Flake quality is crucially important for cost-effective particleboard production. It has a significant impact on downstream production steps such as drying, screening, sifting, gluing and pressing.

Moreover, it affects the final mechanical board properties and the finishing and further processing of raw boards. Optimum flake quality enables savings in the wood raw material and glue required for particleboard production.

The key requirement of flake preparation is achieving an optimum – preferably constant – sieve distribution curve and receiving flat flakes with narrow thickness tolerance, adapted to the required board quality.

Modern particleboard plants mostly use knife ring flakers for flake preparation. In practice, these machines may have difficulty in achieving uniform material distribution in the flaking chamber.

This situation, Maier says, can be significantly improved using the Maier 3D-distribution system.

State-of-the-art Knife ring flakers

All knife ring flakers currently on the market have a similar general design and working principle.

The wood chips are fed into the flaker via a vibration conveyor with magnetic drum and material cleaning system, acting as an air sifter. The air flow used for the sifting process forwards the chips axially through an opening in the machine door into the flaking chamber.

Inside this chamber, the chips impact the rotor axially, are then deflected in the radial direction and guided by the rotor shovels to the knives of the knife ring to be cut into the required flat flakes.

Crucial factors affecting flake quality include: the quality of the wood chips; the adjusted knife ring protrusion; the knife angle and knife relief angle; the gap between the rotor knives and knife ring; and the size of the flake discharge gap.

This gap is determined in the modern knife ring by the wear plates.

The uneven wear of the parts interacting with the material flow at the rotor and knife ring not only reduces the life of the parts themselves but also results in difficulties adjusting knife protrusion, rapid worsening of the cutting conditions and, finally, loss of flake quality.

Uneven Wear problem

A well-known problem is that the material being deflected by the rotor in the radial direction often only impacts the knives of the knife ring over a relatively limited zone. In this zone, the wear of knives and wear plates is faster than in the zones with less material load.

As a result, the entire knife length (knife ring width) cannot always be used evenly.

Another problem with modern flakers is that the feeding via an axial air flow and the force of gravity – combined with particular flaking chamber design – make it impossible to distribute material over the knife ring circumference homogeneously.

As a result, the knife ring has a limited zone with maximum material load, depending on the direction of the rotor's rotation.

This means that a considerable part of the knife ring circumference is not used optimally in the flaking process.

Moreover, the knives throughout the knife ring circumference are also not evenly worn; in the zones with more material load, the wear is greater than in those zones with less load.

Various approaches are used in modern ring flakers to remedy the problem of material distribution.

So-called 'distribution discs' are one approach for influencing the material distribution over the knife ring width.

These are used in two different ways:

  • Static distribution discs, firmly mounted at the rotor;
  • Dynamic, eccentric distribution discs, which are separately driven.

Using the distribution discs does not in practice always guarantee even chip distribution over the knife ring width. In principle, the problem of uneven material distribution over the ring circumference cannot be solved in such a way, says B Maier Zerkleinerungstechnik GmbH.

Various solutions on the market can reduce the wear over the entire knife ring circumference.

For example:

  • Use of a continuously driven knife ring, slowly rotating in the opposite direction to the rotor during the machine's operation.
  • For flakers with a static knife ring, periodic manual rotation of the knife ring during the knife ring exchange.

While these approaches reduce the uneven wear on the knife ring over the circumference, they cannot prevent uneven material loading caused by the type of feeding into the flaker; neither can they influence the wear of knives over the knife ring width.

Unfortunately, none of the current approaches provides a reliable solution to the problem of uneven material distribution over both the width and circumference of the knife ring.

However, a new approach from Maier, a Dieffenbacher subsidiar y company, is designed to solve the problem. Using '3D distribution technology', it ensures the optimum material distribution over both the entire knife ring width (knife length) and also the entire knife ring circumference.

Distribution rotor solution

The key is a special distribution rotor integrated into the flaking chamber.

The axially blown-in chips enter the inner chambers of the distribution rotor, are set into rotation, and are then guided via centrifugal forces through the openings at the front and rear of the system, towards the main rotor.

This, Maier explains, achieves optimum distribution over both the knife ring width and the entire knife ring circumference, allowing the optimum and uniform use of the entire knife length.

Easy Retro-fit, impressive Results

The primary advantages of optimum 3D material distribution are optimisation of flake quality and lower operating costs per ton of material produced.

Overall, the new solution provides the following:

  • Optimum use of the total knife length (both the complete width and the entire circumference of the knife ring), resulting in increased throughput and also extending the service life of the wear parts
  • Uniform wear on all wear parts of the rotor and knife ring affected by material flow. This enables optimised adjustment of the knife ring to improve flake quality
  • Less re-work and re-grinding, for example of the rotor blades and the knives of the knife ring;
  • Optimum cutting conditions over a greater period of time, thus reducing energy consumption during the flaking process.

Implemented as a prototype, the solution was initially tested in a Knife Ring Flaker MRZ1400 at parent company Dieffenbacher's test laboratory.

Comprehensive laboratory tests clearly demonstrated that the material distribution in the flaking chamber could be substantially enhanced, says Maier.

Adapting to different input materials and production conditions is easily achieved by varying the rotation speed of the distribution rotor and by adjusting some parts of the system, it claims.

Based on the successful laboratory tests, a prototype was installed in a particleboard plant to test long-term operation under industrial conditions.

After several months of running reliably, Maier says that the results are promising. Prototype testing was ongoing at the time of writing.

The new distribution rotor is mounted with bearings in the flaker door, making the retrofitting of existing machines very simple: only the door with the distribution rotor and heavy particle separator need to be replaced.

The ability to easily retrofit flakers already on the market was another important target of the new development.

The launch of the new solution is planned for the LIGNA 2017 show in Hannover.

It will be available as an upgrade for existing flaker systems and as a standard component for the latest generation of Maier MRZ knife ring flakers.