ZEN BK2520 Nadelbüchsen (25x32x20)

As a needle roller bearing, this bearing carries high radial loads in a very compact section. The principal dimensions are 25x32x20 mm at a weight of 0.038 kg; the further technical details are listed in the specification table. Because the thin-walled cup takes its raceway form from the housing bore, that bore is part of the bearing arrangement.

The drawn cup needle roller bushing consists of a thin-walled, drawn steel cup in which the needles run. Its design purpose is the same as that of the other needle bearing arrangements — high radial load capacity at the smallest section height — and it achieves it without a solid outer ring. How many needles are accommodated in the rolling chamber, and whether a cage guides them, determines the balance between load capacity and permissible speed: a densely packed arrangement takes more load and suits slow or oscillating movement, a cage-guided one permits higher speeds; which version is present is to be taken from the type designation of the individual item and not inferred from the family.

For mounting, the condition common to all drawn versions applies: the cup is so thin-walled that after pressing in it takes on the form of the housing bore; that bore must therefore be closely toleranced, accurate in form and sufficiently load-bearing, since out-of-roundness or material that is too soft acts directly on the raceway. Without a separate inner ring the needle set runs directly on the shaft, whose surface is thereby the raceway and has to be executed like a bearing component in hardness, surface finish and tolerance.

The design takes no axial force; axial location has to be solved separately, and because of the long contact line of the needles only slight misalignment between shaft and bore is permissible. The open form brings no sealing element with it, so initial filling, relubrication and protection against contamination fall to the surrounding construction.