Patent Publication Number: US-2009236777-A1

Title: Method for Manufacturing Bicycle Crank

Description:
CROSS REFERENCE 
     The present application is a continuation-in-part application of U.S. patent application Ser. No. 11/762,753, filed on Jun. 13, 2007, of which the entire disclosure is incorporated herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for making a crank. 
     2. Description of the Related Art 
     It is a current trend to make a bicycle crank from carbon-fiber composite material. 
     A carbon-fiber bicycle crank generally has a five communication tube connected to each end thereof. However, connections therebetween are not good due to that the carbon fiber composite material is very hard and brittle. To strengthen the structure, the crank generally has metal tubes mounted at pivotal connections. Furthermore, carbon-fiber sheets are adhered on the crank to fix the metal tubes with the crank. 
     To that end, the conventional crank often suffers a structure defect, and it is time consuming during manufacturing. Another problem is that the interior of the crank must be formed with supporting blocks for adhering operation and this incurs increased weight to the crank. Also, when the crank is complete, the metal tubes are buried. However, connection of the crank with the two metal tubes is not solid and strong. Although adhesive is used to increase the connection, the adhesive suffers a problem of buckling. Furthermore, it is difficult to prepare the adhesive. 
     The present invention is, therefore, intended to obviate or at least alleviate the problems encountered in the prior art. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a method for making a crank of a bicycle includes steps 1) preparing a prepreg material and a bladder in a cavity of a mold insert, with the bladder buried in the prepreg material. 2) heat-pressing the prepreg material and the bladder to inflate the bladder and cause the prepreg material to compactly fit with the shape of the cavity. 3) cutting the prepreg material to form two engaging sections. 4) Tight-fitting a first connector with the engaging section and a second connector with the engaging section, respectively. 5) wrapping a carbon-fiber cloth to cover up the prepreg material and the first and second connectors. 6) heating the prepreg material and the first and second connectors that are wrapped by the carbon-fiber cloth in order to snugly attach the carbon-fiber cloth  40  to the prepreg material and first and second connectors. 
     It is an object of the present invention to provide a method for making a light-weight, strong crank against buckling. 
     It is a further object of the present invention to provide a method for making an economical crank. 
     It is yet another object of the present invention to provide a simple method for making a crank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart of a method for making a crank in accordance with the present invention. 
         FIG. 2  is cross-sectional view showing a bladder and a prepreg material mounted in a mold insert, with the bladder disposed inside the prepreg material. Additionally, the bladder has a mouth and a valve is connected at the mouth. 
         FIG. 3  is a cross-sectional view showing the bladder and the prepreg material subject to a heat-pressing process. 
         FIG. 4  is a side view of the prepreg material after the heat-pressing process. 
         FIG. 5  is a side view showing both the prepreg material and the bladder cut to form two engaging sections on two ends thereof. 
         FIG. 6  is a side view showing two connectors utilized for engaging with the two engaging sections respectively. 
         FIG. 7  is a side view showing the connectors fitted in the engaging sections. 
         FIG. 8  is a side view showing a carbon-fiber cloth for wrapping an outer periphery of the prepreg material and the connectors. 
         FIG. 9  is a side view showing the prepreg material and the connectors wrapped by the carbon-fiber cloth. 
         FIG. 10  is a cross-sectional view showing the wrapped prepreg material and connectors subject to a heating process. 
