Air Shaft Applications in the Packaging Industry

In flexible packaging, label and paper packaging production, material travels in roll form at almost every stage. Plastic film, paper, aluminium foil and laminated structures enter the machine as a roll, are processed, and leave as a roll again. One of the most widely used components for gripping these rolls by their core, driving them and handling them safely is the air shaft. This article looks at where air shafts are used on packaging lines, what to check when selecting one, and the problems that come up most often.

What does an air shaft do on a packaging line?

An air shaft, also known as an expanding shaft, grips the core from the inside. When the internal bladder (air tube) is pressurised, lugs or leaves on the shaft surface move outwards and lock against the core. When the air is released, they retract and the roll slides off easily. This allows torque to be transmitted without slippage between core and shaft, keeps the roll centred and speeds up roll changes.

That matters a great deal in packaging, where lines change jobs frequently, rolls are swapped many times a day and operators often have to lift and carry shafts by hand.

Typical applications

Slitter rewinders

On a slitter rewinder a wide parent roll is unwound, cut into narrow strips by knives, and each strip is rewound onto its own core. On the unwind side a single air shaft carries the parent roll, while on the rewind side many cores sit side by side on the same shaft. Small variations in material thickness mean these cores build up to slightly different diameters. To let each core run at its own speed, a friction (differential) air shaft is the usual choice. On this type of shaft each core is driven through friction rings with controlled slip, giving more even winding tension across the strips.

Printing presses

Flexographic and gravure presses use air shafts in their unwind and rewind stations. Print quality depends on the web running at constant tension and on a straight path, so the shaft needs low runout, must keep the core centred and should not generate vibration at higher speeds.

Laminating and coating

Laminators unwind two or more materials at the same time and bond them together. At each unwind station the shaft, brake and tension control have to work as a system. Tension fluctuations can lead to wrinkles, bubbles or layers shifting against each other.

Bag and pouch making

Bag and pouch machines are also fed from rolls. Rolls here tend to be lighter and changes more frequent, so shaft weight and ease of handling become more important.

What to consider when choosing a shaft for packaging

Criterion	Why it matters
Core size	The most common core sizes in packaging are typically 3 inch and 6 inch. The shaft must match the core in use.
Roll weight and width	Determine the load capacity and deflection behaviour required.
Running speed	Balance and runout become more critical at higher speeds.
Roll change frequency	With frequent changes, a lighter shaft makes the operator’s job easier.
Multiple cores	Decides whether a friction solution is needed for slitting.

Shaft material

For shafts that are handled frequently and carry moderate loads, an aluminium air shaft stands out for its low weight. Steel shafts are better suited to unwind stations carrying heavy parent rolls. On wide machines where both low weight and stiffness are needed, carbon fibre shafts are worth considering. The right choice comes from looking at roll weight, shaft length and speed together.

Lugs or leaves?

Lug-type shafts grip the core at discrete contact points and are commonly used on the rewind side and in multi-core applications. Leaf-type shafts provide a larger contact area. Which suits best depends on the core material, roll weight and the application itself.

The shaft does not work alone

Good winding on a packaging line depends on the air shaft working together with safety chucks, brakes, tension control and web guiding.

• Safety chucks secure the shaft to the machine frame and transmit torque.
• Brakes and tension control help keep the web at constant tension on the unwind, even as the roll diameter decreases. A tension controller and brake should be considered together.
• Web guiding prevents the web from drifting sideways along the line; in slitting and printing especially, edge alignment has a direct effect on product quality.

Common problems

• Core slipping on the shaft: often caused by insufficient air pressure, an air leak or worn lugs.
• Loose or telescoping rolls: check tension settings, friction settings and core fit.
• Vibration at speed: may point to a bent shaft, a balance problem or worn journals.
• Marks inside the core: review whether the lug profile and air pressure suit the core material.

Before any inspection or maintenance, stop the machine, isolate and lock out energy sources and release the air from the shaft safely. Always follow the machine manufacturer’s manual for operating pressures and maintenance steps.

The right shaft means less downtime

Productivity on packaging lines depends heavily on how quickly rolls can be changed and how consistent the winding quality is. An air shaft matched to the core size, roll weight and speed makes the operator’s job easier and reduces the risk of waste and stoppages. To find the right shaft type for your application, browse our product pages or get in touch with AYS Makina via our contact page.