SKF deep groove ball bearings with filling slots are available with a shield on one or both sides, designation suffixes Z or 2Z. The shield forms a narrow gap to the inner ring shoulder (fig 1).
Bearings up to and including sizes 217 and 314 are filled with high-quality NLGI class 2 grease with a polyurea thickener, that can be used at temperatures between –30 and +150 °C. The base oil viscosity is 115 mm2/s at 40 °C and 12,2 mm2/s at 100 °C.
Larger bearings are supplied with a high-quality NLGI class 3 grease with a lithium thickener, that can be used at temperatures between –30 and +120 °C. The base oil viscosity is 98 mm2/s at 40 °C and 9,4 mm2/s at 100 °C.
The quantity of grease fills some 25 to 35% of the free space in the bearing. The bearings are lubricated for life and are maintenance-free. The grease life can be estimated according to the method explained for single row deep groove ball bearings (Sealed bearings - Grease life) using diagram 1 for bearings up to and including size 217 and 314 (grease GJN) or diagram 2 for larger bearings (grease MT33). Calculations can be made with the the Grease life for sealed ball bearings calculation.
Shielded bearings should not be washed or heated above 80 °C before mounting.
Shielded bearings are primarily intended for applications where the inner ring rotates. If the outer ring rotates, there is a risk that the grease will leak from the bearing at high speeds.
Details regarding the suitability of shields for various operating conditions can be found in table.