Diamond Systems Tritan Guia de Resolução de Problemas descarregar pdf (Página 23)

Using zero draft

Zero draft is not recommended. It can cause the mold to lock

up during ejection. It can also increase the cost of the mold

signiﬁcantly because of the additional mechanisms required for

ejection.

If zero draft is necessary, it can be more easily accomplished in

cases where the cores are short, the parts are thick so that the

walls will not tend to shrink tightly to the core, or sleeve

ejectors are used. Sometimes side pulls can be used on the

outside of a cylindrical part so that low draft on the inside core

can be easier to release.

Other areas to consider:

• Provide excellent core cooling to prevent the polymer from

sticking to the hot mold surface.

• Polish the core in the direction of draw to aid ejection.

• Add air poppet valves to break the vacuum in areas with deep

draw.

Zero draft is a critical issue. It is wise to discuss the need for

zero draft with your toolmaker or molder.

Undercuts

Stripped undercuts such as “rice grains,” snap rings, or threads

are allowable up to 2%–3% of the part diameter in relatively

thin-walled parts. Undercuts must be rounded and well ﬁlleted

to allow proper ejection.

Mold surface treatment to aid ejection

In some cases, a low draft angle may be required on a part but

the dimensions of the mold may not be suitable for proper cooling.

Surface coatings or treatments that can aid in the ejection of

parts are available. Eastman has completed an extensive study

to determine which coatings and treatments are better release

agents for our polyesters. The top three that we suggest follow.

Poly-Ond

™

coating

This coating is designed to reduce the coefﬁcient of friction

of the tool surface. It is made of a nickel phosphorous alloy

deposition with poly tetraﬂuoroethylene (PTFE or DuPont Teﬂon

™

coating). PTFE is sprayed or dipped onto a microfractured plated

surface. As the outer layer wears, the PTFE captured in the

fracture pores will continue to provide lubricity.

The coating thickness is typically 0.008–0.013 mm (0.0003–

0.0005 in.) of nickel and 0.013–0.018 mm (0.0005–0.0007 in.)

of PTFE. The hardness is 50 Rockwell C (Rc) as applied and can

be heat treated to 68 Rc. The continuous operation temperature

range is –55° to 260°C (–65° to 500°F).

Poly-Ond

™

coating is provided by:

Poly-Plating, Inc.

2096 Westover Road

Chicopee, MA 01022 U.S.A.

Tel: (1) 800-256-7659 or

(1) 413-593-5477

www.poly-ond.com

Tungsten disulﬁde coatings

These coatings have more lubricity than any other dry substance

known. They are applied with pressurized air at ambient

temperatures. Upon application, the steel appears blue-gray.

When this color disappears, the coating should be reapplied.

They can be applied to an SPI A-1 diamond ﬁnish.

The dynamic coefﬁcient of friction is 0.03 against itself. It is a

very thin coating, typically 0.5 microns, or 20 millionths of an

inch. The hardness is 30 Rc.

We suggest Dicronite

™

DL-5

™

from:

Dicronite Dry Lube of New Jersey

121 North Michigan Avenue

Kenilworth, NJ 07033 U.S.A.

Tel: (1) 800-605-8222

www.dicronite.com

WS2 from:

Micro Surface Corporation

465 East Briscoe Drive

Morris, IL 60450 U.S.A.

Tel: (1) 800-248-4221 or

(1) 815-942-4221

www.microsurfacecorp.com

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