Roller Tube Expander Mechanism: How It Works, Parts, Wall Reduction Formula and Uses

How the roller tube expander works

A typical tool has a cage, three or more rolls and a tapered mandrel. As the mandrel rotates and advances, it wedges the rolls outward. The rolls orbit within the tube and expand it until the tube first contacts the hole and then undergoes the selected additional wall reduction.

The visual is a transverse explanatory section. It shows the tube sheet, tube, mandrel, cage and three rolls, but does not reproduce an identified tool's taper, roll length, feed system, torque calibration or axial expansion length.

What this calculator demonstrates

Select tube outside diameter, original wall thickness, diametral tube-to-hole clearance and target wall reduction. The calculator derives the tube-sheet hole diameter, original tube ID, target expanded ID and remaining wall thickness.

These dimensions do not qualify a joint or choose an operating torque. ASME Form QEXP-1 treats minimum and maximum wall reduction, hole tolerance, expansion length, materials, equipment and calibration as procedure-specific variables.

Rolled-ID calculation

Let B be tube OD, t be measured original wall, C be diametral clearance and r be selected wall reduction as a fraction. Original tube ID is F = B − 2t, tube-sheet hole diameter is A = B + C, and total wall reduction across both sides is H = 2tr.

The target expanded ID is I = F + C + H. The displayed remaining wall is t(1−r), consistent with the same diameter arithmetic after the tube has reached the hole. Enter a target from the applicable qualified procedure or equipment guidance.

Selected example

For a 25.40 mm OD tube with 1.65 mm wall, 0.25 mm diametral clearance and 7% selected wall reduction, original ID is 22.10 mm and the tube-sheet hole is 25.65 mm. Total diametral wall reduction is 0.231 mm, giving a target expanded ID of 22.581 mm and a remaining wall of about 1.535 mm.

The numerical target is a geometry result, not proof of leak tightness, pull-out strength, code compliance or a safe torque setting.

Scope and selection boundary

Elliott publishes material-dependent guideline ranges and warns that they may not apply to a particular design. Harder and work-hardening materials generally use lower reduction than copper alloys, but the applicable drawing, code, purchaser specification and qualified tube-expanding procedure govern.

The removed calculator treated an arbitrary 100% wall basis as a physical wall and converted wall reduction into mandrel feed using only taper angle. That relation omitted tube and hole geometry and did not account for tool mechanics, so it has been removed.

Primary technical references

• Elliott Tool Technologies, Basic Principles of Tube Expanding — measured dimensions and rolled-ID calculation.
• Elliott Tool Technologies, Tube Expander Design & Usage — material-dependent guideline ranges, roll-count considerations and expansion boundaries.
• ASME Form QEXP-1, Tube Expanding Procedure Specification — procedure variables including wall-reduction limits, hole tolerance, expansion length, materials, equipment and calibration.

Questions

Is target expanded ID just the tube-sheet hole diameter?

No. The tube first grows through the diametral clearance, then additional ID increase produces the selected wall reduction.

Does the target wall reduction apply to every material?

No. Published ranges vary by material and are guidance; use the applicable qualified procedure and equipment documentation.

Can this calculator set a torque-control drive?

No. It gives a dimensional target. Torque calibration requires representative samples, measurement, the selected tool and the governing procedure.

Does the visual predict contact pressure or joint strength?

No. It does not model material stress-strain behavior, tubesheet elasticity, grooves, friction, axial length, residual pressure, leakage or pull-out load.