African Fusion June 2015

WASA: New tubular welding electrodes

At an SAIW evening meeting held in May, Wiehan Zylstra (lef), technical manager of Welding Alloys South Africa (WASA) introduced the company’s new tubular welding electrodes for manual surface repairs and hardfacing of thin or small parts. WASA’s new tubular hardfacing

W elding Alloys’ core business in South Africa is hardfacing, cladding and build-up repairs. “The dif- ference between hardfac- ing and cladding is simply that hardfacing is about

wire into a thick mixture of carbonate and silicate deoxidants. This paved the way for modern covered electrode development. The evolution of tubular electrodes began some 60 years later with the emergence of flux-cored and Innershield welding wires. Welding Alloys was founded near Cambridge in the UK in 1966 and began manufacturing cored hardfacingwires a fewyears later. “Then, in 2010, as part of Welding Alloys’ Green Electrodeproject, thecompanyacquired tubular hardfacing electrode manu- facturing technology from a Malaysian company and, in 2014, began manufac- turing a successful range of formulations of its own,” Zylstra reveals. WA tubular hardfacing electrodes (TEs), while designed to be used in the same way and with the same power sources as coated shielded metal arc electrodes, are constructed like a cored wireelectrode. Thealloyingconstituents, which are mostly metal powders rather than flux, are contained inside the hol- low electrode by an outer metal sheath. Why? The main advantage of using a cored electrode is the smaller cross sectional area of the conducting path. “If you think of a coredwire, it has a thin

metal sheath that needs to bemelted by the welding current, instead of the rela- tively thick solid wire,” Zylstra explains. “To melt the thinner section, a lower total current is required to achieve the necessary current density. The cored construction, therefore, offers lower heat input and higher deposition rates compared to solid wire electrodes with flux coatings on the outside,” he says. WA’s tubular hardfacing electrodes, which range in diameter from 6.0 mm in diameter to 12 mm, offer extra-low heat input; low dilution and base metal

depositing wear and abrasion resistant materials, while the term cladding is more commonly used to describe a deposit that protects against corrosion,” Zylstra begins. Locally, WASA produces tubular con- sumables and flux-cored welding wires and is the only tubular wire consumable producerinAfrica.“Wemanufacture60to 70 t of product per month, of which 50% is used by one of our own Group compa- nies, Apex Benoni, where we refurbish crushing components and produce CrC overlay plates for wear applications on southern African mines,” he adds. Briefly summarising the history of tubular electrode development, Zylstra says that the first patent for an arcweld- ing process using ametal electrode was awarded in 1892 toCL Coffinof Detroit. A few years later, in the 1900s, Oscar Kjell- berg of Sweden invented the covered or coated electrode by dipping bare iron

A key differentiating feature is the green outer coating, which is designed to offer exceptional moisture resistance. penetration; and smaller heat-affected zones than any solid electrode equiva- lents. “Low dilution is very important when it comes to hardfacing. The more the dilution, the more the alloying ele- ments such as chromium, niobium or vanadium become diluted by the base metal, reducing the wear properties of the hardfacing layer. We usually advise depositing three full hardfacing layers to guarantee the chemistry and properties of thedeposit are fully achieved, but high alloy content in the first layer can allow acceptable properties to be achieved using only two layers,” Zylstra advises. A further advantage of the low heat input associated with the tubu- lar electrode construction is reduced

WA’s tubular electrodes can be welded at low operating currents, which allow thin sections such as the flights of screw conveyors to be hardfaced successfully without destroying the basic geometry. Also, because of the spiral shape of conveyor screws, these products are not so easy to hardface using more automated processes.

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June 2015

AFRICAN FUSION