Abstract:
Flighting for screw conveyors of improved construction and resulting in better wear characteristics and carrying capacity is provided through the use of cold roll manufacturing and a roller which forms the flighting with a shape which moves some of the material being conveyed away from the outside peripheral edge of the flighting and thereby distributes wear over a larger portion of the surface of the flighting.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    I. Field of the Invention 
         [0004]    The present invention relates to conveyors such as augers and other screw conveyors. More specifically, this invention relates to an improved design for the flighting of such conveyors and the equipment and methods used to make such flighting. 
         [0005]    Screw conveyors are one of several inventions and discoveries traditionally attributed to Archimedes in the Third Century B.C. Such conveyors comprise a screw inside a hollow pipe or tube. The screw has a shaft and flighting surrounding the shaft. As the screw turns inside the tube, material is carried by the flighting from one end of the tube to the other. Such material can be a liquid such as water or other aggregate materials such as grain. 
         [0006]    Efforts have been made since the earliest invention of the screw conveyor to improve on the basic invention. Some of these efforts relate to trying to improve the capacity of the screw conveyor by, for example, changing the diameter of the tube and changing the number and angle of the flights. Other efforts have been made to improve the life span of the conveyor which is susceptible to substantial wear especially at the outside peripheral edge of the flighting. In the more than 2300 years since the screw conveyor was first invented, no one has been able to satisfactorily modify the basic design to improve the capacity of the conveyor and reduce wear at the outside peripheral edge of the flighting. 
         [0007]    Historically, the shaft and flighting of a screw conveyor have been integrally formed. More commonly, however, the flighting and shaft are separately formed and then joined together by a weldment. A cold rolling process is typically used to form the flighting. 
         [0008]    The cold rolling process traditionally used has resulted in a helical flighting having an inner edge nearest the shaft which is thicker than the outside peripheral edge nearest the tube surrounding the screw. The outside peripheral edge has traditionally been the portion most subject to wear because of frictional forces between the tube, the material being conveyed and the flighting. 
         [0009]    Various attempts have been made to improve the wear characteristics of flighting by increasing the thickness of the outside peripheral edge. For example, U.S. Pat. No. 1,113,688 to G. M. Porter dated Oct. 13, 1914 discloses several embodiments in which auxiliary helical members are secured to the flighting to augment the thickness of the outside peripheral edge of the flighting for improved wear characteristics. U.S. Pat. No. 1,684,254 to J. O. Bailey dated Apr. 26, 1927 discloses several embodiments including a peripheral bead or thickened portion 7 on the outside peripheral edge of the flighting. Adding auxiliary helical members as disclosed in the Porter patent or beading as disclosed in the Bailey patent increases the time, expense and number of steps required to complete construction of the flighting. Also, these additional efforts have been of marginal utility because, for example, the abrupt edges, points, and transitions of the beading shown in Bailey and the auxiliary members and thin areas near the auger shaft of Porter are subject to wear and the result is still not long lasting flighting. 
         [0010]    U.S. Pat. No. 5,678,440 to Hamilton represents an effort to provide beading similar to that disclosed in Bailey without requiring additional steps, time, or money. However, the flighting disclosed in the Hamilton patent, shown herein in  FIG. 2 , is subject to unacceptable wear. Such wear is particularly acute in the area of the sharp radius on the carrying side of the flighting where the flighting transitions from a thinner area to the thicker area adjacent the outside edge of the flighting. 
         [0011]    II. Related Art 
       SUMMARY OF THE INVENTION 
       [0012]    To improve the wear characteristics and material flow rate, continuous helical flighting for a screw conveyor is provided having three discrete sections—an inside section, a central concave section and an outside section. The inside section has a length of about 30% of the length of the radius of the flighting. The central concave section has a length of about 60% of the length of the radius of the flighting. The outside section has a length of about 10% the length of the radius of the flighting. The inside section is the thickest section and tapers slightly as it extends from the inner edge of the flighting to the transition between the inside section and the central concave section. The outside section is about 75% as thick as the thinnest portion of the inside section. The thinnest area of the central concave portion is about 55% to 60% as thick as the thinnest area of the inside section. To create smoother transitions between the central section and the inside and outside sections, the thinnest area of the central section is not at its midpoint along its length, but instead is between 66% and 75% of the distance from the transition between the inside section and the central section to the transition between the central section and the outside section. Providing a tapered inside section and positioning the thinnest point of the central concave section nearer the outside section results in smooth transitions between adjacent sections of the flighting. As such, the carrying surface is free of ridges, other abrupt transitions and other sharply radiused areas. Ridges, abrupt transitions and sharply radiused areas on the carrying surface of flighting tend to increase friction between the carrying surface and the material being conveyed. Providing these novel and unique surface characteristics not only improves the wear characteristics of the flighting, but also the carrying capacity of the conveyor. 
