A while ago, I believe I had mentioned I’d do a very thorough post on purged heat sinks and my methodology for how I utilize this technique. Well, I was reminded in Philly this past weekend that “Hey, I haven’t done this post yet!” So without further ado… allow me to make up for lost time and strike while the irons hot as they say and present to you, the humble reader with as thorough of an explanation of the use and application of purged heat sinks.
So first, what on earth is a purged heat sink? Lets dive right in. Some know them as simply “heat sinks” or “backer bars”. These are one in the same. A heat sink is simply a block of material, typically sized for the ID of a tube or machined to fit a specific part to draw heat AWAY from the weld site to help minimize HAZ (heat affected zone).
Material choice is key. Althought Aluminum is a wonderful conductor of heat, it is a terrible choice for a heat sink in this application as it can leave trace material behind, builds and maintains heat quite rapidly, and is quite soft so longevity of the tool is poor. Bronze and copper (copper however is incredibly sticky to machine/turn) are excellent choices. Especially bronze for its hardness and ease of turning/machining but also for its heat dissipating qualities. I typically use 932 Bronze specifically.
However, a purged heat sink combines both purging capabilities AS WELL AS heat sinking capabilities. What is purging? Well, this is the replacing of oxygen with the inert gas argon in this application. Titanium and Stainless alloys are reactive with oxygen and acts as a contaminant. So you need to replace oxygen inside and out at the weld site with argon to maintain weld integrity and cleanliness. Purged heat sinks have the one-two punch of both replacing the contaminant (oxygen) with the shielding gas argon AND helping to reduce heat at the weld site which can build and carry as you weld which has the adverse effect of making round tubes oval… Which if you’re a bottom bracket, heat tube or seat tube, creates issues with post weld facing, chasing and machining as you are now contending with increased tolerance issues in addition to possible oxidation of the backside of the weld, which is incredibly hard and shortens tool life (that’s not good since they’re quite expensive). So a purged heat sink is the ideal use case for TIG welding stainless steel and titanium alloys.
You should note that I am a firm believer in purging all of my steel frames as well. This helps minimize distortion, keeps the HAZ small (so material integrity and strength is vastly improved) but all those locations where expensive tools are used are 10 times easier to ream, face and chase as you are not contending with the issues I outlined above (aka bottom bracket, head tube and seat tube). Also, by setting up good practice and approach with steel, you make good habits routine if/when you jump into stainless or titanium alloys. So what are good habits?
First understand that argon is heavier than oxygen. This can be used to your advantage (or disadvantage). As a framebuilder, we’re constantly welding shapes with curves. Argon has a tendency to “roll” off of tubes. So there’s some tricks that can be applied. I typically use a 4″ square plate of .125″ aluminum with a pony clamp to block and pool argon in tight to reach weld areas or in locations where I know argon pooling will be difficult due to the shape of the joint. You can see that here as I weld the seat tube collar in place:
Here’s also an example of argon pooling at the ST/DT crotch area:
And a great example up by the head tube!
Also, knowing argon is heavier than air, you should always have your weld site be the lowest point with 3 points of argon feed and the high point being the vent. You can see these 3 points of argon feed in this image along with the vent being high at the top of the head tube:
Here’s another great example of that 3 point feed with the vent up at the top of the seat tube with weld point being the lowest:
So by constantly going about your welding in this practice, you set good habits for materials that are more demanding. Its critical to understand this little tid bit because as you weld, you’re constantly making adjustments with this “argon is heavier than air” and the “weld site should be the lowest point” throughout the entire process of welding a frame. Weld positioning and your position in relation to that frame should always be one where you are comfortable.
