Chain structure

1. A chain structure comprising:

a sprocket wheel in which a plurality of gear teeth capable of engaging with a chain are formed in an outer peripheral portion; and

the chain in which a pair of side plate members facing to each other are coupled in an endless manner at plural sets in a length direction, and which is wound around gear teeth in the outer peripheral portion of said sprocket wheel,

wherein a protruding plate portion for preventing the side plate member from dropping from a wound state to the sprocket wheel is provided in at least a part of the plural sets of said side plate members,

wherein said protruding plate portion includes a base end plate portion which protrudes out of a center portion of the side plate portion in a longitudinal direction so as to extend in a radially inward direction of the sprocket wheel, an intermediate plate portion which is folded from a leading end portion of the base end plate portion so as to extend in such a direction that goes away from the paired side plate portions, and a vertical plate portion which is folded from a leading end portion of the intermediate plate portion so as to extend in the radially inward direction of the sprocket wheel, and

wherein said side plate member is configured such that a portion of the sprocket wheel side except for the portion where said protruding plate portion is provided is located radially more outward than the intermediate plate portion.

2. The chain structure according to claim 1 , wherein said protruding plate portion is provided in said side plate member having a flight plate attaching portion.

3. The chain structure according to claim 2 , wherein two sets of chain structures are arranged in inner sides of a pair of surfaces facing to each other within a liquid tank so as to be faced to each other, and

said protruding portions are provided only in the side plate members which are arranged in the sides which are faced to each other of a pair of sprocket wheels, or only in the side plate members which are arranged in the opposite sides to the sides which are faced to each other of a pair of sprocket wheels.

4. The chain structure according to claim 1 , wherein two sets of chain structures are arranged in inner sides of a pair of surfaces facing to each other within a liquid tank so as to be faced to each other, and

said protruding portions are provided only in the side plate members which are arranged in the sides which are faced to each other of a pair of sprocket wheels, or only in the side plate members which are arranged in the opposite sides to the sides which are faced to each other of a pair of sprocket wheels.

5. The chain structure according to claim 1 , wherein an annular projection portion is formed in an inner side in the radial direction than the gear tooth forming portion of the sprocket wheel, said annular projection portion protruding in a thickness direction of said sprocket wheel, and having its axis in common with the axis of said sprocket wheel to be formed in a circular ring shape,

wherein said intermediate plate portion and said vertical plate portion are arranged to be faced to an outer peripheral surface of the annular projection portion with a gap therebetween, and

wherein the vertical plate portion is arranged so that its leading end portion extends to a position which is radially inner side than the annular projection portion of the sprocket wheel.

6. A chain structure comprising:

a chain;

a sprocket wheel having a plurality of gear teeth formed in an outer peripheral portion and configured to engage the chain;

a pair of symmetrical link plates arranged on opposite sides of the chain, wherein each link plate includes a side plate portion configured to couple to the chain, a flight plate attaching portion extending from a first side of the side plate portion, and a protruding plate portion extending from an opposite second side of the side plate portion;

wherein the flight plate attaching portion includes a rising portion integrally provided on an upper end portion of the first side of the side plate portion, and an attaching portion extending perpendicularly from the rising portion; and

wherein the protruding plate portion includes a base end plate portion extending out from a part of the respective side plate member, an intermediate plate portion extending perpendicularly from the base end plate portion, and a vertical plate portion extending perpendicularly from the intermediate plate portion.

7. The chain structure according to claim 6 , wherein the side plate portion comprises an upper end portion formed as a horizontally linear shape and a lower end portion having a concave portion formed at the center.

8. The chain structure according to claim 7 , wherein the protruding plate portion is integrally and continuously formed in the center portion of the concave portion and protrudes downward from the concave portion.