If you replace cartridge heaters in the same mould or die again and again, the problem is rarely “bad luck”. In most cases the failure has a clear cause that can be fixed. Here are the seven reasons we see most often at our workshop in Pune.
1. Loose fit in the hole
This is the number one cause. A cartridge heater pushes its heat into the metal by conduction. An air gap – even a small one – acts as insulation, so the heater runs much hotter inside to deliver the same power. The resistance wire overheats and fails.
Fix: measure the real hole size, keep the fit close, and ream holes for high-density heaters. If the hole is worn, order a slightly larger heater diameter or reduce the watt density.
2. Watt density too high
A heater that packs too many watts into a small surface runs hot even in a good hole. Combined with a loose fit or high process temperature, life drops sharply.
Fix: use a longer heater, more heaters, or a lower wattage to reduce the watt density.
3. Moisture in the insulation
The magnesium oxide (MgO) insulation inside a heater can absorb moisture from the air, especially when heaters sit in storage or in humid conditions. This can cause low insulation resistance and leakage current.
Fix: store heaters in a dry place, and heat up slowly at low voltage if a heater has been stored for a long time. Specify moisture-resistant end seals for humid or wash-down areas.
4. Oil, plastic or other contamination at the lead end
Oil, hydraulic fluid, molten plastic or cleaning chemicals entering the lead end can carbonise and cause a short circuit.
Fix: choose sealed lead ends and protect the leads with sleeving or conduit.
5. Lead wire damage and flexing
In moving tools, the lead wires bend every cycle and eventually break where they exit the heater.
Fix: use flexible leads, stainless steel braid or conduit, right-angle exits, or swaged-in leads that resist flexing. Clamp the leads so that the movement happens away from the heater.
6. Poor temperature control
A faulty thermocouple, a thermocouple placed too far from the heater, or an on/off controller with a wide band can let the heater run far above the required temperature.
Fix: check the thermocouple and its position, or use a heater with a built-in thermocouple for faster, more accurate control.
7. Heated section outside the metal
If part of the heated length sticks out of the block, that section has nowhere to send its heat and burns out.
Fix: specify an unheated (cold) zone at the lead end that matches the part outside the block.
Quick checklist when ordering replacements
- Measured hole diameter and depth
- Wattage, voltage and process temperature
- Length that is actually inside the metal
- How the old heater failed (photo helps)
- Lead type and protection needed
We can help you solve repeated failures
Send us a photo of the failed heater and your application details. Thermosys Technologies manufactures custom cartridge heaters in Pune and can suggest a design that lasts longer. See our cartridge heaters, read how to choose the right cartridge heater, or contact us.