         [0013]    U.S. Pat. No. 5,678,440 to Hamilton, in FIGS. 4 and 5, shows a cold rolling apparatus for cold rolling metal into a flighting having the shape represented in FIG. 2 of the Hamilton patent. By modifying the shape of roller 58 and moving the pinch point between the two rollers 56 and 58, the improved flighting of the present invention can be made in a single step cold roll process. Improvements have also been made to the construction of the rollers for increased durability. Also, hydraulic motors attached to a pump and valve arrangement have been provided to replace the motor  88 , speed change selector boxes  72 ,  74  and transmission, clutch and belts to reduce noise generated by the cold roll machine, the cost of the cold roll machine, maintenance thereof, and the time required to change the rollers  56  and  58  when necessary or desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows a side elevation of a section of the shaft and flighting of a conveyor made in accordance with the present invention. 
           [0015]      FIG. 2  shows a transverse section of a prior art screw conveyor over which the conveyor of the present invention offers a substantial advantage. 
           [0016]      FIG. 3  shows a transverse section of a conveyor incorporating the shaft and flighting of  FIG. 1 . 
           [0017]      FIG. 4  is a cross-section of the flighting of the conveyor shown in  FIG. 1 . 
           [0018]      FIG. 5  is a diagrammatic plan view of the machine used to form the flighting shown in  FIG. 1 . 
           [0019]      FIG. 6  is a diagram of the roller assemblies of the machine used to form the flighting shown in  FIG. 1 . 
           [0020]      FIG. 7  shows a side elevation of the roller which forms the carrying surface of the flighting shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The conveyor  10  of the present invention includes a cylindrical outer casing  11  in the form of a hollow pipe or tube, a shaft  12  and a continuous flighting  14  extending the length of the shaft as shown in  FIGS. 1 ,  3  and  4 . The inner edge  16  of the flighting  14  is permanently coupled to the shaft  12  in any standard manner such as by welding so the shaft  12  and flighting  14  rotate together within the casing  11 . The flighting is, of course, helical in shape and projects in a radial fashion from the shaft  12  to an outside peripheral edge  17 . The flighting is formed with a carrying surface  18  and a rear surface  20 . Material to be conveyed contacts the carrying surface  18  and rides along carrying surface  18  as the shaft  12  and flight  14  of conveyor  10  rotate to move the material from one end of the conveyor  10  toward the other. 
         [0022]      FIG. 2  shows a prior art screw conveyor having flighting comprising two sections, an inner tapered section extending from the inner edge joined to the shaft and an outer section adjacent the outside edge. The transition on the carrying surface of the flighting between these two sections is quite abrupt. As such, an area of increased friction and wear is present. As illustrated in  FIGS. 3 and 4 , the carrying surface  18  of the subject invention has three distinct sections—an inside section  22  adjacent the inner edge  16  and the shaft  12 , an outside section  26  adjacent the outside peripheral edge  17 , and a central concave section  24 . A smooth transition  27  is present between the inside section  22  and the adjacent central concave section  24 . Likewise, a smooth transition  29  is present between the central concave section  24  and the adjacent outside section  26 . 
         [0023]    As the inside section  22  extends radially from the inner edge  16  toward the transition  27 , the carrying surface  18  tapers toward the rear surface  20 . As such, the thickness of the inside section  22  at transition  27  is only about 89% of the thickness of the inside section  22  at the inner edge  16 . This tapering makes the transition  27  between the inside section  22  and the central concave section  24  less abrupt. The transition  27  is also less abrupt because the thinnest point  28  of the central concave section  24  is not at the midpoint between the transitions  27  and  29 . Instead, the thinnest point  28  is at about two-thirds the length of the central concave section  24  from transition  27  and thus at about one-third the length of the central concave section  24  from transition  29 . The thinnest point  28  is between about 40% and 80% (and preferably about 50%) as thick as the inside section  22  in the area at or immediately adjacent to inner edge  16 . 
