Abstract:
A method for continuously forming molded parts includes providing an extruder; directing a hollow column of plastic material from the extruder; providing a plurality of die blocks each including planar end segments having differing geometry and joined by the intermediate convoluted segments; continuously moving such die blocks for receiving and forming the hollow column into strut boots with planar end segments and intermediate convoluted segments and advancing the shaped column of plastic material from the continuously moving die blocks and providing a cutter synchronized to the movement of the shaped column for separating the planar end segments to form one or more parts having planar end segments of the same or differing geometry in each part or with differing geometry from part to part.

Description:
This invention relates to methods for corrugating parts and more particularly to methods for corrugating strut boots having planar end segments joined by an intermediate corrugated segment. 
     BACKGROUND OF THE INVENTION 
     Methods for corrugating hollow parts are known in which an extruder directs a hollow column with respect to moveable die blocks that shape the hollow column end to end with a plurality of convolutions. 
     Examples of such molded parts and methods are shown in U.S. Pat. Nos. 3,843,758, 4,319,872, 4,439,130, 4,718,844 and 5,531,583. In the past such molded parts have utilized a mold part that involves formation of a plurality of convolutions end to end of the mold block such that the resultant molded part is a corrugated tube suitable for use in irrigation and other like applications. 
     It is also known to separately mold strut boots and the like that include planar end segments for connection to stationary and moveable members and wherein a plurality of convolutions are formed between the planar end segments for providing for relative movement between the stationary and moveable parts to which the strut boot is attached are formed by one or more molding steps. 
     While suitable for their intended purpose none of the aforesaid prior art methods are able to meet cost and product rate objectives suitable for meeting the cost requirements of motor vehicle manufacturers and other customers requiring high quality, and low cost parts. 
     SUMMARY OF THE INVENTION 
     According to the present invention these objectives are met by a method for continuously forming molded parts including providing an extruder, directing a hollow column of plastic material from said extruder; providing a plurality of die blocks each including planar end segments having differing geometry and joined by intermediate convoluted segments; continuously moving such die blocks for receiving and forming the hollow column with planar end segments and intermediate convoluted segments and advancing the shaped column of plastic material from the continuously moving die blocks and providing a cutter synchronized to the movement of the shaped column for separating the planar end segments to form one or more parts having planar end segments of the same or differing geometry in each part or with differing geometry from part to part. 
     An object of the invention is to provide a process in which such planar end segments are formed with identical geometry and wherein a continuous molded extrusion shape is passed from the moveable mold blocks having a repeating pattern A-B-C-A-B-C defined by the expression (A-B-C) n . 
     A further object of the invention is to provide a process wherein the end segments are formed with differing geometries and wherein the continuous molded extrusion has a repeating pattern A-B-C-C′-B-A-A-B-C-C′-B-A defined by the expression (A-B-C-C′-B-A) n . 
     Yet another feature of the invention is to provide extrudent material for the aforesaid process that is a thermoplastic flexible synthetic polymer such as thermoplastic vulcanizates (TPV&#39;s); thermoplastic polyolefins (TPO&#39;s); ionomer resins, such as Surlyn; flexible PVC resins; thermoplastic elastomers (TPE&#39;s); flexible polyurethane polymers and the base is a rigid thermoplastic such as polypropylene; filled polypropylene; talc-filled polypropylene; polyethylene; high density polyethylene; polystyrene; PVC resins; ABS resins; TPO resins; Nylon resins; Metallocene polymers or a flexible thermoplastic material such as thermoplastic vulcanizates (TPV&#39;s); thermoplastic polyolefins (TPO&#39;s); ionomer resins, such as Surlyn; flexible PVC resins; thermoplastic elastomers (TPE&#39;s); flexible polyurethane polymers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of apparatus for practicing the present invention; 
     FIG. 2 is an enlarged perspective view of a plurality of mold blocks used in the process of the present invention; 
     FIG. 3 is an enlarged side elevational view, partially sectioned, of a part made by the process of the present invention; 
     FIG. 4 is an enlarged side elevational view of mold blocks used in another embodiment of the process of the present invention; and 
     FIG. 5 is an enlarged side elevational view, partially sectioned, of another embodiment of a part made by the method of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to FIG. 1, an extruding machine  10  is arranged to continuously extrude and feed a tube  12  of hot plastic material to a corrugating machine  20 . The corrugating machine includes two sets of moveable mold tracks  30 ,  32  constructed in accordance with the present invention to be respectively driven by vertically spaced concepts  31 ,  33  whereby a continuously formed hollow molded extruded part  14  is directed from the blow molding machine having spaced groups or sets of convolutions  15  separated from each other by planar segments  16 ,  18  having the same or differing geometry and joined to one another as the hollow molded extruded part moves from the blow molding machine. 
     The machine  20  has known sources of compressed heated air  22  that is directed into the tube  12  as it passes through the machine  20 , the air heat expands and shapes the tube  12  against the surface of the mold cavities; can be either blown or vacuum or combination of both. Such shaping molds the annular sets of convolutions  15  and planar end segments  16 ,  18  along the length of the tube  12  as it moves from the blow molding machine or corrugator  20 . 
