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Practical TIG Welding: Gas Lenses and Cups

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Gas Lenses and Cups


00:00 - The secret to TIG welding success lies in its ability to shield the arc from contaminants in the atmosphere using the argon shielding gas we covered in the last module.
00:09 The high pressure argon is connected to a regulator which controls the gas flow rate and supplies it to our welder where we can switch this flow on or off via our torch or foot pedal through an internal solenoid inside the machine.
00:23 We don't have a lot of variables in the supply of shielding gas and while our regulator will allow us to adjust the flow rate, our machine settings can also delay our arc start after the gas solenoid has switched which is known as pre flow.
00:37 You can also set the shielding gas to keep flowing after the arc is stopped which is called post flow.
00:44 We'll explore this in more detail soon but essentially this pre and post flow control gives us the ability to create a shield of gas to prevent minor contamination at the very beginning of the weld arc and for a set period of time after the arc has been terminated to allow the weld pool to cool down.
01:02 The gas cup or nozzle as it's commonly known is a consumable of TIG welding.
01:08 Although it shouldn't wear out, it can be thought of as a consumable because it'll be the first thing to break if you drop your torch on the ground.
01:16 This is because they're made from heat resistant materials like aluminium oxide, pyrex and glass so unfortunately they're inherently brittle.
01:25 These nozzles are available in different sizes and styles for varying TIG welding tasks.
01:31 Specific size torches will suit a range of specific gas cups which screw on or slip over the gas lens or collet body to provide the desired shielding zone for the weld.
01:43 Gas cups are numbered and this number refers to their imperial internal diameter.
01:48 For example, a number 4 gas cup is a quarter of an inch or 6.4 mm inside diameter.
01:54 Each step up in gas cup number adds another 1.6 mm or 1/16th of an inch on top of this.
02:02 So a number 5 cup will have an internal diameter of 8 mm which is 5/16th of an inch.
02:08 These cups range in size from a number 3 for extremely small micro torches to a massive number 24 for extreme gas cover.
02:17 How these gas cups function depends on what TIG torch setup we're running.
02:22 A regular collet body will attach a regular gas cup and these are available in sizes ranging from the number 4 cup to a number 12 cup.
02:31 A gas lens on the other hand will replace the collet body and can attach a wider range of gas lens cups from number 4 all the way up to number 24.
02:41 The reason why a gas lens has so many cup size options lies in its design.
02:46 A regular collet body has a reasonably undisturbed flow of gas through the series of holes that exit into the cup.
02:54 The gas lens on the other hand uses a series of metal screens to diffuse and distribute the gas into the cup.
03:01 Gas is lazy and will take the path of least resistance and by flowing through the holes in the regular collet body our gas exits into the cup and flows onto our workpiece without a very wide coverage.
03:13 This is fine for AC welding aluminium but it's not all that great for more reactive materials like stainless steel or titanium which need a wider spread of gas coverage.
03:24 This is where the gas lens shines.
03:27 By utilising its metal screens to spread the gas coverage, it can be fitted with a much larger cup, allowing for the gas to spread further over our workpiece, shielding the weld and the heat affected area from contaminants and producing a high quality weld finish.
03:44 By removing the turbulent effects that a regular collet body has on the gas, a gas lens can also save our gas usage by being more efficient and more effective.
03:54 If we compare the regular collet body with a number 8 cup side by side with a gas lens, fitted with the same number 8 cup, the regular setup will need a gas flow of around 10 litres per minute, while the gas lens setup will do the same shielding job with just 5 litres per minute gas flow.
04:13 This is going to save you nearly half the cost on your bottle of gas.
04:17 Gas cups for gas lenses range from a number 4 right up to a number 15 and it's at 15 where the cup size begins to taper out larger than the gas lens itself.
04:28 This means that the flow of gas really has no way of spreading the gas any wider than the lens.
04:33 Without more screens on our cup to spread the gas coverage, there'd be no point going any larger than this and more gas flow would simply just push that same diameter of gas further away from the torch.
