Basic Principles Of Tube Expanding
Tube Expanding is the process of reducing a tube wall by compressing the outer diameter (OD) of the tube against a fixed container, such as rolling into tube sheets, drums, ferrules, or flanges. To assure a proper tube joint, the tube wall must be reduced by a predetermined percentage. The following chart can be used to calculate proper wall reduction.
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Determining Proper Wall Reduction
| Tube Test Number | Sample | 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|---|---|
| A | Tube Sheet Hole Inside Diameter (ID) | 1.010 | |||||
| B | Tube Outside Diameter (OD) | 1.000 | |||||
| C | Clearance (A – B) | 0.010 | |||||
| D | Tube Wall Thickness | 0.065 | |||||
| E | Total Wall Thickness (D x 2) | 0.130 | |||||
| F | Tube ID (B – E) | 0.870 | |||||
| G | Target Wall Reduction % | 0.070 | |||||
| H | Total Wall Reduction (E x G) | 0.009 | |||||
| I | Actual Expanded ID (C + F + H) | 0.890 |
- Measure the tube sheet hole ID.
- Determine the tube OD.
- Subtract the tube OD from the tube hole ID.
- Determine the wall thickness.
- Calculate the total wall thickness by multiplying the tube wall thickness “D” x 2.
- Calculate the tube ID by subtracting the tube OD “B” – total wall thickness “D”.
- Determine your target wall reduction % for step “G”.
- Calculate total wall reduction by multiplying total wall thickness “E” by target wall reduction “G”.
- The actual expanded ID target is calculated by adding the tube to tube sheet hole clearance “C” + tube ID “F” + total wall reduction “H”.
This technique is an excellent way to set torque rolling devices. Begin with the first sample tube and roll, measure rolled ID, calculate wall reduction, and determine if more or less wall reduction is required. Adjust torque as needed; roll the next tube, etc until proper torque is set. It is better to error on the side of under rolling. Once torque is set these tubes can then be re-rolled to achieve proper tube wall reduction.
Lubrication
Lubrication is critical in rolling a consistently tight tube joint. Tube expanding creates a great deal of heat and friction, so it is important to use the proper lubrication to obtain good tool life and consistent expansions.
