The method has been used for more than 30 years and has more and more been replacing the manual welding processes used for surfacing.
The strip electrodes are normally 0.5 mm thick and the width is determined by the size and shape of the components to be surfaced. 30, 60 and 90 mm are the standard widths but wider strips can be used. The wider strips require supplementary magnetic control of the melt pool.
Characteristics
The stick-out is typically about 30 mm. The obtained bead thickness is normally 3-5 mm. Welding is normally performed with the strip connected to the positive pole which gives smooth overlapping and the best bead appearance. Negative polarity is also possible and gives an increased deposition rate and less penetration but at the expense of an inferior bead appearance.
Since strip surfacing gives high heat inputs, typically 6-30 kJ/mm, the parent metal needs to be reasonably thick to ensure dimensional stability during welding. A thickness of 100 mm and more is often required but thinner materials can also be used. When surfacing curved objects, care must be taken to prevent the melt pool and flux from running.
Submerged arc surfacing with strip electrodes is characterised by a high deposition rate and a relatively low dilution with the parent metal when comparing with other arc welding processes. With dilution we hereby mean volume fused parent metal divided with the total weld metal volume. The penetration of parent metal is small and uniform. The high deposition rate, uniform welding quality and the simple welding method makes strip electrode surfacing an economically attractive process.
Welding directions for 60 mm strip
Normal welding parameters for a 60 x 0,5 mm strip are: current 700-770 A, voltage 26-28 V and travelspeed 12-15 cm/min. Current affects deposition rate, penetration, dilution and weld metal temperature strongly and are all increasing with increasing current. To minimize the dilution, within a certain current, the travelspeed should be held at a reasonable low level. 120-150 mm/min. Within this range deposition rate is 12-15 kg/h and dilution is 10-20%. Normal penetration is about 1 mm differing only slightly with travelspeed.
Fluxes
To obtain the desired weld metal composition it is of utmost importance to choose the right combination of strip electrode and flux together with correct welding parameters.
The fluxes used for strip surfacing are in most cases slightly different compared to the joint welding fluxes, mainly in terms of current capacity and slag density.
There are two main groups of strip surfacing fluxes -agglomerated and fused. The agglomerated one represents the modern type of strip surfacing flux. The advantage of an agglomerated flux compared to a fused one is the possibility to alloy. The fluxes are commonly alloyed with chromium to compensate for the losses in the arc during welding.
Packaging data
The strips are delivered in coils of 25 to 600 kg with an inner diameter of 300 mm. The coils are labelled with all required information.
Strip width is normally 30, 60 or 90 mm.
