Patent Publication Number: US-2012032014-A1

Title: Blade assembly for paper shredder

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to a shredder and, in particular, to a blade assembly for paper shredder formed by combining a first blade and a second blade back to back. 
     2. Related Art 
     As is well known, the action principle of a shredder for shredding paper is to dispose a plurality of blades on two rotary shafts with spacers in between. A motor and a gearbox are employed to drive the two parallel rotary shafts that rotate in opposite directions. They provide a shearing force on passing paper to cut it into small stripes. 
     In the wake of increasing raw material costs and a competitive market, manufacturers have developed various lightweight blades that are made from thin sheet metal and formed by machine punching. Such blades have the advantages of saving the steel material and reducing the weight of shredder. Therefore, this trend has become the mainstream of the industry. The products introduced in China Pat. Nos. 200620056133.1, 200620014030.9, and 200620014187.1 are such examples. 
     However, it is widely suspected that whether the strength of the cutting edges is sufficient for the stability required in long-time uses if the blade thickness is reduced for saving the steel material. Although the above-mentioned China patents all propose to use protruding rings or protruding ribs to reinforce the blades, the effect only applies to the blade flank. The cutting edges of the blade directly used to cut paper sheets is not strongly supported. Therefore, this could be a serious problem in the trend of using lightweight blades. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the inventor provides a blade assembly for paper shredder to solve the existing problems. 
     The blade assembly for paper shredder consists of a first blade and a second blade combined back to back. Each blade has a circular blade flank formed by punching a thin sheet metal. The blade flank has a hole at its center and integrally extends outwards with at least two cutting edges. Each cutting edge has a base portion extended from the blade flank outwards and on the same plane as the blade flank, a surface portion bent from the base portion to the back of the blade flank and perpendicular to the blade flank, and a tip portion formed between the base portion and the surface portion. The blade flank is integrally formed with several ribs protruding towards the blade flank. A portion of the rib is formed beneath the tip portion to support the cutting edge and to enhance its strength. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein: 
         FIG. 1  is a three-dimensional view of the first blade in the invention; 
         FIG. 2  is a three-dimensional view of the second blade in the invention; and 
         FIG. 3  is a three-dimensional view of the blade assembly composed of the first and second blades. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
     In the following description, please refer to  FIGS. 1 ,  2  and  3  for different three-dimensional views of certain parts of the invention. Each blade is made from a thin sheet metal and is formed with a circular blade flank  1  by punching. In addition to making a polygonal hole  11  at the center of the blade flank  1 , it is integrally extended outwards with at least two cutting edges. 
     Each cutting edge has a base portion  21  extended from the blade flank  1  outwards and on the same plane as the blade flank  1 , a surface portion  22  bent from the base portion  21  to the back of the blade flank  1  and perpendicular to the blade flank  1 , and a tip portion  23  formed between the base portion  21  and the surface portion  22 . 
     To reinforce the ability of anti-bent of the thin blade, the blade flank  1  is integrally formed with several ribs  12  in the shape of camel hump protruding from the back of the blade flank  1 . One of the camel humps of the ribs  12  extends toward the tip portion  23  of the cutting edge to form a conic part  120 , providing a strong support for the cutting edge. This can compensate for the reduced strength due to thin blades. 
     The enforced rib  12  of each blade has several holes  121  or pins  122 . When two blades are combined back to back as shown in  FIG. 3 , the corresponding holes  121  and pins  112  are matched to firmly form a blade assembly for paper shredder. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.