General informations

The ELLI Seites toothed couplings type GDF are produced in sizes from 30 to 200 (the coupling size is simply a numerical code and does not correspond to any dimension of the coupling) and are suitable for the transmission of high torques between two shafts, ensuring an high torsional stiffness.
Thanks to their ability to absorb moderate misalignments between the connected shafts, these couplings protect the driving and driven machine from the stresses which would be induced by these misalignments, if a rigid connection were used instead.
The GDF couplings are composed by two hubs with external teeth and two bells with internal teeth and coupling flanges. The two hubs are fitted onto the two shafts ends to be connected, while the two bells, installed externally to the hubs, are joined along the connecting flange by means of a set of screws.
The teeth are crowned, so as to allow for some movement between the hubs and the bells, thus absorbing limited angular misalignments.
The trouble-free operation and the duration of the coupling between hubs and bells are achieved by means of the internal lubrication of the coupling. In fact, the inner space of the coupling, when correctly installed, is sealed with respect to the surrounding atmosphere thanks to the contact of the flanged surfaces of the bells and to the presence of seals (O-Rings) between the cylindrical end surfaces of the hubs and of the bells.
In this inner space of the coupling a suitable lubricant (grease) is injected, which protects the teeth from the wear during operation. Furthermore, it prevents the entrance of debris which, contaminating the teeth mesh, would soon damage the coupling.
 

The selection of a coupling depends upon the transmitted power and the rotation speed of the connected shafts, in addition of course to the service factor required by the application.
Table on page 5 shows the dimensional and power data of these couplings. As far as the service factor is concerned, it depends upon the type of load of the driven machine and upon the daily duration of operation. When the coupling is installed onto a reducer shaft, it is a good technical practice to select coupling with service factor at least equal to the reducer's one.
From the dimensional point of view, it is necessary to check that the diameters of the shafts to be connected are compatible with the minimum and maximum bores diameters of the selected coupling. 

The technical data required to perform the selection of a toothed coupling (and which should be supplied by the customer with the enquiry) are:

• diameters of the shafts to be connected
• type of driving and driven machine (in particular with reference to the presence of shocks or overloads and to the daily duration of operation)
• applied power
• rotation speed

The grease check and filling-up should be carried out every 1000 hours of operation, while the complete grease change every 3000 hours.
The coupling should be lubricated with grease containing EP (Extreme Pressure) additives. Some brands and types of grease suitable for operating temperature between -20°C and +70°C are listed here below.

• AGIP GR-MU/EP0
• EP1 IP ATHESIA-EP0
• EP1 ESSO PEN-O-LED
• EP350 MOBIL MOBILTEMP 78

A correct lubrication, as well as a good shafts alignment, is the key to achieve a long duration of the couplings.