Patent Publication Number: US-2007119504-A1

Title: Heat dissipating apparatus for cylinders of injection molding machines

Description:
CLAIMING FOREIGN PRIORITY  
      The applicant claims and requests a foreign priority, through the Paris Convention for the Protection of Industrial Property, based on a patent application filed in the Republic of Korea (South Korea) with the filing date of Nov. 28, 2005, with the patent application number 10-2005-0114097, by the applicant, the contents of which are incorporated by reference into this disclosure as if fully set forth herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates, in general, to cylinders of injection molding machines and, more particularly, to a heat dissipating apparatus for cylinders of injection molding machines, which includes both a piston bushing and a slide ring fitted around a valve pin of a cylinder piston, which dissipates heat, transferred from a manifold to the valve pin, to a cylinder housing defining the cylinder therein, and which uses air passing below the cylinder to cool both the valve pin and an inside guide bushing, thereby preventing leakage of resin from the cylinder.  
      2. Description of the Related Art  
      Generally, a cylinder of an injection molding machine has a piston and a valve pin therein, with a plurality of O-rings fitted around the piston to allow the valve pin to easily move while preventing leakage of resin.  
      Furthermore, a guide bushing is installed between a cylinder housing and a manifold, as shown in  FIG. 2 , so that the guide bushing can prevents leakage of resin from the manifold toward the valve pin.  
      A conventional valve pin guide bushing is provided with a groove in an upper part thereof such that the groove has a predetermined width, as shown in  FIG. 3 , so that air can pass through the groove and can cool the pin guide bushing.  
      However, the conventional valve pin guide bushing is configured such that the pin guide bushing is completely embedded in the manifold or in a nozzle, so that the pin guide bushing is undesirably maintained at a temperature equal to the temperature of the heated manifold or of the heated nozzle. Thus, when the manifold or the nozzle has been heated to a high temperature, a temperature difference exists between the valve pin and the pin guide bushing, thus forming an undesired gap between the valve pin and the pin guide bushing.  
      If such a gap is formed between the valve pin and the pin guide bushing, resin may leak through the gap.  
      In the related art, the pin guide bushing is securely embedded in the manifold or in the nozzle, while the valve pin is secured to the piston using an O-ring. Thus, when the valve pin is heated to a high temperature, the O-ring undesirably hardens, so that the O-ring may not perform the original function thereof, that is, a sealing function, resulting in a gap being generated and resin leaking through the gap.  
      In the related art, the O-ring of the valve pin frequently becomes deformed by heat as described above, so that the O-ring must be frequently repaired or exchanged with a new one. Due to the frequent exchange of the O-rings, work efficiency during an injection molding process is reduced. The conventional O-ring also complicates the internal construction of the piston.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a heat dissipating apparatus for cylinders of injection molding machines, in which a valve pin is securely mounted to a piston, a piston bushing is mounted to the valve pin and, thereafter, a piston ring is mounted to the valve pin.  
      Another object of the present invention is to provide a heat dissipating apparatus for cylinders of injection molding machines, in which a head of an inside guide bushing protrudes outside both a manifold and a nozzle such that the inside guide bushing comes into contact with an outside guide bushing, and the outside guide bushing comes into close contact with the cylinder housing, which is called a “mold base” in the related art, thus dissipating heat, transferred to both the manifold and the valve pin, to the cylinder housing and, furthermore, causing the heated inside guide bushing to be secondarily cooled by air actuating the piston.  
      In order to achieve the above objects, according to one aspect of the present invention, there is provided a heat dissipating apparatus for cylinders of injection molding machines, comprising: a piston installed in a cylinder, with a valve pin locking hole formed in the piston; a valve pin coupled to the valve pin locking hole of the piston, with a piston bushing fitted around an upper end of the valve pin, a slide ring fitted around the upper end of the valve pin at a predetermined position above the piston bushing, and a locking ring mounted to the valve pin locking hole at a position below the piston bushing; an outside guide bushing installed between a cylinder housing and a manifold, with both a protrusion and a groove formed on a lower surface of the outside guide bushing; an inside guide bushing installed in the outside guide bushing such that a head of the inside guide bushing protrudes outside an upper end of the outside guide bushing and is inserted into a locking hole of the cylinder housing, with the valve pin passing through the inside guide bushing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a side sectional view illustrating the construction of a cylinder of an injection molding machine having a heat dissipating apparatus according to the present invention;  
       FIG. 2  is a side sectional view illustrating the construction of a conventional cylinder of an injection molding machine; and  
       FIG. 3  is a perspective view schematically illustrating a conventional valve pin guide bushing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.  
