Method for blow molding

Abstract

An improved method for forming blow molded articles of enhanced physical characteristics by orienting the material during the formation of the article. A two-stage blowing operation is provided wherein a pre-form blow mold effects a uniform and controllable transfer of heat from a freely extruded tube. The pre-form is conditioned, both thermally and dimensionally, within the pre-form for most effective orientation during a subsequent final blowing operation. Manipulatively, the disclosed method provides a completely overlapped pre-blowing and final blowing operation, and more than one set of pre-blow and final blow molds may be utilized at a single extruder orifice, if desired. Further, the direction and extent of movement of the molds adapts the method to presently existing blow molding machines, while increasing the machine output. Successively utilized blow tubes form and reform the open or blowing end of the tube to a final configuration. In the manufacture of containers, the two successively utilized blow tubes form an accurate, dimensionally stable finish for a bottle while also severing any neck flash from the finish. .Iadd.

What is claimed is: 
     
       1. In a method of making a blown thermoplastic article having enhanced physical characteristics due to molecular orientation of the article during its formation, successively (1) extruding a tubular parison, (2) blowing the tubular parison into a pre-form which more closely approximates the shape of said article than did the extruded tube and (3) blowing the pre-form into the configuration of the final article and cooling said pre-form intermediate steps (2) and (3) above to an average wall temperature conducive to molecular orientation during the performance of step (3), the improvement comprising the steps of simultaneously closing a pre-form blow mold onto the parison and closing a final blow mold on a previously blown pre-form, simultaneously moving the closed molds, carrying the parison and blown pre-form, from the orifice to a blowing location, carrying out step (2) above in the closed pre-form mold at said blowing location, carrying out step (3) above in the final mold at said blowing location, simultaneously opening both molds while supporting the blown pre-form at said blowing location independently of the molds, and jointly moving the two open molds toward the orifice to repeat the method. 
     
     
       2. In a method of making a container or the like of thermoplastic material, the steps of extruding a freely pendant tube from an annular orifice, enclosing the tube in a pre-form blow mold positioned at said orifice and having an interior cavity, separating the enclosed tube from the orifice, shifting said mold-enclosed tube from the orifice, inserting a first blow tube into the mold-enclosed tube, blowing the tube to the shape of the pre-form mold cavity, opening the pre-form mold while supporting the blown pre-form on the blow tube, enclosing the blown pre-form in a final blow mold having an interior cavity conforming to the shape of the container, withdrawing the first blow tube, moving the pre-form enclosed in the final blow mold to a second and different blowing location, inserting a second blow tube into the pre-form and blowing the pre-form to the shape of the final container. 
     
     
       3. In a method of making a blown container of thermoplastic material, the steps of extruding a freely pendant tube from an annular orifice spaced from separate pre-form blowing and final blowing stations, consecutively blowing said tube into a pre-form and into a final container in separate pre-form and final blow molds positioned at said stations, respectively, reciprocating said molds in fixed spaced relation on a common movable support located generally beneath said orifice, the reciprocation of said support relative to said orifice simultaneously (1) moving the pre-form mold and the final blow mold toward the orifice, and (2) moving the pre-form mold carrying the tube and the final blow mold carrying the pre-form to their respective pre-form blowing and final blowing stations, opening said molds simultaneously prior to movement (1) of said support, closing said molds simultaneously prior to movement (2) of said support, and supporting said blown pre-form independently of either of said molds whenever said molds are both opened to retain the pre-form in position to be enclosed by said final blow mold upon completion of movement (1) of said support. 
     
     
       4. In a method of making a blown article of thermoplastic material, the steps of extruding a tube, enclosing a portion of said tube in a pre-form blow mold while the tube is located at the extrusion location, separating the mold-enclosed tube portion from the orifice, transferring the mold-enclosed tube portion to a first blowing location, inserting a blow tube into said mold-enclosed tube portion, blowing the tube portion into a pre-form, opening the pre-form blow mold while supporting the pre-form on the blow tube, moving the pre-form mold back to the extrusion location, enclosing the blow tube-supported pre-form in a final blow mold, transferring the blown pre-form interiorly of the final blow mold to a second blowing location, blowing the pre-form interiorly of the final blow mold, opening the final blow mold to expose the final blown article, and returning the final blow mold to said first blowing location. 
     
     
       5. In a method of blow molding a thermoplastic article, the steps of extruding a freely pendant tubular parison at a parison location, the extrusion of said parison being performed while a previously extruded parison is enclosed in a pre-form mold at a pre-blowing location and while a previously formed pre-blown shape is enclosed in a final blow mold at a final blowing location, simultaneously blowing both said parison and said pre-form by inserting blow pipes therein, respectively, simultaneously opening said pre-blow mold and said final blow mold while retaining the pre-blown shape in position on said blow pipe at said pre-blow location, transferring the open pre-blow mold and final blow mold from their respective locations toward said parison, closing the pre-blow mold on said parison and closing the final blow mold on said pre-blown shape, withdrawing the blow pipe from said pre-blown shape, simultaneously moving the pre-blow mold and the enclosed parison and the final blow mold and the enclosed pre-blown shape to said pre-blow location and said final blowing location, respectively, and finally blowing said parison at said pre-blow location interiorly of said pre-blow mold to the pre-blown shape and blowing the pre-blown shape interiorly of the final blow mold to the final blown configuration. 
     
