Diamond Systems Tritan Guia de Resolução de Problemas descarregar pdf (Página 16)

It is good practice to gate into areas where the ﬂow path is

continuous and smooth, rather than into notches or ribs.

Streamlining the ﬂow path helps maintain low shear. No sharp

corners or sudden changes in thickness should be allowed. If a

transition is needed from a thick sprue or runner to a thin wall,

the change needs to be smoothly radiused over the available

distance.

Avoid gating into thin sections

If it is necessary to make the wall thickness of a part

nonuniform, gating should be into the thickest area. Gating

into thin sections can cause:

• High material shear, which can cause degradation

• Higher injection pressures during molding

• Difﬁculty in ﬁlling thick sections

Figure 19 shows a part that was improperly gated into a thin

section. Whenever possible, parts should be designed with

uniform wall thickness.

Figure 19 Improper gating

Tunnel gate

Typical tunnel gate guidelines are generally applicable to

Eastman

™

polymers. In Figure 20, we suggest a maximum

tunnel length of 50 mm (2 in.), at a 45° to 60° angle. A

maximum gate land of 1.5 mm (0.060 in.) is suggested. The

tunnel should have a taper of 5° to 20° to ease ejection.

Figure 20 Typical tunnel gate design

Fan gate

One important consideration when designing fan gates is

ensuring that the gate land has the proper length. If it is too

long, a ﬂow restriction that could lead to premature freezing of

the gate is created. This could cause an underpacked part or a

short shot: the material will take the shortest ﬂow path through

the gate and may not use the entire width of the gate effectively

if the land is too long.

It is also important to maintain a constant cross-sectional area

across the gate. Typically, a gradual taper through the thickness

of the gate is used so that equal area is maintained at any cross

section. To minimize shear, radius all corners. See Figure 21.

Figure 21 Fan gate design guidelines

Preferred gate

location

Part

Improperly gated

into thin section

P/LP/L

• 50 mm (2 in.) length, maximum

•

45°–60°

5°–20°

P/L P/L

Radius

Land

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 43 44

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