Abstract:
An improved roller pump having a rotor formed of a plastic material that provides improved performance and longevity as compared to roller pumps having metal rotors.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    I. Field of the Invention  
           [0002]    This invention relates to an improved pump design. More specifically, the present invention relates to a roller pump wherein the rotor and rollers of the pump have improved wear characteristics and a longer life.  
           [0003]    II. Related Art  
           [0004]    A variety of pump types have been used in the past for pumping liquids. These include piston pumps, centrifugal pumps, gear pumps, progressive cavity pumps, diaphragm pumps, peristaltic pumps and open-bladed impeller pumps. One type of pump that has become very popular for agricultural and a variety of other tasks is the roller pump. Roller pumps are used for spraying and transferring a variety of liquids including insecticides, herbicides, fungicides, emulsives, aromatic solvents, liquid fertilizers and many other non-abrasive liquids.  
           [0005]    Roller pumps include a housing, a rotor and a plurality of rollers. The rotor and rollers revolve inside the pump housing to force the liquid to be sprayed through an outlet. The housing and rotors are typically made of cast iron or a corrosive resistant alloy. Rollers have been made of metal, nylon, polypropylene or other plastic materials.  
           [0006]    Roller pumps run efficiently at speeds of 540 to 1000 revolutions per minute. Typical operating pressures range from 100 pounds per square inch to 300 pounds per square inch. Flow rates of anywhere from 2 to 100 gallons per minute can be generated using roller pumps.  
           [0007]    Substantial improvements have been made in roller pump technology. However, problems continue to exist related to the wear and life expectancy of the rollers. Over time as the rollers wear, the performance of the pump can deteriorate. Other problems with roller pumps relate to the sound levels generated by such pumps.  
         SUMMARY OF THE INVENTION  
         [0008]    The primary object of the present invention is to improve the life expectancy of the rollers of a roller pump.  
           [0009]    A related object of the present invention is to provide such a pump with longer sustained performance.  
           [0010]    Still another object of the invention is to provide a roller pump which operates in such a way that the rollers do not become scuffed, flattened or otherwise worn during their normal expected life.  
           [0011]    A further object of the invention is to provide a roller pump that is easily repaired when the rollers do become worn.  
           [0012]    Still a further object of the invention is to provide a roller pump that operates at lower sound levels than currently available roller pumps.  
           [0013]    These and other objects are achieved by providing a roller pump having a body, a cover, appropriate seals and bearings and a drive shaft. The drive shaft is preferably made out of stainless steel and is keyed to a rotor. The rotor has a keyed insert also made out of stainless steel. Surround the stainless steel insert is a rotor body made of a phenolic material, such as Plenco 06401 made by Plastics Engineering Company of Sheboygan, Wis. The rotor body has a plurality of recesses, each of which engage a separate roller. The rollers are preferably made of nylon. In operation, a motor turns the drive shaft causing the rotor and rollers to revolve inside the pump housing. Liquid is drawn into the pump through an inlet in the housing and then forced out the outlet by the action of the rotor and rollers in the housing.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in several views refer to corresponding parts.  
         [0015]    [0015]FIG. 1 is an exploded perspective view of a roller pump constructed in accordance with the present invention.  
         [0016]    [0016]FIG. 2 is a perspective view of the rotor of the pump shown in FIG. 1.  
         [0017]    [0017]FIG. 3 is a front view of the rotor shown in FIGS. 1 and 2.  
         [0018]    [0018]FIG. 4 is a cross-sectional view of the rotor through line  4 - 4  of FIG. 2.  
         [0019]    [0019]FIG. 5 is a cross-sectional view of the rotor through line  5 - 5  in FIG. 4.  
         [0020]    [0020]FIG. 6 is a front view of the rotor insert of the roller pump constructed in accordance with FIG. 1.  
         [0021]    [0021]FIG. 7 is a cross-sectional view of the rotor insert through line  7 - 7  in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    [0022]FIG. 1 shows a roller pump made in accordance with the present invention. The roller pump includes a housing including a body  1  and a cover  2 . A set of hex head cap screws  11  are used to fix the cover  2  to the body  1 .  
         [0023]    Associated with the body  1  and the cover  2  are a pair of lip seals  3 . The lip seals are preferably made of an elastomeric polymer, having excellent resistance to heat, oils and chemicals. Acceptable polymers are sold by DuPont Dow of Wilmington, Del. under the Viton trademark.  
         [0024]    A pair of bearings  4  are also associated with the body  1  and cover  2 . The bearing associated with the body  1  has an end cap  9 . The bearing associated with the cover has an end cap  8 .  
