The inking system, or inker, of most large sheetfed presses in Figure 3-7 usually has at least ten rollers and consists of the following parts:
. Ink fountain - a pan that contains the ink supply.
. Ductor or ductor roller - a transfer roller that alternately contacts the ink fountain roller and the first roller of the inking system, often an oscillator.
. Oscillators or vibrators - gear-or chain-driven rollers that not only rotate but oscillate from side to side, distributing and smoothing out the ink and erasing image patterns from the form roller.
. Intermediate rollers - friction-or gravity-driven (i.e., surface-driven) rollers be-tween the ductor and form roller that transfer and condition the ink; often called distributors if they contact two rollers and riders if they contact a single roller, such as an oscillator.
. Form rollers - a series of three to four rollers, usually of differing diameters, that contact the printing plate and transfer ink to it.
The series of rollers excluding the ink fountain and fountain roller is often referred to as the roller train. The roller is comprised of a series of alternating hard and soft rollers. The hard rollers are usually steel covered with copper, ebonite, or nylon. The resilient rollers (ductor, intermediate, and form rollers) are often made of a synthetic rubber such as PVC (polyvinyl chloride), Buna-N (a copolymer of butadiene and acrylonitrile), or polyurethane. These substances are applied to steel shaft.