Smaller hot runners mean simpler molds.

Tiny hot-runner systems do more than save resin cost and cycle time. They can also fit into molds that take up less space - and money.

Mold designers know that size really does matter - at least when it comes to squeezing tiny parts into a small mold package. Hot-runner components have been shrinking steadily as a result.

These small systems, which tend to have pitch spacing under 20 rom, can bring material and cycle-time savings to even the smallest parts with the tightest cavity spacings. Small hot-runner components can also help you cut tooling costs. Because they enable closer packing of cavities and other mold features, they let you get away with smaller mold bases and less complex mold designs.

These examples of the latest components can help you save more cost and space than ever before.

Packing in the cavities

Multi-drop nozzles aren't new. Nor are expandable cavities. But put these two technologies together and you can wind up with a vastly simplified and less expensive meld, according to Paul Catalanotti, president of Roehr Tool Corp.

Roehr's expandable cavities (also available from D-M-E) eliminate the need for costly side actions on parts with undercuts and similar features. As Catalanotti explains, they allow the undercut to be built into the cavity without hindering ejection. While the mold remains closed, the cavities also stay closed. When the mold opens, the cavities expand along split lines, allowing the parts to eject. Roehr has supplied expandable tooling for parts up to 3.5 in. long.

In a paper at this year's SPE Antec meeting, Catalanotti said expandable cavities may yield the maximum benefit when they are used along with a round multi-tip nozzle. This type of cluster configuration enabled Roehr to design a tool for a 0.5-g PP part that uses 16 four-drop tips and expandable cavities. It cost just over $135,000, whereas a conventional tool with 64 nozzles and side actions would have cost more than $180,000. Catalanotti says using fewer nozzles saved about $35,000 in the multi-drop tool. Eliminating the slides made up the rest of the cost savings.

For some molds, the cluster approach can shrink the mold base considerably. Consider for example a 32-cavity mold for a 0.5 x 0.75 in. part that needs a pair of slides. If built conventionally, says Catalanotti, the mold base would typically measure roughly 19.5 x 29.5 in. By changing the part orientation in the tool, the expandable core/multi-drop configuration can fit the same part into a 13.9 x 23.5 in. mold base occupying 40% less area.

The closer the better

The 250 Series of hot-runner nozzles from Husky, introduced at NPE '97, has a diameter of less than 10 mm and can be arranged in an 18-mm pitch. Husky hot-runner designer Harold Godwin says 18-min may not be the smallest pitch available in one dimension, but few components have smaller pitch in two dimensions. This small spacing has let one Husky customer pack a 64-drop tool into a mold base of 15 x 24 in.

In a recent Husky tool for a flip-top closure, the nozzle is small enough to sit adjacent to the core pin that forms the flip-top opening. Direct gating near the core pin - rather than edge gating - lets the mold designer orient the part in a flat, open position across the mold face, eliminating the side actions required by an edge-gated flip-top.

Nozzles keep shrinking

JPI Technologies, which represents Germany's Heitec Hot Runner Systems, recently expanded its line of externally heated, 230-v micro systems. The company has supplemented its line of fiat nozzles with a new "double flat" version, which adds a second row of individually-controlled tips. Like the original flat nozzle, it has a center-to-center spacing of 0.5 in. within a row. The new double-fiat configuration offers a 0.75-in. spacing between rows, down from about 2 in. with the original flat nozzle. One application is an eight-cavity tool used in continuous molding of an electrical part. In this case, the flat nozzle brought the cavity spacing down to 16 mm to allow the parts to match up with the reel dimensions. (Mold-Masters reports a similar application for its tiny Femto Shot nozzles.) Other applications have included a variety of parts in the 0.5-1 g range, including electrical parts, medical connectors, and acetal gears.

Also new from JPI is a nozzle with a height of only 33.5 min, installation diam. as little as 10 mm, and minimum spacing of 10 min. According to general manager Paul Boettger, the short nozzle works well in edge gating, where a longer nozzle would have a cold slug. Also, he adds, the short nozzle can be turned 90 [degrees] to direct gate parts that would otherwise be edge gated. Boettger notes that a two-row system would shave at least 2.5 in. off the mold base.

Other new small hot-runner components include the following:

* A horizontal edge-gate system from MoldMasters consists of a customized nozzle and special mold layout and enables direct gating of pipettes and similar parts. According to applications engineer Bruce Wilford, the compactness of this method, compared with traditional insulated runners, lets a 64-cavity hot-runner design occupy the same size mold base (11.875 x 15 in.) as a 32-cavity mold. What's more, he says, the tool can run on a press as small as 50 tons because the horizontal hot tip reduces the injection force on the parting line.

* CB Series nozzles from Dynisco/Kona Hot Runner Systems represent a move for this large-part specialist into smaller hot runners. The externally heated CB series, which comes from Dynisco's new Eurotool subsidiary, includes a variety of open-flow bushings with four different gate configurations. The systems offer pitch spacing down to 16 mm, nozzles as short as 36 mm, and a standard manifold thickness of 37 mm.

* Linear multi-tip nozzles from Ewikon have up to four tips in a row rather than in a round cluster. Minimum nozzle spacing is 8 min, while the maximum is 25 mm.