Hot runner having a heat shrinkable tube covering

A hot runner (10) is provided including a canal (11) and a heat-shrinkable tube (12) covering on the canal (11). The heat-shrinkable tube (12) can shrink along the canal (12)'s contour when heated. The present invention further provides a mold (20) using the hot runner.

BACKGROUND

1. Field of the Invention

The present invention generally relates to hot runners and, particularly, to a hot runner used in a mold assembly.

2. Description of Related Art

Insert molding technology using molding machines is a popular molding method. A typical molding machine usually includes a hot runner, a male mold and a female mold. The male mold and the female mold define a mold cavity therebetween. The male mold has a passage defined therein, communicating with the mold cavity. The hot runner is inserted into the passage. Thus, melted plastic can be injected into the mold cavity through the hot runner.

To prevent the melted plastic from leaking out of a combining aperture between the hot runner and the passage, a vertical surface is formed on the outside of the hot runner. The vertical surface is an outer peripheral surface surrounding the longitudinal axis of the hot runner. Correspondingly, the passage has a cooperating surface. The vertical surface is tightly attached to the cooperating surface, thus preventing leakage of melted plastic.

However, after repeated usage, a gap may appear between the vertical surface and the cooperating surface because of abrasion, high temperature, and high pressure. Thus, melted plastic may leak to the outer surface of the hot runner, resulting in damaging other elements, i.e., the heating coil and the temperature-sensing equipment.

Thus, there is room for improvement within the art.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1shows an exemplary hot runner10. The hot runner10includes a canal11and a heat-shrinkable tube12.

The canal11is a hollow tube. The canal11defines a channel111in the center portion therethrough, and includes a sprayer112disposed at one distal end thereof, and a heat insulating layer113attached to and covering an outer periphery of the sprayer112. The sprayer112is tapered. The heat insulating layer113is also tapered, and configured to insulate the hot runner10and a mold assembly20(referring toFIG. 2) for preventing heat transmission from the hot runner10to the mold assembly20. The canal11has a vertical surface114adjacent to the heat insulating layer113. The vertical surface114is an outer peripheral surface surrounding the longitudinal axis of the hot runner10, and has a high machining precision. A heater115is positioned on the outside of the other end of the canal11opposite to the sprayer112. The heater115provides heat to the canal11to maintain good flowing of melted plastic in the channel11.

The heat-shrinkable tube12is made of a macromolecular material having different states when at different temperatures, such as polyvinylchlorid (PVC) and etc. At room temperature, the heat-shrinkable tube12is in a glass state. At elevated temperatures, the heat-shrinkable tube12may shrink and become elastic. When in the glass state, the heat-shrinkable tube12has properties similar to plastic. When in the elastic state, the heat-shrinkable tube12has properties similar to rubber. Therefore, when heated, the heat-shrinkable tube12changes from the glass state to the high-elastic state and automatically shrinks in volume.

Referring toFIG. 3, when assembling the hot runner10, the heat-shrinkable tube12covers the vertical surface114of the canal11, and receives the heat insulating layer113therein. The heater115is then electrified by a power source (not shown) to generate heat, thereby causing the heat-shrinkable tube12to shrink and tightly attach to the contour of the heat insulating layer113and the vertical surface114.

Referring toFIG. 2again, a mold assembly20includes a male mold21and a female mold22. The male mold21and the female mold22cooperatively form a mold cavity23therebetween. The male mold21defines a passage24communicating with the mold cavity23. The passage24is configured for receiving the hot runner10. The passage24has an inner wall, including a tapered surface241, a cooperating surface242and a limiting surface243.

Referring toFIG. 3again, when mounting the hot runner10to the mold assembly20, the hot runner10is inserted into the passage24of the mold assembly20. The heat-shrinkable tube12abuts against the tapered surface241. The cooperating surface242cooperatively engages with the vertical surface114. A periphery wall of the heater115is limited by the limiting surface243. The heat-shrinkable tube12can fill in the gap between the cooperating surface242and the vertical surface114and the gap between the heat insulating layer113and the tapered surface241, thus preventing leakage of melted plastic.