     FIG. 3 represents a strut boot as one typical embodiment of an elastic shaped article according to the present invention. In the diagram, a strut boot  26 . In the strut boot,  26   a  denotes the bellows portion  15  and  26   b ,  26   c  the connecting end portions. 
     The elastic shaped article according to the present invention is useful for the production of boots, ducts, hoses, tubes, other sealing members, covering members and so on which are expected to possess elasticity and oil resistance. Such articles are of the type used in motor vehicles such as automobiles and suvs (sports utility vehicles), snowmobiles, construction machines such as bulldozers, industrial machines such as robots, machine tools, hydraulic machines and pneumatic machines. 
     Depending on the particular use to which the elastic shaped article according to the present invention is put; the hardness of the article may be suitably selected without departing from the spirit of the invention. When the elastic shaped article is used in automotive boots such as shock absorber boots, rack and pinion steering gear boots, suspension strut boots and constant velocity joint boots, it acquires high mechanical strengths and high elastic recovery of bellows, the properties ideal for automotive boots, by fixing the hardness of the TE above the level of 60 by the Shore A scale, the hardness of the soft PVC below the level of 87 by the Shore A scale, and the overall wall thickness ratio of the TE layer to the soft PVC layer in the range of 50:50 to 0.5:99.5. Thus, the boots neither sustains cracks under impacts exerted by flying pebbles nor suffers from separation of joined ends owing to loss of elasticity but are permitted to manifest the features of this invention. 
     In the embodiment of FIGS. 2 and 3 the corrugator  20  includes two sets of a plurality of die blocks  30   a - 30   j  moved on conveyor tracks  31 ,  33  to open and close to form a continuously advancing mold. One of the sets is shown in FIG. 2 with it being understood that a like set is provided that is joined and separated by the conveyors  31 ,  33  to form a mold surface against which the extruded tube  12  is expanded by heated air to continuously blow mold a series of strut boots  26  shown in FIG.  3 . The die blocks  30   b - 30   i  combine to form repeating semi-circular die surfaces generally designated  30   k . The die surfaces  30   k  include spaced sets of alternating ribs and valleys  30   l ,  30   m  joined by end geometry surfaces defined by cavities  30   n ,  30   o.    
     As the tube of hot plastic material is extruded into the rear portion of the blow molding zone, heat compressed air  22  or other fluid under pressure is introduced into the tube to expand the same against the mold cavity  30   k , and thereby mold annular corrugations of alternating ribs and valleys along the length of the tube and the surfaces at cavities  30   n ,  30   o . Also, as is well known, the moving die blocks  30   a - 30   j  are driven in two endless paths by suitable drive means shown schematically at  35  in FIG. 1, which drive means  35  continuously moves the cooperating sets of die blocks on the conveyors  31 ,  33  forwardly along the blow molding zone to deliver the molded corrugated plastic tube  14  forwardly at a predetermined speed. 
     An enlarged view of a portion of the corrugated tube  14  is shown in FIG. 3 wherein it will be observed that the valleys and ribs of the tube  14  are respectively designated at  26   d ,  26   e . The tube may be of lightweight construction preferably with a wall thickness of no greater than about 0.060 inch and may be of a nominal diameter of about 0.040 inches. A tube having a four-inch nominal diameter, for example, may have an internal diameter of about 2.70 inches measured at the interior of the valley  26   d , and an external rib diameter of 3.25 inches. Also, by way of example, the tube may include about 12 ribs per linear foot, with each rib  26   e  having a width of approximately ½ inch, the height of each rib when measured from the annular valleys  26   d  being about 0.26 inch, and the width of the annular valleys taken between the junctures of the side walls of the adjacent ribs  26   e  being about 0.50 inch. 
     The embodiment shown in FIG. 3 includes a mold forming the same part suitable for use in a single application; the complete die mold has two sets of end segments  30   n ,  30   o  formed on either end of two sets of ribs and valleys  30   l ,  30   m . When the die molds are joined by being advanced continuously in the corrugator  20 , they form cavities that define two parts  26 . The parts  26  each have planar end connections  26   b ,  2   c , respectively. The end connections  26   b  have the same planar geometry and are suited for connection to the end of one strut boot application and the ends  26   c  have the same planar geometry suitable for connection to the opposite end of the one same strut boot application. The tube  12  once molded to the aforesaid shape will have a continuous, molded extrusion, generally designated  14  in FIG. 1, that will be directed from the corrugator  20  to a cooling tank  35  thence to a dryer  55  and to a cutter  60  that is programmable to be synchronized to the speed of the molded extrusion as it is moved by a conveyor  55   a  in dryer  55  and operative to cut the continuously advancing molded extrusion  14  at joints  25  formed between the end connections  26   b ,  26   c . The separated parts  24 ,  26  are then segregated from the scrap  28  trimmed by the cutter at a separator  65 . For purposes of definition the segment  26   b  can be defined as a part segment A constituting a non-convoluted geometry in the molded part  26 ; the convolutions  26   a  can be defined as a part segment B of shaped elastic material and segment  26   c  can be defined as a part segment C constituting a non-convoluted geometry in the molded tube  14  of the same geometry of part segment A. In such case, the continuous molded tube  28  has repeating segments A-B-C-A-B-C, etc defined by the following formula: 
     
       
         (A-B-C) n   
       
     
     However, it is more common that the ends of a part are not identical and that the design of the tooling and the process are enhanced when common elements are adjacent to each other for example, the end segments of smaller diameter in different parts are joined and the end segments of larger diameter are joined. In such case, shown in FIG. 5, end segments  42   a ,  44   a  are joined by convolutions  46 . The part segment  42   a  can be defined as part segment A and the part segment  44   a  can be defined as part segment C. In this embodiment the part segment C for one part differs slightly from another part and will be referred to as C′. In such case, a continuously molded tube  48  has repeating segments A-B-C-C′-B-A-A-B-C-C′-B-A, etc defined by the following formula: 
     
       
         (A-B-C-C′-B-A) n   
       
     
     As in the case of the first embodiment, this configuration is formed by a plurality of mold blocks shown in FIG. 4, they combine to form a mold half  50  having a tubular planar segment  52  with a reduced diameter segment  52   a . The reduced diameter segment is in communication with spaced semi-annular cavities  54  having valleys  56  and ridges  58  shaped to form one half of the convolutions  46  in the part shown in FIG.  5 . The mold part  50  further includes a convergent segment  60  that is joined to a semicircular portion  62  of reduced diameter to that of the tubular planar segment  52 . The semicircular diameter portion  62  is joined to a second convergent segment  64  that merges with a radially inwardly located small diameter segment  66  of the mold half  50 . The small diameter segment  66  merges with a generally vertically disposed wall segment  68  that merges with a semicircular surface  70  having a diameter similar to that of the portion  62 . The mold half  50  includes a outwardly divergent semi-annular surface  71  that is joined to spaced semicircular cavities  72  having valleys  74  and ridges  76  to form one half of the convolutions  46  in the part shown in FIG.  5 . The mold half  50  terminates at its opposite end in a semicircular surface  78 . When like mold halves are joined in the corrugator  20  they define the surfaces of the part  48  shown in FIG.  5 . 
     As in the first embodiment, the process includes the steps of extruding a hollow tube of thermoplastic material; providing mold halves having surfaces with the formula (A-B-C-C′-B-A) n ; shaping a tube  12  of heat thermoplastic material against the aforesaid surfaces of the joined mold halves  50  (one shown in FIG.  4 ); continuously feeding a molded tube  48  having ends and convolutions with the formula (A-B-C-C′-B-A) n  from the corrugator  20 ; passing the molded tube  48  through a cooling tank and a dryer then cutting the molded tube  28  between the segments C-C′ to form separated elastic convoluted parts of either the same or differing end connection configurations. 
     Another embodiment is wherein the mold halves are configured with differing geometries and wherein the continuous molded extrusion has a repeating pattern A-B-C-C-B-A-A-B-C-C-B-A defined by the expression (A-B-C-C-B-A) n .