Abstract:
An apparatus and method for forming and applying seamless wear bands to a cylinder, such as a solenoid plunger. The apparatus consists principally of an expanding diameter pushing tool and mating conical mandrel. The pushing tool contacts and moves a flat washer type disc along the sides of the mandrel. As the disc travels along the mandrel it is transformed into a band configuration and snapped into a pre-formed undercut groove on the cylinder.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to solenoid plunger wear bands and, in particular, a method of forming and applying seamless wear bands to a solenoid plunger.  
           [0002]    In the past, methods of forming long cycle life bearing surfaces have been costly. Some past practices have included the use of press fit bushings, plunger coatings, and ground and polished surfaces. Bands made from wear resistant products such as virgin TEFLON or etched RULON sheets have also been used.  
           [0003]    Presently, strip-type bands have been know to encounter problems in installation. The strips are typically formed by hand from sheet stock material and are assembled into the plunger tube while simultaneously being located in machined grooves in the plunger. Assembly of strip-type wear bands is time consuming due to the difficulty of holding a close overall length dimension of the strip. This is because the roll of sheet stock does not lie flat while going through the die. Consequently, a secondary, labor intensive trimming operation must be added. Additionally, the seam created at the point where the strip ends meet is susceptible to ripping if one end comes out of the groove.  
           [0004]    Alternatively wear bands can be molded with a gap to allow stretching over a plunger, these require costly tooling and once tooled, are rather inflexible. The present invention and method provides a seamless wear band that requires less material and is more labor efficient than the above-noted bands and methods. For example, hand forming of the bands during assembly is no longer required. Further, the plunger assembly can be removed from the plunger tube, and reassembled with minimal possibility of losing the band, as was common in earlier methods. The seamless nature of bands formed and installed according to this disclosure alleviates these problems.  
           [0005]    Further, the present invention provides the efficiency and economy necessary to work with standard sized solenoid components such as tubes and plungers.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a novel method for forming and installing seamless wear bands for use on cylindrical objects in need of this type of protection. It is intended primarily for use on solenoid plungers, although it is to be understood that any cylindrical object requiring wear resistant bands may utilize the method disclosed herein.  
           [0007]    The invention includes a flat washer or apertured disc made of bearing material, such as Garlock Multi-fil 426. The apertured disc may be stamped from a sheet of material, or pre-formed in any of a variety of methods, including molding. This washer or disc is ultimately formed into a band and installed on a cylindrical object, such as a solenoid plunger. The use of a washer configuration eliminates the troublesome seam that is a feature of prior art wear bands. The change in shape, from a flat washer to a seamless band, is possible due to the cold flow and stretching properties of the material used and the assembly process that permanently snaps the seamless band onto the cylinder.  
           [0008]    The process whereby the washer is transformed to a band and snapped onto a cylinder includes mating an end of a forming mandrel to one end of the cylinder to receive the resultant band. The mating end of the mandrel is of a diameter equal to the cylinder end, while the diameter of the opposite end of the mandrel is equal to the inner diameter of the washer to be formed. The washer is placed on the opposite end of the mandrel and an expanding diameter tool comes down on the washer, sliding the washer down the mandrel. A lubricant, such as WD-40 may be used to facilitate the downward movement. When the now transforming washer is at the transition between the mandrel and the cylinder end, it is assuming a band shape. As the downward movement continues, the band snaps into a pre-formed groove in the cylinder. Accordingly, since the tube and cylinder to be banded are of pre-determined diameters, the size of the groove to receive the band can be readily determined. The process is completed after the cylinder is pressed through a sizing mandrel in the opposite direction to the band just assembled. The present design lends itself well due to the equivalence in volumes of the pre-formed apertured disc and that of the resultant wear band. It should be apparent that the volume of the disc to be formed remains constant throughout its transformation. If additional bands are needed on the cylinder, the process in completed for each required band.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a partially exploded view of a solenoid plunger in mating relationship with a truncated, conical mandrel and a washer to be formed into a seamless wear band, and their relationship to the expanding diameter pushing tool.  
