Abstract:
A drywall head for applying mastic compound or other similar material to an outside corner edge of two adjoining drywall board sections to cement on a taped-on corner during drywall assembly. The drywall head includes uniquely constructed flow channels that taper from the leading edge of the tool to the trailing edge of the tool. These uniquely constructed flow channels allow the tool to be used in a uni-directional motion.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a corner tool for applying mastic material, compound, or other similar material to an external corner formed by the intersection of two sections of drywall which come together at substantially right angles, and are universally used in interior building walls. 
     Drywall heads for applying mastic compound to unfinished drywall corners are well known in the art. In one outside corner finishing method, a metal corner bead is secured to the outside corner edge of two adjoining drywall board sections using nails and/or screws after which a finishing coat of mastic or plaster material is applied to the outside corner. Many tools have been developed for the application of mastic material to outside corners, particularly outside corners which have been prefitted with a metal corner bead. 
     In a second outside corner finishing method, a first layer of fast set compound or mastic material is applied to the outside corner edge of two adjoining drywall board sections. An unfinished outside corner bead of metal, plastic, or other conventional material, is then applied to the fast set compound or mastic material contained on the outside corner edge of the adjoining drywall board sections. The unfinished corner bead preferably has a sheet of paper material adhered to the outer surface thereof. Such corner beads are generally referred to in the art as “taped-on corners”. The paper material extends a short distance beyond the vertical side edges of the unfinished corner bead such that the paper overlaps the adjacent portion of the drywall board section. An outside corner finishing tool is then used to apply a layer of mastic material to both sidewalls of the outside corner to bond the outside corner edge of the drywall and the taped-on corner. 
     U.S. Pat. No. 5,368,461 to Murphy is directed to an outside corner finishing tool for applying mastic, compound, or plaster material to outside corner edges formed by drywall board sections. The tool is a generally polygonal block-like enclosure of rigid material including a top wall and a bottom wall, a pair of concave inward front walls defining a 90° inner corner adapted to fit an outside corner, and a back wall spaced from the front walls by a pair of spaced sidewalls. The back wall contains a spherical cavity for,receiving a ball socket connector. The cavity is connected to vertically oriented channels in the front wall. A pump-type applicator is connected to the ball socket connector and is operated to direct a regulated flow of mastic material into the spherical cavity. In turn, the mastic material is directed through the manifold to the vertical channels of the front walls for simultaneous application of mastic material along two adjoining wall board sections. 
     The finishing tool described in Murphy &#39;461 patent includes vertically oriented channels that extend between the top wall and the bottom wall of the tool. The channel members have a uniform width so that the tool may be moved in either vertical direction on the outside corner of the drywall to which the material is to be applied. Thus, the channels allow the tool to be moved bi-directionally, up and down, along the outside corner of the walls without removing the tool from contact with the wall as the mastic material is applied. 
     As shown in the Murphy &#39;461 patent, each channel has a uniform width throughout. In operation, mastic material enters the spherical cavity and is directed through each port into its respective dispersing cavity where it is then fed into the channels. The uniform width of the channels permit the tool to be moved in either direction, up and down, along the outside corner and thus permits the tool to be moved bi-directionally on the outside corner of the wall as the mastic material is applied. 
     Although the finishing tool described in the Murphy &#39;461 patent functions reasonably well to apply a strip of mastic material, the finishing tool suffers from several drawbacks. One of these drawbacks is the removable mounting of the head on to the ball joint connector. During use of the applicator head, the ball joint connector can become disconnected from the tool head if the tool head becomes snagged on the drywall as the tool head is applying mastic material. Further, the uniform width of the vertically oriented channels restricts the ability of the tool head to be used to smooth but a section of mastic material after the mastic material has been applied. In many situations, the viscosity of the material causes the strip to expand slightly after it has been applied. If the finishing tool of the Murphy &#39;461 patent is used to go over a strip of previously applied mastic material, the uniform channel may cause the strip to contact the other walls that define the channel and make a mess along the wall. 
     It is an object of the present invention to provide a drywall head for applying a metered amount of continuous, uniform and void-free mastic compound in ribbon form to adjacent walls of an unfinished corner to cement a variety of commonly used taped-on corners to an outside corner in a simple and efficient manner. It is a further object of the present invention to achieve this efficiency through the use of tapered flow channels within the inner walls of the tool. The channels taper from a leading edge of the tool to a trailing edge of the tool such that the tool is designed to be moved in a single direction along the corner. The taper of each channel allows the drywall head to gather and redistribute the strip of mastic compound on the drywall. 
