Diamond Systems Tritan Guia de Resolução de Problemas descarregar pdf (Página 8)

Ribs are generally spaced at a distance at least twice the

wall thickness to allow enough steel between the ribs for

adequate cooling. A draft angle of 1° is suggested to allow

proper part ejection from the mold.

Finally, be sure to add a radius at least 0.2 to 0.5 times

the wall thickness at the base of the rib to reduce stress

concentration effects.

A boss can be thought of as a round rib; therefore, many

of the same design principles apply (see Figure 3). To avoid

thick sections, stand bosses apart from side walls, reinforcing

them with gussets or ribs for rigidity. The boss hole length-

to-diameter ratio should be 5:1 or less. A longer core pin will

be subject to poor cooling and deflection under injection

pressures. A lead-in area should be provided at the top of

the boss to keep stresses in this area low when the screw or

insert is used. Again, a radius of 1⁄

the wall thickness, or 0.4

mm (0.015 in.), whichever is larger, should be placed at the

base of the boss.

Figure 3 Typical boss design

Cooling

By designing parts so that they can be cooled properly, you can

obtain lower cycle times and high-quality parts while reducing

cost.

Good cooling is absolutely critical when designing molds to

run Eastman

™

polymers.

Some effects of poor cooling:

• Increased cycle time

• Uneven cooling across parts or part-to-part

• High levels of residual stress

• Increased warpage

• Sticking and difficulty in ejection

Although all of the above are potentially serious problems,

the most common difficulty when running Eastman

™

polymers is sticking and difficulty in ejection.

We cannot place enough emphasis on the importance

of good mold cooling, especially in cores. By following

good core-cooling principles, you can greatly increase your

processing window and success in part performance.

Suggested mold temperatures

Adequate cooling lines should be provided to accurately

control mold temperatures to these suggested levels:

• E a s t a r

™

copolyesters and DuraStar

™

polymers: 15°–40°C

(60°–100°F)

• Eastar

™

PETG polymers: 15°–25°C (60°–90°F)

• Eastman Tritan

™

copolyester: 38°–66°C (100°–150°F)

In some cases, the use of tower or normal water is adequate.

However, the use of chillers is strongly encouraged to ensure

a proper supply of cool water to molds. Properly sized pumps

and supply lines to the molds are also critical.

1–2.5 mm

(0.040 to 0.100 in.)

Radius R = T/8

R = 0.4 mm

(0.015 in.) min.

0.9 to 1T

Screw/insert O.D.

= 1.2  D

max.

= 5  D

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Diamond Systems Tritan Guia de Resolução de Problemas Página 8

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