Aluminium for Pneumatic Cylinder Manufacturers

What Metline supplies to the pneumatic cylinder industry

A pneumatic cylinder converts compressed air into straight-line motion. Its pressure envelope, normally rated to 10 bar (1.0 MPa) working pressure, is a tube closed by two end covers, with a piston and rod sliding inside. Because the pressures are moderate and weight, corrosion resistance and machinability matter, aluminium is the dominant material for the body parts.

Metline does not make or sell finished cylinders. We supply the aluminium that cylinder makers turn into cylinders: extruded profile barrels and round tubes with finished bores, extruded bar and profiles for pistons and guide bodies, plate for slide tables and manifolds, forgings for end covers on larger bores, and aluminium casting alloy for die-cast covers. The rest of the cylinder, such as the steel or stainless piston rod, tie rods, seals and magnets, comes from the manufacturer's other suppliers.

This page is written for engineers and buyers at cylinder manufacturers, OEMs that build their own actuators, and repair shops that remanufacture cylinders. It explains which parts are aluminium, which alloys and finishes are normal, and the dimensional standards that set the shape of those parts. For the barrel tube alone, see our detailed pneumatic cylinder tube guide.

ISO cylinder standards and the aluminium they use

Cylinder standards fix mounting dimensions and bore sizes so that cylinders from different makers are interchangeable. They do not prescribe materials, but in practice each family has a typical construction.

ISO 15552 (current edition 2018) superseded ISO 6431 and the German VDMA 24562, so drawings that still quote the older numbers can be read as ISO 15552 for mounting dimensions. Within the ISO 15552 range, smaller and medium bores are usually built on a one-piece profile barrel, while the largest bores often use a round barrel held between end covers by four tie rods.

Cylinder features that shape the aluminium parts

Each option a cylinder maker offers changes the aluminium parts behind it. Knowing these links helps when drawing up a material specification or when a part has to be redesigned for a new variant.

Which cylinder parts are aluminium, and in which form

Piston rods (chrome-plated steel or stainless), tie rods, fasteners, seals and magnets are not aluminium; manufacturers buy them separately. Metline supplies the aluminium parts only.

Alloys used in pneumatic cylinders

Values are typical properties from published Aluminum Association / ASM data, not specified minimums. Design to the minimums in ASTM B221 or EN 755-2 and confirm with the mill certificate.

End covers on high-volume cylinders are usually high-pressure die castings in aluminium-silicon alloys such as A380 or the Japanese equivalent ADC12. For low volumes, large bores or covers that must be free of porosity, makers machine covers from 6061 or 6082 plate or bar, or start from a close-to-shape forging to save material and machining time. Metline supplies the plate, bar, forgings and casting ingot for each route.

What a cylinder barrel must achieve

The barrel is the most demanding aluminium part, because the piston seal runs on its bore for millions of cycles. The main requirements are:

• Bore size and roundness: held to an ISO 286 tolerance class agreed with the seal supplier, commonly in the H8 – H11 range depending on the seal design
• Bore surface finish: a smooth, consistent surface, achieved by precision extrusion with drawing, honing or roller burnishing
• Straightness: controlled over the full length, especially for long-stroke and rodless cylinders
• Hard anodised bore: a Type III hard anodic coating gives hardness and wear resistance; it is often finished to reduce friction
• Wall strength: wall thickness sized for the working pressure with a safety margin for proof testing, usually at 1.5 times the working pressure
• Profile features: sensor slots, tie-rod or screw channels and flat mounting faces, all produced in the extrusion

Barrel stock is usually supplied in mill lengths of several metres, or cut to stroke-dependent lengths with square, deburred ends. Bores are protected with caps and the tubes packed to avoid any contact damage. Full details of profile types, bore tolerances and finishing are in the cylinder tube guide.

Theoretical cylinder force by bore

Bore size sets the force a cylinder can deliver and therefore the size of every aluminium part. Theoretical push force is pressure × piston area. The table gives push force at 6 bar and 10 bar, before friction losses; pull force is lower because the rod area is subtracted.

In practice, designers apply a load ratio of roughly 50 – 70 % of theoretical force for dynamic loads, to leave margin for friction, acceleration and pressure drops. Larger bores also call for heavier end covers and stronger cover fixings, which is why the largest ISO 15552 bores often move from profile barrels to tie-rod construction.

Forces are calculated from geometry: F (N) = p (bar) × 0.1 × π × D² ÷ 4, with D in millimetres.

Aluminium in guided, compact and rodless cylinders

Across all of these designs the same pattern holds: extrusions carry the long, precise features such as bores, slots and guide channels, while bar, plate and forgings supply the compact, heavily machined parts such as covers, pistons, carriages and tables. Planning a product range around a small number of shared profiles and bar sizes simplifies material buying, shortens set-up times and keeps stock of semi-finished aluminium manageable for the cylinder maker. It also makes it easier to keep consistent alloy, temper and anodising quality across every bore size in a series.

Machining, anodising and corrosion protection

Aluminium cylinder parts are machined at high speed with sharp carbide tools. 6061-T6 and 6082-T6 give short chips and good finish on covers and pistons; 2011-T3 is preferred on automatic lathes for small turned parts because it breaks chips even more readily. Port threads (G, NPT or M) and mounting threads should be cut in well-supported material, away from thin profile walls.

For food and beverage plants, washdown equipment and marine automation, cylinder makers often move to stainless designs; where aluminium is retained, a thicker anodic layer, sealed properly, and 6061 or 6063 rather than copper-bearing 2011 gives the best corrosion behaviour.

How to specify aluminium for cylinder parts

1. Name the part and the standardFor example: "barrel profile for ISO 15552 Ø63 cylinder, to our drawing". Include the cylinder standard so mounting dimensions are clear.
2. Give alloy, temper and product standardE.g. 6063-T6 to EN 755-2 or ASTM B221 for extrusions; 6061-T651 to ASTM B209 for plate; 2011-T3 bar to ASTM B211.
3. Define critical dimensionsBore size and tolerance class, wall thickness, straightness, cut length and end condition; for bar and plate, size and tolerance.
4. State the finishMill finish for parts you will machine and anodise yourselves, or anodised barrel stock with specified layer thickness.
5. Agree inspection and documentsDimensional reports for bore and straightness, EN 10204 3.1 mill certificates, and packing that protects bores and ends.

Related aluminium products and guides

How to order from Metline

1. Send your requirementDrawings or sizes, alloy and temper, finish, quantities and destination to sales@metline.in or through the contact form.
2. Technical reviewWe check the profile or part against the product standard and confirm tolerances, finish and inspection.
3. QuotationPrice, packing and delivery terms on EXW, FOB, CIF or DAP basis.
4. Production and inspectionMaterial is produced, cut and inspected; dimensional records are kept for bore-critical items.
5. DispatchExport packing with end caps and separators, the EN 10204 3.1 certificate and packing list, shipped by sea or air.

Aluminium for pneumatic cylinders: frequently asked questions