Abstract:
A rotary foam buffing pad is provided with a concave working face which allows the operator to provide true graduated surface contact in applying polish, buffing or glazing compounds, while containing the polishing compound against centrifugal force which would otherwise result in splattering of the compound. The manner in which the concave working face is formed and in which the edge face is formed and dressed results in dynamic balancing of the pad and reducing vibration and operator fatigue. The working surface forming and pad finishing operations further provide a velvetized texture to the pad working surfaces which further enhances the polishing or finishing process.

Description:
This application is a divisional of Ser. No. 08/858,749, filed May 19, 1997, now U.S. Pat. No. 6,044,512. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention pertains to foam pads for buffing and, more particularly, to rotary foam pads for buffing and polishing painted or similarly finished surfaces. 
     Foam buffing pads are now used in many buffing and polishing operations where synthetic or natural fiber pads, such as tufted wool pads, had previously been used. In particular, open cell polyurethane foam pads, with both reticulated and non-reticulated cell structures, have become particularly popular. However, despite the actual advantages of polymer foam pads over fibrous and tufted pads, there are still a number of inherent disadvantages attendant the use of foam pads. These disadvantages include “chatter” or jumping of the pad by excess frictional surface contact between flat working surface portions of the pad and the surface of the work being finished; splattering of the polish or other finishing compound as a result of the compound being thrown radially outwardly by centrifugal force; and, burning of the surface of the work being finished by the high speed outer edge portions of the rotary pad. 
     Attempts have been made to minimize or eliminate these problems by varying the type and density of foam used and by changing the working surface of the pads. Initially, foam pads were made of a generally cylindrical disc with a flat planar working face and, typically, with a radiused outer edge providing the transition between the working face and the outer cylindrical edge face. However, flat pads are particularly subject to chatter and provide little deterrent to the splatter of polish. Flat faced pads also give the operator little control over variations in the working surface actually in contact with the work surface being finished or polished. One attempt at solving the problems presented by flat foam buffing pads was the introduction of buffing pads having working surfaces with a convoluted or waffle shape. One such pad was previously made by Lake Country Manufacturing, Inc. Although this pad provided variable working surface contact by varying operator-applied pressure, surface contact was somewhat difficult to control and the pad did little to prevent splatter. A different approach to solving the prior art problems is shown in U.S. Pat. No. 5,527,215 where a cylindrical foam pad has a recessed center portion or portions within which the polishing compound may be trapped against radial splatter. This pad also provides the ability to alter the working surface contact by varying operator-applied pressure. However, neither of the foregoing pads adequately solves all of the prior art problems and, in addition, neither provides an operator with the ability to create true graduated surface contact which is uniform and predictable. Finally, rotary buffing pads are often inherently unbalanced because of the manner in which the pads are finished or mounted, resulting in undesirable vibrations, added chatter, and operator fatigue. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a rotary foam buffing pad and the manner in which it is manufactured provide a unique solution to all of the foregoing problems with prior art foam buffing pads. The result is a pad with superior performance in the elimination of chatter, prevention of polish splatter, and operator control of the working surface contact area. 
     In its preferred embodiment, the rotary compressible foam buffing pad of the present invention has a working face comprising a concave central contact surface and a peripheral outer contact surface. The outer contact surface provides an area of continuous working contact and encloses the central contact surface, precluding any substantial working contact by the central contact surface when the pad is generally uncompressed, but providing increased radial inward expansion of the area of working contact with increasing pad compression. The concave central contact surface extends radially inwardly from the outer contact surface to a central area of maximum concavity. The buffing pad includes a mounting face opposite the contact surface and an annular edge face which extends between and joins the mounting face and the outer contact surface. 
     The outer peripheral first contact surface preferably comprises a planar annular band. The inner concave contact surface may be conical or spherical. The pad may include a central opening which extends through the pad body on its rotational axis. Further, the annular edge face of the pad which joins the working face and the mounting face may be generally cylindrical or frustoconical and, in the latter case, having a maximum diameter where it joins the working face. The mounting face of the pad adapts the same for attachment to a backing plate, either with a permanent connection or with a demountable fastener, such as a hook and loop type fastening system. 