         [0010]    [0010]FIG. 2 is a longitudinal cross sectional view of the expanding diameter pushing tool and taken along lines  2 - 2  of FIG. 1.  
         [0011]    [0011]FIG. 3 is an exploded view of the expanding diameter pushing tool, used in the assembly of a seamless wear band in a pre-formed solenoid plunger having a pre-formed undercut groove for receiving a wear band.  
         [0012]    [0012]FIG. 4 is a side plan view of a truncated, conical mandrel used in locating the wear band within the undercut groove in the solenoid plunger of FIG. 1.  
         [0013]    [0013]FIG. 4 a  is a top plan view of the mandrel illustrated in FIG. 4.  
         [0014]    [0014]FIG. 4 b  is a longitudinal section view of the mandrel illustrated in FIG. 4, and taken along lines  4   b - 4   b  of FIG. 4 a.    
         [0015]    [0015]FIG. 5 is an alternate embodiment of the mandrel similar to the mandrel shown in FIG. 4.  
         [0016]    [0016]FIG. 5 a  is an alternate embodiment expanding diameter pushing tool for use in manual formation and installation of a seamless wear band to cylinder.  
         [0017]    [0017]FIG. 6 is a perspective view of a pre-formed washer-like disc to be formed into a seamless wear band and for depositing in the aforementioned groove in the solenoid plunger.  
         [0018]    [0018]FIG. 6 a  is a top plan view of the disc shown in FIG. 6.  
         [0019]    [0019]FIG. 6 b  is a diametrical cross section view of the disc shown in FIG. 6.  
         [0020]    [0020]FIG. 7 is a top plan view of a seamless wear band as formed on a solenoid plunger.  
         [0021]    [0021]FIG. 7 a  is a diametrical cross section view of the band shown in FIG. 7 
         [0022]    [0022]FIG. 8 is a side elevational view, partly in cross section, of the expanding diameter pushing tool in the at rest position, and a solenoid plunger arranged to receive its encircling wear band.  
         [0023]    [0023]FIG. 9 is a side elevational view, partly in cross section of the tool shown in FIG. 8 but in with the disc being partially deformed in readiness for its axial movement towards its receiving groove, and in initial contact with a plurality of radially disposed pushing elements.  
         [0024]    [0024]FIG. 10 is a side elevational view, partly in cross section of the tool shown in FIG. 8 but in an intermediate step wherein the pushing elements continue in their movement to stretch and form the wear band as it travels towards its final position.  
         [0025]    [0025]FIG. 11 is a side elevational view, partly in cross section, of the tool shown in FIG. 8, but with the wear band snapped into final position in the groove on the solenoid plunger.  
         [0026]    [0026]FIG. 12 is a side elevational view, partly in cross section, of the hollow sizing sleeve having a portion of its length ground to a relatively polished surface, and in readiness to receive a solenoid plunger having a wear band installed in its groove.  
         [0027]    [0027]FIG. 12 a  is a cross sectional view, partly in cross section, of the sizing sleeve shown in FIG. 12 but showing the plunger and its band being pressed through the precision sizing area.  
         [0028]    [0028]FIG. 13 is a side elevational view, partly in cross section of the sleeve shown in FIG. 12 and showing the solenoid plunger in its final position relative to the sizing sleeve.  
         [0029]    [0029]FIG. 14 is side elevational view of a finished solenoid plunger including a pair of seamless wear bands after installation and sizing.  
     
    
     DETAILED DESCRIPTION  
       [0030]    Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.  
