Closed cell foam plastic molding machine

Abstract

Plastic molding machine, primarily adapted for generating and molding a closed-cell foam plastic material. The foam is generated by introducing a gas inert to the plastic material into a granular mixture of same so that the gas is thoroughly intermixed among the granular particles. The gas is then held under pressure while the granular particles are reduced to a flowable material, said pressure being sufficient to assure that the gas will not be expelled therefrom during the plasticization process. In one preferred embodiment, gas is mixed into the granular plastic in a hopper and held therein under pressure as said granular material is fed into a screw and plasticized thereby. The plastic material is then conducted at a relatively low pressure, such as that generated by the extrusion machine used for plasticizing the material, through a branched system past a check valve in each branch of said system, to an injection assembly. As each injection assembly receives a predetermined amount of plastic material, means are energized preventing more plastic material from entering thereinto but continued operation of the pressure generating device will continue filling other injection assemblies for as long as any thereof are capable of receiving such material. When all injection assemblies are filled, same are actuated simultaneously to drive the plastic material therefrom into the mold cavity. Injection assemblies may supply mold cavities in any pattern, and a single mold cavity may be associated with a given injection assembly or two or more injection assemblies may supply any one given mold cavity. Local zones, preferably subjected to rapid cooling, are provided with undercut notches connected to the sprue, runners or cavity and filled thereby with plastic. Same is cooled ahead of the cooling of the molded part and provides means for holding the mold closed. This permits removal of the mold from the machine prior to cooling of the molded part and opening of the mold which in turn permits more effective use of multiple molds with a given machine.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a plastic foaming and molding device, the combination comprising: a plasticizing and foaming unit for receiving granular plastic material, said unit including means for causing a gas under pressure to permeate said material, and means for converting the material to plasticized foamed plastic material with said gas entrained therein as bubbles;   a plurality of injection assemblies, each comprising an injection chamber having an injection ram;   plural low pressure passageways providing communication from said plasticizing unit to corresponding ones of said injection assemblies;   power means .Iadd.operatively connected to and .Iaddend.continuously operating said plasticizing unit for charging a continuous supply of said foamed plastic material into said low pressure passageways at a predetermined, relatively low pressure;   means defining a one-way valve positioned in each said low pressure passageway to permit flow of said foamed plastic material from said unit to the injection chamber of the corresponding injection assembly but preventing reverse flow from said injection chamber toward said unit and other injection assemblies;   plural high pressure passageways .Iadd.downstream of said low pressure passageways .Iaddend.for conducting said foamed plastic material from each of said injection chambers to a mold cavity and an on-off valve positioned in each said high pressure passageway;   control means .Iadd.operatively interconnected with said injection assemblies and .Iaddend.responsive to the appearance of a predetermined amount of plastic material in each of said injection chambers for applying to said injection rams a relatively high pressure in excess of said predetermined pressure and sufficient to close said one-way valve, and for opening said on-off valve to thereby permit said injection ram to drive said foamed plastic material into a mold cavity.   
     
     
       2. The device of claim 1 wherein said control means includes central means .Iadd.operatively associated with said on-off valves .Iaddend.for opening all of said plurality of on-off valves simultaneously after all said injection chambers have been filled. 
     
     
       3. The device of claim 2 wherein said control means includes individual ram position responsive valves .[.for each ram.]. .Iadd.operatively associated with each ram and .Iaddend.responsive to said predetermined amount of plastic material in the corresponding injection chamber for applying said relatively high pressure to the corresponding ram independently of said central means controlling said on-off valves, so as to apply said relatively high pressure after filling of said injection chamber but before opening of the corresponding on-off valves. 
     
     
       4. The device of claim 1 wherein said control means includes valve means maintaining the same relatively high pressure on the injection ram for terminating further entry into the injection chamber of plastic material by direct closure of said one-way valve and for causing ram movement to inject said foamed plastic material into the mold. 
     
     
       5. The device of claim 1 wherein each said one-way valve is located remotely from said plasticizing unit and substantially more closely to its corresponding injection chamber, so as to be placed as close as physically feasible to the entry of its passageway into its respectively associated injection chamber. 
     
