Film manufacturing apparatus with bubble controlling sensor

A film manufacturing apparatus comprising:

• a circular die having an axis, an inlet for a molten plastic, a lip-shaped circular outlet around the axis for extruding a molten plastic in an annular molten plastic form, and blowing means for blowing pressurized air into the annular molten plastic extruded from the lip-shaped circular outlet to form a bubble of molten plastic;
• a cooling ring containing cooling water and arranged below the circular die to cool the bubble of molten plastic and to restrain the bubble so as to form a tubular plastic film below the cooling ring;
• an ultrasonic sensor arranged near the circular die and substantially extending downwardly obliquely toward a center of the bubble for detecting a distance between a surface of the bubble and the ultrasonic sensor by transmitting an ultrasonic wave toward the bubble at a place between the die and the cooling ring and receiving an ultrasonic wave reflected from the bubble;
• and
• control means for controlling the blowing means in response to an output from the ultrasonic sensor.

A film manufacturing apparatus comprising:

• a circular die having an axis, an inlet for a molten plastic, a lip-shaped circular outlet around the axis for extruding a molten plastic in an annular molten plastic form, and blowing means for blowing air into the annular molten plastic extruded from the lip-shaped circular outlet;
• cooling means for cooling the annular molten plastic to form a tubular plastic film, said cooling means including a cooling ring containing cooling water and arranged below the circular die to cool the molten plastic and restrain a size of the molten plastic to form a bubble between the circular die and the cooling ring and to form the tubular plastic film below the cooling ring;
• an ultrasonic sensor for detecting a distance between the surface of the annular molten plastic and the ultrasonic sensor by transmitting an ultrasonic wave toward the annular molten plastic at a place located between the die and the cooling means and receiving an ultrasonic wave reflected from the annular molten plastic, said ultrasonic sensor being arranged near the circular die, said ultrasonic sensor substantially extending downwardly toward a center of the bubble and extending obliquely relative to a plane perpendicular to the axis of the die;
• and
• control means for controlling the blowing means in response to an output from the ultrasonic sensor.

A film manufacturing apparatus comprising:

• a circular die having an axis, an inlet for a molten plastic, a lip-shaped circular outlet around the axis for extruding a molten plastic in an annular molten plastic form, and blowing means for blowing air into the annular molten plastic extruded from the lip-shaped circular outlet;
• cooling means for cooling the annular molten plastic to form a tubular plastic film, said cooling means including an air cooling means for blowing cooling air to the annular molten plastic so that a frost line appears between the annular molten plastic and the tubular plastic film;
• an ultrasonic sensor for detecting a distance between the surface of the annular molten plastic and the ultrasonic sensor by transmitting an ultrasonic wave toward the annular molten plastic at a place located between the die and the cooling means and receiving an ultrasonic wave reflected from the annular molten plastic, said ultrasonic sensor being arranged obliquely relative to a plane perpendicular to the axis of the die and being aimed at the annular molten plastic between the circular die and the frost line;
• and
• control means for controlling the blowing means in response to an output from the ultrasonic sensor.