The Quality assurance resp. quality management (DIN ISO 9000 to 9004) is of decisive importance in the industrial manufacturing for the technical and economic success of a product.
In many industrial fields, surface-roughness measurement plays an important role in this respect.
In the case of technically produced bodies the surface is more or less strongly destroyed as a function of the
process. The result is a deviation from the ideal surface. An ideal surface, i.e. a geometrically perfect surface
cannot be produced. An approximation to this ideal can be achieved only at great expense, e.g. for flat glasses,
blockgauge measuring faces etc.
On technical surfaces the deviations in shape described here are overlapping, like e.g. deviations of form,
waviness and roughness.
It is know that the functional behaviour of a machine part is influenced decisively by the quality of the surface.
In this context, it is referred to: wearing properties, kind of fit and adhesion, abrasion- and sliding propertis,
lubricating properties etc. For instance the system of fits: in view of the steadily increasing technical
requirements to be fulfilled by the machine parts, it is no longer sufficient to ensure the adherence to dimensional
tolerances. As with a special view to fits with exacting tolerances experience has shown that 50% of the
tolerances are consumed by deviations of form, these deviations (like waviness, surface roughness etc.) must
be limited and recorded by measuring techniques.
According to the latest state of the art, the surface roughness is measured by means of electric contact stylus
instruments in conformity with ISO 3274 (DIN 4772). A contact stylus instrument has to fulfil high requirements.
Roughness parameters *) (acc. to ISO 4287-1 (DIN 4768) and ISO 13565-2 (DIN 4776)) of very different
roughness structures on various types of materials must be measured keeping the uncertainty in measurement
as low as possible. Surface contact stylus instruments of the latest state of art can fulfil these requirements
provided they are sufficiently checked and calibrated. Here - as for all other measuring systems - the exact and
reliable measured-data acquisition depends on quite a number of systematic and accidental errors creating
differing measuring conditions.
In order to ensure uniform measuring conditions for the contact stylus instrument these instruments are checked
and calibrated by means of
HALLE-calibration standards
corresponding to Physikalisch-Technische Bundesanstalt (PTB)-standards
These calibration standards are in conformity with ISO 5436 and, meanwhile are commonly used
worldwide for the measurement of roughness. They are the basis for the calibration of contact stylus
instruments in Deutscher Kalibrierdienst (DKD) and in the draft of an ISO-standard as well.
Depending on the prevailing requirements, the measurement standards will be calibrated either by PTB
(Physikalisch-Technische Bundesanstalt, Braunschweig) or by HALLE GmbH (at present, we are not yet
accredited by DKD but the calibrations performed by us are in relation with PTB).
Through now, the application of these ideal measurement standards by operators of small- and medium-sized
contact stylus instruments e.g. at subordinate measuring places failed because of the high initial costs. Due to
the development of the line of products KNT 4058/03 the roughness measurement standards can now be
delivered at very favourable prices maintaining the same profile characteristics and the same precision as in
case of KNT 4058/01. The price reduction was possible on account of a smaller measuring surface combined
with less calibration work and calibration effected by HALLE GmbH only. Likewise, economically priced depth
measurement standards are available now because of a limitation to only 3 grooves for the most important
measuring ranges and subject to a calibration by us.
Parameters and measurement conditions are according to ISO 4287-1, ISO 4288, ISO 11562, ISO 13562-1
and ISO 13562-2 all issues 1995/96.
*) The most important roughness parameters:
Ra : arithmetical mean deviation Rpk : reduced peak hight
Rz : average peak-to-valley hight Rvk : reduced valley depth
Rmax : maximum peak-to-valley hight Mr1 : smallest material ratio of core profil
Rk : core roughness depth Mr2 : greates material ratio of core profil