Annular die spiral groove configuration

#1. Field of the Invention

#The present invention pertains to the cross-section configuration of a spiral groove in a mandrel surface of an annular die and the method of producing the groove configuration. More specifically, the present invention pertains to the cross-section configuration of a spiral groove cut into a mandrel surface of an annular die where the groove configuration approaches an “almost round” cross-section configuration and the method of cutting the groove.

#2. Description of the Related Art

#Further features of the annular die spiral groove configuration and its method of manufacture are set forth in the following detailed description and drawing figures.

#FIG. 1 is a representation of a cross-section configuration of a prior art spiral groove on an exterior surface of a cylindrical mandrel of a blown film die.

#FIG. 2 is a representation of a cylindrical mandrel of a blown film die having spiral grooves formed in its exterior surface that have the cross-section configurations of the spiral grooves that are the subject of the invention.

#FIG. 2 is a representation of a cylindrical blown film die mandrel having one of the spiral groove configurations of the invention formed in the exterior surface of the mandrel. FIG. 2 is representative of only one type of annular blown film die mandrel on which the spiral groove configurations of the invention may be employed. The spiral groove configurations of the invention may be employed on many other types of blown film die mandrels, as will be explained. The spiral groove configurations of the invention are only disclosed as being formed on the cylindrical exterior surface of the mandrel shown in FIG. 2 to describe the structural features of the spiral groove configurations. It should be understood that the spiral groove configurations of the invention may be employed on other types of annular or blown film die mandrels other than the cylindrical configurations to be described, and that the spiral groove configurations of the invention should not be limited to only spiral grooves on the exterior surface of a cylindrical blown film die mandrel.

#Referring to FIGS. 2 and 3, a first embodiment of the spiral groove configuration of the invention is shown on the cylindrical exterior surface 10 of a blown film die mandrel 12. The cylindrical mandrel 12 has a center axis 14 that defines mutually perpendicular axial and radial directions relative to the mandrel. Each of the spiral grooves 16 formed on the mandrel 12 employ the groove cross-section configuration of the invention to be described. Therefore, the features of the spiral groove configuration will be described by referring to only one spiral groove 16.

#Referring to FIG. 2, the spiral groove 16 has a length that extends around the mandrel surface 10 from a proximal end 18 of the groove to a distal end 20 of the groove. The proximal end 18 of the groove 16 is typically fed from a hot liquid melt stream delivered to the groove through a feeder or port 22. Referring to FIG. 3, the mandrel exterior surface 10 and the groove 16 are shown being opposed by a cylindrical interior surface 24 of another mandrel, or a cylindrical interior surface of the die. There is a narrow cylindrical gap 26 between the mandrel surface 10 and the opposing interior surface 24. The liquid flow received by the groove 16 is directed by the groove from the groove proximal end 18 toward the groove distal end 20. The flow of liquid is also directed axially upward in a flow direction across the spiral groove 16 and across the mandrel surface 10 as shown in FIG. 3 through the gap 26 between the mandrel surface 10 and the interior surface 24. This distributes the flow of liquid across the mandrel surface 10 and around the cylindrical gap 26.