Patent Publication Number: US-2010119327-A1

Title: Self-drilling screw with multi-drilling portions

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a self-drilling screw, in particular to a self-drilling screw including multi-drilling portions. 
     2. Description of the Related Art 
     A conventional drilling screw  1  as shown in  FIG. 1  comprises a head  11 , a shank  12  outwardly extended from the head  11  forming a drilling portion  13  at the distal end thereof, and a set of thread section  14  spiraling round the shank  12 . Wherein, the drilling portion  13  peripherally defines two flutes  131  (only one flute as viewed in the  FIG. 1 ), and a cutting surface  132  is further outwardly extended from the flute  131  so that a cutting edge  133  is formed by the convergence of the flute  131  and the adjoining cutting surface  132 . During operation, the cutting edge  132  renders a preliminary drilling to lead the succeeding thread section  14  screwing into an object (not shown) and fix the screw  1  therein. 
     However, in virtue of the typical punching upon the drilling portion  13  and the sole application of the flutes  131  and cutting edges  133  for processing the cutting and debris guidance, a limited accommodation of debris among the flutes  131  becomes easy to impede the extrusion of the debris in time of drilling and to incur an increment of the screwing torque, which relatively results in snapping of the screw  1 . Moreover, the length of the drilling portion  13  is chiefly decided in view of the thickness of the object. Therefore, once the drilling portion  13  is prolonged, the larger and lengthy die is required, which potentially results in the exhaustion of the die under a term of utilization and renders the high manufacturing cost. 
     The intention of another conventional drilling screw  2  as shown in  FIG. 2  was accordingly invented to remedy the shortcomings of the drilling screw  1 . The concatenation of associated elements and applications same to those of the first prior art are herein omitted. Wherein, a necking  25  is defined between a drilling portion  23  and a thread section  24 , in which an outer diameter d 1  of the necking  25  is smaller than an outer diameter d 2  of the drilling portion  23 . Approaching to the same operation as the conventional screw  1 , a cutting edge  233  on the drilling portion  23  renders a preliminary drilling to lead the succeeding shank  22  screwing into an object (not shown). The generated debris would upwardly travel along the flutes  232 , and the narrow necking  25  would allocate a clearance for assisting the further advancement of debris, which accordingly intends to diminish the obstruction of the debris in the drilling and renders a fastening capability. 
     Nonetheless, such necking  25  are preferred merely for purposes of the debris extrusion, decreasing part of the die length, and therefore reducing the cost of a lengthy die. Moreover, in view of the screw  2  commonly designed to engage with a thicker object (not shown), a larger supporting strength would be needed to carry the drilling portion  23  into the object. However, the thinner and fragile necking  25  with the reduced diameter d 1  would be subjected to a facile snap in view of its lower resistance unable to bear the drilling pressure, which however would decrease the screwing capability and firmness of the screw  2 . Thus, the screw  2  still fails to obviate the deficiencies of the screw  1  and requires improvements. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a self-drilling screw with multi-drilling portions to achieve a speedy drilling and a decreased screwing torque so as to increase the screwing efficiency. 
     The self-drilling screw in accordance with the present invention mainly comprises a head, a shank outwardly extended from the head forming a drilling portion to be disposed opposite to the head, and a set of thread section spiraling round the shank. Wherein, at least one sub-drilling portion is further defined between the drilling portion and the thread section and comprised of a sequence of indentations for rendering the performance of a plurality of cutting ridges. In this manner, the sub-drilling portion along with the cutting ridges assists the drilling portion in advancing a preferable preliminary drilling and has the indentations to provide an efficient extrusion of debris, therefore conducing to attaining a decreased screwing resistance and torque, achieving a rapid screwing, and promoting the screwing efficiency. 
     The advantages of the present invention over the known prior arts will become more apparent to those of ordinary skilled in the art by reading the following descriptions with the relating drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a conventional screw; 
         FIG. 2  is a perspective view showing another conventional screw; 
         FIG. 3  is an elevation view showing a first preferred embodiment of the present invention; 
         FIG. 3A  is an enlarged view showing of  FIG. 3 ; 
         FIG. 4  is a schematic view showing the first preferred embodiment screwed in an object; 
         FIG. 5  is an elevation view showing a second preferred embodiment of the present invention; 
         FIG. 6  is an elevation view showing a third preferred embodiment of the present invention; and 
         FIG. 7  is an elevation view showing a fourth preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing in greater detail, it should note that the like elements are denoted by the similar reference numerals throughout the disclosure. 
     Referring to  FIG. 3  showing the present invention, a self-drilling screw  3  of a first preferred embodiment comprises a head  31 , a shank  32  outwardly extended from the head  31  forming a drilling portion  33  to be disposed opposite to the head  31 , and a set of thread section  34  spiraling round the shank. Wherein, the drilling portion  33  includes a drill bit  331  defined thereon and at least one flute  332  disposed on the drill bit  331 . Particularly, a sub-drilling portion  35  is defined between the drilling portion  33  and the thread section  34 . It should be noted that the sub-drilling portion could be directly and integrally punched by a mold, which further results in a higher strength. 
