VSD Motor Directly Coupled to a Screw Motor

If the motor can continuously deliver enough torque and speed to the conveyor,it will be more efficient to remove the gearbox,thereby eliminating the losses associated with it.

Of course, removing the gearbox will require an alternative mechanical connection between the <...motor...> and the <...screw conveyor...>, as now the two shafts will turn at the same speed - assuming the motor doesn't overload while so doing.

What's next for the <...gearbox...>? An internet auction site by any chance?

Depends on the gear ratio and the conveyor speed requirement....It's possible the motor will be carrying a higher load without the gearbox...

Assuming it's a step down gearbox, the motor will have to deliver more torque if the gearbox is removed. The motor current is proportional to the torque required by the load. You need to determine whether the supply for the motor can deliver the current required and whether this amount of current will overheat the motor.

http://www.gohz.com/vfd-motor-speed-and-torque#:~:text=On%20a%20VFD%2C%20frequency%20is,not)%20be%20rated%20for%20this.

The op states that If the motor can handle the torque requirements.

A servo would be a better choice because it would give more precise control and could prevent reverse operation.

An electric brake on the motor,if a motor is used, could prevent reverse action.

More information is needed like the motor speed and the gearbox output speed.

The slower a motor is run on a VSD the worse the airflow over the motor becomes if the motor has its own included fan and the hotter the motor will become. Having used VFD on motors on screw feeder and wishing to run the motor slower to dose a system I found that it was best to dilute the flocculant and run the motor quicker.

The VFD had a turn down ratio of 10/1 but at under 20% speed the motor overheated due to lack of airflow. You could replace the motor with an 8 or 12 pole motor to match the output speed of the gearbox or more but then the cost goes higher because the motors with more poles have less calling and so the cost is exponential. Besides a multipole motor is much larger and would require a redesign of the mountings. The losses in the gearbox would be inconsequential compared to the costs to direct couple the motor to the gearbox.

I have had experience with conveyors driven by motors through fluid couplings and gearboxes up to 1MW and they were cost effective for maintenance. Some even used CVT type transmissions.

What did the original equipment manufacturer say in response to telephone calls on this topic?

IF the motor has sufficient torque, AND the speed you want to run at is within the turn-down ratio of the motor, then yes, the gearbox would be superfluous.

BUT...

People don't put EXPENSIVE gearboxes on things like screw conveyors for no good reason... So for example if your gearbox has a 4:1 turn down ratio and has a 10HP motor on it now, you would need a 40HP motor to provide the same SHAFT torque at the screw.