Apparatus for controlling back pressure in an extruder

Claim 1

An apparatus adapted for controlling the back pressure at the outlet end of an extruder for molten synthetic resin material, said apparatus comprising in combination: a. a valve body; b. a streamlined flow channel within said valve body, said flow channel having a streamlined narrow section of substantially uniform cross-sectional dimension which opens into a streamlined wide section of larger cross-sectional dimension than said narrow section; c. a valve stem which is slidably mounted for reciprocal axial movement within a stem guide and within said flow channel; d. an axially disposed plunger which is connected to the terminal end of said valve stem and coextensive therewith, said plunger having a first portion of substantially uniform crosssectional dimension slightly smaller than said narrow section and a streamlined end portion, said plunger being adapted for movement within said wide section and said narrow section, wherein the clearance distance between the sidewall of said narrow section and the surface of said first portion of said plunger extending into said narrow section is substantially constant, and wherein the cross-sectional clearance area between said wide section and the surface of said first portion of said plunger lying within said wide section is at least two times as large as the cross-sectional clearance area between said narrow section and said surface of said first portion of said plunger extending into said narrow section; and e. means connected to said stem for reciprocally moving said valve stem and said plunger along their longitudinal axis; wherein the pressure drop change across said narrow section during flow of said molten synthetic resin material through the flow channel, is substantially directly proportional to the axial extent to which the end portion of said plunger which lies within said narrow section.

Claim 2

An apparatus adapted for controlling the back pressure at the outlet end of an extruder for molten synthetic resin material, said apparatus comprising in combination: a. a valve body; b. a streamlined flow channel within said valve body, said flow channel having a streamlined narrow section of substantially uniform cross-sectional dimension which opens into a streamlined wide section of larger cross-sectional dimension than said narrow section; c. a valve stem which is slidably mounted for reciprocal axial movement within a stem guide and within said flow channel; d. an axially disposed plunger which is connected to the terminal end of said valve stem and coextensive therewith, said plunger having a first portion of substantially uniform crosssectional dimension slightly smaller than said narrow section and a streamlined end portion, said plunger being adapted for movement within said wide section and said narrow section, wherein the clearance distance between the sidewall of said narrow section and the surface of said first portion of said plunger extending into said narrow section is substantially constant, and wherein the cross-sectional clearance area between said wide section and the surface of said first portion of said plunger lying within said wide section is at least two times as large as the cross-sectional clearance area between said narrow section and said surface of said first portion of said plunger extending into said narrow section; and e. means connected to said stem for reciprocally moving said valve stem and said plunger along their longitudinal axis; wherein the pressure drop change across said narrow section during flow of said molten synthetic resin material through the flow channel, is substantially directly proportional to the axial extent to which the end portion of said plunger which lies within said narrow section.

Claim 12

An apparatus adapted for controlling the back pressure at the outlet end of an extruder for molten synthetic resin material, said valve comprising in combination: a. a valve body; b. a streamlined flow channel within said valve body, said flow channel having a streamlined narrow section of substantially cylindrical configuration which opens into a gradually flaring streamlined wide section of larger cross-sectional dimension than said narrow section, a portion of said wide section curving to form an angle with the axis of said narrow section, said angle being between 10* and 140*; c. a valve stem which is slidably mounted for reciprocal axial movement within a stem guide and within said flow channel; d. an axially disposed plunger which is connected to the terminal end of said valve stem and coextensive therewith, said plunger having a first portion of substantially cylindrical configuration and a streamlined end portion, said plunger being adapted for reciprocal movement within said wide section and said narrow section, the maximum axial extent to which said first portion of said plunger may move into said narrow section being between 0.25 and 15.0 inches, wherein the clearance distance between the sidewall of said narrow section and the surface of said first portion of said plunger extending into said narrow section is substantially constant along the axial extent of said first portion of said plunger, said clearance distance being between about 0.003 and 2.0 inches, and wherein the cross-sectional clearance area between said wide section and the surface of said first portion of said plunger lying within said wide section is at least two times as large as the cross-sectional clearance area between said narrow section and said surface of said first portion of said plunger extending into said narrow section; e. means connected to said stem for reciprocally moving said valve stem and said plunger along their longitudinal axis; f. means within the plunger for controlling the temperature of the plunger; and g. means for controlling the temperature of the wall defining said narrow section, wherein the pressure drop change across said narrow section during flow of said molten synthetic resin material through the flow channel is substantially directly proportional to the axial extent to which the end portion of said plunger lies within said narrow section.

Claim 13

An apparatus adapted for controlling the back pressure at the outlet end of an extruder for molten synthetic resin material, said valve comprising in combination: a. a valve body; b. a streamlined flow channel within said valve body, said flow channel having a streamlined narrow section of substantially cylindrical configuration which opens into a gradually flaring streamlined wide section of larger cross-sectional dimension than said narrow section, a portion of said wide section curving to form an angle with the axis of said narrow section, said angle being between 10* and 140*; c. a valve stem which is slidably mounted for reciprocal axial movement within a stem guide and within said flow channel; d. an axially disposed plunger which is connected to the terminal end of said valve stem and coextensive therewith, said plunger having a first portion of substantially cylindrical configuration and a streamlined end portion, said plunger being adapted for reciprocal movement within said wide section and said narrow section, the maximum axial extent to which said first portion of said plunger may move into said narrow section being between 0.25 and 15.0 inches, wherein the clearance distance between the sidewall of said narrow section and the surface of said first portion of said plunger extending into said narrow section is substantially constant along the axial extent of said first portion of said plunger, said clearance distance being between about 0.003 and 2.0 inches, and wherein the cross-sectional clearance area between said wide section and the surface of said first portion of said plunger lying within said wide section is at least two times as large as the cross-sectional clearance area between said narrow section and said surface of said first portion of said plunger extending into said narrow section; e. means connected to said stem for reciprocally moving said valve stem and said plunger along their longitudinal axis; f. means within the plunger for controlling the temperature of the plunger; and g. means for controlling the temperature of the wall defining said narrow section, wherein the pressure drop change across said narrow section during flow of said molten synthetic resin material through the flow channel is substantially directly proportional to the axial extent to which the end portion of said plunger lies within said narrow section.