Temperature management on packaging machinery is critical. 10 degrees above the set point melts the film. 10 degrees below – and the seal fails. Either way, the line runs scrap, which accumulates quickly on a form-fill-seal unit producing 60 packs a minute.
In many cases, the cause of the problem comes down to a single design factor: the sensor’s position in relation to the heater. With standard elements, the sensor is mounted away from the heater. With coil heater with thermocouple, it is built-in. The difference looks subtle. On a production line, it makes all the difference.
What packaging machinery requires from the heater
There are three things that heaters used on packaging equipment ask of the heating solution, unlike in any other industrial applications:
Small zones. Sealing bars, crimp jaws, hot melt nozzles and cutting heads provide very limited space. The heater has to deliver the entire wattage from a cross section of just a few millimetres.
Rapid cycling. A sealing jaw contacts the film, heats, seals and moves away, repeating the process again and again, with only a few seconds between cycles. The heat is drawn out of the tooling in each cycle. The heater has to replenish it fast, without overshooting during the gap.
Repeatability from shift to shift. Films suppliers change, ambient conditions fluctuate, line speeds change. The heater system has to maintain the set point despite all this, as the specifications for seal integrity do not change.
Standard heating elements – cartridge heaters or band heaters with separately mounted sensors – handle the first requirement well but have difficulty meeting the others.
The weak point is not in the heater itself but rather in the gap between the element and the sensor.
As the thermocouple is mounted in a separate bore or in the tooling body, it reads the temperature of the metal around it, not the temperature generated by the heater. As it takes time for the heat to transfer from the element through the tooling, the controller constantly works with outdated data.
Here is the typical scenario that occurs on packaging lines:
To compensate for the lagging sensor, maintenance personnel widen the acceptable temperature range. It allows the machine to keep working, although it quietly widens the range of seal quality as well. We explored this in detail in our guide to
Coil heater consists of the nickel-chrome resistance wire wrapped around in a metal sheath, insulated with the compacted MgO for quick heat distribution. It is annealed, which makes it possible to shape into the required profile, ensuring full contact with the tooling surface.
The thermocouple, which is usually either J type or K type, is integrated into the heater during manufacturing process. The sensing junction is placed directly at the element, at the most important spot in the coil.
This design provides for three benefits on packaging line:
Speed. As the controller sees the temperature changes instantly, when they occur at the heater, not seconds later, after the heat passes through the tooling, the PID loop settles quickly, overshooting decreases and rapid cycling stops causing temperature fluctuations.
Consistency. Since the sensor is integrated into the heater and positioned at the same place every time, it does not depend on the skill of the technician who mounts it separately.
Installation ease. One element, one connection, one bore or profile, no drilling for the sensor, no loosening of the sensor over the months of operation.
Distributed wattage creates another advantage. The coil is wound tightly in the spots where heat is lost fastest and generates even temperature distribution across the working surface, instead of the hot core and cold edges. On the sealing bar, even surface is the main goal.
Applications on packaging equipment
Coil heater with thermocouple is a custom-built part. Getting the specifications right is crucial, as the catalog number is not enough. The points to check:
“On the packaging machinery, the positioning of the sensor decides the process. When the thermocouple is integrated in the coil, the controller responds to the element, not to the tooling. This is the key to stability.” – Technical Head, DHE
Since 1989, DHE Heaters manufactures industrial heaters in Ahmedabad, including coil heaters and thermocouples for packaging, plastic and process machinery. Each heating element is custom-made: cross section, wattage distribution, thermocouple type, lead placement and sheath material.
Don’t let an incorrectly specified heater compromise your packaging performance. Whether you’re designing a new machine or replacing an existing heating element, DHE Heaters can provide a custom-engineered solution that delivers precise temperature control, reliable sealing, and long service life. Contact our team today with your application details, and we’ll help you select the right heating element for lasting efficiency and performance.
Survey No. 687/1, Hirapur Cross Road, Mahemdavad Highway, Hirapur-Barejadi Road, Ahmedabad – 382435