     It is another object of the present invention to provide a drywall head for applying mastic compound of the type described which may be used with a pneumatic applicator for providing a constant and controllable flow of mastic material to the tool for application on the outside corner. When the present invention is utilized with the pneumatic applicator, a constant flow of material is supplied to the drywall head so that the material may be applied uniformly and in a constant manner to the outside corner. Use of the drywall head with the pneumatic applicator also reduces the labor effort required to apply the mastic material as physical pressure by the user is not relied upon. Furthermore, the combination of the drywall head with the pneumatic applicator allows for the one time, uni-directional application of mastic material to the unfinished corner. 
     SUMMARY OF THE INVENTION 
     The present invention is a drywall head for applying mastic compound to the adjacent walls of an unfinished corner. The drywall head is constructed of rigid material and comprises a block structure that has two inner guide surfaces set at a generally 90° angle to each other, a top surface, a bottom surface, a back wall surface, an interposed flow chamber situated within the drywall head, and a ball socket. The ball socket opens into the interposed flow chamber, and the flow chamber further opens into ports within each inner guide surface. The ports within the inner guide surfaces open into uniquely constructed flow channels. The flow channels extend between a leading edge adjacent to the bottom surface of the tool, and a trailing edge adjacent to the top surface of the tool. The flow channels are defined laterally by a pair of retaining walls. The width of each of the flow channels at the leading edge is greater than the width of the channels at the trailing edge, as the retaining walls of each channel taper from the leading edge to the trailing edge. The trailing edge of each flow channel further contains a plurality of staggered teeth situated within the flow channel to aid in the uniform deposition of a metered amount of mastic material onto the unfinished corner, thereby providing an adequate amount of mastic to prevent blistering and create a void-free strip. 
     The drywall head of the invention further includes a ball assembly designed to fit into the ball socket located on the back wall surface. The ball assembly allows for pivotal movement of the drywall head in relation to a delivery tool, preferably a pneumatic applicator. The invention is designed so that the tool is used in a uni-directional motion. Application of the mastic material begins when the tool is placed at the juncture of the wall corner, typically near the ceiling. Application of the mastic material continues in one direction down the outside corner to the intersection of the wall corner and the floor. 
     The drywall head of the invention includes a C-spring assembly that provides a resilient means for biasing the drywall head in an upright, operating position relative to the pneumatic applicator that supplies a mastic material to the drywall head. The C-spring assembly orients the drywall head at a known position such that when the drywall head is removed from the corner, the drywall head returns to a known position. Further, the combination of the C-spring assembly and a series of guide wheels allow the drywall head to flex and follow the contour of the drywall as the mastic material is applied. 
     The outside corner head is designed to be used in one direction due to the difference in width of the channel from the leading edge to the trailing edge. If the tool were used in the opposite direction, the previously applied strip of mastic material would enter the head at the narrower trailing edge at exit at the wider leading edge. Thus, going over a previously applied mastic strip with the drywall head oriented in an opposite direction will result in destruction of the strip and a non-uniform width due to the increase in size of the channel. 
    
    
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
     BRIEF DESCRIPTION OF  1 HE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is a perspective view of a drywall head with tapered channels in combination with a pneumatic applicator for use in the application of mastic material to an external corner formed by the intersection of two sections of drywall; 
     FIG. 2 is a perspective view demonstrating the interchangeability of the invention with different heads on a pneumatic applicator; 
     FIG. 3 is a section view taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a section view taken along line  4 — 4  of FIG. 3; and 
     FIG. 5 is a section view taken along line  5 — 5  of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 generally illustrate a dry all head  10  with tapered applicator channels  12  that forms the basis of the present invention. The drywall head  10  is formed from an integral one-piece block of rigid material. The drywall head contains a top surface  14 , a bottom surface  16 , a back wall surface  18 , two side surfaces  22 , and two inner guide surfaces  20  set at a 90° angle to each other. The inner guide surfaces  20  are set at the 90° angle so that the tool may be placed on an external corner formed by the intersection of two sections of drywall that come together at substantially right angles, and which are universally used in interior building walls. 
