Product category:
Temperature sensors
News Release from: Impac Infrared | Subject: Infra-red pyrometers
Edited by the Engineeringtalk Editorial
Team on 06 January 2006
Infra-red pyrometers in induction
hardening
Infra-red pyrometers can be used for many applications in the induction hardening industry, but which types are best suited to which tasks?
Infra-red pyrometers can be used for many applications in the induction hardening industry, including: the classic method of induction hardening; pusher feed hardening; tempering; imaging systems; and process control A critical factor in induction hardening is the correct temperature
This article was originally published on Engineeringtalk on 18 Sep 2003 at 8.00am (UK)
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In particular the temperature influences the resulting quality and durability of parts significantly before quenching.
On one hand a too low temperature results in an insufficiently hardened surface and on the other a too high temperature may result in a damaged part.
A good knowledge of all aspects of induction hardening helps avoid the above mentioned problems.
The temperature measurement is easily handled by precise temperature measurement equipment and the use of pyrometers for noncontact temperature measurement has been proven to be successful for induction hardening applications.
Pyrometers enable the precise noncontact measurement of temperatures.
Further reading
Digital infra-red pyrometers with colour camera
Impac Infrared has expanded its Series 140 pyrometers with the addition of an integral colour camera.
Infra-red pyrometers respond to new requirements
Series 200 are high performance, digital, infra-red pyrometers designed with the OEM company in mind.
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Infra-red pyrometers developed for measuring the temperature of polyethylene and polypropylene film.
Noncontact temperature measurement features the following advantages: continuous monitoring of heating processes; identification of temperature differences which are not visible to the naked eye; fast reaction time; measurement of very small objects; cost effectiveness; and documentation of the measured values to monitor a defined quality standard.
For induction hardening the capture of a temperature distribution of a larger area might be interesting.
This can be achieved by using a line camera or thermal imaging camera.
For induction heating the metal part is placed into an alternating electromagnetic field of an induction coil.
This results in the rapid heating of the metal part.
The part itself radiates heat in a broad range of infra-red wavelengths (spectral range).
The intensity of the emitted radiation (emissivity) is dominant at short wavelengths.
This is the mechanism for precise temperature measurement using pyrometers.
The intensity of infra-red radiation of metals is dominant at short wavelengths.
If this correlation is disregarded and the wrong type of pyrometer is used, the accuracy of the temperature measurement drops significantly.
It can be shown that the pyrometer working at the shortest wavelength produces the smallest measurement errors.
The choice of the correct pyrometer depends in general on various aspects.
The pyrometer should be applicable for metals.
The measurement range of the pyrometer should cover the temperature range of the hardening process.
The spot size of the pyrometer should match at least the size of the target.
The measurement distance to the target selects the correct optic of the pyrometer.
The response time of the pyrometer should match the process speed.
Severe conditions motivate the use of so called ratio-pyrometers or fibre-optic pyrometers.
Impac's product portfolio offers solutions for a multitude of measurement tasks.
Ratio-pyrometers are needed if: the spot size of the pyrometer is larger than the target; the emissivity of the target changes during measurement; or the measurement is affected by ambient conditions, eg airborne particles.
Fibre-optic pyrometers feature a small remote optical head, which is connected via a fibre-optic cable to the transducer.
The advantages of the fibre-optics are as follows: insensitive to electromagnetic radiation; can be installed directly onto the inductor - the optics move along with the inductor in the process; and can be used where the geometry does not allow standard sensors.
In the classical process of hardening neither the inductor nor the target are moved while heating.
Consequently it is quite easy to measure the temperature with a fixed standard pyrometer.
The following reason recommends the use of pyrometers.
To ensure the optimised hardening of the metal surface the part has to be heated rapidly for a defined period of time to the correct temperature before being quenched.
The change in temperature occurs faster than can be monitored by other measurement techniques.
When confronted with severe conditions such as small targets, unfavourable atmospheres or electromagnetic fields the above mentioned ratio-pyrometers offer solutions.
These are available with or without fibre optics.
In contrast to the classical hardening process, in the pusher feed hardening process the inductor and quenching equipment is moved along the metal part.
For some heating processes it is sufficient to measure the temperature of a metal part with a fixed pyrometer.
In this process the temperature is measured at one reference point of the metal part before the inductor hides it and disables the measurement.
If the temperature needs to be measured by moving along the target the pyrometer can be mounted on the inductor.
In most cases a fibre-optic pyrometer is used for this situation.
The optical head is small, lightweight and easy to mount.
For applications where there is target size, emissivity and atmospheric obscuration problems then a ratio-pyrometer should be used.
Induction hardening can leave parts in a potentially brittle condition, due to high surface stresses caused by the rapid heating process.
To remove these stresses the parts go through a tempering process.
This process requires the part to be heated to a lower temperature and then be allowed to cool naturally.
For accurate measurement at these lower temperature the Impac IP 140 pyrometer is recommended.
Impac is a specialist for all areas of noncontact temperature measurement and provides system solutions, solutions for industries and special solutions.
Impac pyrometers feature: high quality standards; fast response time (fast moving objects can be measured); accurate measurements despite the negative influences of factors such as water vapour or dust; full digital signal conditioning; automatic process control features with the DA6000-C high speed controller; unified software protocol for data transmission for all digital units using UPP; and ease of use.
Of great importance for induction heat-treating is the extremely short time it takes to get a metal part to the target temperature and to hold it constant.
The best solution is offered by temperature regulation using a controller that reacts very quickly to any temperature change of the target.
Impac has designed a digital indicator DA6000-C with a proportional controller for temperature control.
The DA6000-C analyses the measured data of the pyrometer and controls the generator, which gives the required energy to the inductor to heat the part.
The proportional controller provides a very fast cycle time of 1ms and ideally suited for induction heating applications.
The desired set point and the width of the control span (hysteresis) is adjustable using the respective parameters of the DA6000-C.
In the heating up period the generator operates at full power until the temperature reaches a lower hysteresis point.
Then the controller then holds the power until the temperature gets to the set point temperature.
Besides single point measurement by pyrometers, Impac offers the measurement of temperature distribution in parts using line-cameras or thermal-imaging systems.
Applications include: optimisation of the magnetic field of an inductor by logging the thermal imaging the temperature data of a target; optimisation of temperature gradients, for example of a gear wheel between the tooth tip and tooth base; detection of the optimal spot for a single point measurement analysing a thermal image; checking if targets which have been heated up in parallel show identical temperature patterns; and logging of image sequences at high speed (eg 60Hz) for later analysis of individual frames (pictures).
Impac also offers software for visualisation, data-logging and analysis for various products.
InfraWin is the standard software shipped with all digital pyrometers from Impac.
Additionally to for visualisation, data-logging and analysis of temperature all parameters of the digital pyrometer can be adjusted using the Universal Pyrometer Protocol (UPP).
This enables the seamless integration of Impac pyrometers into existing user software.
InductoWin includes the standard features of InfraWin.
Additionally this software provides enhanced time management of processes while measuring the temperature.
MultiTemp is a software package for combining data from several pyrometers.
Temperatures are visualised, logged and can be analysed from a central computer.
Also all parameters of all attached pyrometers are adjustable.
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