Why are metering rods replacing doctor/coating blades in some applications?
There are several reasons. First, metering rods apply coating at a more consistent and predictable rate. This allows for a more accurate projection of coating costs. Second, rods do not wear as quickly as blades. Since rods are rotated during operation, the entire circumference of the rod is used in the coating process. Blades can only employ the same edge throughout the coating process. Finally, rods may be used with much faster web speeds. In some high-speed applications blades can experience a ‘hydroplaning’ effect, which causes non-uniform coat weights. Metering rods can operate in high-speed applications because they channel the fluid better, much like good tires on a wet road surface. Also, because metering rods are constantly turning, loose fibers and filler particles do not accumulate to the same extent as with blades.