Ok, so we now know what a heat sink is. We know what purging is and have clearly defined what a purged heat sink is. And we know that argon is heavier than oxygen and that the weld site should always be the lowest point. We also know we need up to three points of argon feed for a frame for any weld on a frame (for small parts/assemblies, depending on the part or assembly 1-2 feeds with a high side vent is sufficient – the point is coverage here and purging oxygen). But how high should this rate of argon purge be? Well, quite simply I use 5 SCFH for steel and 10-12 SCFH for stainless steel and argon. These are constant rates. The feed NEVER stops, is RARELY turned down or is turned off while welding an assembly or frame. Typically I will let the argon flow and purge for a good 10-15 minutes depending on the size of the assembly and frame. More or less time is dependent on first material (steel I just turn up my purge to 5 SCFH and start welding, Stainless Steel and Titanium I turn up to 10-12 SCFH and have to wait). The only time I turn down an argon feed is on stainless steel and titanium hooded dropouts. There will be a specific location along the weld where the feed is directly in-line with the argon shield from the torch and that can cause turbulence, breaking the purge from the torch. I sometimes will lower or even turn off the feed temporarily as I pass by this feed location, but immediately turn it back on once I pass that zone. This is when I’m specifically shielding the hood so the feed internally is constant, but the shield externally to the argon purge of the hood is temporarily turned down or off – here’s a pic of all my dropout purged heat sinks:
The above pic shows curved and strait push to connect fittings (these are custom in-house made). I use these primarily in seat and chainstays to physically put argon exactly where I want it via vent holes. Its a funny anal way of KNOWING I’m getting argon into these tubse. The other purged heat sinks simply shield the backsides of the hoods for a variety of dropouts I frequently use. I also have a variety of in-house made expanding collet type purged heat sinks for bottom brackets, head tubes and seat tubes. Here’s all my bottom bracket, seat tube and head tube heat sinks:
These setups are designed in such a way that the heat sink portion expands into the inside of the ID of the tube so that it is in contact with the ID of the tube or a portion of the ID of the tube to help reduce heat input and maintain tube roundness. Here’s an assembly pulled apart. All stainless steel construction (easy disassembly and cleaning) and 932 Bronze.
So that’s a lot of information to digest. There’s a bit more to go through. What’s happening at the torch you may ask? Well… that’s nuanced. Argon flow specifically. Like I mentioned above, if the flow is too high, it can “push” argon shields away from either the part you’re shielding or from the torch itself. Typically I’m running about 15-20 SCFH at the torch for steel with a 10 second post flow and for stainless / titanium I’m running 20-25 SCFH at the torch with again a 10 or 12 second post flow. A really good trick and habit to get into is to tap the pedal BEFORE you start welding to get your post flow going and wait as argon pools and washes the weld site before you start your arc. IF you time it correctly, you can allow for almost the full length of the post flow to accumulate in tough to weld locations maximizing the amount of argon that is present and THEN start your weld sequence. Once you finish, its critical to keep your torch hand in place and allow the argon post flow to fully complete. This is allowing the weld site to cool while argon is protecting it so no contaminants get sucked into the weld site as its cooling, and you have a clean site to pick up your weld. You can also use both your torch hand and your filler hand as “cups” to help pool and accumulate argon as you weld. Often you may see the palm of my hand resting on a tube of my torch hand further pooling argon and shielding the weld. This is a huge reason why I’m gripping the torch by the nozzle and NOT by the handle. It also puts my hands/fingers closer to the weld and I find I have so much more control over the weld. You can see those subtle techniques in the below image:
So there you have it. An all inclusive beginners guide to heat sinks and purged heat sinks. If you have any questions, be sure to reach out directly as I’m always happy to walk you through any problems you may have. And remember to take notes. Any time you have a problem, you can trace back on your steps and see where the issue may be. 9 out of 10 times with titanium, its your prep. Very rarely its been some sort of issue with the tools involved. Always check all your lines and fittings before you start welding for tightness! Titanium is very finicky with prep. So be thorough, take good notes and set up good habits that carry from material to material and those habits become routine with practice. Also set up a mental checklist with each weld session. I know I’m constantly checking boxes mentally. Another great tip is to play act like you’re welding in a difficult section. This way, you are practicing muscle memory before you even start. Call it a dry run if you will. But good habits are hard to break as they say. Good luck!
But wait… What about my welder settings? Where to start? Well I’ll give you a bonus. Here’s my welder settings for both steel and Ti:
120-125 amps
20-25% peak
5% background
1.2-1.4 PPS
5 SCFH Purge Steel / 10-12 SCFH Purge for Ti+SS alloys
15-20 SCFH at the torch for steel / 20-25 SCFH at the torch for Ti+SS alloys
1/16″ 2% lanthanated tungsten (blue tip)
Matching gas No. 10 gas lens for Steel / No. 12 gas lens for Ti+SS alloys
One last bonus. If you’re not on Flickr, you should be. For every image I post on Instagram, I’ll post 10-20 on Flickr. (The nuts and bolts are this is how I tranfer files from my camera/computer to my phone which then post online). But I have an album of each clients work open to the public AND I have extensive folders detailing tooling, setups, back purging and much more. Here’s the big three free of charge:
Purged Heat Sinks
A while ago, I believe I had mentioned I’d do a very thorough post on purged heat sinks and my methodology for how I utilize this technique. Well, I was reminded in Philly this past weekend that “Hey, I haven’t done this post yet!” So without further ado… allow me to make up for lost time and strike while the irons hot as they say and present to you, the humble reader with as thorough of an explanation of the use and application of purged heat sinks.
