Software for industrial automation is somewhat different then "general purpose" software.
Your software controlling the conveyor belts will have to interact with the conveyor belts. This is through sensors (probably inductive and/or capacitive proximity sensors, maybe mechanical switches, cameras with image processing etc.). The software you write will most likely be reactive to the information coming from the sensors and will act using actuators (electrical pneumatic or maybe hydraulic motors, which stop the line, move a piece from A to B, etc.)
The trick is to interface your software to hardware. In industrial automation this is normally done with PLC-s. We can very generally define them as the hardware platfrom of automation for running sofware. The programming of these is done in 5 standardized languages. For porgramming PLC-s in .net I would like to redirect you here.
If it is not a serial product, just an experiment, you might want to take a look at DAQ boards, with .net compatibility like this one. The DAQ board will be your interface to phyisical signals and the software will run on a PC in .NET.
I can't see what functionality you would expect from a conveyor library. Perhaps you could edit your question to explain what you are trying to achieve. Otherwise, this is looking like a shopping question.
– Mark Booth Dec 14 '15 at 11:13