Blow molding

Claim 1

The method of molding hollow thermoplastic articles of manufacture having predetermined wall thickness distribution which comprises the steps of connecting selected conductive leads to selected resistors within an electrically active circuit to establish a plurality of voltages each of which has a magnitude proportional to a desired predetermined axial movement of a pin with respect to a die casing defining an extrusion outlet, extruding a thermoplastic parison through said extrusion outlet, converting said plurality of voltages to a series of varying fluid pressures, applying said series of varying fluid pressures during said extrusion to move the pin and vary the size of said outlet and consequently the wall thickness of the parison according to a predetermined program related to the desired wall thickness distribution in one of the hollow articles, observing the pin movement resulting from each of the applied pressures to determine if the size of the outlet is in accordance with the predetermined program, automatically adjusting any of said applied pressures in order to maintain the size of the outlet resulting from the pin movement by the originally applied pressures within desired limits, expanding said variable wall thickness parison outwardly within a blow mold to form said one hollow article whereby the extent of reduction of the wall thickness of the varying thickness parison during expansion is such as to provide the desired thickness distribution in said one hollow article, repositioning at least one of said conductive leads on another resistor while continuing said extrusion to instantaneously change the magnitude of the voltage associated with said at least one conductive lead and another resistor and correspondingly change the movement of the pin and alter the wall thickness of the parison portion being extruded when said changed magnitude is converted to a fluid pressure and applied to the pin, thereby conveniently providing a different distribution of thermoplastic in a subsequent article after expansion in the blow mold from that present in said one article.

Claim 2

The method of molding hollow thermoplastic articles of manufacture having predetermined wall thickness distribution which comprises the steps of connecting selected conductive leads to selected resistors within an electrically active circuit to establish a plurality of voltages each of which has a magnitude proportional to a desired predetermined axial movement of a pin with respect to a die casing defining an extrusion outlet, extruding a thermoplastic parison through said extrusion outlet, converting said plurality of voltages to a series of varying fluid pressures, applying said series of varying fluid pressures during said extrusion to move the pin and vary the size of said outlet and consequently the wall thickness of the parison according to a predetermined program related to the desired wall thickness distribution in one of the hollow articles, observing the pin movement resulting from each of the applied pressures to determine if the size of the outlet is in accordance with the predetermined program, automatically adjusting any of said applied pressures in order to maintain the size of the outlet resulting from the pin movement by the originally applied pressures within desired limits, expanding said variable wall thickness parison outwardly within a blow mold to form said one hollow article whereby the extent of reduction of the wall thickness of the varying thickness parison during expansion is such as to provide the desired thickness distribution in said one hollow article, repositioning at least one of said conductive leads on another resistor while continuing said extrusion to instantaneously change the magnitude of the voltage associated with said at least one conductive lead and another resistor and correspondingly change the movement of the pin and alter the wall thickness of the parison portion being extruded when said changed magnitude is converted to a fluid pressure and applied to the pin, thereby conveniently providing a different distribution of thermoplastic in a subsequent article after expansion in the blow mold from that present in said one article.