Maintaining level and alignment on your corrugator.
This article addresses level and alignment of corrugator components. Equipment can settle or shift. My technical services team has observed many out of level or out of alignment situations causing liner and single face web side-to-side temperature differentials of over 90 degrees F resulting in moisture removal differentials of over 2 1/2%. These differentials can cause a loose edge bond of up to 12+" or a twist, "S", flip warp condition. All of these conditions result in waste, customer rejects, and reduced press/finishing production speeds of 50% or more.
Have you observed a loose or floppy edge, roll after roll of liner or medium, and always on the same side of the corrugator? You probably have a serious level or alignment problem! This can cause serious runnability and equipment problems as follows:
* Uneven heat transfer
* Uneven bond across the web
* Loose edge bond to 22+" on a 98" wide corrugator
* Poor web tracking-misalignment waste of 1/2% to 1+% (US$ 10,000 to US$ 20,000 +/ month)
* Increased trim loss of 1/2+% (US$ 10,000 +/month)
* Web breaks, downtime of about 300 MSF per break plus downtime of 10-30+ minutes (lost production)
* Uneven combined board caliper of .003" (medium flute formation issue)
* Flip warp upward to 15"
* Combined board edge wave
* Warp, "S" warp, and Twist warp
* Increased waste levels of 1-2% (US$ 20,000 to US$ 40,000/month)
* Slower run speeds--loss of up to 100+ fpm
* Dissatisfied customers, order rejections
* Warp can reduce press/finishing productivity 50+%
Level and misaligned equipment components can cause equipment problems as follows:
* Abnormal wear on chains
* Abnormal wear on sprockets
* Heavy vibration
* Missed spliced--300 MSF waste and down time
* Bearing failures and up to 75% less bearing life
* Overheating from increased tension loading
* Increased maintenance cost (parts, labor)
* Increased downtime and production losses
Causes of machine components level or misalignment:
* Building settling, flood, foundation erosion, etc.
* Accidental damage
* Normal day-to-day operations/routine maintenance
* Component changes, upgrades
The proper level and alignment of the corrugator's equipment will minimize tension related differential across the web. Loose web edges cause heat transfer differentials and thus poor edge bond, tension related warp, and waste.
Numerous studies have shown that linerboard moisture levels vary with the amount of preheater wrap and speed. One study on 42# liner was conducted to measure the effect on preheater capacity to remove moisture utilizing a fixed level of preheater wrap with about 4.5 ft of liner in contact with the preheater drum's surface. The amount of moisture removed from the liner varied from a high of 4.5% at 100 FPM to a low of 2.0% at 500 FPM. This study also focused on tension differentials (side-to-side) and their effect on moisture removing capacity. It was found that rolls of liner selected with even moisture levels could have their moisture removed unevenly up to 1.5% or more. This results in uneven bond and tension related warp when one side of the liner was loose and one side was held tightly against the preheater's heated surface.
This article describes diagnostic hand tools used to make critical measurements affecting board quality and productivity. The author has developed simple-to-use checklists for measuring level and alignment. The interpretation of these measurements is key to solving a range of corrugator problems.
The tools discussed will be an infrared pyrometer, a machinist level and a 100-foot steel tape measure. These simple tools are used to check the components of the corrugator for proper level and alignment. These checks are critical for uniform tension, heat transfer, and bond necessary to minimize incidents of loose edge bond and twist warp.
The infrared pyrometer is used to check liner, medium, and single face webs' surface temperature from side-to-side (operator-to-drive side). We do not expect a temperature differential of more than six degrees F. If the measured temperature differential exceeds this level consistently on one side, active steps must be taken by maintenance to bring the equipment back to level or in alignment.
Level checks are made on each piece of equipment--hot places; hot plate entry idler rolls; glue machine; preheater drum, wrap and fixed idler rolls; bridge guide idler rolls; single facers; preconditioner drum, wrap and fixed idler rolls, and roll stands, core chucks.
The maximum allowable level specification is +/- .006 inch per running foot. The length of the roll or width of the corrugator is referred to as the "run". You need to know how many "running feet" of width the corrugator has as the machinist level measures level in thousandth of an inch per running foot. To determine the number of running feet of width you divide the width of the corrugator (in inches) by 12. Example: For an 87" corrugator, you divide 87" by 12" which equals 7.3 ft (conversion factor). This conversion factor is the value required when you convert the level's reading into the total amount of inches you must raise or lower a corrugator's component to achieve level. Thus our specification (+/- .006"/ft) is multiplied by the conversion factor (7.3) which equals to +/- .044" (+/- .006"/ft X 7.3 ft = +/- .044").
To determine how much a roll or machine is out of level, take the level's reading and multiply it by the conversion factor (number of running feet of machine width). A level reading of .015 inch/ft would calculate to .110" out of level at the end of the 87" long roll (.015" X 7.3" = 110"). On another roll on the same machine, a roll with a level reading of .020"/ft would be .146" out of level (.020" X 7.3" = .146"). Both rolls require adjustment.
To assign a plus (high) or minus (low) sign in front of the final calculation, we always assume the drive side of our equipment is perfect or a zero point as in alignment checks to be discussed later. This is because maintenance doesn't want to move drive motors, electrical cabinets, steam lines, etc. typically located on the drive side of the corrugator. A sign of + or - indicates the operator side is higher or lower than the drive side respectively. These checks should be done biannually or if a high side-to-side temperature differential is measured over 6 degrees F.
WHAT YOU WILL LEARN
* Why level and alignment are critical for corrugator performance.
* Problems caused by out-of-level and misaligned corrugators.
* Tools and solutions for these problems.
* This is a condensed version of a longer article. To access the complete article, please go to www.tappi.org. Click on "Corrugating International." Click on "Summer 2004."
For information on equipment alignment and solutions to corrugator level and alignment problems, access the complete version of this story on www.tappi.org. Click on "Publications" and then on Corrugating International, Summer 2004 issue.
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RICHARD J. CROKER, GEORGIA-PACIFIC CORP.
ABOUT THE AUTHOR:
Richard J. Croker, is director, technical services, for Georgia-Pacific Corp., Atlanta, Georgia, USA. Contact him by phone at (404) 652-5177, or by email at rjcroker@GAPAC.com.
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|Author:||Croker, Richard J.|
|Publication:||Solutions - for People, Processes and Paper|
|Date:||Aug 1, 2004|
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