Patent Application
20060159799
The present invention relates to an injection molding nozzle and, and more particularly, to a nozzle seal having a gating needle for an injection molding nozzle.
In injection molding processes, pressurized molten plastic material, or melt, is directed from a heated nozzle through a gate into a mold cavity. Typically, the front end of the nozzle may include either a central gating needle or a “torpedo” that extends past the outlet of the nozzle so as to be in proximity to the gate of the mold cavity. The configuration and composition of the gating needle affects the way the melt behaves around the gate. For example, it is known to make the gating needle of a highly thermally conductive material to improve heat transfer to and from the melt in the gate during the molding cycle. A challenge in designing a gating needle is to simultaneously maximize the rate of heat transfer (namely by maximizing the mass of the conductive material in the needle) and maximize the amount of flow that can pass through the needle to minimize the cycling time (namely by maximizing the size of the melt duct through the needle).
Accordingly, it is an object of the present invention to provide an improved nozzle seal and gating needle for an injection molding nozzle.
More specifically, it is an object of the present invention to provide a gating needle for use in a nozzle seal in which the needle provides both high heat transfer rates and high melt flow rates.
These objects, as well as others that will become obvious upon reference to the following detailed description and accompanying drawings, are attained by a needle assembly that is used in an injection molding nozzle which has an outer retaining piece with a central opening adapted to be removably secured to the front end of the nozzle and a gating needle adapted to be secured to the nozzle by the outer retaining piece. The gating needle includes a longitudinal axis and comprises an intermediate cylindrical portion that is symmetrical about the longitudinal axis, a generally conical portion extending axially from one side of the intermediate portion and terminating in a solid point, and a generally cylindrical stem extending axially from the intermediate portion in the direction opposite to that of the conical portion. At least one melt passageway extends linearly (i.e., in a straight line) through the gating needle from the stem through the intermediate portion and exiting in the conical portion rearward of the point of the tip. The exit of the melt passageway is located asymmetrically with respect to the longitudinal axis (i.e., not coterminous with the longitudinal axis) of the gating needle so that the tip of the needle terminates in a solid point.
In another aspect of the invention, the central portion of the gating needle has a diameter such that the outer surface of the intermediate portion is spaced from the adjacent surface of the outer retaining piece. The lower portion of the gating needle may also be spaced from the interior sidewall of the outer retaining piece.
Turning to the drawings, there is seen in
As is typical, the nozzle 10 includes a rear end 12 that abuts the front face of the melt distribution manifold. The nozzle 10 includes a locating flange 14 that seats on a shoulder in the well 16 of the manifold plate (shown in partial fragment at 18), thus forming an insulative air space 20 between the heated nozzle 10 and the cooled mold 16.
The nozzle 10 includes a threaded front end 22 that receives a nozzle seal. The nozzle seal comprises a complimentarily threaded outer retaining piece 24 and a gating needle 26. Preferably, the outer or retaining piece 24 of the nozzle seal is of a material that is thermally less conductive than the gating needle 26, which, as discussed above, is of a thermally highly conductive material.
The nozzle 10 includes a central bore 28 that is in fluid communication with the melt passage of the manifold so as to convey melt therethrough. The melt then flows through a melt duct or passageway (described in greater detail below) in the gating needle 26. The nozzle 10 includes a heater cavity 32 that receives an electrical heating element or core 34 and a thermocouple 36. The nozzle 10 may also optionally include a thermocouple 37 supported on its outer surface so as to reside in the insulative air space 20.
As described in U.S. Pat. No. 5,055,028 to Trakas, which is incorporated by reference herein, the volume of the heater cavity 32 not occupied by the heater core 34 and thermocouple 36 is preferably filled with a substantially void-free, compacted particulate refractory ceramic material such as, for example, magnesium oxide. As described in the referenced patent, the ceramic refractory material of choice, magnesium oxide, provides excellent heat transfer capabilities at high temperatures when it is compacted.
As illustrated, the tip 38 of the gating needle 26 terminates in a point that extends through the distal opening in the outer piece 24. When the nozzle is positioned in the mold 18, the tip 38 of the gating needle 26 is disposed in close proximity to the mold gate 40, through which melt enters into the mold cavity.
As best seen in
Extending axially from the shoulder 46 and generally symmetrically with respect to the longitudinal axis X-X is a generally conical portion 52 that terminates in the tip 38 of the gating needle 26. Extending axially from the shoulder 44 and generally symmetrically with respect to the longitudinal axis X-X is a stem 54. The stem 54 preferably terminates in a concave surface 56, but may alternatively be flat (i.e., perpendicular to the side wall of the stem) or convex. The outside diameter of the stem 54 is closely dimensioned with respect to the inside diameter of the central bore 28 of the nozzle 10 to help accurately center the tip 38 of the needle 26 with respect to the gate 40.
In keeping with an aspect of the invention, the outside diameter of the intermediate portion 42 of the gating needle is smaller that the inside diameter of the outer piece 24 (best seen in
In keeping with another aspect of the invention, the gating needle 26 includes at least one off-center melt passageway that extends linearly (i.e., in a straight line) from the concave surface 56 of the stem 54, through the intermediate cylindrical portion 42, and exits through the conical section 52. Importantly, the exit is located asymmetrically with respect to the longitudinal axis X-X of the gating needle 26 so that the pointed tip of the needle remains intact.
Preferably, the gating needle 26 includes two linear melt passageways 60 (as best seen in
In a further alternate embodiment, shown in
The entrances to the passageways 60 lie in the concave portion 56 of the stem 54, and the juncture between the concave portion 56 and the entrance to each passageway is preferably beveled to facilitate the flow of melt from the central bore 28 of the nozzle 10 into the gating needle 26.
Thus, a needle assembly has been provided that meets all the objects of the present invention. While the invention has been described in terms of a preferred embodiment, there is no intent to limit it to the same. Instead, the invention is defined by the scope of the following claims.
