The characteristics listed in Part 3: Five Benefits of Vacuum Rolls lead to a wide variety of applications for vacuum rolls and belts for the converting industry. A vacuum roll may replace a standard driven roll to do the same job better, or its unique characteristics may be used to alter and improve a process.
For an idea of how some converters have applied vacuum rolls to their advantage, consider the following:
- Transporting Wet/Coated Webs – This takes advantage of single side contact, and is a traditional application for vacuum rolls. In this case, a nip roll or “S” wrap simply cannot be used. Figure 4 shows a vacuum roll located between coater and dryer.
- Replacing Nip Rolls – While initially a bit more expensive, vacuum rolls and belts have proven popular nonetheless as replacements for nip rolls. Vacuum devices may be considered more desirable for one or more of the following reasons.
- Safety improvement by getting rid of nips, a potential source of injuries
- Scrap reduction by eliminating scratches, imprints, wrinkles, and slippage due to nip rolls
- Time savings by eliminating nip adjustment for web thickness, providing better access for web threading, and avoiding the need to manually close nips before starting a line
- Improved line layout from less wrap angle
- Handling Light Weight Film – Moving light weight film through a coating line is very challenging with traditional driven rolls. The positive grip and control of a vacuum roll, even at very low tensions, helps minimize stretching and web breaks.
- Guiding Webs – Gaining popularity is the use of vacuum rolls as part of a web guide. This takes advantage of the vacuum roll’s ability to keep a good grip on the web even as path adjustments are being made by the guide. At the same time, the vacuum roll can replace a nip roll or “S” wrap.
- Dealing with Web Breaks – When a web break occurs, vacuum rolls remain functional. At a minimum, this can keep most of the web in place so less threading is required to restart the line. In more sophisticated applications, a vacuum roll can be used to initiate an alternate path when a web break is detected.
- Implementing a Short-Term Loop Accumulator – Figure 5 shows two vacuum rolls being used to accumulate a length of web. Some process lines, like bag production, may use a recurring start-stop operation. If the web can only be touched on one side, vacuum rolls still allow a start-stop process section to be isolated from the balance of the line. The inlet vacuum roll continuously feeds into the loop, while the exit vacuum roll meters material into the process step intermittently. The reverse is done on the other side of the process step.
- Establishing a Constant Loop – Process lines in which an abrasive or bulky material like sand or reflective particles is added to a web may use a constant loop. This allows excess material that did not adhere to be removed from or fall off the loop in a position below important machine components, reducing repairs.
- Metering and Drawing a Web – Certain processes require both precision metering and a constant pull. Figure 6 shows a vacuum device metering the web, then holding it while another device pulls it with constant tension.
- Releasing Web from a Tenter Frame – The ability of a vacuum roll to provide a very low tension on the inlet side makes it ideal for controlling web tension at a tenter chain release point. See Figure 7.
- Controlling Tension in a Floatation Dryer – Achieving low tensions through a floatation dryer is a classic application for vacuum rolls, shown in Figure 8. A typical layout has vacuum rolls before and after the dryer to isolate tension, and perhaps between zones to help stabilize and guide the web.