10.3.1 Tolerances
and Function
Tolerances meeting the DIN 40 680 standard
are based on application-dependent requirements and the conditions
relative to different ceramic manufacturing procedures and
materials when hard machining is not used.
To achieve higher dimensional, shape or position tolerances
it is necessary to carry out some type of machining (e.g.
grinding, lapping, polishing etc.) of the "as fired"
component after firing. The tolerances that can be achieved
in this way are specified in DIN ISO 2768 (general tolerances
for workpieces produced with machining) and in DIN ISO 1101
(shape and position tolerances).
These are the standards usually applied in machine construction
and related branches of industry.
For economic reasons it is always
necessary to ensure that only those surfaces of ceramic
components, typically functioning surfaces, are specified
with close tolerances, and that general tolerances in accordance
with DIN 40 680 apply to all other surfaces.
The dimensional tolerances described in DIN
ISO 2768 are classified into fine, medium
and coarse (g) categories, depending on the
dimensions of the component. Tolerance classes for selected
shape and position tolerances are also quoted ("H"
for fine, "K" for medium and "L" for coarse).
Requirements that exceeded these specifications, or different
requirements for shape and position tolerances, are dealt
with by DIN ISO 1101.
A corresponding specification of dimensional, shape or positional
tolerances would, for instance, be
DIN ISO 2768-m-K or, for example,
DIN ISO 2768-g-L
For further details see DIN ISO 2768 and
DIN ISO 1101.
The manufacturers of technical ceramic components
have specialised in particular materials and manufacturing
processes. This permits them to manufacture economically,
since the different material groups require entirely separate
production lines and, in some cases, special equipment. Manufacturers
who concentrate on components for machine construction are
regularly confronted with close tolerances, for which reason
they are usually equipped with machines suitable for hard
machining.
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