Technical Paper

Typical Regenerator Air-grid nozzles

this water-jet cutting. Jet velocities of water-jet cutters can reach up to three times the sound velocity!

The performance can drastically be increased if solid particles are added into the water stream. These particles are usually of ceramic nature, especially when fired or sintered. They offer high resistance to crushing because of their hardness.

In addition to the continuous abrasive action of the coherent jet of water, the abrasive particles in the stream create a ballistic effect: the particles bombard the surface, similar to small projectiles with energy levels several times higher than the medium that carries them.

Moreover, the mass differential creates a pulsed erosion process, which is extremely effective on hard-to-cut materials.

- - - - -

thermal erosion;

hydro-abrasive wear; corrosion; cavitation; and others.

Hence, the key parameters for the wear & tear can also be summarised by: •

movement of the particles: impact angle; velocity;

• •

abrasiveness of particles:

hardness; size;


concentration of the abrasive particles in the conveying fluid; environment:

temperature; nature of conveying fluid. Table 1 identifies these types of wear.

5.2 Blast (jet) wear One of the most important parameters, however, is the particle velocity which enters the wear rate calculations of ductile materials by the nth



, where n varies between 1,5 and 3) and for brittle materials by an even higher power.

Which means, in practice, that doubling the particle velocity can multiply the abrasion with a factor 3 to 8 !

Typical abrasion in a Regenerator primary cyclone

In this context water can be seen as one of the mediums for particle transport. The list can be extended with fluids, neutral or corrosive, and gases. But also materials in fluidized state, such as droplets or solids concur with aforementioned.

5 Types of wear

5.1 Identification and the significant characteristics of wear

Besides the typical nature of jet wear, wear can be classified in a larger area of terms all related to erosion. Terminology speaks of "closed" systems, i.e. machines, machine parts, which are lubricated, and "open" systems to which we will limit ourselves, and which are, for example:

With blast wear energy is transferred into the solid surface by impingement of grainy solids (particles), which are either present in the gas stream or are accelerated due to certain forces (i.e. flow regime).

The characteristic is the action of a great number of very small, mostly abrasive

particles, which, with a relative high velocity and under

predominant or varying angles, are continuously conveyed towards and alongside the surface.

The size of a particle plays an obvious part at average or large angles, a large particle is more abrasive than a small one (abrasion is proportional to the squared dimension). However, for a given mass load there are less abrasive particles. Hence, in practice, the abrasion velocity, at a given load, is then inversely proportional to the dimension of the particles.

The concentration of particles is only quasi-proportional to abrasion whatever the conditions, since not all particles are course and not all are



March 2019 Issue

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