A preparation process for a warm core box shell mold of a railway electric locomotive axle box cover

Abstract

This invention relates to a process for preparing a core box shell for axle box covers of railway electric locomotives. The molding sand for the shell includes high-silica sand, thermosetting resin, thermosetting curing agent, and reinforcing agent. The amount of thermosetting resin added is 1.5% of the amount of high-silica sand, the amount of thermosetting curing agent added is 50% of the amount of thermosetting resin, and the amount of reinforcing agent added is 0.2% of the amount of high-silica sand. The mixture is stirred thoroughly. The mold is prepared and positioned, and the mold preheating temperature is set to 160-170℃. The obtained molding sand is injected into the mold cavity from the top of the mold using compressed air, and the hardening process is maintained. The core hardening time is set to 160-180 seconds. After the core hardening time is completed, the mold is opened vertically, and the sand core is ejected upwards to obtain the shell. This invention achieves higher sand core strength and sand mold surface quality, higher waste sand recovery rate through mechanical regeneration, a reduction of casting porosity defects by more than 50%, and significant improvements in labor costs and work efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of electric locomotive component preparation, and more particularly to a preparation process of a warm core box shell mold for an axle box cover of a railway electric locomotive. Background Art

[0002] The purpose of the bogie is to increase the load, length and volume of the railway electric locomotive and increase the running speed of the train. The car body is supported on the bogie to reduce vibration and improve the stability and safety of the wheels. The axle box is an important part of the bogie. The function of the axle box is to connect the wheelset and the side frame or frame together, so that the rolling of the wheelset along the rail is converted into the translation of the car body and bear the weight transfer force of the vehicle. As a key component of the axle box body, the axle box cover has high requirements for its size and quality. Using the traditional resin sand molding process, resin, curing agent and silica sand for molding are generally mixed, and the reaction hardening is carried out in the temperature range of -30℃ to +40℃. It takes at least 40 minutes to produce each mold. The surface strength of the sand mold just demolded is low (tensile strength 0.3MPa-0.4Mpa). Using the traditional resin sand molding process, demolding requires manual vibration of the mold and disassembly of the mold. Before placing the sand, the mold needs to be cleaned and assembled. The sand filling process is compacted, and the work efficiency is low. The hardening of resin sand is greatly affected by temperature, and it is mainly controlled by manual operation, resulting in a large number of scrapped sand molds in the production process.

[0003] Therefore, how to provide a preparation process for a warm core box shell of a railway electric locomotive axle box cover is a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0004] To this end, the purpose of the present invention is to propose a preparation process for a warm core box shell mold of a railway electric locomotive axle box cover, so as to solve the problem of poor shell mold quality caused by the existing warm core box shell mold process for railway electric locomotive axle box cover.

[0005] The present invention provides a preparation process of a warm core box shell mold of an axle box cover of a railway electric locomotive, comprising the following steps:

[0006] S1. The shell mold sand includes high silica sand, thermosetting resin, thermosetting curing agent and reinforcing agent, wherein the amount of thermosetting resin added is 1.5% of the amount of high silica sand, the amount of thermosetting curing agent added is 50% of the amount of thermosetting resin, and the amount of reinforcing agent added is 0.2% of the amount of high silica sand; mix and stir according to the above proportions;

[0007] S2. Prepare the mold and set the mold preheating temperature to 160-170℃; open the mold, spray high-temperature release agent in the upper and lower mold cavities, and then close the mold;

[0008] S3, injecting the molding sand obtained in S1 into the mold cavity at the top of the mold through compressed air, and maintaining the hardening process, and setting the core mold hardening time to 160-180S;

[0009] S4, after the hardening time of the core mold in S3 is over, open the mold in the vertical direction;

[0010] S5. Push the sand core upward to obtain a shell mold.

[0011] It can be known from the above technical scheme that compared with the prior art, the present invention discloses a preparation process for a warm core box shell mold of a railway electric locomotive axle box cover, which adopts the resin sand mixed and stirred in the above ratio to fill the mold through sand shooting, and solidifies at high temperature. The molding strength is higher, the surface quality is better, and the hardening time is short, and the work efficiency is significantly improved. Through pressure, the temperature is 160-170℃, and the hardening time is maintained for 160s-180s. The produced warm core box shell mold has high overall strength and clear contours, avoiding defects such as sand holes and sand inclusions caused by insufficient sand mold strength during the casting process. The surface roughness can reach Ra6.3~12.5μm, the dimensional accuracy can reach CT7~CT9 level, and the shell mold has good disintegration. The surface floating sand can be completely cleaned by shot blasting, reducing the workload of casting cleaning. The recovery rate of regenerated sand can reach more than 95%, the qualified rate of shell mold can reach 98%, and the production cost is low. The present invention achieves higher sand core strength and sand mold surface quality, higher waste sand recovery rate through mechanical regeneration, more than 50% reduction in casting porosity defects, and significantly improved labor costs and work efficiency.

