Underwater Welding and Cutting: A Comprehensive Guide
How to Connect Two Welding Machines in Parallel. When you want to connect two welding machines in parallel, you must use a parallel switch with a capacity of at least 300 amperes. For this, you need a double-pole safety switch. Adjusting two variable power machines for parallel operation involves two phases:
- Each machine should be prepared to send the same amount of current when working in parallel, with each machine sending half of the total current.
- The open circuit voltage of both machines should be identical to prevent one machine from overpowering the other, which could cause a polarity reversal.
Follow these procedures when paralleling welding machines:
- Connect the two machines in direct polarity by identifying the polarity of each lead.
- Temporarily connect a voltmeter and a switch. Any small lever can be used for this purpose.
- Connect the ends of the terminals of each machine to a double-pole parallel switch with a 300-ampere capacity. The cable from each device must be at least 105,000 mil (1/0 50 mm2) in size.
- Connect the lead wire electrode holder and the ground lead. Isolate both conductors.
- Use machines with the same power for similar current values. For machines with different power, adjust the current proportionally to their power. The total current supplied by the two machines should equal the desired current for the work.
- Open the side switch and start both generators. Adjust the open circuit voltage of each generator to the same value if necessary. When using motor-driven welding equipment with a corresponding clutch, ensure the clutch is disengaged during the paralleling process.
- Close the temporary switch. If the voltmeter reads zero, the generators are ready for parallel operation.
- Remove the voltmeter and temporary switch after checking the voltage.
Final Test. Close the parallel switch and perform the following tests:
- If the open circuit voltage does not change, or neither generator changes after the switch is closed, the machines are properly connected in parallel. The ammeter should read approximately zero under these conditions at no load.
- If the ammeter reads over 25 amps without using the working electrode, the generators are not properly set in parallel.
- Open the side switch and check the circuits and voltages. If the circuits are correct, proceed to connect the machines in parallel again.
- If the machines are connected correctly, there will be little or no change in the arc between a single machine or two machines.
- With the electrode holder and ground lead in place, connect the ground lead to the work.
- Proceed as usual for welding or cutting operations, ensuring that the current flow from either machine does not exceed the generator output.
Determining the Polarity of a Generator. If the polarity is not indicated on the device, you can determine it as follows:
- With the power supply off, connect the ground cable and cable clamp to the device’s terminals.
- Place a removed electrode on one side of the body and the clamp on the other side.
- Place the tips of two electrodes in a container of salt water.
- Ensure the operator is well insulated from the mains.
- With the two electrodes about 5 cm apart, apply current. Bubbles will form on the negative electrode and practically none on the positive electrode.
- The polarity is correct if the bubbles rise from the electrode towards the electrode holder. If not, reverse the cables.
In general, cutting and underwater welding are performed in direct polarity, with the electrode connected to the negative terminal of the power source.
Ammeter. Ammeters are devices used to measure the number of amps passing through a point in an electrical current. Clamp-shaped ammeters measure current flow without requiring connections in the circuit. They are very useful in cutting and underwater welding, helping to preset the power required for the work to avoid piercing the hull of a ship with excessive current or using insufficient current for the electrodes.
Electrical Cables for Underwater Cutting and Welding. Electrical cables used for underwater cutting and welding are copper conductors insulated with rubber coating. Their diameters are 1/0 (50 mm2), 2/0 (70 mm2), and 3/0 (95 mm2), and their lengths are 50, 100, 200, and 300 feet. The choice of cable size depends on the specific work being performed.
The 1/0 diameter cable is extra-flexible and recommended for connecting to the torch or electrode holder. The 2/0 diameter cable is typically used for longer distances from the power source to the workplace due to its low resistance. This cable should be used when the total length of cables and conductors for the electrode and ground exceeds 300 feet (91 meters). For distances over 120 meters, use the 3/0 size cable or connect two or more 1/0 or 2/0 cables in parallel to reduce resistance.
Cutting and Welding Electrodes Underwater. Ceramic tubular electrodes (cut by pure electricity) are rarely used and are being replaced by more modern electrodes. Steel tubular electrodes consist of a steel tube covered with flux and a hole for the cutting oxygen. Exothermic electrodes (cut by temperature, non-conductive objects) consist of rods in a copper-coated steel tube. One special alloy is barillas, which do not burn an arc once they are turned on and oxygen flows between the rods.
Until recently, the only electrodes used for underwater welding were the same as those used for above-water welding but with an impermeable surface. Currently, some commercial brands have developed electrodes specifically for underwater use, and the results of underwater welding with these electrodes are very satisfactory.