Slitting & Rewinding
The pros and cons of inline slitting S
litting and winding high quality rolls with proper density control can also significantly decrease
scrap costs. This process allows for easy identification and correction of production quality deviations such as caliper variations across the sheet. Each time a roll of material is handled, the chances of damage to that roll increase. Therefore, eliminating extra process steps reduces the total production cycle, resulting in high quality products that get to your customers faster. Additional scrap is always generated when processing your finished material through an off-line unwinding, slitting and rewinding process. Taking advantage of the pros
(productivity and profitability) of in-line slitting requires the right mix of products and equipment. Industry trends, such as wider and faster production lines, make this more challenging. Extensible films wound to smaller diameters, such as stretch and food wrap films, have traditionally been slit in- line. However, as the widths and speeds increase the consistent achievement of scrapless roll changes, as well as the finished roll removal and re-coring processes, places unique demands on equipment. Other process and equipment challenges must be addressed for in-line slitting of non- extensible materials, especially when wound to finished diameters of greater than four times their core OD (outside diameter).
REQUIREMENTS FOR A SUCCESSFUL IN-LINE SLITTING PRODUCTION LINE: 1 - Consistent quality on the process: For an in-line slitting operation, the process quality of the material being produced must be consistent. Cutting off quality material from 12 slit rolls instead of one parent roll can
drive up production costs. Automated process control systems have substantially reduced off-quality process problems. 2 - Changeover time for slit-width
changes for roll removal and shaft re-coring: Automated slitter positioning systems and roll/re-coring systems make it possible to achieve fast and efficient set-width changes, roll changes and re-coring. However, downtime and/or scrap can be a con when making product width changes or when slitter blade maintenance is required. 3 - Ability to consistently spread and wind
shippable quality rolls: The winder must have a properly designed slit web spreading system and the ability to use all three of the TNT (tension/nip/torque) winding principles to consistently produce properly wound rolls. The ability to wind on differential shafts is necessary for materials with cross machine thickness variations, which need to be wound to larger diameters.
4 - High quality, high-speed transfers and
good starts on new cores with 100 per cent consistency: New transfer systems produce straight-line cuts and transfer the slit web directly to the new cores. Stationary knife transfer concepts provide roll change consistency approaching 100 per cent, regardless of web width or operation speed. These provide the important clean web starts on the new cores. 5 - Scrap generation during the roll
change operation: The quality of the first and last wrap needs to be equal to those in- between. Controlled tension, nip and torque must be maintained throughout the entire winding cycle, including the roll change. 6 - Core size consideration: As production
lines increase in width and speed, the core shaft critical speed and deflection criteria determine the minimum core ID (inside diameter) that your material can be wound on. Just by taking a single centre slit, the stiffness of the roll no longer contributes to the stiffness of the shaft. Off-line slitting and rewinding is still needed for customers with small core sizes.
BECOME A PRO IN YOUR MARKET If any of these requirements are not met, the cons for in-line slitting result in lost production on your process line, increased production cost, increased scrap and even lost customers. Be sure to consider all of these options when evaluating if in-line slitting can make you a pro in your market.
uwww.davis-standard.com
30 March 2017
www.convertermag.co.uk
Producing quality, shippable rolls directly off your production line can increase productivity, lower manufacturing costs, decrease scrap and shorten production cycles. By eliminating an off-line slitting and rewinding operation, you can save between $0.05 and $0.10 per pound in production costs, saysDavis-Standard
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