[0012] Furthermore, the air compressor in S3 controls the sandblasting pressure to be 0.5-0.7 MPa.

[0013] Furthermore, S2 is preheated by a heating rod.

[0014] Furthermore, the molds used in S2 include:

[0015] A mold support, the mold support comprising a base, a top plate, and a support frame connected between the base and the top plate; a raw material inlet is provided on the top plate;

[0016] A sand-shooting assembly, which can move up and down below the top plate and is connected to the raw material inlet;

[0017] A static mold assembly is fixed below the sand-shooting assembly through the support frame, and the sand-shooting assembly can move downward to dock with the static mold assembly to shoot sand;

[0018] A movable mold assembly, wherein the base is provided with the movable mold assembly which can move up and down, and the movable mold assembly and the static mold assembly are closed to form a mold cavity inside;

[0019] An ejector assembly is installed below the movable mold assembly and on the base, and is used to eject the shell mold in the movable mold assembly.

[0020] Furthermore, the sand shooting assembly comprises:

[0021] A plurality of sand-shooting cylinders are fixed to the bottom of the top plate, with the output ends facing downward;

[0022] A sand storage tank, the output end of the sand-shooting cylinder is connected to the sand storage tank, which is communicated with the raw material inlet; and an air compressor connection port is connected to the sand storage tank;

[0023] Sand shooting nozzles, a plurality of sand shooting nozzles connected to the interior of the sand storage tank are fixed to the bottom of the sand storage tank through a fixing plate;

[0024] The raw material in S3 enters the sand storage tank through the raw material inlet and is ejected through the sand ejecting nozzle.

[0025] Furthermore, the static mold assembly includes a static mold positioning platform, which is fixed on the inner wall of the support frame. The static mold positioning platform is fixed with a static mold. The top of the static mold is downwardly provided with a sand inlet corresponding to the sand shooting nozzle, and the side wall of the static mold is provided with a plurality of first fixing holes for fixing the heating rod.

[0026] Furthermore, a chamfer is provided at the sand inlet, and a sealing ring is provided between the outer wall of the sand shooting nozzle and the sand inlet.

[0027] Furthermore, the movable mold assembly includes a movable mold cylinder, which is fixed on the base. A movable mold bracket is supported on the top of the movable mold cylinder, on which a movable mold is fixed. The movable mold is provided with a second fixing hole for fixing the heating rod, and the movable mold cooperates with the static mold.

[0028] Furthermore, the ejection assembly includes an ejection cylinder, which is installed on the base and located on the inner side of the movable mold cylinder, and is lifted upward through a through hole opened on the movable mold bracket. A top core plate is fixed on it, and a plurality of ejector rods are provided above the top core plate, and the ejector rods cooperate with the ejection holes at the bottom of the movable mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0030] Figure 1The accompanying drawing is a flow chart of a process for preparing a warm core box shell mold for a railway electric locomotive axle box cover provided by the present invention;

[0031] Figure 2 The accompanying drawing is a stereogram of the mold used in the present invention;

[0032] Figure 3 The accompanying drawing is a front view of the mold used in the present invention;

[0033] Figure 4 The accompanying drawing shows a cross-sectional view of the movable mold and the static mold in a closed state;

[0034] Figure 5 The accompanying figure shows Figure 4 A magnified schematic diagram of part A. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0036] In the description of the present invention, it is necessary to understand that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0038] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] Due to the use of traditional resin sand molding technology, resin, curing agent and silica sand for molding are generally mixed, and the reaction hardens in the temperature range of -30℃ to +40℃. It takes at least 40 minutes to produce each mold, and the surface strength of the sand mold just after demolding is low (tensile strength 0.3MPa-0.4Mpa). Using the traditional resin sand molding process, demolding requires manual vibration of the mold and disassembly of the mold. The mold needs to be cleaned and assembled before sand is placed. The sand filling process compacts the sand mold, and the work efficiency is low. The hardening of resin sand is greatly affected by temperature and is mainly controlled by manual operation, resulting in a large number of scrapped sand molds in the production process.

