Blow-molding method for resinous molding product and apparatus therefor

A blow-molding method for resinous molding products having thick portions and thin portions, the method comprising the steps of:

• hanging down a parison in a first direction between a pair of metallic molds which are free to open or close together, said parison having a predetermined cross section and a first temperature;
• contacting first portions of said parison with at least one pair of expanding members, said first portions at least partially corresponding to said thick portions after molding, said parison also having second portions at least partially corresponding to said thin portions after molding, said expanding members being arranged on an outer surface of said parison and being movable in a second direction different from said first direction and said second direction being a direction in which said parison expands by blow molding;
• providing the expanding member with a temperature conditioning means and adjusting said first portions of said parison to a second temperature that is lower than said first temperature by contacting said first portions of said parison with said expanding members, said temperature conditioning means being controlled by a controlling means for setting a temperature difference between said first temperature and said second temperature;
• setting the temperature difference between said first temperature and said second temperature in accordance with a preset thickness ratio between said thick portions and said thin portions of said resinous molding product, said ratio being achieved after molding said first portions into said thick portions and molding said second portions of the parison into said thin portions;
• extending said second portion by applying suction through suction means in said expanding members to hold said parison against said expanding members and moving said expanding members up to intermediate positions before said first portions come into contact with molding surfaces of the metallic molds;
• and subsequently
• heating said first portions contacted by said expanding members until the temperature thereof reaches a pre-determined temperature;
• and
• thinning said second portions of said parison by applying suction to said expanding members to hold said parison against said expanding members and moving said expanding members in said second direction and
• closing together said pair of metallic molds and blowing compressed air into said parison so as to conduct blow-molding.

A blow-molding method for resinous molding products having thick portions and thin portions, the method comprising the steps of:

• hanging down a parison in a first direction between a pair of metallic molds which are free to open or close together, said parison having a predetermined cross section and a first temperature;
• contacting first portions of said parison with at least one pair of expanding members, said first portions at least partially corresponding to said thick portions after molding, said parison also having second portions at least partially corresponding to said thin portions after molding, said expanding members being movable in a second direction different from said first direction and said second direction being a direction in which said parison expands by blow molding;
• providing said expanding member with a temperature conditioning means and adjusting said first portions of said parison to a second temperature that is lower than said first temperature by contacting said first portions of said parison with said expanding members, said temperature conditioning means being controlled by a controlling means for setting a temperature difference between said first temperature and said second temperature;
• wherein said temperature conditioning means is provided with a heating means for heating said first portions contacted by said expanding members, a cooling means for cooling said contact surface portions and a switching means for switching the operations of both said heating and said cooling means
• switching the operating states of said heating and cooling means so that said cooling means is operated until an extension process of said second portions is completed, and said heating means is operated upon completion of the extension process;
• setting said temperature difference between said first temperature and said second temperature in accordance with a preset thickness ratio between said thick portions and said thin portions of said resinous molding product, said ratio being achieved after molding said first portions into said thick portions and molding said second portions of the parison into said thin portions;
• thinning said second portions of said parison by moving said expanding members in said second direction;
• and
• closing together said pair of metallic molds and blowing compressed air into said parison so as to conduct blow-molding.