In slitting and rewinding machines, both air shafts and differential air shafts are used for core gripping and rewinding, but they are designed for different operating conditions. For full-width rewinding, single-roll rewinding, or applications where roll diameters remain relatively consistent, a standard air shaft usually provides reliable gripping and torque transmission. However, when multiple narrow rolls are rewound simultaneously on the same shaft and differences in roll diameter and tension begin to appear, a Differential Air Shaft is often the more suitable solution.

Why Are Standard Air Shafts Suitable for Single-Roll or Synchronized Rewinding?

A standard air shaft works by using compressed air to expand lugs, leaves, or other gripping elements outward against the inside of a paper or plastic core. Once the core is locked in place, torque from the shaft is transmitted directly to the core, and the core rotates essentially at the same speed as the shaft.

Common designs include Lug Type Air Shafts, Through-Key Air Shafts, and Leaf Type Air Shafts.

Their advantages include a straightforward structure, reliable core gripping, and stable torque transmission. For this reason, standard air shafts are widely used for unwinding, full-width winding, and single-roll rewinding of paper, film, nonwoven materials, aluminum foil, and other web materials.

The key question is not whether a standard air shaft can grip the cores securely, but rather this:

When multiple slit rolls are rewound on the same shaft, can all of them maintain the same roll diameter and web speed throughout the winding process?

Why Does Tension Become Uneven During Multi-Roll Slitting and Rewinding?

Consider a wide film roll that is slit and simultaneously rewound into 10, 20, or even more narrow rolls.

In theory, all finished rolls should build to the same diameter. In actual production, however, web materials often have small cross-web thickness variations. The difference in a single layer may be extremely small, but as thousands of layers accumulate during rewinding, these variations gradually create measurable differences in finished roll diameter.

This is where the problem begins.

A standard air shaft locks all cores to the same shaft, so they rotate at the same angular speed. Once the finished rolls have different diameters, however, the surface speed required by each roll is no longer exactly the same.

Larger-diameter rolls tend to receive higher winding tension, while smaller-diameter rolls may gradually become looser.

This can result in:

• Uneven roll tightness

• Some rolls being wound too tightly while others remain loose

• Wrinkling of the web

• Telescoping

• Uneven roll edges

• Inconsistent finished-roll hardness

The narrower the slit width, the greater the number of rolls being rewound simultaneously, or the more tension-sensitive the material is, the more significant these problems can become.

How Does a Differential Air Shaft Solve Multi-Roll Tension Differences?

This is the fundamental difference between a Differential Air Shaft and a standard air shaft.

A differential air shaft normally uses multiple independent slip rings or friction units. Each core receives winding torque through its corresponding differential unit.

When individual finished rolls develop different diameters because of material thickness variation, the slip rings can allow controlled relative slipping. This enables each core to rotate at a speed better matched to its actual roll diameter while maintaining the required winding torque.

In other words, a differential air shaft is not designed simply to provide stronger core gripping. Its main purpose is to compensate for speed and tension differences between multiple rolls during simultaneous rewinding.

This is why Differential Air Shafts are widely used in precision slitting and rewinding equipment for applications such as film, labels, aluminum foil, copper foil, optical films, battery materials, and other tension-sensitive web materials.

Air Shaft or Differential Air Shaft: Which Should a Slitter Rewinder Use?

The decision is relatively straightforward when it is based on the actual rewinding process.

If the machine is mainly used for full-width winding, single-roll rewinding, or applications where multiple cores do not require independent tension compensation, a standard air shaft is usually sufficient.

However, if the application involves:

multiple narrow rolls rewound simultaneously on one shaft + increasing roll-diameter differences + high requirements for consistent tension and finished-roll tightness,

then a differential air shaft should be seriously considered.

Therefore, when choosing between an Air Shaft and a Differential Air Shaft, the key issue is not which design is more advanced. The real question is whether multiple cores on the same rewinding shaft need to independently compensate for speed and tension changes caused by differences in roll diameter.

For conventional synchronized winding, a standard air shaft offers a simple and reliable solution. For high-precision multi-roll slitting and rewinding, a differential air shaft can solve inter-roll tension differences that are difficult to control with a standard air shaft.