Aluminium Intercooler Core Tube (CAC Tube) and Inner Fin
An aluminium intercooler core tube, often called a CAC tube, is a wide, thin-wall flat tube that carries hot compressed air through a tube-and-fin charge-air cooler. A corrugated inner fin brazed inside the tube adds surface area and stiffness. This guide explains how the tube and inner fin work together, the materials and sizes used, and what to specify when sourcing them.
- Tube type
- HF-welded flat tube
- Size range
- C30 × 7.6 to C100 × 7.7 mm
- Wall
- 0.26 – 0.5 mm
- Partner part
- Brazed inner fin
What does an intercooler core tube do?
A turbocharger or supercharger compresses intake air, and compression heats it. Hot air is less dense, so an intercooler (charge-air cooler, CAC) cools it before it enters the engine. Cooler, denser charge air lets the engine burn more fuel efficiently, lowers combustion temperatures and helps control NOx emissions.
In an air-to-air tube-and-fin intercooler, the charge air flows inside a row of flat aluminium tubes running between two tanks. Ambient air blows across corrugated external fins brazed between the tubes. Compared with a radiator tube, a CAC tube is much wider and taller, because air is far less dense than coolant and needs a large flow area at low pressure drop.
Air is also a poor heat-transfer medium, so the inside of the tube needs extra surface. That is the job of the inner fin (sometimes called an internal turbulator): a corrugated strip brazed to both tube walls. It multiplies the internal surface, breaks up the boundary layer, and ties the broad tube faces together so they do not bulge under boost pressure.
The CAC tube and inner fin
Aluminium CAC tube
- Thin-wall flat tube roll-formed from clad aluminium strip and closed by high-frequency (HF) welding
- Wide, tall section for low air-side pressure drop
- Clad on the inside so the inner fin brazes to the wall, and on the outside for the external fins and headers
- Supplied cut to length for the core; nose shape matches the header slot
Inner fin
- Corrugated aluminium strip inserted into the tube before brazing
- Offset-strip (lanced), wavy or plain fin forms, chosen for the heat-transfer and pressure-drop target
- Fin height matches the inside height of the tube; fin pitch sets surface area
- Brazed to both walls, so it also acts as a structural tie against pressure
Ordering the tube and inner fin as a matched set avoids the most common assembly problem: an inner fin that is slightly too tall jams on insertion, while one too short leaves gaps that do not braze, reducing both heat transfer and burst strength.
Intercooler core tube specifications
| Item | Typical range |
|---|---|
| Product | Aluminium CAC tube for tube-and-fin intercooler cores |
| Tube type | Flat, HF-welded from clad strip |
| Size range | From about C30 × 7.6 mm to C100 × 7.7 mm (width × height) |
| Width bands | 30 – 40 mm for passenger-car and light cores; 50 – 100 mm for larger and heavy-duty cores |
| Wall thickness | 0.26 – 0.5 mm |
| Matching component | Inner fin made to the tube inside dimensions |
| Length | Cut to the core length |
Notation such as C50 × 7.7 describes the tube outside width and height in millimetres. Wider tubes need a well-brazed inner fin and, often, a heavier wall to meet burst targets, because the unsupported face span grows with width.
Materials for CAC tubes and inner fins
| Part | Typical material | Reason |
|---|---|---|
| Tube core alloy | 3003 or a long-life 3xxx variant | Good weldability and formability; strength after brazing; corrosion resistance |
| Tube cladding | 4343 or 4045 Al-Si filler, inside and outside | Brazes the inner fin, external fins and header joints in one CAB cycle |
| Inner fin | Bare 3003 strip, or clad strip when the tube is clad only outside | Formable and conductive; filler can come from either the tube or the fin |
| External fin | Clad or bare 3003 fin stock, often zinc-alloyed for sacrificial protection | Protects the tube from external corrosion |
| Headers | Clad 3003 or long-life brazing sheet | Matched to the tube for brazing and corrosion |
After brazing, the tube is effectively annealed, so the design relies on the post-braze strength of the core alloy and on the inner fin tying the walls together. Where higher strength or better resistance to internal condensate corrosion is needed, long-life core alloys are specified; confirm the alloy on the drawing. Our guides to brazing sheet coil and fin stock cover these materials.
Internal corrosion matters in engines with exhaust-gas recirculation or where acidic condensate collects in the cooler. Ask your material supplier about long-life alloys if your engine has this risk.
How CAC tubes are produced and inspected
- Clad stripBrazing sheet coil is slit to the exact width for the tube perimeter.
