Resistance wire wound on a ceramic core inside a tight-tolerance stainless steel sheath. Manufactured to h9 tolerance for an exact fit in the mould bore.
Also known as: Cartridge heater · Heater cartridge
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General Information
A cartridge heater consists of NiCr resistance wire wound on a ceramic core placed inside a cylindrical stainless steel sheath. The gap between the wire and the sheath is filled with high-purity MgO powder and compacted in a swaging press. This compaction does two jobs at once: it lets heat pass quickly from the wire to the sheath, and it electrically insulates the sheath.
The single most important factor in product performance is the quality of contact between the heater and the bore it sits in. If the bore is drilled oversize, the remaining air gap traps the heat; the heater cannot dissipate the heat it generates and the wire burns out. For this reason our cartridge heaters are manufactured to h9 tolerance, and we recommend machining the bore to H7 tolerance.
For hot runner and mould applications that require high watt density, heaters can be produced up to 25 W/cm². When this value has to be exceeded, distributed winding is applied by tightening the winding pitch at the ends — this delivers more power to the end zones where the mould loses heat, while the middle section does not overheat.
Applications
- Plastic moulds
- Hot runners
- Packaging sealing jaws
- Laboratory blocks
- Mould preheating
- Dosing units
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Frequently Asked Questions
The bore should be machined to a precision fit with the smallest possible clearance around the heater; heater and bore tolerances are defined for each project. An air gap in an oversize bore interrupts heat conduction and seriously shortens heater life.
Seizing due to oxidation at high temperature is common. Using high-temperature grease during installation and removing and cleaning the heater periodically prevents this problem. For a seized heater we recommend an extraction tool.
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