         [0025]    The bearings  4  assist in maintaining proper alignment of permitting free rotation of a stainless steel drive shaft  6 . The end of the shaft can be coupled to a motor or power takeoff in a conventional manner. Neither a motor nor power takeoff are shown.  
         [0026]    The drive shaft  6  is used to impart rotational motion to a rotor  5 . The rotor is comprised of two pieces, a rotor insert  20  and a rotor body  22 . The rotor insert  20  is preferably made of stainless steel and is keyed as is the drive shaft  6  so that a stainless steel key  7  can be used to couple the rotor  5  to the drive shaft  6  after the rotor  5  has been placed on the drive shaft. The outside of the rotor insert  20  and the inside of the rotor body  22  are shaped such that rotational motion imparted to the rotor insert  20  by the drive shaft  6  is conveyed to the rotor body without any appreciable slippage. In fact, the rotor body  22  can be molded around the rotor insert  20 .  
         [0027]    The rotor body  22  includes a front wall  24 , a back wall  26  and a side wall  28 . The side wall includes a plurality of roller engaging recesses  30 . Each recess  30  has a generally U-shape and is rib free. Each recess  30  is sized to receive a roller  10 . As shown in the drawings, there are eight rollers  10 , one for each of the eight recesses  30  in the rotor body  22 .  
         [0028]    The rotor body  22  is preferably molded of a suitable plastic material. This offers several advantages. First, the use of a plastic rotor body  22  prolongs the life of the rollers  10 . The rollers  10  do not degrade and therefore the pump performs acceptably over a longer span of use. Second, while use of a metal rotor in combination with a metal body can cause galling of the rotor, this does not occur when a rotor body  22  made of plastic is used. Third, use of a plastic rotor body  22  prevents the pump from seizing. When a pump having a metal body and a metal rotor is stored, oxidation between the body of the housing and the rotor body  22  can occur, seizing the rotor in place and destroying the pump. The use of a plastic rotor body  22  eliminates this problem.  
         [0029]    Rotor body  22  is preferably made of a glass fiber filled phenolic molding compound. One such compound is sold under the designation Plenco 06401 by Plastics Engineering Company of Sheboygan, Wis. Thermoset, glass and mineral filled phenolic compounds are particularly advantageous. A rotor body  22  molded of this material is capable of maintaining its structural integrity under the mechanical load and operating temperatures encountered by the pump. The resistance of this material to heat and creep and its dimensional stability all offer important advantage. Also, this material has excellent lubricity and abrasion resistance which is important given the repeated mechanical cycling of the rotor body  22  and its part-to-part contact with the rollers  10  and other parts of the pump. Surface smoothness is also maintained by this material.  
         [0030]    The preferred phenolic material from which the rotor body  22  is molded has a density of about 0.0513 pounds per square inch. Thus, a rotor body  22  made to have a surface area of 53.85 square inches and a volume of 8.48 cubic inches only has a mass of 0.4350 pounds. The nature of this material and the way the rotor  5  interacts with the nylon rollers  10  helps reduce wear of the rollers yielding longer sustained performance.  
         [0031]    Tests comparing the performance of a traditional metal rotor with the rotor  5  of the present invention have shown surprising results. Two pumps, one with a standard metal rotor and another with the rotor of the present invention, were run for 800 hours at 1000 revolutions per minute and at a pressure of 100 pounds per square inch. The pump of the present invention had an initial flow rate of 20 gallons per minute. Even after 300 hours, the flow rate was still over 19 gallons per minute. At 800 hours, the flow rate was still more than 17 gallons per minute. The control pump (i.e., the same pump, but with the metal rotor) had an initial flow rate of about 19 gallons per minute. The flow rate dropped to less than 17 gallons per minute after only about 75 hours of use. After 800 hours, the flow rate was well under 15 gallons per minute. This testing clearly demonstrates that the present invention yields higher pump performance sustained for a substantially longer period of time. This improvement is directly attributable to the increased roller life obtained from the use of the rotor body  22  made of the phenolic material. Other suitable materials for the rotor body  22  include thermoset polyester compounds. These materials can be used to integrally mold a roller body  22  which is sufficiently durable and is also rib free in the contact areas between the roller-engaging recesses  30  and the rollers  10 .  
         [0032]    Other advantages are also derived from the present invention. The pump of the present invention operates at lower sound levels than a pump with a metal rotor. Also, replacement of rollers is an easy task when they do become worn giving the manner in which the pump is assembled.