Welding,Filler Metal,Rods and Fluxes

a)Filler metal:
-The material which is added in the weld pool to assist in filling the gap (or grooves).It forms an integrated part of the weld.
-Filler metal is usually available in stick or in a rod form.This rod is called filler metal.
-Filler rod have the same or nearly the same chemical composition as the base metal.
-Welding filler rods are available in a variety of composition(for welding different materials) and sizes.
Some of them are given in table below.

b)Fluxes:-
-During welding if the metal is heated/melted in air,
oxygen from the air combines with the metal to form oxides
which results in poor quality,low strength welds or in some cases may even make welding impossible. In order to avoid this difficulty, a flux is employed during welding.
-A flux is material used to prevent dissolve or facilitate
removed of oxides and other undesirable substance. A flux prevents the oxidation of molten metal.
-A flux is fusible and non-metallic
-During welding flux chemically reacts with the oxides and a slag is formed that floats and covers the top of the molten puddle of metal and thus helps keep out atmospheric oxygen and other gases.
-Fluxes are available as powders, pastes or liquids.
-Flux may be used either by applying  directly on to the surface of the base metal to be welded or by dipping the heated end of the filler rod in it. The flux sticks to the filler rod end.
-After welding the slag from over the welded joint can be
removed by chipping,filing, or grinding.
-No flux is used in the gas welding of Steel
-Fluxes are used in the gas welding of cast iron,stainless steel,and most non-ferrous metals other than lead,zinc and some precious metals.

   

ADVANTAGES OF RIGHTWARD TECHNIQUE

Rightward techniques has certain advantages over the leftward techniques.

-Up-to 8.2mm plate thickness no bevel is necessary. This saves the cost of preparation and reduces the consumption of filler rod.

-To weld thicker metal, where beveling of plate edges becomes necessary, the included angle of V is only 60 degree which require less filler metal against 80 degree V preparation used in leftward welding technique.

-The welders view of the weld pool and the sides and bottom of the V groove is unobstructed. This result in better control and higher welding speed.

-The smaller volume for deposited metal as compared to leftward welding reduces shrinkage and distortion.

-The weld quality is better than that obtained from leftward technique.

-Due to less consumption of filler metal, the rightward technique involves lower cost of welding than leftward
technique.

WELDING TECHNIQUES

-There are two usual methods depending upon the ways in which welding rod and welding torch are used.
1-Leftward technique or forehand welding method.
2-Righward technique or Backhand welding technique.

1)Leftward Technique
-The welder holds welding torch in the right hand and filler rod in the left hand.
-The welding flame is directed away from the finished weld i.e. towards the un-welded part of the joint.filler rod when used is directed towards the welded part of the joint.(fig-)
-The weld is commenced on the right hand side of the seam, working towards the left-hand side.The blowpipe or welding torch is given small side way movement, while the filler rod is moved steady across the seam. The filler rod is added using the backward and forward movement of the rod allowing the flame to melt the bottom edge of the plate just ahead of the weld pool.
-Since the flame is pointed in the direction of the welding, it preheats the edges of the joint.
-Good control and a neat appearance are characteristics of
the leftward method.
-Leftward technique is usually used on relatively thin metals, i.e having thickness less than 5mm.
-When workpiece thickness is over 3mm bevel the plate edges to produce a V-joint so that good root fusion may be achieved. The included angle of V-joint is 80-90 degree. This large volume weld is uneconomical in terms of time, weld metal deposited and quantity of gases used and may
also over-distort weldmentt and welding thick materials.
Long welding time also leads to overheating of the weld area and thus the weld metal may have coarse grain.
-When welding materials over 6.5mm thick, it is difficult to attain even penetration at the bottom of the V and therefore the quality of the weld decreases as plate thickness increases.
-The leftward technique requires careful manipulation to
guard against excessive melting of the base metal and filler metal. The influence of the base metal on the properties of the weld metal can be very deep.
-Another disadvantage associated with leftward technique
is that the look of the joint edges is interrupted and it
is necessary to remove the end of the rod,(which slow down the welding process) this itself resulting in the oxides formed on the tip of the rod being deposited into the weld pool when the weld is recommenced.

