Okay, so today's our discussion topic is the welding process and in this particular lecture we are going to discuss on these topics. As you can see, we'll first describe what is welding, then types of welding, we'll see gas welding, arc welding, friction welding, resistance welding, electro slag welding, all these different kinds of welding one by one. and finally we'll see some of the welding defects okay but remember uh in this particular workshop uh basically uh hands-on experience that you are going to be exposed to that is uh arc welding one kind of arc welding that is sm aw okay shielded metal arc welding now let us start with the definition of welding what is welding so just try to remember this few points with respect to the welding okay so first point is that it's a permanent it's a permanent joining process remember the joining process of two metals can be permanent or it can be temporary uh how can we temporarily join two metals like with the help of a screw bolt like that so those are uh temporary joint knot and bolt we can easily remove and we can separate the metal plates those are temporary joint but welding remember is a permanent joint okay once you have welded after that you have to break the metal parts you cannot easily remove that welding joint this is the first point the second point remember uh since it's a permanent joint basically it's an atomic bonding that forms at the joint okay so it's an atomic level bonding that happens third point is that two similar or dissimilar metals can be joined through welding.
Okay, that you remember. And next welding can be done with pressure or without pressure. And heat source of welding can be electricity, or it can be chemical reaction, or it can be mechanical friction.
Just in terms of points, you try to remember the definition of welding. Let us see the different types of welding. the welding types are basically uh two types of welding like fusion welding and the solid state welding okay there is another category that is also false uh not exactly under welding but this is very relevant to discuss about the soldering and brazing under this chapter welding now in fusion welding what happens the metal parts that you intend to join they are melted and then they are joined So that is why they are called the fusion welding. And fusion welding can be of different kinds. In this particular topic we are going to discuss on the arc welding and there are again different kinds of arc welding and we are going to discuss shielded metal arc welding or SMAW, a metal inert gas welding or MIG and tungsten inert gas welding that is TIG.
And then again another kinds of fusion welding is the gas welding and within gas welding we are going to discuss on oxyacetylene gas welding. Then we will discuss electro slag welding and thermit welding. These are the different kinds of fusion welding that we are going to see today.
And in a solid state welding you can see it can be resistance welding or it can be friction welding. So in case of... resistance welding or the friction welding directly the metals are not completely melted like in case of fusion welding. Okay, so what is the process? How these are working?
We will come into that. But in the resistance welding, we are going to discuss spot welding and the seam welding and under friction welding, we will see rotary or the inertial friction welding and the linear and the friction star welding. And finally, we will see what are these soldering and brazing which are also very common in industry now coming to the the most important one that we are going to carry out in our lab and that is shielded metal arc welding okay so let us see what is shielded metal arc welding okay so in a shielded metal arc welding what happens there is something called electrode Here you can see these are the different electrodes. Okay, so here in this picture you can see this is basically the electrode.
So this is what is the electrode. And if you carefully look that this electrode, there is something inner core or basically some wear kind of a thing is there. And outside that some coating is there.
So here if you look, this is the inner core material that is going throughout the electrode and outside there is some coating or some covering okay so here you can see this is like the inner core material and outside this is like the covering okay and remember uh this particular core material is most of the cases are the same material as the uh base materials which are basically joined okay suppose we want to join this particular part with this particular part. So this material, most of the cases are similar to the metal that is taken as the core material. Sometimes to improve certain properties, maybe certain alloying elements are also added with the core material. But those are certain specific purpose anyway.
So the thing is that initially what is done that between this electrode and the. metal plate where it is to be joined in between these two you can see some arc is generated. Now how the arc is generated? Let us consider that this is the metal let us consider this is the plate and say this is another plate and you have to make a joint here.
So what you do is that let us consider this end is connected with say positive. And this electrode, say this is the electrode and this electrode is connected with a negative side of a battery. Maybe if it is a DC welding, say this part is negative and this part is positive. Okay, so in that case what will happen?
That if you connect this electrode with the metal plate, then the circuit will be completed. And in this closed circuit, current will flow. It is as simple as that.
But if you maintain a very small gap, if you maintain a very small gap between this metal plate and the electrode, then the circuit will break, right? The circuit will not complete. Then what will happen that since in between these two, there is a strong force that will electromotive force will act and that is why some of the electrons.
from the electrode will pass through the air and coming or fall into the metal. So what is going to happen? So this is the electrode, this is the base maybe and what I have told that the base is suppose connected with a positive and the electrode is connected with a negative.
