Page 142 - Injection Molding Advanced Troubleshooting Guide

14.4 Tooling Techniques 129

With bubblers an overlooked area is the difference in volume between the inner
diameter of the tube and the outer diameter of the tube to the water line diameter.
Use of a high-flow bubbler tube in place of traditional brass bubbler tubes can
allow for better water flow. One aspect of bubblers that is commonly overlooked is
the cross-sectional area of the inner diameter of the tube and the area between the
outer diameter and the water-line diameter. This is one reason we always recom-
mend using high-flow stainless-steel bubbler tubes versus the common brass bub-
bler tubes. For example, with a 0.125-in diameter tube, the high-flow tube has an
inner diameter of 0.109 in, whereas a brass tube at best has an inner diameter of
0.069 in. The high-flow tube thus has 250% more cross-sectional area, which trans-
lates to an increase of 250% in GPM. That is why we never use standard brass
tubes: they decrease your GPM potential.
You must also consider the cross-sectional area between the tube and the water-
line diameter so that you are using the proper tube size. Some will assume that
with a 0.250-in hole you would use a 0.125-in bubbler tube, thinking it is half of
the diameter. But you must consider the area instead.
There have been many cases where creative water line design led to major im-
provements in the cooling capability of a mold. In real-world applications water
lines of as small as 0.060 in have been used to successfully cool difficult areas. In
a case study cycle time was reduced on a mold from 40 seconds to 17 seconds by
adding 0.060 in water lines. Do not overlook options that maybe outside the box.
For example, Figure 14.2 shows a thin bubbler inserted into a skinny core. Note
that bubbler tubes are as small as 0.005 in outer diameter with a 0.002 in inner
diameter!

Figure 14.2 Small cooling line in thin core