Sprocket-wheel, especially for mining machines
BACKGROUND OF THE INVENTION 
     This invention relates to a sprocket-wheel, especially for chain drives of mining machines and equipments such as push-plate conveyors and mining equipment. 
     In known designs of sprocket-wheels the active chain links settle down in seats between the working surfaces of the teeth. The number of these seats equals to that of the teeth of the sprocket-wheel. The construction of the teeth and seats is of such a type that the seat is formed in tooth spaces, and is from all sides limited by side retaining walls. In these seats the active chain links rest. These are sometimes called lying chain links. 
     The results of tests on the work of known sprocket wheels show that the profile of the teeth and seats of the sprocket-wheel cause considerable problems and difficulties in the operation of the sprocket-wheel. These problems and difficulties increase with progress of the wear of chains and sprocket-wheels, and thereby reduces the performance thereof. It results in short life of the chains and sprocket-wheels. 
     Known sprocket-wheels show substantial disadvantages. The effective co-operation of the sprocket-wheel with the chain occurs essentially only within small angular displacement of the sprocket-wheel, usually not exceeding the value of 2π/Z, wherein Z is the number of teeth of the sprocket wheel. Actually only two teeth are loaded and the seat of the sprocket-wheel, which is situated between the teeth. The remaining teeth remaining in contact with the chain links are relieved. The form coupling occuring on small wheel sector between the teeth of the sprocket-wheel and the chain links causes development of high unitary pressures between the rubbing surfaces, as well as relatively severe transmission of pressures from the tooth in mesh with the chain onto that tooth just coming into mesh next on the sprocket-wheel. 
     A very substantial disadvantage of known sprocket-wheels consists also in limited possibility of free displacement of the active chain links within the seats in the sense of rotation of the sprocket-wheel. The length of the seat situated between two teeth is limited thereby. An extension of the length may be achieved only through a reduction of the thickness of the tooth. This, however, also reduces the strength and life of the sprocket-wheel. The limited ability to free displacement within the seats in the sense of rotation of the sprocket-wheel is a cause of stepwise indenting of the active chain links down into the seats in the form of wear of the chain links and of the sprocket-wheel. That occurrence causes seizing of the chain links in the seats, an intensification of the wear of the tooth surface, and necessity to employ chain pushers in drives. Disadvantageous effects of indenting and seizing of the chain links in the seats reside in generating considerable, periodical and dynamic forces in the chain. 
     The object of the present invention is to provide a sprocket-wheel which is free from the aforementioned disadvantages. It is also an object to eliminate chain pushers from the drive. 
     SUMMARY OF THE INVENTION 
     The objects are achieved according to the present invention by providing a sprocket-wheel with teeth and seats formed in such way that the number of teeth is smaller than that of the seats. The seats are open from one side, and are provided with a retaining wall only from the side of the tooth. The bottom lands of two adjacent seats intersect, thereby forming an edge. 
     In the sprocket-wheel according to the present invention, a possibility exists of free positioning the chain links independently of the wear of the seats and providing a degree of permanent elongation of the separate chain links. Due to a substantial part of the load of the chain, they carry the chain links lying in the seats between the chain links, and are coupled by friction with the sprocket-wheel. Load and wear of teeth of the sprocket-wheel are negligible. 
     A further advantage of the sprocket-wheel according to the present invention consists in a considerable reduction of dynamic forces acting within the chain, an increased life of both the sprocket-wheel and the chain, a simplification of the construction and production engineering of the sprocket-wheel, as well as the possibility of removing chain pushers from the drive systems. 
     The sprocket-wheel according to the present invention may be employed in transportation equipment and mining machines provided with coil chain drives or fish-plate chain drives. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained by way of an exemplary embodiment with reference to the accompanying drawing in which:- FIG. 1 is the cross-sectional view of a sprocket-wheel, and FIG. 2 is the top view thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In accordance with the present invention the sprocket-wheel has a number of teeth 1 smaller than the number of seats 2. The seats 2 are open from one side and have the retaining walls 3 only from the side of teeth 1. The bottom land planes of two adjacent seats 2 intersect, thereby forming an edge 4.