Choosing the Right Cleaning Blade Angle for Belt Maintenance and Efficiency
The angle of attack for the cleaning blades against the belt is a crucial consideration. Generally, there are two options: positive-rake (or peeling) blades and negative-rake (or scraping) blades.
Positive-Rake Blades
Positive-rake blades are positioned against the direction of belt travel, while negative-rake blades are inclined in the direction of travel, typically at an angle of 3 to 15 degrees from the vertical, depending on the type of splice. Blades installed vertically, perpendicular to the belt at installation, have a zero-rake angle.
Metal blades in a positive-rake position quickly become razor sharp due to friction with the moving belt, posing a risk of costly damage if knocked out of alignment. They can also experience high-frequency vibration, causing them to "chatter" and repeatedly jab their sharp edges into the belt cover.
Negative-Rake Blades
In contrast, negative-rake blades may accumulate material on their inclined cleaning edge, potentially reducing effective contact for cleaning. However, all belt cleaners, regardless of the angle of attack, require regular cleaning and maintenance to prevent buildup.
For primary cleaners applied at low pressures against the belt, a positive rake is generally considered acceptable. However, for secondary and tertiary locations where higher cleaning pressures and the use of metal blades pose greater risks to the belt, splice, and cleaner itself, negative-rake blades are recommended.