Most of the suppliers of conveyor belting and chains have booklets and text books on design of conveyors. They are always eager to provide these books. One such book is from Goodyear on belt conveyor and belt elevator design. I can not remember the correct name of the textbook but its something in the line of 'Handbook on conveyor design' This is a handy text book covering nearly everything on belt conveyors, from pulley design, power requirements and even acessories to belt conveyors. Most of the necessary formulae is in these booklets/textbooks and its worthwile collecting them.
