Abstract:
A sanding disc comprising an integral structure having a plurality of layers. The layers include a foam backing layer, a middle semi-resilient layer and an abrasive screen layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a motorized sander. Particularly, the present invention relates to a sanding disc used with a motorized sander.  
           [0003]    2. Description of the Prior Art  
           [0004]    In drywall construction, it is necessary after taping and filling the joints between panels to sand the joint. This reduces the joints to the same level as the adjacent panels and, thus, obscures any evidence of a joint. In the past, this had been done with manual sanders consisting simply of a supporting block and a section of abrasive material on the block. As is evident to those in the construction trade, hand sanding of all the joints is a tedious and expensive operation. To increase the efficiency of the sanding operation, motorized sanders have been developed.  
           [0005]    U.S. Pat. No. 5,690,545 (1997, Clowers et al.) discloses one such motorized sander. In particular, Clowers et al. disclose a motorized rotary tool having a head mounted by a pivotal joint. This device included a mechanism that enables the sanding head to pivot through several axes of rotation so that the user does not need to change positions as frequently as is required when using other motorized sanders. A sanding head is mounted by a pivotal joint to a proximal end of a tubular wand. The sanding head includes a sanding pad operatively coupled to the flexible drive shaft.  
           [0006]    A disadvantage of the Clowers et al. device lies in the sanding pad. The sanding pad has a foam backing covered with an abrasive sandpaper material. The sanding pad must be changed relatively often, especially when the joint compound is still moist. Sanding moist joint compound sticks and clogs the abrasive paper of the sanding pad rendering the pad useless for further sanding. Consequently, the sanding pad is changed more often causing a delay in the sanding operation. In addition, the most commonly used abrasive pad is one with 120 grit sandpaper surface. This is most commonly used because of the speed with which it can sand the joint. However, this grit level leaves obvious swirl marks that must then be either hand sanded or a higher grit sanding pad used on the sander. In either case, additional time and cost is required.  
           [0007]    U.S. Pat. No. 5,036,627 (1991, Walters) discloses a dustless sanding device. The dustless sanding device includes a mounting plate having an upper surface, a lower surface, and one or more apertures penetrating therethrough. A hollow tube sealingly is connected to a source of suction at its distal end. A resilient pad, having an upper surface, a lower surface, and side surfaces, is mounted to the lower surface of the plate at its upper surface. The side pad surfaces are sealed. The pad is characterized by being formed from an open weave fiber skeleton exhibiting openings throughout the entire pad structure. The lower surface of the pad defines a substantially smooth plane. A removable apertured sanding sheet is mounted to the lower surface of the pad and is supported thereby in a substantially smooth planar configuration.  
           [0008]    A disadvantage of the Walters device is that the entire sanding pad must be moved back and forth, like prior art sanding blocks, in order to sand a drywall joint. Even though the device may decrease the amount of joint compound dust that gets into the air, it is still a slow and tedious process. In fact, the sanding process is much slower than that provided with a motorized sander.  
           [0009]    U.S. Pat. No. 5,007,206 (1991, Paterson) discloses a dustless drywall sander. The dustless sander has a sanding body with a flat front face. Two exhaust openings open into the back face of the sanding body. Each is associated with a series of vacuum passages that radiate from the exhaust opening. Inlet openings through the front face communicate with the exhaust openings and the vacuum passages. The inlet openings communicating directly with the exhaust openings are smaller in diameter than the inlet openings communicating with the vacuum passages. The sander is equipped with a sanding pad consisting of several layers of fiberglass screen secured together by a bonding material around the edge. This is laid over the front face of the sander and is held in place by an open mesh abrasive sheet clamped to the sander.  
           [0010]    A disadvantage of the Paterson device, like the Walters device, is that it must be physically moved back and forth by the user in order for a user to sand a drywall joint. Like the Walters device, this device may decrease the amount of joint compound dust that gets into the air but it is also slow and tedious compared to a motorized sander.  
