Mixing paddle, mixing device, and method for manufacturing a mixing paddle

Abstract

To provide a kneading paddle where metal contamination is prevented and which can be used for a high temperature material.SOLUTION: A kneading paddle (5) is the paddle attached to a rotary shaft arranged in the housing of a kneader and comprises: a body part (10) having an insertion hole (11) inserted with the rotary shaft; and a ceramic molded article integrally comprising a pair of protrusions (20a, 20b) arranged at mutually corresponding positions at both end surfaces of the body part in an axial direction.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a kneading paddle, a kneading apparatus, and a method for producing a kneading paddle.

Background Art

[0002] A kneading paddle, which is attached to a rotating shaft disposed in a housing of a kneading apparatus and agitates materials charged into the housing, is formed of a metal such as stainless steel from the viewpoint of heat resistance and strength. However, for example, in a twin-shaft type kneading apparatus having a self-cleaning function for kneading paddles, the top (tip surface) of the kneading paddle attached to one rotating shaft passes close to the inner surface of the housing and the arcuate surface (side surface in the rotation direction) of the kneading paddle attached to the other rotating shaft, so there are cases where wear occurs on the outer peripheral surface of the kneading paddle. In such a case, metallic foreign matter may mix into the kneaded material, resulting in metal contamination.

[0003] Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 2014-12344 (Patent Document 1), wear of the kneading paddle has been prevented by providing a build-up layer (reinforcement layer) on the outer peripheral portion of the kneading paddle.

[0004] Furthermore, as disclosed in Japanese Patent Laid-Open No. 2020-6338 (Patent Document 2), a technique of forming a kneading paddle from a resin molded product has also been conventionally proposed.

Prior Art Literature

Patent Literature

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problem to be Solved by the Invention

[0006] Even when a build-up layer is provided on the outer surface of the kneading paddle, as in Patent Document 1, the risk of metal contamination cannot be completely eliminated because the base material contains metal. Furthermore, there is the disadvantage of increasing the manufacturing process for the build-up layer during the production of the kneading paddle.

[0007] As shown in Patent Document 2, when the kneading paddle is made of a resin molded product, metal contamination does not occur, but because its heat resistance is lower than that of metal, it cannot be used in kneading equipment that handles high-temperature materials.

[0008] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a kneading paddle that prevents metal contamination and can be used with high-temperature materials, as well as a method for manufacturing the same.

[0009] Another objective is to provide a kneading apparatus equipped with such kneading paddles. [Means for solving the problem]

[0010] A kneading paddle according to one aspect of this invention is a paddle attached to a rotating shaft located in the housing of a kneading device, and consists of a ceramic molded product integrally comprising a main body portion provided with an insertion hole through which the rotating shaft is inserted, and a pair of protrusions provided at corresponding positions on both axial ends of the main body portion.

[0011] Preferably, the convex portion is annular, and the outer edge of the convex portion has a tapered shape.

[0012] Preferably, the inner circumferential surface of the main body surrounding the insertion hole is provided with a substantially U-shaped groove for receiving a key with a rectangular cross-section provided on the outer circumferential surface of the rotating shaft, and the corners of the groove are rounded.

[0013] The main body includes, when viewed in the axial direction, a pair of arcuate surfaces that bulge out from each other on both sides of the insertion hole in the x-direction, and a pair of tip surfaces located on both sides of the insertion hole in the y-direction, connecting the circumferential ends of the pair of arcuate surfaces. Preferably, the width of the tip surfaces is 5% to 30% of the x-direction length of the main body.

[0014] In a kneading apparatus according to another aspect of this invention, the kneading paddles are arranged in alignment such that their axial positions overlap with each of the two rotating shafts.

