Ordinary hourglass tube
The basic waisted profile without additional dimpling. Used where the core design needs the profile shape but turbulence is supplied in another way or is not required.
Radiator tube guide
Aluminium Hourglass Tube for Radiator & Heat Exchanger Cores
An aluminium hourglass tube is a thin-wall, high-frequency (HF) welded flat tube made from brazing-clad strip, with a waisted, hourglass-style profile and formed dimples or internal channels that strengthen the tube and stir the coolant. It is used in brazed radiator, heater and machinery cooling cores. This guide covers the configurations, clad materials, typical sizes and the details a core designer must confirm before ordering.
- Process
- HF welded from clad strip
- Materials
- 4343/3003/4343 · 4343/3005/4343
- Wall
- about 0.22 – 0.5 mm
- Use
- Radiator & heater cores
What is an aluminium hourglass tube?
In a brazed aluminium radiator, coolant flows through rows of flat tubes while air passes over corrugated fins brazed between them. The tube must be thin for heat transfer, strong enough to hold pressure and resist vibration, and clad with filler metal so it brazes to the fins and headers in one furnace pass. The hourglass tube is one answer to these demands.
The tube is roll-formed from coil of brazing sheet and closed with a longitudinal HF weld. During forming, the broad faces are drawn inwards so the profile narrows towards the middle, and dimples or internal webs are pressed into the walls. Where opposite walls touch, they braze together in the furnace, tying the faces to each other. This prevents the flat faces from ballooning under pressure, lets the wall be thinner than in a plain flat tube, and breaks up the coolant boundary layer to raise heat transfer.
The exact geometry differs from one core maker to another, which is why hourglass tube is always made to a drawing: width, height, wall thickness, dimple pattern and end configuration are all defined by the core design and header slot.
Hourglass tube configurations
Dimple hourglass tube
Dimples are pressed into the broad faces in a defined pattern and area. They stiffen the faces, braze to the opposite wall and stir the coolant. Dimple pitch, depth and position follow the drawing.
Free-end hourglass tube
A plain, undimpled zone is left at each tube end, commonly about 5 – 6 mm, so the tube slides cleanly into the header slots and seals well when brazed. Other free-end lengths are made to suit the header design.
Two-channel tube
The profile is formed with an internal division that creates two parallel coolant channels. The central contact line brazes shut, which roughly halves the unsupported span of each face.
Three-channel tube
Two internal divisions give three channels, used on wider tubes where a single central support is not enough to control face deflection under pressure.
Custom profiles
Where an existing profile is close but not identical to the drawing, roll tooling can be adapted. A tube from a different design family, such as a folded B-type tube, is not a direct substitute.
| Configuration | Choose it when | Confirm on the enquiry |
|---|---|---|
| Ordinary | The core needs the basic hourglass profile only | W × H × T, length, material, tolerances |
| Dimple | The drawing shows a dimple pattern | Dimple pattern, depth, pitch and dimpled area |
| Free-end | Tube ends must be plain for the header | Free-end length at each end, end shape |
| Two-channel | The design needs one internal division | Full cross-section drawing, channel widths |
| Three-channel | Wide tube with two internal divisions | Full cross-section drawing, channel widths |
Clad materials for hourglass tube
Hourglass tube is made from brazing sheet: a 3xxx-series core alloy with a thin layer of 4343 aluminium-silicon filler on one or both sides. Clad on both sides is normal for hourglass tube because the inside surfaces must braze together at the dimples and channel walls, and the outside must braze to the fins and header.
| Layer | Alloy | Key composition (wt %) | Function |
|---|---|---|---|
| Clad layer | 4343 | Si 6.8 – 8.2 | Filler metal; melts at about 577 – 613 °C and flows into joints during brazing |
| Core | 3003 | Mn 1.0 – 1.5, Cu 0.05 – 0.20 | Standard core: good formability, weldability and corrosion resistance |
| Core | 3005 | Mn 1.0 – 1.5, Mg 0.20 – 0.6 | Magnesium raises post-braze strength; Mg content must suit the CAB flux |
| Other cores | Long-life 3xxx variants | To customer specification | Improved post-braze strength or internal corrosion resistance |
Material thickness for this tube family is typically 0.22 – 0.5 mm. After brazing, the core alloy is effectively in the annealed condition, so the tube is designed on annealed strength; for 3003-O, EN 485-2 specifies a tensile strength of 95 – 135 MPa. Clad ratio (cladding thickness as a percentage of total) is set by the strip supplier and confirmed on the mill certificate. For background on clad materials, see our guide to brazing clad strip and coil.
Magnesium above roughly 0.3 % can react with standard potassium fluoroaluminate flux and impair CAB brazing. If you specify a 3005 core, confirm that the brazing process is set up for it.
