What is the load duration rate of welding equipment?

What is the load duration rate of welding equipment? How to calculate? What is the significance for welding equipment selection? How to choose a welding machine according to the brand and diameter of the welding rod?
Answer: For welding equipment, generally, when the welding current flows through the circuit inside the machine, the circuit will heat up due to the existence of resistance. If the temperature rise exceeds the maximum temperature that the circuit insulation can withstand, it will cause the welding machine to heat up and burn out. Therefore, it is stipulated that within a five-minute cycle, the maximum output current of this welding machine will not burn out. The time that the welding machine can work continuously is divided by five minutes, and the resulting ratio is the load duration rate of the currently selected current. For example: BX3-300A welding machine, using 300A current, if it can work continuously for 3 minutes, then the load duration rate of this welding machine is 3/5=0.6 (60%). If it can work continuously for 1 minute, then the load duration rate of this welding machine is 1/5=0.2 (20%). If a 300A welding machine uses 160A current, it can work completely continuously, and the load duration rate at this time is 100%.

Therefore, when choosing welding equipment, the required current and whether it works continuously should be considered. Generally, the current is determined according to the size of the welding rod and the weldment. When choosing the specifications of the welding machine, generally, the specifications of the commonly used welding rods should be determined first, and then the required current should be calculated. Then, the specifications of the welding machine should be determined according to the required current, workload, and the load duration of the welding machine. The approximate calculation formula for the required current of the general manual welding rod is: I=(20+6*D)*D (I is the value of the current, and D is the diameter of the welding rod). For example: The required current of the 3.2 welding rod is approximately: (20+3.2*6)*3.2=125A. The required current of the 4.0 welding rod is approximately: (20+6*4)*4=176A. After determining the current, the maximum current of the required welding equipment can be estimated by the duty cycle: the general formula is: the maximum current that this welding machine can use continuously = the rated current of this model * the square root of the rated duty cycle of this machine, that is: if the candidate model has a 20% duty cycle, the required current is divided by 0.45 as the standard to select the welding machine (0.45?=20%). For example, if a 160 A current is required, 160/0.45=355, so a welding machine with a maximum current of more than 355A needs to be selected. For a 35% duty cycle, the required current is divided by 0.6 as the standard to select the current, such as 160/0.6=267, so a welding machine with a maximum current of more than 267A needs to be selected. For a 60% duty cycle, the required current is divided by 0.77 as the standard to select the welding machine, such as 160/0.77=208, then the selected welding machine model should be greater than 208A. If it works continuously, the current of full load operation must be greater than 208A. Similarly, if the electric welding machine is available, the maximum current value that the welding machine can be used continuously can be obtained by multiplying the standard output current by the square root of the duty cycle! For example: a welding machine with a rated output current of 300A and a duty cycle of 35%, 300×0.6=180, that is: this welding machine can work continuously for 24 hours without stopping when using a current below 180A.

At the same time, ordinary acid welding rods can be welded with AC or DC welding machines, while alkaline low-hydrogen type and non-ferrous metal and alloy welding rods basically must be welded with DC welding machines to complete the welding normally. When choosing an electric welding machine, you should pay attention to the choice of current type. Ordinary J422 and 506 welding rods can be welded with AC or DC, but DC welding has better stability. At the same time, due to the large penetration depth during DC welding (as the saying goes: welding through), DC welding should be used as much as possible when higher quality welding is required. However, 507 welding rods and general alloy welding rods such as stainless steel, cast iron welding rods and other alkaline coated welding rods basically require a DC welding machine for normal welding. The spatter of a DC welding machine is generally much smaller than that of an AC welding machine, and the weld has a beautiful appearance and a uniform weld wave. When a DC welding machine is used, alkaline welding rods generally adopt a DC reverse connection wiring method. At this time, the proportion of the weld width ratio is small, and a wide and shallow weld can be formed, which is conducive to the discharge of welding slag and gas in the molten pool. At the same time, it is good for the stability of the arc, which can significantly reduce welding defects and improve welding quality. Acidic welding rods can be connected either positively or reversely, and have little effect on the welding process and weld quality.

Another issue to note is that when using a DC power supply for welding, due to the characteristics of the DC current itself, it is easy to cause arc magnetic blow during the welding process. This is generally not a failure of the welding equipment. It is due to the uneven current flowing through the two sides of the weld during welding, which causes unequal magnetic field thrust on both sides and produces arc blow. This can be improved by adjusting some parameters of the welding process and changing the operating techniques. Because the intensity of magnetic blow is proportional to the square of the welding current, the magnetic blow phenomenon can be greatly alleviated by slightly reducing the welding current. Changing the ground wire connection position so that the current flowing through both sides of the weld during welding is even can also greatly reduce the arc blow problem during welding.