Page 62 - Injection Molding Advanced Troubleshooting Guide
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5.7 Switches 45
5.6 Mounting
When using mounting plates to attach the hydraulic cylinders to the mold make
sure the plate and bolts are robust enough to prevent flexing and broken bolts from
the stresses. There have been many failures over the years due to inadequate
mounting plate thickness and bolt sizes. Whenever the cylinder rod is attached to
the component with threads make sure the hole is tapped perfectly straight/
square. Also consider doweling the plates in position so everything stays on center
of the cylinder. Threads can work loose over time so lock tight, or a set screw can
be used to reduce the chances.
Whenever possible try to protect a cylinder and the switches on a mold. There are
many examples of damage to molds due to a lack of protection for mold compo-
nents.
5.7 Switches
There are two styles of switches that are typically used with hydraulics for set and
pull position, mechanical switches, and proximity switches. Both types have ad-
vantages and disadvantages and every molder must make an appropriate choice.
Mechanical switches are easy to adjust and verify if they are actuating. They are
normally mounted outside of the mold components and provide for ease of access.
Mechanical switches are not as compact and clean as proximity switches.
Proximity switches are frequently used because they are compact and part of the
cylinder. These typically read magnetically and sense the position of the piston,
either directly on the piston itself with the sensor bolted in a hole in the wall of the
cylinder or through the cylinder wall when made of aluminum or stainless steel.
When using sensors that are bolted in a fixed position, timing of the component for
the set and pull position is critical so the piston is in the correct position and the
sensors can read it in the set and pull position. Sensors that read through the wall
of the cylinder can be adjusted to any position so timing of the component is not as
critical. However, when using aluminum cylinders you need to make sure they will
be adequate with the cavity and hydraulic pressures. Try to stay away from these
in high-temperature or high-cavity-pressure situations because they are not as
robust. Also when using proximity sensors you need to take into consideration the
temperatures they will be experiencing. Most will not read properly when going
over 150 °F.