     
       6. The device of claim 1 wherein each high pressure passageway terminates in an injection nozzle, said nozzle being in direct communication with the discharge of the corresponding one of said on-off valves, a plurality of said nozzles being provided for each of said injection chambers. 
     
     
       7. The device of claim 6 in which said plurality of on-off valves and corresponding nozzles are spaced radially from and circumferentially around their corresponding injection chamber at substantially equal distances therefrom, the high pressure passageway lengths from each said nozzle to its corresponding injection chamber being substantially equal for each injection chamber. 
     
     
       8. The device of claim 1 wherein said low pressure passgeways comprise at least one T-pattern with said injection assemblies being symmetrically fed from the arms of said T-pattern, whereby plastic material will travel an equal distance from the discharge port of said plasticizing unit to the inlet of each of said injection chambers. 
     
     
       9. The device of claim 8 in which said low pressure passageways form at least one series of T-patterns, each T-pattern having an input leg and equal length output arms, the leg of first T-pattern being connected to said plasticizing unit, the legs of a pair of second T-patterns being connected to the arms of said first T-pattern, the arms of an Nth set of T-patterns being connected through corresponding ones of said one-way valves to corresponding ones of said injection chambers. 
     
     
       10. The device of claim 9 in which a pair of first T-patterns are provided, the legs thereof being connected to said plasticizing unit. 
     
     
       11. The device of claim 8 in which a plurality of said injection assemblies are grouped circumferentially and symmetrically around the intersection point of said T-pattern, the portions of said low pressure passageways extending therefrom to said injection assemblies being of equal length, the injection chamber of each assembly being symmetrically and circumferentially surrounded by said pressure passageways and corresponding on-off valves, with said high pressure passageways being all of substantially equal length. 
     
     
       12. The device of claim 1 in which said low pressure passgeways are defined by conduits extending from said plasticizing unit to each of said injection assemblies, the conduit for one said injection assembly including at least one expansion joint intermediate the ends thereof and terminating in said one-way valve at said injection assembly. 
     
     
       13. The device of claim 12 in which said conduit includes a T-block and a fixed pressure block for backing and T-block. 
     
     
       14. The device of claim 1 in which each injection assembly comprises a base block fixed with respect to a portion of a mold, said injection chamber comprising a hollow block fixed to said base block, said high pressure passageways comprising passages formed in said base block.Iadd., .Iaddend.communicating with the adjacent end of said injection chamber and each terminating in a nozzle member extending from said passage formed in said base block, said low pressure passages comprising a conduit secured to said base block and also communicating with said adjacent end of said injection chamber, said on-off valves including activating means mounted on said base block adjacent said injection chamber opposite corresponding ones of said nozzles and having valve rods extending through said base block into said nozzles. 
     
     
       15. The device of claim 6, wherein a single mold cavity is supplied from a single one of said injection nozzles. 
     
     
       16. The device of claim 6, wherein a single mold cavity is supplied from a plurality of said injection nozzles. .Iadd. 17. In a plastic molding device, the combination comprising: a plasticizing unit for receiving granular plastic material, said unit including means for converting the material to plasticized plastic material;   a plurality of injection assemblies, each comprising an injection chamber having an injection ram;   plural low pressure passageways providing communication from said plasticizing unit to corresponding ones of said injection assemblies;   power means operatively connected to and continuously operating said plasticizing unit for charging a continuous supply of said plastic material into said low pressure passageways at a predetermined, relatively low pressure;   means defining a one-way valve positioned in each said low pressure passageway to permit flow of said plastic material from said unit to the injection chamber of the corresponding injection assembly but preventing reverse flow from said injection chamber toward said unit and other injection assemblies;   plural high pressure passageways downstream of said low pressure passageways for conducting said plastic material from each of said injection chambers to a mold cavity and an on-off valve positioned in each said high pressure passageway;   control means operatively interconnected with said injection assemblies and responsive to the appearance of a predetermined amount of plastic material in each of said injection chambers for applying to said injection rams a relatively high pressure in excess of said predetermined pressure and sufficient to close said one-way valve, and for opening said on-off valve to thereby permit said injection ram to drive said plastic material into a mold cavity. .Iaddend.