JP2012076052A - Screen of extrusion granulator and extrusion granulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a durability-improved screen for an extrusion granulator, the extrusion granulator having the screen and a method for forming the screen.SOLUTION: The screen (4) for the extrusion granulator (1) has an inside surface (12), an outside surface (14) and many pores (16) through each of which a material is passed from the inside surface (12) to the outside surface (14). The screen (4) is formed from stainless steel having ≥300 MPa fatigue strength. Each of many pores (16) has a straight line portion (22) on the inside surface side and a tapered portion (24) on the outside surface side and is formed by drilling. The extrusion granulator (1) having the screen (4) and the method for forming the screen (4) are also provided.

Description

  The present invention relates to a screen of an extrusion granulator and an extrusion granulator. The present invention also relates to a method for forming a screen of an extrusion granulator.

  Extrusion that granulates powdered raw materials such as chemicals, seasonings, detergents, processed foods, feeds, fertilizers, fuels, etc., and extrudes the kneaded raw materials from the inside to the outside of a screen with many holes. A grain device is known (see, for example, Patent Documents 1 and 2). The raw material is extruded laterally through the holes of the screen by rotating blades arranged inside the screen, and the granulated raw material has a short rod shape or a spherical shape, depending on the desire of the producer.

  The screen is generally made of stainless steel (SUS304) and has a thickness of about 0.8 to 1.2 mm, for example. Moreover, many holes are formed by punching process, and the hole diameter is about 0.8-1.8 mm, for example.

JP 2001-293353 A JP 2007-061793 A JP 2006-231186 A

  There has been a problem that the above-described screen cannot be used in a relatively short period of time. Specifically, when the blades rotating inside the screen periodically press the raw material against the screen, a part of the screen swells and a crack may occur. This crack is caused by deformation or fatigue failure of the screen. If such cracks occur during production, the extrusion granulator must be stopped at that point, resulting in product loss and reduced productivity. In addition, in order to prevent cracks during production, the screen is replaced with a new screen in a relatively short cycle. That is, even if the screens have the same specifications, their actual durability is not uniform and some cracks occur in one to two weeks. For this reason, even if the actual durability of the screen may be more than 3 weeks, the screen is replaced with a new one in 1-2 weeks, giving priority to not stopping the machine during production. As a result, the cost of the screen increases.

  Patent Document 1 discloses a technique for increasing the thickness of the screen in order to improve the durability of the screen. However, the screen itself becomes heavy, and the burden of replacement work increases.

  Then, an object of this invention is to provide the screen for extrusion granulation apparatuses which improved durability, the extrusion granulation apparatus which has such a screen, and the formation method of this screen.

  The inventor of the present application replaces stainless steel SUS304 (fatigue strength 240 MPa) with stainless steel having a higher fatigue strength (for example, LDX2101 (registered trademark), fatigue strength 500 MPa), and uses the same screen as the conventional one. We tried to improve the durability of the screen by making it. However, contrary to expectations, the durability could not be improved. Therefore, as a result of various trials and errors in order to improve the durability of the screen by using stainless steel having a high fatigue strength as a screen, the present inventor was able to conceive the present invention. .

  In order to solve the above problems, a screen according to the present invention is a screen for an extrusion granulator, having an inner surface and an outer surface, and a large number of holes through which material passes from the inner surface to the outer surface, and has a fatigue strength of at least It is formed of 300 MPa stainless steel, and each hole has a linear portion on the inner surface side and a tapered portion on the outer surface side, and is characterized by being formed by drilling.

  The reason why the durability of the stainless steel screen having high fatigue strength could not be improved was that a large number of holes were formed by punching. That is, when a hole having the same size as that of stainless steel having a low fatigue strength (for example, fatigue strength of 240 MPa) is punched in stainless steel having a high fatigue strength (at least fatigue strength of 300 MPa), the hole is forcibly opened. As a result, internal stress remained, and as a result, the time until fatigue failure was shortened. Further, it was found that the shape of the hole is good in granulation when a tapered portion is formed on the outer surface side. Therefore, when the screen is made of stainless steel having a fatigue strength of at least 300 MPa, each hole has a straight portion on the inner surface side and a tapered portion on the outer surface side, and each hole is formed by drilling. Thus, it has been found that the durability of the screen can be extended compared to a screen formed of stainless steel having a relatively low fatigue strength.

