How to Evaluate Printing Press Performance: Register Accuracy, Ink Lay Consistency and Productivity

Evaluating a printing press properly means looking beyond a single isolated figure. Three core indicators frame the assessment: register accuracy, ink lay consistency and productivity — the baseline for any objective judgement of printing equipment.

Register accuracy describes how precisely successive imprints overlap one another in multicolor work, and it ranks among the most important technical measures of press performance. Whether the machine runs slowly or at full speed, paper transport, handover and printing must all keep the stock in its specified position. For fine printed products and color printing, that requirement is even stricter.

Meeting such precision depends on several links at once: the position and timing of paper transfer and handover, plus the transmission accuracy of both the printing plate and the impression mechanism. When register accuracy is analyzed, the task is therefore to work through every related link and understand what each one contributes.

Ink lay consistency concerns two things: whether ink-layer thickness is even across the printed product, and whether the imprint is clear. It serves both as a further quality measure for the printed result and as an important element in judging press performance. Whichever printing method is used, clear and solid ink demands uniform ink distribution together with sufficient printing pressure — which in turn sets high requirements for the precision and capability of the printing unit, the inking system included.

Productivity is normally expressed as printing speed. Sheet-fed presses are rated in sheets per hour, while web-fed machines use their own corresponding measures. What ultimately determines the level of productivity is the machine's structural configuration and characteristics, together with the technical standard it reaches. Take the flat-bed press fitted with an impression cylinder: it ran noticeably faster than the original flat-bed design, yet the reciprocating motion of the bed plate capped any further gain, so it was gradually superseded by the cylinder-on-cylinder press. Today presses continue to move toward large formats, higher speeds and inline linked operation, in order to push productivity to its maximum.

Beyond working performance, a press's usability rests on three further dimensions: operating performance, safety and reliability, and durability.

Raising the level of automation must not come at the expense of good operating performance. A press usually occupies a relatively large floor area, so several control panels are needed to let operators work from each main station. Every panel should match natural human movement, keep the working position easy to observe, and place adjustment points where they are intuitive and within easy reach.

Safety and reliability bear directly on the personal safety of operators and on the safety of the machine itself. Alongside protective safety devices, a press should also be equipped with safety interlock devices, so that protective action is triggered as soon as a fault occurs.

Durability means the machine still holds its original precision after long-term use — in other words, a long service life, which carries major economic significance for both the enterprise and the country. Achieving it requires sensible selection of part materials and heat-treatment processes so that components deliver the properties required; to improve transmission quality, each mating surface should have sound geometric shape accuracy together with good fitting clearance and lubrication devices.

There is also a design-side requirement: while the main working performance targets are met, the structure should be as simple and compact as possible, with good manufacturability, so as to lower manufacturing cost and make assembly and maintenance easier.

These requirements often constrain one another and can even be mutually contradictory. Register accuracy, for instance, is difficult to guarantee at high running speeds — once printing speed rises, the fast and accurate handover and transfer of paper, the quick drying of ink and the smooth running of moving parts are all heavily affected, making register hard to hold. Adding extra control devices, meanwhile, pushes up the machine's manufacturing cost. Similar conflicts exist between a simple structure and a higher degree of automation, and between printing speed and service life. The workable approach is to treat these requirements as the starting point for analysis, weigh them against what the printing process actually asks of the machine, identify the principal contradiction and the weak links, and balance priorities from an overall standpoint — resolving secondary conflicts on the premise that the main requirements are satisfied. That is also the mindset printing press research and design should follow.

——This article is reprinted from China Packaging Network (pack.cn); original link: http://news.pack.cn/show-369994.html