It is now common practice for many power transmission applications to have a requirement to align two shafts, from drive unit to driven unit. Many of these applications will involve power transfer from electric or hydraulic motors acting as the central drive unit or prime mover operating on a range of equipment including conveyors, fans, mixers, mills, pumps & reciprocating/rotating screens.
Proper motor shaft alignment increases the operating lifespan of rotating machinery, although having no measurable effect on the efficiency of the central drive unit; correct shaft alignment allows for a smooth & efficient power transfer, allowing for reduced stress on rotating parts.
The alignment of two shafts should be considered to have the same final drive performance as for what would be achieved from one single shaft. The aligning of two shafts may seem simple in principle, but even the smallest misalignment can have ongoing effects on your equipment & operation, from excessive vibration, noise, coupling/bearing temperature increases, or premature failure of bearing, couplings or shafts.
When considering alignment between the drive & driven unit, it should always be seen to ensure the alignment of such components is correct, which can in many cases be carried out by laser alignment or measurement. This alignment can have many external factors such as size, weight, operational location, base mounting type. Other considerations to be noted include the dimensions of the power transfer shafts, operational/thermal expansion, and also the awareness that misalignment on a rotating shaft can avail from multiple directions/axis. Types of misalignment include angular (centre would cross upon shaft extension), parallel (centre lines run parallel but offset) or a combination of both.
Solutions
Mounts & Levellers
It is essential when entering into design phases of driven power units, to consider the effects that excessive noise, vibration or shaft misalignment could have on the final drive assembly. Although sometimes seen as a less important aspect at the outset, it should be carefully reviewed to evaluate how this will affect future performance and warranty on equipment.
MIT work closely with their partners at Rubber Design to ensure that all these factors are considered and calculated by utilising the vast knowledge and experience of designing application specific noise control and anti-vibration components in critical operations including the potential for both steel and rubber mountings. One such solution is the MecLev self-adjusting mechanical levelling chock. By utilising the unique features of a specific thread design, easy height adjustment & mounting disc, it allows for reduced fitting time and up to 4º movement at each mounting point to achieve the desired alignment.
Flexible Coupling
Large drive units can be coupled to their driven unit with a rigid or flexible coupling. Rigid couplings remain popular within the market, but they do not compensate for shaft misalignment and can lead to excessive wear of coupling over time, and potential breakdowns. Flexible couplings, however, have the ability to compensate for a small amount of misalignment, providing sufficient tolerance to allow for any misalignment to not affect the daily operation.
Transfluid has developed the B series range of flexible couplings to act as misalignment compensators, using knowledge developed over decades while designing and manufacturing their fluid coupling range. These particular couplings come in a robust & easy to assemble design, utilizing internal rubber elements to provide flexibility to overcome shaft misalignment of up to 2.5mm* , and are virtually maintenance free. These B3M/BM/BMS couplings should not be considered to remove torsional vibrations, although they will allow for damping of shocks and vibrations in applications with up to & exceeding 33100Nm of torque.
*varies per coupling size & application
Correct Installation
Due to limits of coupling flexibility, they should not be utilised to eradicate excessive misalignment, as doing so can cause further damaging effects to the operation.
Precise alignment can be difficult to achieve without the use of correct alignment equipment such a laser alignment tool. Correct procedures for shaft alignment include the fixing & alignment of the driven unit, while then installing the desired flexible coupling, then aligning the shaft for the power unit. Upon calculating correct heights & positions, consider both atmospherically & operational temperature factors such as thermal expansion.
Once installed, equipment should be checked regularly to ensure critical operations are kept running, and any preventative adjustment or maintenance can be carried out.