2)Rightward Technique:
-The welder holds the welding torch in the right hand and the filler rod in the left.
-Welding begins at thew left hand end of the joint and proceeds towards the right, hence the name rightward technique.
-The direction of welding is opposite to that when employing the leftward technique.
-The torch flame in rightward technique is directed towards the completed weld and the filler rod remains between the flame and the completed weld section.
-Since the flame is constantly directed towards the V ahead of the weld puddle no side-wise motion of the welding torch is necessary. As a result a narrower V groove can be utilized than in leftward welding.This provide a greater control and reduced welding cost.
-During welding the filler rod can be moved in circles(within the puddle) or semi-circles (back and
forth around the puddle).
-In rightward welding the weld puddle is less fluid and this result in a slightly different appearance of the weld surface. The ripples are heavier and spaced further apart.
-The rightward techniques is used on heavier or thicker
(above 5mm) base metal.Weld with penetration of approximately12mm can be achieved in a single pass.

GAS WELDING TECHNIQUE

Base Metal Preparation:

Joints used in gas welding are:

i)  Butt joint
ii) lap joint
iii) Edge joint
iv)  T-joint
 v)  Corner joint
Either fillet or groove welds are used depending on the work-piece and on strength requirement.
-Workpiece edges may be prepared by
i)gas cutting
ii)Plasma cutting
iii)Milling
iv)Shaping
v)Planning etc.   
fig--
-In joint preparation it should be ensured that the plate edges are free from rust or oil.this prevents excessive fumes and helps improves the appearance of finished weld.
a strong wire brush is used to dispose of rust and small burns.The parts to be welded may be pre-set to counteract distortion. 

EXTINGUSHING THE FLAME AND STOP WELDING

1)When the welding or cutting operation is finished, close the torch acetylene valve and then turn off the torch oxygen valve.

2)Close the oxygen cylinder valve.

3)Release the pressure in the hose and regulator by opening the oxygen control valve on the torch.

4)Release the pressure in the oxygen regulator diaphragm by turning the regulator to the minimum pressure position.

5)Close the oxygen control valve on the torch.

6)Repeat the same procedure for acetylene.

FLAME ADJUSTMENT

1)To start with, when the oxyacetylene gas welding torch is ignited, it gives an acetylene flame (fig-) in which enough oxygen is drawn in from the atmosphere to burn acetylene partially.From acetylene flame excess of free carbon is released into the air. Air acetylene flame may be used to apply carbon to mold faces in the foundry, because the carbon acts as an insulator between the molten metal and the mold face.

2)As the oxygen valve in the torch is progressively opened, the flame becomes luminous.Then the luminous portion contracts towards the welding tip forming a distinct bright zone within a blue outer envelope. This is Carbonizing flame and has large excess of acetylene.

3)With further increase of oxygen content, the bright zone of the flame contracts farther and is seen to consists of two parts: a brighter inner cone and a pale green feather trailing off its end into the blue envelope. This is a reducing flame.(fig)

4)If at this stage oxygen flame is increased gradually a certain point will reach where one will notice a distinct change in the sound of the flame and a well defined white cone will appear near the tip surrounded by a bluish envelope that is faintly luminous.This is a neutral flame.There is an approximate one to one mixture of acetylene and oxygen to result a neutral flame.

5)Further increase of oxygen content into the mixture will give rise to an oxidizing flame.

LIGHTNG THE WELDING TORCH

                                                                 

 1) Crack the cylinder valve on oxygen and cylinder by opening the valve and closing it quickly in order to blow out foreign matter.

2)Attach the oxygen and acetylene pressure regulator to the respective oxygen and acetylene cylinders.

