Reverse Taper
Rollers
Although widely applied and very effective, the reverse taper roll
is the least understood of all spreader rolls. The reverse taper
(RT) is also referred to as a concave roll, reverse crown or bow
tie roll. The reverse taper roll has a larger diameter at the outer
edges and a smaller diameter at the roll centerline. The roll, as
a result of its profile, creates a surface speed differential at
each different roll diameter. The resulting tension differential,
or higher edge stress, ultimately results in the material climbing
outward toward the larger diameter edges of the roll. To be effective
the web and the roll must be in a state of traction and therefore,
web tension and wrap angle are very important components to the
effectiveness of reverse taper rolls. The amount of taper or crown
depends on the application but generally is .0005" to .001"
per inch, diametrical taper from the roll centerline to the edge.
Reverse taper rolls are the definitely the most cost effective web
spreading devices. They have an advantage in that, even if they
do not achieve the desired action, they can still be effectively
applied anywhere in the line as general idler rollers.
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