         [0024]    The outside section  26  extends between about 10% and 12% of the overall radial length of the flighting  14 . While not as thick as the inside section  22 , the outside section  26  is about 130% thicker than the thinnest point  28  of the central concave section  24 . The transition  29  between the central concave section  24  and outside section is smooth rather than abrupt because the thickness of the material increases gradually from the thickness at the thinnest point  28  to the thickness of the outside section  26 . The smooth nature of transitions  27  and  29  between adjacent sections results in a carrying surface  18  which is free of abrupt changes which can cause increased friction and wear. 
         [0025]    In summary, the radial length of the inside section  22  is between about 25% and 30% of the overall radial length of the flighting  14 . The radial length of the central concave section  24  is between about 55% and 60% of the overall radial length of the flighting  14 . The outside section  26  is thus between 10% and 15% of the overall radial length of the flighting  14  and preferably between 10% and 12% of the overall radial length of flighting  14 . In terms of thickness, the thickness at transition  27  is between about 85% and 92% of the thickness at the inner edge  16 . The outside section  26  is between about 65% and 70% as thick as the thickness at the inner edge  16 . The thinnest point  28  of the central concave section  24  is about 50% and 55% of the thickness at the inner edge  16 . These dimensions and percentages relate to the flighting  14  as formed and do not take into account any changes in thickness occurring at or near the inner edge  16  resulting from attaching the flighting  14  to the shaft  12 . This arrangement, particularly because of the smooth transitions  27  and  29 , results in substantially improved wear characteristics. 
         [0026]    Continuous flighting of the type described above and illustrated in  FIGS. 1 ,  3  and  4  may be produced on a conventional continuous flight rolling machine provided one of the pair of rollers typically used is replaced with a roller designed to produce the flighting profile shown in  FIGS. 3 and 4 . Other improvements may be made to the continuous flight rolling machine and these are illustrated in  FIGS. 5 and 6 . Traditional flight rolling machines include a pair of roller housings in which conical flight-forming rollers are mounted for rotation about transversely offset axes and at a mutual inclination such that the conical rolling surfaces contact one another along respective radial lines. Such a flighting machine is shown in U.S. Pat. No. 5,678,440 to Hamilton granted on Oct. 21, 1997, the disclosure of which is incorporated herein by reference. A threaded connection is usually provided to join each roller to a drive shaft. The arrangement shown in  FIGS. 5 and 6  represents an improvement in terms of strength and in terms of maintenance because the rollers  46  and  48  have their flight-forming portions ( 51  and  53 , respectively) integrally formed with their drive shafts ( 52  and  54 , respectively). 
         [0027]    Also, and as shown in U.S. Pat. No. 5,678,440, prior art flight-rolling machines typically incorporated separate speed reduction gear boxes, couplings, speed change selector boxes, and timing belt transmissions. The two belts were coupled to a clutch driven by an electric motor. As shown in  FIGS. 5 and 6 , the present invention simplifies the construction of the flight forming machine  30  by providing a power plant  32  incorporating a pump  36  driven by an electric motor  34 , a reservoir (not shown) and a control valve assembly  38 . 
         [0028]    Six hoses are connected to the power plant  32 . These include a pressure hose  80 , a return hose  82  and a case drain hose  84  used to couple the power plant  32  to a first hydraulic drive assembly  40  comprising a hydraulic motor and reducer. The six hoses also include a pressure hose  86 , a return hose  88  and a case drain hose  90  used to couple the power plant  32  to a second hydraulic drive assembly  42  comprising a hydraulic motor and reducer. Those skilled in the art will understand that the essential component of each hydraulic drive assembly is its hydraulic motor. Some hydraulic motors have built-in reducers. In other cases, the control valve assembly  38  can provide sufficient control such that the reducer can be eliminated. Thus, the use of the term “hydraulic drive assembly” is intended to be read broadly enough to cover a hydraulic drive incorporating a hydraulic motor whether or not a separate reducer is also present. 
