Thermal processes play a crucial role in plastics processing and therefore temperature is considered to be an important measurement parameter. High, consistent product quality can be ensured only by precise temperature control. Micro-Epsilon provides appropriate measurement technology from a single source for nearly any polymer or material.
Process monitoring is done using non-contact, infrared temperature measurement methods based on infrared cameras for overall measurements and pyrometers for pinpoint measurements. In the plastics processing industry, non-contact measurement technology based on the latest infrared measurement systems provides a number of benefits. Extremely hot measurement objects and rapidly moving or difficult-to-access objects can be easily detected at very fast measurement and response times.
Micro-Epsilon offers the latest infrared measurement systems that are suited for a variety of applications, ranging from molten metals to frozen foods. Based on the product series, these systems can detect a temperature range from -40 °C to +2200 °C. These values should be determined in real-time, and if required, allow the immediate adaption of process parameters to ensure high product quality and also to prevent unnecessary rejects. Pyrometers measure a point, while infrared cameras allow for the documentation of temperature behavior across the whole surface of the material.
In plastics processing, only precise temperature control ensures high, consistent product quality. The process is monitored using non-contact, infrared temperature measurement methods based on pyrometers for pinpoint measurements and infrared cameras for overall measurements.
The advantage of Infrared cameras is that they come with different wavelengths, which makes it possible to determine temperatures of even very thin plastic films, where for instance, longwave thermal imaging cameras are operating at their limits because of the transmissivity of the material.
The Measuring Principle
Every body with a temperature above absolute zero of -273.15 °C (= 0 Kelvin) produces electromagnetic radiation that is in proportion to its own temperature on the surface which is the so called "intrinsic radiation", irrespective of whether the object is hot steel or ice. Infrared radiation is part of this radiation which can be used for measuring temperature. Once this radiation enters the atmosphere, it is focused by a lens (input optics) in the infrared measurement system onto a detector element, and this in turn produces an electrical signal that is proportional to the radiation. The resultant signal is amplified, digitally processed and transformed into an output size proportional to the temperature of the object. The measured value can either be output as an analog signal or shown on a display, which facilitates easy connection to process control systems.
Emissivity, transmissivity and reflection are the three most major factors in IR temperature measurement. A body’s emissivity indicates the amount of radiation it emits compared to an ideal heat radiator which is a black body. The transmissivity differs with the wavelength and is relevant for thin plastic films. It is inversely proportional to the thickness, while thin material is more permeable when compared to thick plastic films. Optimal temperature measurement can be made at wavelengths where the transmissivity is not dependent on the thickness, close to zero.
Polystyrene, nylon, polypropylene and polyethylene are, for instance, IR-impermeable at 3.43 µm. The thermoMETER CTP-3 can be used to determine the temperatures of these measurement objects. The temperature range of this device extends from 50 °C to 400 °C, yet polyurethane, polyester, Teflon, polyamide and FEP are impermeable at 7.9 µm. The thermoMETER CTP-7 is used here, which precisely works within this wavelength range. Without cooling, this powerful thermoMETER delivers precise measurement values in ambient temperatures up to 85 °C. With pigmented and thicker (> 0.4 mm) films, a wavelength between 8 and 14 µm can be chosen for temperature measurements. The emissivity ranges from 0.9 to 0.95.
Part of the thermoMETER CT series, IR temperature sensors feature a modular design and can be employed for a wide range of applications in non-contact temperature measurement. These IR sensors can measure precisely and reliably, from low temperatures prevalent in laboratories or cooling chains, to the highest temperatures in blast furnaces and hot molten metals. Thanks to their compact design, the IR temperature sensors can be easily incorporated in applications where there is limited installation space, for instance, in machine building, OEM applications with multiple infrared measuring positions, or manufacturing of very small devices. The distinctive features of the thermoMETER product group are high resolution, fast response times and high precision. Especially in temperature-critical applications, MicroEpsilon’s IR sensors are the preferred choice to obtain reliable measurements. A wide range of applications are possible for temperature monitoring in production processes:
During the production of injection-molded plastic parts, thermal imaging cameras can be used to monitor the product quality, especially with regards to stability and accuracy of fit. An important factor is the inspection of the cooling process, which ensures that the material densities within the injection-molded parts are consistent. Different material densities can occur due to inhomogeneous cooling and this in turn can negatively affect the material characteristics.