Sorry, electrode is connected with a negative. Okay, now we have not actually connected, the circuit is not completed. You have maintained a very small gap in the order of maybe 2 mm.
In the order of 2 mm gap you have maintained. Then what will happen? The electrons will start flow within this gas.
What is the gas? Gas is maybe the atmospheric air or there may be some other gases. Whatever that may be.
Through that the electrons will flow. And during the passage of electron then this electron will also charge the neutral gas particles. So now the gas particle will become charged particle because of in contact with the electron. Electron is going to strike the metal plate and some of the electrons will reflect back. So what is going to happen in this region?
Lot of interactions are going to take place. What are the interactions? The first is the electrons will collide with the gas particles in this region.
Electron is going to collide with the base metal here. Some of the reflected electrons from the base metal will collide with the incoming electrons. So all these collisions, all these collisions that will take place in this region are basically the source of heat. So huge amount of heat energy will be created at that location. And if you can maintain this small gap.
If you can maintain this small gap, in that case what will happen? This kind of a flow of this is a region where we call this as a plasma state. Plasma means basically the hot ionic gas. Hot ionic gas that is basically flowing. Why ionic gas?
Because all the gas particles or the air particles, whatever is there, they are now charged particles. They are now moving in this region and they are colliding continuously, creating a lot of heat. So this is going to happen in this region.
And that thing. is what is called the arc. So if you can maintain a very small gap between that base object, the working plate where you want to make this welding, if you can make this very small gap, then the arc will be generated. But if the gap is very large, suppose you maintain a gap of say 15 millimeter, that means your hand control is not very good.
So that is why the gap suddenly become very high, then you will find that this arc will extinguish. Arc will not be there. Or if you connect this electrode with the base metal, then you will find that there is no arc. So arc will only be there if you can maintain a very small gap between the metal plate and the electrode.
Clear? So this is what is the arc and that is basically the source of heat. Now what this heat is going to do? If the arc is stabilized, then what will happen?
Because of that heat, the metal that is this metal, which is basically the core metal of the electrode, that will be consumed. Consumed means that will melt. And that molten metal dropwise now fall on that zone.
In that zone, that molten metal is now going to fall. And here you can see that molten metal is gradually falling. Here you observe. The molten metal is gradually drop by drop falling there.
And what you have to do when they are falling on that region where you have to make the joint and then gradually you move in that direction. You move this electrode in that direction. That is what is called the welding direction. So then what will happen gradually drop by drop you are basically depositing on that region. And in that process what is going to happen that because of that much of heat both these metals this base metals melt this electrode melts so all these things ultimately melts and when they solidify the atomic bonds occur and finally they becomes a single material that means the weld actually has been done so this is basically the welding process that happens in case of shielded metal arc welding now the question is why the name shielded is there It is clear because of the covering that is there over the electrode.
You can see this is basically called the flux. This is called flux. Now this flux, what is the function of this flux?
The function of the flux is that you see that when heating is taking place, the temperature is very high. In case of shielded metal arc welding, the temperature is in the order of 5000 degree centigrade. The temperature is in the order of 5000 degree centigrade.
You can understand the melting point of steel is in the order of 1500 degree centigrade. So you can understand this is a very very high temperature. So at this temperature already you know that environmental oxygen is there and here is the metal. So what will happen? Instantly the metal oxide will form at that region.
But this metal oxides are very hard and brittle materials. So, they actually if the oxides form then what will happen that welding region will become very brittle. So ultimately your strength of the welding will be very bad.
So your welding will be very inefficient. So what is then the what is the option then how can we avoid this particular situation this formation of oxide with the environment. How can we protect this heat affected zone from the atmosphere. What we can do is that this flux coating helps here and this flux creates at that high temperature this flux creates some gases. Here you can see these are some gases that is forming and these gases are actually helping to protect or coming oxygen into that zone.
So this is one way. Another way is that. that these flux also are very lighter. These are not very heavier material.
They are generally very light materials. So these light fluxes what happens they generally float over the metal. If this steel is actually heavy and that is why they go downwards and these flux materials they are lighter and that is why they are at the top layer.
So what happens this top layer is basically the flux they actually react with the oxygen. And ultimately they forms which is called the slag. Okay. Now the slag materials are generally very lighter and that is why they are floating at the top.