Typical hourglass tube sizes
The sizes below are examples of dimple hourglass tubes in current supply. They show the scale of the product; other widths, heights and wall thicknesses are reviewed against your cross-section drawing.
| Configuration | Width W (mm) | Height H (mm) | Wall T (mm) |
|---|---|---|---|
| Two-channel | 26 | 1.5 | 0.30 |
| Two-channel | 26 | 1.8 | 0.30 |
| Two-channel | 26 | 2.0 | 0.25 |
| Two-channel | 26 | 2.0 | 0.30 |
| Two-channel | 32 | 2.0 | 0.25 |
| Two-channel | 32 | 2.0 | 0.30 |
| Two-channel | 40 | 2.0 | 0.30 |
| Two-channel | 40 | 2.0 | 0.35 |
| Three-channel | 42 | 1.7 | 0.28 |
| Three-channel | 52 | 1.7 | 0.28 |
| Three-channel | 52 | 1.8 | 0.40 |
| Three-channel | 40 | 2.0 | 0.35 |
Supply details
- Lengths
- Cut to length for the core, with free ends if specified
- Packing
- Bundled or boxed with separators to protect the clad surface and dimples
- Surface
- Clean, oil-free or with evaporative forming oil compatible with CAB brazing
- Documents
- Mill certificate for the clad strip (EN 10204 3.1) and dimensional report
Where hourglass tubes are used
| Application | Why hourglass tube fits | Notes |
|---|---|---|
| Heavy truck radiators | Brazed internal supports resist pressure cycling and vibration over long duty cycles | Wider two- and three-channel tubes are common |
| Off-road and construction machinery | Robust tube for dusty, high-vibration cooling packs | Often combined with heavier fins and thicker walls |
| Passenger car radiators | Thin wall saves weight and cost in high-volume cores | Narrow two-channel tubes |
| Heater cores | Compact cores with good turbulence at low flow | Small widths, free-end tubes |
| Generator sets and industrial coolers | Same brazed construction as vehicle radiators | Sizes follow the core design |
For multi-port extruded designs used in condensers and battery cooling, see aluminium microchannel tube; for charge-air coolers, see intercooler core tube.
How to select the right tube
| Tube type | Construction | Strengths | Typical use |
|---|---|---|---|
| Hourglass / dimple welded tube | HF welded clad strip with formed supports | Economical, high pressure resistance, built-in turbulence | Radiators, heater cores |
| B-type folded tube | Folded clad strip with a central brazed web, no weld | Very thin walls, strong central web | Car radiators, heater cores |
| Flat-oval tube | HF welded plain flat oval | Simple, low pressure drop | Radiators with inserts or low pressure |
| Microchannel (MPE) tube | Extruded multi-port | Very high pressure capacity | Refrigerant condensers, evaporators |
- Start from the core drawing and header slot. Tube width, height and nose shape must match the header punching exactly.
- Choose channels by width. Wider tubes need more internal supports to limit face deflection and meet burst targets.
- Check clad on both sides. Internal brazing of dimples and channel walls needs inside cladding.
- Define test requirements. Burst, leak, pressure-cycle and thermal-cycle targets drive wall thickness and material choice.
- Avoid direct substitution. A tube from another family (for example B-type) changes the internal structure and end design, so the core must be revalidated.
Inspection and testing
- Dimensions: width, height, wall, straightness and cut length checked against the drawing; dimple pattern verified with gauges or optical inspection
- Weld integrity: continuous eddy-current testing of the HF weld seam during production
- Pressure tests: leak and burst testing on samples from each run
- Metallography: weld zone and clad layer checked in cross-section
- Brazeability: trial brazing on sample cores when a new material or profile is introduced
- Traceability: strip coil number and mill certificate linked to each tube lot
How to order hourglass tube
- Share the drawingCross-section with W × H × T, channel layout, dimple pattern and area, free-end length, cut length and tolerances.
- Specify materialClad construction (for example 4343/3003/4343), strip thickness, clad ratio if specified, and any long-life core requirement.
- Profile reviewWe check whether an existing profile matches or whether tooling adaptation is needed, and agree samples.
- Approve samplesSample tubes are supplied for trial brazing and testing in your core.
- Production and shippingTubes are packed to protect the clad surface and shipped on EXW, FOB, CIF or DAP terms with mill certificates.
References and standards
- ASTM B313 – Aluminum and Aluminum-Alloy Round Welded Tubes
- EN 573-3 – Chemical composition and form of wrought aluminium products
- EN 485-2 – Sheet, strip and plate: mechanical properties
- AWS C3.7 – Specification for Aluminum Brazing
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
Aluminium (aluminum) hourglass tube: frequently asked questions
What is an hourglass tube in a radiator?
It is a flat, HF-welded aluminium tube with a waisted profile and formed dimples or internal channels. The internal contact points braze together in the furnace, making the thin-wall tube strong and creating turbulence in the coolant.
Which material is used for hourglass tube?
Usually brazing sheet clad on both sides, such as 4343/3003/4343 or 4343/3005/4343, about 0.22 – 0.5 mm thick. The 4343 layer is the filler metal; the 3xxx core provides strength and corrosion resistance.
What does free-end mean?
A plain, undimpled length at each tube end, commonly about 5 – 6 mm, so the tube fits and seals correctly in the header slot. The length is set by the header design.
Should I choose two-channel or three-channel tube?
Follow the core design. As a rule, wider tubes need more internal supports, so three-channel tubes are used on wider profiles to control face deflection and meet burst requirements.
Can an hourglass tube replace a B-type tube?
Not directly. The two have different internal structures and end designs, so substituting one for the other requires a new core design and revalidation.
Can you make tubes to our drawing?
Yes. Send the cross-section and specification; existing profiles are checked first and roll tooling can be adapted where the drawing differs.
Need hourglass tube for your radiator cores?
Send the drawing, material, quantity and destination. We will review the profile and reply with samples and a quote.
