Strip cladding

Strip cladding

Although most applications of the submerged arc process make use of single or multiwire systems using round wires, electrodes in the form of a strip are often used for cladding purposes. Strips are usually 0.5mm thick, the commonest strip width being 60mm, but wider strips e.g. 100mm can be used without any loss of quality. The big advantage of strip cladding is that penetration is low, particularly with DC electrode negative polarity, and deposition rate is relatively high. Modern fluxes designed for strip cladding have greater current tolerance than earlier types and use of currents up to 1200 amperes with austenitic stainless steel strips gives deposition rates of up to 22mg/hr with DC electrode positive polarity. Inconel can also be deposited and, provided the flux is low silica type and the Inconel strip used contains 2 - 3% Nb, good quality crack free deposits can be obtained. Monel, aluminium, bronze, nickel and 13% Cr strips have also been successfully used as strip cladding electrodes. Good electrical contact between the strip and feed nozzle is essential.

Typical Defects And Causes.
           
Lack of penetration.
            a.         Electrode too large for weld prep.
            b.         Current too low.
            c.         Root face too large.
            d.         Root gap too small.
            e.         Mismatch.
            f.          Wrong polarity.
            g.         Stick out length too long.
            h.         Insufficient cleaning of second side in double sided preps.
           
Porosity.
            a.         Dirt in weld prep.
            b.         Dirt/rust on electrode.
            c.         Damp or contaminated flux.
            d.         Incorrect current type for flux.
            e.         Insufficient flux covering.
            f.          Material defects. (laminations, inclusions, high sulphur)
           
Centreline cracking.
            a.         Current too high.
            b.         Weld prep too narrow.
            c.         Material with high sulphur or phosphorus content.
          
 Slag inclusions.
            a.         Inadequate inter run cleaning.
            b.         Poor joint configuration.
            c.         Poor positioning of weld runs.
            d.         Voltage too low.
          
 Spatter.
            a.         Current too high.
            b.         Incorrect current type for flux.

            Also lack of fusion, undercut, excessive penetration and weld profile defects.

Applications.
            Ship building.
            Heavy fabrication.
            Circumferential welds (e.g. rotated vessels).
            Longitudinal seams (e.g. for pipelines).
            Cladding applications.