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Did You Know?At Elite Machinery Sales, we are always ready to help companies with the information needed to make sound equipment decisions. You'll find basic equipment overviews. We also will provide ways we have learned from the experts to maximize the efficiencies and cost savings of used die cutters, sheeters, folder gluers and packaging machinery. If you don't find your answer here, please call us at 773-399-1675. What is Sheet Finishing?Sheet finishing is cutting paper from rolls, packaging and shipping it to printers or other customers for further processing. There are two categories of converting rolls into sheets: Cutsize and Folio size sheets. A cutsize sheet is a standard sheet in sizes 8 ½”x11”, 11”x17”, 8 ½”x14”, A3, A4, etc. Folio size sheets are all sheets larger than the cutsize sheet – 17 ½”x22 ½” and larger. Let’s start at the unwind section and continue through
each section of the machine to show how each works and can be
modified to increase quality, reduce downtime WEB CONDITIONING The unwind section has had many modifications and improvements over the years. Shafted rollstands are becoming fewer as most have changed to being shaftless. Nevertheless, it’s important to know how to handle shafted rollstands. A typical stationary shafted rollstand will take approximately twice as long to unload and load rolls as a shaftless type. This is not true if a shuttle or turntable type shafted rollstand is used, but this requires additional manpower to load rolls while the machine is running. In shafted rollstands, the shafts are normally supported by babbitted bearings. This, in itself, will impart friction to the shaft and induce tension in the web. Normally the brake disc or drum is fastened to the shaft and the pads or bands are fastened to the rollstand structure. Due to this arrangement, there is a possibility they will misalign
due to shaft Shaftless rollstands have helped increase safety, reduce back injury, reduce lobbing rolls, reduce loading time and increase tension control. Safety has increased by simply eliminating the requirement of lifting the rolls with a crane to load them. The shaftless rollstand lifts the roll of paper by way of short chucks that are permanently mounted to the lifting arms. These chucks can be either tapered or straight. The tapered type enters and interrupts the core, while the straight type mechanically or pneumatically expands once it’s inside the core. Since braking torque is transmitted to the web via the chucks, a good chuck is important to good web tension control. Tension Control Web tension is the single most important item that will affect sheet-length variation, providing the drive train of the sheeter is tight and capable. A steady, well-tensioned web without tension fluctuation will enable any sheeter to hold precision tolerances. Without it, even the best double rotary sheeter cannot hold the precision tolerances required today. The most common devices are load cells, sonic systems and dancers. Load cells read the actual tension in the web and control the brake pressure to maintain the preset tension. Though their systems are quick responding, they have no forgiveness for web fluctuations due to out-of-round rolls. This system is best suited to well wound mill rolls that have not been mishandled. Sonic systems look at the roll diameter and decrease the brake pressure according to the decrease in roll diameter. They do not read tension nor do they correct for out-of-round rolls. Again, this is best suited for good quality rolls. Another tension system is the “mathematical” digressive Brake System. This system measures the speed of the draw roll and compares it to the RPM of the paper roll to determine its diameter. By knowing the roll diameter at any given time, the machine’s computer can calculate output brake pressure that will equate to the desired and preset web tension. This system does not actually measure web tension, and it cannot compensate for out-of-round rolls. The dancer tension system is basically broken down into two systems. The first part of the system is the tension cylinder that actually loads the dancer roll and actually determines the preset tension. The second part of the system is the position transducer that reads the position of the dancer roll and regulates the brake pressure to maintain the dancer in the center position. By virtue of its dancing or pivoting action, it can absorb or compensate for out-of-round rolls and always shows the sheeter a steady, constantly tensioned web. DECURLERS Sheet curl will affect the ability of the sheet to run in the sheeter and in downstream processes like printing or coping. It is important that the web, and hence the sheet, lay flat. There are two types: Angle or bar type and roller type. The angle or bar types are primarily used on uncoated papers and boards. Since they rely on bending the web over a sharp edge, they will scratch a coated web. The roller is used primarily on coated papers and board. Both types work well and rely on web tension or bar/roller penetration to remove the curl. Most new systems are motorized and use indicators to show actual decurler position. WEB CARRYING ROLLS AND SUPPORT FRAMEWORK This is where we get into a compromising situation. The tension system and decurlers need a support framework and additional rolls to maintain individual web paths for best results. To reduce the chance of wrinkling, multiple webs should not wrap any roll more than 15°. If shafted rollstands are used, then this framework must be located between the rollstands and the cutter. This sets up a maze of rolls that are required to separate the webs, tension them, decurl them and bring them back together. In the case of a shaftless rollstand, all tension controls and decurlers are mounted above the rollstand. Though this enables smoother web flows, more room is required. EDGE GUIDING Accurate edge guiding is one of the first quick payback options that can be added to any machine. There are basically two types: Motorized stand shaft and automatic steering rolls. The motorized stand shaft type moves the paper roll at each location. This is normally done by the operator via pushbuttons located at the infeed or slitter section. Once threaded up, it normally takes three to four minutes to get all webs lined up and running. This motorized stand shift approach can be automated to adjust for telescoping rolls or soft wound rolls. An edge sensor will monitor the edge of the web and will move the rollstand over to maintain the same position. The automatic steering roll system actually steers the web just prior to the infeed or slitter section. Once threaded up, it only takes a few seconds to get all webs lined up and running. It also continues to monitor and corrects as the machine runs. These systems have a very good payback since they can reduce trim broke loss by 1%. INSPECTION SYSTEMS To