10.3.2 General
Dimensional Tolerances
10.3.2.1 "As Fired" Ceramic
The general dimensional tolerances in DIN
40 680-1 cover products made of ceramic materials as defined
by DIN EN 60 672-1. This is also applied in an analogous manner
to fine ceramic products for general technical purposes
Dimensional deviations arise due to the peculiarities of ceramic
technologies (see p. 81). Reducing dimensional tolerances
is only possible with increased technical effort, and must
be agreed upon by the manufacturer and customer in the light
of the particular application.
In addition to dimensional tolerances, shape tolerances may
have to be taken into account for some applications (see p.
218).
If ceramic parts are to be glazed or given an electrically
conductive coating, then the dimensions and tolerances apply
to the finished part. The choice of tolerances depends on:
- the necessary precision and
- the feasibility from the point of view of ceramic fabrication
technology, which in turn depends on the material.
Precision grades are divided into
- coarse (g) (which derives from the German
"grob", meaning coarse) for tolerances that can
be maintained by ceramic manufacturing techniques such as
extrusion or casting,
- medium (m) for tolerances that can be
maintained on small parts, especially those used for low
voltage equipment, through, for instance, extruding, unmetered
pressing, metered moist pressing, metered dry pressing and
white wear finishing.
- fine (f) for products where the accuracy
grades coarse and medium are not sufficient. "Fine"
cannot be achieved through ceramic production methods, and
makes special, additional procedures such as grinding or
drilling etc. necessary after firing. If the required accuracy
is fine, then the degree of manufacturing precision in accordance
with ISO tolerances must be agreed between the manufacturer
and user.
The label for a general dimensional tolerance (A) with a
medium (m) precision grade is:
General tolerance DIN 40 680-A-m
Avoid specifying a higher accuracy for all dimensions, as
this increases costs considerably.
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