Here you can see the slag formation takes place. And what is this slag? This slag is nothing but this flux react with the oxygen and they form this slag. And this slag ultimately floats over the surface and further oxygen cannot penetrate this slag.
and cannot come into the heat affected zone. So how the heat affected zone is protected from the environment? By the flux.
How? Because the reaction of the flux with the oxygen creates some of the shielding gases and those shielding gases don't allow coming the oxygen from the environment to that region so that they can form oxides coming in contact with the metal. And another way the slag that is formed they are generally lighter and they are floating over the surface and further oxygen cannot come or penetrate into that slag.
So in these two ways they are protecting that heat affected zone. Now if you have understood the basic welding process, now you can see that here this cross-sectional view, not the cross-sectional view, basically this particular view clears the idea that here is basically the core material is there and outside you can see the coating is there. Okay. And the electrode diameter remember is this diameter.
Okay. It is not considering the flux. Only this diameter is what is the electrode diameter. Okay.
Now coming to the next here you see that In this slide, it has been explained how it is arranged. You can see that this particular thing, what is called the electrode holder. Here you can see this electrode is held by this electrode holder here.
And you can see that one end of the current is connected with the electrode holder. And other end, you can see it is connected with the job. Here, if different kinds of welding is possible, it can be AC or it can be, polarity can be DCEN.
DCEN means direct current electrode negative. Okay, direct current electrode negative. Direct current electrode negative is also called the straight polarity.
Okay, this is also called the straight polarity. and direct current electrode positive which is called the reverse polarity reverse polarity you just remember these names because sometimes in comes of straight polarity and reverse polarity and definitely in case of ac welding there is no question of polarity because in ac welding you know continuously this plus and minus is continuously changing within once again it changes in India is around 50 times. So 50 times in once again this plus and minus is changing because in India you know the our power supply is at 50 hertz.
So 50 times basically it is going to change. So this is what is the idea. So in case of AC you can understand there is no question of polarity. Polarity happens only if it is DC.
So what are the two different kinds of DC connection possible. One connection is DC such that electrode is negative and another one is it is possible that electrode is positive. Okay, now you see these are the settings that you have to do.
Whether you have a DC power source or AC power source depending upon that you have to consider that. Now you can understand these are the only requirement. And after that, the welding process is to be done. you should have some idea about the kind of current range and the voltage range and for that it depends on many factors what should be the current range and voltage range it depends on which diameter what is the diameter of the electrode that you are using okay and what kind of welding you are going to do it based on that the current is to be selected okay so it is very much dependent on the kind of electrode that you are using i do not know exactly what kind of electrode we are going to use. But it is I think it is around 150 ampere current that is what is the current range we are using and we are going to use in our workshop AC welding.
We are going to use AC welding and 150 ampere current and the voltage will be in the order of maybe 40-50 volt in that order. So. you can understand that our power supply is not 40 volt our power supply is maybe the 440 volt or 220 volt so in our workshop it is 440 volt power supply is there so definitely what we have to do so 440 volt ac so we have to with the help of a transformer we have to convert it into 40 volt ac okay so 440 volt ac to 40 volt ac means what kind of transformer you require you required a step down transformer okay and after uh that transformer basically this uh one end will go to the electrode and the other end will go to the welding table and welding table is made of metal so basically the job will get the same polarity or the same connection it's a conductor now coming to the next here you see uh the different welding arc welding equipment very quickly i'm telling you this is what is the uh transformer that i have just mentioned uh because in welding you know that low voltage is required and high current is required and you can understand 150 ampere current means it's a very high current in our uh house uh what is the current range it is uh less than uh 5 ampere or in that order you know that maximum 20 ampere fuse is sufficient So you can understand that the in our house the current that we are using is much much lower than this value. So 150 ampere is a huge current and that is why the special cables are required because ordinary cables will not bear this 150 ampere currents.
So that is why special welding cables are required. So electrode already you have seen what is electrode, electrode holder, workpiece clamp through which that it is connected with the workpiece and here you can see the chipping hammer why the chipping hammer is required i have told you that the uh flux after reacting with the oxygen they form oxides and those are called the slag and those slags actually stays over the welding right so when the welding process will over after that with the help of this chipping hammer uh this slag portion you can see these are the slack portions those are actually removed okay those slags are actually removed if they are very hard and brittle so if you just strike few times you will find that they are easily going out of the surface. The wear brush is also very important because it is very important to prepare the welding surface. Otherwise if lot of darts and oils are there then your welding defects may be different kinds of welding defects may be there. So that is why it is very important that initially you with the help of a wear brush you clean the surface where you have to weld and after that you prepare the edge and after that you do the welding.
