Reference / Paper · 2016
Peak of Flight #432: Making Fiberglass Body Tubes for FAI Rockets - Part 3
Apogee Components' Peak of Flight newsletter, issue 432 (2016-12-13).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2016
Apogee Components' Peak of Flight newsletter, issue 432 (2016-12-13).
Apogee Components' Peak of Flight newsletter, issue 432 (2016-12-13).
ISSUE 432 December 13th 2016 IN THIS ISSUE Making Fiberglass Body Tubes for FAI Rockets - Part 3 www.ApogeeRockets.com/Rocket-Kits/Skill-Level-3-Model-Rocket-Kits/Payloader Making Fiberglass Body Tubes for FAI Rockets - Part 3 By Tim Van Milligan against me. The first is having the tube made from In part two of this series found at: (http://www. epoxy. You have to put this into perspective; epoxy is an adhesive. It is engineered to “stick.” It wants ApogeeRockets.com/education/downloads/ Newsletter431.pdf), the tubes I was making were to stick to the mandrel, because that is its purpose, and true to its nature, sticking it does. beginning to pick up the qualities that I wanted. The only thing that prevents it from sticking to So the initial process for making competition (FAI-style) fiberglass tubes was written down, and the mandrel is the mold release applied to the mandrel. I want to stress how it is a “process,” much like The thing that epoxy has going for it,is that it is cooking or baking. If you do steps in the wrong also in the “plastics” material category. The nice order, or do them incorrectly, the tubes can easily be ruined. I found this out a lot during my experi- thing about plastic is that it is somewhat flexible. That is why if you have two plastic buckets stuck menting. I ruined dozens and dozens of tubes. If you recall, the ultimate goal that I was trying together, you can shoot air or water in between them, and they will separate. The reason this to achieve was to make a colorful, lightweight works is because the plastic is flexible and detube that had a glass-smooth surface. Most forms slightly as the air gets under the edge. In importantly, it had to be fairly easy to make so fact, this is the only way the air can get under the that many tubes of consistent quality could be produced. I needed a lot of tubes for the various edge -- the edge has to deform in order to lift up to allow the air to penetrate. events in the actual competition and for use in And this is the second problem with the situpracticing. ations I had with the tubes and why shooting air “Why Don’t You Shoot Some Air Into It into it never seemed to work for me. The fiberglass portion of the matrix resists deformation. That is Tim?” My biggest problem was ruining a lot of tubes what makes fiberglass strong. It doesn’t stretch like a plastic. while trying to remove the ultra thin wall fiberSo when you try shooting air into it, you are in glass tube from the aluminum mandrel. The tubes effect trying to get the glass fibers to stretch and are so fragile that they are easily torn by rough allow the tube to deform to accept the air bubble of handling. compressed air. What happens is that the indiThe suggestion that I received a lot, after explaining the trials I was going through while trying vidual fibers crack in order to allow the epoxy to stretch. to remove the shell from the mandrel, was “why After the fibers crack, the tube zippers down the don’t you try to shoot some compressed air under side when you try to force the air under the edge. the edge.” I don’t have a picture to show you of this, but trust I tried that a hundred times… I never had me on this… It tears quite readily. These tubes are any luck with removing the mandrel using compressed air. Only in hindsight did I figure out why so thin that they just don’t have any resistance to tearing at all. this might be the case. Shooting air under the edge would probably work just fine if two things weren’t working About this Newsletter You can subscribe to receive this e-zine FREE at the Apogee Components website www.ApogeeComponents.com, or by clicking the link here Newsletter Sign-Up Page 2 Continued on page 3 Newsletter Staff Writer: Tim Van Milligan Layout/Cover Artist: Chris Duran Proofreader: Michelle Mason Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes Continued from page 2 “Try Freezing it Tim” The heat can sometimes deform the fiberglass, and the wax build-up has to be cleaned off as a secondary operation. Another suggestion that