Abstract:
A screw includes a head and a shank combined together. The head is formed with a circumference provided thereon with continuously arranged point-shaped ribs. When the circumference of the head is being locked into a wood piece, the ribs will function to carry out excavating to enable the screw to be locked into the wood piece comparatively easily.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a screw, particularly to one having the circumference of a head provided thereon with continuously arranged ribs, able to lower locking resistance for enabling the screw to be quickly locked into a wood piece. 
         [0003]    2. Description of the Prior Art 
         [0004]    A conventional screw  1 , as shown in  FIG. 1 , is composed of a head  10  and a shank  11 . The head  10  is provided with a circumference  100  that is taper-shaped or arc-shaped and has its surface provided thereon with a plurality of ribs  12  distributed matching the shape of the circumference  100 . The ribs  12  are respectively formed linearly, that is, each rib  12  is connected into a line from an uppermost end  120  to a lowermost end  121 , but the linear ribs  12  can be curved for matching the shape of the circumference  100  or the spiral threads of the shank  11 . The shank  11  of the screw  1  is provided with threads  110  and a cutting blade  111 . 
         [0005]    That the ribs  12  of a conventional screw  1  are made into a linear state may be in view the convenience of the forging process of the head  10 ; nevertheless, the linear ribs  12  are linear projections formed on the circumference  100  of the head  10 . Therefore, although able to excavate a wood piece and advantageous to locking in a wood locking process, yet, the linear ribs  12  will also cause surface resistance. That is to say, when the head  10  of the screw  1  is being locked and embedded into a wood piece (A), the linear ribs  12  will contact with the hole wall AO of the wood piece (A), as shown in  FIG. 3 , and produce too large a locking resistance, thus failing to smoothly carry out locking of a screw and hence lowering locking velocity. 
       SUMMARY OF THE INVENTION 
       [0006]    The objective of this invention is to offer a screw, able to lower resistance when the screw is being locked into a wood piece for enabling the screw to carry out locking smoothly and quickly. 
         [0007]    The screw in the present invention has the circumference of a head provided thereon with continuously arranged dot-shaped ribs for carrying out point contact, not surface contact, between the ribs and the walls of excavated holes of a wood piece, able to lower locking resistance. 
         [0008]    The circumference of the head of this invention is provided with a plurality of ribs formed matching with the shape of the circumference. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    This invention will be better understood by referring to the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a front view of a conventional screw; 
           [0011]      FIG. 2  is a cross-sectional view of the line A-A in  FIG. 1 ; 
           [0012]      FIG. 3  is a schematic view of the conventional screw locked into a wood piece; 
           [0013]      FIG. 4  is a front view of a screw in the present invention, applied to a wood screw; 
           [0014]      FIG. 5  is a cross-sectional view of the line B-B in  FIG. 4 ; 
           [0015]      FIGS. 5A-5E  are schematic views illustrating various preferred embodiments of ribs in the present invention; 
           [0016]      FIG. 6  is a cross-sectional view of a head of the wood screw in the present invention; 
           [0017]      FIGS. 6A-6C  are cross-sectional views of various preferred embodiments of a rib member in the present invention; 
           [0018]      FIG. 7  is a front view of a screw in the present invention, applied to a self-tapping screw; and 
           [0019]      FIG. 8  is a cross-sectional view of the screw locked into a wood piece in the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    A preferred embodiment of a screw  2  in the present invention, as shown in  FIGS. 4-5D , includes a head  20  and a shank  21 . 
         [0021]    The head  20  is provided with a circumference  200 , which can be formed into various shapes, such as an arcuate shape shown in  FIG. 4 , or a conical shape shown in  FIG. 7 . The circumference  200  is provided thereon with a single rib  22  or plural ribs  22 , and each rib  22  is composed of a plurality of dot projections  220  arranged continuously, as shown in  FIG. 5 . Between every two dot projections  220  is formed a distance (d) that can be smaller than or equivalent to or larger than the outer diameter (r) or the width (w) of the dot projections  220 , and the dot projections  220  of two adjacent ribs  22  are arranged in a straight line as shown in  FIGS. 5A and 5C , or arranged in a intercrossing condition, as shown in  FIGS. 5B and 5D . If arranged in a straight line, the dot projections  220  of every two adjacent ribs  22  lie on a same basic line L 1  or L 2 , and the rest can be done in the same manner, and if arranged in an intercrossing condition, the dot projections  220  of every two adjacent ribs  22  are not located on the same basic line L 1  or L 2 , and the rest can be deduced accordingly, and each mode of arrangement mentioned above has its own advantages. When the dot projections  220  of every two adjacent ribs  22  are arranged in an intercrossing condition, the wood waste of a hole wall AO, which are not yet excavated by the dot projections  220  of the previous rib  22 , will be continuously excavated and removed by the dot projections  220  of the latter ribs  22 , thus enhancing locking velocity. 
         [0022]    The ribs  22  on the circumference  200  can be provided in a straight line, as shown in  FIGS. 4 and 5 , or in a V shape or an inverted-V shape or a triangular shape, as shown in  FIGS. 5A and 5B , or in an intersecting X-shape, as shown in  FIGS. 5C and 5D . In other words, the ribs  22  formed on the circumference  200  of the head  20  can be formed into various types so long as they can function to excavate a wood piece and remove wood waste. 
         [0023]    In addition, the dot projections  220  of the ribs  22  can be formed into an arcuate shape or an oval shape, as shown in  FIGS. 6 and 6A , a square shape or a rectangular shape, as shown in  FIGS. 5E and 6B , or a tapered shape or a conical shape as shown in  FIG. 6C , that is to say, the rib members  220  of the ribs  22  can be made into various shapes so long as they can function to excavate a wood piece and remove wood waste. 
         [0024]    Further, the screw  2  of this invention can be applied to a wood screw or a self-tapping screw, which has a head provided with a circumference  200  and which makes use of ribs  22  for excavating a wood piece and removing wood waste. 
         [0025]    Referring to  FIG. 8 , when the screw  2  of this invention is used for locking a wood piece (A) and makes use of the ribs  22  on the circumference  200  of the head  20  to excavate the surface of the wood piece (A) and form a hole Al that matches with the circumference  200 , the dot projections  220  will function to carry out excavating toward the hole wall AO of the wood piece (A). Since the dot projections  220  of each rib  22  are arranged continuously, it is able to lower contact resistance between the rib  22  and the hole wall AO of the hole Al of the wood piece (A). Moreover, the wood waste of the hole wall AO of the wood piece (A), which is not completely excavated and removed by the dot projections  220  of the previous rib  22 , will be excavated and removed by the dot projections  220  of the latter rib  22 . By so designing, the screw  2  of this invention can be locked into a wood piece with quickness. 
         [0026]    While the preferred embodiment of the invention has been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications that may fall within the spirit and scope of the invention.