NTN 6305 ZNR Kugellager (25x62x17)

The principal dimensions are 25x62x17 mm at a weight of 0.24 kg; the further technical details are listed in the specification table. The closed side wards off, the open side supplies — which is why the shield belongs towards the surroundings and the free rolling chamber towards the lubricant reservoir of the assembly. The single shield turns an otherwise symmetrical bearing into a directional component, and most of what has to be observed with this version follows from that.

On the closed side a sheet-metal part fixed in the outer ring reaches close to a shoulder of the inner ring without touching it; the remaining gap holds back coarse contamination and in doing so generates neither a frictional torque nor a heat source. On the open side the rolling chamber remains accessible: lubricant from the surrounding space can reach the rolling contact, frictional heat can be carried away with it, and relubrication through the assembly is possible in principle — properties that a doubly closed version does not offer.

The mounting direction is thereby part of the design and not left to the assembly floor: the shield faces the loaded surroundings, the open side faces the clean interior supplied with lubricant. Two further points hang on the same asymmetry. First, the grease charge is held back on one side only, so with a vertical shaft, high speed or heavy vibration it has to be checked whether the lubricant remains in the rolling chamber.

Second, the gap is no barrier against liquid or fine dust, so for wet surroundings a contact version or an upstream seal is to be provided. Normal radial clearance is matched to one interference-fitted ring and a moderate temperature difference; because the shield does not touch the rings, it exerts no influence on the clearance itself. Through-hardened standard bearing steel sets the temperature and load frame of the rings.