  In the screen embodiment of the present invention, preferably the screen is cylindrical or a portion thereof, and the outer surface of the screen is shot peened.

  If the screen is cylindrical or part thereof, flat stainless steel must be bent. On the other hand, when the screen breaks due to fatigue, the screen often bulges outward and cracks. Thus, by subjecting the outer surface of the screen to shot peening, the screen can be curved, and at the same time, an internal stress that resists outward bulging of the screen can be left in the screen. As a result, the durability of the screen could be further extended.

  In the screen embodiment of the present invention, preferably, the thickness of the screen is 0.8 to 1.2 mm.

  In the screen thus configured, the screen according to the present invention can be replaced with a conventional screen as it is.

  In order to achieve the above object, an extrusion granulator according to the present invention is characterized by having the above-described screen.

  In order to achieve the above object, a method for forming a screen of an extrusion granulator according to the present invention comprises the steps of preparing a stainless steel plate having an inner surface and an outer surface and having a fatigue strength of at least 300 MPa, Forming a large number of holes in the plate by drilling, each hole having a straight portion on the inner surface side and a tapered portion on the outer surface side.

  In the forming method according to the present invention, preferably, the step of bending the stainless steel plate so that the outer surface becomes convex by shot peening the outer surface of the stainless steel plate in which a large number of holes are formed by drilling. Have

  According to the present invention, it is possible to provide a screen for an extruding granulator having improved durability, an extruding granulator having such a screen, and a method for forming such a screen.

It is a front view of an extrusion granulation apparatus. It is a top view of an extrusion granulation apparatus. It is a perspective view of the screen by this invention. FIG. 3 is a cross-sectional view of a hole in a screen according to the present invention. It is sectional drawing of the modification of the hole of the screen by this invention.

  1 and 2 are a front view and a plan view of the extrusion granulator, respectively. The extrusion granulator 1 shown in FIG. 1 is for granulating a kneaded material made by kneading powdery raw materials. The raw materials are, for example, chemicals, seasonings, detergents, processed foods, feeds, fertilizers, and fuels.

  The extrusion granulator 1 includes a cylindrical hopper 2 into which a kneaded raw material is charged, a cylindrical screen 4 disposed under the hopper 2 and having substantially the same diameter as the hopper, and inside the hopper 2 and the screen 4. It has a plurality of rotating blades 6. The hopper 2 is provided with a charging port 2a.

  FIG. 3 is a perspective view of the screen. As shown in FIG. 3, in this embodiment, the screen 4 is divided into two screen portions 4a and 4b. Each screen portion 4a, 4b has a semi-cylindrical screen body 8 and connecting portions 10 provided on both sides of the screen body 8 for connecting the screen portions 4a, 4b to each other by bolts or the like. The screen body 8 has an inner surface 12 and an outer surface 14, and a number of holes 16 through which material passes from the inner surface 12 to the outer surface 14. When the screen 4 is attached to the extrusion granulator 1, the screen 4 may be attached together with a frame (not shown) that reinforces its periphery.

  Referring again to FIGS. 1 and 2, the extrusion granulator 1 includes an annular discharge conveyor 18 disposed below and around the screen for discharging material that has passed through a number of holes 16 in the screen 4. And a discharge chute 20 provided at one location of the discharge conveyor.

  The screen 4 is made of stainless steel having a fatigue strength of at least 300 MPa, preferably at least 500 MPa. Such stainless steel is, for example, LDX2101 (registered trademark, fatigue strength 500 MPa), SUS301H (fatigue strength 640 MPa). The fatigue strength is measured by a test specified in JIS Z2275. In this test, the number of repetitions until the specimen breaks down for each stress is measured, but the test piece is defined as not causing fatigue breakage at a stress at which the number of repetitions is 10 7 or more. The stress at the 10th power is called fatigue strength.

  FIG. 4 is a cross-sectional view of a hole in the screen. Each hole has a linear portion 22 on the inner surface side and a tapered portion 24 on the outer surface side. The cross-sectional contour of the tapered portion may be a straight line or may be curved so as to be convex toward the center of the hole (see FIG. 5). Each hole is formed by drilling. Moreover, it is preferable to have a chamfered portion 26 at an inner surface side end portion of the linear portion 22.

  The thickness W of the stainless steel is, for example, 0.5 to 50 mm. Moreover, many holes are formed by a drill process, and the hole diameter D is about 0.8-1.8 mm, for example. The length L of the straight line portion 22 is, for example, 0 to 1.8 mm. Further, the taper angle θ of the tapered portion is, for example, 0 ° to 45 °.

