Plasma: a versatile heat & surface treatment process

Plasma is proving its performance in an increasingly wide range of materials, from mainstream copper alloy and aluminium wire to specialist medical tubes and ropes, jewellery strands, aerospace materials, electronics and semiconductor wire and strip.

Most significant is Plasmait’s success in the stainless steel and nickel alloy wire and tube markets. Deployments included annealing lines for large and intermediate stainless steel wire boasts a single line output of 170 kg/h and more for martensitic stainless steels. Stainless steel wires from 1 to 10 mm can now be produced scratch-free and pile-free at high speed. Superior surface and homogenous recrystallization with small grain improves subsequent drawing and reduces the number of wire breaks on the drawing machine.

The new fine wire annealing line allows recrystallization annealing at up to 25 m/s on a range of fine stainless steel and nickel alloy wires. It is now possible to anneal fine stainless wires in-line with the drawing machine. Annealing fine wire at up to 20 times the speed of traditional strand furnace means fewer take-ups and payoffs and hence lower cost of total capital investment. The PlasmaANNEALER can cold start production in a few minutes and can be stopped immediately. This avoids long heating-up and cooling-down times and associated energy costs that are symptomatic for a conventional tube furnace.

The first plasma annealer for taped copper conductors has been in operation for more than a decade. The latest one was installed in 2015 year. The shortcomings of the traditionally used batch annealing process can be avoided with continuous plasma annealing and cleaning is used in front of the taping line. Round or rectangular conductors can be plasma annealed and cleaned in-line with a conventional taping line. Plasma annealed conductors feature better accuracy in mechanical properties and above all, better surface finish, which results in superior tape adhesion.

Plasma heat and surface treatment can be effectively deployed for plating applications. Plasma-treated copper or aluminium wires can be hot-dip coated or electroplated without the need for chemical cleaning or fluxing. For example, PV ribbon can be annealed to a super-soft state and tinned without the need for chemicals.

Plasma surface activation can also improve lubricant pickup in a drawing line. Plasma surface treatment ensures good lubricant adhesion during the drawing of stainless steel or titanium rods. Surface activation is achieved at low temperatures, which makes the process particularly economical compared to expensive-to-run traditional processes such as brushing, acid treatment or sand blasting.

Among the latest deployments was also a plasma annealer for stranded conductors and ropes. The annealer was designed to allow for rapid heat penetration through the cross-section of the stranded construction. With plasma heat treatment, the individual wires can be annealed or stress relieved to equal temper/softness.