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Heat Input Formula

Under arc welding process, heat input and arc energy are the measures of energy that has been supplied to the piece to form a weld. Both are measured in units of energy per unit length.
It refers to a characteristic or dimension such as weld length, a bead, the diameter of a weld spot or cross section. The amount of heat input which goes into a weld is determined as a function of time.

The heat input formula is given by,
Heat input = Voltage(V) × current(A) x time / distance travelled×1000

The accurate measurement of arc voltage is the difficulty here, but we mostly measure load voltage at the output terminals of the current source.

Example1
Determine the heat input of the engine which operates in 2000 V with a current of 5500 calories. The distance is 10 ft with time 40 sec.

Solution:
Given data parameters are

Voltage = 2000 V
Current (A) = 5500
Distance travelled = 10 ft
Time = 40 sec

Substitute all the values in the given formula.

Heat input = Voltage × current × time / distance travelled × 1000

= 2000×5500×40 / 10 ×1000

Therefore, Heat input = 44000 Joules / ft.

Example 2
A heat engine operates at a voltage of 1500 V with a current of 3400 A. Determine the heat input if the distance is 24 ft with time 80 sec.

Solution:
Given parameters are
Voltage = 1500 V
Current (A) = 3400 A
Distance = 24 ft
Time = 80 sec

Substitute all the values in the given formula.

Heat input = Voltage × current ×time / distance travelled×1000

= 1500 × 3400 × 80 / 24 x 1000
Therefore, Heat input = 17000 joules / ft.