[0040] In view of this, the embodiment of the present invention discloses a preparation process of a warm core box shell mold of a railway electric locomotive axle box cover, see the attached Figure 1 , including the following steps:

[0041] S1. The molding sand of the shell mold includes high silica sand, thermosetting resin, thermosetting curing agent and reinforcing agent. The resin and curing agent are used as binders, and the reinforcing agent is added to improve the strength of the sand mold. The amount of thermosetting resin added is 1.5% of the amount of high silica sand, the amount of thermosetting curing agent added is 50% of the thermosetting resin, and the amount of reinforcing agent added is 0.2% of the amount of high silica sand. Mix and stir according to the above ratios. The curing agent can be Bonnie B-1 (thermosetting) curing agent; the resin can be Bonnie BNHG-04 (thermosetting) resin.

[0042] S2. Prepare the mold and set the mold preheating temperature to 160-170℃; open the mold, spray high-temperature release agent in the upper and lower mold cavities, and then close the mold;

[0043] S3, injecting the molding sand obtained in S1 into the mold cavity at the top of the mold through compressed air, and maintaining the hardening process, and setting the core mold hardening time to 160-180S;

[0044] S4, after the hardening time of the core mold in S3 is over, open the mold in the vertical direction;

[0045] S5. Push the sand core upward to obtain a shell mold.

[0046] Taking the preparation of a shell mold requiring 28 kg of high-silica sand as an example, the amount of thermosetting resin added is 1.5% of the amount of high-silica sand, that is, the weight of the added thermosetting resin is 420 g, the amount of thermosetting curing agent added is 50% of the resin, that is, the weight of the added thermosetting curing agent is 210 g, and the amount of reinforcing agent added is 0.2% of the amount of high-silica sand, that is, the weight of the added reinforcing agent is 56 g.

[0047] The mold adopts a vertical opening and closing mold structure and horizontal parting, which is convenient for workers to operate and can eject the sand core, thereby reducing the possibility of the core mold falling off and other damage to the sand core.

[0048] If the sand shooting pressure in S3 is too low, the molding sand will be poorly formed and the sand mold will not be compact enough, which will affect the product quality; if the sand shooting pressure is too high (it will cause sand leakage at the sand shooting nozzle and parting surface, and the sealing ring at the sand shooting nozzle will wear faster), the leaked sand will affect the workshop environment.

[0049] Therefore, it is advantageous that the air compressor in S3 controls the sand blasting pressure to 0.5-0.7 MPa.

[0050] In the above embodiment of the present invention, preheating is performed by a heating rod in S2.

[0051] See attached Figure 2-3 , the mold used in S2 of the present invention includes:

[0052] A mold support 1, the mold support 1 comprises a base 101, a top plate 102, and a support frame 103 connected between the base 101 and the top plate 102; a raw material inlet 1021 is provided on the top plate 102;

[0053] A sand-shooting assembly 2, which can move up and down below the top plate 102 and is connected to the raw material inlet 1021;

[0054] Static mold assembly 3, below the sand shooting assembly 2, the static mold assembly 3 is fixed by the support frame 103, and the sand shooting assembly 2 can go down to dock with the static mold assembly 3 to shoot sand;

[0055] The movable mold assembly 4 is provided on the base 101 and can move up and down. When the movable mold assembly 4 and the static mold assembly 3 are closed, a mold cavity is formed inside.

[0056] An ejector assembly 5 is installed below the movable mold assembly 4 and on the base 101 , and is used to eject the shell mold K in the movable mold assembly 4 .

[0057] The above-mentioned mold adopts a horizontal parting surface of the static mold component 3 and the dynamic mold component 4, which is conducive to the demolding of the artificial sand core, and the two molds are opened and closed vertically, which is convenient for workers to operate, and the ejection component 5 ejects the sand core from the bottom, reducing the situation of damage to the sand core such as the core mold falling off.

[0058] Advantageously, the sand shooting assembly 2 comprises:

[0059] A plurality of sand-shooting cylinders 201 are fixed to the bottom of the top plate 102, with the output ends facing downwards;

[0060] The sand storage tank 202, the output end of the sand-shooting cylinder 201 is connected to the sand storage tank 202, which is in communication with the raw material inlet 1021; an air compressor connection port 2021 is connected to the sand storage tank 202; specifically, the raw material inlet 1021 and the sand storage tank 202 are an integrated structure, and the mixed resin sand enters the sand storage tank through the raw material inlet 1021. The raw material inlet 1021 and the sand storage tank move up and down with the sand-shooting cylinder 201, wherein the raw material inlet can be a cylinder with a certain length, with a top plate inserted at the top, and can move with the sand-shooting cylinder;

[0061] Sand shooting nozzles 203, a plurality of sand shooting nozzles 203 connected to the interior of the sand storage tank 202 are fixed to the bottom of the sand storage tank 202 via a fixing plate;

[0062] The raw material in S3 enters the sand storage tank 202 through the raw material inlet 1021 and is ejected through the sand ejection nozzle 203; thus, sand storage and sand ejection are integrated together, the structure is compact, and it is convenient to eject sand into the static mold.

