Troubleshooting
Why Do Heaters Fail?
The Constrictor Retaining System
Maintaining consistent coil-to-tool contact as an open coil heater expands under thermal load.
The problem
An open coil heater expands as it heats. As the coil grows, it loosens its grip on the tool, and the loss of contact reduces heat transfer, slows tool recovery and gives an internal thermocouple a less representative reading.
The solutionThe Constrictor is an optional retaining accessory that expands and slides over an open coil heater after the heater has been installed on a tool. It maintains continuous tension on the heater during operation, countering the coil’s natural thermal expansion so contact with the tool remains consistent throughout the heat cycle.
Why consistent contact matters
By maintaining contact between the open coil heater and the tool as the heater expands, the Constrictor is designed to improve heat transfer and stabilize temperature response during operation.
- Faster tool recovery — improved contact supports more effective heat transfer into the tool.
- Better thermocouple feedback — when an internal thermocouple is used, improved contact can provide a more representative temperature response.
- Reduced heat loss — the alloy’s high thermal reflectivity directs heat back toward the tool, supporting overall energy efficiency.
Application at a glance
Diameters
Wide range of standard sizes
Standard length
30 mm for flexible positioning
Recommended use: tools > 60 mm
End zones only; center left open
Recommended placement on longer tools
For tools longer than 60 mm, the recommended configuration is to apply the Constrictor at the end zones only while leaving the center section as open coil. This placement reduces heat buildup at the center of the tool, which can otherwise thermally damage the tool or the product being processed.
ConstrictorOpen coilConstrictor
TipTool length > 60 mmHead
Performance on a hot runner nozzle
The test profile below compares three heater configurations on a hot runner nozzle: a standard open coil, a pressed-on sheath over the entire length, and the Constrictor applied at the tip and head end with the center left as open coil.
Test observation
With the Constrictor in place at the tip and head end, the nozzle held higher, more even tip temperatures, provided more accurate thermocouple feedback, and improved manifold temperature, while the open center protected the plastic from heat-related damage between molding cycles.
Available sizes
Standard configurations
The Constrictor is stocked across a wide range of standard diameters to match existing coil heater installations. A standard 30 mm length provides flexibility in positioning along the tool.
Troubleshooting
Why Do Heaters Fail?
Sensors
Understanding Different Temperature Sensors
Electrical
Basic Electrical Parameters for Heater Circuits
Talk with Nexthermal engineering
Contact our engineering team to discuss matching a Constrictor retaining system to your current nozzle or tool design.
