Heater for forming plastic bodies

Claim 1

A MOLDING DIE FOR CONTACTING PLASTIC SHEET MATERIAL AND MOLDING ARTICLES FROM THE SAME, SAID MOLDING DIE COMPRISING A BASE MEMBER, AN UPSTANDING FORMING MEMBER OPERATIVELY SECURED TO SAID BASE MEMBER, SAID FORMING MEMBER HAVING AN ANNULAR SIDE WALL, AN ELECTRICALLY ENERGIZABLE HEATING ELEMENT FIRMLY EMBEDDED IN SAID UPSTANDING FORMING MEMBER AND INTEGRALLY DISPOSED THEREIN SAID HEATING ELEMENT BEING SHAPED IN THE FORM OF A SPIRAL WITH CONVOLUTIONS AND A SPACE BETWEEN EACH OF THE SPIRALS, SAID HEATING ELEMENT INCLUDING A REVERSE HELICALLY SHAPED PORTION WHICH HAS CONVOLUTIONS IN THE SPACE BETWEEN SAID FIRST NAMED CONVOLUTIONS, THE CONVOLUTIONS OF SAID HEATING ELEMENT HAVING A SUBSTANTIALLY CIRCULAR CROSS SECTION WITH DIAMETER D, EACH OF THE CONVOLUTIONS OF THE SPIRAL HEATING ELEMENT BEING SPACED FROM THE EXTERIOR ANNULAR SIDE WALL BY A DISTANCE WHICH IS FROM ONE TO TWO TIMES THE DIAMETER D AS MEASURED FROM THE SPIRALLY SHAPED AXIAL CENTERLINE PASSING THROUGH THE CONVOLUTIONS TO THE EXTERIOR ANNULAR SIDE WALL, THE VERTICAL SPACING BETWEEN EACH OF SAID CONVOLUTIONS AS MEASURED FROM THE AXIAL CENTERLINE PASSING THROUGH EACH OF TWO VERTICALLY SPACED ADJACENT CONVOLUTIONS BEING FROM 0.10 TO 0.50 TIMES THE OVERALL DIAMETER D OF THE SPIRAL IN A HORIZONTAL PLANE PASSING THROUGH ONE OF THE CONVOLUTIONS FROM WHICH MEASUREMENT IS BEING MADE, AND ELECTRICAL TERMINAL PORTIONS OPERATIVELY ATTACHED TO SAID HEATING ELEMENT AND EXTENDING OUTWARDLY FROM SAID BASE.