Abstract:
In a process for making a porous drainage medium composed of entangled strands of thermoplastic resin, subsequent to forming a tubular preform, the preform is formed with necked-down sections at intervals along the length thereof before proceeding to a cooling tank. As such, the drainage medium can be flexed in the cooling tank and can be discharged continuously and conveniently out of the cooling tank without being cut.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a process for manufacturing an extruded drainage medium, more particularly to the manufacture of a multi-sectional subsoil porous drainage pipe for applications in the field of civil engineering.  
           [0003]    2. Description of the Related Art  
           [0004]    As shown in FIG. 1, a conventional porous drainage pipe is fabricated from thermoplastic resin by extruding molten resin material to form a plurality of strands  2  that travel downwardly after exiting the extruder 1 . The strands  2  are led to a forming apparatus  3  for making a tubular preform  201 . While passing through the forming apparatus  3 , the strands  2  are in a plasticised or softened condition and are blown by a fluid of high velocity, so that the strands  2  will be entangled to form a matrix with sufficient structural strength and possessing water permeability after setting. The tubular matrix exiting the forming apparatus  3  will travel through a roll unit  4  to smoothen the outer diameter thereof, and will subsequently enter into a cooling tank (not shown) located below the roll unit  4 .  
           [0005]    Several disadvantages may be encountered in the above-described process for fabricating the porous drainage pipe. Particularly, when the preform  201  emerges from the tip rolls of the roll unit  4  and enters into the cooling tank, it becomes inflexible due to a sudden drop of temperature and forms a rigid pipe. Thus, the cooling tank must have a depth sufficient to receive a certain length of rigid pipe before cutting. Moreover, since the depth of the cooling tank is limited, the pipe has to be cut off after extending downward to a predetermined length.  
         SUMMARY OF THE INVENTION  
         [0006]    An object of this invention is to provide a process for fabricating a subsoil porous drainage medium which is capable of being delivered easily from a cooling tank.  
           [0007]    Another object of this invention is to provide a flexible, multi-sectional porous drainage medium consisting of a plurality of links connected by flexible necked-down sections which can be cut into pieces with a desired number of the links.  
           [0008]    According to the present invention, there is provided a process for making a porous drainage medium. The process includes the steps of: extruding a molten thermoplastic resin material to form a plurality of strands; blowing the strands in a plasticised condition using a high-velocity fluid to entangle the strands while passing the strands through a forming device, so as to result in a preform consisting of entangled strands; pinching the preform to form necked-down sections at intervals along the length of the preform, thus providing a plurality of links interconnected by the necked-down sections; and cooling the preform having the necked-down sections to form the porous drainage medium. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The above and other objects, features and advantages of the invention will become clear from the following description of the preferred embodiment with reference to the accompanying drawings:  
         [0010]    [0010]FIG. 1 is a fragmentary schematic partly sectional view illustrating a conventional process for the manufacture of a porous drainage pipe;  
         [0011]    [0011]FIG. 2 is a schematic view showing the preferred embodiment of a process for manufacturing a drainage medium according to the present invention;  
         [0012]    [0012]FIG. 3 is a perspective view showing a pinch device for forming necked-down sections on a tubular perform according to the present invention;  
         [0013]    [0013]FIG. 4 is a plan view showing the pinch device in an opened position with the preform disposed between a pair of die members;  
         [0014]    [0014]FIG. 5 is a plan view similar to FIG. 4 but showing the die members in a closed position;  
         [0015]    [0015]FIG. 6 is a schematic view showing an application of individual links of the drainage medium manufactured by the process of the present invention; and  
         [0016]    [0016]FIG. 7 is a schematic view showing another application of the drainage medium manufactured by the process of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    As stated hereinbefore, in the aforesaid conventional process for manufacturing drainage pipes, the melt blown preform directly travels to the cooling tank and becomes rigid therein. Therefore, the depth of the cooling tank is an important consideration associated with the movement of the preform.  