[0015] A method for manufacturing a kneading paddle according to another aspect of this invention is a method for manufacturing a kneading paddle that is attached to a rotating shaft arranged in the housing of a kneading device, and includes a molding step of forming a primary product by forming a main body portion having a convex lens shape in plan view with an insertion hole and a keyway from a disc-shaped member made of ceramics as a raw material, and forming a pair of protrusions at mutually corresponding positions on both axial ends of the main body portion; a sintering step of sintering the primary product; and a polishing step of forming a secondary product by polishing both end faces of the pair of protrusions on the sintered primary product. [Effects of the Invention]

[0016] According to the present invention, metal contamination can be prevented. Furthermore, the kneading paddle of the present invention can be used with high-temperature materials. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view showing the overall configuration of a kneading apparatus according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the mounting structure of a kneading paddle in a kneading apparatus according to an embodiment of the present invention. [Figure 3] This is a front view of a kneading paddle according to an embodiment of the present invention. [Figure 4] Figure 3 is a side view of the mixing paddle as seen from direction IV. [Figure 5] This is a cross-sectional view of the kneading paddle along the VV line in Figure 3. [Figure 6] It is a schematic diagram showing the shape and depth of a key groove (groove portion) in a kneading paddle according to an embodiment of the invention. [Figure 7] It is a schematic diagram showing the shape and depth of a key groove (groove portion) in a kneading paddle according to an embodiment of the invention. [Figure 8] It is a front view of a known kneading paddle viewed in the axial direction. [Figure 9] It is a cross-sectional view of a known kneading paddle taken along line IX-IX in FIG. 8. MODE FOR CARRYING OUT THE INVENTION

[0018] Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and repeated description thereof will be omitted.

[0019] <Example of overall configuration of kneading apparatus> The overall configuration of a kneading apparatus 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing the overall configuration of the kneading apparatus 1. FIG. 2 is a cross-sectional view showing the mounting structure of the kneading paddle 5 in the kneading apparatus 1, and corresponds to line II-II in FIG. 1.

[0020] The kneading apparatus 1 kneads a plurality of types of raw materials in a highly corrosive environment to produce a kneaded material used as a material for products such as batteries, for example.

[0021] The kneading apparatus 1 includes, for example, a double cylindrical housing 2, and two rotating shafts 3 parallel to each other are arranged inside the housing. The two rotating shafts 3 extend horizontally at the same height. In the following description, the direction of the axis O of the rotating shaft 3 is referred to as the axial direction. Further, the direction orthogonal to the axial direction on the horizontal plane is referred to as the left-right direction.

[0022] The housing 2 is axially elongated and has a raw material input port 2a at the upper end on one longitudinal side (in the direction of the cylinder axis) and a mixed material discharge port 2b at the lower end on the other longitudinal side. Bearing boxes 2c, which incorporate bearings, are attached to both longitudinal ends of the housing 2. The mixing device 1 is a continuous twin-shaft mixing device that continuously supplies raw materials and discharges the mixed material formed by kneading the raw materials.

[0023] A pair of rotating shafts 3 are arranged within a kneading chamber 2e, which is separated by a trough 2d in the housing 2. Each rotating shaft 3 is rotatably supported by bearings in bearing boxes 2c on both end faces of the housing 2 and is rotationally driven by a drive mechanism (e.g., a motor) not shown. The pair of rotating shafts 3 are rotated in the same direction relative to each other.

[0024] Multiple screws 4 and multiple kneading paddles 5 are mounted axially on each rotating shaft 3. As shown in Figure 2, the rotating shaft 3 has a circular cross-section, and a key 3a with a rectangular cross-section extending axially is provided on its outer surface. The screws 4 and kneading paddles 5 are mounted so as to fit into this key 3a. As a result, the screws 4 and kneading paddles 5 rotate together with the rotating shaft 3. A heat transfer medium or the like can be circulated within the jacket 2f surrounding the outer periphery of the kneading chamber 2e.

[0025] When the rotating shaft 3 is in operation, raw materials are introduced from the inlet 2a of the housing 2. The raw materials are agitated by the kneading paddle 5 and then sent axially toward the other side (discharge port 2b side) by the screw 4. The kneaded material generated by agitation within the housing 2 is discharged from the discharge port 2b.

[0026] Each of the pair of rotating shafts 3 is fitted with a kneading paddle 5, each mounted at an angle that differs by, for example, 45 degrees. The corresponding left and right pairs of kneading paddles 5 are fitted with a phase difference of 90 degrees. Furthermore, kneading paddles 5 are mounted on each of the pair of rotating shafts 3 so that their axial positions coincide. In other words, within the housing 2, multiple kneading paddles 5 are arranged in a manner that their axial positions overlap on each of the two rotating shafts 3.

