The torpedo system is one of the first hot runner heated nozzles introduced to the moldmaking industry. The concept is simple - a cartridge heater is inserted into a gun-drilled hole running through the center of several flow channels.

  When replacing a torpedo-style cartridge heater, several things should be remembered.
Does the hole have a flat bottom? This is important for the thermocouple to sense correctly, as air is an excellent insulator. With standard construction cartridge heaters, the disc end is concave due to the manufacturing process. To ensure an accurate measurement, a gun-drilled hole with a flat bottom and a flat bottom cartridge heater should be used to achieve optimum contact.

 What is the diameter of the hole of the cartridge heater being inserted? It is important that close tolerances be maintained in this area. With the high watt density required within this type of heater, a centerless ground heater is highly recommended. Standard tolerances by most manufacturers are q 0.002".

  With a centerless ground heater, a q 0.0008" tolerance is achieved. This greatly increases the life of the unit due to more contact within the body of the nozzle, allowing a better transfer of heat from the cartridge heater to the nozzle body.
Where is the thermocouple located? The thermocouple must be located at the disc end to ensure proper temperature measurements.

What are the requirements for the internal thermocouple junction? As today's manufacturers of controllers have different requirements, consult your controller manufacturer for these specs if you do not already have them.         

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