Rocket Team is requalifying a standard, consumer off-the-shelf, pneumatic tie rod air cylinder for use with pyrotechnics. The component was purchased from McMaster-Carr with part number 6491K254.
Integration Procedure
Note: The modified 1/4 NPT plug is a standard stainless steel plug with a 1/4-20 hole drilled and tapped through the middle.
Materials: Piston, 1/4 NPT Tee Adapter, Modified 1/4 NPT Plug, FireBolt, nitrile gloves, safety goggles
Steps:
- Obtain all required materials and inspect parts for defects.
- Insert and screw a modified 1/4 NPT plug into one of the two female ends of the 1/4 NPT tee adapter.
- Insert and screw the FireBolt into the modified 1/4 NPT plug using Teflon tape, only applying the tape above the slot in the FireBolt. Be sure that the E-match is shorted.
- Repeat steps 2 and 3 for the other female end of the 1/4 NPT tee adapter.
- From here on, use appropriate PPE of nitrile gloves and goggles.
- Measure out the required amount of black powder on a scale.
- Carefully pour the black powder into the male end of the 1/4 NPT tee fitting.
- Seal the male end of the 1/4 NPT tee fitting using CA glue.
- Apply one drop at a time, gently jiggling the tee fitting after each drop. Use a flashlight to ensure that you are gradually saturating the black powder.
- If you are only using a small amount of powder, it may be easier to seal from the end of the tee fitting opposite to the end in contact with the powder.
- Insert and screw the entire assembly into the air inlet hole of the piston. Use Teflon tape to ensure a good fit.
Testing
Testing commenced on October 10/28/17 with results summarized below.
Procedure
- Perform integration according to the integration checklist above.
- Run wires from outside to inside the blast chamber. Make sure that the wires are shorted on the outside of the blast chamber. On the inside, unshort the e-match leads and connect it to the wires.
- Push the piston rod all the way in.
- By conservation of momentum, the piston should not move upon ignition (in theory), but just in case, put a shop towel underneath to reduce scratching damage. Don't put the piston near anything it could fall off of.
- Only after exiting the chamber and closing the door, perform a countdown and connect the outside wires to a voltage source.
- In the event of a misfire, disconnect the battery and wait at least 60 seconds before allowing anyone to enter the chamber and approach the test article.
Results
| Test Number | Grams BP Used | Glue Type | Results | Notes |
|---|---|---|---|---|
| 1 | 0.5 | Zap-A-Gap Medium CA+ | Approximate equilibrium extension of 5.5in It was at approximately ambient pressure when we unscrewed it which meant that the bolt didn’t go shooting out. A lot of residue on the walls—could be improved by using much less glue. Couldn’t fully clean before the next test as a result. Small amount of movement–maybe the gas was able to leak out a little bit? The piston was definitely pressurized when we got to it at approximately ambient pressure but it wasn't at the same volume because the rod had moved. | May have lost small amount of black powder and/or displaced other powder when getting rid of excess glue. We performed a tap test and black powder did not come loose once the glue was dry |
| 2 | 1.0 | Insta-Cure Super Thin 1-3 sec | Very loud noise, the epoxy was blown of the FireBolt and then conservation of momentum worked against us. Even though the piston was clamped down, it was able to slide forward significantly. |
Videos and Images
Observations and Suggested Improvements
- Slot the 1/4 NPT cap instead of the Firebolt
- Only use a drop of glue at a time otherwise it won't dry.
Disassembly and Cleaning
Disassembling the piston was surprisingly difficult. When it was finally disassembled, we noticed that the black powder residue didn't extend very far up into the bore. We theorize that this is because the reaction occurred faster than the piston rod could move up the bore.