[0027] The pair of kneading paddles 5, aligned left and right, rotate in close proximity so that the tip surface of one paddle always rubs against the arcuate surface (side surface in the direction of rotation) of the other. Furthermore, the gap between the inner surface of the trough 2d and the kneading paddles 5 is small, thus suppressing material adhesion to the kneading paddles 5 and the inner surface of the trough 2d. In this way, the kneading paddles 5 have a self-cleaning action. In addition, there is a shearing action between the left and right kneading paddles 5, and between the inner surface of the trough 2d and the kneading paddles 5.

[0028] <Composition of the mixing paddle> (Regarding the basic configuration) Referring to Figures 3 to 5, the basic configuration of the kneading paddle 5 in this embodiment will be described. Figure 3 is a front view of the kneading paddle 5. Figure 4 is a side view of the kneading paddle 5 as seen from direction IV in Figure 3. Figure 5 is a cross-sectional view of the kneading paddle 5 along line VV in Figure 3. In these figures, directions that are orthogonal to each other when viewed in the axial direction (viewed from the front) are shown as the x and y directions, and the axial direction is shown as the z direction.

[0029] The kneading paddle 5 in this embodiment is a ceramic molded product. Ceramics are non-metallic, inorganic solid materials, and in particular, include materials composed of non-metallic elements (e.g., silicon and diamond) and inorganic compound materials that are combinations of metallic and non-metallic elements (oxides, carbides, nitrides, etc.). By using ceramics as the material for the kneading paddle 5, it is possible to prevent the inclusion of metallic foreign matter in the kneaded product, thereby improving the quality of the kneaded product compared to when a general metal kneading paddle is used.

[0030] The kneading paddle 5 integrally comprises a main body 10 through which a rotating shaft 3 is inserted, and a pair of protrusions 20 provided at corresponding positions on both axial ends of the main body 10 (front 10a and back 10b). The main body 10 has a constant thickness (T1), and the through hole 11 is a round hole that penetrates the main body 10 in the thickness direction (axial direction). The diameter φ of the through hole 11 is approximately equal to the diameter of the rotating shaft 3 (slightly larger by the amount of overlap). Note that the protrusions 20 are not shown in Figure 1 above.

[0031] The main body 10 has a convex lens shape when viewed from the front (in the axial direction), and includes a pair of arcuate surfaces 12a, 12b that bulge out from each other on both sides of the insertion hole 11 in the x direction, and a pair of end surfaces 13a, 13b located on both sides of the insertion hole 11 in the y direction, connecting the circumferential ends of the pair of arcuate surfaces 12a, 12b. These arcuate surfaces 12a, 12b and end surfaces 13a, 13b constitute the outer circumferential surface (side surface) of the main body 10.

[0032] The front surface 10a and back surface 10b of the main body 10 are each provided with protrusions 20a and 20b surrounding the insertion hole 111. The main body 10 and the protrusions 20a and 20b are integrally formed from the same material. The planar shape of the protrusions 20a and 20b is annular with respect to the axis O. The surfaces of the protrusions 20a and 20b are mutually parallel flat surfaces perpendicular to the axial direction, and their surface areas are equal. Note that "equal" does not mean that they are perfectly identical, but rather that manufacturing tolerances are allowed. The portion of the front surface 10a excluding the protrusions 20a, and the portion of the back surface 10b excluding the protrusions 20b, are also mutually parallel flat surfaces perpendicular to the axial direction.

[0033] The portion around the insertion hole 11 (the portion where the protrusions 20a and 20b are provided) constitutes a boss portion 15 for receiving the rotating shaft 3. A groove portion (hereinafter referred to as "keyway") 14 continuous with the insertion hole 11 is provided on the inner circumferential surface of the boss portion 15. The keyway 14 is a recess formed by recessing one point in the circumferential direction of the insertion hole 11 radially outward, and engages with the key 3a of the rotating shaft 3. The keyway 14 extends in the depth direction, penetrating the front protrusion 20a, the main body portion 10, and the back protrusion 20b. The shape of the keyway 14 will be described later.