I’ve heard dozens of times when explaining the process of removing the tube from the mandrel is: “Why don’t you freeze the mandrel to shrink it?” I’ve tried this a bazillion times too. Have you tried handling the super cold metal mandrel to try to slide the fiberglass shell off? It is so cold, you can’t hold it for longer than 30 seconds. So you have to use thick gloves to hold it. And now you can’t grip it well, and it is the rougher handling Figure 1: The different types of products that I experiwhich then tears the fragile part. mented with as mold releases. I should have looked this up earlier. But the The automotive carnauba wax is a paste that is reason why freezing doesn’t work is due to the coapplied and then buffed off the mandrel. It was a efficient of thermal expansion of aluminum versus the epoxy/fiberglass matrix. Aluminum has a lower disaster. Avoid it as a mold release. Next was the Challenge #95 from BJB Entercoefficient of thermal expansion than that of fiber reinforced epoxy (http://www.engineeringtoolbox. prises. It is a thick viscous liquid with wax emcom/linear-expansion-coefficients-d_95.html). So bedded into it. You paint it on with a brush, and when chilled, the epoxy/fiberglass matrix shrinks then buff most of the wax off before laying down faster than the solid aluminum mandrel. In effect, the fiberglass and epoxy resin. It does work, but takes a lot of slow labor to work the tube off the it gets tighter on the mandrel the colder it gets. mandrel. It was my new go-to release for a long Because of the miserable results I got when I tried freezing the mandrel and using compressed time. But even then I still ruined a bunch of tubes, air to remove the fiberglass tubes I ended up con- so I continued to search for a different release. centrating on different types of mold releases. Experimenting With Mold Releases In the previous newsletters I talked about the first three on the left in the photo (Figure 1). The Crown #3470 aerosol wax was the old stand-by. It does work, but you have to heat the mandrel in order to melt the wax to get the tube to slide off. Blue Magic My mandrels were pretty shiny. I polish them with ultra fine 0000 steel wool between lay-ups. I want them as smooth as possible, so that the epoxy has fewer scratches to seep into. One product that I tried as a way to make them smoother as well as a mold Continued on page 4 www.ApogeeRockets.com/Building_Supplies/Parachutes_Recovery_Equipment/Parachutes Page 3 Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes Continued from page 3 release is a “metal polish.” Until this experiment, I had never tried this stuff, and I was very impressed at how shiny the mandrel became. It is a rubbery paste. Rubbery is how I describe it, because when you shake the can, you can feel it shaking around in response. It is just weird stuff. When you apply the blue colored goo and start spreading it around with rubber gloves, the stuff turns pitch black. That is how it works. Once it is black, you buff it off with paper towels. In a couple of minutes of effort, it is super shiny. There are several brands, but they all do much of the same thing. They bring out the shine in the aluminum, almost to a mirror appearance. I did some research on metal polishes and found it is mostly a chemical cleaning. Regardless of the brand you get, they work in three ways to bring out the shine: 1. Mechanical: It contains abrasives which remove the microscopic “peaks” (which show up as dullness) from metal. 2. Chemical: It contains solvents which “clean” the metal, removing oxidation, grime, and debris from the mechanical polishing process. Removing the oxidation is what really brings out the shine. 3. Sealant: Most also contain some sort of sealant (typically silicone-based) which “seals” the metal and protects it (for a short time) against future oxidation. It was like a miracle when I saw it, especially how little effort it took to shine it up. So I suspected that it really wasn’t as smooth as it looked. But the jar said it had a silicone agent in it, so I thought I’d try it out. As an experiment, I took an old aluminum mandrel and split it in two with a strip of tape (see Figure 2). On one side I used the Challenge 95 release because it was my old reliable release, and on the other side, I tested the new product as a mold release. I did this for all the future experiments to speed things up. Figure 