Protective shield is very important. I have already mentioned that the temperature is in the order of 5000 degree centigrade. So at a very high temperature the UV rays are coming from that region.
So to protect our eyes it is very important to use the protective shield. Now coming to the electrode specification. I was mentioning about the electrode. That electrode specification you see that here something is written that AWS here. AWS means American Welding Society.
And according to their specification here you see it is written E6018. E6018 or it can be E6013 or E7013 like that. Different kinds of possible.
Here you can see the different names that is possible. Now what are the meaning of each of these letters? The meaning of E, this E indicates the electrode. Okay, and second you see this particular digit that is this two digits that is 60. Remember this 60 is basically in KSI unit that means 60 kilo pound per square inch. 60 kilo pound per square inch means 60,000 PSI pound per square inch.
Okay, 60,000 PSI or you can write 60 KSI. That means 60 kilo pound per square inch. So this is what is the minimum tensile strength of the material of the electrode. Okay. This is minimum tensile strength of the material.
Minimum tensile strength. What is tensile strength and all that, that we will learn gradually. But right now you just try to remember that this is the strength of the material.
Okay. So tensile strength, minimum tensile strength that is required is 60. And Last two digits, if you see the last two digits, this first one, the first digit here you see this is written 1. This 1 actually indicates the welding position. This indicates welding position. So at which position the welding can be done. Here you can see that the meaning of 1 is like basically all.
This one means all that means in all positions the welding can be done. What we mean by the all positions here you can see different positions are there like here it is written F, V, OH, H. F means what? F means flat, V means vertical, OH means overhead, H means horizontal.
Okay so this one means all positions you can work with that. So if it is one that means in all position you can work. But if it is 2 then there are certain restrictions. Maybe only with flat and horizontal in that case maybe it is possible. So that table is not there present.
So these are certain restrictions. So here this is one thing and this last two digits that is 1, 3 as a whole 1, 3 as a whole this particular digit indicates the flux material what flux material is used okay and what is the current conditions and all that so these things are actually mentioned though the current conditions and all that are mentioned by some other digits are sometimes written afterwards and but this one three gives some idea about the flux material definitely and what is the flux material you can see in case of 6013 which is very common six zero one three uh it is used the high titania potassium okay in case of one eight you can see it is low hydrogen potassium and iron powder so it is not that this flux material is something which is fixed it again depends on the kind of electrode and remember from the electrode specification itself it will be possible to know that what is the particular flux material that is used so for that what you require you require this kind of a handbook okay there is uh American Welding Society handbook this specification. So from that you will get all those data. But for the time being you just remember what are the meaning of the different symbols, this specification of the electrode.
I have not shown the actual procedure how it is actually done in case of SMAW because that will be done in detail. You are also going to carry out in our college. Koshik sir already done this in detail.
So probably in the next class we are going to discuss that thing in detail. So that is why I am not showing how the process is actually going on. Now we will come to the next very important arc welding technique that is metal inert gas welding. And this metal inert gas welding is also called the GMAW or gas metal arc welding. Okay, the same thing.
Okay, now First see this particular video and after that I will tell you certain important points that you have to only remember for the metal inert gas welding. Why I am showing this video so that you can actually get some idea of what the physical feel that how this kind of welding is done. So what is MIG welding? MIG stands for metal inert gas welding.
The American Welding Society calls this process gas metal arc welding or GMAW. You might also hear it called wire welding. In mid welding, a thin wire acts as the electrode.
This wire is fed from a spool mounted on a gun or inside the welding machine, through a flexible tube, and out of the nozzle on the welding gun or torch. The wire is fed continuously when the trigger on the welding gun is pulled. When this trigger is pulled, it also switches on welding current and a shielding gas.
An electric arc forms between this wire electrode and the workpiece and heats both metals above their melting point. These metals mix together or coalesce and solidify to join the workpieces into a single piece. The metal in these parts to be joined is called the base metal, and the metal that comes from the melting wire electrode is called filler metal.
