Machine alignment is the first thing you should check when experiencing web performance problems. If machine stands are not properly aligned, other attempts to "fix" the problem may be a waste of time. Though most machines are aligned when first installed, misalignment can develop later due to vibration, improper machine or roller maintenance or tension over time.

If machine modules are not aligned from one unit to the next, your web could experience problems trying to correct its entry angle from one module to the next. Poor alignment between rollers can cause a wide variety of web problems including drift, stretching, and wrinkling. Straightening out even the slightest misalignment is critical to achieving high quality web operation.

Though alignment services can be costly, they may save you time and money over other remedies that simply do not work. Checking machine alignment is an essential starting point and a good investment.

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Idler rolls that are not cylindrical in shape will cause the web to naturally turn if the roll is bigger on one side than the other. A roll with poor geometry will skew the web and then the next roll will attempt to correct its own entry angle by trying to turn the web back the other way. This usually results in a wrinkle.

Poor roll geometry can come from poor craftsmanship in the manufacturing of the roll, from excessive surface wear, or from inadequate design specifications leading to roll failure or diminished performance.

Even poorly wound parent rolls represent a type of cylindrical geometry on the line that can cause web-handling problems. Excessive parent roll run-out or taper can translate into vibration and web flutter. In other words, the condition of the material itself, as a poorly wound parent roll, can end up creating wrinkles through the whole process. If poorly wound rolls can't be avoided, a good tension dancer system can help adjust for much of the web tension variance coming off the parent roll.

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The force of the web causes deflection in a roll as it changes direction. When the web starts to apply force, or load, to the roll surface, the roll bows, or deflects. The greater the load, the greater the force that can result in roll deflection. If the deflection is excessive the result can be wrinkling or bagging.

Roll deflection is often identified when the web bunches near the midsection of the web directly around the roller. However, the presence of deflection may be much more subtle. Consider a situation in which you have twenty thousandths of an inch deflection on an idler, and 50 idlers in the system. By the time the web gets from one end of the machine to the other, the web on the outside has to travel one inch more than the web on the inside. This is an example of accumulated effect due to deflection. It's not the effect of single roll that causes the problem - it's the effect of the total system.

Like so many other situations, the extent of the problem will depend greatly upon the web characteristics. Some webs recover quickly edge to edge when stretched slightly, others do not.

Small-diameter idlers with long face lengths should raise a red flag for any qualified roll supplier. Deflection is, perhaps, the single most important factor that determines roll construction. Roll material (steel, aluminum, or carbon fiber), roll diameter, wall thickness, face length, web width, shaft sizing, and bearing location all have to take load, or deflection, into consideration.

Excessive deflection can also lower critical speed-the point at which harmonic vibrations occur in the roll. A lower critical speed will force you to run the line slower. Be aware that two identical rollers could have different critical speeds based on different degrees of web wrap load, deflection, and/or mounting.

To avoid problems of this kind, be sure your rolls are properly specified. When ordering, you should know the amount of web wrap (usually stated in terms such as 10 o'clock to 3 o'clock), web tension (PLI), any nip load (PLI), web width, and maximum expected line speed. If you haven't thought of them in advance, a Webex applications engineer will walk you through these questions and can even help you troubleshoot much of this over the phone.

Shaft deflection is just as critical as roll deflection. The problems surface in several forms. The shaft may start vibrating inside the roll or the angular misalignment of the shaft through the bearing can also cause premature bearing failure.

Sometimes changing the mounting to a more rigid set-up can help. If you have a short-faced roll with an extra-long shaft, like a 60-inch roll with a 120-inch shaft, you may be better off using an 80-inch or 90-inch roll. The resulting angle is going to be less, and you'll have a stiffer shaft/roll configuration. The bearings will also last longer because they experience less angular misalignment. In other cases, using a larger tubular shaft within the roller may reduce shaft deflection significantly.

Getting the right shaft is as important as the right roll. Count on Webex to help you determine the specifications based on the same criteria: wrap, load, speed, and deflection.

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You must have enough idlers to avoid long areas of unsupported web. However, there is no special formula to tell you how many. Too little support can result in bagging and wrinkling. Too many idler rolls can result in unwanted drag and excessive tension.

Unsupported webs are also susceptible to other environmental factors, such as the drafts of a nearby motor or normal plant ventilation. We've seen examples in which an open door caused enough draft to result in wrinkling. As so often is the case, the strength and weight of the web will have a lot to do with the number and location of idlers needed.

We encourage customers to send an elevation side view indicating roller locations and where the wrinkling occurs. A Webex applications engineer can use this to help troubleshoot your problem. If there's a short span between rolls where it's wrinkling, we explore alignment first. If there is a long span, we investigate support solutions or additional idlers. When evaluating whether your span is short or long, consider the width of the web. A tentative rule of thumb is:

short = less than the width of your web
long = 3x the width of your web

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Excessive web tension can contribute to web marking by pulling on the web and intensifying any flaw that may be in the roller's surface. It can wrinkle, stretch, or break the web and cause unwanted roll deflection. Excessive tension can come from too much drag on idler rolls, bearing friction, roll weight, etc. or from too may idler rolls between drive sections. Excessive tension is often identified by stretched edges and slack centers on the web.

