Infrared Application of the Month:
Automatic Plastic Welding
The manufacturer of plastic draining pipes wished to phase out their hot-melt adhesive process of pipe inspection chamber construction. Hot-melt poses some environmental concerns in addition to the high cost of that method. A specially designed infrared heat system from Heraeus Noblelight -- featuring quartz glass heaters shaped to match the product contours -- reduced production cycle times, nearly eliminated fumes from the process, and saved energy.
Click for more examples of IR for industry... [ Back to Top ]
Infrared Application of the Month:
Hot Embossing of Holographic Foils
The manufacturer of an extensive range of stamping foils -- used in many products from food packaging to picture frames -- sought an efficient heat source for the hot embossing component of production. The previous heat method (hot oil filled rollers) did not allow precise control over the heat, thus slowing the process.
A carbon mediumwave infrared heat system from Heraeus Noblelight helped increase line speeds and provided improved control. The quick on/off properties of infrared allow quick line stoppage when needed, reducing product waste.
Click for more IR heating applications... [ Back to Top ]
Tech Center Spotlight: Optical Pyrometers
For temperature measurement and closed loop control this small sized optical non-contact temperature sensor is perfect for most industrial applications. Excellent optical resolution, high ambient operating temperature and accurate control are only a few of the outstanding features of this small footprint device.
Features
- Precise noncontact temperature measurement from -40 to 900°C
- Small infrared sensor with 22:1 optical resolution
- Rugged and usable up to 180°C ambient temperature without cooling
- Separate electronics with easy accessible programming keys and LCD backlit display
- Selectable analog output: 0/4-20mA, 0-5V, 0-10V, thermocouple type K or J
- standard air purge jacket keeps lens clean
Read more about Optical Pyrometers... [ Back to Top ]
Special Designs:
ICM Modular Infrared Heater System
Manufactured from a standard engineering design, the ICM has nearly unlimited flexibility. Unlimited in size in both length and width, large heating fields are possible with any combination of heater types and sizes. Modular in design, additional ICM modules can be built and added as your production changes. Constructed from stainless steel, these units offer many options such as pyrometers, sight tubes, air-knives, ceramic infrared glass protection covers, slide rails for adjustable heater placement, and exhaust plenums. The ICM is custom designed to exactly match your application in both performance and size.
Learn more about the ICM System from Heraeus Noblelight.
[ Back to Top ]
Non-contact Temperature Measurement and Control
In recent years infrared ovens and systems used to dry or heat materials in continuous web form or sheets running edge to edge have become more sophisticated by using automatic (closed loop) control systems. The temperature of the moving material is continuously measured with a non-contact radiation thermometer known as a radiation pyrometer, and the reading compared with a stabilized voltage representing the desired temperature, or set point. Any difference between the two voltages is amplified and fed to a thyristor solid state controller to correct the infrared intensity, and thereby hold the temperature of the product within specified limits.
Such is the importance of the concept of non-contact temperature measurement that this chapter is devoted to explaining the basic principles of these instruments and their application.
All bodies above the absolute zero temperature of -273°C emit infrared radiation. Measurement of this emitted radiation makes it possible to determine the surface temperature of a body, provided its emissivity value is taken into account. The transmitted radiation is received by a sensitive instrument containing an optical system, to focus the radiation onto a sensor which produces a small electrical signal related to temperature. This is the basis of non-contact thermometry. It is worth noting that even temperatures below 0°C can be measured with these instruments, but as the radiant energy varies as the fourth power of the absolute temperature, the signals are very weak.
In the process heating field, the vast majority of applications are in the range of 50°C to 600°C, but even so, the signals produced are of the order of just a few micro-volts per degree centigrade. In theory the viewing distance between the hot body and the instrument is immaterial provided the target area required by the optical system is of an adequate size to fill the viewing aperture. The viewing angle is also immaterial provided the target area is filled. The air space between the product and the thermometer should not contain water vapor or carbon dioxide as these absorb infrared radiation at certain wavelengths.
However there are convenient windows in the infrared spectrum which allow these absorption bands to be avoided. The most useful band of spectral response for infrared process heating applications is from 8 to 14 microns; sufficient energy is available in that segment. Moreover, only relatively low gain amplifiers are required to drive the control system, and allow for emissivity compensation.
Linearizing circuits can also be used when necessary to remove the fourth power component from the temperature signal, otherwise the readings produced by an indicator or recorder would be cramped at the lower end of the temperature scale and expanded at the top end.
The detectors which convert temperature readings to electrical signals are available in various forms, each one containing features relating to the spectrum of operation, temperature range, and time response.
- The thermopile, which is an adaptation of the thermocouple, uses multiple low mass hot junctions in series placed at the focal point of the instrument lens system. The micro-volt outputs of each thermocouple in the pile are therefore additive, giving good overall sensitivity for driving an indicating instrument or recorder direct, or a temperature controller via a built-in solid state amplifier. Response time is in the range 50 milliseconds to one second, depending upon the mass of the thermopile.
- Resistive detectors normally use a Wheatstone Bridge arrangement with a thermistor (temperature sensitive resistor) in one arm of the bridge. The bolometer falls within this group of instruments. The thermistor alone receives focused heat energy via the instrument's lens system causing the bridge to become unbalanced. A millivolt output is then obtained across the appropriate arms of the bridge. Being a thermal filament device, the response time is in the range of 100 to 200 milliseconds.
- Photon detectors employ the same basic optical system as in 1 and 2 above. Photo-conductive, photovoltaic or photo-emissive cells are used to produce electrical signals. Fast response is a feature of these detectors, being of the order of a few milliseconds.
In addition to the temperature control systems described above variations are available for processes such as moisture removal from paper or textiles. One or more detectors convert moisture content across the width of the web to electrical signals which act on the heaters via solid state controllers.
To be continued in our next issue...
View more technical bulletins... [ Back to Top ]
That's it for this month's issue of Application Notes for IR Heating. Feel free to encourage your colleagues to subscribe. Just click HERE to send them an invitation to subscribe. It's quick, easy, FREE, and no-obligation.
|