[0034] (Regarding the protruding part) As described above, the kneading paddle 5 in this embodiment has protrusions 20a and 20b on both the front surface 10a and the back surface 10b of the main body 10. The relative proportions of the kneading paddle 5 in this embodiment are shown in Figures 8 and 9. Figure 8 is a front view of a typical metal kneading paddle 100 and corresponds to Figure 3. Figure 9 is a cross-sectional view of the kneading paddle 100 along the line IX-IX in Figure 8 and corresponds to Figure 5.

[0035] A known kneading paddle 100 integrally comprises a main body portion 110 with an insertion hole 111 through which a rotating shaft 3 is inserted, and a protrusion 120 provided on one axial end face of the main body portion 110 (for example, the front surface 110a). The other axial end face of the main body portion 110 (for example, the back surface 110b) is a flat surface without irregularities. The total thickness T13 of the kneading paddle 100 is the sum of the thickness T11 of the main body portion 110 and the thickness T12 of the protrusion 120.

[0036] In the installed (used) state, the surface of the protrusion 120 of the kneading paddle 100 is in close proximity to or surface contact with the back surface 110b of another kneading paddle 100 adjacent to it on one axial side. This protrusion 120 functions as a spacer, thereby absorbing the axial displacement of two adjacent kneading paddles 100 in the left-right direction. Specifically, it suppresses interference between the first kneading paddle 100, which is the nth one mounted on one rotating shaft 3, and the second kneading paddle 100, which is the (n-1) or (n+1)th one mounted on the other rotating shaft 3.

[0037] On the other hand, the kneading paddle 5 in this embodiment has protrusions 20a and 20b on both the front surface 10a and the back surface 10b of the main body 10. Therefore, in the mounted state (use state), the protrusion 20a on the front surface of the kneading paddle 5 is in close proximity to or surface contact with the protrusion 20b on the back surface of another kneading paddle 5 adjacent to it on one axial side. The protrusion 20b on the back surface of the kneading paddle 5 is in close proximity to or surface contact with the protrusion 20a on the front surface of another kneading paddle 5 adjacent to it on the other axial side. Although ceramics have lower strength than metal, the configuration in which the protrusions 20a and 20b are in contact with each other can mitigate the impact of contact. In addition, the distance between the main body 10s of two axially adjacent kneading paddles 5 can be made larger than when using a known kneading paddle 100. As a result, the risk of the ceramic kneading paddle 5 being damaged (cracking) due to contact can be reduced.

[0038] Furthermore, by providing protrusions 20a and 20b on both axial sides of the kneading paddle 5, even if the axial positions of two adjacent kneading paddles 5 in the left-right direction are slightly misaligned, contact between the first kneading paddle 5 attached to one rotating shaft 3 and the second kneading paddle 5 attached to the other rotating shaft 3 can be prevented. Therefore, the kneading paddle 5 in this embodiment can also be applied to a two-shaft type kneading device 1.

[0039] It is desirable that the outer edges 21 of the protrusions 20a and 20b be chamfered. As shown in Figure 5, the outer edges 21 of the protrusions 20a and 20b have a tapered shape. This reduces the impact when the protrusions 20a and 20b come into contact with each other. The gradient angle θ of the outer edge 21 with respect to the axial direction is between 30 and 60 degrees, for example, about 45 degrees. It is desirable that the outer edge 21 be chamfered so that the ring width of the surface of the protrusions 20a and 20b is constant (maximum) around the entire circumference. Therefore, when the kneading paddle 5 is viewed from the front, the outer circle of the surface of the protrusion 20a (the small diameter circle radially inward of the outer edge 21) is inscribed in the arcuate surfaces 12a and 12b.

[0040] (Regarding the dimensions of the main body) Referring to Figures 3 and 8, the dimensions of the main body 10 of the kneading paddle 5 in the x and y directions will be described. In a known kneading paddle 100, if the length in the y direction (vertical width) L12 is, for example, about 50 mm, then if the length in the x direction (horizontal width) L11 of the main body 110 is 1, then the length in the y direction (vertical width) L12 is 1.9 or more. Also, the difference between the diameter of the cylindrical inner surface 2g (see Figures 1 and 2) of the housing 2 (trough 2d) that houses the kneading paddle 100 and the length in the y direction L12 is very small (1.0 mm or less).

