How
to Use a Valve Gate for Injection Molding
A hot runner system with
a valve gate can lower the production cost of molded plastic parts.
A hot runner system offers some significant
advantages in injection molding. A key component of such a system is the valve
gate. The valve gate shuts off the flow of molten plastic to the mold at a
specific time right at the part surface. This allows a part to be molded
without a sprue or runner remaining on the part. Eliminating the sprue or
runner improves the appearance of the part, may shorten cycle times, eliminates
the need for a runner removal operation and eliminates the waste associated
with a discarded runner or sprue.
How to use a Valve Gate in Molding
1
Size and select a valve gate in
tandem with the hot runner system. The hot runner system provider will aid in
the selection process. In many cases, the mold maker will coordinate this
effort. The material to be molded and the overall part design will be the
fundamental keys to sizing a valve gate.
2
Install the mold with a hot
runner system and the valve gate in an injection press. The electronic controls
for the valve gate will need to be tied to the press timer that times the
injection cycle. Additionally, valve gates are often pneumatically or
hydraulically actuated. Ensure that proper controls are set up to actuate the
valve.
3
Determine the time in the
injection cycle when the gate should be closed. This will be a function of the
rate of material flow and the size of the part. Once the mold has been
sufficiently filled by molten plastic to produce acceptable quality, there is
no need for additional plastic to be injected. This is when the gate can be
closed and the melt procedure for the next cycle can begin.
4
Set the actuator on the valve
gate to shut when the injection timer reaches the time determined in the
previous step.
5
Set the actuator on the valve
gate to open when the injection timer is reset at the beginning of the next
cycle.
6
Commence operating the
injection press as per normal operating conditions.
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