Closing Pressurized Tubes: 4 Ways to Make a Tube End Gas-Tight and Pressure-Resistant
Gas springs, accumulators, airbag inflators, refrigerant tubes and heat pipes must hold gas or liquid pressure after the tube end is closed. Spin closing is cold forming and leaves a fine closure line at the center, so the higher the internal pressure, the more a closed end needs a finishing step. There are four common approaches by pressure level.
1. Direct full closing (low pressure)
The tube end is spun fully closed in one step. Suitable for low internal pressure or dust/water sealing – furniture, strollers, low-pressure containers. If closing is pushed too far or pressure is too high, the center can crack, so one of the methods below is used.
2. Close with a small hole + TIG fill weld (medium pressure)
The end is spun closed leaving a deliberate small hole, which is then filled by TIG welding. The weld is tiny with little heat input and gives a 100% leak-free end for medium-pressure cylinders and containers.
3. Full closing + die pressing (medium-high pressure)
After full closing, the end is pressed in a die to densify the closure, even out wall thickness and give the final shape, then checked by a hydraulic leak test.
4. Full closing + heating + die forming (ultra-high pressure)
For ultra-high pressure parts such as airbag inflators, the closed end is heated and die-formed so the material fully bonds, verified by burst testing.
Comparison
| Method | Pressure level | Welding | Typical parts |
|---|---|---|---|
| Direct full closing | Low | None | Furniture, strollers, general tubes |
| Hole + TIG fill | Medium | Small fill weld | Cylinders, containers |
| Full closing + die pressing | Medium-high | None | Gas springs, hydraulic cylinders, accumulators |
| Full closing + heat forming | Ultra-high | None | Airbag inflators |
Tube requirements
- Enough ductility; on welded (ERW) tube the seam must be sound or it will split during closing.
- OD and wall must match – the larger the OD, the more the wall range matters.
- Softer, more ductile stainless tube closes more easily.
How TONG DA can help
- We recommend a closing route for your pressure requirement and supply the closing machine (TD-31040, TD-31050, TD-382 NC) or OEM closing.
- Send samples for trial closing, then run your own leak or burst tests.
FAQ
Is a spun closed end gas-tight by itself?
At low pressure, yes. At higher pressure we recommend a fill weld or die pressing for long-term leak-free performance.
Can we test before deciding?
Yes, send samples for trial closing.
How do I ask?
Email OD, wall, material and internal pressure to sales@tdco.com.tw and we will recommend a method.