Plasmait GmbH from Austria is seeing an increasing demand for its high-output plasma heat treatment lines for stainless steel products especially in Asia. For example Plasmait deployed a 30kW plasma annealer to a renowned stainless steel wire producer in South East Asia, who used plasma to replace its traditional tube furnace for production of flat ferritic and austenitic product with widths up to 30mm. The HPA30 plasma annealer with output capacity of 100kg per hour will allow the manufacturer to half the energy cost per kilogram of output whilst allowing for a considerable cost saving in terms of peak power consumption. Much lower power connection requirements of plasma annealer means also cheaper cabling installation for connecting power.
The new compact single-line production will have the same output as the old multiline furnace and will take just about one third of shop floor space. A single-line production will also reduce material manipulation and limit the investment into the associated takeups, payoffs and transport system. A typical plasma annealer installation for stainless steel applications can substitute around 10 traditional lines on a conventional strand furnace.
Plasma annealer allows accurate heat input and hence more uniform recrystallization, which is reflected in homogenous grain size in the longitudinal and transversal direction. The HPA30 annealer features also an extended tempering zone to allow for extended dwell time or slow cooling, which is necessary for selected ferritic grades of stainless steel.
The new annealer combines the advantages high speed bright annealing and superior scratch-free surface finish. Processed material does not touch plasma chamber when at high temperature which reduces the risk of surface scratching. This is different to the conventional strand furnace where tubes remain in contact with the furnace guiding supports also during the maximum elevated temperatures when they are most vulnerable to the surface damage.
A unique feature of plasma annealing is that heating is conducted in low-pressure inert atmosphere, for which a vacuum installation and accurate material guiding is necessary. The advantage of vacuum system is that purging gas (usually hydrogen or forming gas) is supplied at low pressure, which reduces overall purging gas consumption.