NASA's clever technique to make combustion chambers

so imagine this it's the 1970s and you're an engineer at Nasa not just any engineer you're a literal rocket scientist rocket power is the key to Greater accomplishments in space designing the next generation of high performance rocket engines the stuff you're working on now will eventually go into the space shuttle except you need to make something that is impossible to manufacture with traditional tools the year was 2023 you could just 3D print it out of metal but that's not an option because it's the 70s and metal 3D printing doesn't exist yet and so it's time to break out your secret weapon wax yeah seriously I mean they used a fancy wax but essentially it's candle wax and it was absolutely critical to manufacturing the most important part of the space shuttle's engine the main combustion chamber I've been in love with this technique ever since I first heard about it so I decided to make my own scale model of the main combustion chamber to demonstrate how the technique works first we probably need a quick crash course on Rocket chamber layout and how it all works I am definitely not a rocket scientist so this is just a very high level overview so that we're all on the same page most people are probably familiar with the large Bell shape at the bottom of a rocket engine it's the most iconic and noticeable part of any rocket what we're talking about today is directly above the Bell the section up here is known as the main combustion chamber and it's where all the combustion originally takes place through combustion in the thrust chamber great amounts of energy are released it's not dissimilar from the combustion chamber inside of a car engine we're mixing together Fuel and oxidizer and igniting it to create some type of force which we use hot expanding gas escapes through the nozzle throat unlike a car engine the temperatures and pressures inside of this main combustion chamber are are truly staggering talking about upwards of 3 500 degrees Celsius and pressure is in excess of 6 000 pounds so if you'd like to keep your combustion chamber from just melting into a pool of metal you need some way to protect it or actively cool it there are a lot of ways to do this but the most common technique is called regenerative cooling where you pump the fuel or the oxidizer through channels or tubes along the surface of the combustion chamber to draw the heat away from it and keep everything from melting it's kind of like water cooling a PC except you're using cryogenic liquid hydrogen instead everyday astronaut has a really good video on this topic exploring all the different ways to cool a rocket so if you're interested in more details on that check it out the Link's down in the description so back in the early days of space flight if you wanted to use regenerative cooling you often braised thin pipes along the exterior of your combustion chamber and the pipes are what flowed the coolant throughout the system to extract the Heat this is the method used on the F1 engine on the Saturn V rockets and you can see the tubes running up and down the nozzle here and they extend up into the main combustion chamber the fuel is rooted through the many tubes which stack together in this manner the fuel cools the chamber and protects it from the high combustion gas temperatures within but this technique does have some issues It's relatively heavy because you have all these thousands of extra steel pipes that you need to bond onto the engine adding a whole lot of extra mass the brazing process generates thousands of joints that need to be inspected to make sure that all of them are absolutely perfect and it's just not thermodynamically all that ideal you've got the heat which needs to transfer through the chamber wall and then through the pipe wall before it can get to the coolant ideally we would have those coolant channels built directly into the chamber itself so that it's all one monolithic piece it'd be a simpler system lighter and cool better it's like a win-win-win unfortunately it's also impossible to machine conventionally the machines used by the machinists are called Machine Tool internal cooling channels that conform to the shape of the chamber are impossible to drill out with straight drills and bent drills just don't really work that well for some reason so NASA and their contractors came up with a pretty brilliant solution to this problem and did it using a technique that's kind of like the original additive manufacturing before 3D printing was ever a thing so let's machine a replica of the combustion chamber and then I'll walk through the process about how this works [Music] thank you [Music] this is a moderately faithful replica of the main combustion channel of the rs-25 engine the engine used on the space shuttle it's made out of copper like the original MCC but there are some differences I machine mine out of a single piece of copper but that wouldn't have been remotely possible for the space shuttle just given the size of the engines it would have been prohibitively expensive to machine it out of a single piece instead they used a vacuum melting and centrifugal casting technique to get the raw casting which was then later machined to the final Dimensions the shuttle also used a special copper alloy known as narloy z a copper silver zirconium mix copper is used because it transfers heat so well but pure copper is not really strong enough to be used in the main combustion