     In accordance with a preferred method for making a rotary foam buffing pad of the present invention, a generally cylindrical preform of foam material is utilized, which preform has generally flat parallel front and rear faces which are interconnected by a cylindrical edge face, the method comprising the steps of: rotating the preform on its axis, and dynamically forming a concave working face on the front face during rotation. The method may also include the step of dynamically forming a conical surface on the edge face during rotation. The preform is preferably rotted by supporting the same by its rear face on the backing plate, and grinding the front face of the pad while it is being rotated to move material from the face to provide the concave working face. The grinding step preferably includes texturizing the working face to enhance buffing performance. The edge face may also be ground and texturized in a similar manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of a foam buffing pad of the present invention. 
     FIG. 2 is a vertical section through the pad taken on line  2 — 2  of FIG.  1 . 
     FIG. 3 is a vertical section similar to FIG. 2 showing an alternate embodiment of the concave working surface. 
     FIG. 4 is a vertical section similar to FIG. 2 showing another embodiment of the invention. 
     FIGS. 5,  5 A and  5 B are vertical sections, similar to FIGS. 2-4, showing another embodiment of the invention in various stages of graduated surface contact. 
     FIG. 6 is a front elevation of a schematic depiction of an apparatus for forming the working surface of pads of the present invention. 
     FIG. 7 is a schematic top plan view of the apparatus shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, a rotary foam buffing pad  10  of one embodiment includes a generally cylindrical body  11  having a flat planar mounting face  12  by which it is attached to a backing plate  13 . The backing plate  13  includes a central hub  14  having a tapped bore or other means for mounting the pad on the driven shaft  15  of a powered rotary buffing machine, all in a manner well known in the art. 
     The cylindrical buffing pad body  11  is, also in a manner well known in the art, cut from a sheet of foam material using a knife or hot wire apparatus to form the conventional cylindrical shape. The working face of such prior art pads, on the side of the body opposite the mounting face  12  and not shown in FIG. 1 is also flat. Buffing pads of this type have been widely used, but are subject to the inherent problems of splattering and pad chatter described above. 
     Pads made of open pore polyurethane foam, with either reticulated or non-reticulated structure, have found particular favor in the prior art. The surfaces of such pads, including both the rear mounting face and front working face, as well as the knife or hot wire cut side face  16 , all initially exhibit a smooth texture. Such a smooth texture, particularly on the flat working face of prior art pads, contributes to initial pad chatter and jumping because of enhanced friction between the smooth textured pad surface and the surface being buffed or polished. 
     Referring also to FIGS. 2-4, there are shown vertical sectional views of three embodiments of a rotary foam buffing pad in which the working face  17  is finished in accordance with the present invention. In all three embodiments, the working face  17  includes a concave central portion which provides improved performance both in the reduction of chatter and in preventing the splattering of polish, glazes and other finishing pounds applied by the buffing pad. In addition, the manner in which the concave working face  17  is formed provides a texturized surface which also helps to reduce initial pad chatter. Further, the method of forming the concave working face provides a dynamic balance to the pad previously unattainable in prior art foam buffing pads. In the FIG. 2 embodiment, the working face  17  of the pad  19  is provided with a spherical concave recess  18  having a maximum depth or maximum concavity in the center on the axis of pad rotation. It is believed that the concave recess  18  should have a maximum depth of at least ¼″ (about 6 mm) and should not exceed about ¾″ (about 19 mm). Ideally, the recess should be about ½″ (about 13 mm) deep. The concave recess  18  tapers radially outwardly to an outer peripheral contact surface  20  which, in this embodiment, comprises a very narrow planar annular band  21 . 
     In FIG. 3, the working face  17  of the pad  23  is provided with a conical concave recess  22 . The pad  23  is otherwise identical to the pad  19  of the FIG. 2 embodiment. Thus, both pads  19  and  23  are of generally cylindrical shape and include a cylindrical edge face  24  and a radiused transition  25  between the edge face  24  and the respective planar annular bands  21  and  26  of the two pad embodiments. 
