Bowed rollers, sometimes called banana rollers because of their shape, utilize a center shaft which has a curved axis. The bowed roller center shaft has many ball bearings mounted across its' length. The ball bearings, in turn, support multiple segments, which support a continuous, smooth rubber sleeve.
Bowed rollers gain most of their anti-wrinkle action by way of the web handling principal that states a web will seek to be 90 degrees to a roller in its' entry span to that roller. Any given point across your web will try to be 90 degrees to the curved axis centerline of the bowed roller.
Getting the most from your bowed anti-wrinkle roller is mostly about geometry.
- Use minimal wrap angle. If your bowed roller isn't removing web wrinkles or it is causing problems instead of helping, try decreasing the wrap angle. Typically, wrap angle should be less than 30 degrees.
- Most of the anti-wrinkle action takes place in the entry span to the bowed roller. The longer the lead-in (unsupported web distance leading into the bowed roller) distance the greater the anti-wrinkle affect.
- Remember, as with any anti-wrinkle device, bowed rollers will only remove wrinkles coming into the roller. It can not remove wrinkles post placement. So, keep lead-out (unsupported web distance leading out of the bowed roller) distance to a minimum. Supporting the web with a plain roller immediately following the bowed roller will keep wrinkles out of your web.
- More bow means more wrinkle removal but also more potential to distort your web. Non-adjustable bowed rollers are typically available with .5%-3% of face width bow amount. 1.5% Bow is very common, middle of the road amount of bow, effective for most applications. Too much bow will distort your web by increasing tension in the center of your web and decreasing web tension toward the web's edges. So be careful not to over specify the bow amount required if opting for a non-adjustable bowed roller.
- Adjustable bowed rollers are available. These bowed rollers are an excellent choice for tailoring the bowed roller for optimal anti-wrinkle performance, while limiting web distortion. Adjustable bowed rollers are an excellent choice if you run a wide array of web materials.
- Bowed rollers are available with many types of rubber sleeves. Make sure to specify when the bowed roller may be subject to high heat, chemicals, excessive ozone (attacks rubber), abrasive webs or webs with exposed adhesive. Rubber sleeves can be manufactured to perform optimally for these applications.
- Bowed rollers can be supplied with reinforced rubber sleeves for extremely high-speed applications.
- The placement of the bow, relative to the plane of the web is critical to wrinkle removal and potential web distortion. Bowed rollers are supplied with special mounting brackets which are designed to properly house the bowed rollers' curved center shaft (standard pillow block type blocks will not work; they are designed for typical, straight shafting). These brackets will allow for roller orientation with your web for optimal performance. Brackets which include a handwheel adjustment for bowed roller rotation and orientation are useful because orientation can be optimized while the web is in motion.