       FIG. 1  is a side sectional view illustrating the construction of a cylinder of an injection molding machine having a heat dissipating apparatus according to the present invention.  
      As shown in  FIG. 1 , the heat dissipating apparatus for cylinders of injection molding machines according to the present invention comprises a piston  2 , which is installed in a cylinder  1 , with a valve pin locking hole  3  formed in the lower part of the piston  2 . A valve pin  4  is axially coupled to the valve pin locking hole  3  of the piston  2 . In the above state, a piston bushing  5  is fitted around the upper end of the valve pin  4 , while a slide ring  6  is fitted around the upper end of the valve pin  4  at a predetermined position above the piston bushing  5 . Furthermore, a locking ring  7  is mounted to the valve pin locking hole  3  at a position below the piston bushing  5 , thus supporting the piston bushing  5  in the valve pin locking hole  3  of the piston  2 . An outside guide bushing  10  is installed between a cylinder housing  8  and a manifold  9 . Both a protrusion  11  and a groove  12  are formed on the lower surface of the outside guide bushing  10 . An inside guide bushing  13  is installed in the outside guide bushing  10  such that the head of the inside guide bushing  13  protrudes outside the upper end of the outside guide bushing  10  and is inserted into a locking hole  14  of the cylinder housing  8 . The valve pin  4  passes through and is coupled to the inside guide bushing  13 . In the drawing, the reference numeral  15  denotes a cylinder cover.  
      The above-mentioned heat dissipating apparatus for cylinders of injection molding apparatuses according to the present invention will be operated as follows.  
      When the manifold  9  is heated during the operation of the injection molding machine, heat from the manifold  9  is transferred to the cylinder  1  through the valve pin  4 .  
      In the above state, because the inside guide bushing  13  is in contact with both the outside guide bushing  10  and the valve pin  4  at a predetermined position above the manifold  9 , the heat can be dissipated by being transferred to the cylinder housing  8  through the inside and outside guide bushings  10  and  13 . Thus, the heat dissipating apparatus of the present invention protects the cylinder  1  from the heat of both the manifold  9  and the valve pin  4 .  
      Described in detail, because the manifold  9  is in contact with the upper surface of the outside guide bushing  10 , heat from the manifold  9  is transferred to the cylinder housing  8 . Furthermore, the head of the inside guide bushing  13  is inserted into the locking hole  14  of the cylinder housing  8 , so that, when air is introduced into the locking hole  14  to actuate the cylinder  1 , the head of the inside guide bushing  13  can be cooled by the inlet air.  
      The valve pin  4 , which is coupled to the locking hole  3  of the piston  2 , is protected from heat by the piston bushing  5 , thus protecting the O-ring fitted around the piston  2  from thermal damage. Furthermore, the slide ring  6  is fitted around the upper end of the valve pin  4 , so that the valve pin  4  can be smoothly operated.  
      In the operation of the above-mentioned heat dissipating apparatus according to the present invention, the outside guide bushing  10 , which is in close contact with the inside guide bushing  13 , thermally expands to come into close contact with the cylinder housing  8 . Thus, heat, which may be transferred to the valve pin  4 , is transferred and dissipated to the cylinder housing  8 , so that no gap is formed between the inside guide bushing  13  and the valve pin  4 , thus preventing resin from leaking through the gap between the inside guide bushing  13  and the valve pin  4 .  
      As apparent from the above description, the heat dissipating apparatus for cylinders of injection molding machines according to the present invention provides advantages in that a valve pin is coupled to a piston, a piston bushing is coupled to the upper end of the valve pin, and a piston ring is mounted to the valve pin. The head of an inside guide bushing protrudes outside both the manifold and the nozzle and is inserted into a locking hole of a cylinder housing. The inside guide bushing is also in close contact with the outside guide bushing, which is in close contact with the cylinder housing. Thus, heat, transferred from both the manifold and the valve pin, is efficiently dissipated to the cylinder housing. Furthermore, the head of the inside guide bushing is secondarily cooled by air, which actuates the piston. The heat dissipating apparatus of the present invention has a simple construction, thus being produced through a simple production process. Furthermore, the valve pin is in close contact with an inside guide bushing, so that resin can be prevented from leaking.  
      Furthermore, in the present invention, both the inside guide bushing and the outside guide bushing thermally expand and come into close contact with the cylinder housing, thus efficiently sealing the gap between the pin guide bushings and the cylinder housing without using a conventional O-ring between the piston and the cylinder housing. Thus, the expected life span of the piston is maximized while the construction thereof is simplified. Furthermore, the present invention is free from the disadvantages caused by the conventional O-rings.  
      Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.