     
       6. In a method blowing a thermoplastic article, the steps of extruding a freely pendant tubular parison at a parison location, simultaneously with the extrusion of said parison performing the steps of (1) blowing a previously extruded parison at a pre-blowing location to a pre-blown shape and (2) blowing a previously formed pre-blown shape to a final blown configuration at a final blowing location, said steps (1) and (2) being performed in a pre-blow mold and a final blow mold, respectively, simultaneously opening said pre-blow mold and said final blow mold while retaining the pre-blown shape in position at said pre-blow location, transferring the open pre-blow mold and final blow mold from their respective locations toward said parison, closing the pre-blow mold on said parison and closing the final blow mold on said pre-blown shape, simultaneously moving the pre-blow mold and the enclosed parison and the final blow mold and the enclosed pre-blown shape to said pre-blow location and said final blowing location, respectively, and finally blowing said parison at said pre-blow location interiorly of said pre-blow mold to the pre-blown shape and blowing the pre-blown shape interiorly of the final blow mold to the final blown configuration. 
     
     
       7. In a method of blow molding a thermoplastic article, the steps of extruding a freely pendant tube from an annular orifice spaced from separate pre-form and final blow molds shiftable towards and away from the orifice, shifting the pre-form blow mold into alignment with said orifice while shifting the final blow mold toward the orifice, closing the pre-form blow mold on the tube while closing the final blow mold on a previously blown preform supported on a blow pipe in spaced relation to the orifice, withdrawing said blow pipe, shifting said mold-enclosed tube and said mold-enclosed pre-form from the orifice, inserting blow pipes into the mold-enclosed tube and the mold-enclosed pre-form, blowing the tube to the shape of a pre-form mold, blowing the pre-form to the shape of the final article, opening both molds while supporting the blown pre-form on a blow pipe, and shifting both blow molds toward the orifice to repeat the method. .Iadd. 8. In a method of blow molding a thermoplastic article, the steps of: (1) extruding a freely pendant tubular parison from an annular orifice,   (2) blowing the tubular parison in a first blow mold to a pre-form which more closely approximates the shape of said article than did the extruded parison,   (3) blowing the pre-form in a second blow mold to the configuration of the final article,   (4) jointly reciprocating said first and second blow molds so that the two blow molds are collectively movable to a total of three stations, only the first mold being movable to a first of said stations at which step (1) above is carried out, only the second mold being movable to a second of said stations spaced from said first station, and both of said blow molds being movable to a third station which is intermediate said first and second stations, two of said stations being blowing stations at which steps (2) and (3) above are carried out,   (5) substantially simultaneously (a) closing said first mold onto said parison at the first station and (b) closing said final blow mold onto a previously blown pre-form at the third station,   (6) substantially simultaneously (a) moving the closed first mold from the first station to the third station and (b) moving the closed second mold from said third station to said second station;   (7) substantially simultaneously (a) opening said first mold at the third station to expose a blown pre-form and (b) opening said final blow mold at the second station to expose a final blown article,   (8) substantially simultaneously and preparatory to repeating step (5) above (a) returning the open first mold to said first station and (b) returning the open second mold to said third position,   (9) supporting said pre-form at said third station independently of both the first and second molds during the performance of steps (7) and (8) above, and   (10) performing steps (2) and (3) above intermediate the performance of   
     
     
        steps (5) and (7) above. .Iaddend..Iadd. 9.  In a method of making a blown plastic article by successive blow molding operations carried out in separate sectional pre-form and final blow molds carried by a common support reciprocable to two positions relative to an extrusion station, the steps of: (1) moving said support to a first position with the sectional blow molds both open, the pre-form mold being aligned with a parison depending at the extrusion station and the final mold being aligned with a blown pre-form pendantly suspended at a second station; (2) closing both molds; (3) moving said support with both molds closed to position the pre-form mold at said second station and to position the final mold at a third station; (4) while said molds are closed, blowing the parison to the configuration of the pre-form blow mold and blowing the blown pre-form to the configuration of the final blow mold; (5) opening both said molds after the performance of step (3) to expose the blown pre-form at the second station and to expose the final blown article at said third station; (6) repeating step (1) preparatory to the next blowing cycle; and (7) pendantly suspending the blown pre-form at said second station from a blow pipe during the performance of steps (5) and (6). .Iaddend..Iadd. 10. In a method of blow molding plastic articles, the steps of: (1) extruding a parison at a first station; (2) closing a pre-form blow mold on said parison at said first station; (3) closing a final blow mold on a previously blown parison at a second station; (4) moving the closed pre-form blow mold to said second station and moving said closed final blow mold to a third station; (5) blowing the pre-form in said closed pre-form blow mold and blowing the final article in said closed final blow mold; (6) opening the pre-form blow mold at said second station while supporting the blown pre-form independently of said pre-form blow mold; (7) opening the final blow mold at said third station to release the final blown article therefrom; and (8) returning the open pre-form mold to the first station and returning the open final blow mold to said second station, preparatory to the next cyclic performance of steps (2) and (3) at said first and second stations respectively. .Iaddend.