Abstract:
The invention provides a screw conveyer which has a helically wound member (23) attached to the screw which member extends from each turn of the screw towards the next turn and is of decreasing diameter along the screw.

Description:
BACKGROUND TO THE INVENTION 
     This invention relates to helical conveyors of the kind having a helical flite fixed to a rotary shaft within a casing. Such conveyors are used with success with a great variety of pulverous and semi-fluid products. 
     Considerable difficulty however has been experienced in dealing with products which tend to solidify and jam between the screw and housing. For example, combustible waste products are heated to a very high temperature e.g. 1650° F. for removal of moisture and are fed through a conveyor into a furnace. These products are very fluid at that temperature and run freely through a downpipe into the entry end of the conveyor where they rapidly become cooled e.g. to 300° F. at which temperature the products tend to solidify and pack together and stop the helical conveyor. Attempts have been made to overcome this problem by using a larger horsepower motor to drive the conveyor and for example from a nominal 3 horsepower successive tests finally reached 25 horsepower which is obviously impractical. 
     OBJECT OF THE INVENTION 
     The object of the invention is to devise a helical conveyor which will enable such products to be conveyed without undue increase in horsepower. 
     Various ideas were considered but the present invention proved successful on test. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The invention will be described by way of example with reference to the accompanying diagrammatic drawings wherein: 
     FIG. 1 is a part vertical section of a helical screw conveyer made in accordance with the invention; and 
     FIG. 2 is an end view thereof. 
    
    
     The conveyer has a conveyer casing 10 which in this example is tubular and is within an outer tube 11 with a space between the casing and tube for flow of heating or cooling medium. 
     A central hollow shaft 12 extends through the casing and heating or cooling medium can flow through the shaft. 
     The bearings for mounting the shaft are of well known construction and need not be shown or described. Similarly means for inlet and outlet of product to be treated and means for inlet and outlet of heating or cooling medium are too well known to need description or illustration. 
     Surrounding the shaft in contact therewith is a flat ribbon helical pad 18 which is welded to the shaft at its ends. A helical lead flite 19 surrounds the shaft and seats on the pad 18 and is welded to it only at its ends. A helical back plate 20 is then welded at its outer edge to the lead flite 19 and at its inner edge to the pad 18 thereby making a hollow flite through which heating or cooling medium can flow. Then a helical flat ribbon type barrier member 23 is welded to the back plate so as to project from each helix of the back plate towards the next adjacent lead flite a distance of 30 to 50 percent of the total distance &#34;A&#34; between the back plate and lead flite. The member 23 is of decreasing diameter towards the outlet end of the conveyer (left hand end in FIG. 1) thereby providing blocking space 25 of decreasing size. This has the effect of receiving a mass of the product which barely moves if at all and the remaining space 26 is of increasing size so enabling the product to move forward. 
     In addition barrier plates 28 are fixed to the back plate and extend more or less radially from the outer edge of the helical conveyer flite towards the barrier member 23 i.e. they project from the flite in the same direction as the barrier member 23. These plates form a further hindrance and prevent packing and jamming of the product.