           [0011]    Therefore, what is needed is a sanding disc that has an improved useful life, especially when used on high speed motorized drywall sanders. What is also needed is a sanding disc that can be cleaned and re-used in the event that the sanding disc becomes clogged. What is further needed is a sanding disc that provides the sanding efficiency of a larger grit abrasive and the smoother finish of a smaller grit abrasive.  
         SUMMARY OF THE INVENTION  
         [0012]    It is an object of the present invention to provide a sanding disc that has a longer useful life than currently available sanding pads. It is another object of the present invention to provide a sanding disc that can be easily cleaned and re-used in the event that the sanding disc becomes clogged. It is a further object of the present invention to provide a sanding disc that can be used on high speed, motorized, drywall sanders. It is still another object of the present invention to provide a sanding disc with the sanding efficiency of a larger grit abrasive and the smoother finish of a smaller grit abrasive.  
           [0013]    The present invention achieves these and other objectives by providing a unitary sanding disc having a foam layer, a middle semi-resilient layer, and an abrasive screen material. The foam layer, middle semi-resilient layer and the abrasive screen material are bonded to each other using an adhesive. The sanding disc has a central opening configured to allow a clamping mechanism of a motorized sander to securely hold the sanding disc in place. Typically, the clamping mechanism includes a washer for grasping the central portion of the sanding disc and a nut for securing the washer and sanding disc to the motorized sander housing.  
           [0014]    The foam layer or foam pad is configured to make up a major thickness of the sanding disc. Because of the high speed of the motorized sander, the foam pad acts in a cushioning capacity to provide better user control over the amount of drywall compound removed during the sanding process. The nonporous, semi-resilient middle layer provides sufficient planar rigidity for supporting the abrasive screen against the foam pad. On the other hand, the semi-resilient middle layer is sufficiently resilient to provide the user with a wider range over which the user may vary the sanding pressure exerted by the user onto the drywall compound during the sanding process. It also acts to keep the drywall dust from penetrating the foam pad and loading the foam pad with ground drywall compound dust. Unlike conventional 120-grit sandpaper, the abrasive screen makes it easier to clean the screen of the loaded drywall dust thus extending the useable life of the sanding disc. The silicon carbide coating on the screen cloth is harder and more durable an abrasive compound than aluminum oxide. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective view of the present invention.  
         [0016]    [0016]FIG. 2 is a front view of the present invention showing the abrasive screen material.  
         [0017]    [0017]FIG. 3 is a back view of the present invention showing the foam layer and the concentrically extending middle layer.  
         [0018]    [0018]FIG. 4 is a cross-sectional view of the present invention showing the foam layer, the middle layer and the abrasive screen material layer.  
         [0019]    [0019]FIG. 5 is an exploded perspective view of the present invention showing the adhesive layer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    The preferred embodiment of the present invention is illustrated in FIGS.  1 - 5 . FIG. 1 shows an isometric view of sanding disc  10 . Sanding disc  10  includes a foam backing layer  20 , a middle layer  30  and an abrasive screen material layer  40 . Sanding disc  10  has a central opening  12 . Central opening  12  is sized to receive a disc fastening system typically used on a rotary sander. Foam backing layer  20  is typically die-cut to size to fit the particular sander. Foam backing layer  20  is preferably sized to fit a motorized rotary tool typically used for drywall sanding. Such a motorized rotary tool is available from Porter-Cable Corporation of Jackson, Tenn.  
         [0021]    Foam backing layer  20  is a resilient foam pad to provide a cushioning effect to the abrasive screen layer  40  when in use. The resilient nature of foam backing layer  20  allows the user to vary the pressure on the area being sanded, thus providing the user the ability to smooth the drywall compound to a “featheredge” more easily. This is important especially when using a high speed motorized sander such as the one previously described. Middle Layer  30  has an outside diameter that is larger than the outside diameter of foam backing layer  20 . Typically, the diameter of middle layer  30  is about 9 inches. The outside diameter of abrasive screen layer  40  is coextensive with the outside diameter of middle layer  30 .  
