The Land Galvanneal Strip Thermometer - GST has been specifically developed to provide continuous and accurate measurement of temperature and emissivity on freshly 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.
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The furnace is optimized to reduce heating costs, maximize throughput and avoid excessive over-reaction.
The GST is used with the new application dedicated Landmark Graphic GS signal processor.
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.
THE PROBLEM
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. 5 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 SOLUTION
The GST utilizes an extremely accurate infrared radiation thermometer coupled to an intelligent signal processor containing a unique emissivity relationship algorithm.
Once set, the system can recognize 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.
System optimisation is facilitated using the LAND APCOS software supplied with the LMG GS processor
THE BENEFITS
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 optimized to reduce heating costs, maximize throughput and avoid excessive over-reaction which may otherwise produce powdering or flaking of the coating during subsequent forming operations.
SYSTEM OUTPUTS
The LMG GS processor provides digital indication of temperature and current outputs for connection to the galvanneal furnace control system.
The emissivity indication is provided by an analog 0.1 to 1.0 volt output, representing surface emissivity values in the range 0.1 to 1.0, for connection to data recording equipment or the furnace control system.
Specification
Thermometer type:
GST
Processor type:
LMG GS
Measurement range (specified):
350 to 550°C/662 to 1022°F
Display range:
300 to 600°C/600 to 1100°F
Response time:
1s to 98%
Target size:
89mm/3.5 in at 2m/78.0in
Resolution:
2°C/4°F
Absolute accuracy:
±5°C/9°F after optimization with APCOS (in application)
System output Temperature:
0 to 20mA or 4 to 20mA (normally non-isolated, isolated option available; nominal load resistance 500 ohms, max load including wiring 600ohms)