Lack of tension causes "bagging" meaning web edges are loose while the center is slack or just the opposite. Baggy edges and loose webs can result in folds, creases, and wrinkles. Lack of sufficient tension can come from loosely wound parent rolls, unsupported spans of web travel, drive sections out of sync, and/or lack of nip or web pull through the line.

If you have a tension problem from rolls that are too heavy (drag), be cautious about simply replacing them with smaller rolls. Smaller rolls will have more deflection, which can cause just as many problems.

Lighter weight rolls may be the solution for tension problems experienced during startup or speed changes. They can supply support without excessive drag. If your problem occurs once you are up to speed, an idler designed with special free-running bearings may be a good solution.

If you suspect your tension problems come from too many rolls or rolls that are too heavy, try some experiments. Spin individual idlers by hand. Are they hard to turn? Can you selectively remove or replace some rolls and see problems lessen? Rolls of the same size but made of lighter material, such as aluminum or carbon fiber with free running bearings could help. Webex provides rolls with specially designed free-running bearings with optimal lubrication.

Converters running different web materials on the same line have to find a balance among various solutions that will work best for all runs. Often, you need to determine which material will be run most and focus on maximizing production for that material. We need to know this so that your rolls can be designed and balanced to meet the most demanding specifications of your application.

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Entrapped air is a cushion of air between the web an the roll and is often found when rolls do not spin up to line speed. It becomes more of a problem as the line goes faster. Fox example, as plastic film has become stronger, it has been produced in thinner gauges. These lines can now be run at higher speeds, meaning air entrapment can become a problem.

When you get an air barrier buildup, the web loses contact with the roll. The roll then does not spin at the same speed. When it does make contact, it can skid and mark the web. This happens mostly with lighter tensions at high speeds. You get web flutter, side-to-side drifting, and lack of web control. If this happens on steering rolls, your web guide will quickly become ineffective.

In extreme cases of air entrapment, the web doesn't make any contact with the roll, and the roll speed is significantly less than the web speed. If all your rolls are wrapped or configured the same, and one isn't rotating, or it is rotating slowly, then suspect bearing drag. If the web is floating over numerous rolls, then suspect air entrapment.

Webex offers grooved or machined surface options that can help eliminate air entrapment, such as a spiral V-groove surface, a micro-groove surface and a diamond-knurled surface. A spiral V-groove design is specified most often for air entrapment problems. Other patterns are determined by specific application and type of web.

When considering solutions, think about what grooved configuration could be used without marking your web. If a standard V-groove won't work, you may need to use a micro-groove pattern, which is a much smaller groove but has a lot more of them. A diamond knurl and a micro-groove surface perform much the same. We can guide you though the various details of specifying the right surface configurations.

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When the web adheres, or sticks to the roll surface, it can pick off coating from the web or cause tension fluctuations and web marking.

The most common solution to this problem is to increase the release characteristics of the roller. This can be achieved by decreasing the surface contact area of the roller and/or using special coverings, such as high release plasma, ceramic coatings or silicone rubber coverings on the roller surface.

A good release surface will eliminate or reduce coating buildup on the edge of the roll and also facilitate roll cleanup. For example, a plasma-coated roll lets operators easily peel off accumulated coating on the roll's edge. Rolls cleaned right on the line don't have to be removed for soaking and cleaning. Be aware that any coating buildup can also affect the balance of the roll.

Should you want to move or turn a coated or sensitive web without any roller contact whatsoever, an air turn may be the ideal solution. Here the web travels on a controlled blanket of air emitted from the air turn. Contact a Webex applications engineer to discuss your air turn application.

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Web marking is readily caused by flaws in a roll or drag in a roller when a roll is not turning up to speed. A repetitive mark is likely caused by a spot defect in a roll. A streak normally comes from roll drag or a circumferential defect in the roll. A repetitive streak or blemish may also come from the roll scuffing the web as air entrapment or web tension fluctuates.

Rolls not spinning up to speed due to air entrapment or poor bearing performance can cause web marking. If a roll is not spinning up to speed, check for air entrapment or poor bearing performance. A lighter weight roll may also be a simple solution, or consider a rubber-covered roll for increased traction.

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The causes of vibration can vary greatly; from inadequate machinery mounting to poor roll balance to other external influences. Before spending money on rolls or machinery, be sure you investigate all the possibilities.

Check if your line is properly isolated from the vibration of adjacent machinery. Improper roll mounting can also cause vibration. Webex can help identify your first critical speed based on your operating parameters. Knowing this, you can better plan your lines' performance.

Roll balance is very important. Some so-called roll suppliers do not even have dynamic balancing capability. Webex balances all rolls to tolerances that exceed industry standards. Rolls can become unbalanced due to a number of causes, including losing counterweights; excessive wear; buildup such as from coatings; or being bent by careless handling during maintenance on changeovers.

You can often locate the vibration-causing roll simply by feel. Vibration testing is also available through firms specializing in preventive maintenance. Has that roll always vibrated at that speed? Has the mounting changed? The wrap? Sometimes, a little historical investigation can turn up the variable that started the problem.

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