MIG welding always adds filler metal to the joint. Because the wire electrode melts as it's being used, MIG is called a consumable electrode process. Here's the MIG wire going through the wire feeder into a flexible tube or conduit liner.
The liner goes through the hose or welding lead all the way to the torch nozzle. At the nozzle, the wire is fed through a contact tip and comes out at the point of the weld. Shielding gas is also fed through the welding lead.
It goes through a gas diffuser and flows out of the nozzle. This shielding gas, which is often a mix of argon and CO2, protects the molten metal from reacting with oxygen. water vapor, and other things in the atmosphere. The shielding gas is stored in high pressure cylinders like these. The pressure is reduced to a usable level by a device called a regulator.
In MIG welding, all the machine controls are set on the machine itself. Most important of these are polarity, wire speed, and voltage. The trigger on the gun is just an on-off switch.
For most MIG welding, the current is direct current, or DC. DC is like the current flowing from a car battery. One wire is always the negative, and one is always positive. In DC MIG welding, the electrode is usually positive and the workpiece is negative.
The term DCEP is used, indicating that the current is direct current and the electrode is positive. This is also called reverse polarity, but DCEP is a more descriptive term. In an electric circuit, the current flows in a loop. In MIG welding, the current has to flow in a complete circle from the machine, to the torch, into the work, and back to the machine. A work lead is clamped to the work to complete the circuit from the workpiece back to the machine.
So, in summary, MIG welding is an electric arc welding process that uses a consumable wire electrode, filler metal is added automatically and the shielding gas comes from a high pressure cell okay uh so i think uh you have understood the process how it is going on i just want to mention few important points that you have to remember for the big welding the the first thing that you have to remember this is an arc welding process this is not a gas welding process though the name is metal inert gas welding but this is arc welding process So that is the first thing that you have to remember. This is arc welding process. Second thing that you have to remember for the shielding purpose, that means it is always required to protect environment from that heating zone, right? So in case of shielded metal arc welding, we have seen we have used the flux coating over the electrode. So here what is used for that?
So for that we are using some shielding gas and that shielding gas is the inert gas that we are using. So what inert gas we are using? We are using argon and carbon dioxide. These are used as the shielding gas that you have to remember in case of inert gas welding.
So inert gas is acting as a shielding gas to protect that heating zone from the environment. That is the only objective of using the inert gas. And what is the filler material? Filler material that is continuously supplied in the form of where you have observed.
that was in our case in shielded metal arc welding that was the core material that was the filler material and outside the core in the last example smaw we have seen that was the flux coating but here it is the only filler material in the form of wear that was fed into the welding zone and to protect it from environment this argon gas and carbon dioxide gas which are used as inert gas okay so these are the few things that you have to remember and it is obvious that the filler material is consumable because that is melted and continuously you have to supply the filler material so this is all about the metal inert gas welding in other way it is exactly similar uh like what we have seen in case of smaw now coming to the next one that is tungsten in natural building so again we'll see what is the process how it is done what is TIG welding TIG stands for tungsten inert gas welding the American Welding Society calls this process gas tungsten arc welding or GTAW you might also hear it called in Keeley arc welding TIG welding uses a tungsten electrode tungsten has an extremely high melting point when you TIG weld the electrode gets hot but it doesn't melt we say that it's a non-consumable electrode. It doesn't mean it lasts forever. It just means that it doesn't melt and become part of the weld. You see in a lot of other welding processes the electrode melts and becomes filler metal.
Those are consumable electrode processes. So here's the tungsten electrode being held in a TIG torch. The electrode slips into a collet. The collet tightens up against the collet body.
You can adjust the length that the electrode sticks out of the holder. By loosening up the end cap. When you tighten the end cap, the collet clamps down on the electrode. TIG works by melting the base metal, and that is the metal that makes up the two pieces that are to be joined.
The heat is generated by an electric arc that forms between the base metal and the tungsten electrode. You can control the amount of heat with a foot pedal or with a thumb wheel on the torch. For most metals, the current is direct current, or DC.
DC is like the current flowing from a car battery. One wire is always the negative and one is always the positive. In DC TIG welding, the electrode is usually negative and the workpiece is positive.
The term DCEN is used for this, indicating that the current is DC and the electrode is negative. This is also called straight polarity. but DCEN is a more descriptive term. DCEN puts most of the heat on the workpiece, and it's the most common setup. When welding aluminum, however, AC is used.
