How Velocity Drying Can Increase Productivity

How Velocity Drying Can Increase Productivity

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Is your drying system holding you back?

While recognized as a factor in overall production, the contribution that drying technology can make to the productivity of the converting line is not always fully appreciated.

For many, the main consideration about dryers is simply that they should do their job, not hold up production and not disproportionately add to costs. Reliability, efficient energy use and similar factors are simply given.

However, the reality is that many drying systems impede press speeds, reduce output and consume more energy than necessary.

Based on relatively high drying velocity, recent optimizations in drying technology have proved to be a significant contributor to optimized press performance. Uniquely,this optimized technology can be used for flexo, gravure and digital presses and coaters handling any type of substrate: carton,shrink sleeve, label, bag, film, paper and packaging applications. The technology is available in vertical and horizontal configurations, depending on press and space constraints. It can be used with inline or CI presses – and retrofitted.

Hanging it out to dry

The technical definition of "drying" refers to a mass transfer process, or the removal of water or solvent from coating and ink. The printing and converting industries have a variety of drying methods, but all include one or more of the three ways of transferring heat: conduction, convection and radiation. The challenge has always been to expose the substrate to enough heat to dry the ink completely, but not damage the image, coating, or the substrate.The more sensitive the substrate, the greater the control of the drying process is needed.

The best analogy to explain a high velocity drying solution is to think of a washing line with the basic variables temperature (heat), humidity (moisture), and wind speed (velocity). Good drying days combine the right combination of these factors, but the air velocity is the key factor in any drying process – just think of these examples: A hot, low humidity day with a light breeze works well, as does a cooler, low humidity day with stronger wind.

**B2BIMGEMB**1**

As illustrated by the graphs below, speeding up the air velocity significantly increases the evaporation rate, while a rise in temperature only brings a marginal increase.

**B2BIMGEMB**2** **B2BIMGEMB**3**

By controlling these variables, and introducing nozzles to focus the air stream, high velocity dryers can deliver optimal conditions for the substrate, ink and coating used.

Optimized high velocity drying technologies are based on a convection system augmented by impinging stream jets to increase the velocity and optimally direct the air to the web in the drying process. Impinging stream drying (ISD) technologies might be described by thinking of a hair dryer. A modern hairdryer will have one or more nozzles to form the right flow, to create the desired effect (concentrators, diffuser, etc.). There are controls for heat levels (temperature) and fan settings (velocity) as well.

High velocity drying uses jet air nozzle to create high impinging air velocities, and a web guidance system to precisely position the substrate to ensure peak heat and mass transfer (evaporation) rates.The appropriate combination of temperature, humidity and velocity results in the optimum mass transfer to dry the coating or ink medium in the shortest possible time, without impacting the substrate, while maintaining print quality and enabling higher press speeds.

In short, the higher the drying velocity, the higher the heat and mass transfer, resulting in less drying time.

The more efficient the drying, the higher the production speeds possible.

Today, converters are successfully drying ink as well as flood coatings at speeds up to 800m/min. In addition to process and ink type versatility, high velocity drying systems can be used on presses of web widths rangingfrom600mm to 3000mm.

Also contributing to performance, the press room environment, and the savings possible is the combination of efficient heat recovery and good thermal insulation properties used.

Using a controlled sequence of dehumidifying and pre-heating, the air quickly reaches operating temperature, saving three to four minutes per job. A re-circulation loop also contributes to efficiency, reducing energy consumption further by introducing only 15-20 per cent new air into the process, minimizing the energy needed for heating the air already in the system. Central and motors meeting the newest efficiency standards keep total efficiency losses to a minimum. Converters have the choice of using gas or electricity as heat sources.

The system can be tuned to work with various ink and coating thicknesses, including specialist applications like coatings on paper products. For example, converters moving from laminates to water-based coatings in the production of paper cups and plates (for recycling and environmental reasons) can dry these coatings quickly and effectively.

Updating the drying technology you can increase productivity

Today’s drying systems may be specified with either gas or electricity as heating source for high velocity drying to meet the environmental requirements of converters and their customers while ensuring drying efficiency. Apart from having the choice when installing new equipment, heat sources can also be changed when retrofitting.

By adding high-velocity drying technology, your press line can run faster and increase your output and productivity – while maintaining print quality and achieving energy efficiencies. Moreover, these benefits are possible while using your existing press,ink, coatings, substrates, workflow software and workforce.

Equally, with enhanced speed and reliability, more jobs per day are possible, creating opportunities for new customers – or more jobs from existing customers.

For safety precautions it is worth mentioning that the latest ATEX certification EN 1539:2015 is important for converters using solvent ink or working in hazardous environments.

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