[0041] In contrast, in the kneading paddle 5, if the x-direction length (width) L1 of the main body 10 is 1, then when the y-direction length (vertical width) L2 is, for example, about 50 mm, the y-direction length (vertical width) L2 is, for example, 1.7 or more and 1.9 or less. Note that the x-direction length corresponds to the length of the line segment passing through axis O and connecting a pair of arcuate surfaces 12a and 12b by the shortest distance, and the y-direction length corresponds to the length of the line segment passing through axis O and connecting a pair of tip surfaces 13a and 13b by the shortest distance.

[0042] Thus, the y-direction length L2 of the main body 10 in this embodiment is slightly shorter than the y-direction length L12 of the main body 110 of the known kneading paddle 100. The difference between the diameter of the cylindrical inner surface 2g (see Figures 1 and 2) of the housing 2 (trough 2d) that houses the kneading paddle 5 and the y-direction length L2 is 1.0 mm or more and less than 3.0 mm. Note that the above aspect ratio is effective for kneading paddles with a y-direction length of, for example, 40 mm or more and 60 mm or less.

[0043] In this way, it is possible to prevent the tip surfaces 13a and 13b of the main body 10 of the kneading paddle 5 from coming into contact with the inner surface of the trough 2d or with the arcuate surfaces 12a and 12b of the main body 10 of other kneading paddles 5 adjacent to it in the left-right direction. Therefore, the risk of the ceramic kneading paddle 5 being damaged (cracking) due to contact can be reduced.

[0044] Since the y-direction length L2 of the kneading paddle 5 is shorter than the y-direction length L12 of the metal kneading paddle 100, the width L3 of the tip surfaces 13a and 13b of the kneading paddle 5 shown in Figure 4 is larger than the width of the tip surfaces 113a and 113b of the metal kneading paddle 100. The width L3 of the tip surfaces 13a and 13b of the kneading paddle 5 is determined to be in a range of 5% to 30% of the x-direction length L1, taking into consideration the self-cleaning action of the kneading paddle 5. As an example, the width L3 of the tip surfaces 13a and 13b is 10% to 20% of the x-direction length L1. The x-direction length L1 of the kneading paddle 5 does not often change significantly regardless of the length L2, provided that the diameter of the rotating shaft 3 is constant. Therefore, the above ratio of the width L3 of the tip surfaces 13a and 13b applies to both relatively small kneading paddles with a y-direction length L2 of 20 mm to 90 mm and relatively large kneading paddles with a y-direction length L2 of 100 mm to 200 mm.

[0045] The thickness of the kneading paddle 5 will be explained with reference to Figures 5 and 9. The overall thickness T4 of the kneading paddle 5 is the same as the overall thickness T13 of the known kneading paddle 100, but the thickness T1 of the main body portion 10 is less than or equal to the thickness T11 of the main body portion 110 of the known kneading paddle 100.

[0046] In other words, the combined thickness T2 and T3 of the protrusions 20a and 20b (the dimension of projection from the main body 10) is greater than or equal to the thickness T12 of the protrusion 120 of the known kneading paddle 100. The thicknesses T2 and T3 of the protrusions 20a and 20b are typically equal to each other. It is desirable that the combined thickness T2 and T3 of the protrusions 20a and 20b be between 1 / 20 and 1 / 5 of the total thickness T4 of the kneading paddle 5, for example, between 1 / 15 and 1 / 10 of the thickness T4.

[0047] Thus, in this embodiment, by making the thickness T11 of the main body 10 relatively small, the kneading paddles 5 can be incorporated into the rotating shaft 3 in the same arrangement as the known kneading paddles 100.

[0048] (Regarding keyways) The shape of the keyway 14 will be explained with reference to Figure 6. Figure 6 is a schematic diagram showing the shape of the keyway 14, and is an enlarged view of a part of Figure 3 (the part enclosed by line VI). Also in Figure 6, for ease of understanding, the key 3a of the rotating shaft 3 that is housed in the keyway 14 is shown.

