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Practical TIG Welding: Purging

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00:00 - In motorsport we use TIG welding to weld a lot of pipe work and it's common to see the finished products in engine bays flowing liquids, gases and pressurised air.
00:09 A good looking TIG weld on the outside will be important but we need to be aware of what's happening on the inside as well.
00:16 A constant supply of argon on our external welds is critical in producing a good TIG weld and the same can be said for the back side of this weld.
00:25 Reactive materials like stainless steel and titanium for example can have real peformance and strength issues if the back side of the weld is left to react with the atmosphere.
00:36 As our pipework is usually fairly thin, it would be typical for our weld to penetrate all the way through to the inside of our pipe and this penetration then reacts with the atmosphere inside the pipe and fails to create a sealed seam or worse creates a jagged mess of ugly build up that could even be dislodged and cause mechanical damage to internal engine components.
00:59 To shield the back side of our weld, we need to use the same argon that we're using on our TIG welder to fill the inside of our pipework and this process is called purging.
01:09 In this context, purging refers to the removal of the atmospheric air and replacing it with inert gas.
01:16 Every pipe we make in motorsport applications will have some form of entry and exit hole so to fill this pipe work with argon, we need to cap both ends and create an entry point for the argon as well as an exit point for the atmospheric air to be pushed out through.
01:33 We can use our argon bottle that's already connected to our TIG welder for purging by purchasing a second flow regulator that uses a T piece to connect up to our pressure regulator This additional flow meter will tell us how much gas is being pumped into our workpiece.
01:49 Around the same amount of flow that your TIG welder is already set on, will do the job for purging and because this work usually requires a large cup, that's typically going to be somewhere around the 10 to 15 litres per minute mark.
02:03 Depending on the proximity to the heated area, we can use a number of items to plug our pipe work, ranging from specifically machined aluminum bungs, aluminium foil, high temperature tape and even a tennis ball drilled to accept an inlet and outlet tube.
02:20 Keep in mind that we don't want to pressurise the pipe work.
02:23 That's why we have an exit hole in our upper plug.
02:26 If we didn't have one and we got to the end of our weld, the pressure inside the pipe would blow our molten weld pool into our tungsten and make a real mess out of what could have been a nice neat job.
02:37 The plugs that we use for purging don't have to be expensive but keep in mind we are trying to eliminate contaminants in our material so anything that leaves a trace like tape residue on our tube for example will take extra time to clean off.
02:51 The ultimate purge plugs are those that are made from heat resistant silicon and these range in diameter to suit our specific application.
03:00 These silicon plugs that are designed specifically for purging, also come with the benefit of incorporating a metal screen to diffuse the argon and spread it through the tube evenly.
03:10 This is the same type of metal screen used in our gas lens and essentially does the same job but with an internal gas cloud.
03:18 Remembering that argon is heavier than atmosphere, the inlet of the gas needs to be at the lowest point in your pipe work and you need to allow enough time for the argon to fill the workpiece before welding starts to ensure that all of the atmospheric air has been removed from inside the pipe.
03:34 We'll be demonstrating this in detail during the practical examples in the course so don't worry, you're going to get a better understanding of how this all works before the course is finished.
03:45 When the back side of the weld has sufficient argon coverage, it can be as smooth as the external weld, creating a perfectly strong seam that can pass fluids, air or gases with optimal performance.
03:58 By having a perfectly sealed weld join on the inside of our pipe, we reduce potential stress raisers and weak points and increase the life expectancy of our workpiece.
04:08 Take an exhaust for example.
04:10 If we don't purge the pipe, we then create an avenue for carbon to build up inside the weld seam.
04:16 This carbon, mixed with expansion, contraction and vibration can cause cracking and failure of the weld over time.
04:24 Keep in mind that you don't have to purge everything you weld.
04:27 In motorsport fabrication we commonly TIG weld metals such as aluminium alloys and these don't require purging.
04:34 High and low carbon steels which include mild steel and chromoly don't require it either but then titanium and stainless steels do require it but not all the time.
04:44 Now that might sound a little confusing so let me try and clear it up.
04:48 Titanium is one of the most reactive materials that we'll work with in motorsport and it needs purging 100% of the time, no questions asked.
04:57 Stainless steel on the other hand benefits from the purging process but won't necessarily require it all of the time.
05:04 This is really something that you can decide on for yourself and spending a little extra time setting up and purging your work will improve the strength and performance of it.
05:13 It really comes down to your budget and how refined your fabrication work is getting.
05:18 With good fitup and a very controlled arc you can weld stainless without creating build up inside the tube due to the limited amount of penetration but of course this weld isn't going to be as strong as a full penetration purged weld.
05:33 Let's take a quick look at the important points from this module before finishing up.
05:37 Purging our workpiece is the key to a good strong weld when working with reactive metals like stainless steel and titanium.
05:45 Remember that argon is heavier than air and that means that where the gas is being pumped in, needs to be the lowest point of the workpiece and the exit needs to be at the top.
05:55 You'll need somewhere for the air to escape so that you don't end up pressurising your workpiece.

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