Vortex Breaker Plate thickness

Yes, vortex breakers are meant to be rigid, though for practical purposes they may flex a small amount.

We can not give you an answer for a thickness because it depends on a lot of information you are not giving us: density, velocity, flowrate, slurry, temperature, material, corrosion allowance, is the breaker spanning the walls of a cone, how long of a span, segemental baffles with stiffeners/supports, will it be a single plate or a cross, ....................

From the information you gave all I can say is: yes, they do need to be as rigid as practical and probably way thick too.

No where near enough information given for any sort of half decent answer to be given but generally theyare under considerable stress and need to be very strong