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It is important to maintain suggested tool temperatures at the

interface with the part. An independent cooling circuit in close

proximity as shown is always suggested. Another viable solution

for temperature control is a water-jacketed insert. These are

sometimes custom fabricated but are also available as standard

items from some of the manufacturers. These usually result

in a witness around the gate which may need to be taken into

consideration. Special care should also be taken to ensure the

valve pin seats well to ensure good contact. Even with adequate

cooling and good contact, there are limitations with gate size.

Gate sizes 3.00 mm (0.125 in.) and below generally result in

the best aesthetics. Gates larger than this are often difﬁcult to

cool and result in poor gate aesthetics due to sticking. Another

factor affecting gate area aesthetics is crystallization. The

degree of crystallization will vary with the material’s propensity

to crystallize, and an Eastman technical service representative

should be consulted to determine whether or not this will be an

issue with your particular material candidate.

Careful consideration to the amount of insulation used at the

drop from the mold is still needed with valve gates. Vespel

™

insulators have also been suggested for these gates.

Processing conditions using hot runner systems

In general, manifold and drop temperatures should be set near

the actual on-cycle melt temperature value. The manifold and

drops should be balanced for uniform ﬂow. Many molders use

hot drops to gate into a small, cold subrunner. This allows the

beneﬁts of cold runner gates while reducing regrind or scrap.

Some polyester materials such as PET tend to crystallize and

whiten at the gates. Thus, it is often beneﬁcial to gate into

noncritical areas or to gate into a post or tab that can be hidden

or removed. Consult your Eastman Technical Representative

and hot runner supplier for more detailed information on gate

placement, gate size, and other hot runner system details.

Venting and ejection

Venting allows gas replaced by the melt front to escape from

the mold. Short shots, burning, and material degradation can

occur if parts are not adequately vented. To prevent this:

• Provide adequate venting in the proper location.

• Check and clean vents regularly.

• Use ejector pins as vents where possible.

• Avoid vents that require mold disassembly for maintenance

access.

Typical venting in molds

designed for Eastman

™

polymers

Figure 28 illustrates a vent layout for a mold running Eastman

™

polymers. A good starting vent depth for molds designed to run

Eastman

™

polymers is 0.012–0.025 mm (0.0005–0.001 in.) for

small parts or vents close to the gates and 0.025–0.038 mm

(0.001–0.0015 in.) for larger parts. A typical land is 3–6 mm

(0.125–0.250 in.) long, opening up into a larger channel that

allows gas to vent from the mold.

Figure 28 Vent layout

Part

P/L

0.012–0.025 mm (0.0005–0.001 in.)

for small parts

0.025–0.038 mm (0.001–0.0015 in.)

for larger parts

3–6 mm

(0.125–0.25 in.)

1.0–1.5 mm

(0.040–0.060 in.)

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