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Introduction to coating bars
 Metering bars are in widespread use for the accurate control of wet film thickness.
Metering bars give consistent coating thickness across the web.
On every occasion they can be relied upon to reproduce the results of earlier production.
Metering bars work as wiper blades, removing excess mix from the web, leaving an even wet film of high integrity
They are made in the form of plain un-clad rods or bars covered with a wire winding.
Bars are used for applying:
- solvent based (referring to organic solvent solutions and suspensions)
- water based (referring to the use of water or mainly water solutions, emulsions and suspensions)
- hot melt (petroleum waxes and similar substances relying on heat to reduce viscosity or make liquid)
- multi-part cure hardening (solvent free) mixtures.
The system is for both 'on-machine' and 'off-machine' coating by the board and paper industry.
Other coating applications are textiles, specialised technical films (including photo-sensitive materials), multiple coated packaging films, and any application requiring high integrity and accurate coatings.
Bar coating is particularly attractive in situations where precise control of coating weight is required, together with a high standard of finish. This is very important where the coating used is expensive and it is necessary for economic reasons to control the coating weight close to the lower limit of the specified range. The accuracy of the bar system makes it possibly one of the best for this purpose.
The capital cost of equipment is low, while maintenance is simple and inexpensive. This reduces the risk factor of financial loss due to lower depreciation rates of capital values, comparing favourably with systems which are more expensive, mechanically more vulnerable and less flexible. Unexpected and unforeseen changes in the market requirements are much more easily accommodated by a metering bar coater.
Bars are generally used singly but coating heads employing two or more bars are also in commercial use. Compound heads can give excellent coating quality and greater flexibility, while very rapid trial runs are achievable and flying changes save both time and materials
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