Plasma technologies are applied for cleaning of different metal products:
Pipes (pipe-welding plants, field pipe repair, new pipe laying, old pipe reconstruction)
Plasma technology for pre-cleaning of strips from scale and rust may be of great interest for pipe-welding plants. Plasma heads may also be applied for edge cleaning before welding. With this technology the quality of a weld seam is getting much higher and a ready pipe has clean inner and outer surfaces prepared for deposition of any protective coating. At the same time, usage of this technology solves the problems of non-contact inner flash removing (Russian Federation Patents 2.145.913, 2.147.953, 2.138.352 –1998) and of protective coating deposition within the process of electric-welded pipe production. Plasma technologies have been developed for cleaning of metal piece-works from scale and rust (Russian Federation Patent 2.145.643 – 1998) and for cleaning of hot ferrous and non-ferrous metal billets (temperature of steel billets can reach 1 260ºÑ) (Russian Federation Patent 2.145.643 – 1998). The preliminary plasma cleaning of hot billets (for rolling, forging, pressing, milling) enables substantially improve quality of finished products, especially of non-ferrous metals. Water descaling cannot practically provide that level of cleaning quality, though power inputs for both technologies are equal (approximately).
Hot-rolled metal strips and sheets
Plasma technologies have been developed for cleaning of ferrous or any non-ferrous metals and alloys (copper, titanium) strips or rod wire (where strips or wire go through the unit or is spooled inside it). The latter can be used for cleaning and coating deposition (zinc, brass, copper) in one-pass operation with 2-6 m/s of speed.
Plasma-arc cleaning guarantees a very high quality of metal surface preparation for plating by pressure or explosion welding (Russian Federation Patent 2.180.365 – 1998); such quality is practically unreachable with use of traditional ways of surface preparation. The technologies developed enable to combine cleaning process with metal coating deposition (in hot way or in vacuum) (Russian Federation Patents 2.153.025, 2.135.315 – 1998).
Welding wire (engineering plants, shipbuilding yards)
Plasma-arc technologies for welding wire cleaning may be of interest for large engineering plants, shipbuilding yards and tube-rolling mills.
At present expensive copper-plated welding wire is mainly used. The copper coating is not inspired by environmental considerations or attempts to increase weld seam strength. On the contrary, the use of copper coatings on welding wire results in large-scale and dangerous pollution of not only welding shop area but also a whole plant and environment.
It is known that all copper compounds are carcinogenic, toxic and abnormally dangerous for human health. Employing of 100-150 tones of welding wire with copper coating (5-8 microns) within a month results in 0,07-0,12 tones of dangerous copper compounds spread out into ambient air. During a year it will make 0,9-2,0 tones.
In terms of weld seam quality, the presence of copper is also undesirable; welders have known this.
The main purpose of copper coating of welding wire is to guarantee a good electrical contact when welding current is fed to wire. The other purpose is to protect welding wire from corrosion while in transportation or in storage, although it is known that copper coating is not a good corrosion protector for steel.
Plasma-arc cleaning excludes the necessity of copper-plated wire usage. Copper is only used for making current-carrying rollers. Before welding the surface of welding wire without any coatings but with any contaminations is cleaned with use of plasma-arc technology. Wire cleaned in this way can be stored without corrosion for years.
The plasma-arc technologies developed by ZAO “Petroplasma” enable to clean and outgas welding wire before its usage; it is performed environmentally friendly, cheap and of high quality. Simultaneously welding material is thermal-vacuum treated, and that enhances quality of welding still further. The cost of plasma-arc cleaning is substantially lower that that of acid or other cleaning. The use of welding wire without copper coating (after plasma-arc cleaning) enables to save up to 20-40% per tone of wire cost. Plasma-arc unit for cleaning of welding wire of 1,0-
Foil and thin strips
Plasma-arc cleaning guarantees a very high quality of metal surface preparation for plating (Russian Federation Patent 2.180.365 – 1998); such quality is practically unreachable with use of traditional ways of surface preparation.
Plasma-arc units for cleaning of aluminum foil and thin strips of non-ferrous metals and their alloys have been developed at ZAO “Petroplasma” (Russian Federation Patents 2.142.519, 2.151.815 – 1998); they successfully passed the trials.
These units not only enabled to accomplish cleaning and sterilization of foil and thin strips, but also to deposit ion-plasma coatings of any metals, titanium nitride and carbide (including deposition on polished stainless steel strips for cupolas and roof coverings).