Chute Parts of Spiral Separator for Mineral Beneficiation Technical Field The present invention relates to a chute part of a spiral separator for mineral beneficiation. Background of the Technology Existing chute separator for mineral beneficiation is configured to be spiral, and in order to lower down the cost for transporting and storing, fan-shaped plates are used as chute parts in the existing spiral chute separator for mineral beneficiation. During transporting and storing, the fan-shaped plates are packed separately; and when assembling, the fan-shaped plates are fit together, that is, the lower radial side of the upper fan-shaped plate is connected to the upper radial side of the lower fan-shaped plate. However, the existing connection between the fan-shaped plates is unreliable and inconvenient to use, therefore, the connection mode of the plates needs to be improved. Summary of the Invention The object of the present invention is to overcome the defects of the prior art, and provide chute parts of spiral separator for mineral beneficiation. In the present invention, the connection between two fan-shaped plates is more reliable, and has a simpler structure. The technical solution of the invention is as follows: A chute part of spiral separator for mineral beneficiation, including a fan-shaped plate sloping downward spirally, wherein the plate includes an upper radial side, a lower radial side, an outer circular arc and an inner circular arc, wherein a plurality of buckles are arranged on the lower radial side, and a plurality of holes are provided in the upper radial side, wherein the number of the buckles corresponds to the number of the holes, and the shape and size of the buckles match the shape and size of the holes. 1 Further technical solutions of the invention are described as follows. A first wedge-shaped slot is provided at the juncture between the upper radial side and the outer circular arc, a second concave-shaped slot is provided at the juncture between the upper radial side and the inner circular arc, a first wedge-shaped tenon is provided at the juncture between the lower radial side and the outer circular arc, and a second convex -shaped tenon is provided at the juncture between the lower radial side and the inner circular arc, wherein the shape and size of the first tenon match the shape and size of the first slot, and the shape and size of the second tenon match the shape and size of the second slot. A first positioning rib is provided on the lower radial side, a positioning slot is formed between the first positioning rib and the buckle; a second positioning rib and the holes are provided on the upper radial side, wherein the holes are in close proximity to the inner side of the second positioning rib and cooperate with the buckles to form a chucking position. The buckle includes an elastic arm and a hook head. After the buckle has been connected to the hole, the outer side of the buckle abuts against the first inner side of the hole, and there should be a tapered elastic space between the inner side of the buckle and the second inner side of the hole to produce an elastic deformation space when the hook head passes through the hole. After the hook head passes through the hole, the buckle will be back to normal shape, and the hook head will hook the outer end of the hole tightly, such that the hole is stuffed up by the root of the buckle. A plurality of intersectant reinforced ribs are provided on the rear side of the fan-shaped plate. The advantages or principle of the invention are described as follows: 1. The fan-shaped plates are packed separately during transporting and storing to reduce space and transport costs, and adjacent fan-shaped plates are fit together by buckles and holes when assembling, which causes a reliable connection and a simple structure; 2. The first tenon sticks into the first slot, and the second tenon sticks into the second slot, so as to make the upper radial side connect with the lower radial side tightly with accurate positioning, to avoid the two adjacent fan-shaped plates 2 becoming loose, mismatching, or getting off. 3. A first positioning rib is provided on the lower radial side, and a second positioning rib is provided on the upper radial side. The first positioning rib is contacted with the second positioning rib when installation, which make the connection between the two adjacent fan-shaped plates more reliable, and has an enforced effect on three-dimensional direction, so as to avoid the fan-shaped plate distorting or breaking, and improve the stiffness and strength of the fan-shaped plate. Brief Description of the Drawing Figure 1 shows a structure view of the fan-shaped plate of the invention. Figure 2 shows a back side view of the fan-shaped plate. Figure 3 shows a top view of two fastening fan-shaped plates. Figure 4 shows a section view of A-A in Figure 3. Figure 5 shows an enlarged view of B in Figure 4. Figure 6 shows a revolved sectional view of C-C in Figure 3. Figure 7 shows an enlarged view of D in Figure 6. Figure 8 shows an