         [0022]    Turning now to FIG. 2, there is illustrated a front view of sanding disc  10 . Abrasive screen layer  40  is preferably an abrasive screen, which is made of an abrasive screen cloth that utilizes an open mesh design. The abrasive screen cloth is typically made of a waterproof material that is coated on both sides with an abrasive. Silicon carbide is the preferred abrasive. A commercially available screen cloth that may be used in making the present invention is available from Norton Abrasives and known as a drywall and plaster sanding screen. The open mesh design resists clogging when used on drywall and plaster surfaces and makes it easier to knock out or remove the drywall dust that becomes loaded within the mesh.  
         [0023]    Abrasive screen layer  40  preferably has an outside diameter  40   b  that is coextensive with the outside diameter  30   b  of middle layer  30 . Typically, the inside diameter  40   a  of abrasive screen layer  40  is larger than the inside diameter  30   a  of middle layer  30 . This larger inside diameter exposes a central portion  30   c  of middle layer  30  sufficient for the washer of the clamping mechanism to grasp sanding disc  10 . Because of the resilience of foam backing layer  20  along with the strength and semi-rigid (semi-resilient) nature of middle layer  30 , the washer and nut of the clamping mechanism squeeze the foam against the sander housing and causes the washer and nut to be recessed below the plane of abrasive screen layer  40 .  
         [0024]    [0024]FIG. 3 is a back view of sanding disc  10 . Foam backing layer  20  has an inside diameter  20   a  that is coextensive with the inside diameter  30   a  of middle layer  30 . The outside diameter  20   b  of foam backing layer  20  is smaller than outside diameter  30   b  of middle layer  30  and of outside diameter  40   b  of abrasive screen layer  40 . Inside diameter  40   a  of abrasive screen layer  40  are indicated by dashed lines to show that inside diameter  40   a  is not coextensive with the inside diameters  20   a ,  30   a  of foam backing layer  20  and middle layer  30 , respectively.  
         [0025]    [0025]FIG. 4 is a cross sectional view of sanding disc  10 . The larger outside diameters  30   b ,  40   b  of middle layer  30  and abrasive screen layer  40 , respectively, provide a peripheral portion  40   c  of sanding disc  10  absent of foam backing layer  20 . This provides a more resilient area of sanding disc  10  better suited for “featheredging” a drywall compound or plaster surface. Middle layer  30  is a nonporous material such as, for example, a layer of cardboard with a thickness in the range of about 0.020 inches to about 0.080 inches. Preferably, the cardboard used for middle layer  30  is a piece of a record album cover.  
         [0026]    Turning now to FIG. 5, there is illustrated an exploded view of sanding disc  10 . A coating of adhesive  50  is placed between foam backing layer  20 , middle layer  30  and abrasive screen layer  40  and the three layers are combined, allowing the adhesive to dry and/or set. Although a variety of adhesives will work in the present invention, an acceptable adhesive was found to be a spray adhesive available from 3M.  
         [0027]    In testing, the inventor discovered that the combination of an abrasive screen material  40  with the middle layer  30  and foam backing layer  20  into an integral sanding disc  10  outperformed conventionally available sanding discs. In drywall sanding operations, sanding disc  10  of the present invention typically lasted 2 to 3 times longer than currently available sanding discs of comparable design. Further, the sanded drywall compound surface was smoother, i.e. less pronounced sanding marks and a finer finish, where sanding disc  10  of the present invention was used compared to a drywall compound surface where conventional sanding discs were used. This meant less time was required to complete the finish (hand) sanding operation because less hand sanding was required due to the smoother finish provided by sanding disc  10  of the present invention.  
         [0028]    Economically, the present invention provides for reduced costs by requiring less hand sanding time to complete drywall sanding operations as well as less time wasted changing sanding discs because of the longer useful life of the present invention. In addition, the abrasive screen layer is less prone to clogging than other typical sanding discs. Further, when clogged, the open mesh of the abrasive screen makes it easier to remove the loaded drywall dust from the abrasive screen. The combination of the open mesh design, the hardness of the silicon carbide, the semi-resilient middle layer, and the foam pad contributes to the cost savings and increased useful life of the present invention.  
         [0029]    Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.