         [0031]    With reference to the drawings, and in particular to the views of FIGS.  1 - 3 , the novel apparatus in the form of an expanding diameter pushing tool  10  is shown. The expanding diameter pushing tool, or apparatus,  10  is used to form and install seamless wear bands  12  onto a pre-formed, undercut, groove  14  on a cylinder, such as a conventional cylindrical solenoid plunger  16 . The expanding diameter pushing tool  10  comprises, in general, a housing  18 , a washer  20 , a plurality of finger pushers  22  that are radially biased for longitudinal movement by coil springs  24  seated within the bore  26  of a respective pusher  22 . A spring capturing ring  28  includes an inner surface  30  abutting against the opposite end of a respective spring  24 . An end piece  32  includes dividers  34  for circumferentially spacing and receiving the finger pushers  22 . The expanding diameter pushing tool  10  is further provided with means for manual longitudinal movement thereof. As seen in FIG. 2, a longitudinally extending spring  36  is mounted on a return core  38 . One end  37   a  of the longitudinally extending spring  36  abuts a radially extending flange portion  40  of the return core  38 , while the opposite end  37   b  of the spring  36  rests on a raised stationary spring retainer portion  42  of the base member  44 . The end piece  32  and base member  44  are each attached to opposite ends of the housing  18  by means of mounting screws  47  and  49 , respectively. The threaded screws  47  and  49  are respectively received by the apertures  47   a  and  49   a  of the housing  18 , and are seated in threaded bores  47   b  and  49   b  of the end piece  32  and the base member  44 . The spring  36  provides upward bias of the return core  38 , as shown in the view of FIG. 2. A stabilizing rod  46  runs through the center of the spring  36  and provides axial stability for the spring  36 . The expanding diameter pushing tool  10  receives a truncated conical mandrel  48  as seen with respect to FIGS. 4, 4 a , and  4   b . The mandrel  48  includes a bore  50  for receiving an upstanding pin  39  of the return core  38  (See FIGS. 1 and 2), and further includes a distended end portion  52  having an undercut chamfered radial area  54 , and a constricted end  56 . The undercut area  54  is dimensioned to seat the mandrel  48  on an end of the solenoid plunger  16  to be fitted with the wear band  12 , to be later described.  
         [0032]    An alternate embodiment mandrel  48   a  is seen in FIG. 5. The alternate mandrel  48   a  is somewhat more elongated than the preferred truncated mandrel  48  shown in FIG. 4, but may be used to manually install seamless wear bands  12  on a cylindrical object such as a solenoid plunger  16 . The alternate mandrel  48   a  is to be used with an alternate embodiment pusher tool  10   a  (seen in FIG. 5 a ). Both mandrels  48 ,  48   a  serve similar purposes.  
         [0033]    Referring now to FIGS.  6 - 7   a , a pre-formed, apertured disc  11  and resultant wear band  12  are shown. The apertured discs  11  are pre-formed from a material such as Garlock Muli-fil 426. The apertured discs  11  may be manufactured in a variety of manners including, stamping, molding, or cutting into the desired configuration. Although other material may be used, only material having requisite properties will perform satisfactorily. For example, the material must stretch during assembly into the retaining groove  14  in the solenoid plunger  16  and then partially return to its original shape. Further, once the material is in the retaining groove  14  it must flow at room temperature as it is forced through the final sizing tool  60 . Once the band  12  has been sized, the material needs to remain dimensionally stable at the operating temperature of the cylinder on which it is installed and should not change dimensions while under normal loading over time or when exposed to chemical compounds typically found in the application environment.  
         [0034]    The various stages of accomplishing the procedure and operation of this invention are best described with reference to the views of FIGS.  8 - 14 , inclusive. In the present procedure, the apparatus and method are used to form and install a seamless wear band  12  on a pre-formed groove  14  in a solenoid plunger  16 . The preferred band is transformed from the aforementioned apertured disc-like configuration shown in FIGS. 6, 6 a , and  6   b  to the band-like configuration of FIGS. 7 and 7 a , and sized to a height approximately the longitudinal length of its groove  14  and a thickness slightly greater than the depth of groove  14 . The resultant band  12  will have an outer diameter slightly smaller than the inner diameter of the tube (not shown) in which the plunger  16  will slide.  