     In the FIG. 4 embodiment, the foam buffing pad  27  includes a spherical concave recess  28  in the working face  17  which is similar to the concave recess  18  of the FIG. 2 embodiment. In the FIG. 4 pad  27 , however, the outer peripheral contact surface  30  comprises a planar annular band  31  which is somewhat wider than the band  21  of the FIG. 2 embodiment. The pad  27  also includes a tapered edge face  32  resulting in a somewhat sharper radiused transition  33  between the edge face  32  and the contact surface  30  of the working face. 
     By a selective application of varying amounts of pressure by the operator in use, each of the pads  19 ,  23  and  27  of the embodiments of FIGS. 2-4 can provide controlled graduated working contact surface in a manner which will be described in detail with respect to the pad in FIGS. 5,  5 A and  5 B. The buffing pad  34  in FIG. 5 includes a backing plate and mounting system which is different from the embodiments of FIGS. 2-4. The pad  34  is demountably attached to a cushioned backing plate  35  with a hook and loop fastener  36  of a type well known in the industry. The cushioned backing plate includes a rigid backing plate  37  (similar to the backing plate  13  previously described) to which an intermediate cushion pad  38  is attached, the opposite face of which includes half of the hook and loop fastener  36  to which the pad  34  is attached by its mounting face  40 . The pad  34  and the cushion pad  38  are provided with through bores  41  to receive a nut (not shown) for attachment to a threaded driven shaft  42  of a buffing machine. The through bores  41  may also be utilized to align the pad with the cushioned backing plate  35  for pad attachment or reattachment. 
     The pad  34  of the FIG. 5 embodiment includes a tapered edge face  43  and a radiused peripheral edge  44  which provides the transition to a peripheral contact surface  45  on the working face  46  of the pad. The peripheral contact surface  45  comprises a planar annular band  47 , similar to the previously described embodiments, but somewhat larger in radial width. The radial inner edge of the planar annular band  47  joins the outer edge of a spherical concave recess  48  generally similar to the recesses  18  and  28  of the FIG.  2  and FIG. 4 embodiments, respectively. The spherical concave recess  48  is, of course, interrupted centrally by the through bore  41 . 
     The FIG. 5 pad  34  provides the same improvements over prior art pads as do the pads shown in FIGS. 2-4 and previously described. The concave recess  48 , when the pad is in the substantially uncompressed state shown in FIG. 5, may contain the polish, buffing or glazing compound being used to finish a surface. The concave recess is completely enclosed by the planar annular band  47  which provides full contact with the surface being finished. This enclosure of the polish or finishing compound prevents splattering when the pad is rotated and centrifugal force throws the paste material radially outwardly. In addition, initial startup of the pad in the FIG. 5 position minimizes pad chatter because of the minimal contact by the working face  46 , namely, only the planar annular band  47 . However, as the operator provides added pressure to the pad  34 , by forcing the shaft mounted backing plate  37  downwardly, the spherical concave recess  48  begins to flatten and the working face  46  expands in a radially inward direction, as shown in FIG.  5 A. As operator pressure is increased and the pad compresses further, the entire concave recess  48  will eventually be flattened and there will result full working face contact with the workpiece being finished, as shown in FIG. SE. This graduated working face contact provides the operator with far greater control over the active working surface than do pads of the prior art including flat-faced pads, waffle-faced pads, or stepped or slotted recess pads. 
     The particular embodiment of the FIG. 5 pad, and to a lesser extent the pad  27  of FIG. 4, provide additional benefits in terms of working face control and enhanced utility to the operator because of the tapered frustoconical edge faces. The tapered edge face  43  in the FIG. 5 embodiment permits the working face to flatten more readily under increasing operator pressure than does the tapered edge face  32  of FIG. 4, and even more so with respect to the cylindrical edge faces  24  of the embodiments of FIGS. 2 and 3. This increased flexibility is also important in helping to prevent burning of the workpiece surface being finished, particularly since the outer peripheral contact surface portion  45  of the pad is moving at the greatest actual velocity. The cushion pad  38  forming a part of the backing plate  35  is also typically made of a foam material, but a material which is substantially more dense than the foam used in the pad  34 . Typically, the cushion pad  38  will not undergo significant compression until the foam buffing pad  34  has been virtually fully compressed to the condition shown in FIG.  5 B. 
