Hollow Shaft with a Locking Mechanism
The second method for connecting the shaft of the gearbox to the head shaft pulley of the gear drive is to use a hollow shaft with a locking mechanism. This second coupling option is slightly more expensive than using a straight hollow bore, due to the drive being shipped with a locking mechanism on the low-speed shaft (such as a Tollok shrink disk or a Rexnord TA taper bushing), and a tighter tolerance required on the conveyor pully shaft.
This coupling is the method of connection commonly used on conveyors with head shaft pulleys in the 4-8" range. The advantage of using this connection option is that the locking mechanism makes it more likely the drive is removable without cutting the head shaft pulley of the conveyor, but removal is far from guaranteed. Similar to the hollow bore shaft mounting option, this low speed shaft configuration is also susceptible to dirt, debris, and general fretting that can effectively weld the conveyor pulley shaft to the hollow low speed bore of the gear drive. An additional disadvantage of this method is a longer assembly time due to the shrink disk installation requiring a very specific tightening pattern and sequence. This can cause the drive to slip on the pully shaft and fail prematurely if not followed correctly.
To offset some of the disadvantages of the shrink disk-related problems, Rexnord has developed a TA taper bushing that is the easiest to put on and least likely to fret onto a shaft. The TA taper bushing offers a significantly simplified solution by allowing the bushing to be mounted on the conveyor drive pulley prior to drive installation, only requiring one nut be tightened. Due to the use of dissimilar metals, special coatings, and a tapered design, this is the hollow shaft solution most capable of removal after prolonged use without cutting the head shaft pully of the conveyor. This option is also used in the 4-8” conveyor head shaft pulley size range.
MCF Rigid Mount Coupling
The third option for connecting the gearbox shaft to the gear drive pulley is to use a rigid mount coupling like the MCF. Rexnord’s rigid mount coupling solution, the MCF, is typically used on head shaft pullies that are greater than 8” in diameter. The design of an MCF Coupling guarantees the ability for the drive to be removed from the head shaft pulley of the conveyor but does so at the cost of mounting the drive further away from the head shaft pulley bearing. This causes the need for larger supporting bearings and a larger supporting structure.
MCF couplings were designed with the needs of mining and aggregate industries in mind, although they are suited for other applications too. The durability makes them ideal for most processing and mining phases including extraction, handling, and preparation of coal, copper, iron ore, potash, and other such materials. If a rigid shaft connection, as opposed to a hollow low-speed shaft connection, is needed or preferred, MCF couplings are a reliable choice.
The MCF coupling was specially designed as an add-on for V-Class drives, but it can also be retrofitted to A, Y, and other legacy units. The engineered design of the MCF makes it easy to install and remove. Of the coupling options, the MCF is the simplest to mount and can always be removed from the head shaft pulley. This design makes the MCF a cost-effective option in the long run.
It's also important to note that Rexnord now offers an RSB (Rough Stock Bore) Hub version of this coupling, meaning the coupling is available half or full without a bore in it. Customers can put a bore in at the time of installation (guidance on dimensions are available through your Rexnord consultant and in the catalog). This option allows you to have a spare drive on hand for future use. The RSB version is also a good option if you've wrecked your head shaft pulling a drive off and don't know the exact dimension of your new head shaft.