Breviary Technical Ceramics






10.3.2 General Dimensional Tolerances "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.