Welding Formulas

Welding Formulas:

Q1: A pressure of 20 volts is applied across ends of a wire, and a current of 5 Amperes flow through it. Find the resistance of the wire in ohms:

Ans: R= V÷I = 20÷5= 4 ohms

 

Q2: A welding resistor has a resistance of 0.1 ohms. Find the voltage drop across it when a current of 150 Amperes is flowing through it.

Ans: V= I X R, i.e, V= 150 X 0.1= 15 volts drop

 

Q3: A welding generator has an output of 80 volts, 250 Amperes. Find output in Kilowatts and Joules per second:

Ans:

 V= 80

A= 250

W= 80 X 250 = 20000

KW= 20000/1000= 20 KW

20000 J/s

Q4: How do you find Chromium equivalent if Si= 0.8% and Cr = 19.0%?

Ans: Formula:

      % Cr + % Mo(1.5 X %Si) + (0.5 X % Nb)

       % Cr + % Mo(1.5 X % Si) + ( 0.5 X %Nb)

        %  19.0 + 1.2 + 0

        %  20.2

 

 

Q5: How do you find Nickel equivalent if C = 0.03%, Mn = 0.7%, Ni = 10.0% ?

Ans= Formula=

  % Ni + (30 X % C) + ( 0.5 X % Mn)

% 10.0 + 30 X 0.03 + 0.5 X 0.7

% 10.0 + 0.9 + 0.35

% 11.25

 

Q: What is definition of dilution?

Ans: When two metals are fusion welded together by metal arc, TIG, MIG or submerged Arc processes, the final composition consists of an admixture of parent plate and welding wire.

Formula:

% percentage dilution =  weight of parent metal in weld     X  100

                                                Total weight of weld

If there are 15 parts by weight of parent plate in75 parts by weight of weld metal then the dilution is 15/75 X 100 = 20%

Average values of dilution for various processes are:

Metal Arc:                  25-40%

SAW:                          25-40%

MIG (S.T)                   25-40%

MIG (D.T)                   15-30%

TIG                              25-50%

 

 

 

Q6: What will be the approximate composition of the final weld if there is 40% dilution? With 40% dilution the plate will contribute 40% and the welding wire 60%. If 9% Nickel plate, 80% composition welding wire Nickel, 20% chromium:

Nickel Plate = 40 / 100 X 9 = 3.6

80% Ni welding wire= 60/100 X 80 = 48

20% Cr welding wire = 60/100 X 20 = 12

Iron = 40/100 X 91 = 36.4

So, %

Nickel = 3.6 + 48 = 51.6 %

Chromium = 12 %

Iron = 36.4%

 

 Q7: A plate of an alloy of composition 70% Ni, 30 % Cu is to be welded to a plate of alloy steel of composition Cr-18%, Ni-12%, Fe-70% using a wire of composition 75%, Ni-15%, Cr-8% Fe.

Assuming 30% dilution, what will be the approximate composition of the final weld?

With 30% dilution each plate will contribute 15% and the welding wire 70%.

Nickel: 15/100 X 70= 10.5

A plate of alloy steel: 15/100 X 12 = 1.8

Welding wire:  70/100 X 75 = 52.5

So, Nickel is: 10.5 + 1.8 + 52.5 = 64.8%

Chromium:

15/100 X 18 = 2.7

70/100 X 8 = 10.5

So, Chromium is = 2.7 + 10.5 = 13.2

Copper:

15/100 X 30 = 4.5

Iron:

15/100 X 70 = 10.5

70/100 X 8 = 5.6

10.5 + 5.6 = 16.1
 

Q8: How do you find Arc energy (KJ/mm)?

Ans: Arc energy (KJ/mm) = arc voltage X welding current

                                                 Welding speed (mm/s) X 1000

                                               

Q9: How do you find Heat Input by Japanese standard?

Ans: Heat = Ampere X Volts X 60

                    Travelling speed

                                            

 Heat=                        170 X 25  X 60 = 17000 Joules/cm

                            15

If you require in KJ then,

Heat =  170 X 25 X 0.06  = 17 KJ/cm

                        15

 

Q10: What is Arc Energy ?

