- December 31, 2005, Timothy J. Walker, TJWalker & Assoc. Inc.
Walk by any slitter and more likely than not, it won’t be running. Why? Besides having no input material or no demand for slitting, your slitter likely is not running because the slitter operator is busy doing all the work needed to support the slitter. Your slitter may not be running, but I bet your slitter operator is!
From an equipment uptime analysis, most slitter/rewinder operations inherently are inefficient. Few slitting processes can justify the capital expense of automatic unwind splicing or rewind roll starts. This makes for busy slitter operators. When the slitter stops, the operators go to work, cutting off and unloading the finished rolls, loading and starting the new cores. But the operators’ work doesn’t stop there; knife setups, unwind splicing, roll packaging, paperwork, etc., also take time.
Operating a slitter can be divided into several categories: actions completed every input jumbo; actions completed every knife change; actions completed every cut; and actions completed every order.
For a single short order of ten rolls, converting one jumbo in one cut, the following might be typical times for these slitter tasks: For each input jumbo of material: inventory and load/unload = 20 min. Each knife change (including core cutting) = 12 min. For each cut: unload rolls, load, and attach new cores, packaging of finished rolls = 22 min. After each order is complete: paper work and pallet handling = 10 min. Oh, I almost forgot, for each cut: run time = 6 min (cut length divided by speed, ignoring accel/decel time).
If all these tasks are completed by a single operator, it would take about an hour to finish this simple one-cut order. In that hour, the slitter was running only for 6 min—less than 10% uptime.
There are several ways to improve slitter uptime. Take more time to slit each cut. Either run slower (which doesn’t make much sense) or run longer cuts. Most customers like longer rolls—the challenge is making larger rolls and avoiding increases in waste. Write a note to yourself: Not all slit rolls cost the same. Short and narrow mean more slitting overhead per square yard.
No product gets out the door without running through the slitter. To improve slitter productivity, uncork the bottleneck. Dedicate your resources to getting the bottleneck—the slitter—back up and running.
Looking at all the actions of a slitter operator, often only two-thirds of the tasks are on the critical path. One-third of the operator’s time is spent on non-critical tasks. A second operator dedicated to completing the non-critical tasks reduces your time between cuts by a third. But a second slitter operator can do more; he or she can assist the first operator with the critical tasks. The second operator can load and splice a new input roll while the first operator changes the rewind cuts. For products with lots of narrow cuts, the two operators can combine their effort and speed up the roll unloading and loading cycle time. For short or narrow cuts, the two-operator team nearly can double the output of your slitter.
Lastly, you could eliminate your slitter by sending material to a contract converter. But be careful—outsourcing the slitting process has expenses of its own that may wipe out any savings.
“Why isn’t your slitter running?” may be the wrong question. Instead, ask yourself, “What does my slitting operation cost?”
Timothy J. Walker has 20+ years of experience in web handling processes. He specializes in web handling education, process development, and production problem solving. Contact him at 651/686-5400; email@example.com; tjwa.com.