chamber so narloy Z was developed to provide a stronger alloy the silver and zirconium help strengthen the copper and make it withstand the forces involved after the chamber takes on its characteristic hourglass shape thin slots were machined along the exterior of the chamber these are the coolant slots that will allow liquid hydrogen to flow up and down it and pull that heat away but right now these are just slots and we need enclosed channels so the next process is known as the closeout where we form an outer layer or jacket on top of the inner copper core this is a two-step process and the first step is where we use our secret weapon wax a rigid machinable wax is melted into the channels and then carefully scraped and sanded off by hand the purpose of this is to fill up all the channels and make a smooth continuous profile along the exterior of the chamber I use Jeweler's wax which is a very similar type as to what they used it's hard and machinable and it's not gummy like a beeswax would be it ended up being very challenging to work at this scale because the wax doesn't really adhere well to metal and the slots are so thin that there's just not a lot of material for it to grip onto so I spent approximately my entire life melting wax into these channels carefully filing sanding scraping it out then going back to fix all the points where the wax had dislodged itself and I needed to refill a channel so it was very tedious but I eventually got a completely covered surface that we can move on to the next step with I did also try using super glue which was thickened with either fume silica or graphite and that did an okay job it certainly bonds to the metal better but extracting it at the end proved awfully challenging so the wax ended up being the best method after the slots are finished being filled the next step is to create the outer Jacket using electroplating if you're not familiar with electroplating I have an older video where I used it to strengthen 3D prints and it does a pretty good job explaining it from a technical perspective but from a high level you can think of electroplating as a special solution that contains metal ions and when you apply an electric current the ions come out of the solution and deposit onto the thing you're trying to electroplate forming essentially a small thin layer of metal there are a handful of different Metals this works with but the main ones that are used are copper and nickel copper is typically used because it's fairly conductive and it also plates really easily so it can be used as a base layer and nickel is a relatively stiff and strong metal so it's good for durability purposes NASA used a very thin layer of copper first followed by a very thick layer of nickel on top the copper acts as a shield to prevent hydrogen embrittlement of the nickel and steel layers on the outside the liquid hydrogen flowing through these channels will embrittle nickel and steel over time causing them to be structurally unsound and you don't really want that in a rocket engine so the copper X is a little shielding layer to prevent the hydrogen from escaping the nickel layer that's put on top is the main structural layer and they plated it pretty thickly to provide enough strength for the chamber so I dropped my model into a copper Electro plating bath and let a thin layer of copper form across the surface you can see it spreading across the wax here but wait if you're at all familiar with electroplating you know that plating only works on conductive surfaces and wax most definitely is not conductive so how is this working best I can tell NASA buffed a fine silver powder onto the surface of the wax which made the wax conductive this technique is also used on other engines like the Vulcan on the Aryan 5 and I saw in a documentary that their wax was black which I'm not positive but I'm assuming that means it's filled with graphite to make it conductive so I followed that technique and doped my wax with a whole bunch of graphite powder until it was reasonably conductive it has just enough conductivity to allow the copper to spread across the surface and once you have a thin layer it doesn't matter anymore and it just builds up from there I let this plate for a couple hours pulled it out rinsed it off and put it in the nickel electroplating bath next this takes a very long time so NASA plated a centimeter or two of nickel onto the surface of their chamber and and most plating baths deposit somewhere between 20 and 30 micrometers per hour so you can imagine how long it takes to build up a centimeter of material I plated mine for 24 hours then pulled it out and machined off the surface to see how much more was needed to fill in all the gaps and realized we had quite a bit of work to do so I repeated the process a few more times totaling I think about 72 hours in the plating bath and you can still see that even at the end of it we don't have a very uniform surface but although it's a little ugly it did close out the surface and I think we can proceed to the final step which is removing the wax from the channels when I started on this project I originally assumed NASA just melted the wax out because that seems the most logical thing but in actuality I found a paper saying that they dissolved it with perchloroethylene which kind of makes sense you want to make sure all the wax gets out without leaving any type of like carbon residue from a burning or melting process despite that I tried melting it first