[0049] The keyway 14 is formed in a roughly U-shape and has a bottom surface 14a, two side surfaces 14b, and corner portions 14c between the bottom surface 14a and each side surface 14b. The key 3a of the rotating shaft 3 is rectangular in shape, and the corner portion 3c of the part that is housed in the keyway 14 is roughly right-angled. In contrast, the corner portion 14c of the keyway 14 is rounded. That is, the shape of the corner portion 14c is a rounded shape (R-shape) that smoothly connects the bottom surface 14a and the side surfaces 14b.

[0050] The keyway 114 of the known kneading paddle 100 shown in Figure 8 has a shape corresponding to the shape of the key 3a, and the corners of the keyway 114 are approximately right angles. The width W1 of the keyway 114 is approximately equal to the width of the key 3a of the rotating shaft 3 (slightly larger by the amount of overlap). Also, the depth D10 of the keyway 114, relative to the inner circumferential surface (circumferential wall) of the insertion hole 111, is approximately the same as the protrusion dimension D1 of the key 3a (Figure 6), relative to the outer circumferential surface of the rotating shaft 3. Therefore, in the installed state, the bottom surface and almost the entire surface of both sides of the keyway 114 are in contact with the keyway 114.

[0051] In this embodiment, the width W1 of the keyway 14 of the kneading paddle 5 is approximately equal to the width of the key 3a of the rotating shaft 3, similar to the known kneading paddle 100. On the other hand, the depth D2 of the keyway 14 is deeper than the protrusion dimension D1 of the key 3a by the amount of the corner portion 14c. Therefore, in the mounted state, the keyway 14 contacts the key 3a only at both sides 14b, and the bottom surface 14a is spaced apart from the key 3a.

[0052] In this way, by making the depth D2 of the keyway 14 deeper than that of a known kneading paddle 100, it is possible to ensure contact area on both sides 14b of the keyway 14 while preventing the corner portion 3c of the key 3a from contacting the corner portion 14c of the keyway 14, thereby reducing the risk of damage to the corner portion 14c. Another advantage is that the kneading paddle 5 of this embodiment can be assembled onto the rotating shaft 3 without adjusting the key 3a of the rotating shaft 3. In other words, the housing 2 and rotating shaft 3 of the kneading device 1 can be used as they were in the past.

[0053] Furthermore, as shown in Figure 7, the depth D3 of the keyway 14A may be made the same as the depth D10 of the keyway 114 of the known kneading paddle 100, and the protruding dimension D4 of the key 3b of the rotating shaft 3 or the diameter of the rotating shaft 3 may be reduced accordingly.

[0054] The depth D2 of the keyway 14 in this embodiment is, for example, 0.07 to 0.11, where the diameter φ of the insertion hole 11 is 1. The corner portion 14c of the keyway 14 has a rounded shape with a radius of, for example, 0.01 to 0.10, where the diameter φ of the insertion hole 11 is 1. The specific radius of the rounding of the corner portion 14c is, for example, 0.1 mm to 5.0 mm, and preferably 2.0 mm or less.

[0055] Furthermore, the intersection 14d between the keyway 14 and the insertion hole 11 may also be rounded. Additionally, multiple keyways 14 may be provided.

[0056] <About the manufacturing method of the kneading paddle> The kneading paddle 5 in this embodiment can be manufactured mainly by following the steps below.

[0057] (1) Preparation process Prepare the raw materials. The raw materials should preferably be materials classified as oxides among fine ceramics, and among these, it is preferable to use one of the following that are used as "structural materials": zirconia, alumina, falselite, zircon, mullite, steatite, or cordierite. It is also possible to use aluminum nitride, silicon nitride, silicon carbide, or titanium nitride, which are classified as non-oxides among fine ceramics.

[0058] The raw materials should preferably contain zirconia (zirconium dioxide). The zirconia content may be 100%, or it may contain other materials (e.g., alumina). Since zirconia has the highest strength and toughness among ceramics, it is desirable to include at least 20%. The desirable zirconia content will be discussed later.

[0059] (2) Molding process Based on raw materials containing zirconia, a primary processed product having the general shape of a kneading paddle 5 is formed from a disc-shaped member. In this forming process, for example, an insertion hole 11 and protrusions 20a, 20b (boss portion 15) are formed using a lathe, and wing portions (arc surfaces 12a, 12b) and tip surfaces 13a, 13b continuous with the boss portion 15 are machined using a machining center or the like. In addition, a keyway 14 connected to the insertion hole 11 is formed.