         [0035]    The view of FIG. 8 shows the expanding diameter pushing tool  10  in the at-rest position with the cylindrical object, such as a solenoid plunger  16  adapted to receive the wear band  12  (seen as an apertured disc  11  in this view) and resting on the truncated conical mandrel  48 . The mandrel  48  includes a constricted end portion  56  and a distended end portion  52 . The constricted end portion  56  is positioned to be in contact with the inner diameter of the apertured disc  11  to be formed, while the distended end portion  52  is mated with one end  17  of the solenoid plunger  16 . In this view, the apertured disc  11  is shown resting on the return core  38 . A downward force F is shown by means of an arrow, and is applied by means of any conventional type of press (not shown) common to manufacturing, such as an arbor press. The press (not shown) rests against the exposed end  17  of the solenoid plunger  16 . In an alternate embodiment, the downward force F may be supplied manually, in which case an alternate embodiment mandrel and pushing tool such as that previously shown and discussed with reference to FIGS. 5 and 5 a , may be used.  
         [0036]    Referring next to the view of FIG. 9, it will be noted that the spring  36  has begun compression. As the spring  36  compresses, the solenoid plunger  16  and its mated mandrel  48  move with the apertured disc  11  into the expanding diameter pushing tool cavity  58  (detailed in FIG. 2). This movement forces the inner diameter (seen as ID in FIG. 6 a ) of the apertured disc  11  to make initial contact with the finger pushers  22 . Continued downward movement of the solenoid plunger  16  further compresses the spring  36 , as seen in FIG. 10, such that the individually spring biased finger pushers  22  force the inner diameter ID of the now deforming apertured disc  11  over the conical surface of the mandrel  48  and along its sides. As this movement occurs, the apertured disc  11  begins to take a band form. The spring  36  allows compression to a maximum point that is equal to the distance the solenoid plunger  16  or other cylindrical object and mated mandrel  48  must travel to ensure proper band  12  seating within the pre-formed groove  14 .  
         [0037]    In the preferred embodiment, it is recommended that the banding procedure include a final sizing step, as illustrated in FIGS. 12 and 13. This step obviates the tolerance stack up that occurs during manufacturing of the apertured disc  11  and cylindrical object or solenoid plunger  16 . After the band  12  is snapped into place in the pre-formed groove  14  by the expanding diameter pushing tool  10 , as discussed above, the solenoid plunger  16  and its band  12  are pushed through a sizing tool  60  in a direction opposite the motion of the initial banding. The sizing tool  60  includes a large radiused lead-in precision sizing area  62  having a polished surface. A lubricant such as WD-40 may be used to facilitate the downward movement. As the solenoid plunger  16  is pushed through the initial lead-in area  62 , the installed band  12  is compressed to its final configuration. The solenoid plunger  16  is pushed longitudinally through the sizing tool  60  until the banded area passes the lead-in precision sizing area  62 . The remainder of the length of the sizing tool  60  has a diameter greater than that of the banded solenoid plunger  16 , thus allowing the finished solenoid plunger  16  to readily pass through without the application of further longitudinal force. If the solenoid plunger  16  or other cylindrical object requires more than one wear band  12 , the procedure described above is repeated.  
         [0038]    The alternate embodiment of the pushing tool  10   a  and mandrel  48   a  combination previously described with reference to FIGS. 5 and 5 a , is to be used manually and includes a multi-fingered pushing tool  10   a . This tool  10   a  comprises an integrally formed member defined by a series of circumferentially spaced fingers  8 . Each of the fingers  8  is arranged to be compressed inwardly against the bias of a garter or band  7 . The size of the band  7  is chosen to compress the distal end  8   a  of the fingers  8  to form and install the wear band  12  within an encircling pre-formed groove  14  of a cylindrical object, such as a solenoid plunger  16 , by means of manual force.  
         [0039]    The above-described embodiments of this invention are merely descriptive of its principles and are not to be limited. The scope of this invention instead shall be determined from the scope of the following claims, including their equivalents.