[0063] The static mold assembly 3 used in the present invention includes a static mold positioning platform 301, which is fixed on the inner wall of the support frame 103, and a static mold 302 is fixed on the static mold positioning platform 301. The top of the static mold 302 is downwardly provided with a sand inlet 3021 corresponding to the sand shooting nozzle 203, wherein the number of sand shooting nozzles and sand inlets corresponds to each other, and both include multiple sand inlets, which are all over the static mold, and the side wall of the static mold 302 is provided with multiple first fixing holes 3024 for fixing the heating rod. The static mold 302 is fixed to the static mold positioning platform 301 by screws.

[0064] In the embodiments of the present invention, see the attached Figure 3 and 4 The sand inlet 3021 is provided with a chamfer 3022, the chamfer is 10X45°, and a sealing ring 3023 is provided between the outer wall of the sand shooting nozzle 203 and the sand inlet 3021. Therefore, during debugging, the mold is opened and closed in the upper and lower directions to ensure that there is no air leakage and avoid hidden dangers such as looseness.

[0065] The movable mold assembly 4 of the present invention includes a movable mold cylinder 401, which is fixed on the base 101, and a movable mold bracket 402 is supported on the top of the movable mold cylinder 401, on which a movable mold 403 is fixed, and a second fixing hole 4031 for fixing a heating rod is provided on the movable mold 403. The movable mold 403 cooperates with the static mold 302, and the movable mold can open and close the mold in the upper and lower directions without hindrance. The movable mold and the movable mold bracket 402 are fastened by bolts.

[0066] In S3, the molding sand obtained in S1 is injected into the mold cavity at the top of the mold by compressed air, and the hardening process is maintained. If the heating hardening time is too short, the sand core is not hardened thoroughly and the strength is insufficient; if the heating time is too long, the sand core will be powdered or cracked. Therefore, the core mold hardening time is set to 160-180s, preferably 170s;

[0067] The heating rods of the moving mold and the static mold are connected to the heating rod circuit system to synchronously control the heating. The core mold is preheated by the electric heating rod, and the mold preheating temperature is set to 165°C.

[0068] More advantageously, the ejection assembly 5 includes an ejection cylinder 501, which is mounted on the base 101 and located on the inner side of the movable mold cylinder 401, and is lifted upward through a through hole 4021 provided on the movable mold bracket 402, on which a core plate 502 is fixed, and a plurality of ejector rods 503 are provided above the core plate 502, and the ejector rods 503 cooperate with the ejection holes at the bottom of the movable mold 403.

[0069] After the core mold hardening time is over, the movable mold cylinder is controlled to separate the movable mold from the static mold, and then the ejection assembly lifting cylinder is controlled to rise to eject the solidified shell mold from the static mold and take out the shell mold.

[0070] The present invention adopts the resin sand mixed and stirred in the above proportions to fill the mold through sand shooting, and solidifies at high temperature. The molding strength is higher, the surface quality is better, and the hardening time is short, and the work efficiency is significantly improved. The air compressor controls the sand shooting pressure to 0.5-0.7MPa, the temperature is 160-170℃, and the hardening time is maintained for 160s-180s. The produced warm core box shell mold has high overall strength (normal temperature tensile strength 4-45MPa; normal temperature bending resistance 1.2-1.6MPa) and clear contours, avoiding defects such as sand holes and sand inclusions caused by insufficient sand mold strength during the casting process. The surface roughness can reach Ra6.3-12.5μm, the dimensional accuracy can reach CT7-CT9 level, and the shell mold has good disintegration. The surface floating sand can be completely cleaned by shot blasting, reducing the workload of casting cleaning. The regenerated sand recovery rate can reach more than 95%, the shell mold qualification rate can reach 98%, and the production cost is low. The present invention achieves higher sand core strength and sand mold surface quality, higher waste sand recovery rate through mechanical regeneration, more than 50% reduction in casting porosity defects, and significantly improved labor costs and work efficiency.

[0071] The present invention uses high-silica sand as raw sand, fills the mold by air pressure sand shooting, and hardens by heat method to obtain a sand core with high strength, stable size and high surface quality. All shell mold surfaces do not need to be painted. Due to the high strength of the sand core, there is no sand washing or sand falling during the pouring process, and the surface quality of the obtained casting is good. When the casting solidifies, the sand core collapses due to heat, and the floating sand on the surface can be cleaned by shot blasting, which is easy to clean. The used sand can be reused by mechanical regeneration to reduce costs.