3)Attach the hoses to the pressure regulators.

4)Attach the other ends of the two hoses to the welding torch.

5)Select the proper tip(nozzle) and mixing head and attach it to the welding torch.

6)Back off the regulator screws on both units until the screws turns freely.This is necessary to eliminate a
sudden surge of excessive pressure on the working side of the regulator when the cylinder is turned on.
7)Make sure that both torch needle valves are turned off  (clock-wise).

8)Open the acetylene cylinder valve 1/4 to 1/2 turn. Open the oxygen cylinder valve all the way.

9)Open the acetylene (torch) needle valve one full turn.Turn the adjusting screw on the acetylene pressure regulator clockwise until acetylene gas comes from the torch tip.

10)Light the welding torch using a spark lighter.

11)The acetylene pressure regulator screw should then be adjusted until there is a gap of about 6mm between the torch tip and the flame.This is the proper pressure for the size of the tip being used regardless for the gauge pressure shown on the working pressure gauge on the regulator.

12)Oxygen needle valve on the torch is then opened to adjust the welding flame.

CHEMISTRY OF OXY-ACETYLENE WELDING FLAME

-The maximum temperature of oxy-acetylene flame is 3100 - 3500 degree Celsius and the center of the heat concentration is just at the extreme tip of the white cone. Combustion of gas mixture is recognized as taking place in two main stages.

Stage 1 : Oxygen and acetylene in equal proportion by volume burn in the inner white cone.The oxygen combines with carbon of the acetylene and form carbon monoxide ,while the hydrogen is liberated.

2 C2H2 + 2O2  ---->  4CO + 2H2 

 Stage 2: Upon passing into the outer envelope  of the flame two more reactions takes place as combustion is completed. The carbon monoxide use the oxygen supplied from the air surrounding the flame and as a result of burning forms carbon-dioxide. The hydrogen also burns with the oxygen (from the atmosphere) and forms water-vapor (H2O).

4CO + 2H2 + 3O2  --> 4CO2 + 2H2O

Combining the above two equations 

2C2H2 + 5O2 ---> 4CO2 +2H2O

It can be seen that the above two-fifth of the oxygen necessary for the complete combustion of acetylene is got from the cylinder whereas the rest comes from the surrounding  atmosphere.

  

WELDING FLAMES

Neutral Flame:
-A neutral flame is produced when approximately equal volume of oxygen and acetylene are mixed in the welding torch and burnt at the torch tip.
-The temperature of the neutral is of the order of about 3260 degree Celsius.
-The flame has a nicely defined inner core which is light blue in color. It is surrounded by an outer flame envelop produced by the combination of oxygen in the air and superheated carbon monoxide and hydrogen gases from the inner cone.This envelop is usually a much darker blue than the inner cone.
-A neutral flame is named so because it effects no chemical change in the molten metal and therefore will not oxidize or carburize the metal.
-The neutral flame is commonly used for the welding at:
1) mild steel
2) stainless steel
3) Cast steel
4) Copper
5) Aluminum
Oxidizing Flame:
-If after the neutral flame has been established the Oxygen supply is increased to produce Oxidizing flame.
-Oxidizing flame can be observed by the small white cone which is shorter,more bluer and more pointed than the neutral flame.
-An oxidizing flame burns making a roaring sound.and is much hotter than the neutral flame due to excess of oxygen supply causing the temperature to rise up to 6800 degree  Celsius
-A slightly Oxidizing flame.is helping welding most metals like  (1) Copper-base metal  (2) Zinc-base metals
(3) A few types of ferrous metals such as manganese steel and cast iron.
-The Oxidizing atmosphere in these cases creates a base metal oxide that protects the base metal.
Reducing Flame:
If the volume of Oxygen supplied in the metal flame is reduced the reducing flame will be a carburising flame
rich in acatylene.
-A reducing flame can be observed by acetylene feather which exists between the inner cone and the outer envelope.The outer flame envelope is longer than neutral flame an is usually much brighter in color
-A reducing flame does not completely consumes the available Carbon, therefore the burning temperature is
lower and the left over carbon is forced into the molten metal. With iron and steel it produces very hard  and brittle substance known as iron carbide.This chemical change makes the metal unsuitable for many applications in which the weld may need to be bent or stretched. Metal that tend to absorb Carbon should not be welded with reducing flame.
-A reducing flame has an approximate temperature of 5500 degree Fahrenheit.A reducing flame may be distinguished from a carburizing flame in the fact that a carburizing  flame contains more acetylene than a reducing flame.
-A carburizing flame is used in the welding of lead  and for surface hardening process.
-A reducing flame on the other hand does not carburize the metal rather it ensures the absence of oxidizing condition. It is used for welding of low alloy steel and for those metals ( e.g non-ferrous) that do not tend to absorb carbon. This flame is very well used for welding high carbon steels.      
-

