Diamond Systems Tritan Guía para resolver problemas descargar pdf (Pagina 40)

“Reading” parts as they are molded

Often some very small marks and other visible features of a

part can tell much about improvements needed in the molding

process. It is usually best to examine the entire shot, including

sprue, runner, and parts from all cavities when deﬁning a

problem in molding. It is also advisable to do this at the operating

machine so that guesswork concerning molding conditions can

be avoided. Watching how the screw travels during the entire

injection period and relating that to the parts ﬁlling at the gate

ﬁrst (fountain ﬂow) can help understand what is happening.

Part failure: causes and analysis

In general, part failures can be minimized by utilizing proper

design techniques, selecting the proper material, and processing

the material properly. Figure 34 demonstrates that there are

many items that must be addressed to make a successful

molded product. When a part fails, this chart can be used to

guide the investigative process, which will hopefully point to the

cause of failure and allow it to be remedied.

Crystallinity

Composition

Cooling

Assembly

Welding, cold forming

Deflections

Sticking and breaking in mold

Cavity imbalance

Gate in thin

area of part

Part design

Environment

Contamination

Chemicals

Additives

Other mat’l

Regrind

Small % shot

Long cycle

Time/temp

Drying

Pellets

flow/M.W.

Location

Packing

% Additives/

% stabilizer

Molded-in stress

See overpacking

Eject timing

Undercuts

Cooling

Notches

Nonuniform

wall thickness

Weld line

Chemicals

Radiation

Heat

Gate size

Gates

Runner size

Cold melt

Cold mold

Overpacking

Runners

Cooling/temp

Family mold

Hot drops

Molding

Color comb.

Mold rel.

Pellets

Time

High melt temp

Long holdup time

Temp

Dew point

Airflow

Broken

parts

Test

flow

for

M.W.

Not

degraded

Degraded

Original

properties

Figure 34 Part failure analysis ﬁsh bone

1 2 ... 35 36 37 38 39 40 41 42 43 44

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Diamond Systems Tritan Guía para resolver problemas Pagina 40

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