2: Split testing of mold releases. A mandrel was divided in half by green tape so I could see which mold release worked better. The right side has Challenge 95 mold release on it, but not buffed off yet. Unfortunately, the metal polish did not work very well. I didn’t take any pictures of it at the time, but it just wouldn’t lift up. I could only get it to dislodge from the mandrel by tearing it off. Even though I don’t use it as a mold release, I keep it around and shine up the mandrel every once in while. It just looks really cool when it has a mirror appearance. Continued on page 5 www.apogeerockets.com/Rocket-Kits/Skill-Level-2-Model-Rocket-Kits/SkyMetra Page 4 Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes The Liquid Wrench has been retired to my garage, where I use it to spray my snow shovel in the winter. Silicone mold releases At this point, I started calling around and getting Next I tried an aerosol silicone spray (Liquid recommendations. The engineers at BJB recomWrench brand) that I purchased from my local mended two products that I might try. The first was hardware store. This stuff was by far the worst stuff I tried, at least as bad as the automotive car- Release #79. They thought that this might work nauba wax. Figure 3 shows how it left the epoxy well for my application, because they said that a company that made pole-vault poles used it to stuck to the mandrel when the fiberglass cloth make their 18-foot long shafts. Based on this, I was pulled off. ordered up a can. The Release #79 is pure liquid silicone. You simply paint it on with a brush or air gun, and apply the fiberglass/epoxy right over the top. This stuff did work. I’d say it worked about as well as the Challenge #95. Maybe a little better, because with the Challenge #95 you had to worry about little spots on the mandrel that didn’t get covered well with the thick paste-type liquid. The Release #79 was water-thin, and easily spread out when you covered the mandrel. Pulling the tube off the mandrel was ok, but different in a way. It left liquid on the surface of Figure 3: The epoxy stuck too well to the aluminum with the mandrel. So you have a bit of water-like surthe liquid wrench release. face tension between the fiberglass tube and the mandrel. It was just a different technique than was I can tell you that I spent a couple of hours trying to get all the epoxy removed from the man- used to using compared to the Challenge #95 mold release. drel after this experiment. You have to carefully The disadvantage of the Release #79 was that scrape off the surface with a knife blade - working it had a very oily touch to it. In other words, it was slowly to avoid scratching the mandrel with the metal blade (steel is harder than aluminum, so it hard to remove the oil from the finished fiberglass tube. If it is hard to glue fins to a tube with wax on can be easily scratched). Then you have to remove the remainder of the epoxy with steel wool. the surface, it is twice as hard to get them to stick to oily silicone. You do this once, and I guarantee that you don’t ever want to repeat it. Continued on page 6 Continued from page 4 www.ApogeeRockets.com/Rocket_Kits/Scale_Rockets Page 5 Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes Continued from page 5 Out of desperation, I tried the “Part All Hi-Temp Wax” mold release from Rexco. This is a pastetype wax, but it has Teflon® in it as well. It is put on like a car wax: you apply it with a cloth, let it dry, and then buff it off. But you don’t let it fully dry; you want it just “mostly dry” so that it buffs off easier. If it is fully dry, it is very stiff and it is difficult to remove the build-up by buffing. But as a mold release, it was by far the best of anything I tried! And I’d recommend it 100%. The surface tension between the tube and the mandrel is easy to break by pushing the bubble around the tube. I made a video showing how I run my thumb around the tube to break the surface of the tube free from the mandrel. You’ll find the short video at: https://www.youtube.com/ watch?v=nCCRh226Avg You can also break the surface tension by slightly twisting the tube. This takes a bit of practice to get the technique right, because if you twist too hard, you’ll snap the tube right off. I’ve done that a number of times too. Once you break the entire surface free from the mandrel, the tube can be slid off. But when you