because it seemed like the easiest thing to do at my scale with this little replica and it sort of worked but it didn't clear all the wax so I also ended up trying to dissolve it out chemically using xylene and hot oil like canola oil but eventually I got the channels cleared and we can see the final result it's definitely not as polished or professional looking as what nasico produce it's a little ugly but honestly I am I'm really excited that this worked at all like it's really cool to see that nickel layer on the outside bonded to The Copper with just a hollow channel in between I think I ended up depositing about 500 microns of nickel and I machine that back to roughly 300 microns all the way around it's cool to think that this is exactly the same process as used by NASA and Rocketdyne to make the rs25 engine just you know scaled up much larger and controlled in a much better manner it's really just such a clever and ingenious method when you think about it Engineers were able to fabricate a monolithic combustion chamber with internal conformal cooling channels at a time before 3D printing ever existed it's just it's so cool had some leftover material that I wasn't really going to use for anything so I decided to just machine up a few more of these Chambers they're not really useful for anything but they make a cool little desktop widget or maybe a gift for a fellow space nerd I only made a handful but if that sounds like something you might want to buy there's a link down below this technique is not without its downsides as I mentioned it's pretty slow and it requires a lot of hand work by humans to scrape and polish and sand everything electroplated metals can have a pretty significant amount of tensile or compressive stress depending on the composition of the bath and in one of my early attempts you can see that I didn't plate the nickel thick enough and the internal stress of the plating actually made it come unattached from the copper core the new SLS rocket which recently had its Maiden flight is also using the rs-25 engine just like shuttle but Rocketdyne has modernized a few of the features of the engine including the main combustion chamber instead of using this sort of tedious electroplating process they're now using something known as hot isostatic pressing this uses intense heat and pressure to bond a prefabricated outer jacket to the copper core this is much faster and much less human hand-holding to get the process done and it also generates a stronger component so it's all around just a better technique even though NASA has moved on from melting wax and electroplating it has a special place in my heart because it's just such a great example of clever problem solving to work around manufacturing constraints and I think ultimately that's what I love about manufacturing it's usually an accumulation of small little tips and tricks and creative problem solving to build the thing that you're trying to build and once you know a tool or a technique it's in your toolbox forever you can use it on future projects I was recently doing something where I electroplated Diamond onto custom ground tools for a glass Machining project that I'm working on if that sounds interesting to you I published a video about it on nebula nebula is a streaming platform created and owned by content creators and it's a place where we can publish what we want without having to please an algorithm this diamond electroplating project is a perfect example I've been sitting on this footage for honestly ages so this is my super janky quick setup to see if this idea would work it was a little strange for me to be Milling carbide the next step is to electroplate this with our nickel Diamond slurry and then we pop it in the CNC and hit the go button and I just couldn't bring myself to edit together a video about it because it's too small and too Niche to really do well on YouTube just given kind of the constraints of the platform time spent editing that video together could have been better spent on on a project with wider appeal and I don't have a team it's just me so I have to be careful about what I choose to spend my time on for YouTube but now that I've joined nebula I actually have a reason to publish these videos I mean it's still a small and Niche topic like that's not going to change but the folks watching it on nebula help support the channel more than ads on YouTube ever would given the size of the project and of course there are tons of other creators on nebula practical engineering real engineering strange Parts Bobby broccoli Wendover like the list goes on I know you'll probably like them because I watch all these channels myself nebula has no ads many creators publish exclusive content to nebula and there's a host of other features like classes and newsletters and podcasts yeah [Music] cereal is better without milk if that sounds interesting there's a link down below it helps support me directly and gets you a pretty good discount I think it's like 40 off and if you sign up for the annual plan it's just two dollars and fifty cents a month I'm still working on lots of cool stuff for this Channel on YouTube and I'm pretty excited for some of the projects that are coming out in the future so I think that's all I got for you thanks for watching I'll see you next time

Channel: Breaking Taps

Views: 867,431

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Id: H4YZxb2E5PA

Length: 16min 18sec (978 seconds)

Published: Fri Apr 21 2023