Apparatus for vacuum thermoforming

Claim 1

IN AN APPARATUS, FOR PLUG-ASSIST VACUUM-THERMOFORMING WHICH COMPRISES A FORMING DIE AND AN ASSIST PLUG, SAID FORMING DIE HAVING A CAVITY PROVIDED WITH A NUMBER OF SMALL PORTS LEADING FROM THE CONCAVE FORMING SURFACE TO A MEAND OF APPLYING A VACUUM INTERNITTENTLY, THE IMPROVEMENT WHICH COMPROSES AN ASSIST PLUG WHICH IS GENERALLY CONVEX AND TAPERED, HAVING A HORIZONTAL CROSS-SECTION OF A SHARP SIMILAR TO THE HORIZONTAL CROSS-SECTIONAL SHAPE OF THE AFORESAID CAVITY IN THE FORMING DIE AND A TAPER FROM 1* TO 30* GREATER THAN THE TAPER OF THE WALLS OF THE FORMING DIE CAVITY, SAID ASSIST PLUG BEING HALLOWED OUT AT ITS SMALLER, LOWER END PROVIDED A DEPRESSION FORMING AN INTERNAL RECESSED SURFACE INSIDE THE NOSE OF THE PLUG, SAID DEPRESSION HAVING A SMALLER PORT AT THE APEX WHICH LEADS TO A CHANNEL THROUGH THE PLUG LEADING TO THE TOP SURFACE OF SAID PLUG AND A SURFACE AREA BETWEEN 40% AND 100% OF THE AREA OF THE BASE OF THE CAVITY IN THE AFORESAID FORMING DIE, SAID ASSIST-PLUG BEING EQUIPPED WITH MEANS FOR DETERMINING AND CONTROLLING ITS TEMPERATURE AND MEANS FOR LOWERING AND RAISING SAID PLUG INTO A ND OUT OF THE CAVITY OF THE FORMING DIE.