In the Corrugated (Cardboard) and Paper industries, the mill roll stands are equipped with pneumatic tension brakes and mechanical core chucks and in some cases with ejection systems.

Mill roll stand – comparing ejection systems

What are ejection systems for?

When a reel is completely unwound or a reel change is necessary, the ejection systems manage the release of the reel cores or of the paper rolls which could not occur just opening the roll stand arms.

When the machine is not equipped with an ejection system, the cores and the rolls can remain blocked on one of the two mechanical core chucks of the roll stand and the operator needs to manually unlock them in a dangerous and unsafe way for himself and for the machine.

The following comparing table shows the expulsion technologies currently available on the market:

  1. Roll stand without ejector
  2. Core chuck with ejection spring
  3. Pneumatic ejector with fork
  4. Mechanical chuck with spring ejection cylinder
  5. DUPLEX, mechanical chuck with pneumatic piston which is concentric to the chuck

Some examples:

roll stand
without ejector		mechanical chuck
with spring		pneumatic
ejector
with fork		mechanical chuck
with spring
ejection cylinder
reel core ejection
ejection of 1000 mm diameter roll
ejection of 1600 mm diameter roll
coaxial thrust force of the ejector
roll ejection 100% ensured
ejector free of dust and debris always working
absence of axial counter thrust during the loading phase
automatic re-enter of the ejector
complete visibility and safety during loading
no maintenance
total safety of the operations always ensured

In the table the most critical parameters for the operators have been considered:

  1. The production of both Corrugated Cardboard and Paper finds the need to be able to eject cores and reels of different sizes in total safety for the operator and for the machine
  2. Continuity in operations and expulsion always ensured without down time of the machine for expensive maintenance procedures
  3. The need of the widest possible visibility during the reel centering and reel loading operations
  4. Cost-effectiveness of the solution
Mill roll stand – comparing ejection systems
Duplex mechanical chuck with pneumatic piston

The comparison table shows that:

CORES AND ROLLS EXPULSION

All the technologies in comparison guarantee the expulsion of the cores of the rolls. The pneumatic ejector with fork and Duplex mechanical chuck with pneumatic piston guarantee the expulsion of the reels with a diameter of up to 1000 mm.

However, only Duplex technology allows the expulsion of the reels with a diameter of 1600 mm and up to 5000 kg.

This is because the Duplex is equipped with a pneumatic piston that works in two stages at 6 BAR; the first stage generates an axial ejection force of 2000 kg and the second stage of 1000 kg.

The mechanical chuck with spring ejection cylinder exerts a coaxial thrust force with progression from 800 kg to 400 kg causing a reaction force on the mechanical part of the roll stand which is degenerative for its components.

The pneumatic ejector with fork instead works at 10 BAR and generates a misaligned thrust force of 700-800 kg.

CONTINUITY IN OPERATIONS AND EXPULSION ALWAYS ENSURED

In the production of paper and corrugated cardboard, debris and dust can creep into mechanical ejection systems, jamming their functioning. This entails downtime and maintenance of the components to resume their operation.

The mechanical chuck with spring ejection cylinder for example requires cleaning from dust outside the machine and the use of a mechanical press to ensure a safe disassembly.

This is not the case of the mechanical chucks with spring because they require occasional and superficial cleaning directly on the machine.

The Duplex chuck with pneumatic piston also requires no maintenance as it is designed with a dust seal so that debris does not enter the cylinder and works in a sealed manner, guaranteeing continuity of operations.

Mill roll stand – comparing ejection systems
Mechanical core chuck with ejection spring

WIDE VISIBILITY OF OPERATIONS

A maximum visibility during reel change is possible in the absence of ejector and therefore in the presence of a mechanical head with or without spring. The ejection systems reduce the visibility during the reel centering.

The return of the flange of the core chuck in the case of the pneumatic ejection with fork and the return of the piston in the case of the mechanical chuck with spring ejection cylinder spring ejection cylinder occur after the roll centering and while closing the roll stand arms.

The Duplex instead can automatically retract the pneumatic piston and go back to its initial position and dimensions of a standard mechanical chuck before any new roll loading, ensuring wide visibility during the reel centering.

COST-EFFECTIVENESS OF THE SOLUTION

The least expensive systems available on the market are certainly the mechanical chucks and the pneumatic ejection system with fork. The mechanical chuck with spring ejection cylinder and the mechanical chuck with pneumatic piston are the least economic tecnologies.

In any case, the Duplex solution guarantees a fast return on investment because it is the only ejector that allows you to reduce the waste of paper that can occur:

  • During the splicing phase
  • Due to the incomplete unwinding of the reels
  • Due to damaged cores, which therefore can no longer be used
  • Due to lateral damage of the roll