start, as you’ll see in the previously mentioned video, you have to “pull” it from the small end. You have to pull until you break the vacuum that is created in the transition portion of the rocket. You’ll see in the video that at one point I started pushing from the fat end and nearly crumpled the tube. Fortunately I caught it before the fiberglass cracked, and I continued pulling from the motor end. One additional benefit of the Part-All Hi-Temp Wax is that it doesn’t leave any residue on the inside or outside of the tube. The tube is ready to accept the glue for the fins and any rings you want to put inside. The “Part All Hi-Temp Wax” works almost too good. I never thought I’d ever say “too good”, but there is a point where a tube can come off too easily. I’ll cover that in the next article. Continued on page 7 Minimum Diameter Motor Retainers! Apogee is your one stop shop for your minimum diameter rockets projects! • Fly High • Fly Fast • Impress Your We Have: • Minimum Diameter Retainers • Motor Extenders • Threaded Forward Closures • Adapters for Cesaroni Cases Friends! www.ApogeeRockets.com/Building_Supplies/Motor_Retainers_Hooks Electronics Hardware Installation Kit Think of the convenience of getting everything to professionally install your dual-deployment or other electronic payload into a e-bay of your rocket! Includes: nylon standoffs, screws & nuts, wire, push-switch, drill & tap, ejection charge cannisters, barrier strips, wire ties, and step-bystep DVD instructions. https://www.apogeerockets.com/Electronics_Payloads/Electronics_Accessories/Electronics_Mounting_Kit Page 6 Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes The tricky part was how much time you had to wait for it to stiffen up. For reference, I was using Fixing Surface Imperfections the West Systems brand epoxy, which takes a After finding the right mold release agent to full 24 hours to cure. I found that I had to wait an help remove the tube from the mandrel, I shifted hour after putting the epoxy onto the fiberglass my focus to another small issue. That was getting before it was ready to go into the mold. a high-quality surface finish on the rocket. But because it was stiff, it wouldn’t go into the Looking at Figure 4, you’ll see two problems rubber mold easily. This led to a process of applythat I had. The biggest one was the fiberglass ing epoxy twice to the mold. The first batch was cloth shifting positions and leaving a gaping hole applied to the fiberglass that was on the mandrel in the side of the tube. and allowed to thicken. Just before it was slid into the mold, the mandrel was coated with a layer of fresh epoxy, which acts as a lubricant to allow it to slide into the mold easier. Obviously, two layers of epoxy can be heavy. So the first layer has to be as thin as possible. Initially, as shown in Figure 15 and Figure 16 in the previous newsletter (https://www.apogeerockets.com/education/downloads/Newsletter431.pdf), I’d wet out the cloth with epoxy on a sheet of glass and then transfer it to the mandrel. That way, only a little epoxy remained on the cloth. Figure 4: The two problems shown here are the fabric This would then sit for one hour to stiffen up. shifted when the it was inserted into the silicone rubber At that point in time I’d put a second layer of fresh mold, and a dimple of epoxy on the surface of the tube (at epoxy on the fiberglass and then shove it into the the arrow point). rubber mold. As it went into the mold, the excess The cloth was shifting position during the epoxy is squeegeed off by the silicone as it slid process of sliding it into the silicone rubber mold. into the mold. From here it would sit and cure Essentially, the liquid epoxy was acting as a lubrifully overnight. cant. Therefore, the problem of the glass cloth shiftThe solution was easy to fix. I had to let the eping around was fixed by “process.” I didn’t change oxy start to cure a little bit and stiffen up before I materials, just the order and time when they were shoved it into the silicone tube that served as the applied. female mold. Continued on page 8 Continued from page 6 Quick-Change Motor Adapters • Allows you to use smaller diameter motors in your rocket kits (adds versatility) • Change out motors in seconds • Works with all single-use and re-loadable motors • Four sizes available www.ApogeeRockets.com/Building_Supplies/Motor_Mount_Kits_Adapters/Ready-to-use_Motor_Adapters