1) are arranged above the molding machine housing (7). A transportation pipeline (2) is connected to the bottom of each storage sand box (1). Each transportation pipeline (2) enters the molding machine housing (7) after passing through the top of the molding machine housing (7). A plurality of sand distribution pipes are respectively connected to each transportation pipeline (2). M sand distribution branch pipes are connected to each sand distribution pipe, where M≥2. A sand injection head (3) is installed at the bottom of each sand distribution branch pipe; The M sand injection heads (3) are arranged in a row; A molding die (8) and a heating device (5) are provided in the molding machine housing (7). The molding die (8) is placed on the heating device (5). All the sand injection heads (3) are located directly above the molding die (8); The injection molding machine further includes a limit disk (9). The sand distribution branch pipe is a telescopic pipe. The limit disk (9) has a plurality of limiting holes. The bottoms of all the sand distribution branch pipes pass through the limiting holes one by one, and each sand distribution branch pipe is in tight fit with the limiting hole; The injection molding machine further includes a transmission device. The transmission device includes a motor (11) and a lead screw (10). The output shaft of the motor (11) is fixedly connected to the lead screw (10). The lead screw (10) passes through the limit disk (9) and is threadedly connected to the limit disk (9); The method for performing layered injection molding of a coated sand shell mold by using the injection molding machine includes the following steps: S1: Put N kinds of coated sands with different particle sizes into the N storage sand boxes (1) respectively; S2: Place the molding die (8) into the molding machine housing (7), and use the heating device (5) to heat the molding die (8) to 150 - 200 °C; S3: After adjusting the sand blasting pressure, sand blasting time, and the distance from the sand injection port to the molding die (8), start sand blasting; The sand blasting process is carried out in sequence according to the process of increasing the particle size of the coated sand. When a layer of the coated sand with a small particle size covers the molding die (8), then lay the coated sand with a larger particle size, and so on, laying the innermost layer, the middle layer, and the outermost layer; S4: After all the coated sands of all particle sizes have been injected, stop heating. After the molding die (8) and the coated sand inside it are naturally cooled and the sand mold is fixed, take out the sand mold; In step S3, the sand blasting pressure is controlled at 2 - 10 MPa; In step S3, the distance between the sand injection port and the molding die is 20 - 50 cm; In step S3, the sand blasting time is controlled at 10 - 30 s.

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