Diamond Systems Tritan Anleitung zur Fehlerbehebung PDF herunterladen (Seite 10)

A typical bubbler conﬁguration is shown in Figure 6. A bubbler

is very similar to a bafﬂe, except water is supplied to the end

of the core with a bubbler tube. Water returns from the core

through the annular space between the bubbler tube OD and

the core ID.

Figure 6 Typical bubbler conﬁguration

Regardless of the core cooling method selected, several key

design points relating to the use of Eastman

™

polymers and long

core geometries follow:

• Water channels should come in close proximity to the end

of the core to ensure proper heat removal from this area.

• Polishing core surfaces in the direction of draw to a smooth

ﬁnish minimizes the required ejection forces.

• Eliminate any ﬂow restrictions in water supply lines.

• Heat transfer is optimized with turbulent water ﬂow

through the bafﬂe or bubbler.

Providing turbulent coolant ﬂow

One effective and critical technique for cooling is to ensure that

turbulent water ﬂow exists in the cooling lines. If the water ﬂow

is laminar, the heat from the mold goes only into the outer layer

of the water as it ﬂows through the channels. The outer layers

of water do not mix with the cooler inner layers, and the cooling

potential is not fully utilized.

Turbulent ﬂow is achieved when the Reynolds number goes

above 4,000. The best cooling exists when this number is

between 4,000 and 5,500. A Reynolds number below 2,000

indicates laminar ﬂow. This provides only 1⁄

the cooling of

turbulent ﬂow.

Calculating Reynolds number

Formulas for calculating Reynolds number follow. When laying

cooling lines, plug the appropriate numbers for the variables

into the formulas and check the magnitude of the resulting

number. Use the values for the kinematic viscosity of water at

various temperatures shown in Table 1. Viscosity is dependent

on temperature.

Calculating Reynolds number—metric units

V = Fluid velocity in meters/second

D = Diameter of passage in millimeters

Q = Coolant ﬂow rate in liters/minute

n = Kinematic viscosity in centistokes

= (990·V·D)/n or (21,391·Q)/(D·n)

Rule of thumb: At least 0.3 times the cooling line diameter

(mm) is needed as liters per minute (L/min) ﬂow rate to

achieve turbulent ﬂow.

Calculating Reynolds number—English units

V = Fluid velocity in feet/second

D = Diameter of passage in inches

Q = Coolant ﬂow rate in gallons/minute

n = Kinematic viscosity in centistokes

= (7,740·V·D)/n or (3,160·Q)/(D·n)

Rule of thumb: At least 2 times the cooling line diameter

(inches) is needed as gallons per minute (gpm) ﬂow rate to

achieve turbulent ﬂow.

Part

P/L

Polish core in

direction of draw

Water out

Water in

Core pin

Sleeve ejector

P/L

Bubbler tube

Water in close

proximity to

the end of

the core pin

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 43 44

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