Page 7 Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes Continued from page 7 Getting Rid of the Epoxy Dimples The other problem shown in Figure 4 (Page 7) is the little dimples of epoxy on the surface of the tube. In the last newsletter, I mentioned that I could simply sand them off. But that adds a secondary operation, and it scuffs up an otherwise shiny tube. The dimples were occurring because of air bubbles that were trapped in the silicone rubber molds that I was using. Normally, I’d degas the silicone by putting the entire mold in a vacuum chamber. But these were really big molds, and my vacuum chamber couldn’t hold them. Here’s why the dimples were forming. What was happening was when the PVC tube containing the silicone mold and the mandrel was being pressurized, excess epoxy, instead of sliding out from under the silicone mold (or evenly flattening out under the surface of the silicone rubber), was depressing the air bubbles in the silicone and staying on the surface (Figure 5). Once it hardened, it would leave a dimple of epoxy. The solution was to change the type of silicone I used to make the rubber molds. Instead of using a soft silicone rubber (it had a blue color), I switched to a harder rubber. In engineering terms, the rubber went from a shore hardness of 25 to 40. Because it was harder, the epoxy could not easily push into the voids under the surface of the rubber. The result was instantaneous. I got perfectly smooth tubes every single time! There was no additional secondary process (like sanding away Figure 5: Cut-away view of the silicone (blue part). When an air bubble (called a void) is trapped in the silicone near the inside surface, the epoxy can deform the silicone and squeeze into the void, leaving a dimple on the surface of the part. blemishes) needed to make smooth tubes. They just came out nearly flawless, and only needed to have the ends trimmed to be a usable tube. The only difference I noticed was how physically hard it was to remove the silicone from the aluminum mandrel (the very first time when making the mold). It was a Continued on page 9 https://www.apogeerockets.com/index.php?main_page=redirect&action=banner&goto=56 Page 8 Issue 432 | December 13th, 2016 Making Fiberglass Body Tubes Continued from page 8 really difficult time, because the rubber is so stiff and hard. I did have to use compressed air and a huge amount of effort to get the mandrel out of the silicone without cutting it apart. In hindsight, I’d make the wall thickness of the silicone rubber mold a lot thinner, just to be able to remove it more easily from the mandrel. The good news is that once you are making a real part with fiberglass over the mandrel, it comes out really easy. books: “Model Rocket Design and Construction,” “69 Simple Science Fair Projects with Model Rockets: Aeronautics” and publisher of the “Peakof-Flight” newsletter, a FREE e-zine newsletter about model rockets. You can email him by using the contact form at: https://www.apogeerockets. com/Contact Next time In the final installment in this series, I’ll describe some of the other little tips and tricks that I developed, and then list the final step-by-step sequence that I now use to make fiberglass tubes. About The Author: Tim Van Milligan (a.k.a. “Mr. Rocket”) is a real rocket scientist who likes helping out other rocketeers. He is an avid rocketry competitor, and is Level 3 high power certified. He is often asked what is the biggest rocket he’s ever launched. His answer is that before he started writing articles and books about rocketry, he worked on the Delta II rocket that launched satellites into orbit. He has a B.S. in Aeronautical Engineering from Embry-Riddle Aeronautical University in Daytona Beach, Florida, and has worked toward a M.S. in Space Technology from the Florida Institute of Technology in Melbourne, Florida. Currently, he is the owner of Apogee Components (http://www. apogeerockets.com) and also the author of the You get: (4) AT 29/13 (4) AT 41/18 (2) AT 56/18 (2) AT 66/18 (1) AC-56 (1) AC-66 You get: (6) AT 13/18 (6) AT 18/18 (6) AT 24/18 (6) AT 33/18 www.ApogeeRockets.com/Building_Supplies/Body_Tubes Need Rail Buttons And Stand-Offs? www.apogeerockets.com/Building_Supplies/Launch_Lugs_Rail_Buttons/ Rail_Buttons https://www.apogeerockets.com/Rocket-Kits/Skill-Level-3-Model-Rocket-Kits/Slo-Mo Page 9 Issue 432 | December 13th, 2016