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Calculating coat weights (rolled bars)

Calculation of the volume and resulting wet thickness from a rolled bar is complicated and depends on the pitch, depth and form of the thread being rolled.

Most current paper mill users will have arrived at their objective coating weight long ago and those needs will rarely change. Converters will usually have a specific and changing requirement for each product and their needs can only be realised through a series of laboratory or on-machine experiments using Mayer bars.

Calculating coat weights (wired bars)

Very accurate control of coating weights can be achieved using Meyer bars. Plain, unwound bars of lower diameters deposit the least wet-film thickness and result in the lowest dry coat weight. Single wound bars deposit approximately 10% of the wire diameter in wet thickness, while Compound (double wound) bars give a higher coating weight for a given pitch, as well as an improved surface quality. Triple wound bars fulfil the need for very heavy coatings.

The Longfield Wire Calculator is available to help determine the most appropriate wire sizes for your particular needs. Please note that this method only estimates the coating weight as machine speed, coating mix viscosity and absorbency of substrate all influence the dry coat weight. A better guide is to determine the wire diameter for the objective coating weight by data plotting from previous results.

Sample graph

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Longfield Coating and Engineering Products Ltd, 2015