maintain a high degree of quality, especially on expensive coated sheets, inspection systems can be used. They range from the simple splice detector to the more complex web inspection system. The splice detector is normally mounted on one side of the web where it is looking for a change in density (capacitance) which can be a splice or a tear-out. Once detected, it sends a signal to an alarm or reject gate where the sheets are removed. The full web inspection system is looking at the full width of each web. It is programmed to pick up flaws in the coating or paper making process. Once a flaw is found, it sends a signal to an alarm or reject gate where the sheets are removed. AUTOMATIC WEB SPLICERS Web splicers are primarily used when you have long orders of the same size or frequent roll changes due to small roll diameters. They are basically broken down into two basic types: Non-stop splicers and quick splicers. Non-stop splicers, sometimes referred to as flying splicers, automatically change from one roll to another without stopping the sheeter. Some splicer manufacturers use a festoon (web storage section) to store enough paper to allow them to decelerate the old roll to a stop, splice on the new roll and accelerate the new roll up to line speed all without the sheeter stopping. Other manufacturers accelerate the new roll up to speed and match roll circumference speed with web speed. At the proper time, the old web is pressed against the new roll where tape has been placed to pick up the old web to carry it through the sheeter. This is also done at normal running speed. The quick splicers on the other hand require that the sheeter be stopped to allow the splice to take place. The actual splice takes only a few seconds. SLITTER SECTION Conventional Manual Slitters Conventional old style slitters normally have a universally adjustable top slitter assembly mounted on a slide tube. The bottom slitter is a round band mounted on a powered drive shaft. Adjustment of the bottom slitter is done by loosening a clamp collar and moving it to the new location. A tape measure is used to measure the distance between the bottom slitters thus determining position. The top is adjusted to meet the bottom slitter with approximately 1/8” penetration and 1° toe-in angle. This type of arrangement has been around for years and works satisfactorily, providing you have qualified and trained operators. But, what often happens is that the slitter width will not be set properly, the depth will be too deep, the point of contact will not be correct and the toe-in will be 3° to 10°. This will result in a wrong size sheet, bad cut quality and slitter life that will deteriorate quickly. Air Loaded Slitters Air loaded top slitters have reduced many of the problems conventional slitters once had. The top slitter has a locking toe-in angle that can be set very precisely on or off machine. The point of contact between the top and bottom slitter can be set during installation and will never need to be moved again. The only two adjustments now required of the top slitter are position and penetration. The frequency of the penetration adjustment can be reduced by having your top slitters ground in large sets and ground all to the same diameter. The bottom slitter, though still a ring, can be installed on
an air drive shaft that will This approach can reduce size change time by 50% and will increase
quality of cut Automatic Position Slitters By automating the slitter position, you have virtually removed
this constraint on CUTTING SECTION Conventional Fixed Bed Knife Cutter These conventional systems have done a very good job of cutting
all kinds of papers Double Rotary Knife Section The double rotary knife section has basically replaced the fixed
bed knife systems on all high-capacity, multi-web sheeting being
sold today. Its ability to penetrate and cut the web from both
sides gives it its higher cutting capacity on all grades. This
basically As paper manufactures continue to add more fillers, shorter fibers,
and more binders, the sheet has become more difficult to cut and
handle. This has already been seen in Automatic or Remote Sheet Squaring To further reduce time for set-up, especially when using a servo
motor drive system, a TAPE SECTION Wide or Full Width Bottom Belts The basic premise for all new machines is the same – eliminate the number of adjustments the operator must make. By going to wider bottom belts or full width belts, the operator does not have to move them to enable the sheet to be conveyed correctly. If edge turner, ie. shoes, separators, etc. are used, then an additional doctor board and tape roll is added to mount the edge turners. This allows the edge turners to be moved and placed anywhere across the width of the machine without moving the bottom belts. Static Reducer If the machine is not in a humidity-controlled building or the
sheet has low moisture OVERLAPPING SECTION Most of a sheeter’s speed is limited in this section. All the machinery builders have spent a lot of time and money in this section to effectively overlap a sheet at high speeds. There are basically three types of systems: Air foil, vacuum box and knock-down cam. The air foil uses high pressure air to create a vacuum similar to the Venturi action of an automotive carburetor. The foil uses no moving parts. It pulls the bottom sheet down and relies on the sheet to sheet adhesion to pull the other sheets down. The vacuum box system uses true vacuum from a vacuum pump to pull the tail down to each sheet. The vacuum is timed with the tail of each sheet. It also relies on the sheet to sheet adhesion to pull the other sheets down. The knock-down cams physically push the tail down out of the way before the next sheet enters. The cams are timed so that they only push the tail down and are traveling at web speed to eliminate any marking that might occur. The knock-down cams are normally used with some type of vacuum slice to remove entrapped air. By adding these types of overlapping systems to an existing machine, increased speed and through-put can be realized. This is especially true on lightweight papers. The basic components of the piler have not changed much over the years. They have just been refined. The basic components are back joggers, side joggers, kick-off air, frontstops and piler platform. The back joggers have been upgraded to ensure a high quality
jog front-to-back. They ensure that the sheets are moved from
the last kick-off roll into the pile without The side joggers have changed from the mechanical oscillating
type to a telescoping Kick-off air is especially important on lightweight, coated sheets.
It enables the The frontstops have not changed much but have become more rigid.
This rigidity and The piler platform is one of the most important items in the
piler. Its stable and Above information provided courtesy Brent Burdick of Maxson Automatic |
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