     Moreover, the sub-drilling portion  35  further includes a sub-drill body  351 , an upper region  352  disposed close to the edge of the thread section  34 , and a lower region  353  adjoined with the drill bit  331 ; the sub-drill body  351  provides with a sequence of indentations  354  and prominent areas  355  defined between the upper and lower regions  352 ,  353 , and each indentation  354  has one side thereof upstream extending to perform a cutting surface  356  so that a cutting ridge  357  is formed where the cutting surfaces  356  and the adjacent prominent area  355  meet. Further, the cutting ridge  357  is parallel to a shank axis α as plainly shown in  FIG. 3 ; alternatively, it should be noted that the cutting ridge  357  could also be inclined to the axis α of the shank  32  as shown in  FIG. 5 . Herein the descriptions to the operation in this and following embodiments are mainly utilized in connection with the performance of the cutting ridge  357  being in a parallel statement. 
     Referring to  FIG. 4  showing the operation of the self-drilling screw  3 , the drill bit  331  is preliminarily drilled into an object  4  so as to gradually bring the drilling portion  33  drilling thereinto. Hereby, a snap incurred by a large screwing torque can be preferably prevented by means of the sub-drilling portion  35  possessing a constructively higher resistance. Subsequently, the sub-drilling portion  35  continuously contacts the object  4 , and the cutting ridge  357  further assists the drilling portion  33  in drilling more deeply so as to aid with the swift advancing of the succeeding thread section  34  through the object  4 . Concurrently, the debris generated during the screwing is able to be smoothly moved along the flute  332  (or from the distal end of the drilling portion  33 ) toward the indentations  354  and thence extruded out. Such gradual drilling substantively prevents the debris from being over accumulated and efficiently obviates the increment of screwing resistance and torque. Therefore, it accordingly averts bluntness resulting from a long term of the screwing friction on the drill bit  331  and promotes the drilling competence. 
     Referring to  FIG. 6 , a third preferred embodiment of the present invention also comprises a head  31 , a shank  32 , a drilling portion  33 , a set of thread section  34  and a sub-drilling portion  35 . The concatenation of correlated elements and applications same to those of the first preferred embodiment are herein omitted. This embodiment is in characterized in that an outer diameter D 1  of the upper region  352  is larger than an outer diameter D 2  of the lower region  353 , whereby the improvement wherein the sub-drill body  351  is of a gradual reduced diameter from the edge of the thread section  34  toward the drilling portion  33  so as to form a necking structure. Thus, a larger accommodation of debris around the sub-drilling portion  35  is further formed thereby to appropriately receive the debris and allow smoothly extruding the redundant debris out, which efficiently lessens the screwing obstruction. Besides, the gradual-reduced structure of the sub-drilling portion  35  could auxiliarily assist the drilling portion  33  in chipping debris and provide the smooth guidance of redundant debris, thereby attaining the diminished drilling resistance and debris obstruction, a swift screwing, and promoting the screwing efficiency. Please notice that the screw  3  in this embodiment is also not restricted to the performance of the cutting ridges  357  of the sub-drilling portion  35  on account of that the cutting ridge  357  is either parallel (shown in  FIG. 6 ) or inclined with respect to the shank axis α (not shown) attains the same objects and purposes set forth above. 
     Referring to  FIG. 7  showing a fourth preferred embodiment of the present invention, the self-drilling screw  3  also comprises a head  31 , a shank  32 , a drilling portion  33 , and a set of thread section  34 . In this embodiment, the screw  3  has a plurality of adjoining sub-drilling portions  35  formed between the drilling portion  33  and the thread section  34 . Herein, the subsequent illustration is according to the sub-drilling portion  35  presenting of two, and each of the sub-drilling portions  35  still includes the same concatenations of elements as the same as those of the first preferred embodiment. Further, the cutting ridges  357  in this embodiment can perform in parallel to the shank axis α, or perform to be inclined to the shank axis α (not shown). Wherein, the screw  3  of this embodiment operates equivalently to the first embodiment and attains performances of the speedy screwing, decreased torque, as well as promoted screwing efficiency. 
     Giving the contrary comparison of the direct punching at once in the first embodiment, those sub-drilling portions  35  of  FIG. 7  are able to be discretely punched, which means a die, whose length is identical to that of one sub-drilling portion  35 , could be individually applied several times to form the joining and plural sub-drilling portions  35 . Therefore, it needs not the large dies (not shown) to implement the integral molding at once, and such separate molding correspondingly conduces to a high strength and a reduced defective rate of the products as well. Hence, a technique level can be economized and the manufacturing costs can be reduced. 
     To sum up, the present invention takes advantage of at least one sub-drilling portion defined between the drilling portion and the thread section to lead an auxiliary drilling and provide a substantial guidance of debris. The swift extrusion of the redundant debris is hence obtained to avert a large screwing resistance as well as torque. Therefore, a favorable screwing efficiency is thence achieved and promoted. 
     While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.