  Next, a method for forming the screen 4 will be described.

  The method of forming the screen 4 comprises preparing a stainless steel plate having an inner surface 12 and an outer surface 14 and having a fatigue strength of at least 300 MPa, preferably at least 500 MPa, and drilling a number of holes 16 in the stainless steel plate. A step of forming.

  The step of forming the hole 16 by drilling includes the step of forming the straight portion 22 on the inner surface side and the step of forming the tapered portion 24 on the outer surface side. These drilling processes are appropriately performed from the inner surface side or the outer surface side. It is preferable to provide a chamfered portion 26 at an inner surface side end portion of the linear portion 22.

  The reason why the holes 16 are not formed by punching is that the stainless steel has high fatigue strength and is hard, and thus the screen 4 may be cracked after processing. Moreover, a large force is required for processing, that is, stainless steel is pulled during processing, and internal stress that adversely affects fatigue strength remains after processing. The reason why the hole is not formed by laser processing or photoetching processing is that it is difficult to form the hole having the shape described above.

  When the screen 4 is cylindrical or a part thereof, the method of forming the screen 4 further includes a step of bending a stainless steel plate having a large number of holes so that the outer surface 14 is convex.

  The step of bending the stainless steel plate may include a roll processing step in which the stainless steel plate is sandwiched between two large rolls and moved between them, and before the roll processing step, The outer surface 14 of the stainless steel plate may be curved by shot peening. With appropriate shot peening, the screen 4 can be curved and at the same time internal stresses that resist the outward bulging of the screen 4 can be left in the screen 4, thereby extending durability. Can be made. The shot peening process mentioned here is a method in which a sphere is hit against the metal surface at high speed and compressive residual stress is applied to the metal surface. This is a known processing method. However, shot peening has not been performed only on one side of a thin metal plate screen having a large number of holes as in the present invention. Since the shot-peened surface is deformed into a convex surface, it is possible to reduce the burden of molding by further roll processing.

  Next, the operation of the extrusion granulator 1 will be described.

  The raw material to be granulated that has been previously kneaded is charged into the hopper 2 from the charging port 2a. The raw material pushed downward by its own weight and / or by blades (not shown) is extruded by the blades 6 from the inner surface 12 of the screen 4 toward the outer surface 14 through the holes 16 of the screen 4 and is granulated as a result. The granulated raw material is conveyed to the discharge chute 20 by the discharge conveyor 18 and discharged from the discharge chute 20.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims. Needless to say, these are also included within the scope of the present invention.

  In the above embodiment, the cylindrical screen 4 is divided into the two screen portions 4a and 4b. However, the cylindrical screen 4 may be formed by one screen portion, or may be divided into three or more screen portions. .

  In the above embodiment, the cylindrical or part of the screen has been described. However, in the case of an extrusion granulating apparatus in which the screen is positioned below the blades 6 and the raw material is extruded downward, the screen may be flat. Good.

DESCRIPTION OF SYMBOLS 1 Extrusion granulator 4 Screen 12 Inner surface 14 Outer surface 16 Hole 22 Straight line part 24 Tapered part

Claims (6)

A screen for an extrusion granulator,
Inner and outer surfaces;
A number of holes through which material passes from the inner surface to the outer surface;
Formed of stainless steel with a fatigue strength of at least 300 MPa,
Each of the holes has a straight portion on the inner surface side and a tapered portion on the outer surface side, and is formed by drilling. The screen is cylindrical or a part thereof,
The screen according to claim 1, wherein an outer surface of the screen is shot peened.   The screen according to claim 1 or 2, wherein the screen has a thickness of 0.8 to 1.2 mm.   An extrusion granulation apparatus comprising the screen according to any one of claims 1 to 3. A method for forming a screen for an extrusion granulator, comprising:
Providing a stainless steel plate having an inner surface and an outer surface and having a fatigue strength of at least 300 MPa;
Forming a number of holes in a stainless steel plate by drilling; and
Each hole has a linear portion on the inner surface side and a tapered portion on the outer surface side.   6. The forming method according to claim 5, further comprising a step of bending the stainless steel plate so that the outer surface becomes convex by shot peening the outer surface of the stainless steel plate having a large number of holes formed by drilling. .

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