Picture 13: measurement of the inner diameter of a press-fit plain bearing
The installation dimensions and tolerances of iglidur® plain bearings are a function of the material and wall thicknesses. For each material, the moisture absorption and the thermal expansion are decisive factors. Plain bearings with low moisture absorption can be designed with a minimal bearing clearance. The rule of thumb for wall thickness: the thicker the wall of the bearings, the larger the clearances must be.
Therefore, different tolerance classes exist for iglidur® plain bearings. Within these tolerances, iglidur® plain bearings can operate in the permissible temperature range and in humidity conditions up to 70% according to the installation recommendations. Should higher air moisture levels be present, or the bearing be used underwater, materials with low moisture absorption are to be preferred.
iglidur® plain bearings are press-fit bearings for holes with the H7 standard hole. This press-fitting of the bearings fixes the bearings in the housing, and the inner diameter of the plain bearings is also formed upon press-fit.
The bearing size test is performed when the bearing is installed in a hole with the minimum specified dimension; both using a dial gauge and a plug gauge.
The "Go-Side" of the plug gauge, pressed into the hole, must pass easily through the bearing.
At the measuring levels (compare Fig. 13), the inner diameter of the bearings must lie along with the dia tester within the specified tolerance.
Fig. 13: positions of the measurement lines (1, 2, 3 = measurement lines)
In spite of careful manufacturing and assembly of the bearings, differences and questions regarding the recommended installation dimensions and tolerances can result.
For this reason, we have compiled a list of the most frequent reasons for differences. In many cases, with this troubleshooter, the reasons for the differences can be found quickly:
The hole is not chamfered correctly, so the bearing material is scraped off upon press-fitting.
A centring pin was used, which expanded the inside diameter of the bearing during press-fit.
The bore does not correspond to the H7 tolerance.
The housing is made of a soft material that was expanded by the bearing during press-fit.
The shaft does not have h tolerance.
The measuring does not take place within the measuring lines.