So first, what on earth is a purged heat sink? Lets dive right in. Some know them as simply “heat sinks” or “backer bars”. These are one in the same. A heat sink is simply a block of material, typically sized for the ID of a tube or machined to fit a specific part to draw heat AWAY from the weld site to help minimize HAZ (heat affected zone).
Material choice is key. Althought Aluminum is a wonderful conductor of heat, it is a terrible choice for a heat sink in this application as it can leave trace material behind, builds and maintains heat quite rapidly, and is quite soft so longevity of the tool is poor. Bronze and copper (copper however is incredibly sticky to machine/turn) are excellent choices. Especially bronze for its hardness and ease of turning/machining but also for its heat dissipating qualities. I typically use 932 Bronze specifically.
However, a purged heat sink combines both purging capabilities AS WELL AS heat sinking capabilities. What is purging? Well, this is the replacing of oxygen with the inert gas argon in this application. Titanium and Stainless alloys are reactive with oxygen and acts as a contaminant. So you need to replace oxygen inside and out at the weld site with argon to maintain weld integrity and cleanliness. Purged heat sinks have the one-two punch of both replacing the contaminant (oxygen) with the shielding gas argon AND helping to reduce heat at the weld site which can build and carry as you weld which has the adverse effect of making round tubes oval… Which if you’re a bottom bracket, heat tube or seat tube, creates issues with post weld facing, chasing and machining as you are now contending with increased tolerance issues in addition to possible oxidation of the backside of the weld, which is incredibly hard and shortens tool life (that’s not good since they’re quite expensive). So a purged heat sink is the ideal use case for TIG welding stainless steel and titanium alloys.
You should note that I am a firm believer in purging all of my steel frames as well. This helps minimize distortion, keeps the HAZ small (so material integrity and strength is vastly improved) but all those locations where expensive tools are used are 10 times easier to ream, face and chase as you are not contending with the issues I outlined above (aka bottom bracket, head tube and seat tube). Also, by setting up good practice and approach with steel, you make good habits routine if/when you jump into stainless or titanium alloys. So what are good habits?
First understand that argon is heavier than oxygen. This can be used to your advantage (or disadvantage). As a framebuilder, we’re constantly welding shapes with curves. Argon has a tendency to “roll” off of tubes. So there’s some tricks that can be applied. I typically use a 4″ square plate of .125″ aluminum with a pony clamp to block and pool argon in tight to reach weld areas or in locations where I know argon pooling will be difficult due to the shape of the joint. You can see that here as I weld the seat tube collar in place:
Here’s also an example of argon pooling at the ST/DT crotch area:
And a great example up by the head tube!
Also, knowing argon is heavier than air, you should always have your weld site be the lowest point with 3 points of argon feed and the high point being the vent. You can see these 3 points of argon feed in this image along with the vent being high at the top of the head tube:
Here’s another great example of that 3 point feed with the vent up at the top of the seat tube with weld point being the lowest:
So by constantly going about your welding in this practice, you set good habits for materials that are more demanding. Its critical to understand this little tid bit because as you weld, you’re constantly making adjustments with this “argon is heavier than air” and the “weld site should be the lowest point” throughout the entire process of welding a frame. Weld positioning and your position in relation to that frame should always be one where you are comfortable.