     As can be seen in FIG. 3, the drywall had  10  includes a flow chamber  24  that is situated within the surfaces of the drywall head  10 . The back wall  18  includes a mounting portion  25  that defines spherical cavity or ball socket  28  designed for receiving a ball assembly. The ball assembly consists of a ball member  26  designed to fit into the ball socket  28 , an arm member  30 , and a coupling member  32 , as shown in FIG.  1 . The arm member  30  includes a hollow interior that allows material to be moved from the applicator  34  to the drywall head  10 . The arm member  30  is curved so that the drywall head  10  may be parallel to the wall surfaces while a user is holding the pneumatic applicator  34  at an angle to the wall and drywall head  10 . The coupling member  32  is designed to attach the drywall head  10  to the pneumatic applicator  34 . 
     As best seen in FIG. 4, each of the inner guide surfaces  20  of the drywall head  10  include a tapered channel  12  extending from a leading edge  40  to a trailing edge  42 . The width of the tapered channel  12  is defined by a pair of retaining walls  44 . The width between the retaining walls  44  at the leading edge  40  is greater than the width between the retaining walls  44  at the trailing edge  42 , thus creating a flow channel that tapers from the leading edge  40  to the trailing edge  42 . 
     The tapered channels  12  are each designed such that the volume of mastic material that enters at the leading edge  40  is greater than the volume of mastic compound deposited on the wall at the trailing edge  42 . In the present invention, the increase in volume at the leading edge  40  is due primarily to the greater width of the channel  12  at the leading edge  40  compared to the width of the channel  12  at the trailing edge  42 . However, it is also contemplated by the inventor that the depth of the tapered channel could be greater at the leading edge  40  as compared to the trailing edge  42  to further aid in gathering and redistributing the mastic compound. The tapered flow channels  12  contain a number of protruding teeth  46  located at the trailing edge  42  for the purpose of profiling the strip and metering the amount of mastic compound applied. 
     Referring back to FIG. 3, the flow chambers  24  connect the ball socket  28  to the cavity  38  formed in each of the tapered channels  12 . Specifically, the interposed flow chambers  24  are situated entirely within the drywall head  10  and branch into each of the respective cavities  38 . As shown in FIG. 4, each branch of the flow chambers  24  includes a port  36  that feeds into a cavity  38  set between the inner retaining walls  44  of each tapered channel  12 . 
     When the ball member  26  is placed within the ball socket  28 , the ball member  26  is retained within the ball socket  28  by a retaining bracket  33  including an extended flange  35 , as best seen in FIG.  5 . The retaining bracket  35  allows the drywall head  10  to move pivotally in relation to the pneumatic delivery tool  34 . However, too much play in the pivotal movement of the drywall head  10  creates difficulty in controlling the drywall head  10  during application of mastic compound to unfinished drywall corners. To restrict such movement, a C-spring assembly  48  is employed to facilitate control of the drywall head  10  during application of mastic compound. 
     As shown in FIG. 5, the C-spring assembly  48  consists of a C-spring  50  that is attached to the back wall  18  of the drywall head  10  at a first end  52 . A second end  54  of the C-spring  50  is attached to a pin  55  positioned between a pair of brackets  57  mounted to the arm member  30  of the ball assembly. The means for attaching the C-spring  50  to the drywall head  10  and the arm member  30 , respectively, may be achieved in many different ways, all well known within the art. 
     During operation of the pneumatics applicator  34  and the drywall head  10 , the C-spring  50  biases the drywall head  10  into a known orientation, as illustrated in FIG.  1 . Thus, when the drywall head  10  is removed from the corner, the drywall head  10  returns to the position shown in FIG.  1 . Further, the C-spring  50  holds the drywall head  10  in position as the drywall head  10  is moved into contact with the corner. The bias force created by the C-spring  50  allows accurate placement of the drywall head on the corner by a user. 
     During application of the mastic material to the corner, the C-spring  50  flexes, which allows the angle between the pneumatic applicator  34  and the drywall head  10  to vary to allow for smooth application of the mastic material to the drywall. Thus, the C-spring assembly  48  in combination with the ball member  26  allows the drywall head  10  to move relative to the arm member  30  while returning the drywall head  10  to a known, biased position. 
     Referring now to the FIGS. 1 and 3, the drywall head  10  includes a pair of guide wheels  56  mounted to each of the side surfaces  22 . As illustrated in FIG. 3, the guide wheels  56  contact the face surface  57  of the drywall and allow the drywall head  10  to move smoothly along the drywall during application of the mastic material, thus preventing wear on the block, which would affect the amount of material being applied. 
