At
the nozzle of the barrel, molten material can flow continuously, especially
during part ejection. This can be noticed inside between two open mold platens.
Once in contact with the cooler mold surface, this continuously flowing
material cools and solidifies. As the mold closes on this cooled material, this
solidified material can be caught in the closed mold and cause mold damage.
This process of continuously flowing material out of nozzle is referred to as
drool. Drooling can be found not only at the nozzle but can also occur at the
sprue bushing, hot tip, or at the gate. Here are some causes and solutions
below for Nozzle Drool.
The
presence of moisture causes a reduction in the molecular weight of the material
and promotes drooling as well. Solutions: Drying the material according to
recommended times and temperatures is needed to prevent drooling in this case.
The
excessive melt temperature of the material is another cause of drool. Barrel
temperatures set too high will increase the melt temperature of the material. Solutions:
Lowering the barrel temperatures starting with the middle zones, will lower the
material viscosity and reduce drool. Lowering the setting of the nozzle
temperature will also reduce drool.
Location
of the nozzle heater too close to the nozzle orifice can cause drool. Solutions:
Relocating the nozzle heater farther back on the nozzle will reduce the
temperature at the tip and orifice of the screw. Nozzle shutoff valves have
been used as another option to prevent material from drooling between mold
halves.
High
back pressures can create drooling due to excessive working of the material,
increasing the melt temperature. Solutions: Lowering back pressures can
eliminate or reduce drool. The use of decompression or suck back forces the
melt back into the nozzle and can be used to prevent nozzle drool.
More information please click www.olimy.com
More information please click www.olimy.com
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