Engineering art in deep groove ball bearings: Assembly using the Conrad and slot-fill radial bearing method

You may have heard of the “Conrad method” when it comes to the assembly of deep groove ball bearings. But did you also know that there is another method for filling the balls in the bearing? It has the somewhat awkward name “slot-fill radial bearing method”, but this exactly describes the type of construction and how it is used. Below we explain the exact differences in assembly and construction method is more common.

Vektorgrafik von zwei Rillenkugellagern mit Darstellung der verschiedenen Konstruktionstypen, Vector graphic of two deep groove ball bearings showing the different types of construction

The Conrad method

When assembling a deep groove ball bearing using the Conrad method, the inner ring is first placed in an eccentric position relative to the outer ring. This means that the inner ring is aligned upwards towards the outer ring. Thus, the balls can easily be inserted into the lower outer ring. Thanks to the central grooves on the inside of the inner and outer rings (which give deep groove ball bearings their name), the balls stay in position without rolling back out.

The inner ring is then aligned to be concentric and the balls are positioned equidistant to one another around the ring. In the last step, the cage is attached to keep the balls in place. In type 6208 C3, for example, the sheet steel cage is divided into two components and is attached around the balls on both sides. Most deep groove ball bearings are assembled using this method.

The slot-fill radial bearing method

As the name suggests, the slot-fill radial bearing method increases the radial load capacity. This design features a recess in the form of round, crescent-like notches located opposite one another on the inner and outer ring. Together they form what is called the “filling slot”.

During assembly, the inner ring is positioned concentrically at the outset, i.e., in the middle of the outer ring. To be able to insert the balls requires the filling slot, though which the balls enter. Here too, the grooves in the inner and outer rings ensure that the balls remain in the bearing and do not fall out before the cage is added.

One example of a deep groove ball bearing with a filling slot is type 208 C3. This is the same bearing type with the same dimensions as the previously mentioned deep groove ball bearing 6208 C3. However, the differences in the designation indicate a different design. In order to increase the radial load capacity, more balls must be inserted than with Conrad bearings. However, this design reduces the axial load capacity. In the last step, the cage is mounted again.