enlarged view of E in Figure 6. Figure 9 shows a side view of two fastening fan-shaped plates. Figure 10 shows a disconnect view of F-F in Figure 9. Figure 11 shows a disconnect view of G-G in Figure 9. Figure 12 shows an enlarged view of H in Figure 10. Figure 13 shows an enlarged view of I in Figure 11. Explanation of the reference signs in the drawings: 1. fan-shaped plate, 2. upper radial side, 3. lower radial side, 4. outer circular arc, 5. inner circular arc, 6. buckle, 7. hole, 8. first slot, 9. second slot, 10. first tenon, 11. second tenon, 12. first positioning rib, 13. second positioning rib, 14. outer side of the 3 buckle, 15. positioning slot, 16. elastic arm, 17. hook head, 18. reinforced rib, 19. inner side of the buckle, 20. tapered elastic space, and 21. root of the buckle. Detailed Description of the Invention The embodiments of the invention are described in detail below. A chute part of spiral separator for mineral beneficiation is shown in Figure 1-13, the chute part includes a fan-shaped plate 1 sloping downward spirally, the plate 1 is formed with an upper radial side 2, a lower radial side 3, an outer circular arc 4 and an inner circular arc 5, wherein a plurality of buckles 6 are arranged on the lower radial side 3, and a plurality of holes 7 are provided in the upper radial side 2, wherein the number of the buckles 6 corresponds to that of the holes 7, and the shape and size of the buckle 6 match those of the hole 7. A first wedge-shaped slot 8 is provided at the juncture between the upper radial side 2 and the outer circular arc 4, a second concave-shaped slot 9 is provided at the juncture between the upper radial side 2 and the inner circular arc 5, a first wedge-shaped tenon 10 is provided at the juncture between the lower radial side 3 and the outer circular arc 4, and a second convex-shaped tenon 11 is provided at the juncture between the lower radial side 3 and the inner circular arc 5, wherein the shape and size of the first tenon 10 match the shape and size of the first slot 8, and the shape and size of the second tenon 11 match the shape and size of the second slot 9. A first positioning rib 12 is provided on the lower radial side3, a positioning slot 15 is formed between the first positioning rib 12 and the buckle 6; a second positioning rib 13 and the holes 7 are provided on the upper radial side 2, wherein the holes 7 are in close proximity to the inner side of the second positioning rib 13 and cooperates with the buckles 6 to form a chucking position. The buckle 6 includes an elastic arm 16 and a hook head 17. After the buckle 6 has been connected to the hole 7, the outer side of the buckle 14 abuts against the first inner side of the hole 7, and there should be a tapered elastic space 20 between the inner side of the buckle 19 and the second inner side of the hole 7 to produce an elastic deformation space when the hook head 17 passes through the hole 7. After the hook head 17 passes through the hole 7, the buckle 6 will be back to normal shape, and the hook head 17 will hook the outer 4 end of the hole 7 tightly, such that the hole 7 is stuffed up by the root of the buckle 21. The dorsal part of the fan-shaped plate 1 is provided with a plurality of intersectant reinforced ribs 18. The embodiment has the following advantages: 1. The fan-shaped plates are packed separately in transportation and store to reduce space and transport costs, and adjacent fan-shaped plates are fit together by buckles 7 and holes 6 at installation, causing a reliable connection and a simple structure; 2. The first tenon 10 sticks into the first slot 8, and the second tenon 11 sticks into the second slot 9, so as to make the upper radial side 2 connect with the lower radial side 3 tightly with accurate positioning, to avoid the two adjacent fan shaped plates becoming loose, mismatching, or getting off. 3. A first positioning rib 12 is provided on the lower radial side 3, and a second positioning rib 13 is provided on the upper radial side 2. The first positioning rib 12 is contacted with the second positioning rib 13 when installation, which make the connection between the two adjacent fan-shaped plates more reliable, and has an enforced effect on three-dimensional direction, so as to avoid the fan-shaped plate distorting or breaking, and improve the stiffness and strength of the fan-shaped plate. A detailed description of one or more preferred embodiments of the invention is provided above along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications, and equivalents. For the purpose of example, numerous specific details are set forth in the description above in order to provide a thorough understanding of the present invention. The present invention may be practised according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. Throughout this specification and the claims that follow unless the context requires 5 otherwise, the words 'comprise' and 'include' and variations such as 'comprising' and 'including' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge of the technical field. 6