Ans: ARC Energy = (KJ/mm) =       Volts  X  Ampere

                                                Travel speed (mm/sec)  X 1000

                              

 

 

 

 

 

 

MAG Process:

Volts = 24

Ampere = 240

Travel Speed = 300 mm/ per minute

Arc Energy (KJ/mm) =                Volts  X Amperes

                                                Travel speed (mm/sec) X 1000

=          24 X 240 X 60

               300 X 1000

=          345600

            300000

Arc Energy = 1.152 or 1.2 KJ/mm

 

Important:

Thermal Efficiency factors:

SAW (Wire Electrode) :                   1.0

MMA (Covered Electrode):               0.8

MIG /MAG:                                           0.8

FCAW (with or without gas shield): 0.8

Tungsten Inert Gas (TIG):                 0.6

Plasma:                                                0.6

 

 

 

 

 

Heat Input (KJ/mm) = volts X Amperes X 60 X K

                                    Travel speed (mm/sec) X 1000     

 

Volts = 24

Amp= 240

v = 300 mm/per minute

 

Heat Input (KJ/mm) = Volts X Amperes X 60 X K

                                    Travel speed (mm/sec) X 1000

Heat Input (KJ/mm) = 24 X 240 X 60 X 0.6

                                      300 X 1000

Heat Input (KJ/mm) =  207360 / 300000 = 0.6912 KJ/mm

           

 

 

 

Q10: How do you find Heat Input by American Standard?

Ans: Root = 140 X 14.5 X 60 = 121800/ 2.300= 52.9 KJ/mm

                        1000 X 2.3

Filling = 160 X 16 X 60 = 153600/ 1500 = 102.4 KJ/ mm

               1000 X 1.5

Capping = 150 X 15 X 60  = 135000 / 1500 = 90 KJ /mm

                   1000  x 1.5

 

 

Travelling Speed :

Root: 140 X 14.5 X 60 = 121800/ 52950 = 2.3 X 25.4 = 58.4mm/min

            1000 X 52.95

Filling: 160 X 16 X 60 = 153600 / 102400 = 1.5 X 25.4 = 38.1mm/min

            1000 X 102.4

Capping: 150 X 15 X 60 = 135000 / 90000 = 1.5 X 25.4 = 38.1 mm/min

                 1000 X 90

Q11: How do you calculate Welder Travel speed?

Ans:

Welder Travel= 4 inches

Time :           50 seconds

Formula:  4 / 50 = 0.08 inch per/sec

0.08 X 60 sec/per min= 4.8 inches /per min

 

Conversion formula:

4.8 inches X 2.54 = 12.1cm/min

12.1cm X 0.393 = 4.8 inches/min

 

Important:

Shield Metal Arc Welding:

Electrode Holder: Maximum Current Range Resistance: 150A – 500A Normal Range. If metal thickness less than 5mm then Gap will be between 1mm -2mm and if thickness is 5mm – 8mm and the gap will be between 2mm-4mm without any special preparation.

Lap weld:

(i)            Parent metal should be proper cleaned

(ii)          Pipes to have different diameters

(iii)         Not recommended above 10mm thickness

(iv)         Metal is wasted in providing a lap

Butt Weld:

(i)            When the material thickness exceeds 8mm, it is often difficult to achieve full penetration with square edge preparation.

(ii)          Then prepared by machining to V configuration.

(iii)         When plate thickness above 20mm, it is better to have double V edge preparation. This helps in achieving good quality weld without distortion.

 

Current Adjustment:

If plate thickness is between 5mm-60mm, the electrode size is recommended between 3mm-6mm.

SMAW operation:

(i)            In a welding transformer usually two settings for OCV are available say 80 V and 100V.

(ii)          The OCV setting for a D.C. power source is usually 10-20% lower than in a welding transformer of the same current ratings.

(iii)         It is often observed that the weld bead becomes wide and peaky at the point of restarting; this is usually due to over welding of the crater. This should be avoided , as far as possible, because it is not only un-slightly but also can be the source of weld defects like slag entrapment, porosity and cracks.

 

 

 

 

Electrode Motions:

 

The width of the weld bead formed under normal welding conditions in SMAW is between 1.5-2.5 times the diameter of the electrode; with well penetrated and smooth passage of the deposited metal to the work piece surface.

Cellulose coated electrodes: E6010

These are usually light coated, all position electrodes with a forceful penetrating arc. The weld metal is highly ductile.

Rutile coated Electrodes: E6012

It is an all position electrode with good penetration and quick freezing slag. Easy to operate.

Rutile coated Electrodes: E6013

All positional electrode, gives low spatter and easy to remove slag.

Rutile plus Iron Powder: E7014

A medium heavy coated all position electrode containing iron powder that enables the use of heavy current which consequently leads to higher welding output with a deposition efficiency of up to 110%.

Rutile plus Iron Powder: E7024

It is a heavy coated electrode with high deposition rate for down hand butt and fillet welds as well as horizontal fillet welds. Very easy to manipulate, low spatter rate, high welding current and deposition efficiency is nearly 140%. It can be used as a touch electrode.

Rutile plus Iron Powder: E7024

A super heavy coated iron powder electrode with a metal recovery rate of about 210%, suitable for high speed welding of down hand butt, fillet and horizontal fillet weld.

Acid Coating: E 6020

A medium heavy coated electrode producing a fluid slag for down hand horizontal, and vertical welding. For low carbon steel where high strength and high quality weld.