Page 58 - Injection Molding Advanced Troubleshooting Guide

5 Mold Hydraulics

„ „5.1„ Hydraulic Uses

Hydraulics are used for a number of reasons in the injection molding industry.
They are used for slides, core pulls, ejection, reverse ejection, gas assist over flows,
gas assist valve pins, valve gates, locks, unscrewing molds, etc. [1].

„ „5.2„ Set and Pull Pressure

In situations where hydraulic cylinders are used set/pull pressures and speed
must be considered. Set/pull pressures and speed can directly affect downtime
with leaks and repairs. Pressure and speed can be your friend and foe. Time is
money so speed is your friend from this viewpoint. But whenever speed is causing
an impact with a mechanical feature that you can hear when it is set or pulled, it is
causing stress, wear, and at some point broken components with T-slot couplers or
threaded rod ends. There are a few options to protect components from the nega-
tive impacts of speed. Cushions can be added in the cylinder. It is preferred to have
your cylinder bottom out versus your component on the pull direction. On set
position your component needs to be home so you typically do not want your cylin-
der bottoming out. Evaluate how speed will impact your component and potential
failures.
Hydraulic pressures can also have a negative impact on components. On the set
position, if the component is relying on hydraulic pressure to overcome plastic/
cavity pressure a high set pressure may be required. If the component is locked in
place with a lock angle on the stationary half it does not need to use excessive hy-
draulic pressures, but rather just enough pressure to move the component. Also
with the pull action only enough hydraulic pressure is required to pull the com-
ponent back.