Open coil heating elements are widely used in thermoforming machines due to their efficient heat transfer, fast response time, and cost-effectiveness. Here's how they work in this specific application:
Working Principle of Open Coil Heating Elements in Thermoforming Machines
1. Structure: Open coil elements are made from resistance wire (typically NiCr – nickel-chromium alloy) that is wound into a coil and mounted on ceramic or mica insulators. These coils are "open," meaning they're not encased, which allows for direct radiation and convection heating.
2. Heat Generation: When electric current passes through the resistance wire, it heats up due to Joule heating (resistance to the electric flow). The wire glows and emits infrared heat rapidly.
3. Heat Transfer to Plastic Sheet: In a thermoforming machine:
A plastic sheet is fed into the forming station.
Open coil heaters positioned above or below the sheet heat it uniformly to its forming temperature (usually between 120°C to 200°C, depending on the material).
The fast heat-up time ensures quick cycle times, which is essential for productivity.
4. Forming Process: Once the plastic reaches the proper temperature, it becomes pliable. Then:
A vacuum, pressure, or mechanical force shapes the heated sheet into the mold cavity.
The formed part is cooled and then trimmed to size.
Advantages of Open Coil Heating Elements in Thermoforming
Fast heat-up & cool-down time for rapid cycling
Direct radiant heat for efficient heating
Cost-effective and easy to replace
Customizable shapes and sizes for different machine zones
Zoned control possible for precise heat distribution
Typical Applications in Thermoforming
Packaging trays
Clamshell containers
Blister packs
Automotive interior parts
Disposable cups and plates
