Diamond Systems Tritan Guia de Resolução de Problemas descarregar pdf (Página 21)

Venting problems can also be attributed to improper location of

vents. Venting problems can sometimes be solved by relocating

the gate so that the last area to ﬁll is shifted to an area that has

better venting.

Ejection systems in molds

designed for Eastman

™

polymers

In general, Eastman

™

polymers can run in molds designed for

other polymers without the need for additional ejection. As with

any other polymer, use plenty of ejector pins or ejection sleeves

where practical. Inadequate ejection can cause part distortion.

Because polyester materials tend to stick to hot (>50°–65°C

[120°–150°F]) mold surfaces, generous cooling will greatly

ease ejection.

Be sure to include enough “daylight” in the tool to eject the part

without hanging or scufﬁng.

A smooth, polished mold surface makes the part easier to eject.

However, overpolishing the surface can result in a vacuum being

drawn during ejection.

Alloys for mold construction

There are several factors to consider when selecting steel for

the mold:

• Wear resistance

• Toughness

• Machinability

• Polishability

• Dimensional stability

The steels most often used are P20, H13, and S7.

Core and cavity steels. P20 steel is supplied prehardened at a

Rockwell hardness (Rc) of 30 to 32, which eliminates the need

for heat treatment. P20 will polish to a very high ﬁnish, but

rust-preventive greases will be required during shutdowns to

preserve the ﬁnish; otherwise, plating will be necessary. Plating

can be an impediment during repairs. The thermal conductivity

of P20 is better than that of H13, 420, and S7, but its conductivity

could eventually be impeded by cooling channel corrosion. P20

costs less than H13 and 420.

H13 steel typically requires heat treatment for more hardness

and durability. H13 has less toughness and thermal conductivity

but higher wear resistance than P20. Because of its higher

hardness, parting lines in H13 hold up longer than those of P20.

With reduced thermal conductivity, increased cooling should be

considered. H13 can also rust if not properly protected during use.

Although 420 stainless steel has lower thermal conductivity

than H13, it offers rust resistance on the polished surface and

cooling channels that is not available with P20 or H13. Heat

treatment similar to that of H13 is required for 420SS. Some

suppliers also have a 414SS prehardened the same as P20, at an

Rc of 30 to 32, which eliminates the need for heat treatment.

Slides and lifters. S7 tool steel is often used for hardened slides

and lifters. Wear plates and gibs are often constructed from O1,

O6, and A10. Bronze or bronze-coated (Lamina

™

bronze) plates

are also used adjacent to sliding surfaces.

Inserts. Eastman often suggests utilizing inserts in areas that

may be difﬁcult to cool such as tall, relatively thin standing core

details. Two common thermally efﬁcient alloy families utilized

for this are Moldmax

™

from Materion Brush, Inc and Ampcoloy

™

from Ampcometal S.A. Special care should be taken to ensure

the inserts have proper cooling. Relieving the insert for ease of

assembly should be minimized to eliminate the formation of

insulting air gaps. In addition, a cooling line in close proximity

is crucial when relying on cooling from the main tool body. In

extreme cases, the inserts should be designed with integral

cooling passages to ensure proper heat removal.

Because processability is dependent on the mold, it is necessary

to consider material options and toolmaker recommendations

carefully. Mold investments will pay huge dividends in production.

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