- 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
Is your spreader functioning properly?
Spreaders are found on most converting machines. Their most common role is to flatten a web prior to a critical process such as coating, embossing, laminating, printing, slitting, winding and so on. Sometimes spreaders are needed to reduce wrinkling so that a web might merely cross a roller without creases and foldovers. Spreaders are also used to separate slit webs prior to winding and to permanently widen some nonwoven products.
A spreader is any device which makes the web wider. As seen in Figure 1, the web is wider at the spreader than it is upstream. Much or all of this extra width, which results from CD (cross direction) tension is temporary. This is why one should place the spreader immediately upstream of the critical process. On some materials, such as tissue, stretch film and some nonwovens, one can easily measure the width increase with a tape. On less extensible materials, such as paper, the width increases are there, but are imperceptibly small.
Thus, one way to determine if a spreader is functioning properly is to check for a width increase. Similarly, we should expect to see a gap width increase as slit webs proceed from the slitter, over the spreader and to the windup. Finally, we could check for a visible flattening of the web at the spreader. If spreading is not detected by these means, the spreader may not be functioning, effective and/or needed.
Indeed, many spreaders are actually causing wrinkling due to setup or application problems. A common example here is a loss of traction on a bowed roller. Sometimes the so called ‘spreader’ is not based on sound physical principles. A common example here is the spiral grooving which is erroneously thought to provide a spreading action. Table 1 lists known web spreading systems.
Table 1 – Web Spreading Systems
- Concave Roller
- Bowed Roller
- Bent Pipe & D-Bar
- Dual Bowed Roller
- Pos-Z Spreader
- Expander Rollers
- Edge Pull
- Nipped Stretcher Rollers