In AC, the positive and negative voltages switch back and forth between the electrode and the workpiece. This puts more heat on the electrode, but it has a cleaning effect on the workpiece. You see aluminum forms oxides that float to the top of the weld pool.
and prevent a good weld. AC current helps control these oxides. In an electric circuit, The current flows in a loop.
In TIG welding, the current has to flow in a complete circle from the machine to the torch, into the work, and back to the machine. A work lead is clamped to the work to complete the circuit from the workpiece back to the machine. Now you can TIG weld with or without filler metal, and that's not a choice you have in a lot of other processes.
If you want to add filler metal to a TIG weld, use a filler rod, which is just a rod of metal with a specific alloy. You want to make sure that the filler metal you're using is compatible with the base metal and that it has the strength required to do the job. In TIG welding, the molten metal is protected by a shielding gas. This gas, usually argon and sometimes helium or other gases, keeps the molten metal from reacting with oxygen and water vapor in the atmosphere.
This shielding gas is stored in high-pressure cylinders like these. The pressure is reduced to a usable level. by a device called a regulator the shielding gas flows through a hose and comes out right at the point of the weld so in summary tig welding is an electric arc welding process uses a non-consumable tungsten electrode the filler metal is added separately in the form of filler rod the shielding gas comes from a high pressure cylinder okay so what is tig well so the important points that you have to remember with respect to tungsten inert gas welding It is that here the electrode that is used is the tungsten electrode.
Okay. And that tungsten electrode is not acting as a filler material because previously in case of SMAW which is also called the stick welding. Okay.
This is also called the stick welding or in case of MIG welding we have seen that the electrode is continuously consumed that is melted the filler material is melted right in both the cases but in case of tungsten inert gas welding that tungsten electrode do not melt so why the tungsten electrode uh is there tungsten electrode is there to create that arc because arc is created between the tungsten electrode and the job and because of that heating the metal surface actually melt and the welding is possible or sometimes it is also can be done that separately some filler material that can be added. So with or without filler material TIG welding can be done. Okay. So separately that filler material that filler material actually consume. But remember this one is not consumable.
So this is the difference with the MIG welding. And here again to protect it from the environment again the inert gas is used. That is why the inert gas is written over there.
And that inert gas is again iron or helium this kind of gases are. most of the cases it is the argon which is used now coming to the next which is the gas welding now see in case of gas welding uh let us first see that what are the different how the gas welding actually is done okay everyone today we're going to do some oxy so here you can Here you can see that in case of gas welding definitely the gas is required and you can see that this one is the oxygen gas cylinder and this one is the acetylene gas cylinder. So what is the color of the cylinders that is very important that you have to remember and you can see that for the oxygen cylinder it is the black color and for the acetylene cylinder it is the red color. Okay.
So oxygen and acetylene. These are the two gases which is used for the oxyacetylene gas welding. And here you can see that with the cylinders there are two gauges which are connected.
One of the gauge is used to check that how much gas is left to check that and another one is there to check what is the pressure. Okay. So you can control the pressure over here that what is the pressure that is required for that particular welding.
that can be controlled from here we can see that and exactly similar thing here also you can see the two gauges uh of the oxygen these are like the regulators through which actually these are set and how to how it is so here you can see this is what is called the uh gas welding torch and You can see again there are two valves over there. Here this red one is for the acetylene and there is another control valve which is for the oxygen. Okay. And here you can see this is what is the nozzle from where basically the gas flame is coming out. Safely use your torch.
and how to do some basic fusion welding with some lap bar this is just regular steel so first off setting up your tanks a before o There's a tiny little hole here. We need to make sure that the tip is clean. Hard to see.
We need to make sure the tip is clean. The right size for the one that fits in that hole. First, we're going to do the acetylene first.
We're going to open up the main valve here half a turn. So if this is my start, I want it to get to here. I draw a little line here to help remember.
Half a turn. Now the last person who used this did not purge the valves. But usually when you get to it, let me just purge that valve for a second.
There's the pressure on my regulator. There we go. This is basically how much fuel is left in the cylinder and this is how much pressure will be coming through. So in order for me to increase pressure that is going to be coming out of my torch, I'm going to have to adjust the regulator.
I'm going to open up the knob on my torch handle for the settling or the fuel. Just open it up. Don't worry about how big it is yet. I'm going to adjust the regulator here. I'm going in the plus.