TYPES OF WELDING FLAMES

To Ignite a Flame
Open the acetylene control valve of the welding torch and after the system has been flushed to clean the torch nozzle the gas is ignited. At this stage enough oxygen is drawn in from the atmosphere to burn acetylene partially.
The acetylene control valve is then adjusted until the flame ceases to smoke. The oxygen control valve of the welding torch is then opened in order to adjust the proportion in which acetylene and oxygen are required to mix and burn.
Types of Flame:

                                                                     fig-1

                                                                         fig-2

1-Neutral flame (Acetylene Oxygen in equal proportions)
2-Oxidising flame (Excess of Oxygen)
3-Reducing flame (Excess of Acetylene)

In oxy-acetylene welding flame is the most important tool.All the welding equipment simply serves to maintain and control the flame.The correct type of flame is essential for the production of satisfactory welds.
The flame must be of proper size,shape and condition in order to operate with maximum efficiency. 

GAS WELDING PROCESS AND EQUIPMENTS

Gas welding is a fusion welding processes which joins metals using the heat oh combustion of an oxygen/air and fuel gas (i e. acetylene,hydrogen,propane or butane ) mixture. The intense heat (flame) thus produced melts and fuses together the edges of the parts to be welded, generally wit the addition of filler metal.

OXY-ACETYLENE WELDING

When acetylene is mixed with oxygen wit appropriate proportion in the welding torch and ignited, the flame resulting at the tip of the torch is sufficiently hot to melt and join the parent metal.
The oxy-acetylene flame reaches a temperature of about 3200 degree Celsius and thus can melt all commercial metals during welding,actually flow together to form a complete bond. A filler metal rod is generally added to the molten metal pool to build up the seam slightly for greater strength.
Oxy-Acetylene welding does not require the components to be forced together under pressure until the weld forms and solidifies. 

PRACTICAL APPLICATIONS OF WELDING

Welding has been employed in industry as a tool for
(a) Regular fabrication of automobile cars, air-crafts, refrigerators etc.
(b)Repair and maintenance work, e.g. joining broken parts, rebuilding worn out components etc.
A few important applications of welding are listed below.

1. Aircraft Construction:
 (a)  Welded engine mounts
(b) Turbine frame for jet engine
(c)  Rocket motor fuel and oxidizer tanks.
(d0 Ducts, fittings and cowling components etc.

2 Automobile Construction:
 (a) Arc welded car wheels
(b) Steel rear axle housing.
(c) Frame side rails.
(d) Automobile frame, brackets etc.

3. Bridges:
 (a) Pier construction
 (b) Section lengths
 (c )  Shop and field assembly of lengthe etc.

4. Buildings:
 (a) Column base plates
 (b) Trusses
 (c) Erection of structures, etc.

5. Pressure vessels and tanks
 (a) Clad and lined steel plates
 (b) Shell construction
 (c) Joining of nozzle to the shell etc.

