Method and apparatus for silencing of webs

In combination, a first fixed guide bar of substantially circular perimeter providing an arcuate guide surface area over which a tensioned web is adapted to run at a speed such that in the off-running angle between the web and the curved perimeter of the first bar, air moving in the direction of the web in such angle would tend to follow the curvature of the first bar (Coanda effect) and cause splitting of the air between the web and the first bar and thereby generate noise-causing vibration of the span of the web moving away from the first bar, and a second fixed guide bar of substantially circular perimeter spaced downstream from said first fixed guide bar and also having an arcuate guide surface area across which the web is adapted to run at the downstream end of said span, the improvement comprising:

• spoiler means located in a plane extending substantially tangentially from the off-running side of said arcuate guide surface area for avoiding the Coanda effect and for stabilizing air moving with the web and thereby inhibiting noise-causing vibrations of said span of the running web moving away from the first bar;
• and spoiler means located in a plane extending substantially tangentially topward the on-running side of said arcuate guide surface area of said second guide bar and cooperating with the spoiler means of said first guide bar for stabilizing air moving with the web toward said guide surface area of the second bar.

In a method of inhibiting noise-causing vibrations in the span of a tensioned web running over and away from an arcuate guide surface area of a circular perimeter first fixed guide bar at a speed such that in the off-running angle between the web and the curved perimeter of the first bar, air moving in the direction of the web in such angle would tend to follow the curvature of the bar (Coanda effect) and cause splitting of the air between the web and the first bar and thereby generate noise-causing vibration of said span of the web, and a second fixed guide bar of substantially circular perimeter spaced downstream from said first fixed guide bar and also having an arcuate guide surface area across which the web runs at the downstream end of said span, the improvement comprising:

• locating spoiler means in a plane extending substantially tangentially from the off-running side of said arcuate guide surface area of said first bar, and thereby avoiding the Coanda effect, and stabilizing the air moving with the web and inhibiting noise-causing vibrations of said span of the running web moving away from the first bar;
• and locating spoiler means in a plane extending substantially tangentially toward the on-running side of said arcuate surface area of said second guide bar and cooperating with the spoiler means of said first guide bar and thereby stabilizing air moving with the web toward said guide surface area of the second bar.