Keith,
The different media will have different levels of aggressiveness. Plastic, as well as wheat starch and bicarbonate of soda, will be gentle, glass will leave a sheen, steel shot may leave ferrous contamination (rust).
When you say "automatic system", what level of automation are you considering? Or better yet, what quantity of wheels do you need to process? Do you plan to build your own machine or purchase? You can use air blast for high velocity blast (small quantities of wheels) or wheel blast system for high volume of media and high quantities of wheels to blast.
You might consider using a contract job shop at first to refine your process or seek a machine builder that can do small quantity production during your development program.
Jack
