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Slitting Of Nonwovens

Slitting a combination of art and technology

Slitting Of Nonwovens Slitting a combination of art and technology Slitting equipment for nonwovens and other web-based products is becoming more sophisticated through the use of computerized components and controls. Determining the optimum slitting system and the appropriate blades for a specific type of nonwoven still requires actual trials on a number of units. Fortunately, many suppliers of slitting equipment maintain pilot facilities for the use of their customers and provide evaluations of customers, and potential customers, existing slitting equipment. For example, Dienes Corp., Spencer, Mass., sponsors slitting seminars that cover the theoretical and practical applications of slitting.A slitter is used to sever the web completely along its length and to provide a clean-cut line without skips along the machine direction. Slitters should operate for as long as possible between blade changes or sharpening. Because slitting and inspection are often the final operations before shipping, producing uniformly slit and good looking roll goods is a necessity. Selection FactorsWhat is the type, width, density and abrasive character of the material being slitDoes the material require careful control of tensionDoes the material generate a lot of dust from slittingIs the slitting to be done on a continuously operating line or is it to be done off-lineHow many daily setup changes are requiredThe physical properties of the material being slit will influence the type of slitting system and the type of blades to be used, as well as the processing speeds of the units. Web tension is a factor in determining web horsepower and the quality of a wound roll. Low web tension can result in web slippage on the idler rolls, which results in overlaps during slitting.On-line slitting systems on continuously operating nonwoven lines such as spunbonds, SMS lines and wet-laid units, require programmable control systems that enable changes in cut roll widths to be made without shutting down the processing line. Slitting MethodsThe most common methods of slitting are shear, core and razor slitting. Each method has its advantages and limitations and is dependent upon the materials to be processed and other processing requirements.Shear slitting is the vertical displacement of the material as it enters a shearing nip between two opposing edges. The opposing edges can be two straight blades, as in a guillotine, or two rotating disks. Because the upper blade projects through the web during slitting, the proper selection of the blade profile is important. Shear slitting is quite common and is used for materials ranging in properties from foils to heavy sheet plastics.When blade profile angles are gradually increased from a more square-like configuration to a more acutely pointed configuration, the shearing mechanism is modified. The material deflection path gradually changes from a vertical (shear stress) displacement to a lateral (tensile stress) displacement. The shearing mechanism gradually changes from a pure shearing action and merges into a slicing or cutting action as the blade profile narrows.Score, or crush, slitting consists of an upper knife that is pneumatically or spring loaded against a material web with a hardened, sleeved anvil behind it. In this cutting method, the material is actually crushed or split apart. Major factors affecting this process are as follows:nip forces the extent and effect on the blade and anvil roll;blade tip profiles;the metallurgy of the slitting blades and anvil rolls; andthe mounting geometry of the blade relative to the anvil roll.Composite webs like paper, textile fabrics and nonwovens have relatively low density with interfiber voids that allow some displacement of the material by the slitter blade. This allows relatively low nip forces in the range of 50,000 psi for tissue-like materials and up to 150,000 psi for much heavier, stiffer materials. Laminated webs can exhibit interlayer slippage or displacement along the slit edge. Since these types of materials are thicker than single-layer materials, they require higher nip forces in the range of 150,000 to 250,000 psi.Razor slitting involves razors mounted on pneumatic cylinders for activation in or out of the web. Razor slitting is mostly used for processing lightweight plastic film materials. Laser Positioning For Precision Cutting RequirementsDienes Corp. sells a laser-positioning unit, Module IIL, for shear-cut slitting systems requiring precise cutting widths. The combined laser positioner and digital linear scale provides proper alignment of both knife holder and bottom knife. The precise knife setting is set by turning a handwheel until the desired dimensional value is shown on the control panel. Twenty knife sets can be made on the unit in less than 5 minutes, and knife separation can be as little as 0.008 to 0.010 inches. This type of system is well-suited for off-line slitting operations. 
For higher speed, more continuously operating nonwoven lines like spunbond operations, Dienes supplies its Module IV motor-driven slitting system. The Module IV system allows the operator to change the slitting setup from a digital display menu. The laser scans the current knife positions. The top knife holder and bottom knife rings are moved by servomotors so that the operator is away from the actual knife units as they are moved. Bottom knife separation can be as little as 0.004 inches.Parkinson MachineryandManufacturing Co., Woonsocket, R.I., specializes in slitting and winding equipment for the nonwovens industry. The company makes shear, score and razor slitting systems, and can provide systems that have roll-to-roll or automatic on-the-fly capability. An important service Parkinson can provide to the nonwovens industry is its Laser Alignment Service. Equipment installed within a process line is often set from one point based on the preceding piece of equipment. This type of installation procedure does not ensure all of the components are properly aligned. Trained laser technicians have state of-the-art laser equipment that enables them to align nonwoven winders, slitters and other processing equipment to within 0.0001 per foot. Web Guidance For Slitting UnitsErhardt+Liemer Inc. (E+L), Duncan, S.C., sells web-guidance systems for slitting and rewinding nonwovens, as well as a wide range of other products. One unit, the FE5001 Color Line Sensor, has the ability to be changed over between line and edge guiding in a short period of time. Both the sensor and the actuator are fully digital. This unit can be set to guide from lines, intermittent lines or color repeats. All settings for the FE5001 can be set with the four keys on top of the sensor. Nonconventional Slitting SystemsWater-jet systems are used successfully for slitting and cutting spunbonds and other types of nonwovens in the United States. Water-jet cutting is used on a wide range of materials in addition to fabrics, including metals (even titanium), rubber and foam. Major advantages of using water-jet cutting systems include the elimination of dust and thermal stress in materials. Unlike blade cutting and slitting systems, water-jet units do not have to be refurbished as blade slitting systems do. One of the major suppliers of water-jet cutting systems in the United States is Jet Edge, a division of TCl American Monorail, St. Michael, Minn.As the use of lasers for cutting and engraving operations becomes more widespread and prices decline, they may have the potential for use for slitting of specialized types of nonwovens. Laser cutting is already in use for cuffing specialized fabrics and composite materials. A wide range of materials can be laser-cut including many man-made as well as natural fibers, leather, stone and metals. Beam Dynamics, San Carlos, Calif., develops laser based cutting systems for industrial companies. The company has developed cutting systems and techniques for composites in aircraft and aerospace applications. The material that follows is adapted from Beam Dynamics website.It is a common misconception that a laser beam cuts by acting as a small torch that burns through materials. On the contrary, for non-metallic materials, the focused laser beam actually vaporizes or ablates the material it contacts. For very thick non-metallic materials, laser heat can produce secondary oxidation and can sometimes produce charred edges. Paper products, leather, and natural and synthetic textiles can be cut easily with a laser. The lack of thickness and their high combustion heat requires only a few hundred watts of laser energy and produces edges clean and free from fraying. Most fabrics can be cut with a carbon dioxide (CO2) laser. The Beam Dynamics system uses a sealed CO2 laser mounted on a moving carriage containing a lens that focuses the beam to an extremely small spot and is equipped with safety devices to protect the operator from the laser beam. The units are equipped with an exhaust system to remove fumes and debris.

May 2001