Sigma offers servo service

Edale's new Sigma narrow web packaging press is configured in-line with the web running vertically out of the printing stations for drying, like the company's best selling Beta model. Unlike its predecessor, however, the Sigma is shaftless - each driven axis being equipped with digital servo drives. It can also be upgraded with independently servo driven print rolls to provide infinitely variable print length control from 0.1-2 per cent.

According to Edale, this technology enhances control of web handling, printing and converting, providing benefits when working with substrates which require skilful handling. Each driven axis can be balanced precisely to ensure constant torque is applied to the web as it runs through the press. This is said to maintain extremely stable web tension throughout the speed range to ensure accurate registration. Automatic register control can be supplied if required, the servo control of each print station making it relatively simple and inexpensive to incorporate the upgrade.

Independent control

Shaftless technology also provides the Sigma with four independent, controllable tension zones. Once a particular tension profile has been selected for a substrate, the data can be stored and recalled for repeat jobs. Job change-overs are rapid., thanks to the in-line arrangement of the print stations. After the 'unload' button has been pressed, the print cylinder, anilox roller, inking roller and ink tray can all be lifted straight out of the print head.

The converting cassettes are designed for durability and ease of access. Again, each is independently servo driven, providing smooth and accurate tool control and the optional ability to convert different repeat lengths with the same tool, says the company.

The rewinder is also servo driven within a closed-loop tension system claimed to ensure accurate control with even the thinnest of substrates.

Control of all machine functions, including insetting, is through a touchscreen that can be positioned at any point along the press. In addition to the standard press controls, the screen also enables job data to be recalled.

Edale joint managing director James Boughton relates: "Over the last three years we have achieved our aim of providing a complete product range with the Alpha, Beta and Sigma models. The Alpha is a compact, entry level machine, the Beta is a modular in-line workhorse for unceasing production, and the Sigma - dedicated to flexo packaging or folding carton production - is capable of converting a range of substrates from 12 micron film to 600 micron board. It will always be a bespoke machine, tailored to customers' individual requirements."

Tavistock, UK, based Tamar labels has installed the first Sigma, a 430mm web width model. This has four flexo stations followed by twin die cutters, using solid or magnetic shims. The unwinder can accommodate reels up to 1.27m diameter and is servo braked. Running at up to 150m/min, even when die cutting, the press is employed on a wide range of products, such as labels, boxes, and card inserts.

Label and board jobs requiring extra colours are preprinted with a shorter print length then run through the machine a second time using the insetter control. This stretches the web to register the overprint to the preprint by means of servos, which regulate the speed of the impression rollers independently of the web.

Tamar managing director Alan Jones reports: "The running print register is so good there is no need for an automatic control. With servos, little effort is required to achieve and maintain incredible register accuracy when insetting. As to substrates, we are converting anything that will go through the machine, be it self adhesive stock, unsupported film or cartonboard. We're now consuming over 10t of cartonboard a week and have conducted trials with substrates down to 60 micron. With many substrates and products, the wastage is as low as one per cent."

UV prospect

Tamar prints with water based IR inks. "We are still concerned about the safety aspects of the UV process but will adopt UV in the near future," he confirms. "We would not, however, convert solely to UV and hence the printing decks would be equipped with UV dryers in addition to the existing IR ones."

The Sigma is housed in a new factory built to comply with the BRC/IOP standard.