idling Materials in Bulk 57 



shaft or drum in a trough. The material it poured 

 into one end of the trough and moved length- 

 wife by the spiral motion of the flight. Conveyors 

 of this type are well adapted for handling fine 

 material such as seeds, grain, sand, and cement. 



v can handle large quantities with compara- 

 tively little power. In general, the material is 



; but one of the advantages of this type of 

 conveyor is that it can serve as a drier as well 

 as a transporting agent. This function is helped 

 by breaking up the flight into a series of paddles, 

 arranged spirally as broken sections of the flight. 

 Their action is then a combined one of stirring 

 the material while it is moved forward. This 

 action also breaks up lumps in certain classes of 

 material. For light materials which slide easily, 

 such as cotton seeds, the troughs are usually U- 

 shaped, made of sheet steel, and fit the conveyor 

 closely so that the material slides along the 

 smooth surface. The material fills the lower 

 portion of the trough, part way up to the shaft. 

 Where the material is gritty, wear on the trough 

 is eliminated by leaving a considerable space be- 

 tween the conveying screw and the trough. This 

 space fills with material which is practically at 

 rest, and the moving material slides along on 

 itself. Spiral conveyors arc made in sections 

 from six to twelve feet in length, which may be 

 arranged in a series, each section discharging into 

 the next. Each length must be straight, but they 

 can be turned at the connections in any direction. 

 The diameter of the screws varies from four to 

 eighteen inches, and the total length of a conveyor 



