- Part 1: Seven Common Web Spreading Systems
- Part 2: Concave Web Spreading Rollers
- Part 3: Bowed Web Spreading Rollers
- Part 4: Bent Pipe and D-Bar Web Spreading Rollers
- Part 5: Dual Spreader Rollers
- Part 6: Expander Web Spreading Rollers
- Part 7: Edge Pull Web Spreading Rollers
- Part 8: Benefits of Web Flattening without Web Spreading Rollers
Traction is Vital for the Bowed Web Spreading Roller
Bowed Web Spreading Rollers, as seen in Figure 3, have a curved stationary axle upon which a rotating sleeve(s) are mounted over numerous bearing sets. The axle may have either a fixed or variable bow. The sleeve is typically a one-piece flexible tube of a soft synthetic composite, or may consist of numerous narrow metal shells.
The amount of bow is very important because too little will reduce the effectiveness of the spreader, while too much will also reduce spreading and may even generate wrinkles. Unfortunately, the historical tendency has been to overbow. As a rule of thumb, most bowed rollers should have a 1/8% bow, unless the material is slit, very flexible or very troughed where the bow might be increased to as much as 1/2-1% of roller width. Since traction is vital for the spreading function, the bowed roller should be wrapped about 15-45 degrees and the cover must be grippy. The feel of an acceptable cover is like the surface of a tire, while one that is worn and in need of replacement feels slippery like plastic pipe. Finally, the cover may need grooving for high speed applications and the roller may need to be driven at web speed when used on light or weak webs.