NOVOTON® "barrel" couplings type NT... in their several executions, are recommended for its setting-up in the drives of rope drums for cranes, capstans or conveyors.
Its setting-up eliminates the occurrence of a statically indeterminate case which appears when there is a rigid coupling between the shaft of the reducer and the drum. This sort of installation requires a considerable time of initial alignment and even so, the prejudicial effect over bearings and over gear-wheels produced by additional stresses as a consequence of deformations in supports and wear and tear of operating parts can not be prevented. In the installation recommended, the barrel coupling plays the role o a knuckle, making the assembly statically determined. The jointed coupling operates as axially free and this is why the support-bearing of the opposite side of the drum has to bear the axial stresses which can be generated. As a special application the barrel coupling can be designed, under demand, as a joint which can withstand axial stresses in itself.
The barrel coupling is basically made up by a sleeve-flange with semicircular internal teeth, a hub having external teeth with the same shape and a series of hardened steel rollers which are housed between both parts. The internal transmission area is made tight by mounting a cover at each side with their corresponding retainers, preventing, in this way, any foreign substances from getting in as well as preventing the lubricant from leaking. Two retainer rings mounted on the hub, one at each side of the teeth, limit the axial displacement of the barrel rollers inside their housing. To this regard there are 2 different constructive models. Basic models, named as NT..., in which retainer rings are directly in contact with the barrels and new generation models, named NTSG..., in which extra thrust rings are installed in between the barrels and retainer rings. These NTSG...models comply with German Steel Industry standard SEB 666212 (issue January 1991) (Stahl-Eisen-Betriebsblatt) as well as French Steel Industry standard. The crowned shape of the rollers, which we call "barrels", and the internal spaces in the teeth permit to accept ±1º of angular misalignment in the coupling and an axial displacement gap which ranges ±3mm up to ±10mm depending on the sizes, for angular aligned position.
The Torque is transmitted to the receiving flange of the drum, usually, through two diametrically opposed flat carrier faces which can be found at the periphery of the coupling flange. The friction effect of the attachment screws of both flanges also takes part in this transmission. Other systems, as adjusted bolts or similar, can also be used preparing the flanges accordingly.
The described design can withstand big Radial Loads, being distributed over wide barrel support surfaces, and it minimizes the reversed bending stress of the Torque over the teeth, which are short and have a wide root section. Apart from this, due to "flatness polishing" of the hardened barrel over the tooth profile, the resistance to wear is greatly improved.