Arc Welding – Part II AG 221 – Metals and Welding

Controlling distortion (Volume changes of expansion followed by contraction during cooling) Do not overweld. Avoid continuous welds. Consider chain intermittent Or staggered intermittent Use fewer beads (passes). Backstep Weld Use Wedging

Welding Machines Types AC Transformer DC Generator DC Rectifier AC-DC (Transformer-Rectifier) Welders may be adjusted by levers, cranks, wheels or plug-in arrangements DC welders may be Straight polarity (electrode negative) Reverse polarity (electrode positive)

AC (Alternating Current) Welder Single phase transformer Least expensive – initial cost Lightest and smallest (not portable) 180, 200, 300, 400, 500, 750 and 1000 amp output Maximum current is 25% more than rated output) Forceful arc – little sticking problem

AC (Alternating Current) Welder For using low hydrogen electrodes (higher carbon steels) like E7018 No arc blow Fast welding – large electrodes, high amp Little maintenance required Economical in operation Use only AC electrodes Doesn’t work well in thin metal welding

AC Welder Parts Primary Circuit Secondary Circuit Input lead cable (240 Volts AC grounded cable) Power source outlet to primary coils of welder Secondary Circuit Secondary coils to electrode holder and ground clamp 25-85 volts usually 0-250 amps usually

Transformer Two types of winding materials Step down type Copper – best Aluminum – loses power with heat Step down type Primary coils Many windings Small wire Great magnetic field

Transformer Secondary coils few windings Large wire Current established by induction Volts and amps are inversely related (more amps = less volts) Volts directly related to number of windings

DC (Direct Current) Welders Range 150-600 amps 150-200 amps - light shielded arc welding 200, 300, 400 amps – industrial welding 600 amp – submerged arc welding and carbon arc cutting

DC Generator May be driven by Single or 3 phase motor Gasoline engines PTO

Characteristics of DC Welders Have a forceful arc Not affected by changes in power (line voltage drop) Reserve power is available Variable use – weld all metals and alloys Requires maintenance Subject to blow Voltage and amperage are readily adjusted Polarity may be adjusted Expensive

DC Rectifier AC power use – DC welder advantages and disadvantages Quiet operation Welds well at low currents Soft arc Arc blow

AC-DC Transformer-rectifier AC transformer or DC rectifier operation straight polarity or reversed polarity Require little maintenance Weld well at low currents Versatile – weld all metals and alloy’s Expensive Subject to arc blow on DC 3 phase- smoother arc Single phase less expensive Uses AC power

Definitions Duty Cycle – measure of a welder’s ability to perform at its “amp-volt” rating under practical welding conditions it indicates the percentage of working time and idling time for which the machine is safely designed 60% duty cycle means 36 minutes working per hour at rated load (.60*60 minutes = 36 minutes) Welder Efficiency – power consumed (output) related to power used (input) in welding (Efficiency = output/input )