[0072] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0073] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A process for preparing a warm core box shell mold for a railway electric locomotive axle box cover, characterized in that: The following steps are involved: S1. The shell mold sand includes high silica sand, thermosetting resin, thermosetting curing agent and reinforcing agent, wherein the amount of thermosetting resin added is 1.5% of the amount of high silica sand, the amount of thermosetting curing agent added is 50% of the amount of thermosetting resin, and the amount of reinforcing agent added is 0.2% of the amount of high silica sand; mix and stir according to the above proportions; S2, the mold is ready, and the mold preheating temperature is set to 160-170℃; the mold is opened, and a high-temperature release agent is sprayed in the upper and lower mold cavities, and then the mold is closed; in S3, the air compressor controls the sand-shooting pressure to 0.5-0.7MPa; S3, injecting the molding sand obtained in S1 into the mold cavity at the top of the mold through compressed air, and maintaining the hardening process, and setting the core mold hardening time to 160-180S; S4, after the hardening time of the core mold in S3 is over, open the mold in the vertical direction; S5, eject the sand core upward to obtain a shell mold; The molds used in S2 include: A mold support (1), the mold support (1) comprising a base (101), a top plate (102), and a support frame (103) connected between the base (101) and the top plate (102); a raw material inlet (1021) is provided on the top plate (102); A sand-shooting assembly (2), the sand-shooting assembly (2) being movable up and down below the top plate (102) and being in communication with the raw material inlet (1021); A static mold assembly (3), below the sand-shooting assembly (2), the static mold assembly (3) is fixed via the support frame (103), and the sand-shooting assembly (2) can move downward to dock with the static mold assembly (3) for sand-shooting; A movable mold assembly (4), wherein the base (101) is provided with the movable mold assembly (4) which can move up and down, and the movable mold assembly (4) and the static mold assembly (3) are closed to form a mold cavity inside; An ejector assembly (5), the ejector assembly (5) being installed below the movable mold assembly (4) and located on the base (101), and being used to eject the shell mold (K) in the movable mold assembly (4); The sand shooting assembly (2) comprises: A plurality of sand-shooting cylinders (201) are fixed to the bottom of the top plate (102), with their output ends facing downward; A sand storage tank (202), the output end of the sand-shooting cylinder (201) being connected to the sand storage tank (202), which is in communication with the raw material inlet (1021); and an air compressor connection port (2021) being connected to the sand storage tank (202); Sand shooting nozzles (203), a plurality of sand shooting nozzles (203) in communication with the interior of the sand storage tank (202) being fixed to the bottom of the sand storage tank (202) via a fixing plate; The raw materials in S3 and S4 both enter the sand storage tank (202) through the raw material inlet (1021) and are ejected through the sand ejection nozzle (203); The static mold assembly (3) comprises a static mold positioning platform (301), the static mold positioning platform (301) is fixed on the inner wall of the support frame (103), a static mold (302) is fixed on the static mold positioning platform (301), a sand inlet (3021) is provided on the top of the static mold (302) facing downwards and corresponding to the sand shooting nozzle (203), and a plurality of first fixing holes (3024) for fixing the heating rod are provided inwardly on the side wall of the static mold (302); The movable mold assembly (4) comprises a movable mold cylinder (401), wherein the movable mold cylinder (401) is fixed on the base (101), and a movable mold bracket (402) is supported on the top of the movable mold cylinder (401), on which a movable mold (403) is fixed, and a second fixing hole (4031) for fixing a heating rod is provided on the movable mold (403), and the movable mold (403) cooperates with the static mold (302); The ejection assembly (5) comprises an ejection cylinder (501), which is mounted on the base (101) and is located inside the movable mold cylinder (401), and is lifted upward through a through hole (4021) provided on the movable mold bracket (402), on which a core plate (502) is fixed, and above the core plate (502) there are a plurality of ejector rods (503), and the ejector rods (503) cooperate with ejection holes at the bottom of the movable mold (403).

2. The process for preparing a warm core box shell mold for a railway electric locomotive axle box cover according to claim 1, characterized in that: S2 is preheated by a heating rod.

3. The process for preparing a warm core box shell mold for a railway electric locomotive axle box cover according to claim 1, characterized in that: A chamfer (3022) is provided at the sand inlet (3021), and a sealing ring (3023) is provided between the outer wall of the sand shooting nozzle (203) and the sand inlet (3021).

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