Consistent, accurate temperature measurement is critical in the plastics industry to ensure correct finishing of thermoformed products. In both stationary and rotary thermoforming applications, low forming temperature produces stresses in the formed part; while temperatures that are too high can cause problems such as blistering and loss of colour or gloss.
Thermoforming is the process by which a thermoplastic sheet is made soft and pliable by heating, and bi-axially deformed by being forced into a three-dimensional shape. Heating the thermoplastic sheet is one of the most crucial stages in the thermoforming operation. Thermoforming machines typically use sandwich-type heaters, which consist of panels of infrared heaters above and below the sheet material.
Increasingly the plastics industry is discovering the benefits of non-contact infrared technology for process temperature measurement and control. Infrared-based sensing solutions are useful for measuring temperature under circumstances in which thermocouples or other probe-type sensors cannot be utilised, or do not produce accurate data. Non-contact IR thermometers can be employed to monitor the temperature of fast moving processes quickly and efficiently, measuring product temperature directly instead of the oven or dryer. Users can then easily adjust process parameters to ensure optimal product quality.
Specific advantages offered by infrared technology:
• It is fast, allowing for more measurements and accumulation of data.
• It facilitates measurement of moving targets.
• Measurements can be taken of hazardous or physically inaccessible objects.
• Measurements can be taken in high-temperature environments.
• There is no interference – thus, no energy is lost from the target.
• There is no risk of contamination and no mechanical effect on the surface of the object.
The overall benefits of an automated IR sensing system include:
• Improved part quality.
• Simplified quality control monitoring and setup capability.
• Identification of over-heated or under-heated sheets before making defective (off-spec) parts.
• Ability to thermoform more difficult parts.
• Ability to archive and provide customers with a thermal image of every part manufactured for quality documentation and ISO compliance.
• Increased throughput by reducing part residence time in the heating section.
• Higher yields by significantly cutting down equipment set-up and qualification times.
• Early detection of heater problems affecting process efficiency and energy consumption.
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