Page 113 - Injection Molding Advanced Troubleshooting Guide
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11.10 Hot Runner Troubleshooting 99
11.9 Zones and Wiring
Hot runners have zones, typically identified with numbers, which are dependently
controlled with a heater and a thermocouple. It is important to have the wires la-
beled for each zone so it is easier to troubleshoot versus having to chase wires
down, especially when multiple zones are used. A hot runner schematic should be
on the side of the tool showing each zone, location, and the heater watts.
The power plug/connection and the thermocouple plug/connection are also iden-
tified by zones. So, for example, the zone 1 heater leads would be to zone 1 on the
power plug and the thermocouple to zone 1 on the thermocouple plug. The two
wires coming off the heater are the same but on the thermocouple they are not.
The thermocouple has a positive and negative wire that must be wired to the cor-
rect location on the plug or it will not function properly. Similar to the battery in
your car, it is not complicated but will not work if wired in reverse. Also, thermo-
couples come in different types but the J type with the red and white wires is most
common. The positive wire is magnetic, and is the white wire for the typical J type,
and the red one is the negative. If you are ever in doubt which one is the positive
wire you can use a magnet to find out. Make sure to use the proper thermocouple
for the chosen hot runner controller. With thermocouples be cautious adding wire
extensions unless you are experienced with proper methods and problems with
cold junctions. With the heater and thermocouple any connections with extensions
must be insulated.
11.10 Hot Runner Troubleshooting
There are some things you can do in the molding machine to troubleshoot hot
runners instead of pulling the mold for repair. A first thing to try when having hot
runner issues is to change out the cables and controller. Long experience has
shown that the controller or cables are often the source of the issue. Also, just be-
cause the controller shows a zone at the proper set temperature does not necessar-
ily mean that this is the case if you are having an issue. Also verify the pins in the
plugs, because at times they can get pushed in not making contact with the con-
nection on the cable plug.
Use a pyrometer with a 0.040″–0.060″ diameter sheath thermocouple to verify
temperatures inside the hot drops or the inlet channel. With valve gates you pull
the valve pin back to get inside the drop flow channel (note: always use proper
safety precautions including face shields and move the injection unit away from
the mold to avoid a blowout while probing tips). Make sure to contact the steel in