In addition, incomplete molded parts that cannot be detected by visual inspection are instantly identified. For monitoring purposes, a component is conveyed directly in front of the thermal imaging camera during the manufacturing process using an automatic handling system for storage and removal of components, which are normally equipped in modern injection molding systems
The moldCONTROL thermal imager is the inline thermography system used for component testing, which allows quick, continuous and cost-effective quality inspection of molded plastic components directly in the processing line. The moldCONTROL thermal imager includes a number of components such as a thermoIMAGER infrared camera, the moldCONTROL software, a ready-for-use industrial PC and a communication interface for machines. It can be installed into existing machine control systems and removal systems at moderate cost. The main benefits of this inline thermography system are the early detection of quality fluctuations and, based on the quantified values, faster production start-up together with optimal tool temperature adjustment to reduce waste.
In production of injection-molded plastic parts, thermal imaging cameras enable the monitoring of product quality, particularly with regards to stability and accuracy of fit.
Blown Film Extrusion
In the case of blown film extrusion, the temperature of the tubular film needs to be precisely measured at different points so as to ensure consistency, high product quality and minimal waste. The frost line’s position is a major factor, which if detected precisely, prevents blocking of the take-off rollers.
With blown film extrusion, the temperature of the tubular film must be measured precisely at different points in order to ensure high product quality, consistency and to minimize waste.
In thermoforming of plastic films and sheets made from thermoplastics, the material is first heated in the molding machine until the material is fully plasticized. As soon as a predefined temperature is obtained, the material is sucked into a predefined mold through a vacuum. The heating time depends on the material surface and also on the material itself. For instance, dark plastics can be heated more rapidly compared to light-colored plastics, which means it is important to have reliable temperature control, or else the temperature would need to be detected in various, expensive test runs, which can be prevented using non-contact temperature monitoring.
In thermoforming of plastic sheets and films made from thermoplastics, the material is heated in the molding machine until the material is plasticized. When the predefined temperature is achieved, the material is sucked into a predefined mold via a vacuum.
(Injection) Stretch Blow-Molding
(Injection) stretch blow-molding is meant for thermoplastics such as PP, PET and PVC, which are normally processed into bottles. PET bottles are produced using hollow plastic parts. The preforms are initially heated to temperatures between 80 °C and 120 °C, and the plastic material eventually becomes viscous and clamped into a mold. During the supposed compensation times, the preforms are no longer heated further and their temperature is compensated for across the whole wall thickness. In the second step, the actual molding process occurs in a blowing wheel of the stretch blow molder and the finished molded bottle is finally cooled with water.
(Injection)Stretch blow molding is intended for thermoplastics such as PET, PVC and PP, which are often processed into bottles.
Particularly, it must be ensured that the process where the bottles are heated to an appropriate processing temperature is controlled so as achieve high-quality molding of the preforms. Infrared cameras allow the monitoring of temperature across the entire surface of the preforms.
Flat Film and Sheet Extrusion
During the extrusion process of flat sheets and films, molten material is pressed through huge, slotted nozzles and additionally processed in a calender, where the extruded components are cooled down in a number of steps. At several points, infrared measurement is needed to regulate the film temperature and also to guarantee smooth processing. Hence, surface defects, overheating and cracks become visible. As an essential instrument, fast defect detection helps to prevent high rejection rates and costs.
In the extrusion process of flat films and sheets, molten material is pressed through large, slotted nozzles and further processed in a calendar, where the extruded parts are cooled down in stages.
Temperature measurements are major factors for ensuring smooth production and quality, and hence they are very important in plastics processing. Based on the respective application, temperature can be established point by point using pyrometers or alternately covering the entire surface area using an infrared camera. Fast response times and high precision temperature detection directly in the processing line are the major advantages of these systems. This is how infrared temperature measurement helps to reduce waste and its related high costs. Potential system control errors are determined in real time, allowing for rapid intervention measures.
As a full-service provider, Micro-Epsilon provides suitable measurement technology for nearly any material employed in the plastics industry. The range of infrared temperature sensor products includes both infrared cameras and pyrometers. Based on the application, these infrared cameras and point sensors can be integrated together, which allows for high standards of quality in the production process. Micro-Epsilon also provides cross-product consulting, sales and support services from a single source.
This information has been sourced, reviewed and adapted from materials provided by Micro Epsilon.
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