         [0018]    As shown in FIG. 2, the setup of this invention includes an extruder  100 , a forming apparatus  200  and a pinch device  300 .  
         [0019]    The early stages of the process according to this invention are similar to those of the prior art described hereinbefore. When the strands  10  exit the extruder  100 , they proceed to the forming apparatus  200  in a plasticized or softened condition. While passing through the forming apparatus  200 , the strands  10  are blown by a high-velocity fluid to result in a tubular preform  10 ′ constituted by a matrix of entangled strands  10 .  
         [0020]    Unlike the previously described prior art, after the preform  10 ′ exits the forming apparatus  200 , the preform  10 ′ travels through the pinch device  300  where it is pinched at intervals and is formed with necked-down sections  11 ′ along the length of the preform  10 ′. The diameter of the preform  10 ′ is thus reduced at the sections  11 ′ to such a degree to make the preform  10 ′ flexible at the necked-down sections  11 ′ after cooling and setting.  
         [0021]    Referring to FIG. 3, the pinch device  300  comprises a pair of movable die members  310 ,  320 , each including a driving rod  330 ,  340 . The opposing front edges of the die members  310 ,  320  are arcuately contoured to act as pinching faces  310 ′,  320 ′. During each stroke of the pinch device  300 , the movable die members  310 ,  320  reciprocate to move toward and away from each other between an open position shown in FIG. 4 and a closed position shown in FIG. 5. In the open position, the pinching faces  310 ′, 320 ′ are spaced apart from each other with a gap wider than the diameter of the preform  10 ′, while in the closed position, the die members  310 ,  320  overlap each other at the opposing edges thereof. In this way, reciprocation of the die members  310 ,  320  squeezes the softened wall of the tubular preform  10 ′ and forms one necked-down section  11 ′ during each stroke. The continuous tubular preform  10 ′ is thus formed into a multi-sectional drainage medium or drainage pipe  20  which looks like sausage in appearance, with oblong units or tubular links  21  interconnected by the necked-down sections  11 ′.The multi-sectional drainage pipe  20  with the successive links  21  is flexible due to the necked-down sections  11 ′, and can be flexed to change its direction of movement in a cooling tank  400 .  
         [0022]    Each individual tubular link  21  of the drainage pipe  20  has a first tapered end  23  and a second tapered end  24  opposite thereto. The contiguous ends of two tubular links  21  are connected by a necked-down section  11 ′ resulted from the pinching force exerted by the die members  310 ,  320 .  
         [0023]    Referring back to FIG. 2, after exiting the pinch device  300 , a first tubular link  21  of the drainage pipe  20  proceeds downwardly into the cooling tank  400  located directly below the pinch device  300 . The cooling tank  400  has an inclined side wall  401  in this embodiment, and the vertical distance between the pinch device  300  and the inclined side wall  401  of the cooling tank  400  is slightly longer than the length of each tubular link  21 . Therefore, as soon as a second tubular link  21  succeeding the first link  21  emerges from the pinch device  300 , the first tubular link  21  will turn to lie against the side wall surface of the cooling tank  400  upon contact. Therefore, dimensional constraints of the cooling tank  400  will be lifted.  
         [0024]    The preform  10 ′ discharged from the cooling tank  400  can be either wound into a coil, or cut at the necked-down sections  11 ′ into individual links  21 .  
         [0025]    [0025]FIG. 6 illustrates an application of the drainage pipe  20  made according to the present invention. The tubular links  21  of the drainage pipe  20  are buried in the land of mountain slope in parallel, with one end extending into the water-bearing stratum and the other end located nearby the land surface. Thus, water can be drained to the land surface through the tubular links  21  made of water permeable matrix.  
         [0026]    Another application of the drainage pipe  20  according to the present invention is illustrated in FIG. 7. The multi-sectional drainage pipe  20  is utilized by laying the same directly along a riverbank to prevent bank collapse.  
         [0027]    While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.