Background of Invention In an injection molding apparatus, the nozzle of the apparatus is heated to maintain the plastic material in a molten state. The plastic material is injected through the nozzle into the mold cavity. The mold is then cooled so that the plastic material in the mold cavity will solidify or"freeze", allowing the molded part to be removed from the mold cavity.

The plastic material in the nozzle is molten since the nozzle is heated. At the tip of the nozzle and extending into the molded part, there will be a transitional region between the molten material and the frozen material. Normally, a sprue will be designed into the mold cavity so that this transitional region will not affect the molded part. In most cases, the conventional process of injection molding will produce superior parts.

However, a problem arises when the injection molding process uses raw materials having a high melt flow index. A material with a high melt flow index will be more"watery". As a result, a greater length of time is required before the melt in the sprue will solidify sufficiently for removal from the mold. If the part is removed from the mold cavity before the melt has fully solidified, a fine string or"black hair" is formed as the part separates from the injection nozzle. The black hair has a tendency to separate from the sprue and cling to the molded part. The black hair tends to be very fine so that it is very difficult to detect by eye. However, the presence of the black hair becomes readily apparent after the molded part is painted and finished. The black hair must then be removed and the part re-painted, adding additional costs.

Summary of the Invention The disadvantages of the prior art may be overcome by providing an insert in the tip of an injection nozzle which positions a pin that extends from the tip and into a sprue cavity.

According to one aspect of the invention, there is provided an insert for an injection molding apparatus having a nozzle defining a flow channel and an exit channel and a pair of mold halves cooperating to define a mold cavity. At least one of the mold halves has a sprue cavity extending between the exit channel and the mold cavity. The insert has a finned body sized to frictionally fit within the flow channel to position and stabilize a pin extending from a leading end of the body in the exit channel. The pin prevents melt from collecting at the exit channel promoting clean removal of the molded part from the mold cavity.

According to another aspect of the invention, there is provided a method of minimizing a formation of black hair from an injected molded part. The method includes the steps of providing a heated injection nozzle with an exit channel. A pin is positioned in the exit channel. A flow of plasticized melt is caused to flow through the injection nozzle and out the exit channel and into a mold cavity. The plasticized melt is allowed to solidify in the mold cavity and the exit channel to form a molded part having a sprue defined by the exit channel. The molded part is removed from the mold cavity.

Description of Drawings In drawing that illustrate a preferred embodiment of the present invention, Figure 1 is a sectional view of an injection molding apparatus incorporating an insert of the present invention; Figure 2 is a perspective view of the insert of the present invention; Figure 3 is a section view of the insert of Figure 2 along the lines 3-3; and Figure 4 is a perspective view of a sprue molded utilizing the insert of the present invention.

Description of the Invention Referring to Figure 1, an insert 10 of the present invention is illustrated. The insert 10 is fitted within a flow channel 15 of nozzle 12. Nozzle 12 is connected to a hot runner system 16 mounted in cavity 14. Hot runner system 16 communicates with inlet 18 to transfer plasticized melt to a plurality of like nozzles 12. Nozzle 12 extends into a mold half 20. Cavity 22 is provided for receiving nozzle 12.

Communicating with cavity 22 is sprue cavity 24. Mold half 20 cooperates with mold half 26 to define a mold cavity 28. Nozzle 12 is preferably heated as is well known in the art of injection molding. An example of such a molding apparatus is described in United States Patent no. 5,284,436.

Referring to Figures 2 and 3, the insert 10 of the present invention is illustrated in detail. The insert 10 generally comprises a tri-part body 30 having longitudinally extending fins 32,34,36 extending from a triangular core 38. The leading end of the core 38 has a pin 40. The trailing end of insert 10 is tapered.

The radial extent of the fins 32,34,36 is such that insert 10 frictionally and slidingly fits within the flow channel 15 of the nozzle 12. The fins 32,34,36 have a relatively narrow thickness and aerodynamically configured to minimize resistance to flow of the molten plastic. The trailing end of the body 10 is tapered and contoured to minimize frictional resistance to the flow. Preferably, the trailing end has an axial point that concavely merges with each of the fins 32,34,36 along a trailing edge thereof. The leading edges of the fins 32,34,36 are shaped to complementarily fit within the end of flow channel 15.

Referring back to Figure 1, flow channel 15 communicates with a tapered exit channel 44 which cooperates with the sprue channel 24 of mold half 20. Pin 40 is positioned to extend into the tapered exit channel 44. Preferably, pin 40 is generally axially and concentrically aligned with the longitudinal extent of the exit channel 44.

The length of pin 40 depends upon the characteristics of the melt and the nozzle. The nozzle 12 is heated. The mold half 20 is preferably cooled at predetermined times to speed the cooling of the plasticised melt from about the freezing point to below. There will be a transition zone between the solidified material and the plasticised melt. The pin 40 should have a length to extend into the fully solidified region of the sprue.

In operation, the mold halves 20,26 are closed to define the mold cavity 28.

A plasticized melt will be injected into the inlet 18 and caused to flow through the hot runner to each of the nozzles 12. The melt will flow past the insert 10, into the sprue cavity and into the mold cavity 28. Once the mold cavity is packed out or filled, the flow of melt is terminated and allowed to freeze. The mold halves 20,26 are opened and the molded part is removed, together with the solidified sprues 46.

Referring to Figure 4, a molded sprue 46 is illustrated. The end of the sprue 46 will have a cavity 48 formed therein. Cavity 48 is formed by and will correspond to pin 40.

Since the melt in the sprue cavity will solidify from the outside in, the center portion will still be molten while the outside has solidified. Pin 40 displaces the melt from the critical region between the solidified material and the melt, thereby minimizing the formation of black hair as the sprue 46 is removed from the sprue cavity. The molded part can be removed from the mold cavity 28 cleaner than previously achieved.

In the preferred embodiment, the insert 10 is described as having a tri-part body. It is possible to have a bi-part body. However, there is a risk that the pin 40 will not extend into the center of the exit channel 44. Further, a bi-part body may cause uneven flow rates on opposite sides of the insert resulting in a pressure differential. Additionally, the body of the insert could have four or more fins.

However, the greater number of fins present increased flow resistance, which is undesirable.

In the present embodiment, the insert 10 is shown positioned in a one piece nozzle. It is now apparent to those skilled in the art that the insert 10 of the present invention could also be utilized in a two piece nozzle, wherein an end piece closes the delivery end of the nozzle.

The above-described embodiment of the invention is intended to be an example of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention.