The rotary press was invented in the mid-1800s by Robert March Hoe. Rotary presses have evolved somewhat to accommodate automation through electricity, the core machine remains more or less unchanged. The typical rotary press functions by passing a substrate (the material to be printed onto) between two rotating drums. One of the drums will be partially submerged in a large inkwell. This drum will have the image to be applied to the substrate curved over its surface, either on a specialized plate or the drum itself will be engraved with the image. As the drum turns toward the substrate, its surface is scraped by a doctor blade. The function of doctor blade is to ensure that excess ink does not reach the substrate. At the point of contact between the substrate and the inked image, the second drum or impression cylinder presses the paper against the inked drum, creating the image transfer. Rotary printing presses are used to do three main types of printing: rotogravure, flexography and offset printing.
These are some diagrams that I felt best help me to understand the process visually:
This is a more old fashioned design:
This is a more modern and commonly used press:
This diagram demonstrates the way that the technology works:
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