04:46 Because of this, large gas cups will incorporate a second and sometimes 3rd row of metal screens to diffuse the gas and make it spread as it exits through the cup.
04:56 By having these metal screens to diffuse the gas and help spread it over our workpiece, we can then raise the flow rate of the gas at our bottle to increase its effectiveness.
05:06 It's worth noting that if your gas flow rate is set too high for a given cup size, this can result in a very unstable arc and this can be particularly noticeable when switching from DC to AC as the gas flow requirements can differ significantly between the two.
05:22 If you have the gas flow set too high, it can take a while to work out why the arc is so unstable, particularly given all of the other available settings that come into play for AC welding which we'll cover shortly.
05:34 Because we can't see the gas exiting our cup, we do need to just check our flow rate at the bottle to make sure we're in the ballpark before we start welding.
05:43 The general rule of thumb here is to be somewhere around the same gas flow in litres per minute as the size of the cup we're using and the more effort the manufacturer has put into the design of their screens and diffusers inside the cup, the more efficient it will be, meaning that we won't need as much gas flow but the manufacturer should also provide information guiding you on what's required for the particular cup you're using.
06:09 Larger cups do have their downsides though.
06:13 It can sometimes be difficult to see the weld in a tight spot, due to the size of the cup.
06:18 But this can be solved by using glass or pyrex cups that usually have their own slip on gas lens atttachment.
06:25 By having the ability to see through the cup, you can have great control, visibility and shielding all in one.
06:32 Sometimes though the larger cups can also physically limit your ability to get into tight spots to perform a weld and this is where increasing the amount of tungsten stick out, which essentially means you're extending the tungsten electrode further out of the collet, will come in handy because it brings the arc point further away from the bulky cup.
06:53 The larger the cup you have fitted, the longer the stick out can be.
06:56 This would be especially useful when fabricating an exhaust collector for example where a large cup with a lot of stick out would make it a walk in the park.
07:05 If you're needing to have a long tungsten stick out, it's really important to understand that the argon shielding gas is heavier than atmospheric air and this causes it to naturally flood into corners.
07:17 This means that you should run plenty of pre flow gas and position your workpiece so that the gas collects in the area that you're going to be welding.
07:26 If you need to work outside or in a breezy workshop, consider trying to block the flow of atmospheric air around your workpiece.
07:34 Gas lenses do a great job of diffusing the gas and creating laminar flow but it does come at the expense of direction and it won't take much of a breeze to reduce the effectiveness of the gas.
07:46 This can lead to some porosity and inclusions in your weld which are small air holes that infiltrate your weld pool.
07:53 By turning up the flow rate of gas or adding a curtain around your work bench, you can improve the quality and reliability of your welds.
08:01 With all of this information in mind, the best move here is to run a gas lens for DC welding.
08:07 This is going to save you money on gas and improve the quality of your finished welds.
08:11 Due to aluminium's reduced reactive nature, a gas lens for AC welding is not as important.
08:17 This is because aluminium doesn't need a wide coverage of gas and the extreme heat from the AC welding process will damage your expensive cup anyway.
08:26 So fit a smaller cup over your gas lens for AC welding, or revert back to the original collet body that the welder came with.
08:34 Just remember, you'll have to raise the gas flow rate by around 20% when doing so.
08:39 This has been a bigger module that's covered a lot of ground so let's take a look at the most important points to remember.
08:45 Gas nozzles are numbered according to size from a number 3 for micro torches to a massive 24 for extreme coverage.
08:53 These provide a relatively direct flow of gas which is great for welding aluminium but more reactive metals require better coverage which is where a gas lens comes in.
09:03 These follow a similar numbered convention and diffuse the argon, allowing it to spread out further and better shield the work area.
09:11 When it comes to flow rate for these lenses, remember that the general rule of thumb here is to be somewhere around the same litres per minute gas flow as the size of your gas lens.

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