Page 183 - Gear Technology Solutions

The contact patterns in Figure 17 show a full flank surface contact, which is on
top and root only limited by the topland chamfers. Coordinate measurements
with nominal flank coordinates and normal vectors are possible with the flank
form generating module in GEMS which generates CMM download files and
also has corrective information for G-AGE corrections.

®
12.4.2 Fixed Curvic Couplings

They are precision face splines with a mostly 30° pressure angle, no backlash
and a very small root clearance. Root fillets are ground with a gable bottom in
order to avoid ridges or steps. The members of a fixed Curvic coupling are
bolted together to connect two or more rotating units, such as impellors of a
turbine for example and form one operating unit. Fixed Curvic couplings are
self-centering and have to be manufactured by grinding with a high accuracy
such as AGMA 13 [2].

®
12.4.3 Semi-Universal Curvic Couplings

Semi-universal Curvic couplings are commonly designed with a zero-degree
pressure angle and with backlash. The coupling between the two members is
rather loosely and includes axial play to permit up to 2° of shaft misalignment.
The profile on the teeth of one member is curved to keep localized contact and
provide a nearly uniform motion between the two coupled shafts [2].

®
12.4.4 Releasing Curvic Couplings (Clutches)

Releasing couplings or clutches have a helical surface to maintain proper tooth
contact during engagement and disengagement of the clutch. For smaller size
clutches, this is often approximated with a special localized contact bearing.
The two members of overload clutches are held in the engaged position by
spring load. The spring load and the pressure angle are used to control the
point of disengagement. Pressure angles of releasing clutches and overload
clutches are mostly between zero and 10°. Also shift clutches are considered
releasing clutches. To achieve smooth shifting and engagement, the toplands
have a slope angle in circumferential direction and are chamfered [2].

12.4.5 Manufacturing of Curvic Couplings

Often the outer diameter of the rotor hubs is large, for example 1,500mm, where
the Curvic coupling which is an integral part of the rotor hub only has a diameter of
750mm. It requires special grinding machines, which can accommodate these large

168