         [0029]    The first hydraulic drive assembly  40  is coupled to the drive shaft  52  of roller  46 . The second hydraulic drive assembly  42  is coupled to the drive shaft  54  of roller  48 . The control valve assembly  38  controls the flow of hydraulic fluid to the hydraulic motors of the hydraulic drive assemblies  40  and  42  and, thus, the speed at which the rollers  46  and  48  turn. This arrangement offers various advantages over prior art arrangements, not the least of which are the ability to provide a soft start-up, the ability to gradually impart torque and speed to the flight-forming rollers  46  and  48 , and a substantial reduction in noise associated with operation of the equipment when forming the flighting. 
         [0030]    In addition to the improvements to the drive mechanism of the flight-forming machine  30  described above, changes have also been made to the flight-forming roller  48  which are critical to provide the flighting shape described above and shown in  FIGS. 3 and 4 . 
         [0031]    As noted above, the principal advantages of the present invention are achieved by replacing the rollers shown in U.S. Pat. No. 5,678,440 with rollers designed to form the flighting material  50  into the shape of flighting  14 .  FIGS. 5 and 6  show how, when the rollers  46  and  48  spin on their respective axes, flighting material  50  is passed between the rollers  46  and  48  to create the flighting  14  of the desired shape. To achieve the desired shape, the flight forming portions  51  and  53  of the rollers are provided with different profiles. The flight forming portion  51  of roller  46  has a cylindrical section and a conic section as best shown in  FIG. 6 . Roller  46  produces the shape of the rear surface  20  of the flighting  14 . Roller  48  produces the shape of the carrying surface  18  of the flighting and has a more complex shape as illustrated in  FIG. 7 . 
         [0032]      FIG. 7  specifically shows roller  48  has a flight-forming portion  53  and an integrally formed drive shaft  54 . The flight-forming portion  53  includes a circular cylindrical section  60  joined to the drive shaft  54 . Extending upward from the cylindrical section  60  is a first frusto-conical section  64 . The frusto-conical section has a base  62 , a top surface  66  extending along a plane parallel to the base  62  and an outer wall extending between the base  62  and top surface  66 . Extending upwardly from the top surface  66  is a second frusto-conical section  68 . The base of the second frusto-conical section  68  has a smaller diameter than the top surface  66  of the first frusto-conical section  64 . Also, the top of second frusto-conical section  68  has a smaller diameter than the base  70  of the tip section  72  of the flight-forming portion  53 . It is also important to note the tip section  72  is not actually conical. Instead, the outer surface  74  of the tip section  72  is bulged outwardly between the base  70  of the tip section  72  and the termination point  76  at the top of the tip section  72 . Given this configuration, the material  50  of the flighting  14  will be formed into the desired shape of the flighting shown in  FIGS. 1 ,  3  and  4  as it is passed between the rollers  46  and  48  as shown in  FIGS. 5 and 6 . 
         [0033]    Those skilled in the art will recognize various changes in the shape of the flighting can be achieved by modifying the profile of rollers  46  and  48 . By increasing the amount of bulge in the tip section  72 , the changes in diameter between the sections  64 ,  68  and  72  of the roller or the height of the three sections  64 ,  68  and  72 , the shape of the flighting  14  can be altered as desired. Thus, the shapes shown are not intended to be limiting except as set forth in the claims. 
         [0034]    By using a roller such as  48  to form the flight  14 , the durability of the radially outward portions of the flighting  14 , and particularly the outside peripheral edge  17  and outside section  26 , is improved. Also, the shape of the carrying surface  18  of the flighting distributes wear over a larger portion of the surface. This improved wear distribution is achieved by providing a central concave section  24  and the thicker outside section  26 . The central concave section  24  tends to move some of the material being carried by the conveyor  10  away from the outside peripheral edge  17  thereby distributing the load and wear over a larger portion of the carrying surface  18  and significantly increasing the useful life of conveyor  10 . The other changes to traditional flighting machines described above reduce manufacturing costs and also the time and expense required to maintain flighting equipment. More specifically, the improvements described above result in reduced roller failure and bearing failure because the improved equipment permits a soft start-up and the ability to gradually impart torque and speed to the flight-forming rollers  46  and  48 .