Ok, so we now know what a heat sink is. We know what purging is and have clearly defined what a purged heat sink is. And we know that argon is heavier than oxygen and that the weld site should always be the lowest point. We also know we need up to three points of argon feed for a frame for any weld on a frame (for small parts/assemblies, depending on the part or assembly 1-2 feeds with a high side vent is sufficient – the point is coverage here and purging oxygen). But how high should this rate of argon purge be? Well, quite simply I use 5 SCFH for steel and 10-12 SCFH for stainless steel and argon. These are constant rates. The feed NEVER stops, is RARELY turned down or is turned off while welding an assembly or frame. Typically I will let the argon flow and purge for a good 10-15 minutes depending on the size of the assembly and frame. More or less time is dependent on first material (steel I just turn up my purge to 5 SCFH and start welding, Stainless Steel and Titanium I turn up to 10-12 SCFH and have to wait). The only time I turn down an argon feed is on stainless steel and titanium hooded dropouts. There will be a specific location along the weld where the feed is directly in-line with the argon shield from the torch and that can cause turbulence, breaking the purge from the torch. I sometimes will lower or even turn off the feed temporarily as I pass by this feed location, but immediately turn it back on once I pass that zone. This is when I’m specifically shielding the hood so the feed internally is constant, but the shield externally to the argon purge of the hood is temporarily turned down or off – here’s a pic of all my dropout purged heat sinks:
The above pic shows curved and strait push to connect fittings (these are custom in-house made). I use these primarily in seat and chainstays to physically put argon exactly where I want it via vent holes. Its a funny anal way of KNOWING I’m getting argon into these tubse. The other purged heat sinks simply shield the backsides of the hoods for a variety of dropouts I frequently use. I also have a variety of in-house made expanding collet type purged heat sinks for bottom brackets, head tubes and seat tubes. Here’s all my bottom bracket, seat tube and head tube heat sinks:
These setups are designed in such a way that the heat sink portion expands into the inside of the ID of the tube so that it is in contact with the ID of the tube or a portion of the ID of the tube to help reduce heat input and maintain tube roundness. Here’s an assembly pulled apart. All stainless steel construction (easy disassembly and cleaning) and 932 Bronze.
So that’s a lot of information to digest. There’s a bit more to go through. What’s happening at the torch you may ask? Well… that’s nuanced. Argon flow specifically. Like I mentioned above, if the flow is too high, it can “push” argon shields away from either the part you’re shielding or from the torch itself. Typically I’m running about 15-20 SCFH at the torch for steel with a 10 second post flow and for stainless / titanium I’m running 20-25 SCFH at the torch with again a 10 or 12 second post flow. A really good trick and habit to get into is to tap the pedal BEFORE you start welding to get your post flow going and wait as argon pools and washes the weld site before you start your arc. IF you time it correctly, you can allow for almost the full length of the post flow to accumulate in tough to weld locations maximizing the amount of argon that is present and THEN start your weld sequence. Once you finish, its critical to keep your torch hand in place and allow the argon post flow to fully complete. This is allowing the weld site to cool while argon is protecting it so no contaminants get sucked into the weld site as its cooling, and you have a clean site to pick up your weld. You can also use both your torch hand and your filler hand as “cups” to help pool and accumulate argon as you weld. Often you may see the palm of my hand resting on a tube of my torch hand further pooling argon and shielding the weld. This is a huge reason why I’m gripping the torch by the nozzle and NOT by the handle. It also puts my hands/fingers closer to the weld and I find I have so much more control over the weld. You can see those subtle techniques in the below image:
So there you have it. An all inclusive beginners guide to heat sinks and purged heat sinks. If you have any questions, be sure to reach out directly as I’m always happy to walk you through any problems you may have. And remember to take notes. Any time you have a problem, you can trace back on your steps and see where the issue may be. 9 out of 10 times with titanium, its your prep. Very rarely its been some sort of issue with the tools involved. Always check all your lines and fittings before you start welding for tightness! Titanium is very finicky with prep. So be thorough, take good notes and set up good habits that carry from material to material and those habits become routine with practice. Also set up a mental checklist with each weld session. I know I’m constantly checking boxes mentally. Another great tip is to play act like you’re welding in a difficult section. This way, you are practicing muscle memory before you even start. Call it a dry run if you will. But good habits are hard to break as they say. Good luck!
But wait… What about my welder settings? Where to start? Well I’ll give you a bonus. Here’s my welder settings for both steel and Ti:
120-125 amps
20-25% peak
5% background
1.2-1.4 PPS
5 SCFH Purge Steel / 10-12 SCFH Purge for Ti+SS alloys
15-20 SCFH at the torch for steel / 20-25 SCFH at the torch for Ti+SS alloys
1/16″ 2% lanthanated tungsten (blue tip)
Matching gas No. 10 gas lens for Steel / No. 12 gas lens for Ti+SS alloys
One last bonus. If you’re not on Flickr, you should be. For every image I post on Instagram, I’ll post 10-20 on Flickr. (The nuts and bolts are this is how I tranfer files from my camera/computer to my phone which then post online). But I have an album of each clients work open to the public AND I have extensive folders detailing tooling, setups, back purging and much more. Here’s the big three free of charge:
Heat Sinks and Back Purging.
Tooling
All things Titanium