6. Storage tanks:
 (a) Oil, Gas and Water storage tanks.

 (7) Rail Road Equipment:
 Locomotive
(a) Under frame
(b) Air Receiver
(c) Engine
(d) Front and rear hoods etc 

8. Piping and Pipelines:
 (a) Rolled plate piping
 (b) Open pipe joints
 (c) Oil, Gas and Gasoline pipelines, etc

9. Ships:
 (a) Shell frames
 (b) Deck beams and Bulkhead stifeners.
 (c) Girders to shells
 (d) Bulkhead webs to plating etc.

10. Trucks and Trailers.
11. Machine tool frames, cutting tools and des
12. Earth moving machinery and cranes.

In addition to arc welding finds following application in repair and maintenance work.
 12. Repair of broken and damaged components and machinery such as tools, punches, dies, gears, shears,
       press and machine tool frames.
 13. hard facing and rebuilding of worn out or undersized parts rejected under inspection.
 14. Fabrication of jigs, fixtures, clamps and other work holding devices. 

COMMON WELDED BASE METALS

Metals can be classified as:
1) Ferrous
2) Non-Ferrous

Ferrous materials are the most important metals/alloys in the metallurgical and mechanical industries because of their very extensive use.
Ferrous materials finding day to day applications are:
1-Wrought Iron
2-Cast Iron
3-Carbon steels(Low,Medium and High Carbon Steels)
4-Cast Steels
5-Alloy Steels
6-Stainless Steels
Non-Ferrous materials are those that are not iron based.
Like ferrous materials non-ferrous materials also find extensive industrial applications.
Non-ferrous materials finding day to day welding applications are:
7-Alluminium and its alloys.
8-Copper and its alloys
9-Magnesium and its alloys.
10-Nickel and its alloys
11-Zinc and its alloys.

CLASSIFICATION OF WELDING PROCCESS

-There are about 35 different welding processes and several soldering methods in use by industry today.
-There are various ways of classifying the welding and allied processes and may be classified on the basis of:
1) Source of heat,flame,arc etc.
2)Types of interaction i.e liquid/liquid (fusion welding) or solid/solid (solid state welding).
-In general various welding and allied processes are classified as follows.
A) Gas Welding                                  C)Resistance Welding
-Air acetylene welding                         -Spot Welding
-Oxy -acetylene welding                      -Seam Welding
-Oxy - Hydrogen welding                    -Projection Welding
-Pressure Gas welding                         -Resistance Butt Welding
B) Arc welding                                    -Flash Butt Welding
-Carbon arc welding                            -High Frequency Resistance Welding
-Shielded metal Arc Welding                D)Solid State Welding
-Flux Cored Arc Welding                     -Cold Welding
-Subnerged Arc Welding                      -Explosive Welding
-TIG Welding                                       -Friction Welding
-MIG Welding                                      -Roll Welding
-Plasma Arc Welding                            -Diffusion Welding
Electro slag Welding                              -Forge Welding
Electric Gas welding                              -Hot Pressure Welding
-Stud Arc Welding                                -Ultrasonic Welding

E)Thermo-Chemical Welding Processes
-Thermal Welding
-Atomic Hydrogen Welding

F)Radient Energy Welding Processes
-Electro Beam Welding
-Laser Beam Welding
-

Welding-A Fabrication Process

Welding is a method for joining different metals.The large number of materials that are welded are metals and their alloys, although the term welding refers to the joining of other materials such as thermoplastics.
Welding joins different metals alloys with the help of a number of processes in which heat is supplied either electrically or by a gas torch.
In order to join two or more pieces of metals together the most essential requirement is heat.Pressure may also be employed, but this is not essential in many processess.
The use of welding in today's technology is extensive. It had a phenomenal rise since 1930; this growth has been faster than the general industrial growth. Many common everyday use items e.g. automobiles,aircraft,ships,electronics equipments,machinery,household appliances etc, depends upon welding for their commercial construction.