Hydrodynamic metering

Metering with smooth rods – equivalent to metering with coater blades – is based on the hydrodynamic principle. The pressure generated in the dosing zone is of decisive importance for the coating volume.

This pressure is subject to the laws of fluid mechanics:

• Machine speed (example 1)
• Geometry (diameter) of metering system (example 2)
• Color rheology (example 3)

Increasing the machine speed by 100 m/min can increase the coat weight by almost
10% starting at 8 gsm to 8,8 gsm.

Example 1

This volume can also be increased with larger diameters: 5 mm diameter increase likewise results in approx. 10% more coating.

Example  2

In most cases, the dominant value for the coat weight is the color rheology or solids content. A "relatively" small increase of solids content by 3% can result in 50% increase of coat weight.

Example 3

In practice, stable production conditions are only possible at comparatively high contact pressures. An increase in coating volume over insufficient contact pressure leads to unstable behaviour, and thus fluctuations in coat weight.

Why larger metering bar diameters increase production disproportionately

Generally, 10 to 15 mm diameter metering rods with smooth surface are applied in direct coating, or with profiled surface in the filmpress.

Depending on the content of abrasive components in the coating media, a service life of two to four weeks can be reached. This practice applies to paper machines operating 24/7 throughout the world. However, since it prevents innovative advantages, the motto "Never change a running system" is counter-productive in an increasingly tougher competition.
When each additional production hour and waste minimization count, metering rods must offer a longer service life and less frequent revision cycles. A simple technological solution is the use of metering rods with a larger diameter, allowing above average run times.

Smooth metering rod diameters - A question of the correct size

We have a comprehensive product portfolio that allows us to offer optimum metering rods to suit any application and production conditions.

The diameters of smooth metering rods start at 9.75/10 mm and go up to 25 mm. We supply hollow, smooth metering rods from 24 to 38 mm diameter. This makes it possible to design the geometry of the metering system specifically to suit the required coating application.

Application example for profiled rods - Surface sizing with filmpress

This is without doubt the most important application for the profiled, chrome plated metering rod with a diameter ranging from 10 to 15 mm. In contrast to smooth metering rods, the profiled rod can be applied in an extremely broad range of viscosity. Thus, it is also ideally suited for very low viscosity starches. In 24/7 operation, a service life of up to four weeks can be easily achieved if the starch is largely free from abrasive components.

Contour coat for folding boxes and high-quality paper grades
When the focus is on very uniform color distribution and coverage, the increased application of profiled metering rods is interesting to note. Compared to traditional air knives or modern curtain coaters, today it is possible to achieve coating results of comparable quality with profiled metering rods. The correct setting of all parameters can produce an economically attractive service life, particularly with ceramic coated rods.

Rod ends (for smooth metering rods) - Solutions from start to finish

Not only the metering rod but also the rod ends are decisive factors in determining the quality of the coating. Our rod ends take this fact fully into account.

We offer six customized rod ends for various types of systems or mounting points. Their common features: perfect fit, high quality, easy to install.