Welding trials using a moving copper skid
Moving contact arc welding (MCAW) involves a sliding or rolling electrical contact which supplies current to a shaped metal core along limitless lengths of flux-covered lying consumable (RidgebackT). The new process being developed at TWI uses low cost portable equipment, is readily automated, simple to operate and shows great potential for application in general fabrication and shipbuilding.
Typical cross section of MCAW RidgebackT consumable
More specifically, it is ideal for hardfacing and creates opportunities for pipe joining.
The technique differs from the traditional Firecracker (Elin Hafergut) and lying consumable welding processes because this novel consumable can carry greater currents and enables infinite lengths to be used in one operation.
a) Large diameter consumable with length tailored to suit joint
b) Electrode profiles including flux shapes which provide arc gap & focus arc
c) Sub-arc variant with compacted flux electrode supports
d) Hollow consumables with supplementary wire feed
e) Rolling contact wheel
f) Automatic system with arc deflection
g) Pipe joining
It works as follows: an arc is struck between the shaped metal core on the consumable and the workpiece. This is usually done using a fuse or fine wire wool at the arc end to ionise the consumable/substrate arc gap. The thickness of the flux covering, between the consumable core and the substrate, ensures that a controlled arc length is maintained throughout welding. The arc burns along the consumable electrode leaving a weld deposited on the workpiece.
Potential for restricted access welding
The flux-covered consumable is designed to provide a very narrow exposed ridge, with flux concentration either side to minimise spatter and deflect the arc downwards. Arc control is also aided by the work return supply being positioned up stream, i.e. with welding being carried out away from the current return connector. Inherent magnetic fields tend to deflect the arc directly towards substrate.
MCAW is well suited for remote operation or for applications where there is restricted access. It enables use of consumables which are both longer and larger in cross section, allows greater productivity and has reduced stop/start compared with conventional flux-covered consumable techniques.
Hollow-core consumable electrodes can also be used, here the metal core is supplemented by feeding an additional wire consumable into the arc zone. This wire feed technique can introduce additional metal to the weld deposit and also provides a conduit for delivery of metallic powder and or active/inert shielding gases.
Development work is currently under way at TWI to improve process control and welding productivity, and to tailor the technique to meet the requirements of specific applications.
TWI has filed for patents on MCAW.
For more information, please contact us.