- Roll formingA series of roll stands forms the strip into the flat profile.
- HF weldingHigh-frequency current heats the strip edges, which are pressed together to form a continuous seam without filler.
- Sizing and cuttingThe tube is sized to final dimensions, straightened and flying-cut to length.
- Inner finStrip is corrugated, cut to length and inserted, or supplied separately for insertion at the core maker.
- InspectionEddy-current testing of the weld seam, dimensional checks, burst testing and metallographic examination of the weld.
Specifying the inspection plan up front, including burst-test frequency, eddy-current sensitivity and dimensional tolerances, makes supplier qualification faster and avoids disputes later.
Where intercooler core tubes are used
| Application | Duty | Typical tube |
|---|---|---|
| Passenger car turbo engines | Compact front-mounted or top-mounted coolers | Narrower tubes, about 30 – 40 mm wide |
| Trucks and buses | Large coolers, long running hours, high boost | Wide tubes, 50 – 100 mm, heavier walls |
| Diesel generators and industrial engines | Continuous high load | Wide tubes with robust inner fins |
| Construction and agricultural machinery | Dust, vibration and high ambient temperatures | Wide tubes, thicker walls |
| Performance and aftermarket coolers | High boost, varied core sizes | Range of widths to the core design |
Some engines use liquid-cooled charge-air coolers, which often have a stacked-plate design rather than tube-and-fin; the tube discussed here is for air-to-air tube-and-fin cores.
CAC tube compared with other heat exchanger tubes
| Tube | Medium inside | Typical section | Internal enhancement |
|---|---|---|---|
| CAC tube | Compressed air | Wide and tall flat tube | Brazed inner fin |
| Hourglass radiator tube | Engine coolant | Narrow, thin flat tube | Formed dimples and channels |
| B-type tube | Engine coolant | Folded flat tube | Central brazed web |
| Oil cooler tube | Oil | Flat tube | Inserted turbulator |
| Microchannel tube | Refrigerant | Thin extruded multi-port | Many small extruded channels |
A frequent source of confusion: intercooler piping is the round tube or hose that connects the turbo, intercooler and intake manifold. The core tube discussed here sits inside the intercooler itself. For round connecting pipe, see our aluminium tube range.
How to order CAC tubes
- DrawingTube width, height, wall, nose shape, length and tolerances; inner-fin form, height, pitch and thickness.
- MaterialCore alloy, clad alloy and sides clad, and any long-life alloy requirement.
- TestingBurst, leak and eddy-current requirements and sampling frequency.
- SamplesSample tubes and fins for trial cores and validation testing.
- SupplyPacking to protect the clad surface, with mill certificates, shipped on EXW, FOB, CIF or DAP terms.
References and standards
- ASTM B313 – Aluminum and Aluminum-Alloy Round Welded Tubes
- EN 573-3 – Chemical composition and form of wrought aluminium products
- AWS C3.7 – Specification for Aluminum Brazing
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
- SAE J1726 – Charge Air Cooler Internal Cleanliness, Leakage, and Nomenclature
Aluminium (aluminum) intercooler core tube: frequently asked questions
What is an aluminium CAC tube?
It is the flat, thin-wall aluminium tube inside a tube-and-fin charge-air cooler. Compressed air flows through it while ambient air passes over external fins, and an inner fin brazed inside adds surface area and strength.
What sizes of CAC tube are available?
Typical tubes range from about C30 × 7.6 mm to C100 × 7.7 mm with walls of 0.26 – 0.5 mm. Other sizes can be made to the core drawing.
Why does a CAC tube need an inner fin?
Air transfers heat poorly, so the inner fin multiplies the internal surface and creates turbulence. Because it is brazed to both walls, it also stops the wide tube faces from bulging under boost pressure.
What is the difference between an intercooler core tube and intercooler piping?
The core tube is inside the intercooler and does the heat exchange. Piping is the round tube or hose that carries air between the turbocharger, intercooler and engine.
Which alloy is used for CAC tubes?
Usually a 3003 or long-life 3xxx core clad with 4343 or 4045 brazing alloy, so the tube brazes to the inner fin, external fins and headers in one furnace cycle.
Can you supply tubes and inner fins together?
Yes. Supplying a matched tube and inner fin to the same drawing is recommended, so fit and brazing are consistent.
Need intercooler core tubes?
Send your tube and inner-fin drawing, material, volume and destination. We will reply with a profile review, samples and a quote.
