Abstract:
A hot runner ( 10 ) is provided including a canal ( 11 ) and a heat-shrinkable tube ( 12 ) covering on the canal ( 11 ). The heat-shrinkable tube ( 12 ) can shrink along the canal ( 12 )&#39;s contour when heated. The present invention further provides a mold ( 20 ) using the hot runner.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to hot runners and, particularly, to a hot runner used in a mold assembly. 
         [0003]    2. Description of Related Art 
         [0004]    Insert molding technology using molding machines is a popular molding method. A typical molding machine usually includes a hot runner, a male mold and a female mold. The male mold and the female mold define a mold cavity therebetween. The male mold has a passage defined therein, communicating with the mold cavity. The hot runner is inserted into the passage. Thus, melted plastic can be injected into the mold cavity through the hot runner. 
         [0005]    To prevent the melted plastic from leaking out of a combining aperture between the hot runner and the passage, a vertical surface is formed on the outside of the hot runner. The vertical surface is an outer peripheral surface surrounding the longitudinal axis of the hot runner. Correspondingly, the passage has a cooperating surface. The vertical surface is tightly attached to the cooperating surface, thus preventing leakage of melted plastic. 
         [0006]    However, after repeated usage, a gap may appear between the vertical surface and the cooperating surface because of abrasion, high temperature, and high pressure. Thus, melted plastic may leak to the outer surface of the hot runner, resulting in damaging other elements, i.e., the heating coil and the temperature-sensing equipment. 
         [0007]    Thus, there is room for improvement within the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the hot runner and the mold assembly can be better understood with reference to the following drawings. These drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present hot runner and the mold assembly. Moreover, in the drawings like reference numerals designate corresponding parts throughout the several views. 
           [0009]      FIG. 1  is a disassembled cross-sectional view of a hot runner, according to an exemplary embodiment. 
           [0010]      FIG. 2  is a cross-sectional view of a mold assembly. 
           [0011]      FIG. 3  is a cross-sectional view of the mold assembly engaging with the hot runner. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0012]      FIG. 1  shows an exemplary hot runner  10 . The hot runner  10  includes a canal  11  and a heat-shrinkable tube  12 . 
         [0013]    The canal  11  is a hollow tube. The canal  11  defines a channel  111  in the center portion therethrough, and includes a sprayer  112  disposed at one distal end thereof, and a heat insulating layer  113  attached to and covering an outer periphery of the sprayer  112 . The sprayer  112  is tapered. The heat insulating layer  113  is also tapered, and configured to insulate the hot runner  10  and a mold assembly  20  (referring to  FIG. 2 ) for preventing heat transmission from the hot runner  10  to the mold assembly  20 . The canal  11  has a vertical surface  114  adjacent to the heat insulating layer  113 . The vertical surface  114  is an outer peripheral surface surrounding the longitudinal axis of the hot runner  10 , and has a high machining precision. A heater  115  is positioned on the outside of the other end of the canal  11  opposite to the sprayer  112 . The heater  115  provides heat to the canal  11  to maintain good flowing of melted plastic in the channel  11 . 
         [0014]    The heat-shrinkable tube  12  is made of a macromolecular material having different states when at different temperatures, such as polyvinylchlorid (PVC) and etc. At room temperature, the heat-shrinkable tube  12  is in a glass state. At elevated temperatures, the heat-shrinkable tube  12  may shrink and become elastic. When in the glass state, the heat-shrinkable tube  12  has properties similar to plastic. When in the elastic state, the heat-shrinkable tube  12  has properties similar to rubber. Therefore, when heated, the heat-shrinkable tube  12  changes from the glass state to the high-elastic state and automatically shrinks in volume. 
         [0015]    Referring to  FIG. 3 , when assembling the hot runner  10 , the heat-shrinkable tube  12  covers the vertical surface  114  of the canal  11 , and receives the heat insulating layer  113  therein. The heater  115  is then electrified by a power source (not shown) to generate heat, thereby causing the heat-shrinkable tube  12  to shrink and tightly attach to the contour of the heat insulating layer  113  and the vertical surface  114 . 
         [0016]    Referring to  FIG. 2  again, a mold assembly  20  includes a male mold  21  and a female mold  22 . The male mold  21  and the female mold  22  cooperatively form a mold cavity  23  therebetween. The male mold  21  defines a passage  24  communicating with the mold cavity  23 . The passage  24  is configured for receiving the hot runner  10 . The passage  24  has an inner wall, including a tapered surface  241 , a cooperating surface  242  and a limiting surface  243 . 
         [0017]    Referring to  FIG. 3  again, when mounting the hot runner  10  to the mold assembly  20 , the hot runner  10  is inserted into the passage  24  of the mold assembly  20 . The heat-shrinkable tube  12  abuts against the tapered surface  241 . The cooperating surface  242  cooperatively engages with the vertical surface  114 . A periphery wall of the heater  115  is limited by the limiting surface  243 . The heat-shrinkable tube  12  can fill in the gap between the cooperating surface  242  and the vertical surface  114  and the gap between the heat insulating layer  113  and the tapered surface  241 , thus preventing leakage of melted plastic. 
         [0018]    It is to be understood, however, that even through numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of sections within the principles of the invention to the full extent indicated by the broad general meaning of the terms, in which the appended claims are expressed.