     Referring now to FIGS. 6 and 7, the presently preferred apparatus and method for making foam buffing pads of the present invention will now be described. It should be understood, however, that buffing pads with concave recessed working faces of the type described in the various preceding embodiments may be formed by other methods and using other apparatus. As will be described, the present method and apparatus, in addition to providing inherent efficiencies in the manufacture, also results in certain improved pad features. 
     A cylindrical flat-faced pad body  50  (which may be identical to the pad body  11  shown in FIG. 1) is attached to a backing plate (either of the permanent type backing plate  13  or the demountable type backing plate  35 ). The pad body  50  and backing plate are attached to a driven rotary spindle  51  which is mounted on a horizontally reciprocable slide carriage  52 . The slide carriage  52  operates generally beneath a vertically reciprocable first tool slide  53  which carries a driven first grinding wheel  54 . The upper portion of the slide carriage  52  includes a cam surface  55  which cooperates with a cam follower  56  carried on the first tool slide  53 . A second tool slide  57  is mounted for horizontal reciprocating movement toward and away from the slide carriage  52 . The second tool slide carries a second grinding wheel  58  which is also rotatably driven, preferably in the same direction as the rotary spindle  51  on which the pad body  50  is mounted. 
     Although the sequence of operation may be reversed, the first tool slide  53  is moved vertically upwardly away from the slide carriage  52  to an inoperative upper position, as with an air cylinder actuator (not shown) or similar positioning device. With the pad body  50  rotating on the driven spindle  51 , the second tool slide  57  is moved horizontally toward the slide carriage  52 . The second grinding wheel  58  includes a profiled peripheral face  60 . Using the buffing pad  27  of the FIG. 4 embodiment as an example, the profile of the second grinding wheel  58  is shaped to form the tapered edge face  32  and radiused transition  33  simultaneously as the rotating grinding wheel  58  is brought into contact with the rotating pad body  50 . The second tool slide  57  is then withdrawn horizontally and the first tool slide  53  is moved vertically downward from its inoperative upper position to bring the first grinding wheel  54  into contact with the unfinished flat working face  61  of the pad body  50 . The first grinding wheel  54  is moved against the flat working face  61  of the rotating pad body  50  and moved further downwardly to the desired depth of the spherical concave recess  28  at which time the slide carriage  52  is moved horizontally (to the left as viewed in FIGS. 6 and 7) with engagement of the cam surface  55  with the cam follower  56  causing the first tool slide  53  to move vertically upwardly, overcoming the bias of the air cylinder or other slide positioning device, causing the peripheral surface of the first grinding wheel  54  to move in a shallow circular arc relative to the pad body and to form the spherical concave recess  28 . 
     The result of the dynamic pad side edge and working face formation described above is a perfectly rotationally balanced buffing pad not previously attained in the prior art. Where the buffing pad  27  of the FIG. 4 type is formed with a permanently affixed backing plate  13 , the pad is effectively balanced for its full useful life. If a demountable buffing pad, attained and can be retained in subsequent demounting and reattachment (via the hook and loop fastener  36 ) by utilizing the through bores  41  as pilot holes. 
     An alternate method of forming a concave recess on the working fate of a foam buffing pad utilizes permanent deformation of a pad body with an initial flat face, rather than cutting or grinding the material from the face. In such a method, a concave heated platen is used to apply a layer of melted plastic, such as polyethylene to the rear mounting face of the pad and, as the pad is pressed into the platen, the opposite front working face is drawn into a concave shape. After the polyethylene layer has been cooled and set, the concave shape of the front working face is retained. The polyethylene bonding layer may also be utilized to attach one-half of a hook and loop fastener material to the mounting face of the pad as well. 
     In addition, by utilizing abrasive grinding tools on both the first and second grinding wheels  54  and  58 , the typically smooth surface of virgin open cell polyurethane foam stock is roughened in the forming process. This roughened or texturized surface provides a velvetizing effect which has the beneficial effect of providing a softened buffing surface and reducing initial pad chatter because of reduced friction.