Considering and evaluating slitter

Introducing a checklist for flexible packaging converters

Slitting and rewinding is almost the final process before finished reels and before pouching or form, fill, and sealing operations. Following a series of converting operations on flexible packaging material, it is the last step for the converter before shipping the reels to the customer for forming, filling, and sealing. In some cases, the converter uses these reels for pouching to provide these to customer specifications.

The performance of the slitter rewinders is directly related to the quality and visual appeal of the finished reels or pouches. Being at the end of the converting processes, any interruption during the slitting operation would result in the pile-up of expensive inventory into which all the material and previous processes have contributed costs and time.

The slitting process is critical from the perspective of quality, throughput, delivery, and the customer's time to market. Therefore, the technology required to support this process is no less demanding than the printing and lamination operations. The inherent challenges of slitting and rewinding can challenge the design and testing abilities of the best converters and equipment manufacturers.

A combination of higher speeds, thicker substrates, and smaller rewind reel diameters result in shorter production cycles and more frequent reel changeovers, often just a few minutes apart. The machine or system is required to ramp up to full speed and down to zero quickly and repeatedly, subjecting the machine components to high stress.

Like any other web-fed machine, maintaining the tension levels and stability of the substrate is crucial for the smooth operation of a slitter-rewinder. The difficulty goes up by several notches because the web may have significant calliper variations across the web at the infeed side, and after slitting – the multiple reels on the output side cannot be of a uniform standard without differential rewinding.

The high frequency of rewind reel changeovers, coupled with the fact that multiple reels are to be changed each time, reduces the productive time of the machine to less than 50% of the total time consumed. Unless these changeovers are quicker, the incremental output or throughput resulting from the higher speeds of the slitting operation would be far below pro rata. This less-than-linear production can put a big question mark on the wisdom of opting for higher-speed machines and investing in their underlying technology.

As the co-founder of a company that has focused exclusively on slitter-rewinders for the past two decades, it is refreshing to see buyers in recent years exercising the same, if not more diligence while selecting this equipment as they have been doing in case of co-extrusion, printing, and lamination equipment.

This series of articles is committed to pointing out the critical criteria that a flexible packaging converter or buyer of slitting and rewinding machines should keep in mind while evaluating and zeroing in on the equipment. Subsequent monthly issues of Packaging South Asia will continue the conversation by discussing each of the 12 important considerations in this process.

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