Carrying out of oleodynamic couplings applications

The advantages of the oleodynamic coupling are well known: easy start-up and correct sizing of the motorisation, progressive acceleration of the driven machine, overloads protections, high degree of torsional shock absorbers and consequent increase of the resistance "under stress" of all transmission components. Torque limit transmitted to a established value, maximum performance of the electric motor power used without limit the specifications of the torque motor with star-angle start-up or using converters of static frequency (inverter), irreversible operation.
The interposition of the oleodynamic coupling between the motor and the driven machine, allows to reduce the torque resistant according a cubic law and to reach in short time the rating speed, without any motor overload.

The start-up time T [sec] will depend by the power P [kW] of the motor, by the r.p.m. n and by the inertia of the driven machine GD² [Kg] .

In the applications where such time is not acceptable, it is possible to use a "Blaffe Disc", thhs furtherly reducing the start-up time, through an additional reduction of the absorbed torque. (Coupling at low torque start-up).

The oleodynamic coupling operation is very simple: two turbo-machines integrally transmit the driven torque through the interposed fluid (mineral hydraulic oil SAE 10/30, synthetic oil, water-glicole mixtures) which also acts as lubrication fluid on the internal bearings, at operating speed, with a coupling proper sizing it is possible to obtain very high performances 97-98%, This, anyway, involves the definition of sliding.

The sliding is the difference in percentage between the inlet rpm number and the outlet rpm number, and it represents the lost due to sticky friction inside the oleodynamic coupling.

Should the motorization not be properly determinated by the user, the oleodynamic coupling will operate, even at operating speed, with sliding values always over than the acceptable one: 5%

Where: Nm = motor r.p.m number (and inside driving impeller)
Nu = coupling outlet r.p.m. number (and driven impeller)

Please note that the efficiency R of an oleodynamic transmission is:

In order to select the proper coupling type to be used, it will be necessary to examine the attached selection diagrams where, first of all, it is needed to know the motor power and its the operating rate (asynchronous electric motors).
Tracing the point in the diagram (P,n) it will be possible to establish, as a first estimation, the type of coupling to be used.

A second check must be carried out according to the clock-wise motor start-ups and to the GD2 of the driven machine.

To this purpose, always fill in the attached form for the selection of the coupling to be installed.

For the application on endothermic motors, our Project Department needs to receive the torque curve.

The oil filling in the coupling: has to be carried out according the modalities indicated in the "Instruction for the correct installation" sheet enclosed in the supply. This operation must be carried out by unscrewing the plug with hexagonal key size 3/16" for plugs size G 1/8" and with key ¼" for plugs G ¼". The coupling has to be located vertically, with the filling hole in the upper part and aligned with the vertical symmetric axis.

Then close the plug tightening it in a reasonable way. With such filling it is possible to reach the maximum performances allowed by the oleodynamic coupling (less sliding with maximum load).

If more elastic couplings are required, it is possible to operate with a lower filling to be checked later-on, when the installation has been done, from the operational point of view, acceptable with the application.

Never mix oils of different nature or type amongst them.

The oil temperature limit is of 80°C and it can reach 90°C for short periods. For installations termically heavy, on request or for particular working conditions (evaluated by our Design Department), rotating seals in Viton or PTFE will be fitted, thus ensuring the operation even with temperatures of 140°C.

Please however note that transmission lockings or start-up phases oblige the coupling to work at high slidings and, in exceptional limit conditions, to reach temperatures even higher than 90°C. Therefore, for safety reasons, the oleodynamic coupling is supplied with fusible plug which burns out at 140°C.

In case of plug burning, the oil goes out, thus preserving the whole motorization from the locking of the machine or from overheating. So, the use of an oleodynamic coupling allows the maximum reliability, the minimum maintenance and the minimum wear of the machinery where it is installed.

All our couplings are manufactured with base Hole shrink system having tolerance H7.

The oleodynamic coupling type "Ing.G.Miotto" is defined by a number corresponding to the outside Diameter D of the impellers. This diameter distinguishes in prevalent way the torque transmissible by the coupling.

The execution at double turbine impeller and double pump impeller, allows to duplicate such value. Some type of couplings so manufactured are indicated by "dash 2" ( /2)..

Notes:

1. Values calculated for a sliding at 5% for light alloy couplings (up to type 420/2)

2. Values calculated for s sliding at 2.5% for cast iron couplings (from type 480/1)

3. On request all the cast iron couplings can be supplied in light alloy.

4. Powers in (Kw) multiplying the table values by 0.735.

ALUMINUM COUPLINGS SELECTION TABLE

 TECHNICAL DRAWINGS ALUMINUM SERIES

TECHNICAL DRAWINGS CAST IRON SERIES

Series couplings in cast iron box for marine and industrial applications