Why did an existing board mill change its roll packing method?
In spring 2012, a leading board mill was rebuilt to substantially increase its production capacity. Whilst the board machine was being rebuilt, the roll finishing system, slitter winder and roll packing line also had to be moved and updated.
Phased production line rebuild to avoid interruptions in production
The production capacity of this line was originally 50,000 tonnes a year. By the time of the rebuild, this had been quadrupled through continuous process improvements and system upgrades, without making any changes to the dimensions of the main machine hall. With this upgrade, the wrapper had to be moved backwards to make more space for parent reel handling and for the new slitter winder. The customer wanted increased capacity and full automation of the finishing operations, as this would markedly improve operational efficiency. However, all this threatened to push the roll wrapper out through the back wall of the machine hall, which would cause a significant jump in the cost, severely limiting the return on the overall investment.
From the beginning, this mill had been wrapping its rolls in kraft paper, but its semi-automatic kraft paper wrapper (installed in 1988) was approaching a respectable quarter-century service life. For this machine, the wrapping was done in one station, with wrapping phases controlled by a full-time operator, who had to manually place both the inner and outer heads. The labelling, automated in an earlier rebuild, was carried out by an industrial robot at the exit station in front of the ramp to the warehouse.
Rebuilding this existing packing machine was not financially viable, and was also operationally too complicated to execute. The modifications to the finishing area had to be done without disturbing the ongoing production. The plan was to install and start up the new wrapper behind the existing one, and then to convert the roll stream from the original winder to the new wrapper. After that, the existing wrapper could be dismantled and the new slitter winder installed in its place. In the third phase, the old winder could then be dismantled, and the new parent reel-handling and board machine upgrade could then be completed with the shortest possible production break.
The old wrapper had served them extremely well, so the most obvious choice for the mill’s project team seemed to be a new fully automated kraft wrapper from the same supplier. But after the first layout sketches for the new finishing area were completed, it was noticed that the BM building needed extending by two column spaces (2 × 6 m) to accommodate the new, fully automated kraft packing line. At this point, the project team understood that they should investigate all of today’s available alternatives as a part of their feasibility study. This posed the question: are there acceptable alternatives that both fulfill pre-determined quality requirements and take up less floor space?
Finding the best alternative
For good reasons, kraft wrapping has been the dominant packing method in paper mills for printing grades. The boundaries of stretch wrapping have expanded in recent times, though, due to the improved packing materials, machines and handling systems that can be found today along the entire supply chain. The modern business environment in which the paper industry operates has given an extra push towards finding more cost-effective operational solutions, including roll wrapping and handling. Stretch wrapping tends to enable simpler, space-saving layouts compared to kraft wrapping.
The polarized “for-or-against” thinking that surrounds the stretch vs. kraft debate is both outdated and unnecessary nowadays. The fundamental question is: What is the best protection in the specific transportation chain, and what is the most economical way to achieve it?
The belief that stretch-wrapped rolls cannot tolerate clamp truck handling like kraft-wrapped rolls is not accurate. It is a myth that stems from comparing plain axially or radially wrapped rolls, the film being too loose or simply wrong type of film being used. The main benefit to axial wrapping is to seal the roll ends; radial wrapping both seals and strengthens the roll body whilst providing corner protection.
In this case, the client was quite ready to accept stretch-wrapped rolls without any extra testing due to their previous experience at another mill, where board rolls had been wrapped with a radial stretch wrapping for the past few years. In both cases, the transportation chain was relatively short. Two further points should be noted: First, the space available for the wrapper at the other mill was limited, and secondly, the stretch concept had been shown to provide sufficient protection for the rolls whilst offering considerably lower investment costs compared to kraft wrapping alternatives.
Simple solution – clear savings
Compared to the alternative kraft wrapping layout, the simplicity of the stretch wrapping concept is striking. The required wrapping capacity for 1.8 m diameter board rolls was 60 rolls per hour. There are three key points here: First, the number of head stacks and head robots required can be cut by half, as only corrugated heads are used with stretch film wrapping. Secondly, kraft wrapping requires four times as much wrapping material to be kept in stock than radial stretch wrapping. This gives clear savings with wrap material costs. Hot-melt glue consumption is also higher with kraft wrapping. Thirdly, the heavy-duty head press station is not needed with stretch wrapping. It should also be noted that roll labelling was the same for both alternatives.
The total investment cost, including the civil engineering, at the mill for the stretch wrapping system was one-third of that of the alternative kraft wrapping concept. Half of the cost savings result from the much simpler structure of the stretch wrapping system. The other half is down to the stretch solution not requiring any building extension work – the kraft wrapper would have needed two extra column bay widths. Across its whole life cycle, it is estimated that the total cost of operating the stretch wrapping solution will be around half that of a comparable kraft paper wrapping system.
Any feasibility study should always be approached with an open mind to fully evaluate the need to provide adequate protection against transportation and storage issues. Stretch wrapping is certainly not suitable for every application, but there are surely many more paper mills around the world that would likely benefit from its installation. Suppliers should be challenged to present alternatives that are accompanied by clearly articulated pros and cons of each system. The key to an optimally functioning finishing system is an intelligent, well-engineered layout. As is always the case: the better the information available at the investment planning stage, the better the result.