Method and apparatus for blow molding a plastic drinking vessel

A method for forming a plastic drinking vessel by blow molding, said drinking vessel including a rim with a bead thereon, the rim having internal and external surfaces, comprising the steps of:

• forming a substantially cylindrical plastic parison;
• introducing the parison into a blow mold having internal walls with a shape corresponding to that of the desired drinking vessel including a peripheral recess for forming the bead;
• expanding the parison within the blow mold against said internal walls to form said vessel and the bead;
• providing a cutter head assembly adjacent the peripheral recess in said blow mold and axially spaced therefrom, said cutter head assembly including an annular cutter blade with an outside diameter slightly less than the inside diameter of wall surfaces of the blow mold adjacent to said peripheral recess, said cutter blade and cutter head assembly forming a dome-shaped top in response to expansion of the parison,
• said dome-shaped top having sidewalls connected at the external surface of the rim of said bead;
• moving the cutter blade and cutter head assembly axially of the vessel into the blow mold in order to curl the sidewalls of the dome-shaped top inwardly into contact with the interior of the vessel rim at a region just below the peripheral recess in the walls of the blow mold;
• controlling the temperature of the cutter blade at said region to thereby soften and secure the sidewalls of the dome-shaped top at said region;
• retracting the cutter blade and cutter head assembly axially from the blow mold to thereby at least partially sever the dome-shaped top from the vessel;
• removing the vessel and dome-shaped top from the blow mold;
• and
• cutting the sidewalls of the dome-shaped top at said region to completely sever the dome-shaped top from the vessel;
• whereby the curl formed from the dome-shaped sidewalls forms a smooth internal surface of the vessel rim.