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CHRIS-MARINE Surface Parameters

9. SURFACE PARAMETERS

9.1. Determining the Surface Condition

Diesel engine designers often specify their require-ments in terms of Ra, Rz, Rmax and Mr as well as in

cross-angle pattern for cylinder liner surface finish.

The following sections will define these parameters.

Chris-Marine regularly test-hone cylinder liners from

various diesel engine manufacturers and have ac-

cumulated considerable knowledge on this subject.

By using Chris-Marine honing equipment and main-

tenance methods, a diesel engine benefits not only

from an extended working life for cylinder liners

and piston rings but also consequential cost reduc-

tion from e.g. reduced lube oil consumption owing

to surface irregularities.

Surface condition

The diagram shows schematically three profile sec-

tions of a cylinder liner wall.

Fig.1:Prior to honing the diagram shows an almost

completely glazed surface.

Fig.2:After coarse (basic) honing the diagram shows

a rough surface with deep groves and high peaks.

Work has been done to remove ovality and scuffing.

Fig. 3:After fine (plateau) honing the high peaks have

been honed down providing a smooth running sur-

face for the piston rings.

Surface condition before and after honing

Recording from a Surface Roughness Instrument

Following readings have been recorded by a surface

roughness instrument after a fine (plateau) honing.

Recording of surface roughness after fine (plateau) honing (example)

Doc. No110b/E Address: P.O. Box 9025

2002-11-01 S-200 39 Malmo, Sweden

Copyright Chris-Marine AB Phone: +46-4021 03 20. Fax: +46-40 21 40 68 - 1 -


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Surface Parameters CHRIS-MARINE

9.2. Cylinder Liner Requirements

9.2.1. Introduction

Any deviation from a geometrically ideal surface

has an influence on the functional behaviour of a

machine part. The ever increasing technical de-

mands on machines and machine parts makes, it

clear that it is ever more important, not only to

meet size tolerances, but also to consider sur-

face texture.

Surface irregularities

In a cylinder liner, besides deviations of size, the

following surface irregularities may occur:

Deviations of form(Form errors), i.e. deviations

of a bore outline from the ideal circle.

The cylinder bore might be oval or lobed

(e.g. four-clover wear).

Waviness, i.e. wave-form irregularities of a

bore outline (W-profile).

Roughness, i.e. irregularities in form of groves,

score marks, flakes or protuberances (R-profile).

These surface irregularities may be found in a

combined form described as Superimposed Sur-

face Irregularities(P-profile).

Differences between Surface Irregularities

The main distinctive feature of superimposed

surface irregularities (form, waviness and rough-

ness) is their horizontal pattern.

The form error (Fa) is the long-wave surface tex-

ture with only a few undulations (Large-scale ir-

regularities). An ideal cylinder liner, for example,

is constituent with only one undulation (cylinder).

The waviness (Wt) texture and the roughness (Rz)texture differ in spacing (Small-scale irregularities).

Deviations of form (Form error)

Waviness

Roughness

Superimposed irregularities

Surface irregularities

Oval Lobed Wavy

Large-scale irregularities (example of Form errors)

Superimposed Surface Irregularities (Unfiltered P-profile)

Address: P.O. Box 9025 Doc. No.: 110b/E

S-200 39 Malmo, Sweden 2002-11-01

- 2 - Phone: +46-4021 03 20. Fax: +46-40 21 40 68 Copyright Chris-Marine AB


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Evaluation (measuring) length and Reference line

Assessment of surface parameters is only possible within defined evaluation

limits (Evaluation length and Reference line).

The horizontal limitation for the assessment of surface parameters is theevaluation or measuring length, defined to a value between 0.4 and 40 mm

depending on the roughness (groove) spacing, or the average value of several

sampling lengths. The evaluation length determines the portion of the long-

wave surface components (waviness and form error) that will be included in

the measurement result, i.e. the longer the measuring length the higher the

assessed profile height (Pt).

Effect on evaluation length (lm) on profile height (Pt)

The reference line is a mathematically calculated mean line which is fitted into

the profile where the sum of areas enclosed by the profile above the line

equals the sum of those below.

Parameters to be assessed from a roughness profile (R-profile), e.g. Rz, Rmax,Ra and Mr (Tp), must not be affected from waviness or form components.

These components require a clear separation, that can only be done by means

of electrical filters in a laboratory.

A mean line representing the waviness is fitted into the unfiltered profile

(P-profile). The deviation from the mean line is the roughness.

Unfiltered profile (P-profile) separating Waviness (W-profile) and Roughness (R-profile)

For assessing the R-profile the waviness components must be eliminated by

subtracting the mean line from the actual profile.

The reference line of the filtered roughness profile is a straight mean line.

Filtered profile (R-profile) for assessment of roughness

Doc. No110b/E Address: P.O. Box 9025

2002-11-01 S-200 39 Malmo, Sweden

Copyright Chris-Marine AB Phone: +46-4021 03 20. Fax: +46-40 21 40 68 - 3 -


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Surface Parameters CHRIS-MARINE


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Ra(Arithmetical Mean Roughness)

Ra is the arithmetical average deviation from the mean line throughout the

evaluation (sampling) length (lm).

Theoretically, Ra is the distance between two imaginary lines above and below Tm(odeviati)Tj10.02 0 0 10. 10 j

ment ofo Tm3 Tm( )TjETEMC/P >BDC0 0 0 scnBT/TT5 1 Tf0 Tcd

p m


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