Diamond Systems Tritan Guia de Resolução de Problemas descarregar pdf (Página 14)

Figure 13 High-conductivity sprue bushing

Mold/sprue cooling example

Figure 14 shows a part with inadequate cooling. Notice the long

sprue, with low draft and poor cooling. The part has poor cooling,

and there is an air poppet valve under the sprue. This design

resulted in extreme molding difﬁculties.

Figure 14 Inadequate cooling

Figure 15 shows suggested modiﬁcations to the mold. The

standard steel sprue bushing has been replaced with a shorter,

performance alloy sprue bushing. There is better cooling around

the sprue, and more cooling was added in the cavity and the

core. The air poppet valve was moved away from the sprue.

With these design modiﬁcations, the part was easily and

successfully molded.

Figure 15 Improved cooling

Hot sprues

Hot sprues can be used for amorphous copolyesters. As with

hot runners, the keys to proper design are low shear, good

cooling at the part or sprue/runner end, uniform heating, and

good temperature control.

Runner design

When designing runner systems, use the same guidelines that

apply to most engineering polymers. As shown in Figure 16,

the runners should be designed for smooth, fully balanced ﬂow.

Generously radiused transitions reduce material hang-up and

shearing. Cold slug wells are useful in trapping slugs of frozen

material at the ﬂow front. Vent the runners generously.

Figure 16 Typical runner layout

5.6 mm

(0.219 in.)

•

Stainless steel nozzle seat

– Wear resistant

– Nozzle heat resistance

•

Rigid sprues for pickers or

grabbers

U.S. Patent 4,950,154

•

Reduces cycle times

•

Enhances release of

molded parts

Air poppet

111 mm (4.375 in.)

41.6-mm/m

(0.5-in./ft) taper

76.2 mm (3.0 in.)

Air poppet

Shorten sprue

bushing

Provide cooling

around sprue

area

2.5–3 D

Performance

alloy sprue

bushing

Cold slug wells

Generously

radiused runner

transitions

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 43 44

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