US 5,672,365 A · Die assembly for molding a lead screw

Abstract

To reduce the need for manual work, improve productivity and reduce the fabrication cost in the method for molding a lead screw for converting a rotational movement into a linear movement, there are provided a method and a die assembly which may involve the steps of forming a plurality of holes in a wall of a tube in a spiral arrangement, preparing a metallic die assembly provided with a cavity defining a thread groove adapted to form the thread crest matching in position with an array of the holes, placing the tube in the cavity, and injecting synthetic resin material into the cavity so that the synthetic resin material may flow in two separate flows, one flowing inside the core tube, and the other flowing along the outer surface of the core tube. The thread crest is connected to the synthetic resin material filled in the core tube, and can be securely attached to the core tube. Optionally, an annular rotor may be fitted onto the base end portion of the lead screw. The synthetic resin material is first filled into the annular gap defined around the annular rotor before it is filled into the interior of the annular rotor so that the rotor may be prevented from being damaged by the tensile stress produced by internal pressure acting on the annular rotor.

Claims11

Dependent claims

A die assembly for molding a lead screw around a core tube having a required mechanical strength and provided with holes at portions matching in position with a thread crest of a prescribed screw thread, comprising:

a die member having a one-piece first die section defining a substantially cylindrical cavity including a thread groove formed in a die surface thereof, and having a second die section defining a substantially cylindrical cavity coaxially aligned with the cylindrical cavity of the first die section, the first and second die sections having a radial parting line;
means for coaxially positioning said core tube in said cavity of the first and second die sections;
gate means for injecting synthetic resin material both into an internal bore of said core tube, and into an annular gap defined between an outer circumferential surface of said core tube and an opposing die surface;
and
means for separating the first section and second section of said die member in an axial direction to allow a molded lead screw to be removed.

2 more elements

a die member defining a substantially cylindrical first cavity including a thread groove formed in a die surface thereof, and a substantially cylindrical second cavity for receiving said rotor member fitted coaxially onto said core tube, said first and second cavities being disposed coaxially with each other, and in mutual communication;
means for coaxially positioning said core tube in said first and second cavities;
means for coaxially positioning said rotor member, as fitted on said core tube, in said second cavity;
gate means for injecting synthetic resin material into an internal bore of said core tube, a first annular gap defined between an outer surface of said rotor member and an opposing die surface, and a second annular gap defined between an outer surface of said core tube and an inner surface of said rotor member, the flow of said synthetic resin material filled inside said second gap being controlled in such a manner that the pressure of said synthetic resin material filled into said first annular gap is substantially dominant over that filled into said second annular gap;
and
means for opening said die assembly to allow a molded lead screw to be removed.

3 more elements

Dependencies are inferred from the claim text.

Die assembly for molding a lead screw

Life of this patent

Die assembly for molding a lead screw

Life of this patent

Abstract

Claims11