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FLEXO Magazine : January 2010
48 FLEXO JANUARY 2010 www.flexography.org geographical locations. Landfill and hauling fees in Europe, for example, are generally significantly higher than in the U.S. Here is a conservative, average estimate of disposal costs that does not account for recycling or biomass projects: • Average cost per ton = $100 • Average cost per pound = $0.05 • Average cost per msi = $0.012 ($0.05 x 0.234) Adding the purchase price of the material to the disposal cost, we arrive at a total value of wasted material: • Purchased value = $0.35 per msi • Disposal cost = $0.012 per msi • Total value = $0.362 per msi STRIP WASTE Now we're ready to evaluate the other three components of waste, starting with the most dangerous person in your pressroom---the operator with a utility knife. Even if the floor is clean and care is taken in getting rolls to the press, our observations indicate that you will incur some strip waste. In discussing this issue with converters, the stripping of four lay- ers of stock off a new roll is a reasonable average. Here is the result, over a year's time, of this level of strip waste: • Four layers on 30in. diameter roll = 31.4Lft. • At 16in. web width = 6.032 msi/roll • At 4,000 rolls/yr. = 24,127 msi/yr. • Total of 24,127 msi/yr. or 5,646 pounds/yr. • Total value = $2.18/roll ($0.362 x 6.032 msi) • Total value = $8,720/yr. (4,000 rolls/year x $2.18/roll) Strip waste at this level represents 12.6 rolls wasted per year. That goes right against your bottom line. The challenge for owners and managers is to go out to the floor, see what your operators are doing, and encourage them to use the util- ity knife with greater precision! CORE WASTE One of an operator 's worst nightmares is having to re-web the press. As such, he or she will always make sure that there is no danger of miscalculating when the running roll is about to expire. Around the world, we find that about 150ft. is a reasonable average length of substrate left on the core at each manual roll change. In our production model, we'll use a more conservative 100ft. • 100ft./roll = 19.2 msi • At 4,000 rolls/yr. = 76,800 msi/yr. • Total of 76,800 msi/yr. or 17,971 pounds/yr. • Total value = $6.95/roll ($0.362 x 19.2 msi) • Total value = $27,800/yr. (4,000 rolls/year x $6.95/roll) Core waste at this level comes to an equivalent of 40 rolls per year. Operator training may help reduce this, as may a more advanced method of detecting the end of the roll. An automatic roll changer (splicer) with accurate roll diameter calculation---or better yet, a means of unwinding the roll down to and even off the core---can significantly reduce the amount of core waste. MANUAL ROLL CHANGE WASTE Any time the press is stopped, whether to change rolls or for some other reason, material is wasted. Web that is in the press at a stop is usually not saleable. And with older presses, there is a greater tendency to move out of register during deceleration from and acceleration to production speed, creating even more waste than we might see on newer servo drive presses. In our model, we will assume that waste for a manual roll change equals one press web length of 150ft. Here is the an- nual loss: • Press length 150ft./stop = 28.8 msi/stop • Un-saleable product due to slow down and speed up = one more press length of 150ft. = 28.8 msi/stop • Total loss of substrate = 300Lft. = 57.6 msi/stop (300Lft. x 16in. press width) • At 4,000 rolls/yr. = 230,400 msi/yr. or 53,913lbs./yr. • Total value = $20.85/stop (57.6 msi x $0.362/msi) • Total value = $83,400/yr. (4,000 rolls/year x $20.85/stop) As the above calculations demonstrate, even this conserva- tive production model has a very high level of material waste associated with it. To put it another way, this model, with two shifts of production operating 250 days per year, is wasting material at an annual rate of: • 173 rolls, or • 39 tons, or • $120,000. AUTOMATING ROLL CHANGES As can also be seen, the largest component of this waste is due to stopping and starting for manual roll changes, the elimination of which is one way to reduce your waste signifi- cantly. The use of an automatic butt splicer and automatic rewinder provides possibilities for significant savings, includ- ing not only reduced waste on expensive raw materials but also reduced downtime on an expensive press. A return-on- investment (ROI) calculation is a good place to start, both for identifying wasted material and downtime, and for determin- ing how much savings you can expect from automatic roll changing. TIME IS WASTE Most ROIs will attempt to account for time waste due to manual roll change. In our model, the calculation would look like this: • Manual roll change takes 7min. (average) • Hourly rate for your press line $240/hr. $4/min. • Total loss on revenue = $28/change (7min. x $4 press rate per minute) • Total value each year = $112,000 (4,000 rolls/yr. x $28/roll change) • Total time loss/yr. = 467hr. (= 29 days or nearly 6 weeks in a 2 shift operation) TURNOVER LOSS Perhaps a more informative calculation is to consider the saleable value of the products produced by the press and the people who operate it. Price per 1,000 is reasonably common. Whenever, during its agreed operating time, the press is not PLANTS & PROCESSES
Sustainable EOY 2009