The Land GST has been specifically developed to provide continuous and accurate measurement of temperature and emissivity on coated steel strip during the galvanneal reaction.
This system allows close control of the reaction and position of the reaction zone, thus giving much tighter control of product quality.
It allows for rapid changes of line speed and furnace power with changes of substrate or coating weight, in order to maintain control of the reaction zone.
The furnace is optimised to reduce heating costs, maximise throughput and avoid excessive over-reaction which may otherwise produce powdering or flaking of the coating during subsequent forming operations.
A Land GST system ensures the production of consistent, high quality, premium-coated steel, demanded by the automotive industry.
Without the close control provided by a GST system, manufacturers of lower grade coated steels cannot sell to customers requiring premium-grade products.
FEATURES AND BENEFITS:
- Accurate non contact temperature measurement on galvannealing steel.
- Automatic emissivity compensation allows for variations in the reaction zone.
- Continuous emissivity readout for indication of extent of reaction.
- Reliable, drift free operation with a minimum of maintenance.
Following the brief immersion of the steel strip in the zinc bath, the iron-zinc diffusion reaction is initiated at the metallic interface.
Subsequent reheating maintains and accelerates the reaction so that after a few seconds iron particles start to appear at the surface.
Just prior to this the emissivity is very low, being that of the molten zinc, but the emergence of the iron creates areas with a solid, crystalline and microscopically rough surface.
In a short period of time (approx. five seconds) the emissivity value increases about fourfold and the non greyness factor (ratio of emissivities at two close wavelengths) also changes markedly.
This renders conventional single wavelength or ratio thermometer systems very inaccurate.
The position of the reaction zone within the galvannealing furnace will depend critically on temperature, line speed, coating weight, alloy type, strip width and gauge.
This makes control of the zone position difficult to achieve without very accurate knowledge of the temperature and the extent of the reaction (i.e. surface condition.)
The GST utilises an extremely accurate infrared radiation thermometer coupled to an intelligent signal processor containing a unique emissivity relationship algorithm.
Once set, the system can recognise and compensate automatically for the emissivity changes as they occur.
Target emissivity, as well as temperature, is output by the processor to provide an indication of the extent of the galvanneal reaction.
As a result of experience gained from many site trials and installations, it has been found that slight variations are required in the temperature calculation coefficient values, in order to maximise the system accuracy at each measurement point.
A unique feature of the GST thermometer is the ability to optimise each unit individually.
This may then improve the measurement accuracy at each location.
Optimisation requires a small number of temperature comparisons to be made on a representative sample of product types, against the GST Surface Reference Probe. This device features an emissivity enhancing optic.
Optimisation is performed using APCOS (Application Processor Configuration and Optimisation Software), provided as standard with the LMG GS processor. APCOS processes data and submits a relevant solution for the temperature calculation.
- Document download: galvanneal_strip_thermometer.pdf
- Top of snout/entry dip (can utilize the wedge method given appropriate sighting)
- Exit cooling (Top roll entry)
AMETEK Land recommends:
- Top of snout/entry dip
- Exit of soaking zone
- Exit cooling (Top roll entry)