[0060] In other words, a primary processed product is formed by creating a main body portion 10 with a convex lens shape in plan view, having an insertion hole 11 and a keyway 14, from a disc-shaped member made of ceramics, and forming a pair of protrusions 20a and 20b at corresponding positions on both axial ends of the main body portion 10.

[0061] During the molding process, when forming the keyway 14, the corner portion 14c of the keyway 14 is rounded (R-shaped). In other words, the molding process includes the step of rounding the corner portion 14c of the keyway 14. The radius of rounding of the keyway 14 at this stage is larger than the radius of rounding of the finished product (0.1 mm to 5.0 mm), taking into account shrinkage during the subsequent sintering process. For example, if the zirconia content is 100%, the size will be reduced to about half during the sintering process, so the radius of rounding in the molding process may be about twice the radius of rounding of the finished product.

[0062] (3) Sintering process The primary processed product is sintered (fired). The sintering process includes a first step of heating to a maximum temperature at a predetermined heating rate, a second step of continuing heating at the maximum temperature for a predetermined holding time, and a third step of cooling the molded body from the maximum temperature at a predetermined cooling rate. When the ceramic molded body is heated in the first step, adjacent raw material particles gradually adhere to each other, reducing the gaps between particles and causing the entire body to shrink. Depending on the raw materials, shrinkage may also occur in the final cooling step. The optimal conditions for the heating rate, maximum temperature, and holding time in the sintering process are determined through trial and error.

[0063] (4) Polishing process After sintering, the end faces of the pair of protrusions 20a and 20b, the sides 14b of the keyway 14, and the insertion hole 11 of the primary processed product are polished.

[0064] (5) Heat treatment process The secondary processed parts are heat-treated to obtain the finished product.

[0065] Primary processed products containing zirconia shrink significantly during the sintering process before the polishing process. The above conditions in the sintering process are set to prevent damage due to thermal shrinkage. However, if the corner portion 14c of the keyway 14 is not rounded during the molding process and the corner portion is a right angle, stress will concentrate at the corner portion, and cracks may occur starting from the corner portion. In contrast, in this embodiment, the corner portion 14c of the keyway 14 is rounded during the molding process, so that cracks at the corner portion 14c due to stress concentration during thermal shrinkage can be prevented or suppressed. In addition, there are cases in which the bottom surface 14a of the keyway 14 is in a gentle arc shape.

[0066] Considering that the primary processed product shrinks during the sintering process, making it prone to cracking at the corner portion 14c of the keyway 14, it is desirable to determine the content ratio of zirconia to other materials such as alumina (materials with a lower thermal shrinkage rate than zirconia). Furthermore, if the zirconia content is low, the thermal shrinkage rate during the sintering process can be suppressed. For example, if the zirconia content is 80% or less, the corner portion 14c can be made smaller, to 2 mm or less.

[0067] In this case, the bottom surface 14a of the keyway 14 can also be made to contact the key 3a, which is advantageous in terms of increasing the contact area. It is also possible to increase the contact area even when the corner portion 14c has a relatively large curvature by making the corner portion 3c of the key 3a of the rotating shaft 3 a similar rounded shape (the bottom surface 14a of the keyway 14 can also be made to contact the key 3a), but this would require more effort to process the rotating shaft 3 and is therefore undesirable.

[0068] Considering the thermal shrinkage during the sintering process as described above, it is desirable to keep the zirconia content below 80%. If it exceeds 80%, the curvature of the corner portion 14c of the keyway 14 needs to be relatively large to account for the thermal shrinkage during the sintering process, which may reduce the contact area between the (normal) rotating shaft 3 and the key 3a.

[0069] As mentioned above, the lower limit of the zirconia content is 20%. In this embodiment, in order to mitigate impact from contact, protrusions 20a and 20b are provided on both axial ends of the kneading paddle 5, and the y-direction length of the kneading paddle 5 is made shorter than the y-direction length of the metal kneading paddle 100 (the width L3 of the tip surfaces 13a and 13b is made relatively large), which makes it possible to set the zirconia content to such a low value.

