- January 01, 2011, By Craig Thomson, Martin Automatic Inc.
Much of the global discussion on sustainability has centered on the concepts of “renew, recycle, and reuse.” These are important topics, but the discussion should start with preventing as much waste as possible.
This focus applies to all printing and converting processes, including those involving paperboard. Our analysis of the causes and cures of waste — and thus our discussion of sustainability — starts not with the press itself, but where all roll-fed processes start: the unwinding roll.
Nonstop Roll Change
Each time a roll-fed press or process press stops, it creates waste. Automatic splicing will eliminate material waste, but one factor that may go overlooked or unaddressed is core waste. That is, how much usable stock is thrown away at the end of a roll, and can that waste be reduced?
On many splicers, the standard method of detecting that the roll is expiring is by diameter calculation. The operator sets the diameter at which the splice will be initiated, and when the roll reaches the splice diameter set point, the splicer makes the transfer while the accumulator pays out web to the press at full speed.
The amount of core waste resulting from this typical method of splice initiation depends upon three factors: the outer diameter (O.D.) of the core, the caliper of the board, and the operator's set point. For consistently low waste, it is beneficial for the core O.D. to remain consistent. Because cores often vary in thickness and thus in O.D., even by just a few thousandths of an inch, it is not atypical for the operator to set the splice diameter slightly higher than if the cores were consistent. In this way, a marginally thicker core will not result in the web running off the core; conversely, a marginally thinner core will leave more wraps and generate more waste.
Recycled stocks are a good application for this method of splice initiation. The advantages of this method are that it is simple, effective, accurate, and generally repeatable. But can an automatic roll changer (splicer) do more to help reduce the amount of stock left on the core? Yes. Here are three other methods currently employed on automatic butt splicers. (See Figure 1.)
The first method allows the web to run down to, and in many cases, all the way off the core before clamping the trailing end of the roll. “Tailgrabbing” is not dependent on material caliper, core O.D., or operator input. The result is that the amount of core waste is greatly reduced to less than the web span between the core and the splice unit.
There are several considerations to bear in mind regarding tailgrabbing:
- Core Detachment | The material must come off the core cleanly.
- Material Strength | The stock must be strong enough to tolerate a hard stop. Certain recycled boards may not be good candidates.
- Material and Core Contrast | The web must differ from the core in reflectivity. This requirement also negates the use of transparent stocks such as clear plastic folding carton stock.
- Slippage | Heavily coated or slippery stock may slide through the clamp, possibly affecting splicing efficiency, marring the stock, or creating lateral movement of the web.
- Lateral Alignment | When detached from the core, the web may move laterally, causing a misaligned splice. This may or may not be acceptable, depending on the process.
- Winding Quality | Winding issues at the core or damage to material near the core may compromise splice efficiency or process quality.
- Infeed Quality | The infeed must be able to absorb the temporary tension spike or disruption resulting from the hard stop.
Typical applications for tailgrabbing would be general folding carton work using virgin stocks.
An alternative to the above “active mode” of letting the web detach from the core is to run the tailgrabbing feature in a backup or failsafe mode of initiating splices. The advantage in this is to give the operator a greater confidence to dial the diameter calculator closer to the core without the fear of losing the web, with the result being greater material use without the above considerations related to core detachment.
Splicer users who have employed tailgrabbing in this manner have experienced a core waste reduction of more than 60% compared to using diameter calculation only. (See Figure 2.)
Waste Reduction System
The third method of reducing material loss at the core in an automatic splicer is through the use of a Waste Reduction System (WRS). In fact, this method goes beyond mere waste reduction; it enables running all the usable material from a roll through the exercise of additional control over the web.
Such a system can operate in one of two alternative modes:
- Web Attached Mode | Upon reaching the end of the roll, the splicer initiates the transfer immediately, leaving the web attached to the core and avoiding the possible negative effects of core detachment discussed above. This is essential in applications when, for example, lateral misalignment at the splice is unacceptable.
- Web Detached Mode | Upon reaching the core, the splicer will pull a specific length of web before initiating the transfer. In this mode, the web detaches from the core, and all the usable stock is fed through the splice unit, stopping the web with as little as 12 in. (300 mm) of material loss.
In addition to allowing the absolute maximum usage of a roll, a WRS overcomes many of the material and tension control concerns associated with typical diameter calculation and tailgrabbing systems. A WRS does have its considerations, however. As with tailgrabbing with optical sensors, the stock must be opaque and differ in reflectivity from the core.
In terms of cost, such a system will see a much quicker return on investment the more expensive the material in question. For this reason, applications such as liquid or aseptic packaging or products made from expensive laminates would be good candidates for a waste reduction system.
While the preceding discussion has concerned waste at the core, the reality remains that the number of wraps discarded at the O.D. of a roll will add up much more quickly. It will take more than five wraps at the core to equal the loss of one outside layer on a roll 72 in. (1828 mm) in diameter, pointing to the importance of addressing that waste point by considering roll handling, floor cleanliness, operator training, and other impacts.
Sustainability & Profitability
The technology exists and is being employed in the paperboard industry to reduce material loss at the beginning of the process by maximizing the amount of material used. Printers not only gain more salable product from their rolls of paperboard, they also reduce the need for and cost of handling and disposing waste material.
An important aspect of sustainability is the responsible use of resources. Minimizing the amount of material discarded from a roll of paperboard is very responsible. It is a truer practice of sustainability because it eliminates waste rather than tries to determine what to do with waste. Utilizing the maximum amount of material on a roll results in higher profitability and greater sustainability and will enable your company to claim a stake in leading sustainability efforts elsewhere.
Craig Thomson has more than 20 years' experience in web handling and roll changing. He is southeast (US) regional manager and marketing manager for Martin Automatic Inc., Rockford, IL, a global provider of automatic splicing, rewinding, and tension control systems. He can be reached via e-mail at email@example.com.