wear rate loesche

8/17/2019 Wear Rate Loesche

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Optimize your grinding parts

Maintenance News

Customer Service


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Every comminution process is accompanied by the

phenomenon of wear. Wear is a loss of material from

the surface of components. The area subject to the

most intensive wear in Loesche mills is that of the

grinding tools, i.e. grinding roller and grinding plate.

The prevailing form of wear in the grinding roller –

grinding plate system is abrasion, i.e.:

• hard particles penetrate into the grinding tools,

• whereby the depth of penetration is dependent on

the hardness of the grinding body material;

• in the case of multiphase materials (chilled castings

– embedded carbides) local score grooving proc-

esses occur, resulting in a selective removal of

material.

The harder the particles to be ground, the greater the

removal of material or wear. Increasing wear has a

negative impact on the comminution effect of the

grinding tools.

The choice of wear material which is to be used

in vertical mills is determined not just by the abrasivity

of the grinding stock. What is required is a considera-

tion of all the economic factors, such as costs, plant

availability, simultaneity of utilisation of all the

wear parts – referred to in their entirety by the term

“LIFE CYCLE COST”.

Loesche offers the right material for every application.In practice three different material groups have gained

acceptance:

• Grinding parts made from chromium alloy

cast iron

• Hardfaced grinding parts

• Grinding parts made from composite casting


Typical wear pattern on a Loesche tyre


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Sign of wear at a grinding plate Collar formation on a worn-out tyre

Worn tyre Worn tyre when installed together with grinding plate


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Grinding parts made from chromium

alloy cast iron

Chromium alloy cast iron has proven itself as the

standard material used for grinding parts in everyday

applications. These materials are known for example

by the trade names Ni-Hard IV and Cromodur.

The carbon in the cast iron is present in chemically

bonded form as iron carbide or chromium carbide. This produces a very hard structure which offers

high wear resistance. The matrix is usually modified

by heat treatment to martensite so as to offer the hard

carbides a firm hold and thereby further increase wear

resistance.

In order to avoid embrittlement of the material and with

it a risk of fracture, it is necessary for the components

to be tempered by further heat treatment. Tempering

leads to a loss of hardness and wear resistance. Due

to this, tempering is only carried out at very low tem-

peratures. Despite these low temperatures the impact

resistance is appreciably improved. The manufacture of grinding parts containing high

levels of chromium requires detailed knowledge of

materials and plenty of experience. To achieve the

desired material properties, it is essential to adhere

exactly to the parameters of temperature and heating

duration.

Materials containing high levels of chromium have

good to very good resistance to abrasion. The general

hardness of 630 to 800 HV20 produces uniform,

anticipated wear. Grinding parts made from this

material are used in coal mills and in raw meal and

cement mills. Although contrary statements are made in the

literature, grinding parts made from chromium alloy

cast iron can nowadays be armoured safely and

economically. Thanks to hardfacing the useful life

can be significantly increased compared with wear-

resistant castings.

The down-times caused by hardfacing are unavoida-

ble. Depending on the amount of material to be

deposited, down-times ranging between a few days

and more than a week may be anticipated. The number

of repeatable weld deposits on a grinding part is de-

pendent on the previous service life, the load and the

condition of the previous deposits. The correct combi-

nation of hardening and tempering leads to a wear re-

sistant material with sufficient impact resistance for

many functions and which can also be regenerated.

Tyre made from Cromodur with worked seat

Structure of hardened Ni-Hard IV

100 µm



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Hardfaced grinding parts

Hardfacing refers to the deposition of a high-alloy

material as surface protection on heavily stressed

metallic components. The grinding tools are made

from either a weldable cast steel or alternatively wear-

resistant iron castings. Hardfacing can be completed

with a layer thickness of up to 80 mm.

Welds are deposited with a filler wire in order to

minimise the application of energy to the grinding

parts.

The welding materials contain high levels of chromium

and carbon. Depending on the degree of wear resist-

ance required, further carbide-forming materials, such

as niobium, vanadium, etc. are used.

A weld-deposited hard layer increases the wear resist-

ance of the ductile cast steel.

In this thermal process high-strength carbides are

formed within a matrix, resulting in a highly wear-

resistant layer.

For most tribological systems there are appropriate

filler metals to suit the parent metal.

Some of these material combinations are mechani-

cally machinable, offer a high degree of safety against

fracture, and provide a far greater useful life than grind-

ing parts made from a wear-resistant casting.

Hardfacing can be carried out inside or outside

the mill.

Regular wear measurements provide information

on the state of wear of the grinding parts. Evaluation

of these measurements produces specific wear rates,

makes it possible to provide a good assessment

of the utilisation ratio and the remaining service life,

and provides information on when to introduce

necessary regeneration measures or when to acquire

new grinding parts.

Completed weld-deposited tyre

Tyre during regeneration

Structure of a hardfacing application


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Grinding parts made from composite casting

In the case of composite materials two or more materi-

als are structurally bonded in such a way that each

component is stressed in that area in which it demon-

strates the best properties. Grinding tools are made

up of a so-called metal matrix composite (MMC). This

involves shaped ceramic pieces being embedded

in ductile cast iron. The shaped pieces themselvesare sintered from non-metallic oxides together with

chromium carbides. This combination makes the

grinding tools particularly hard and wear-resistant with

simultaneously high impact strength. The matrix of

cast iron increases the mechanical machinability of the

grinding tools.

Then heat treatment is also required here in order to

achieve the final hardness.

These composite materials provide a longer useful life

than standard materials and also hardfacing.

The material is already being used by various custom-

ers and has received an entirely positive evaluation.

It must be noted that regeneration by hardfacing is notpossible once the wear limit has been reached.

The advantages at a glance:

• Highly wear-resistant

• Very high impact resistance

• Simple machinability

• No hardfacing necessary

• Thus investment in a welding machine not

necessary

Tyre made from composite material. The shaped ceramic pieces can be clearly made out.



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Wear rate of different wear materials as a function of the grinding stock

W e a r r a t e [ g /

t ]

Coal mill Raw meal mill Cement mill

HardfacedChromium alloy cast iron Composite casting

Wear of grinding parts has a negative

effect on:

• Mill throughput

• Product quality

(fineness, specific material surface

and grain size distribution)

Improving wear protection results in:

• Reduction of costs

• Stabilisation of product quality and

mill throughput

• Increase in availability

• Reduction of down-times

• Prolongation of maintenance

intervals

If you require further information or have a specifi c query, e-mail our Customer Service team

at: [email protected]


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Loesche GmbH

Hansaallee 243

40549 Düsseldorf, Germany

Tel. +49 - 211 - 53 53 - 0Fax +49 - 211 - 53 53 - 500

E-Mail: [email protected]

www.loesche.com

Loesche LM 46.2+2 C/S roller grinding mill, Kingston, Jamaica, 2006

wear rate loesche

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