[0070] In this embodiment, although the shape of the kneading paddle 5 is designed to mitigate impact from contact, in order to maintain the required strength of the kneading paddle, it is desirable that the zirconia content be set in the range of 50% to 80%, and more preferably in the range of 70% to 80%.

[0071] As described above, the kneading paddle 5 in this embodiment does not contain metal and is made only of a ceramic molded product, so no metal contamination occurs. Furthermore, since there is no need to provide a reinforcing layer to a metal kneading paddle as in the conventional method, the manufacturing method of the kneading paddle 5 can be simplified. In addition, since the ceramic molded product has higher heat resistance than the resin molded product, the kneading paddle 5 can be used even under high temperature conditions of, for example, 300 degrees Celsius or higher.

[0072] Furthermore, as described above, the shape of the kneading paddle 5 has been modified to prevent damage from contact when it is installed, so the kneading paddle 5 in this embodiment can be used in the same way as the metal kneading paddle 100.

[0073] As described above, according to this embodiment, a high-quality kneading paddle 5 can be provided.

[0074] <Variation> In this embodiment, an example is shown in which the protrusions 20a and 20b are formed in an annular shape around the insertion hole 11, but the embodiment is not limited to this example. For example, the protrusions 20a and 20b may be provided at a position radially outward from the insertion hole 11 (for example, on the outer diameter side of the keyway 14). Also, the shapes of the protrusions 20a and 20b do not have to be annular, and they do not have to be the same shape.

[0075] Furthermore, although this embodiment was described using a twin-shaft type kneading device 1 as an example, the kneading paddle 5 in this embodiment is also suitable for a single-shaft type kneading device.

[0076] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0077] 1 Mixing device, 2 Housing, 3 Rotating shaft, 3a, 3b Keys, 5, 100 Mixing paddle, 10, 110 Main body, 11, 111 Through hole, 14, 14A, 114 Keyway, 20a, 20b, 120 Protrusions.

Claims

1. A paddle attached to a rotating shaft located inside the housing of a kneading device, It consists solely of a ceramic molded product that does not contain metal, comprising a main body portion having an insertion hole through which the rotating shaft is inserted, and a pair of protrusions provided on each of the axial end faces of the main body portion, as an integral part. A kneading paddle in which each of the aforementioned protrusions is located in a position that is in close proximity to or in surface contact with a protrusion provided on the axial end face of another paddle adjacent to it in the axial direction when mounted.

2. A substantially U-shaped groove is provided on the inner circumferential surface of the main body portion surrounding the insertion hole to receive a key with a rectangular cross-section provided on the outer circumferential surface of the rotating shaft. The kneading paddle according to claim 1, wherein the corners of the grooves are rounded.

3. The main body includes, when viewed in the axial direction, a pair of arcuate surfaces that bulge out from each other on both sides of the insertion hole in the x direction, and a pair of end surfaces located on both sides of the insertion hole in the y direction, connecting the circumferential ends of the pair of arcuate surfaces. The kneading paddle according to claim 1, wherein the width of the tip surface is 5% or more and 30% or less of the x-direction length of the main body.

4. A kneading apparatus in which the kneading paddles according to any one of claims 1 to 3 are arranged in alignment on each of the two rotating shafts such that their axial positions overlap.

5. A method for manufacturing a kneading paddle that is attached to a rotating shaft located inside the housing of a kneading device, A molding process in which a primary processed product is formed by creating a main body portion with a convex lens shape in plan view, having an insertion hole and a keyway, from a disc-shaped member made of metal-free ceramics, and forming a pair of protrusions on each of the axial end faces of the main body portion, A sintering step for sintering the aforementioned primary processed product, The process includes a polishing step in which a secondary product is formed by polishing both end faces of the pair of protrusions on the primary product after sintering, A method for manufacturing a kneading paddle, wherein in the molding process, each of the protrusions is formed in a position that is in close proximity to or in surface contact with a protrusion provided on the axial end face of another paddle adjacent to it in the axial direction when mounted.

6. The method for manufacturing a kneading paddle according to claim 5, wherein the molding step includes a step of rounding the corner portion of the keyway.

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