You can see plus or minus. I'm going plus, and I'm going to increase it to about 6 psi. Here we go.
We're at 3. four five six you look very closely there and you can hear the settling actually coming out go ahead and turn off your knob this one is set and ready to go next we have our oxygen so you have understood that how we can set the uh pressure and now the psi is just to protect your eyes Mostly your eyes. This is the protective shield. I'm going to set up my two pieces of flat bar here with a slight gap in between. So I have my metal setup and my torch all ready to go. All I have to do is open my acetylene valve just a little bit, or fuel valve.
This one's using acetylene. Open up just enough that you can feel it on your hands, or you can put it up in your ear and actually listen. I'm wearing these working glasses. Just enough to feel it.
Take your striker, hold it on a slight angle, side here, and get a nice sooty flame. All that black stuff is carbon. We want to get rid of that or it makes a big mess.
I'm going to open up my acetylene valve until that black smoke goes away and I have a nice feathered flame. Delicious. If you're doing thinner material, you don't need as hot of a flame.
In this case, we're doing flat bar so i'm going to open that up we'll get a nice roar i don't have a special number for this beautiful next we're going to open up our oxygen and add some oxygen to this mix watch carefully what happens to the flame now if you look at it it looks like we have two different cones here we've got a very bright one we have a longer one here don't try to get don't try to touch it but you can get pretty close without feeling any heat i'm not going to purposely do that though all right i'm going to adjust some more oxygen until that one cone gets nice and tiny so here's just like set the exposure on the camera down a little bit so you can see this so here you can see that how actually the flame looks like it has a two part you can see that one is the inner core and another one is the outer core okay that is clearly visible from this angle two different columns when you first adjust the settling you got that okay now let me show you I'm gonna do my tap weld with... Now let us see the gas welding process....by heating the two up together. Get it almost a puddle.
I like to get this nice and hot before just sticking a cold rod on top of there. Just a quick tap. And do the same thing to the other end before it expands or contracts. so evenly so here you can see uh in the other hand what is there uh this thing is basically the filler material that is separately used uh for the gas welding purpose and for the heating purpose this uh gas torch which has been used the welding torch which has been used Now I'm ready to run my DEP. Now then, so just quickly, I'm going to stop there and we can take a look at it.
Settling. So I hope you got some idea that how the gas welding process is actually going on. Okay, so now...
Let's go to this part. This is very important. There are three different kinds of flame that is created. We can create by changing the ratio of the oxygen and the acetylene.
So if we can maintain oxygen and acetylene in the ratio 1 is to 1. that means that oxygen and acetylene is in the stoichiometric ratio in that case you are going to get this neutral flame and you can see in the neutral flame there is one inner core and there is bluish outer core which is there this is the bluish outer core is there and the temperature of this inner core is in the order of 13 100 degree centigrade whereas these outer core temperature is in the order of 1200 degree centigrade okay So average in the order of 3000, you will get some in the order of this much, maybe 200, 2500 or 3000 in that order. Now, if you increase the percentage of acetylene more with respect to oxygen. Okay, so let us consider this is oxygen is to acetylene, oxygen is to acetylene. And if the oxygen is to acetylene if we maintain say 1 is to 1.5.
That means acetylene is 1.5, okay. Acetylene is 1.5 is acetylene and 1 is oxygen, okay. So if this is the ratio in that case acetylene is more and then you are going to get this carburizing flame and in the carburizing flame is also called the reducing flame and here you can see that excess amount of carbon will be present, excess amount of acetylene is there because It is more than this tritiometric ratio in favor of acetylene.
That is why when you try to weld something, then there is a chance of formation of metal carbide. OK, sometimes intentionally to add carbon to make it more hard, we use this carburizing flame. OK, and you can see the there are three different cores. So one is inner core and another one is outer core, which is the bluish one. But there is another region you can see a reddish kind of an area which is called the acetylene feather.
And in case of oxidizing flame, definitely oxygen is more. So the ratio is like say 1.5 is to 1 if we use. So oxygen is more and acetylene is less.
In that case, you will find that the inner core temperature is very high. and that is 3300 degree centigrade and the outer core temperature in all the cases is it is in the order of 1200 degree centigrade okay and in case of oxidizing flame again there is a chance of oxidation because more oxygen is there so depending upon the application we use different kinds of flames and you get some idea about the their temperature ranges let us stop today