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Be Careful When Combining Trim Removal Systems

In most converting operations webs are edge trimmed somewhere in the process. Normally, the webs edges are slit and typically disposed or recycled. Two methods for removal of the edge trims include rewinding the edges into a roll and then disposing of the roll. The other method is to pneumatically capture and convey the edge trims to a collection area.

Pneumatic trim removal systems have many advantages to rewinding slit edges into roll form. These advantages include:

  • The ability to slit very narrow edge trims, saving raw material costs
  • The ability to run continuously without concern for slit edge roll formation
  • Slit edges can be conveyed long distances, directly to a waste collection area
  • Rewound rolls of slit edges typically include a cardboard core. This may be a problem if you want to recycle this waste. Pneumatic trim removal systems can deliver the edge trim waste without the cardboard core contaminant.

Modular, pneumatic trim removal system designs vary. However, typically their modular nature means they include an air motivator for each web trimming location. Often times, modular pneumatic trim removal systems are stand-alone systems. In that they include trim entry points and convey trim to an exit point.

If several modular trim removal systems exist in close proximity, there may be a desire to combine their discharge ducts (the conveying portion of the trim removal system) into one duct and then run the one duct to the collection area. While this is certainly a viable option, be careful! There are two main concerns here:

  1. You cannot combine multiple ducts into the same size duct. Doing so will double the air flow resistance thru the combined duct. The result will, most likely, be decrease suction at the pickup point for each trim removal system. For example, if you have two modular trim removal systems, each with 4" diameter discharge ducts and you combine the two discharge ducts into a single 4" diameter duct, this will, most likely, cause performance issues with each of the trim removal systems. The area of the combined duct must be approximately 2X the 4" diameter duct to accommodate two 4" ducts. In this example, combining two 4" diameter ducts into a single 6" diameter duct would be acceptable.
  2. Considering the example above; now that you have sized the single, combined, discharge duct properly; you can never run just one system. The reason is that the single, combined discharge duct area requires the air flow from both systems. In this case, if one system is run, instead of both systems, when the discharge air enters the 6" duct, pressure will drop and air speed will slow. This may prevent you from conveying the trim properly through the system. So, bottom line, if you combine two modular systems into one properly sized duct, both systems must be run all the time, to push the proper amount of air through the system. This may not be the most energy efficient option for you.

These are just some of the concerns when considering combining several modular systems into one duct length. Often times it makes the most amount of sense to keep modular systems separate from each other from trim entry to exit points.

Jeff Damour, Converter Accessory Corporation

**DISCLAIMER - A great deal of time has been invested in the development of our weekly tech tips. To the best of our knowledge, they are accurate. It is up to the user to verify all results.


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