     It is also possible to place a removable bull nose centering block (not shown) at the intersection of the inner walls  20 . Such bull nose centering block would be used when applying mastic compound to a drywall corner that is formed by a pair of walls that do not extend to the apex of the corner. The removable bull nose centering block would prevent flow of mastic compound into such an unfinished corner. 
     In operation, the pneumatic delivery tool  34  pushes mastic material through the arm member  30  and the ball member  26  into the ball socket  28 , as illustrated in FIG.  3 . The mastic material disperses into the interposed flow channels  24 , which subsequently feeds the mastic material equally through each port  36  into the tapered flow channels  12 . As the mastic material enters the tapered flow channels  12  from the ports  36 , the mastic material accumulates in the cavity  38 . 
     The drywall head  10  is placed flush onto the wall corner at the juncture of the wall corner and the ceiling. As the mastic material fills the cavity  38 , it is dispersed within the tapered flow channel  12 . At the same time, the user will begin to direct the drywall head along the outside corner of the wall, in a unidirectional motion, so that the mastic material is deposited along the outside corner in two strips which are spaced at a distance from the apex of the outside corner. The unique construction of the tapered flow channel  12  requires that the drywall head  10  to move along the corner in only one direction due to the difference in width of the flow channel  12  from the leading edge  40  to the trailing edge  42 . The flow of mastic material from the cavity  38  exits the tool through the staggered teeth  46  of the trailing edge  42 . Significantly, the staggered teeth  46  located within the tapered channel  12  help disperse the mastic material evenly as it flow out of the drywall head  10  at the trailing edge  42 . Thus, the mastic material exits the drywall head  10  at the trailing edge  42  in an evenly dispersed strip of a volume adequate to provide a void-free band without excess wasted material. 
     After the initial strip of mastic material has been applied to the corner, the orientation of the drywall head  10  can be rotated 180° and additional mastic material can be applied or the drywall head  10  can be used to further smooth the mastic material already applied. Specifically, the leading edge  40  is wider than the strip of material applied to the wall, such that the leading edge  40  can gather the strip even if the strip has expanded in width due to the viscosity of the material. Thus, it is important that the drywall head  10  be moved in the direction that permits the leading edge  40  to contact the already applied mastic material before the trailing edge  42 . 
     As can be understood from FIGS. 1 and 4, the drywall head  10  is designed to be used in one direction due to the difference in width of the flow channels  12  from the leading edge  40  to the trailing edge  42 . If the tool were used in the opposite direction, i.e. if the trailing edge  42  lead the tool up the wall instead of following it down, the previously applied strip of mastic material would enter the drywall head  10  at the narrower trailing edge  42  and exit at the wider leading edge  40 . Thus, going over a previously applied strip of mastic material would result in destruction of the strip. 
     Referring now to FIG. 2, thereshown are alternate types of the drywall head  10  being contemplated as being within the scope of the present invention. FIG. 2 illustrates a mastic strip applicator  58  that is used to apply a single strip of mastic material anywhere along a drywall surface. As is illustrated in FIG. 2, the strip applicator  58  includes a single channel  60  that has a leading edge  62  and a trailing edge  64 . The leading edge  62  of the strip applicator  58  is volumetrically larger than the trailing edge  64  such that the strip applicator  58  is also used in only one direction. The remaining components of the strip applicator  58 , including the C-spring  50 , are identical to those included in the drywall head  10  previously discussed. 
     Also shown in FIG. 2 is an inside corner drywall head  66  that is used to apply two strips of mastic material to an inside corner formed by two sections of drywall. The inside corner head  66  also includes a pair of flow channels  68  each defined by a leading edge  70  and a trailing edge  72 . Once again, the leading edge  70  is volumetrically larger than the trailing edge  72  such that the inside corner head  66  is designed to be used in only one direction. The inside corner head  66  operates in a nearly identical manner to the outside drywall head  10  previously described. Additionally, the inside corner head also includes the C-spring assembly  48  used to bias the finishing head in a known position. 
     It is understood that the dimensions for the width of the tapered channel at the leading edge, the width of the tapered channel at the trailing edge, the depth of the cavity, and the spacing of the channels from the corner apex may be varied as desired for use with the size of the taped-on corner being utilized. Likewise, it is understood that the materials of construction for the drywall head  10  may include a variety of materials including, but not limited to, metal, hard plastic, or wood. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.