         FIG. 11  is a perspective view of the crank in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  shows a prepreg material  10  and a bladder  11  for making a crank of the present invention. The prepreg material  10  and the bladder  11  are mounted in a cavity  2  of a mold insert  1 . The mold insert  1  may be configured of two complemently fitted mold inserts, and the cavities  2  of the respective mold inserts  1  are configured to correspond with each other. Additionally, the bladder  11  is buried in the prepreg material  10  and the prepreg material  10  leaves a gap  12  with a minimum size to allow a mouth  13  of the bladder  11  to expose outside the prepreg material  10 . Preferably, the gap  12  is with a size such that an outer periphery of the mouth  13  is in contact with the prepreg material. Further, the prepreg material  10  and the bladder  11  may have a first space  14  therebetween at this stage. Furthermore, the prepreg material  10  any the cavity  2  may have a second space  15  therebetween at this stage. Moreover, a valve  3  may be connected at the mouth  13  of the bladder  11  to facilitates the bladder  11  to connect with an air supply 
       FIG. 3  shows the prepreg material  10  and the bladder  11  subject to a heat-pressing process. Upon the heat-pressing process, the bladder  11  is inflated by air until the first space  14  is eliminated, and thus the bladder  11  is compactly fitted with the prepreg material  10 . Also, the prepreg material  10  is inflated by the bladder  11  until the second space  15  is eliminated, and thus the prepreg material  10  is compactly fitted with the shape of the cavity  2 . 
       FIG. 4  shows that the prepreg material  10  removed from the mold insert  1  after the heat-pressing process. After the heat-pressing process, the prepreg material  10  becomes solid and the bladder  11  is snugly retained with an inner periphery of the prepreg material  10 . 
       FIG. 5  shows that the prepreg material  10  and the bladder  11  cut to form two engaging sections  16  and  17 . The two engaging sections  16  and  17  are utilized to receive a first connector  20  and a second connector  30  respectively, as shown in  FIG. 6 . The first  20  and second  30  connectors are utilized to connect with a transmission gear of a bicycle (not shown) and a pedal (not shown), respectively. It is understood that rider can operate the pedal to turn the crank and the crank can control rotation of the transmission gear. Additionally, the first  20  and second  30  connectors are preferably made of metal. Further, the first  20  and second  30  connectors are tight-fitted with the two engaging sections  16  and  17 , respectively, as shown in  FIG. 7 . In the preferred embodiment, the first connector  20  includes a protrusion  21  and the engaging section includes a recess  131  for tightly engaging with the protrusion  21 . Likewise, the second connector  30  includes a protrusion  31  and the engaging section  14  includes a recess  141  for tight-engagement with the protrusion  31 . 
       FIG. 8  shows that a carbon-fiber cloth  40  is utilized for wrapping the prepreg material  10  and the first  20  and second  30  connectors, so the prepreg material  10  and the first  20  and second  30  connectors are covered up by the carbon-fiber cloth  40 , as shown in  FIG. 9 . 
     After the carbon-fiber cloth  40  is wrapped, the crank is subject to a heating process. Preferably, the crank is mounted in the mold insert  1  during the heating process. After the heating process, the carbon-fiber cloth  40  is snugly attached to the prepreg material  10  and the first  20  and second  30  connectors, as shown in  FIG. 10 . Additionally, the final product of the crank is shown in  FIG. 11 . 
     Referring to  FIG. 1 , a flow chart of a method for making a crank in accordance with the present invention includes 1) preparing a prepreg material  10  and a bladder  11  in a cavity  2  of a mold insert  1 , with the bladder  11  buried in the prepreg material  10 . 2) heat-pressing the prepreg material  10  and the bladder  11  to inflate the bladder  11  and cause the prepreg material  10  to compactly fit with the shape of the cavity  2 . 3) cutting the prepreg material to form two engaging sections  16  and  17 . 4) tight-fitting a first connector  20  with the engaging section  16  and a second connector  30  with the engaging section  17 , respectively. 5) wrapping a carbon-fiber cloth  40  to cover up the prepreg material  10  and the first  20  and second  30  connectors. 6) heating the prepreg material  10  and the first  20  and second  30  connectors that is wrapped by the carbon-fiber cloth  40  in order to snugly attach the carbon-fiber cloth  40  to the prepreg material  10  and first  20  and second  30  connectors. 
     While the specific embodiments have been illustrated and described, numerous modifications are possible without significantly departing from the spirit of invention, and the scope of invention is limited only by the scope of the accompanying claims.